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2017
Identifying the impacts of climate change and human activity in Kosciuszko Identifying the impacts of climate change and human activity in Kosciuszko
National Park National Park
Jorja Vernon
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Recommended Citation Recommended Citation Vernon, Jorja, Identifying the impacts of climate change and human activity in Kosciuszko National Park, BEnviSc Hons, School of Earth & Environmental Science, University of Wollongong, 2017. https://ro.uow.edu.au/thsci/152
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Identifying the impacts of climate change and human activity in Kosciuszko Identifying the impacts of climate change and human activity in Kosciuszko National Park National Park
Abstract Abstract This research project aimed to expand upon knowledge of the recent paleoclimate of the alpine region of Kosciuszko National Park, as well as evaluate its response to human impacts. This was achieved through evaluating a series of sedimentary, geochemical and biological proxies that were extracted from a core obtained from Blue Lake, a remote alpine lake situated in the Snowy Mountains region. The results were utilised to reconstruct changes in erosion, organic productivity, fire regime and the biology of the lake over the 3,500-year history of the core. Proxy evidence suggested that the KNP would have initially experienced a relatively cool and wet period at the earliest stages of the cores history (approximately 3,500 cal. yr BP), followed by a gradual transition to a comparatively warm, dry period, until approximately 1,800 – 1,500 cal. yr BP. After the dry episode, it is suggested conditions may have become gradually wetter in the KNP alpine zone until the arrival of Europeans in Australia.
Most importantly, the most significant changes in the proxy data was evident following European settlement in Australia ( 1800 AD to present). This was interpreted to imply a substantial shift in the sedimentological, ecological and geochemical function of the environment after this time. The changes are proposed to provide evidence for several human activities which have taken place since this time, including grazing in the Snowy Mountains, as well as the establishment/expansion of industrial activities and agricultural practices in wider south-east Australia. Furthermore, it is suggested that the timing of these changes correspond closely with the 1°C global temperature rise since the advent of the Industrial revolution, therefore possibly implying a response to warmer conditions. In light of these findings, the results presented here are considered to server as a baseline record of the sensitivity of KNP alpine zone to change. Consequently, it is suggested that the alpine landscape is likely to undergo further significant change into the future.
Degree Type Degree Type Thesis
Degree Name Degree Name BEnviSc Hons
Department Department School of Earth & Environmental Science
Advisor(s) Advisor(s) Samuel Marx
Keywords Keywords Kosciuszko national park, European impact signal, limnology
This thesis is available at Research Online: https://ro.uow.edu.au/thsci/152
Identifying the impacts of climate change and
human activity in Kosciuszko National Park
Jorja Vernon
Supervisors:
Dr. Samuel Marx
Dr. Craig Woodward
Dr. Krystyna Saunders
October 2017
Submitted in partial fulfilment of the requirements for the degree of
BACHELOR OF ENVIRONMENTAL SCIENCE (HONOURS)
Environmental Science Program
School of Earth and Environmental Sciences, Faculty of Science, Medicine and Health
The University of Wollongong
i
The information in this thesis is entirely the result of investigations conducted by the author, unless
otherwise acknowledged, and has not been submitted in part, or otherwise, for any other degree or
qualification.
- Jorja Vernon
21st October 2017
ii
Acknowledgements:
First and foremost, I would like to extend my deepest thanks to my university supervisor, Sam, and my
industry supervisors, Craig and Krystyna. Each of you have helped me so much throughout this year,
from trekking back and forth around the Snowy Mountains to collect my core, to guiding me through
all of my lab work and providing great feedback. Without all of your constant encouragement,
enthusiasm and knowledge, this thesis would not have been possible.
I would also like to thank Atun and Sabika, for helping me carrying out 210Pb dating, Patricia for carrying
out Itrax analysis, and the rest of the Environmental Research Institute team for providing me with
support, laughs and always making me feel welcome at ANSTO, it made my year significantly more
enjoyable. I’d also like to thank Alan and the rest of the ANSTO AMS Radiocarbon Dating team for all
your help dating my core. Your efforts to make sure I received my ages as quickly as possible, even with
your heavy work load, is greatly appreciated.
Thank you to my wonderful friend, Hayley, for hiking around the mountains with me, all the car pools
to ANSTO, helping with lab work and writing, and for being the best person to go through this honours
year with. I really appreciate your support.
A special thanks to my parents, my siblings, and all my friends for always encouraging me and
supporting me throughout the year.
And lastly, thank you to Will, you have kept me sane, I couldn’t have done it without you.
iii
Abstract:
The alpine zone of the Kosciuszko National Park (KNP) is a unique and valuable Australian landscape;
however, it is an environment that is under threat from over-exploitation by humans and climate
change. In order to assist in the management and preservation of the alpine zone, it is necessary that
we gain an understanding of how the KNP environment has responded to past environmental processes
and the sensitivity of the region to change. Achieving this requires the construction of a comprehensive
database that incorporates as much palaeoclimatic and palaeoenvironmental data from the region as
possible. However, currently there are only a small number of these studies conducted in the Snowy
Mountains area, and only a few studies which have focused on changes encompassing the last 2,000
years and arrival of Europeans. In light of this, this research project aimed to expand upon knowledge
of the recent palaeoclimate of the alpine region of Kosciuszko National Park, as well as evaluate its
response to human impacts.
The aim was achieved through evaluating a series of sedimentary, geochemical and biological proxies
that were extracted from a core obtained from Blue Lake, a remote alpine lake situated in the Snowy
Mountains region. The results were utilised to reconstruct changes in erosion, organic productivity, fire
regime and the biology of the lake over the 3,500-year history of the core. Proxy evidence suggested
that the KNP would have initially experienced a relatively cool and wet period at the earliest stages of
the cores history (approximately 3,500 cal. yr BP), followed by a gradual transition to a comparatively
warm, dry period, until approximately 1,800 – 1,500 cal. yr BP. After the dry episode, it is suggested
conditions may have become gradually wetter in the KNP alpine zone until the arrival of Europeans in
Australia.
Most importantly, the most significant changes in the proxy data were evident following European
settlement in Australia (~1800 AD to present). This was interpreted to imply a substantial shift in the
sedimentological, ecological and geochemical function of the environment after this time. The changes
are proposed to provide evidence for several human activities which have taken place since this time,
including grazing in the Snowy Mountains, as well as the establishment/expansion of industrial activities
and agricultural practices in wider south-east Australia. Furthermore, it is suggested that the timing of
these changes correspond closely with the 1°C global temperature rise since the advent of the Industrial
revolution, therefore possibly implying a response to warmer conditions. In light of these findings, the
results presented here are considered to server as a baseline record of the sensitivity of KNP alpine
zone to change. Consequently, it is suggested that the alpine landscape is likely to undergo further
significant change into the future.
iv
Table of Contents
Acknowledgements: ...............................................................................................................................ii
Abstract: ................................................................................................................................................ iii
List of Figures:........................................................................................................................................ vi
List of Tables: ....................................................................................................................................... viii
1. Introduction: .................................................................................................................................. 1
1.1 Introduction .......................................................................................................................... 1
1.2 Research Aims and Objectives ............................................................................................... 3
1.3 Thesis Outline and Scope ....................................................................................................... 3
2. Literature Review: .......................................................................................................................... 5
2.1 Recent Palaeoclimate in the Australian Environment ............................................................ 5
2.1.1 Palaeoclimatic Studies from the South-east Australian Region ...................................... 5
2.1.2 Evidence of the Medieval Warm Period and the Little Ice Age ...................................... 8
2.1.3 Palaeoclimatic and Palaeoenvironmental Research in the Snowy Mountains .............. 10
2.2 Anthropogenic Influences in the Snowy Mountains ............................................................ 13
2.2.1 Aboriginal Settlement and Land Use in the Snowy Mountains ..................................... 13
2.2.2 Development of the Kosciuszko National Park Post-European Settlement .................. 14
3. Physical Setting and Methods: ..................................................................................................... 18
3.1 Regional Setting ................................................................................................................... 18
3.1.1 Geology ....................................................................................................................... 20
3.1.2 Climate ........................................................................................................................ 22
3.1.3 Vegetation ................................................................................................................... 23
3.2 Blue Lake and its Catchment ............................................................................................... 24
3.3 Core Collection and Sampling .............................................................................................. 27
3.4 Core Description .................................................................................................................. 27
3.5 Chronology .......................................................................................................................... 28
3.5.1 210Pb Dating ................................................................................................................. 28
3.5.2 14C Dating .................................................................................................................... 28
3.5.3 Mass Accumulation Rate ............................................................................................. 29
3.6 Dry Bulk Density .................................................................................................................. 29
3.7 Grain Size............................................................................................................................. 29
3.8 Geochemistry ...................................................................................................................... 29
3.9 Macro-Charcoal ................................................................................................................... 30
3.10 Chironomids ........................................................................................................................ 31
v
3.11 Loss-On-Ignition .................................................................................................................. 31
4. Results: ........................................................................................................................................ 33
4.1 Core Description .................................................................................................................. 33
4.2 Chronology .......................................................................................................................... 35
4.2.1 210Pb Ages .................................................................................................................... 35
4.2.2 14C Ages ....................................................................................................................... 37
4.2.3 Bayesian Age/Depth Model Based Off 210Pb and 14C Ages ............................................ 38
4.2.4 Mass Accumulation Rate ............................................................................................. 39
4.3 Dry Bulk Density .................................................................................................................. 41
4.4 Grain Size............................................................................................................................. 42
4.5 Geochemistry ...................................................................................................................... 43
4.5.1 Principle Component Analysis of Elements .................................................................. 43
4.5.2 Elemental and Magnetic Susceptibility Variation Down Core....................................... 44
4.5.3 The Upper Section of the Core .................................................................................... 46
4.5.4 Indicators of Anthropogenic Geochemical Perturbation in Blue Lake .......................... 48
4.5.5 Evidence of Changing Dust Deposition in Blue Lake ..................................................... 49
4.6 Macro-Charcoal ................................................................................................................... 50
4.6.1 Charcoal Concentration and Sedimentation Rate ........................................................ 50
4.6.2 The Top 10 cm of the Core .......................................................................................... 51
4.7 Chironomids ........................................................................................................................ 52
4.7.1 Chironomid Species Percentages ................................................................................. 52
4.7.2 Chironomid Principle Component Analysis .................................................................. 54
4.7.3 Sub-family Percentages ............................................................................................... 55
4.8 Loss-On-Ignition .................................................................................................................. 56
4.8.1 Changes in Organic Content ........................................................................................ 56
5. Discussion: ................................................................................................................................... 58
5.1 Climate ‘Phases’ Present Within the Studied Core ............................................................... 59
5.1.1 The Transition out of the Neoglacial ............................................................................ 61
5.1.2 An Extended Warm and Dry Period ............................................................................. 63
5.1.3 A Return to Wetter Conditions .................................................................................... 63
5.1.4 Difficulties with Determining Evidence of the MWP and LIA Climatic Events ............... 64
5.1.5 Evidence of Distinct Palaeoenvironmental ‘Episodes’ in the Late Holocene ................ 64
5.1.6 Possible Influence of the ‘Freshwater Reservoir Effect’ on 14C Ages ............................ 65
5.2 Land Degradation in Kosciuszko National Park following European Settlement .................. 67
vi
5.2.1 Environmental Changes due to Grazing in the Alpine Zone ......................................... 67
5.2.2 Pb Pollution due to Mining and Leaded-petrol ............................................................ 69
5.2.3 The Effects of Agriculture Expansion on the Kosciuszko National Park Environment ... 72
5.3 The Impact of Recent Climate Change on Kosciuszko National Park .................................... 74
6. Conclusion and Recommendations: ............................................................................................. 76
6.1 Conclusion: .......................................................................................................................... 76
6.2 Recommendations for Future Work .................................................................................... 77
References:.......................................................................................................................................... 79
List of Figures:
Figure 1: Map of south-eastern Australia showing the study sites mentioned in section 2.1.1. (Source:
Google Earth, 2017) .............................................................................................................................. 8
Figure 2: Location of the Kosciuszko National Park, divided into the Alpine, Subalpine zone and
Montane and Tableland Zones (Source: Pickering & Growcock, 2009) ................................................ 18
Figure 3: Map of the Mt Kosciuszko Alpine Area (Adapted from Worboys & Pickering, 2002). Blue Lake
is circled in red. ................................................................................................................................... 19
Figure 4: Location of Blue Lake and associated moraines (Source: Good, 1992) .................................. 24
Figure 5: Sample sites and their ages from Barrows, et al, 2001 (Source: Barrows, et al, 2001) .......... 25
Figure 6: Bathymetry and surface geology of Blue Lake (Source: Raine, 1982) .................................... 26
Figure 7: Core image divided into five distinct stratigraphic units, a representative grainsize
distribution plot is presented for each unit. ........................................................................................ 33
Figure 8: Supported (A) and unsupported (B) 210Pb activity in the top 14 cm of the BLUE01 core. ...... 36
Figure 9: 210Pb Ages Produced from CRS (Blue) and CIC (Orange) age models. .................................... 37
Figure 10: 210Pb (orange) and 14C ages (blue) in yr BP (before 1950) against depth (cm). 210Pb ages
project into negative ages as they occur after 1950. ........................................................................... 38
Figure 11: Bayesian age/depth model constructed using 210Pb and 14C ages through the studied core.
............................................................................................................................................................ 39
Figure 12: Change in MAR throughout the studied core. ..................................................................... 40
Figure 13: Dry Bulk Density data plotted against depth (cm), age (cm) and the core image x-ray. ...... 41
Figure 14: Percentage sand, silt and clay (A), mean grainsize (B), and grainsize frequency (C), plotted
against depth (cm) and the core x-ray image. ..................................................................................... 42
Figure 15: PCA plot of axis 1 and 2 showing elements with a minimum of >100 counts, normalised to
Mo Ratio. The table shows the cumulative percentage varience for each axis (1, 2, 3 and 4). ............ 44
vii
Figure 16: Elements normalised against the Mo Ratio and plotted against depth (cm), age (cal. yr BP).
Two bands are highlighted to show episodes of elevated counts in all plotted elements. The magnetic
susceptibility for the corresponding depths is plotted on the core image. .......................................... 45
Figure 17: Changes in elemental deposition from after European settlement in Australia, highlighting a
region of variability among all elements (orange) and a point of low values for all elements except Pb
(blue), plotted against depth (cm) and age (AD). ................................................................................. 47
Figure 18: Change in Pb/Ti ratio throughout the core, plotted against depth (cm) and age (AD). ........ 48
Figure 19: Changing geochemical composition through the BLUE01 core as shown by Nd/K ratio
plotted against Ta/Ti ratio. Blue points represent the time before 1800 AD and orange points
represent the time after 1800 AD. ...................................................................................................... 49
Figure 20: Charcoal Concentration (mm2/cm2) (A) and Sedimentation Rate (mm2/cm2.yr) (B) plotted
against depth (cm) and age (cal. yr BP), respectively. .......................................................................... 50
Figure 21: Sedimentation Rate (mm2/cm2.yr) of charcoal plotted against age (AD). ............................ 51
Figure 22: All Chironomidae species identified throughout the core, expressed as a percentage per
sample................................................................................................................................................. 53
Figure 23: Common Chironomid species per sample, plotted against depth (cm) and age (cal. yr BP). 53
Figure 24: The table shows the PCA result summary from all axes. The plot shows Axis 1 and Axis 2 of
the PCA, indicating species and sample variation. Samples that were taken from the region before
1800 AD are represented in blue and samples after 1800 AD are represented in red. ........................ 54
Figure 25: Percentage of each sub-family (Chironominae, Orthocladinae, and Diamesinae), PCA1 and
PCA2 overall variance, and sum of Chironomid head capsules per sample, plotted against depth (cm)
and age (cal. yr BP). ............................................................................................................................. 55
Figure 26: Organic Content (determined by %LOI) plotted against depth (cm) and age (cal. yr BP). .... 56
Figure 27: Assessment of the relationship between proxies of organic content using Organic Content
(determined by LOI), Mo Ratio and Br. ................................................................................................ 57
Figure 28: Comparison of changes in Magnetic Susceptibility, MAR (g/cm2/y), Charcoal Concentration
(mm2/cm3), DBD (g/cm3), Mean Grain Size (μm), Organic Content (%LOI) and Chironomid Sub-families
(% Sample), plotted against depth (cm) and age (cal. yr BP). ............................................................... 59
Figure 29: Weathering index/age profiles for a core from Club Lake in the Snowy Mountains. Mobile
elements (Ca, Sr, and Ba) are depleted during weathering. (Source: Stromsoe, et al, 2013) ............... 68
Figure 30: Weathering index/age profile (Ti/Ca) of BLUE01 core. ........................................................ 68
Figure 31: The change in global surface temperature from 1880 to 2016 AD (Source: NASA/Goddard
Institute for Space Studies, 2016). ....................................................................................................... 74
viii
List of Tables:
Table 1: List of the eight coldest and warmest 25-year periods in the temperature reconstruction.
(Source: Cook, et al, 1992) .................................................................................................................... 9
Table 2: 210Pb Activity and dates. Samples are relative to March 2017. ............................................... 35
Table 3: 14C ages through the Blue Lake Core. Ages were calculated using SHcal13 (Hogg, et al, 2013).
............................................................................................................................................................ 37
Table 4: Mass Accumulation Rate (MAR) ............................................................................................. 40
1
PART 1
1. Introduction:
1.1 Introduction
The Australian alpine region represents only a small portion of the Australian continent (0.3% of its land
mass), yet it holds both national and international significance (Slattery, 1998). Not only are the
Australian Alps the most extensive contiguous alpine landscape on mainland Australia, they are also
renowned for their unique geological and sedimentary characteristics (Kirkpatrick, 2003), as well as for
encompassing a wide range of ecosystems with unique flora and fauna species (Costin, 2000; Green,
2002). The Kosciuszko National Park (KNP), in particular, is a designated 526,000-ha protected area of
the Australian alpine region (Worboys, et al, 2001), which has gained formal international recognition
as one of the 440 Biosphere Reserves distributed throughout the world by the UNESCO Man and the
Biosphere Program (MAB) (Australian Government, 2008). The MAB program classified the region as
an outstanding example of an alpine and subalpine environment, containing unique communities, and
areas of unusual natural features of exceptional interest (Scherrer & Pickering, 2001). Further to this,
the KNP contains Blue Lake, a ‘RAMSAR’ listed wetland (Australian Government, 2008). The Blue Lake
Ramsar Site has been internationally recognised for maintaining biological diversity within its
biogeographical reserve, as well as being an environment that supports rare, endemic, endangered and
vulnerable populations of animals and plants (Australian Government, 2008).
The Australian alpine area also holds significant economic value. The major land uses since European
settlement have included grazing practices, which occurred over a period of approximately 120 years
(1820’s to the 1940’s), power generation from the Snowy Hydro-electric Scheme, as well as tourism
and recreation. The development of the Snowy Hydro-electric Scheme, in particular, has played a major
role in growing and shaping modern society in the region and Australia as a whole. For instance, at
present, the Snowy Hydro-electric Scheme accounts for 38% of the total hydro-electric power
generated in Australia (11% of Australia’s total energy), and supplies water resources for $3 billion
worth of irrigation based agricultural products every year (Theobald, et al, 2015). Additionally, tourism
in the Snowy Mountains generates substantial income for the region, with ~$600 million spent by
~1,440,000 visitors annually (NSW Government, 2017). Studies having attributed the substantial
increase in visitor numbers since the mid-1950’s to improved access to the area (Good, 1995), increased
2
public interest and environmental awareness (Mercer, 1992), as well as effort of the winter resorts that
reside in the KNP to diversify and promote summer activities (Good, 1995).
Despite its importance as a unique and valuable Australian landscape, the Australian Alps and the
Kosciuszko National Park are a natural environment under threat from over-exploitation by humans
(Scherrer & Pickering, 2001) and climate change (Slayter, 2010; Batterbee, et al, 2012). In order to assist
in the preservation of these alpine ecosystems, as well as predict future effects of changes on the
landscape, it is necessary that we gain an understanding about past environments in KNP and the
sensitivity of the region to change. Achieving this requires the construction of a comprehensive
database that incorporates as much palaeoclimatic and palaeoenvironmental data from the region as
possible. However, currently there are only a small number of palaeoclimatic and palaeoenvironmental
studies which have focused on the Australian alpine environment (Costin, 1972; Raine, 1974; Martin,
1986;1999; Barrows, et al, 2001; Stanley & De Deckker, 2003; McGowan, et al, 2010, Marx, et al, 2010;
2011;2014; Kemp & Hope, 2014; Stromsoe, et al, 2013;2015;2016). These studies have largely focussed
on understanding natural Quaternary environmental change. There has been few studies that have
focused on recent changes (with the exception of the studies of Marx et al, 2010 and 2014, as well as
Stromsoe, et al, 2013, 2015), particularly changes encompassing the last 2000 years and arrival of
Europeans, which is likely to have resulted in major perturbation to environmental systems within KNP.
This period is of particular significance because it likely represents the current climate regime, ie. It is
after the more major changes which occurred in KNP during the Last Glacial Maximum (LGM) and the
subsequent ‘recovery’ of the region during the early to mid-Holocene (Barrows, et al, 2001, Martin,
1999, Marx, et al, 2010, Stromsoe, et al, 2016).
One widely adopted method for obtaining palaeoenvironmental information is through analysis of lake
sediments, whereby the sedimentary record yields valuable evidence concerning the nature of an
environment through time (Roberts, 2014). While sediment records do not possess the precision, and
rarely produce the resolution, of observational data, they have proven to be useful for identifying long-
term patterns of environmental development, as well as for identifying recent changes in
environmental conditions. This is possible because lake sediments generally accumulate consecutively,
and continue to do so up to the present day (Roberts, 2014). Several studies, including within Australia,
have demonstrated the usefulness of a multiproxy approach for gaining the most comprehensive and
holistic understanding of changes in the lake sediment record (eg. Dodson, 1994; Mooney, 1997;
Mooney & Dodson, 2001; Williams, et al, 2006; Black, et al, 2006; Kershaw, et al, 2007; McGowan, et
al, 2008; Petherick, et al, 2008;2009;). For instance, Mooney (1997) used records of pollen, charcoal,
total carotenoids, magnetic susceptibility and sediment composition extracted from a core obtained
3
from a lake in central Victoria, to identify changes in vegetation/productivity, fire regime and patterns
of erosion over the past 2000 years. Similarly, Mooney and Dodson (2001) explored changes in erosion,
productivity, pollen and fire within the same lake environment using these proxies, and also made
comparisons of environmental changes that have occurred during the post-European period with those
of the preceding 2000 years. Considering these examples, it is expected that by employing a multiproxy
analysis approach to a lake record obtained from a remote site in the Snowy Mountains, we will be able
to successfully detect variations in climate and impacts of human activity on the Kosciuszko National
Park.
1.2 Research Aims and Objectives
The primary aim of this project is to quantify the impact of natural and anthropogenically induced
environmental changes which have occurred in the Kosciuszko National Park over the late Holocene
timeframe (~3,500 years). The specific objectives of this study are:
I. To develop records of the past environmental conditions in KNP over the past 2000 years and
assess the response of KNP lakes to major recent climate events such as the Medieval Warm
Period and Little Ice age.
I. To provide a baseline record of the sensitivity of KNP to change.
II. To evaluate the significant characteristics of anthropogenic disturbance in KNP in the context
of natural palaeoenvironmental variability.
III. To determine whether climate change had led to distinguishable changes to the ecological and
geochemical function of the Kosciuszko National Park and the likely future impact of climate
change to the park through these findings.
This will be achieved by evaluating a series of sedimentary, geochemical and biological proxies
extracted from a core obtained from Blue Lake, a remote alpine lake in the Snowy Mountains region.
1.3 Thesis Outline and Scope
This thesis is divided into four parts, these are:
Part 1 – The Introduction and Literature Review, the objective of which is to develop the research
questions and put the research in context of previous work.
4
Part 2 – Methods and Physical Setting, the objective of which is to provide an overview of the physical
environment of the study area and to outline the various methods employed to analyse the lake core
collected for this study.
Part 3 – The Results and Discussion, the objective of which is to present and analyse the data generated
by this study and to address the thesis aims.
Part 4 – The Conclusion, which provides a general conclusion with regard to the aim and objectives of
the study, along with this, recommendations are given for future research.
This research project occurred within the scope of a 24-credit point thesis, undertaken over a 9-month
period. The study focused on analysing multiple proxies within one core extracted from Blue Lake. This
was deemed an effective method for obtaining a detailed understanding of the Blue Lake environment
because it allowed a greater number of proxies to be analysed in the relatively short timeframe. Blue
Lake was chosen from among the four major alpine lakes within Kosciuszko National Park. It is
considered representative of other lake environments in the Snowy Mountains. Furthermore, as a
RAMSAR listed wetland which is internationally recognised for its high ecological value (Australian
Government, 2008), understanding both natural and anthropogenic change within Blue Lake is of
particular importance.
5
2. Literature Review:
2.1 Recent Palaeoclimate in the Australian Environment
Reconstructing past climatic variation using proxies stored in geologic archives is a well-established
approach in palaeoenvironmental research (Morellon, et al, 2011). Recently, an increasing emphasis
has been placed on the environmental changes which have occurred over the past 2,000 years, during
the late Holocene (eg. Cook, et al, 1992; Mooney, 1997; Dodson, 1994; Mooney & Dodson, 2001). The
Holocene epoch is considered to be of crucial importance for understanding the controls of Earth’s
climate under comparatively stable boundary conditions (Gliganic, et al, 2014), as well as the role of
anthropogenic influences in modifying the climate system (Roberts, 2014). Inferences can be made for
human impacts on environmental and climatic conditions because the beginning of this period
corresponds with the time when humans began to develop sophisticated agricultural practices, which
led to the rise of human societies over large parts of most of the major land masses (Roberts, 2014).
Geologic records from the last 2,000 years enable us to evaluate historical climate variation and
subsequently, the impact of climate change on humans (Mooney, 1997). Reconstructions of Holocene
climate variability in the Southern Hemisphere has been conducted using a number of environmental
proxies, particularly through tree rings (LaMarche, 1979), speleothems (Bar-Matthews, et al, 2010),
peat mires, (Ledru, et al, 2005; Marx, et al, 2008), lake cores (Bush, et al, 2007), corals (Gagen, et al,
1997), swamp deposits (Maldonado & Villagran, 2006) and ice cores from high snow accumulation rate
areas (Villalba, 1994). In Australia, a number of records exist from the south-eastern region, however,
the resolution from this period tends to be coarse and few studies to date have focused on climatic
variation within the last 2,000 years (Cook, et al, 1992). Palaeoclimatic research from the south-eastern
region of Australia, as well as the work that has been conducted in the Snowy Mountains, will be
discussed further in the sections which follow to provide insight into what is known about the recent
palaeoclimate of the Australian environment.
2.1.1 Palaeoclimatic Studies from the South-east Australian Region
Research into the recent palaeoclimate of south-eastern Australia has identified several broad-scale
trends in climatic change over the past thirty thousand years (Fig.1) (See Petherick, et al, 2013; Reeves,
et al, 2013). The glacial period (~30 – 18 ka BP) has been widely characterised as having had a cool
climate, with evidence of glacial and periglacial activity in the southeast Australian and Tasmanian
alpine regions during this time (Barrows, et al, 2001;2004). Additionally, these climatic conditions have
also been indicated by dramatic shifts in vegetation assemblages, for instance, increased
6
representation of herbaceous taxa at the expense of arboreal taxa found at a number of areas in the
region (Dodson, 1975; Kershaw, et al, 2007). At the Last Glacial Maximum (LGM), estimates of maximum
temperature depression range between 6.5°C, using qualitative inferences of maximum tree-line
depression from pollen records (Colhoun, et al, 1999), to between 3.7 and 4.2°C, using quantitative
pollen-based transfer functions (Fletcher & Thomas, 2010). Furthermore, evidence of δ18O of the
planktonic foraminifera Globigerinoides ruber in marine sediment cores suggest that sea surface
temperatures off the coast of NSW were as much as 3 – 5°C lower than present at the LGM (Bostock,
et al, 2006).
The deglacial (~18 – 12 ka BP) climate in SE Australia is thought to be a time of significant environmental
change, with increased temperatures, and sea level rise. Increasing temperatures have been indicated
by the rapid retreat of ice in the Snowy Mountains and Tasmania, commencing from 18 ka (Barrows, et
al, 2001;2004). Several studies have produced pollen records which reveal evidence of the re-
emergence of arboreal taxa (Casuarinaceae, Eucalyptus) and the decline of herbs and shrubs
(Asteraceae, Chenopodiaceae), indicating warmer and wetter conditions (Markgraf, et al, 1986; Hopf,
et al, 2000; Williams, et al, 2006). Sea level rise has also been indicated during this time, for instance,
through research by Gingele, et al (2007), where a palaeoclimate reconstruction of the south-east
Australian continent was achieved through studying the terrigenous component of a deep-sea core,
collected off the coast of South Australia. Results from the investigation demonstrated that the input
of fluvial material from a common MDB source would have ceased by 13.5 ka BP, when it is estimated
that the mouth of the River Murray would have been at least 150 km away from the core site (Gingele,
et al, 2007).
The early Holocene (~12 – 6 ka) climate in south-eastern Australia has been characterised as relatively
warm and wet, however, studies have suggested there has been some climate variability over this time.
The previously mentioned research by Gingele, et al (2007) demonstrated that increased Murray River
discharge occurred between 13.5 to 11.5 ka, and 9.5 to 7.5 ka BP, respectively, and these results were
suggested to reflect periods of increased precipitation and a more humid climate in the region. This
coincided with increasing lake levels in western Victoria (Jones, et al, 1998). Furthermore, Gingele, et
al (2007) suggests that the region would have experienced relatively drier conditions during the period
between 11.5 ka and 9.5 ka BP, as indicated by a decrease in illite content and an increase in grainsize
in the sediment. Additionally, other research has presented pollen records which reflect abrupt changes
in vegetation from approximately 12 ka onwards, indicated by the further expansion of arboreal taxa
(Kershaw, et al, 2007).
7
The mid-Holocene (~6 – 4 ka) is suggested to have been a period when the region experienced
generally warmer and wetter conditions, with increasing variability and enhanced dry intervals related
to a more pronounced El Nino mode of ENSO (Reeves, et al, 2013). One study demonstrated a period
of higher precipitation, followed by drier conditions at Lake George, NSW (Fitzsimmons & Barrows,
2010), seen through fluctuations in lake level. Wetter conditions during this time was also affirmed in
a study by Gliganic, et al (2014), where he presented palaeo-hydrological evidence of elevated lake
levels between 5.8 - 5.2 and 4.5 ka from sites in the Flinders range and surrounding lowlands.
The late Holocene (4 ka to present) has been characterised as having a highly variable climate, both
spatially and temporally. In general, this period is associated with increased rainfall variability, including
both droughts and pluvial episodes, in association with the strengthening and increased frequency of
ENSO and the Indian Ocean Dipole (Gliganic, et al, 2014; Gouramanis, et al, 2013, Marx, et al, 2009;
Petherick, et al, 2013). One sedimentological study of peat mires in the Australian Capital Territory
suggested variable geomorphic activity and drier conditions at 3.5 ka cal. yr BP due to a number of peats
corresponding with that age being capped by a sandy layer (Hope, et al, 2009). While a different study
by Gliganic, et al (2014) demonstrated several phases of elevated lake levels at 3.5–2.7, and 1 ka cal. yr
BP. Additionally, an event known as the Neoglacial is agreed to have occurred between ~5 to 2 ka
(centred around 5,000 cal. yr BP) (Porter, 2000). In south-east Australia, studies have characterised the
Neoglacial as having a cooler, wetter climate and enhanced geomorphic activity (Costin, 1972; Martin,
1999; Marx, et al, 2011). Other studies have also demonstrated episodic drier/wet phases through
evaluating of records from Lake Keilambete in central Victoria. Results of these studies each implied a
general trend of drier conditions from 5 ka to present (Mooney, 1997; Bowler & Hamada, 1971;
Dodson, 1974;1975; De Deckker, 1982; Mooney & Dodson, 2001; Wilkins, et al, 2013).
8
Figure 1: Map of south-eastern Australia showing the study sites mentioned in section 2.1.1. (Source: Google Earth, 2017)
2.1.2 Evidence of the Medieval Warm Period and the Little Ice Age
The Medieval Warm Period (MWP) refers to an abnormally warm period between 900 – 1300 AD.
(Mann, 2002a). During this time, it is suggested that temperatures were comparable to (if not
exceeding) those of the late 20th century (Mann, 2002a). Some-time after the MWP, a period of cool
temperatures led to significant mountain glacier expansion, especially in alpine regions of the Northern
Hemisphere (Mann, 2002b). The period was termed the ‘Little Ice Age’ (LIA) and is conventionally
defined as the period between the 16th – mid-19th century AD (Mann, 2002b). Whilst there is extensive
evidence of both the MWP and LIA climatic events in Europe and neighbouring regions such as the
North Atlantic Ocean, there is a high level of uncertainty surrounding the extent to which they impacted
other parts of the globe, particularly in parts of the Southern Hemisphere, such as Australia (Cook, et
al, 2002; Bradley & Jones, 1993). In some areas of the Southern Hemisphere, including New Zealand
and South America, research has found substantial evidence of the MWP and LIA climate events (Cook,
et al, 2002; Lorrey, et al, 2008). In Australia, however, there is little evidence of either event (See
Petherick, 2013), apart from a small number of studies which demonstrate evidence of both events
occurring at a smaller scale (Cook, et al, 1992; Mooney, et al, 1997; Marx, et al, 2014; Cohen, et al,
2012).
Despite there being little evidence of the MWP and LIA in Australia, tree ring studies from the
climatically-sensitive Tasmanian ‘Huon pine’ (Lagarostrobos franklinii) showed evidence of both the
9
MWP and LIA (Cook, et al, 1992). In particular, the evidence of the MWP was interpreted through
above-average temperatures between 940 – 1000 AD and 1100 – 1200 AD. This is further affirmed by
four of the eight warmest 25-year periods (Table 1) falling within the conventionally agreed timeframe
of the MWP (Cook, et al, 1992). Evidence of the LIA was interpreted through below average
temperatures at two intervals within the LIA timeframe, the 17th century and the mid-15th century.
Furthermore, three of the eight coldest 25-year periods fell within the LIA timeframe (Table 1).
However, it was suggested that the southern oceans may have significantly moderated the effect of the
LIA in Tasmania, since these years only account for 75 years of the 500-600 candidate years.
Table 1: List of the eight coldest and warmest 25-year periods in the temperature reconstruction. (Source: Cook, et al, 1992)
Another record which gave evidence of both events was a study conducted at Lake Keilambete in
Victoria, by Mooney (1997). That study demonstrated changes in total carotenoids, magnetic
susceptibility and sediment composition, as well as charcoal and pollen, corresponding with MWP and
LIA, respectively. Results demonstrated high organic and carbonate content and concurrent low
minerogenic fraction at 1,150, between 1065 – 989 and 909 – 800 cal. yr BP. This was interpreted to
indicate brief warm periods interrupted by colder temperatures, approximately at the timing of the
MWP. Additionally, evidence of the LIA was suggested to have been demonstrated through a
substantial change in pollen concentration and decrease in the concentration of charcoal at the
approximate timing of the event. These proxies were expected to reflect cooler temperatures because
these conditions would have affected plant species type and abundance, as well as the fire regime
(Mooney, 1997).
10
2.1.3 Palaeoclimatic and Palaeoenvironmental Research in the Snowy Mountains
In comparison with the volume of palaeoclimate research from lowland areas, there have been
relatively few studies conducted in the Snowy Mountains region. Of those which are available, however,
the most widely studied and well documented climatic event is the Late Pleistocene Glaciation. Whilst
it is known that the Kosciuszko Massif in the Snowy Mountains was the only area of irrefutable Late
Pleistocene glaciation on the Australian mainland, the interpretation of its glacial geology has
historically been debated (Barrows, et al, 2001). Some of the earliest work was presented by David, et
al (1901), who speculated that the region would have experienced three glaciations, with an initial
icecap, followed by an episode of valley glaciation and then cirque glaciation in the Late Pleistocene.
Subsequent work by Galloway (1963) argued that only one period of glaciation would have taken place,
claiming that the evidence for the initial icecap that had been presented by David, et al (1901) was able
to be explained by other phenomena. Costin (1972) then examined glacial and periglacial sites in the
alpine region through radiocarbon dating of organic sediments from the Kosciuszko Massif. Results
were interpreted in relation to site characteristics and the present climate, with dates indicating a
‘widespread cold period’ between 34,000 – 31,000 years ago (Costin, 1972). Results further implied a
period of deglaciation between 20,000 and 15,000 years ago, followed by a warmer period, and then a
colder phase approximately 3,000 – 1,500 years ago (Costin, 1972).
More recently, Barrows, et al (2001) explored the extent to which glaciation occurred in the alps
through geomorphic mapping of the area and 10Be cosmogenic exposure dating on 24 morainic deposits
(boulders). The geomorphic map of glacial landforms on the Kosciuszko Massif built on the earlier
observations of David, et al (1901) and Galloway (1963), showing additional glacial and nivational
features. The exposure dates provided evidence for at least two distinct glaciation events, known as
the ‘Early Kosciuszko Glaciation’ (EKG) and the ‘Late Kosciuszko glaciation’ (LKG). The EKG was
concluded to have consisted of a single glacier advance before 59,300±5,400 (Snowy River advance)
and the LKG was concluded to have comprised of three glacier advances, 32,000±2,500 (Headly Tarn
Advance), 19,100± 1,600 (Blue Lake Advance), and 16,800±1,400 years ago (Mt. Twynam Advance)
(Barrows, et al, 2001). Subsequent research by Barrows, et al (2004) further utilised cosmogenic
exposure dating, that time using 36Cl, to directly date periglacial deposits from a site in the Snowy
Mountains. Ages from the non-glacial deposits were in agreeance with the observations of Barrows, et
al, (2001) demonstrating similar timing of maximum cold conditions (between 16 and 23 ka) during the
LGM in south-eastern Australia (Barrows, et al, 2004).
Other studies have utilised pollen records to infer broad environmental changes in the region (Raine,
1974; Martin, 1986; Martin, 1999). Raine (1974) analysed pollen species from a series of lake sediment
11
cores obtained from Blue Lake. The samples demonstrated an apparent absence of vegetation before
17 ka BP, after which, snow patch and feldmark communities appeared. Increased pollen counts for
these species types occurred from 17 to 13 ka cal. yr BP, which then steadied until ~8.4 ka cal. yr BP.
After this time, a large increase in total pollen deposition rate was suggested to mean a rise in tree-line
to its present position, along with further development of vegetation. Later works by Martin (1986)
produced a vegetation assemblage of the area using pollen extracted from two cirque bogs. Similar to
the study by Raine (1974), results identified several broad changes in pollen species abundance,
however, that study focused on more recent changes. Importantly, results displayed a reduction in
Eucalyptus/Poaceae values which was concluded to indicate that the region experienced a period of
dryness and relatively cooler temperatures between ca. 3,200 and 1,800 B.P. More recently, Martin
(1999) identified a decline in Snowgum (Eucalyptus pauciflora) pollen between 5200 and 1900 cal. BP,
further providing evidence for cooler conditions during this time.
Similar to this study, Stanley and De Deckker (2003) conducted research at Blue Lake in the Snowy
Mountains, however, that study focused on Holocene sedimentation through studying the quartz grain
component of a lake core. The study demonstrated that two types of quartz grains were present within
the core. One type consisted of angular grains and was shown to have originated from the granitic
lithologies of the catchment, the other type was rounded to sub-rounded, and was considered to have
been deposited by aeolian processes (Stanley & De Deckker, 2003). The mass of rounded to sub
rounded grains was interpreted to indicate changes in the degree of aridity/climate variability in the
Snowy Mountains and surrounding regions, with a high amount thought to indicate more arid
conditions. A reduction in rounded to sub-rounded grains was identified at 7.6 to 5.5 ka, indicating low
aeolian activity and therefore higher precipitation during this period. The last 1.6 ka was demonstrated
to have the strongest fluctuations in aeolian activity, with overall high aeolian dust deposition
interrupted frequently by intervals of reduced activity. This was interpreted through episodic influx of
above-average sized grains, which was taken to imply increased wind strength and stormy conditions.
More recent research conducted by Marx, et al (2011), presented substantially higher resolution dust
deposition reconstructed from a peat bog in the headwaters of the Snowy River, where fluctuations in
dust deposition were interpreted to provide information about the Snowy Mountains palaeoclimate
during the mid-late Holocene. More specifically, the mass of dust deposition was taken to indicate
changes in the degree of aridity/climate variability within the Murray-Darling Basin (MDB), the main
source of dust transported to the Snowy Mountains. It is suggested that due to the Snowy Mountains
occurring at the same latitude as the MDB, these results may also be taken to imply changes in the
moisture regime of the Snowy Mountains. Results showed that the lowest rates of dust deposition over
12
the last 6500, cal. yr BP occurred from 4,000 to 2,000 cal. yr BP, this was suggested to mean increased
precipitation and it was concluded that enhanced ENSO conditions at this time resulted in wetter
conditions in the MDB and therefore wet conditions were similarly likely to affect the Snowy Mountains.
Additionally, results from that investigation indicated a substantial increase in dust emission from 2,000
cal. BP to present, implying decreased rainfall and drier conditions (Marx, et al, 2011). Importantly,
results from this investigation demonstrated a significant increase in dust deposition over the last 130
years, coinciding with the arrival of Europeans, and the advent of broad land clearing and agriculture.
It is suggested that these activities destabilised the soils, leading to wind erosion that substantially
exceeded dust deposition during the preceding 6,500 years.
Dodson, et al (1994) analysed lake sediments obtained from the Club Lake basin in the Snowy
Mountains using a series of geochemical, biological and sedimentary proxies. The purpose of this
research was to compare environmental changes from prehistoric and historic (after European
settlement) periods through interpreting changes in vegetation, erosion, productivity and fire regime
over the preceding one thousand years (Dodson, et al, 1994). Results of the investigation demonstrated
that disturbance in the prehistoric period was minimal, and were mainly activated by fire (Dodson, et
al, 1994). The historic period, however, demonstrates results which were interpreted to imply increased
erosion and fire regime, as well as increased variability in pollen species.
13
2.2 Anthropogenic Influences in the Snowy Mountains
2.2.1 Aboriginal Settlement and Land Use in the Snowy Mountains
Research conducted in the Snowy Mountains have identified a range of archaeological evidence that
suggest visitation by Aboriginal people since the mid to late Holocene. One study speculated that the
region would have first been inhabited either as soon as glacial conditions decreased after the last
glacial maximum (Flood, 1980), or following economic shifts around 7,000 – 8,000 years ago (Theden-
Ringl, 2016). However, the latter is more likely since it has been shown that soil and peat would not
have established in the Snowy Mountains until approximately 9,000 years ago (Stromsoe, et al, 2016).
Studies have also offered evidence for uses of the alpine region by Aboriginals, for instance, an early
study by Flood (1973) studied the ethnographic records pertaining to Bogong moth (Agrostis infusa)
feasts, and proposed a functional occupation model over the past 3000 years which linked to the
seasonal exploitation of the moth for food resources. Flood (1980) proposed that larger occupation
sites, possibly the result of repeated and/or extended visitation at various times of the year, would be
found at altitudes up to 1200 m. Between 1200 m and 1500 m, smaller lithic scatters would be the
dominant site type, reflecting short term summer camps possibly associated with specialised activities.
This model of archaeological site distribution has been supported by most studies, however, some
research has suggested that Flood may have overemphasised the influence of the Bogong Moth in
interpreting traditional Aboriginal occupation and resource use in the region (Bowdler, 1981). Bowdler
(1981) alternatively argues that the tubers of the ‘Daisy Yam’ (Microseris longifolia) would have been a
more reliable staple food, with the Bogong Moth harvesting restricted to special and infrequent
ceremonial occasions. Lennon (1999) also suggested intensive seasonal use of the high country from
~4,500 BP, with his research similarly attributing this increase in activity to the availability of the Bogong
Moth and the Daisy Yam.
Despite there being substantial evidence of Aboriginal visitation in the Snowy Mountains, there is little
evidence of permanent residence (Aplin, et al, 2010). Aplin, et al (2010) focused on mapping all sites of
early aboriginal occupation in the south-eastern highlands and found only two higher altitude sites
(>1,000 m asl), Yarrangobilly Y258 (Aplin, et al, 2010) and Nursery Swamp 2 (Rosenfeld, et al, 1983),
which revealed definite occupation older than 3,000 years (Aplin, et al, 2010). Aplin, et al (2010)
speculated that the absence of evidence from the early to mid-Holocene may have been related to
regional expansion of wet sclerophyll forest in response to the Holocene Optimum, which could have
affected the accessibility of the region until 4,500 year ago when wetter forest conditions declined. In
contrast, one study has offered evidence of Aboriginal significant activity in the alpine regions, that are
14
interpreted as permanent occupation, that date back to approximately 21,000 years ago (Sullivan &
Lennon, 2004). Another study similarly gave evidence of Aboriginal occupancy in the lower valleys that
pre-dated other works, with a total of 280 sites in the Snowy River valley being identified and dated
back to 10,000 to 15,000 years ago (Good, 1992). However, it is commonly agreed that frequent activity
began to take place around 4,000 years ago and continued their use of the Alps until the arrival of
European graziers from the 1820s in New South Wales (Crabb, 2003).
In addition to ethnographic records and archaeological research, a number of studies have found
evidence for increased fire activity in the higher altitudes from approximately 3000 years ago, which is
speculated to be attributed to humans (Hancock, 1972; Good, 1992). This was concluded because the
increase in fire activity corresponds with ethnographic records and Aboriginal oral tradition which
suggest the region would have been shared by tribes during the summer (Hancock, 1972; Good, 1992),
with fire said to be used for Aboriginal corroborees, settling disputes, marriages and initiation
ceremonies.
2.2.2 Development of the Kosciuszko National Park Post-European Settlement
The Kosciuszko National Park has been subject to several human activities since European settlement
(Scherrer & Pickering, 2001), with some of these activities having had a significant impact on the KNP
environment. Most notably, extensive grazing practices in the alpine region (Scherrer & Pickering,
2001;2005; Dodson, et al, 1994; Costin, 1954, Good, 1992; Stromsoe, et al, 2013), and increased
tourism within the Park (Johnson & Johnson, 2004; Pickering & Growcock, 2009; Scherrer & Pickering,
2001;2010) have been demonstrated to have had quantifiable impacts on the alpine landscape. More
broadly, studies have also shown how wider industrial activities such as coal mining and metal
production, as well as increased agricultural activity since European settlement have impacted the
region (Marx, et al, 2010). The following section will discuss the history of land use in the KNP since
European settlement, as well as the evidence which has been presented about the effects of these
activities on the Australian alpine environment.
Use of the Snowy Mountains for pastoralism began as early as 1829, after establishing pastoral stations
at lower altitudes (Good, 1992; Sullivan & Lennon, 2004). According to Green, et al (2006), grazing in
the alpine region was initially used in response to drought conditions at lower altitudes, however,
practices steadily increased until most of the alpine and subalpine areas were being grazed every
summer. This use of the alpine region was originally unregulated until the introduction of grazing leases
in the 1880’s, however, it is documented that illegal grazing still occurred (Scherrer and Pickering,
2010).
15
A push for protection of the Snowy Mountains from the impacts of grazing began to occur following a
key political decision made by NSW Premier, Sir William McKell in 1944 (Worboys & Pickering, 2002).
McKell responded to the increasing concern for the way in which grazing activities and associated
burning was degrading much of the catchment area by introducing an Act of Parliament that brought a
new form of management to the Snowy Mountains of NSW known as the Kosciusko State Park Act of
1944 (Worboys, et al, 2001). The act established a high-level trust of eight members to have ‘care,
control and management’ of an assigned ‘Kosciuszko State Park’ area spanning 526,000 ha (Worboys,
et al, 2001). This Act provided for ‘improvement, development and maintenance’ of infrastructure as
well as the ‘prevention and control of fires’ and nature conservation efforts (Worboys, et al, 2001).
Importantly, the Act enabled elected management to have control over activities including grazing,
mining and timber cutting in the park. After the establishment of the Act, grazing was removed from
the immediate alpine area, however it wasn’t until 1967, when the Kosciuszko State Park became the
Kosciuszko National Park with the NSW National Parks and Wildlife Act (1967), that grazing practices in
the mountains ended completely (Worboys & Pickering, 2002). This new Act established that the
National Parks and Wildlife Service (NSW NPWS) were to take over management of the Park, including
the alpine area (Worboys & Pickering, 2002).
A number of studies have highlighted the introduction of grazing as the first human activity to
substantially alter the Australian alpine landscape, most notably through disturbance of its alpine
vegetation and accelerated erosion of the organic humus soils (Scherrer & Pickering, 2001;2005;
Dodson, et al, 1994; Costin, 1954; Good, 1992; Stromsoe, 2016). The earliest ecological research to
document the effects of grazing in the alps was undertaken in the late 1800’s by botanists Baron
Ferdinaud von Mueller, John Maiden and Richard Helms, who attempted to raise concerns for the
degradation of the vegetation in the alpine and sub-alpine zone (Good, 2014). Despite these early
observations, the impacts of grazing went unnoticed until an ecological survey by Byles (1932) revealed
the extreme and continuing decline of the alpine vegetation, as well as the massive loss of organic soils
from some alpine catchments due to unrestricted grazing. Subsequent conservation research (Costin,
1954, Costin, 1958; Costin, et al, 1959; Durham, 1959) further affirmed the findings of Byles (1932).
Importantly, the impacts of grazing on soil erosion have been identified in a number of studies. One
study, in particular, which was conducted during the time when grazing was taking place in the
mountains, demonstrated that these practices had caused severe erosion of the alpine landscape
through analysis of soil erosion plot studies (Costin, 1954). Results indicated an average erosion rate of
approximately 460 ± 220 (SE) t/km2/year in areas where the ground cover had been disturbed by
livestock, as compared to vegetated areas where erosion was undetectable (Costin, 1954). A later study
16
by Bryant (1971) conducted soil surveys in the Guthega catchment only a few years after grazing
stopped in the KNP, and determined that 30 km2 of the 90 km2 catchment was ‘slightly to severely
eroded’. More recently, Stromsoe, et al (2016) produced estimates of late Holocene soil production
and erosion in the Snowy Mountains from radiocarbon ages of soil organic matter obtained from
hillslope deposits. Results implied a hillslope erosion rate of 60 t/km2/y, with a range of 10-90 t/km2/y
over the past 100 years at both sample sites, Guthega and Club Lake. The upper estimate was compared
with the results of Costin (1954), and it was suggested that there had been significant decrease in mean
erosion rate over the last ~60 years, approximately since grazing was excluded from the alpine zone.
In addition, changes in sediment composition at sites in the KNP have been interpreted as an erosion
response to grazing. This is exemplified by Stromsoe, et al (2013), where changes in the metal ratios
Rb/Sr, Th/Ba, Ti/Ca and Nd/Sr were interpreted to indicate a change from deposition of rock weathering
material to soil erosion material corresponding with the time of grazing. Furthermore, results showed
an increasing then steadying or decreasing delivery of more highly weathered material to the lake
within the last 150 years, corresponding with the introduction and then elimination of grazing from the
Snowy Mountains.
In addition to vegetation change and erosion signals, changes in fire regime have been associated with
the grazing period in the Snowy Mountains. This is because pastoralists extensively used vegetation
burning as a management tool to remove areas of health, unpalatable tussocks, and to stimulate fresh
growth (Irwin and Rogers, 1986). Significantly high concentrations of charcoal have been identified by
Dodson, et al (1994) and Sharp (1992) (cited by Zylstra, 2006).
In recent decades, tourism (and associated developments, i.e Ski resorts) has become one of the main
land uses of the Kosciuszko National Park, with continued growth from the mid-1950s through until
present (Pickering & Growcock, 2009). Tourism has become one of the most significant issues for
management in the alpine zone, with several studies associating significant changes to the alpine
environment with the increased visitation (Good 1992; Buckley, et al, 2000). For instance, Johnston &
Johnston (2004) demonstrated this through a comparison of vegetation and soils near roads and
adjacent areas in the Kosciuszko National Park. Results found that soils on the road verges had
significantly less humus, more gravel and sand, lower levels of nutrients, lower pH and electrical
conductivity than soils sampled 10 m away from the road where there was native vegetation. This study
also found that vegetation composition and cover were affected, with roadsides having more bare
ground and weed cover than nearby ‘natural’ sites. Furthermore, Pickering and Growcock (2009)
evaluated the impacts of bushwalking in the KNP, and demonstrated how trampling effects vegetation
communities within the alpine-subalpine zone, even those which are considered to be the most
17
resistant of the alpine-subalpine communities. The two communities investigated, the tall alpine
herbfield and subalpine grassland, showed limited recovery with damage still evident one-year post
trampling (Pickering & Growcock, 2009).
Outside of the immediate land uses of the Kosciuszko National Park, the alpine environment has been
impacted by wider human activities since European settlement, including the accumulation of metals
due to industrialisation and increased agriculture (Marx, et al, 2010;2011;2014; Stromsoe, et al, 2013).
A study by Marx, et al (2010) explored the history of atmospheric metal contamination in the Snowy
Mountains through analysis of two peat bogs from remote alpine sites in the Kosciuszko National Park.
The study presents evidence of historic atmospheric metal pollution, specifically Pb, Zn, Cu, Mo, Ag, As,
Sb, Zn, In, Cr, Ni, Ti and V, and concluded that each of these metallic elements have been accumulating
in its surficial environment at approximately 2-5 times the natural rate recorded prior to European
settlement (Marx, et al, 2010). Marx et al (2010) ascribed several of the pollutants to major polluting
industries, including metal production, agriculture and coal combustion. Importantly, Pb enrichment
was interpreted to be closely tied with mining and smelting operations at Broken Hill and an increase
in the otherwise stable yttrium/holmium (Y/Ho) ratio was interpreted to imply pollution of phosphate
fertilizers from agricultural practices.
The work of Marx, et al (2010) has been subsequently affirmed in research conducted by Stromsoe, et
al (2013), where metal contamination was examined in two lake cores obtained from Club Lake. The
enrichment values, however, were significantly lower than those of Marx, et al (2010). This was
suggested to have been due to dilution by natural sediment (Stromsoe, et al, 2013). These conclusions
were further demonstrated in a subsequent study examining contaminate metals throughout the
Snowy Mountains environment (Stromsoe, et al, 2015). Furthermore, Stromsoe, et al (2013) aimed to
investigate whether there had been a significant environmental impact on the region from AgI seeding
agents, an operation that had been implemented by the Snowy Hydro Scheme several years prior. It
was found that no significant increase in Ag accumulation was found, implying that cloud seeding was
not affecting the lake.
18
Part 2
3. Physical Setting and Methods:
3.1 Regional Setting
The Australian Alps are located within the Lachlan Fold Belt, extending from the high country of the
Australian Capital Territory (ACT), through the Snowy Mountains in New South Wales (NSW), to the
highlands of Victoria (Scherrer & Pickering, 2010). This region makes up the southern portion of the
Great Dividing Range, a formation that spans a distance of >3,500 km and runs parallel (at
approximately 50 to 150 kilometres inland) to the east coast of Australia (Scherrer & Pickering, 2010).
This thesis focuses on a remote site, Blue Lake, a lake within the alpine area (A.K.A the Snowy
Mountains) of the Kosciuszko National Park. The KNP is a protected area network which spans
approximately 6,500 km2 and lies between latitude 35°30’ and 37°00’ and longitude 148°00’ and
148°30’ (Fig.2) (Wyborn, 1977).
Figure 2: Location of the Kosciuszko National Park, divided into the Alpine, Subalpine zone and Montane and Tableland Zones
(Source: Pickering & Growcock, 2009)
19
The Snowy Mountains is the alpine zone of the KNP (>1,850 m) and encompasses the four highest peaks
in the Australian alps, Mt Kosciuszko, Carruthers, Twynam and Tate (Fig.3) (Raine, 1974). The Snowy
Mountains have traditionally been characterised as a high elevation plateau (~1,500-2,200 m ASL) of
moderate relief (Dodson, et al, 1994, Stromsoe, et al, 2016), with the highest peak, Mt Kosciuszko,
reaching a maximum elevation of 2,228 m. In character, the Kosciuszko plateau is a rolling upland with
broad valleys, sloping gently north-westwards from its highest point at Mt. Kosciuszko (Raine, 1974).
To the east, the plateau is deeply dissected by the valleys of the Crackenback (Thredbo) and Snowy
Rivers. To the west, the country falls steeply from the plateau level of approximately 2,000 m to the
floor of the Geehi valley and the Swampy Plains Rivers (Raine, 1974). It has been suggested that the
Snowy Mountains region demonstrates distinct differences in its age, formation and geology in
comparison with other mountainous regions around the world, particularly due to its low-set
topography and moderate slopes, as well as its intra-plate setting and resulting tectonic stability (Costin,
et al, 2000, Galloway, 2004, Scherrer & Pickering, 2010). Due to these characteristics, as well as its
limited Pleistocene glaciation history (Barrows, et al, 2001), the Snowy Mountains exhibits a relatively
gently sloped, soil-mantled landscape in contrast to the icy, rugged features of alpine areas in Europe,
Asia, America and New Zealand (Kirkpatrick, 2003).
Figure 3: Map of the Mt Kosciuszko Alpine Area (Worboys & Pickering, 2002). Blue Lake is circled in red.
Blue Lake
20
3.1.1 Geology
The present geological and topographic characteristics of the Snowy Mountains demonstrate the
remains of an ancient palaeoplain surface, with its two main rock types of granite and altered sediments
(Wyborn, 1977; Wyborn, et al, 1990; Galloway, 2004). Considerably more than half of the Snowy
Mountains area and surrounding regions is made up of a large granitic batholith, which is generally
characterised as elongate and concordant with the north-south striking sediments (Kolbe & Taylor,
1996). The ‘Kosciuszko Batholith’ forms the central mass of the area, stretching approximately 105
kilometres from south of the Victorian border to north of Kiandra and forming most of the Kosciuszko
Plateau (Kolbe & Taylor, 1996). To the west, it is terminated by a narrow strip of Silurian sediments and
metamorphic rocks. On its eastern side, it is separated from the Berridale Batholith by Upper Ordovician
sediments and faulting. The main mass of Kosciusko Granite is intruded by additional granites at
Jindabyne, Island Bend and Eucumbene (Kolbe & Taylor, 1996). The ‘Kosciuszko Batholith’, like most
granites, is primarily composed of feldspar ((KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8) and quartz (SiO2), with
minor constituents of mica KAl3Si3O10(OH)2 and amphiboles (Frost, et al, 2001).
The geological evolution of the Snowy Mountains has been sub-divided into four, broad, time-based
groups, these include: (1) the Ordovician to Lower Devonian (approximately 30-370 million years old);
(2) the Tertiary (50-2 million years old); (3) the Pleistocene (last 2 million years); and (4) the Holocene
(approximately the last 11,000 years) (Galloway, 2004). During the Ordovician to Lower Devonian,
sedimentary rocks of mainly sandstone, mudstone and shale, which formed quartz-rich greywackes,
were deposited in deep marine environments (Wyborn, 1977). Remnants of these rocks are present
within the geological record of the Kosciuszko region, although transformed into hard quartzites, softer
phyllites, and schists (Galloway, 2004). Periods of folding, uplifting and sedimentation continued during
the Ordovician, into the Silurian and early Devonian periods with intrusion of granitic rock (Wyborn, et
al, 1990; Good, 1992). From the mid-Devonian, a period of extensive erosion dominated the landscape
for approximately 250-300 million years, causing the area to become a lowland with ridges on more
resistant rocks (Galloway, 2004). After this, a period of extensive uplift characterised the Tertiary,
resulting in fracturing and faulting (Costin, et al, 2000). The major fracture patterns in the rocks
provided zones of weakness along which the streams rapidly eroded and produced deep linear valleys
(Costin, et al, 2000). Volcanic activity during the Miocene resulted in the eruption of basalts which
became deposited in these valleys (Galloway, 2004).
Unlike most alpine regions around the world, where repeated growth and decay of ice sheets occurred
during Pleistocene, it is suggested that mainland Australia only developed small cirque glaciers, believed
to be restricted to above 1850 and covering a maximum area of 15 km2 in the Kosciuszko National Park
21
during the Late Pleistocene (Barrows, et al, 2001). Evidence of glacial conditions is demonstrated
through remnant features such as cirques, moraines, lakes, erratics and ice-scratched surfaces
(Galloway, 2004). Thirteen cirques have been identified and are mainly found in the lee of the Main
Range where accumulation of snow was maximal and melting minimal (Barrows, et al, 2001). Following
deglaciation, five glacial lakes were formed within these cirques. Of these, Blue Lake is the only lake
that was formed by glacial erosion of the bedrock (the others formed behind morainic dams), indicating
it was the major glacier on mainland Australia (Galloway, 1989;2004).
Despite there being limited glacial landforms, periglacial activity across the Snowy Mountains is likely
to have been considerably more widespread during this time (Galloway, 1965; Barrows, et al, 2004).
Periglacial processes have been identified through features such as solifluction, frost-shattered
bedrock, boulder fields and several others which have been identified at altitudes of 600 metres and
above (Galloway, 1965;2004; Barrows, et al, 2004). Furthermore, periglacial slope processes were
considered sufficient to initiate widespread stripping of the pre-existing soil and vegetation, producing
stony rubble which today underlies much of the alpine/subalpine zone (Costin, 1972).
The Holocene in the Snowy Mountains is marked by the melting of the last glaciers as the climate
warmed with the deglacial period estimated to have ceased by approximately 15,000 years ago (Costin,
1972; Barrows, et al, 2001). By ~11,000 years ago, the climate was relatively similar to that of the
present day, and therefore, it is generally agreed to be when the development of soils and vegetation
began (Galloway, 2004). For instance, one study dated the transition from mineral to organic
sedimentation in a core obtained from the Caledonia Fen (1280 AHD) by this time (Kershaw, et al, 2007).
This has been supported by pollen data from Mt. Kosciuszko at elevations between 1955-1960 AHD,
which suggested grassland was not present in the alpine tract until 11 ka yr cal. BP with the transition
to the current alpine community occurring sometime after 9 to 7 ka y cal. BP (Martin, 1986). Some
research, however, have speculated a return to suitable conditions for soil development earlier than
this time. One study, for example, obtained several cores from Blue Lake, one of which produced basal
dates of ~15.3 ka for organic material overlying glacial till (Raine, 1974). Another study, produced
slightly older dates from their core of Blue Lake which dated to ~15.8 ka (De Deckker and Shakau,
unpublished data cited in Barrows et al, 2001). In addition to soil development, other land forming
processes that characterise the Holocene include solifluction of frost-scattered debris, erosion of soils
and other fine textured materials, stone movement by snow pressure and nivation (Costin & Wimbush,
1973).
22
3.1.2 Climate
The alpine region of the Snowy Mountains experiences a cool, montane climate, with mean
temperatures varying from 18°C in the summer to -7°C in winter and annual precipitation of
approximately 1400 mm (BOM, 2017). The region lies toward the northern limits of the influence of the
mid-latitude westerly wind belt, where an interaction between tropical and extra-tropical weather
systems play an important role in the generation of precipitation (Theobald, et al, 2015). In the winter
and spring seasons, these westerly sector winds dominate, causing the western slopes to receive heavy
rain and snowfall which is enhanced by orographic uplift as the mountains are perpendicular to the
prevailing westerlies (Brown & Milner, 1989). A precipitation spill over effect occurs on the eastern side
of the range. This declines with distance from the mountain peaks (Brown & Millner, 1989). In general,
continuous snow cover is present for up to 4 months of the year with isolated snow patches sometimes
persisting over the entire year (Stromsoe, et al, 2016).
Due to the Snowy Mountains being located up wind of the Murray-Darling Basin (MDB) (and making up
its eastern boundary), conditions in the alpine zone are influenced by climatic variability that is
experienced in the MDB. For this reason, it is necessary that a broad description of the MDB climate be
made. In general, the MDB is a large, semi-arid basin which extends from the subtropics to the mid-
latitudes. Due to the extent of the MDB, the northern and southern regions are generally influenced by
different weather systems. In particular, the northern MDB is primarily affected by tropical systems (i.e
Australian Summer Monsoon) and interactions between tropical and extra-tropical systems, while the
southern MDB is mostly influenced by extra-tropical systems (ie. Mid-latitude westerlies) (Gallant, et
al, 2012). Due to these systems, the northern MDB receives the majority of its annual rainfall during
the warmer months (November to April), while the southern MDB mainly receives rainfall in the cooler
months (May – October) (Gallant, et al, 2012). Since the Snowy Mountains are located closer to the
southern portion of the MDB, the climate of this region more heavily influences conditions in the alpine
zone.
23
3.1.3 Vegetation
Due to the highly diverse group of environments present within the Kosciuszko National Park, the area
has developed a wide range of distinctive vegetation types (Costin, et al, 2000). The flora found in the
Kosciuszko National Park have been divided into three floristic/elevational zones, these are alpine
(>1,850 m); subalpine (1,500 – 1,850 m) and lowland (300 m – 1,500 m). The main low land
communities consist of savanna woodlands of the Eucalyptus pauciflora-Eucalyptus stellutata alliance
with patches of dry sclerophyll forests of the Eucalyptus macrorhyncha-Eucalyptus rossii alliance on dry
stony sites (Costin, et al, 2000). The vegetation in the subalpine region changes fairly abruptly from tall
forests to lower-growing and more open, sub-alpine woodland and scrub of the Eucalyptus niphophila
(snow-gum) alliance. The snow-gum is the main tree species found in this region (Costin, 2000). In the
high altitude alpine regions, above 1,860 m, the main growth forms are perennial herbs and shrubs that
typically do not grow taller than one metre (Costin, et al, 2000). Some of the flora found in the alpine
and subalpine region includes Asteraceae (daisies), Poaceae (grasses) and Cyperaceae (sedges),
followed by Apiaceae (carrot family), Ranunculaceae (buttercups), Juncaceae (rushes) and
Epacridaceae (heaths) (Costin, et al, 2000).
In addition to native flora, there are a number of introduced species in the KNP, including weeds which
pose a threat to the ecology of the Australian Alps (Johnston & Pickering, 2001). Their abundance has
increased rapidly over the past century as a result of anthropogenic disturbance (Costin, et al, 2000).
24
3.2 Blue Lake and its Catchment
Blue Lake is located within the alpine region (~1890 m AHD) of the Kosciuszko National Park,
approximately 3 km north-west of Charlotte Pass, on the eastern side of the Snowy Mountains main
range, on Mt Twynam, (36°24’16” S and 148°18’55” E) (Google Earth, 2017) (Fig.4). It occupies a
catchment area of 1.9 km2, with the catchment lithology characterised by two granite plutons and
metasediment outcrops which form bands that run NNE-SSW across the catchment (Wyborn, et al,
1990). The rocky outcrops dominate the catchment, with only sparse areas covered with a thin layer of
peaty sediments (Stanley & De Deckker, 2003). Blue Lake is the largest (0.144 km2) and deepest (28 m)
of the four cirque lakes in the Snowy Mountains (Stanley & De Deckker, 2003), but is the lowest in
elevation. The geomorphology of the lake lends itself as a sedimentation sink due to occupying the
lower (and larger) basin of a two-storeyed cirque on the southeast face of Mt Twynam, as well as being
partially dammed by a terminal moraine at its eastern side (Dulhunty, 1945). The small, upper cirque is
called the Upper Blue Lake Cirque. Another smaller cirque, Mt Twynam cirque, occurs on the northeast
face of Mt Twynam (Good, 1992).
Figure 4: Location of Blue Lake and associated moraines (Source: Good, 1992)
25
The Blue Lake valley contains four terminal moraine ridges (Fig.5) (Barrows, et al, 2001). The oldest
feature in the valley is the flat crested, outermost moraine (BL-I) (59.3 ± 5.9 ka BP), which lies above
the Snowy River and another similar moraine (‘Helms moraine’) (18.9 ± 1.7 ka BP). The downstream
south-eastern extent of Blue Lake consists of a longitudinal, subglacial carved ridge (15.9 ± 1.4 ka BP),
with a series of three distinct terminal moraines ridges (BL-II, BL-III, BL-IV) extending below this
(Barrows, et al, 2001). The weighted means of the three youngest moraines were dated to be 32,000 ±
2500 yr (BL-II), 19,100 ± 1600 yr (BL-III), and 16,800 ± 1400 yr (BL-IV) (Barrows, et al, 2001). At the
north-eastern extent of Blue Lake, a small outflowing stream known as Blue Lake Creek flows
downslope into Headley Tarn.
Figure 5: Sample sites and their ages from Barrows, et al, 2001 (Source: Barrows, et al, 2001)
Blue Lake is approximately trapezoidal in shape with a length of 540 m and width of 360 m (Raine, 1982)
(Fig.6). The bathymetry of the lake is uneven and relatively deep in sections, with a series of parallel
moraine ridges extending into the lake (Raine, 1982). The unique shape of Blue Lake has mainly been
attributed to glaciation in the Pleistocene (Barrows, et al, 2001), where glacial action enabled its
excavation (Stanley & De Deckker, 2003). The deglaciation that followed allowed Blue Lake to emerge
as a deep lake consisting of two main basins (Australian Government, 2008). Bathymetric data has
demonstrated that these two basins have maximum depths of just over 26 m and 28 m and are situated
near the centre of the lake and close to the outlet, respectively (Raine, 1982).
26
Figure 6: Bathymetry and surface geology of Blue Lake (Source: Raine, 1982)
Sediment has been accumulating in these basins for 15.4 ka i.e. since deglaciation (Raine, 1974). It has
been suggested that most of the minerogenic component of the sediment, eg. Quartz grains, are the
residuals of erosion of the granite lithologies within the catchment area, however, some of the
Holocene aged sediments have also been shown to have originated from aeolian formations from the
mallee region to the west of the Snowy Mountains (Stanley & De Deckker, 2003). Blue Lake is noted for
being the only dimictic lake in mainland Australia, meaning it exhibits a well-developed thermal
stratification regime (Raine, 1982). The intensity of the stratification appears to vary over the year, with
Raine (1982) suggesting that epilimnetic temperature peaks in summer months. This behaviour is
attributed to its relatively great depth, cover of ice in winter and low ratio of inflow to volume (Raine,
1982).
27
The water in Blue Lake is primarily derived from surface run-off (Cullen & Norris, 1989), which has been
regulated by climatic conditions. During the winter, precipitation is primarily snow and the lake is
generally frozen from June to November, therefore the rate of outflow is low (Australian Government,
2008). During summer, snow thaw and increased rainfall causes a significant increase in both the inflow
and outflow from Blue Lake. The lake water has been characterised as having low conductivity, turbidity
and neutral pH (Stanley & De Deckker, 2003).
3.3 Core Collection and Sampling
In February 2017, a 0.85 core (BLUE01) was collected from Blue Lake, a basin which is located on the
south-eastern side of the Main Range on Mt Twynam (36 ͦ24’16” S, 148 ͦ18’55” E). The core was
collected from a depth of 23-metres (36° 40’52” S, 14° 31’65” E), close to the deepest point of the lake.
Collection was achieved by using a Universal Corer Device connected to a 1.5-metre-long polycarbonate
coring tube, which was operated from a floating platform. The procedure to extract the core involved
inserting the coring tube in the lake bed, trapping the sediment using a flow actuated valve at the top
of the corer and then capping the bottom so that it could be taken ashore. Once removed from the lake
bed, it was sealed at the top using Sodium polyacrylate powder (Tomkins, et al, 2008) for return to the
laboratory.
The core was transported to the Australian Nuclear Science and Technology Organisation (ANSTO)
where it was split using a Geotek core splitter. One half of the core (BLUE01a) was selected for
destructive analysis and sub-sampled at 5 mm intervals with a stainless-steel scalpel and spatula. The
outermost 2 mm of each sub sample was excluded in order to prevent contamination by smearing of
material down the side of the PVC pipe during core collection. Upon completion of core subsampling,
a series of analyses including dating, chironomid and macro-charcoal was undertaken. The other half
of the core (BLUE01b) was utilised for core description, bulk density, grainsize and Loss-On-Ignition
analysis.
3.4 Core Description
BLUE01b was examined visually in order to produce a down-core description of the sediment. Visually
distinguishable changes in colour and composition of the sediment was utilised to divide the core into
sections. The colour of the sediment was determined using a Munsell Colour book.
28
3.5 Chronology
Core chronology was determined using 210Pb for the last ∼150 years and Accelerator Mass
Spectrometry (AMS) radiocarbon dating (14C) for older samples. Both 210Pb and 14C dating were
performed at ANSTO. Results from these analyses were then combined and a Bayesian age-depth
model was produced using the R package, ‘Bacon’.
3.5.1 210Pb Dating
A total of 14 subsamples from the uppermost 14 cm of BLUE01a were selected for 210Pb (n = 14) dating.
Approximately 1.0 g of dry weight sample was analysed from each 5-mm thick sub sample for 210Pb
activity using α-spectroscopy. 210Pb dating is a technique based on the decay of the naturally occurring
radio-isotope lead-210, an unstable isotope with a half-life of 22.3 years and a dating range of 100-200
years (Appleby, 2001). Changes in 210Pb activity in the core were determined by measuring the total
210Pb activity, and its two components, the ‘supported’ and ‘unsupported’ 210Pb activity in the samples.
The supported 210Pb derives from in situ decay of the parent radionuclide 226Ra, and unsupported 210Pb
derives from atmospheric flux (Appleby, 2001). Total 210Pb activity is determined by measuring 210Po,
the grand-daughter isotope of 210Pb, with which it is assumed to be in secular equilibrium. The
supported component is determined by 226Ra activity and the unsupported 210Pb is determined by
subtracting supported 210Pb activity from that of the total 210Pb activity (Appleby, 2001). 210Pb dates
were then calculated using the Constant Rate of Supply model (Appleby & Oldfield, 1978), assuming
constant deposition between samples which were spaced approximately 5 – 10 mm apart. Errors in
returned 210Pb dates were estimated from counting uncertainty (Stromsoe, et al, 2013).
3.5.2 14C Dating
Charcoal fragments obtained from 6 subsamples from BLUE01a were selected to undergo AMS
radiocarbon dating. The charcoal fragments were isolated from the sediment matrix by treating them
with potassium hydroxide (KOH), then put in a hot bath for 30 minutes. The samples were then filtered
using a sieve mesh size of 90 µm and then transferred into small vials. Charcoal fragments were
handpicked from each sample using tweezers and a binocular microscope and finally weighed. The
charcoal samples were submitted for AMS radiocarbon dating at ANSTO, where they were pre-treated
using the AAA (Acid-Alkali-Acid) procedure. The AAA procedure involves treatment with HCl to remove
carbonates and NaOH to remove mobile carbon. The resultant radiocarbon dates were calibrated to cal
ka BP (BP = 1950 CE) using the Southern Hemisphere calibration curve ‘SHCal13’ (Hogg, et al, 2013).
29
3.5.3 Mass Accumulation Rate
Mass accumulation rate’s (𝑀𝐴𝑅) (g/cm2/y) were calculated from the product of the increment volume,
derived from the age model and the corresponding dry bulk density, according to equation (1).
𝑀𝐴𝑅 = 𝑆𝐴𝑅 × 𝐵𝐷 (1)
Where 𝑆𝐴𝑅 is the linear sediment accumulation rate (cm/yr) and 𝐵𝐷 is bulk density (g/cm3).
3.6 Dry Bulk Density
Eighteen subsamples were selected for dry bulk density analysis. A syringe with a radius of 11 mm was
utilised to collect approximately 1 cm3 from each depth. The volume and weight of the wet sediment
was recorded and the samples were placed in an oven at 65°C for 3 days. Once dry, the samples were
reweighed and dry bulk density calculated by dividing the weight by volume. Results were interpreted
in excel and presented to demonstrate changes in dry bulk density down core.
3.7 Grain Size
Eighteen subsamples from horizons at 5 cm intervals were prepared for grainsize analysis using the
following procedure: Firstly, each sample was sieved to <1 mm (limit of the Mastersizer), then treated
with a 80° C, 10% hydrogen peroxide (H2O2) solution to dissolve the organic component of the
sediment. The samples were transferred into vials and then centrifuged, decanted, refilled with water
and centrifuged for a second time to remove the acid component in the sample. Grainsize was then
measured using a Malvern MasterSizer 2000 laser sizing instrument at UOW. Results from the analysis
were then interpreted in excel and ‘C2’ program, to demonstrate changes in grainsize down core.
3.8 Geochemistry
Geochemical and magnetic susceptibility analyses was carried out on BLUE01a using the Itrax micro-
XRF Core Scanner at the Institute for Environmental Research, Australian Nuclear Science and
Technology Organisation (ANSTO). This technique is non-destructive and gives data in the form of
counts, which is a ‘semi-quantitative’ value that reflects relative abundance of various elements
throughout the core (Croudace, et al, 2006). All data was collected at a step size of 200 microns. Optical
and radiographic images were also produced by the Itrax micro-XRF core scanner at the same
resolution. Magnetic susceptibility was measured at 5 mm intervals. The resulting data was processed
30
in Microsoft Excel and elements with maximum readings of <100 kilo counts per second (KCPS) were
removed (Van der Bilt, et al, 2015). Elemental counts were then normalised over the ratio of incoherent
and coherent scattering of molybdenum (Mo Ratio) to account for water/organic content (Davies, et
al, 2015). Mo-ratio acts as a proxy for the organic content of the material as samples high in organic
matter tend to be composed of lighter elements, resulting in more incoherent scattering of the Mo.
Heavier elements cause more coherent scattering, leading to a lower Mo(Inc/coh) ratio (Guyard, et al,
2007). Data was imported into the computer program ‘Canoco for Windows 4.5’, in order to perform a
Principle Component Analysis (PCA). The PCA was performed in order to visualise the complex
multivariate dataset and determine which elements are most ‘important’ (i.e. correlated to Axis 1), as
well as help to determine the main types of variation in the elements (i.e. between Axis 1 and Axis 2).
Normalised elements that co-varied (their vectors pointed in the same direction) were selected and
presented against depth, age and magnetic susceptibility.
The ratio of Pb/Ti has also been plotted to indicate Pb enrichment in the core. Additionally, Ta/Ti has
been plotted against Nd/K to demonstrate geochemical changes in the sediment.
3.9 Macro-Charcoal
Analysis of macroscopic charcoal was performed on 61 subsamples from BLUE01a, in order to explore
the history of fire activity in the KNP (Mooney & Tinner, 2010). Analysis of macroscopic charcoal was
chosen over microscopic charcoal because it reflects fire at a local scale, whereas microscopic charcoal
is generally interpreted to be sourced from regional and extra-regional areas (See Mooney & Tinner,
2010). All subsamples between 0 cm and 20 cm (at 5 mm intervals) were selected, as well as a
subsample every 2 cm after this until the base of the core. The procedure used to carry out this analysis
followed the methods of preparation and image analysis set out by Mooney & Black (2003). Subsamples
were extracted from the core and their volume estimated using water displacement. 10% Hydrogen
peroxide (H2O2) was then added to the samples for 7 days. The purpose of this was to oxide less
resistant organic matter in order to aid the identification of charcoal particles. The samples were then
washed with distilled water through a 90-μm sieve to separate macro-charcoal sized material, which
was then collected. The material was then photographed in a petri dish using a four-megapixel digital
camera. The area of charcoal was calculated using image analysis software (ImageJ), where threshold
adjustment was used to identify unbleached charcoal particles (black). Results have been expressed as
mm2/cm3 of sample (concentration) or mm2/cm3/year, representing the charcoal sedimentation rate.
31
3.10 Chironomids
Chironomidae, commonly referred to as ‘Chironomids’, are true flies in the order ‘Diptera’ (Class
Insecta) (Wright, 2005) and one of the most abundant invertebrates in freshwater ecosystems. Due to
their occupation of a variety of conditions, ranging from arctic and alpine regions to all temperate and
tropic regions (Cranston, 1995), chironomids are recognised as useful biological proxies for inferring
past climatic change (Brooks & Birk, 2001). Considering this, Chironomid fossils were extracted from
ten subsamples (5 – 10 cm intervals) and then identified in order to plot changes in the ecology of the
lake over time. The procedure involved deflocculating the samples by heating in a 60°C 10% solution
of potassium hydroxide for 30 minutes. Samples were then rinsed through a 90-μm sieve and the
remaining material collected. The samples were examined under a binocular microscope and
approximately 50 chironomid head-capsules picked with tweezers and mounted onto glass slides in a
drop of Euparal©, then covered with a glass cover-slip. A target of 50 head-capsules was decided upon
as this number has been shown to sufficiently represent the variety of chironomid species within a
sample (Heiri & Lotter, 2001). An attempt to orientate the head-capsules ventral side up was made, to
assist identification. A compound light microscope at x400 magnification was utilised to identify
chironomid species. Chironomid species were identified using a composite of various identification
guides (Schakau, 1993; Epler, 2001; Chang, 2015). The data was then converted to percentages of the
total head-capsule count per sample. Results were analysed by PCA and presented as percentages per
sample against depth and age.
3.11 Loss-On-Ignition
A total of 18 subsamples at 5 cm intervals were taken from BLUE01b for Loss-On-Ignition (LOI) analysis.
LOI is a well-established technique for determining organic content following the methods of Dean
(1974) and Heiri, et al (2001), but is undertaken at a lower sampling resolution than can be achieved
when using the Mo ratio from the Itrax data. LOI analysis involved the initial weighing of 18 crucibles.
Sediment from each horizon (5 mm in width) was then placed within a crucible and reweighed. The
samples were drier at 65°C for three days and then reweighed. Following this, the samples were placed
in a furnace and combusted at 450°C for another 12 hours. The samples were then reweighed on pieces
of weighing paper and transferred to small vials. In order to examine the organic content as a
percentage of each sample, the post combustion weight (PCW) had to be divided by the dry weight
(DW) and then multiplied by 100 to give the % mineral content. This was then subtracted from 100 to
give the organic content (OC) (Equation 2).
32
𝑂𝐶 = 100 − (𝑃𝐶𝑊
𝐷𝑊× 100) (2)
Results were interpreted in excel and presented to demonstrate down core changes. Additionally,
organic content using the LOI technique has been compared to the results from different proxies of
organic content (Mo-ratio, and Br content) so that the relationship between these proxies could be
quantified.
33
Part 3
4. Results:
4.1 Core Description
BLUE01 core is 86.5 cm in length. The core was, in general, composed of highly organic, silty mud,
however, five stratigraphic units (Fig.7) were identified through the core, based on their colour and
texture.
Figure 7: Core image divided into five distinct stratigraphic units, a representative grainsize distribution plot is presented for
each unit.
Unit 1 (0 – ∼7 cm): Unit 1 is fine grained, comprised mostly of silt, exhibiting a unimodal distribution
and with a mean grainsize of 11.13 μm. It is a dark gray (7.5 YR 3/1) colour. Two distinct darker bands
are present at ∼4.5 cm and ∼5.0 cm. Both bands exhibit sparse sand grains that are ∼1 – 3 mm in
diameter, set in a silty matrix. In the lower part of the unit, there are some organic fragments seen on
the surface (twigs).
Unit 2 (∼7 – 14 cm): Unit 2 is also dominated by silt, however, it is coarser than unit 1(mean = 20.29
μm). It has a slightly bimodal grainsize distribution, with a second, very small, coarser sand peak. Unit
2 is black (7.5 YR 2.5/1) in colour. No larger fragments of sand (>1mm) appear to be present in this unit.
34
Unit 3 (∼14 – 43 cm): Unit 3 is characterised as an organic rich, silty sand, once again demonstrated by
a slightly bimodal grainsize distribution in the representative sample. Mean grainsize decreases slightly
in this unit by comparison to Unit 2 (mean = 18.45 μm). It is again black (7.5 YR 2.5/1) in colour. There
are three bands of slightly darker colouration at 27 – 30 cm, 32 – 34 cm and 37 – 40 cm. Although there
is less sand by comparison to Unit 2, infrequent rock fragments are present on the surface which have
an approximate diameter of 1-2 mm.
Unit 4 (∼43 – 72 cm): Unit 4 is classed as a silty sand, once again exhibiting a slight bimodal distribution
and a black (7.5 YR 2.5/1) colour. Mean grain size increases in this unit to 26.66 μm, implying higher
sand content compared with the Unit 3. In addition, there are infrequent rock fragments present which
were measured to be ∼1 – 2 mm in diameter.
Unit 5 (∼72 – 86.5 cm): Unit 5 is classed as silty sand. It again has a slightly bimodal distribution and
black (10YR 2/1) colouration. The mean grain size is identical to the overlying unit (mean = 25.05 μm),
once again implying low sand content. The unit overall appeared darker and more organic than the
units above.
35
4.2 Chronology
4.2.1 210Pb Ages
Returned 210Pb Activity (total, supported and unsupported) and ages are shown in Table 2. Total 210Pb
activity decreases toward zero, with the uppermost sample having a concentration of 612±29 Bq/kg
and background reached at approximately 13.0 – 13.5 cm (6±5 Bq/kg).
* Extrapolation.
Figure 8 demonstrates the supported and unsupported 210Pb activity used to determine 210Pb ages.
Figure 8A shows the supported 210Pb activity that 210Pb produced within the sediment and Figure 8B
shows the unsupported 210Pb activity. Supported 210Pb activity demonstrates very similar
concentrations with depth, indicating a similar production rate throughout the core. Unsupported 210Pb
activity (Table 1, Fig.8B), generally displays an exponentially decreasing trend, as is expected for
radioactive decay, however, there are some data points (T221=465±22 Bq/kg, T254=804±33 Bq/kg ,
T255=776±34 Bq/kg & T222=589±28 Bq/kg), found between depths of 3.0 – 4.5 cm, which diverge
Lab
Code
Depth (cm) Dry
Bulk
Density
(g/cm3)
Cumulative
Dry Mass
(g/cm2)
Total
210Pb
(Bq/kg)
Supported
210Pb
(Bq/kg)
Unsupported
210Pb
(Bq/kg)
Unsupported
210Pb Decay
corrected to
17-Mar-17
(Bq/kg)
CRS Age
(years)
CIC Age
(years)
T218 0.0 – 0.5 0.4 0.1±0.1 675±29 64±5 612±29 612±29 2±1 3±3
T219 1.0 – 1.5 0.4 0.5±0.1 550±23 52±4 499±23 498±23 9±3 13±3
T220 2.0 – 2.5 0.4 0.9±0.1 423±18 55±5 368±19 367±19 17±4 23±3
T221 3.0 – 3.5 0.4 1.3±0.1 521±22 57±5 465±22 465±22 26±5 -
T254 3.0 – 3.5 0.4 1.3±0.1 867±33 63±6 806±33 804±33 26±5 -
T255 3.5 – 4.0 0.4 1.5±0.1 835±33 61±5 776±34 776±34 34±6 -
T222 4.0 – 4.5 0.4 1.7±0.1 658±27 69±6 589±28 589±28 46±7 -
T256 4.5 – 5.0 0.4 1.8±0.1 242±10 51±4 192±11 192±11 55±7 49±4
T257 5.5 – 6.0 0.3 2.2±0.1 198±8 63±5 135±9 135±9 66±7 58±4
T223 6.0 – 6.5 0.3 2.4±0.1 187±9 50±4 137±9 137±9 71±8 62±4
T224 8.0 – 8.5 0.3 3.0±0.1 121±6 42±4 79±7 79±7 99±10 79±5
T225 10.0 – 10.5 0.3 3.7±0.1 74±3 43±4 31±5 31±5 132±11 95±5
T226 11.5 – 12.0 0.2 4.1±0.1 61±3 35±3 26±4 26±4 161±13 105±6
T227 13.0 – 13.5 0.2 4.4±0.1 53±3 46±4 6±5 6±5 188±18
*
113±6*
Table 2: 210Pb Activity and dates. Samples are relative to March 2017.
36
from this trend, all exhibiting higher 210Pb Activity, therefore a high 210Pb concentration at the time of
deposition. Furthermore, there is a discrepancy between data points taken from the same depth of 3
– 3.5 cm. This discrepancy could imply human error during sample preparation or that 210Pb
concentration in the sample was not homogenous. Alternatively, it is possible that this represents a
change in origin of material being deposited or that there is some translocation of material in the core.
Figure 8: Supported (A) and unsupported (B) 210Pb activity in the top 14 cm of the BLUE01 core.
Figure 9 shows the results from the two age models used to calculate ages from the 210Pb data, the
Constant Initial Concentration (CIC) and Constant Rate of Supply (CRS) age models (Appleby, 2001). The
CIC model assumes that sediments have a constant initial 210Pb concentration, regardless of
accumulation rates. Consequently, the supply of 210Pb to the sediment record must vary directly in
proportion to the sedimentation rate, therefore is commonly used when all measured 210Pb data points
closely follow the expected exponentially decreasing trend (Appleby, 2001). Conversely, CRS suggests
that surface concentrations should vary inversely with the sedimentation rate, therefore is utilised
when there is variation in the data set. In order to produce a CIC age model for the data, outlying points
from T221, T254, T255 & T222 were excluded as they varied significantly from the exponential trend.
Both the CIC and CRS modelled ages exhibit strong linear trends (R2 = 0.99, R2 = 0.98, respectively),
however, there is difference between the two models. Specifically, the models diverge at greater
depths, with the lowest depth showing a ∼55 years difference. The oldest sediment was found to be
188 ±18 years old using the CRS model, and 113 ± 6 years old, using the CIC model. However, these
37
ages are thought to be based on extrapolation, as the error given for this sample is nearly as large as
the 210Pb concentration itself (6 ± 5 Bq/kg).
Figure 9: 210Pb Ages Produced from CRS (Blue) and CIC (Orange) age models.
4.2.2 14C Ages
Returned 14C ages are given in Table 3. Ages appear to decrease steadily, with the uppermost age, at a
depth of 18 – 18.5 cm, estimated to be 890±80 cal. yr BP, and the basal date estimated to be
3,410±150 cal. yrs BP at a depth of 86 – 86.5 cm.
Lab Code Depth (cm) Radiocarbon age (years
BP)
Calibrated Age (cal
years BP)
PMC 1σ error Yrs BP 2σ error
OZV418 18 – 18.5 1,060±30 890±80
OZV419 30 – 30.5 1,310±180 1,160±360
OZV420 54 – 54.5 2,260±25 2,240±80
OZV421 64 – 64.5 2,835±35 2,890±110
OZV422 80 – 80.5 3,210±35 3,370±110
OZV423 86 – 86.5 3230±45 3,410±150
Table 3: 14C ages through the Blue Lake Core. Ages were calculated using SHcal13 (Hogg, et al, 2013).
38
Lead-210 (CRS modelled ages) and calibrated 14C ages are shown in figure 10. Discontinuity in the age
trend is evident between the bottom 210Pb date (13 – 13.5 cm) and the top 14C date (18 – 18.5 cm).
Figure 10: 210Pb (orange) and 14C ages (blue) in yr BP (before 1950) against depth (cm). 210Pb ages project into negative ages
as they occur after 1950.
4.2.3 Bayesian Age/Depth Model Based Off 210Pb and 14C Ages
The Bayesian age-depth model (Fig.11) was constructed using the 210Pb (CRS modelled ages) and
calibrated 14C ages. Discontinuity is demonstrated within the model, between the lowest 210Pb age and
the uppermost 14C age. This is shown by a difference of ∼680 cal. yr BP over 5 cm of sediment, between
the lowest 210Pb and upper most 14C dates. This may be taken as either a change in sedimentation rate
or, an artefact of complex carbon pathways which has affected the upper most 14C date. There also a
slight decrease in rate of deposition between ∼55 cm (cal. ∼2248 yr BP) and ∼70 cm (cal. ∼3120 yr
BP).
39
Figure 11: Bayesian age/depth model constructed using 210Pb and 14C ages through the studied core.
4.2.4 Mass Accumulation Rate
Table 4 and Figure 12 show the Mass Accumulation Rates (MAR) calculated through the core. A
decrease in MAR is evident from the base of unit 5 (0.015 g/cm2/yr), until the middle of unit 4, i.e,
approximately 0.004 g/cm2/yr at ~2350 cal. yr BP. This is followed by an increase in MAR within unit 3
to 0.13 g/cm2/y at ~1120 cal. yr BP, and then a subsequent decrease to the lowest accumulation rate
(0.002 g/cm2/y) at the transition between unit 2 and unit 3 (~ 100 – 600 cal. yr BP). Unusually for a
sediment core, MAR increases in the top units (1 and 2), with the highest MAR (0.048 g/cm2/y) occurring
in unit 1 (after ~100 cal. yr BP).
40
Figure 12: Change in MAR throughout the studied core.
Unit Depth (cm) Age (BP) Bulk density (g/cm3) SAR (cm/y) MAR (g/cm2/y)
Unit 1 1.5 -50 0.541 0.088 0.048
6.5 0 0.445 0.058 0.026
Unit 2 11.5 90 0.319 0.014 0.005
Unit 3 16.5 440 0.333 0.007 0.002
21.5 1120 0.324 0.040 0.013
26.5 1250 0.302 0.036 0.011
31.5 1390 0.349 0.030 0.010
36.5 1550 0.304 0.026 0.008
41.5 1740 0.313 0.026 0.008
Unit 4 46.5 1930 0.276 0.027 0.007
51.5 2120 0.284 0.022 0.006
56.5 2350 0.263 0.015 0.004
61.5 2670 0.293 0.016 0.005
66.5 2977 0.296 0.027 0.008
71.5 3160 0.275 0.035 0.010
Unit 5 76.5 3310 0.283 0.037 0.010
81.5 3440 0.282 0.041 0.012
85.5 3540 0.272 0.054 0.015
Table 4: Mass Accumulation Rate (MAR)
41
4.3 Dry Bulk Density
The general trend in DBD throughout core is increasing from the base (0.27 g/cm3) to the top (0.54
g/cm3) of the core (Fig.13) This is a result which is uncharacteristic of most lake cores as one would
expect sediments to become more compressed over time (Ballantyne, et al, 2011). From the base (85.5
cm) (~3540 cal. yr BP) to 71.5 cm depth (3160 cal. yr BP), DBD remains relatively constant (ranges
between 0.27 and 0.28 g/cm3). After this point, a minor increase is exhibited between 66.5 cm and 61.5
cm depth (0.29 g/cm3). At 56.5 cm depth (~2350 cal. yr BP) DBD is at its lowest (0.26 g/cm3), after
which, there is a steady increase until 31.5 cm depth (0.35 g/cm3), followed by a slight decrease (0.30
g/cm3) which remains approximately the same until 11.5 cm depth (0.32 g/cm3). From this point, there
is a rapid increase in DBD to the top of the core (1.5 cm depth), where DBD is at its highest (0.54 g/cm3).
In addition, figure 13 demonstrates the x-ray image obtained from the Itrax micro-XRF core scanner. At
the top of the x-ray, from ~ 10 to 0 cm, there is much darker region than the rest of the image, this
makes sense with the bulk density data as the denser a medium is, the less light can travel through to
the detector. Similarly, the x-ray demonstrates a darker region at ~ 30 cm, roughly corresponding with
the slight increase in DBD seen at 31.5 cm. Conversely, a very dark section in the x-ray appears at ~42
cm, however, the corresponding DBD is relatively low.
Figure 13: Dry Bulk Density data plotted against depth (cm), age (cm) and the core image x-ray.
42
4.4 Grain Size
Figure 14 displays various grain size characteristics through the core. In figure 14A, clay, silt and sand
percentage is plotted against depth. Silt is the dominant grainsize, ranging between 74.1% and 87.71%
through the core. There are low values for clay and sand in comparison. Silt content increases from the
base of the core to the top, while sand content decreases and clay increases slightly at the top but
remains relatively constant for most of the core. The upper most sample (1.5 cm) has the highest clay
content (12.61%) and lowest sand content (1.64%). In general, sand content decreases from the base
of the core (85.5 cm depth = 17.06%) to the top (1.5 cm depth = 1.64 %), with a relatively sharp increase
at 11.5 cm depth (18.05%). The sample with the highest sand content was evident at 51.5 cm depth
(22.53%). The opposite occurs in the silt content, as it increases from the base (85.5 cm depth =78.98%)
to the top (1.5 cm depth = 85.75%). At 11.5 depth, there is a relatively low value for silt content
(77.61%). There is a slight decrease in silt content from 85.5 cm depth to 51.5 cm depth (73.75%),
followed by a slight increase to 16.5 cm depth (87.71%), which is the highest silt content from the
samples. Additionally, at 71.5 cm depth and 46.5 cm depth, there appears to be a slight increase in silt
content, and decrease in sand content, respectively. Figure 14B demonstrates a steady increase in grain
size down core. The sample at depth 1.5 cm (11.13 μm) has the smallest mean grain size and 51.5 cm
(30.07 μm) has the largest. Figure 14C illustrates the frequency of grain bin sizes. It is evident that grain
size generally varies between ~5 to 60 μm. Additionally, there are some areas of high frequency (4.0)
at approximately 15 cm, 30 cm, 62 cm and 85 cm.
Figure 14: Percentage sand, silt and clay (A), mean grainsize (B), and grainsize frequency (C), plotted against depth (cm) and
the core x-ray image.
43
4.5 Geochemistry
Geochemical variability and magnetic susceptibility through the core was determined using the XRF
attached to the Itrax core scanner. The results of these analyses are presented here as a down core
analysis of geochemical variability. Additionally, a Principal Components Analysis (PCA) was undertaken
to determine the importance of the element counts through the BLUE01a core. The results of the PCA
are presented first as this is used to select elements for which to examine the downcore variability in
more detail.
4.5.1 Principle Component Analysis of Elements
Results of the PCA (Fig.15) show that changes in the element counts (which had a minimum of >100
kilo-counts/second) can be described by four independent axes. This implies that there are at least four
causes of change in group element associations (95% confidence interval). Elements with components
along axis 1 (PCA1) (Fe, Ti, Mn, K, Cr, Rb, Si, Pb & Inc:coh), explained the greatest percentage of the
variance (25.6%), while elements with components along other axes explained less variance.
Specifically, axis 2 (PCA 2) explained 5.7% of the variance, and similarly, axis 3 (PCA3) and 4 (PCA4) each
explained 5.1% of the variance (Fig.15). PCA1 predominantly demonstrates Mo ratio (inc:coh) to the
left of the plot (negative PCA 1 scores) and Fe, Ti, Mn, K, Cr, Rb, Si and Pb, to the right of the plot
(positive PCA 1 scores). This is interpreted to mean that a change in Fe, Ti, Mn, K, Cr, Rb, Si and Pb would
imply an opposite change in organic content. This is because ‘inc:coh’ (Mo-ratio) acts as a proxy for the
organic content of the material due to samples high in organic matter tending to be composed of lighter
elements, which results in more incoherent (inc) scattering of the Mo. Samples composed of heavier
elements results in more coherent (coh) scattering. Therefore, if the ‘inc’ scattering is larger than the
‘coh’ scattering, Mo Ratio will be larger (Guyard, et al, 2007).
44
Figure 15: PCA plot of axis 1 and 2 showing elements with a minimum of >100 counts, normalised to Mo Ratio. The table
shows the cumulative percentage varience for each axis (1, 2, 3 and 4).
4.5.2 Elemental and Magnetic Susceptibility Variation Down Core
Elements (Fe, Ti, Mn, K, Cr, Rb, Si, Pb) that were found to account for the greatest proportion of the
variance in the core (Fig.16) were normalised against Mo Ratio and plotted against age/depth in figure
16. In general, counts are low and do not vary much between 86.5 and 14 cm, however, some minor
changes are evident for all plotted elements except Pb. These include a decrease in elemental counts
from the base (86.5 cm = ~3500 cal. yr BP) of the core to approximately 74 cm (~ 3200 cal. yr BP),
followed by a small peak in element counts from ~74 cm to 69 depths (~3,200 and 3,000 cal. yr BP).
Elements then decrease between ~69 and 52.5 cm (~3000 to 2150 cal. yr BP). After this point, there
is a slight increase in the element counts until 45 cm, where there is another small peak between ~44
and 39 cm depth (~1,850 and 1620 cal. yr BP). Following this, element counts continue to increase
between 39 cm and 14 cm (~1620 to 140 cal. yr BP) From 14 cm depth the most significant changes in
the core occur (~140 cal yr BP to present). That is, the counts of the plotted elements increase
significantly.
45
Magnetic susceptibility follows the same pattern as the plotted elements, showing a decrease from the
base to 74 cm depth, after which, there is a corresponding increase between 69 – 74.5 cm, followed by
a region of decreased magnetic susceptibility between 69 and 52 cm depth. Magnetic susceptibility
then gradually increases from 52 to 10 cm depth, with a period of higher magnetic susceptibility
between 44.5 and 39 cm depth. From 10 cm to 0 cm, magnetic susceptibility increases significantly.
Figure 16: Elements normalised against the Mo Ratio and plotted against depth (cm), age (cal. yr BP). Two bands are
highlighted to show episodes of elevated counts in all plotted elements. The magnetic susceptibility for the corresponding
depths is plotted on the core image.
46
4.5.3 The Upper Section of the Core
Figure 17 examines the period of most pronounced change in the core in more detail. There is, in
general, an increase in counts of the plotted elements from ~10 to 0 cm depth (~1890 AD to present),
with a further increase and high variability in the plotted elements between ~6 to 4.25 cm (~1955 to
1975 AD). All plotted elements except for Mn, exhibit a small peak at ~5.5 cm depth, followed by a
decrease until ~5 cm depth (~1970 AD) where relatively low values are evident for Ti, (290.0 KCPS),
Mn (103.0 KCPS), K (194.7 KCPS), Cr (130.0 KCPS) and Si (7.9 KCPS), while Fe (26871.5 KCPS), Rb (78.3
KCPS) and Pb (81.6 KCPS), reach their highest concentration. After this point, Fe and Pb decrease, while
other plotted elements exhibit an increasing trend. At 4.8 cm depth (~1972 AD), Ti (404.1 KCPS), Mn
(153.8 KCPS), K (300.6 KCPS), and Cr (221.0 KCPS) exhibit a peak. At ~4 cm (~ 1980 AD) there is a
significant decrease in all plotted elements, except for Pb, which exhibits a peak (45.7 KCPS). From
~3.5 to 1 cm depth (~ 1985 to 2010), plotted elements stabilise, with only minor variation evident.
From 1 – 0 cm (~ 2010 to 2017 AD) plotted elements of Fe, Ti, Mn, Cr, Rb and Pb decrease, while Si and
K continue to increase. Magnetic susceptibility appears to show variability at the same regions as the
plotted elements, with a decrease at 5.5 cm depth, followed by a peak at 5 cm depth. Magnetic
susceptibility then shows a decreasing trend until ~4.5 cm depth, where there is a peak. The peak is
then followed by a point of low magnetic susceptibility and then a gradual increase until ~3.5 cm depth.
After this point, magnetic susceptibility remains relatively constant, with only a small dip evident at
~1.75 cm depth (~2000 AD).
47
Figure 17: Changes in elemental deposition from after European settlement in Australia, highlighting a region of variability
among all elements (orange) and a point of low values for all elements except Pb (blue), plotted against depth (cm) and age
(AD).
48
4.5.4 Indicators of Anthropogenic Geochemical Perturbation in Blue Lake
Figure 18 shows the ratio of Pb to Ti plotted through the core. In the plot, Ti represents a conservative
element associated with mineral input, whereas Pb is known to be enriched in the environment from
anthropogenic processes (Marx et al, 2010). Deposition of catchment material only would result in a
consistent ratio, however, an increase in the ratio implies the introduction of anthropogenic Pb
deposited in the lake from dust and aerosols (Stromsoe, et al, 2013). The Pb/Ti remains relatively
consistent for the majority of the core (~85 to 20 cm depth), although the ratio is higher and more
variable between 85 and 70 cm depth. Above 20 cm depth however, the Pb/Tibegins to increase.
Initially the ratio does not increase above that previously recorded between 85 and 70 cm depth,
however above 9 cm (~1910 AD) the Pb/Ti exhibit a major in increase after which the ratio is higher
than that recorded in the older sections of the core. Significant peaks are evident at ~5.4 cm (~1965
AD), 5 cm (~1970 AD) and 4 cm (~1980 AD). From 4 cm depth, the Pb/Ti gradually decreases the
surface of the core, despite its decline after 1980 AD values are still higher, on average, than the values
evident before 9 cm depth. Collectively therefore, the increase in Pb/Ti after 9 cm depth may represent
the onset of Pb contamination in Blue Lake.
Figure 18: Change in Pb/Ti ratio throughout the core, plotted against depth (cm) and age (AD).
49
4.5.5 Evidence of Changing Dust Deposition in Blue Lake
In a small and relatively geochemically simple catchment, such as Blue Lake, it would be expected that
ratio of conservative elements resistant to weathering would remain the same through time. Within
the Blue Lake core, however, the ratio of conservative elements changes in the uppermost section of
the core. For example, Figure 19 shows that a change in Nd/K and Ta/Ti ratio of sediment occurred
within the upper 10 cm of the core (i.e. after 1800 AD). The change in this ratio implies a contribution
of sediment with a different Nd/K, Ta/Ti composition. This implies a non-catchment derived source of
sediment to Blue Lake, the most obvious source being changing aeolian input, that is, the changing
ratios possibly imply an increasing aeolian contribution. By comparison to sediment deposited before
1800 is likely to consist of largely catchment derived sediment, although likely to still contain a more
minor aeolian contribution (Marx et al., 2011).
Figure 19: Changing geochemical composition through the BLUE01 core as shown by Nd/K ratio plotted against Ta/Ti ratio.
Blue points represent the time before 1800 AD and orange points represent the time after 1800 AD.
50
4.6 Macro-Charcoal
4.6.1 Charcoal Concentration and Sedimentation Rate
The major pattern evident in the macro-charcoal counts was a significant increase in charcoal
concentration in the top ~15 cm of the core (Fig.20A). Before this change, only minor variability in
charcoal concentration occurs, with minor peaks at 66.25 cm depth (2.61 mm3/cm2) and 54.25 cm
depth (2.37 mm3/cm2). After 14.75 cm depth, an increase in charcoal concentration occurs. At 5.25 cm,
there is a peak in charcoal concentration (7.83 mm3/cm2), after which, concentration decreases, apart
from a small spike at 1.25 cm (0.83 mm3/cm2). Figure 20B shows the sedimentation rate of charcoal
over time. Two minor increases are seen at ~2970 cal. yr BP (0.03 mm3/cm2.yr) and ~2220 cal. yr BP
(0.02 mm3/cm2.yr), after which, there is an extended period of low charcoal concentration until ~140
cal, yr BP, when a dramatic sedimentation rate of charcoal occurs.
Figure 20: Charcoal Concentration (mm2/cm2) (A) and Sedimentation Rate (mm2/cm2.yr) (B) plotted against depth (cm) and
age (cal. yr BP), respectively.
51
4.6.2 The Top 10 cm of the Core
High variability in the charcoal sedimentation rate occurs after 1800 AD (Fig.21). Two smaller spikes are
evident at a point between ~1800 and 1810 AD (0.38 mm3/cm2.yr) and 1825 AD (0.05 mm3/cm2.yr). A
larger spike occurs at ~1865 AD (0.14 mm3/cm2.yr). The highest sedimentation rate (0.49 mm3/cm2.yr)
corresponds with ~1965 AD (0.49 mm3/cm2.yr), followed by a much smaller spike (0.18 mm3/cm2.yr)
which corresponds with ~2006 AD.
Figure 21: Sedimentation Rate (mm2/cm2.yr) of charcoal plotted against age (AD).
52
4.7 Chironomids
4.7.1 Chironomid Species Percentages
The identified species of Chironomidae throughout the core are shown in Figure 22. The most abundant
species was Chironomus (constituting ~45 to 80% of total abundance of Chironomidae individuals in
each sample). All other species each accounted for ~1 to 15% of the species abundance in the studied
samples (when combined, they equalled 20 to 67% of total abundance of the Chironomidae species per
sample). At 80.25 cm, a slight change in species composition is evident, with Chironomus at its lowest
abundance (45% of total individual counts), and several others (Compterosmittia, Coronenura,
Cricotopus howensis, Cricotopus parbicinctus, Eukiefferiella, S01) among their highest abundance.
Another spike in Chironomus occurs at 64.25 cm (71%), corresponding with a decrease in all other
species. After this, a decline in Chironomus species occurs until 10.25 cm, where there is a sharp
increase. Corresponding with the decline in Chironomus, variability in all other species abundances is
evident, whereby several of the species appear to have higher abundance (Polypedilum,
Compterosmittia, Cricotopus parbicincus, Eukieffieriella, Paralimnophyes, Parochlus, and Podochlus)
and others appear lower (Cricotopus howensis, and M05). At 4.25 cm depth, Chironomus and Parochlus
have their highest percentage abundance value (80% and 9%, respectively), while all other species
accounted for 3% or lower of the total species abundance in the sample. In addition to species
composition, the sum of total collected head capsules is presented in figure 22. It is demonstrated that
Chironomid abundance varied significantly throughout the core, with the top sample (0.25 cm) having
low abundance, with only 19.5 head capsules collected. The layer with the most abundance was found
at 30.25 cm depth (67.5 head capsules). All other layers varied between 35 and 55 head capsules.
53
Figure 22: All Chironomidae species identified throughout the core, expressed as a percentage per sample.
Figure 23 indicates only species which were identified in more than one sample, the species presented
are those which have been used in the Principle Component Analysis (Fig.24).
Figure 23: Common Chironomid species per sample, plotted against depth (cm) and age (cal. yr BP).
54
4.7.2 Chironomid Principle Component Analysis
A PCA was constructed using only species which were identified in more than one sample, these were
Chironomus, Polypedilum, Compterosmittia, Cornoneura, Cricotopus howensis, Cricotopus parbicintus,
Eukieferiella, Genus Australia B, ‘MO5’, Orthoclad Morphotype I, Parakeifferiella, ‘SOI’, ‘SO2’, Parchlus
and Podochlus. Figure 24 demonstrates the results of the PCA plot, with components along Axis 1
explaining the largest variation (27.9%), and axes 2, 3 and 4, explaining 21.1 % 14.2%, and 12.5%,
respectively. Figure 24 displays the two axes, (Axis 1 and Axis 2) that describe the biggest variances in
the PCA. Samples are plotted in space to show which samples correlate to which species types. It is
evident that where there is a change in Chironomus, Polypedillum, and S02, there is a statically opposite
change in Eukieffierella, Podochlus and S01. Similarly, when there are changes in Parakiefferiella, there
are opposite changes in Parochlus and Cricotopus howensis. Additionally, figure 24 demonstrates that
samples from 0.25 and 4.25 cm depth; 10.25 and 17.25 cm depth; 80.25 and 86.25 cm depth; as well
as 30.25, 40.25, and 64.25 cm depth, are relatively similar each other in terms of species composition.
Figure 24: The table shows the PCA result summary from all axes. The plot shows Axis 1 and Axis 2 of the PCA, indicating
species and sample variation. Samples that were taken from the region before 1800 AD are represented in blue and samples
after 1800 AD are represented in red.
55
4.7.3 Sub-family Percentages
Figure 25 demonstrates a generalised view of the Chironomid data, indicating the percentage of the
sub-families ‘Chironominae’, ‘Orthocladinae’ and ‘Diamesinae’ per sample. Results shows that species
in the ‘Chironominae’ sub-family have dominated the environment through most of the 3,500-year
history of the core, particularly in the top depths of 4.25 and 0.25 cm (~-28 to – -66 cal. yr BP). However,
results suggest that species of the ‘Orthocladiinae’ sub-family tend to have higher abundance when
‘Chironominae’ decline. This is evident at 10.25 cm (~64 cal. yr BP) and 80.25 cm (~3410 cal. yr BP).
The abundance of species of the ‘Diamesinae’ sub-family generally remain constant throughout the
core, however, a minor increase (19%) is exhibited at 54.25 cm depth (~2220 cal. yr BP), followed by a
decline to 0.25 cm depth. PCA 1 and PCA 2 (Fig.25) indicate overall change throughout the core as
described by the PCA (Fig.24). For PCA 1, the greatest variation occurs between 10.25 and 4.25 cm
(~64 to -28 cal. yr BP, approximately 1890 to 1980 AD), as well as between 80.25 and 64.25 cm (~3550
to 2860 cal. yr BP)). A decrease from 64.25 and 10.25 cm depth (~2860 to 64 cal. yr BP) is also evident.
PCA 2 shows less variability than PCA 1 but still demonstrates significant change from 4.25 to 0.25 cm
depth. There is also a small decrease from 64.25 to 30.25 cm (~2860 to 1350 cal. yr BP) and an increase
from 17.25 cm to 4.25 (~576 to 64 cal. yr BP).
Figure 25: Percentage of each sub-family (Chironominae, Orthocladinae, and Diamesinae), PCA1 and PCA2 overall variance,
and sum of Chironomid head capsules per sample, plotted against depth (cm) and age (cal. yr BP).
56
4.8 Loss-On-Ignition
4.8.1 Changes in Organic Content
Figure 26 exhibits changes in organic content, as determined by Loss-On-Ignition (LOI), throughout the
core. In general, organic content decreases from the base of the core (84.25 cm = ~22.9%) to the top
(1.25 cm = ~ 13.3%). At the base of the core (84.25 cm = ~3510 cal. yr BP), organic content is at its
highest (22.9 %). Above 76 cm depth, there is a significant decrease in organic content until 66.25 cm
(~2970 cal. yr BP) (LOI = 16.9 %). Organic content increases again after this point, remaining relatively
constant from 61.25 cm (20.7%) to 41.25 cm (21.0%) (~2650 cal. yr BP). A decline in organic content
occurs at 31.25cm (~1380 cal. yr BP), followed by a steady rise until 11.25 cm depth (84 cal. yr BP).
After this point, a dramatic decrease in organic content occurs (13.3%).
Figure 26: Organic Content (determined by %LOI) plotted against depth (cm) and age (cal. yr BP).
Figure 27 is a comparison of organic content (determined by LOI) results to other proxies of organic
content, specifically the Mo Ratio and Bromine content. Bromine is taken to imply organic content due
to its tendency to bind with organic matter (Davies, et al 2015). The purpose of this plot is to
57
demonstrate the relationship between different proxies of organic content. In general, the LOI
(expressed as % organic content) and Mo Ratio data appear to correspond closely with one another,
however, there is a more pronounced decline in the LOI data compared with the Mo Ratio at 34.25 cm.
This is expected to have occurred due to a relatively large rock fragment which was contained within
the LOI sample at this depth. There is also some minor variation in the Mo Ratio data which is not
present in the LOI data, this is expected to be due to the low resolution of the LOI data.
When comparing the LOI and Mo Ratio results to the Br results, it is evident that the general pattern is
similar, however, since the Br data is noisy, that is, there is abundant readings where Br counts equal
zero, there are only slight variation which can be identified when the data has been smoothed.
Specifically, a slight increase in Br occurs approximately at the same depth/age of the first peak which
is evident in the LOI and Mo Ratio records (11.25 cm = ~84 cal. yr BP). Br also slightly declines from this
point, followed a period of relatively constant input and then a slight increase at the base of the core,
these trends appear to relatively match the trends of the LOI and Mo Ratio data. Apart from these
broad trends, Br has not demonstrated any significant changes which correspond with the LOI and Mo
Ratio data. Overall, it appears that Br is not indicative of organic content in this case due to the number
of zero counts for Br.
Figure 27: Assessment of the relationship between proxies of organic content using Organic Content (determined by LOI), Mo
Ratio and Br.
58
5. Discussion:
This chapter will discuss the results of this study, with regard to the broader context of the Snowy
Mountains and south-east Australian palaeoclimatic research, as well as the history of human activity
after European settlement in Australia. The primary focus of this thesis was to expand upon existing
knowledge about the palaeo-environment of the KNP and provide insight into how natural and
anthropogenic influences have altered the alpine lacustrine environment. In order to do so, we must
evaluate synchronous changes in the proxy records and speculate whether they can be attributed to
possible climatic variability. Results of this study offer some indication about climatic variability during
the period from the late Holocene (~3,500 cal. yr BP) to present.
The first section of the discussion will evaluate climate changes during the late Holocene period (~3,500
to present). Synchronous proxy changes will firstly be interpreted at face value, indicating what our
data might imply for palaeoclimatic change. Following this, we will discuss what the data implies in light
of other palaeorecords from the Snowy Mountains and south-eastern Australia.
The second section of the discussion will describe in more detail the changes which have taken place
following European settlement in Australia.
59
5.1 Climate ‘Phases’ Present Within the Studied Core
The proxies explored in this investigation show several synchronous changes over the last ~3,500 years.
These changes are suggested to provide evidence for a series of broad climatic ‘phases’ over the late
Holocene (Fig.28). These phases are discussed in the remainder of this section.
Figure 28: Comparison of changes in Magnetic Susceptibility, MAR (g/cm2/y), Charcoal Concentration (mm2/cm3), DBD (g/cm3), Mean Grain Size (μm), Organic Content (%LOI) and Chironomid Sub-families (% Sample), plotted against depth (cm)
and age (cal. yr BP).
Phase 1 (~3500 to 3000 cal. yr BP): Initial cool/wet conditions and a transition to a warmer/drier
climate?
It is speculated that the KNP environment may have experienced a comparatively cooler/wetter climate
during the earliest stages represented in the Blue Lake record (~3500 cal. yr BP). Evidence of initially
high Mass Accumulation Rates (MAR) (Fig.12, 28 and Table 4), sedimentation rates (Fig.11), magnetic
susceptibility (Fig.16 and 28) and counts for lithogenic elements (Ti, K, Rb, and Si) (Fig.16) are
interpreted to imply increased sediment delivery, while high organic content (Fig. 26, 27 and 28) is
60
suggested to indicate increased organic productivity during this time. These results are expected to
reflect a wetter climate because increased precipitation typically increases vegetation productivity,
which consequently facilitates chemical weathering due to the production of chelating ligands, organic
acids and increased subsurface CO2 (Larsen, et al, 2014). Additionally, low charcoal
concentration/sedimentation rates (Fig.21 and 28) imply a cooler and wetter climate as these climatic
conditions are associated with decreased occurrence of fire (Black & Mooney, 2006). Cooler conditions
are also implied through Chironomid records from the lowest depths (Fig.22 to 24 and 28), where the
Chironominae sub-family initially exhibit relatively low percentages, and the Orthocladinae and
Diamesinae sub-families demonstrate higher percentages. This is suggested to be indicative of a cooler
climate because Orthocladiinae and Diamesinae species generally prefer cooler, oxygenated water
(Lindegaard, 1995; Epler, 2001) while Chironomus (the dominant Chironominae species identified) are
often associated with warmer conditions due to their tolerance of warmer water and anoxic conditions
(Woodward, et al, 2017) (which are experienced when lakes become thermally stratified in warmer
conditions). It is suggested that these conditions would have been caused by an intensification of the
mid-latitude westerly winds, resulting in increased snow and rainfall (Theobald, et al, 2015). This is
hypothesised to represent the final stages of the ‘Neoglacial’, a period where cooler climatic conditions
are believed to have been experienced in the Southern Hemisphere between ~5 to 2 ka cal. yr BP
(Porter, 2000). After this time, proxy results begin to demonstrate opposite changes, with MAR,
sedimentation rate, magnetic susceptibility and organic content exhibiting a decreasing pattern, while
charcoal concentration slightly increases. This is suggested to imply a gradual transition out of the
Neoglacial period.
Phase 2 (~3,000 to 1900 cal. yr BP): A period of relatively warm and dry conditions?
Following approximately 3,000 cal. yr BP, the Blue Lake proxy records demonstrate evidence, albeit
slightly, of a continued decrease in MAR, sedimentation rate, magnetic susceptibility, organic content
(See Fig. 28) and lithogenic element input (Fig. 16). This is expected to imply less organic productivity
and sediment being supplied to the lake after this time. In addition, an increase in charcoal
concentration/sedimentation rates implies a more fire-prone environment (Black & Mooney, 2006),
and an increase in the abundance of the Chironomus species and decline of the Orthocladinae and
Diamesinae sub-family species suggests a change in the biology of the Blue Lake environment. These
results are speculated to reflect a period of relatively warmer, drier conditions in the KNP, with the
height of this proposed climatic episode expected to have occurred some-time around 2,300 cal. yr BP
(with MAR exhibiting its lowest value and charcoal concentration at its highest around this time). It is
questioned whether drier conditions would have been a result of the southward repositioning of the
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mid-latitude westerly wind belt, as implied by Marx, et al (2011). However, that study suggests this was
the cause for a period of dryness after 2,000 cal. yr BP, rather than after 3,000 cal. yr BP. In fact, the
proposed dry conditions between 3 and 2 ka cal. yr BP contrasts with the conditions proposed by Marx,
et al (2011), where it was suggested that the climate during that time would have been wet.
Phase 3 (~1900 to 140 cal. yr BP): Return to wetter conditions?
Phase 3 is characterised by a steady increase in MAR, organic content, mineral input and magnetic
susceptibility, as well as a decrease in charcoal concentration/sedimentation rate (Fig. 28) (other
geochemical and sedimentary proxies remain relatively constant). Additionally, the Chironominae sub-
family gradually declines, whilst the Orthocladinae and Diamesinae sub-families become more
abundant. This evidence is believed to imply a return to slightly wetter conditions in the KNP alpine
zone as it indicates increased organic productivity and sediment delivery to the lake.
Phase 4 (1800 AD to present): Impact of European settlement
The proxy records demonstrate the most dramatic changes in the top 10 cm section of the Blue Lake
core, corresponding with the last ~200 years (See Fig.28). This is evident through a dramatic increase
in MAR, sedimentation rate, magnetic susceptibility, lithogenic material, charcoal
concentration/sedimentation rates and DBD, a decrease in grain size and organic content as well as a
change in sediment geochemical composition (Fig.19) during this time. In addition, a substantial
increase in Chironominae abundance and decrease in Orthocladinae and Diamesinae species is evident
from this time, implying a shift to relatively warmer conditions. Unlike the previous phases identified in
the Blue Lake record, these changes correspond with the time after European settlement in Australia,
and the subsequent introduction/development of several human activities (eg. farming, industrial
activities and tourism). It is therefore suggested that these human activities have substantially
influenced the changes evident within the BLUE01 core.
5.1.1 The Transition out of the Neoglacial
The timing of Phase 1 is suggested to coincide with the Neoglacial (centred around ~5,000 cal. yr BP),
which is a widely documented period when the Southern Hemisphere is suggested to have experienced
a cooler climate due to an increase in south-westerly airflow in the mid-latitudes (Porter, 2000). Several
studies have provided evidence of synchronous glacial advances and enhanced geomorphic activity
during the Neoglacial, predominantly through dating of glacial deposits, analysis of peat development
and palynological studies from South America and New Zealand (Markgraf, et al, 1992; Porter, 2000;
62
Shulmeister, et al, 2004; Stansell, et al, 2013). In the Australian alpine landscape, however, there is less
obvious evidence of this period compared with active glacial environments since glaciation on the
Australian mainland ceased after approximately 15 ka years (Barrows, et al, 2001). Nevertheless, some
research conducted in the Snowy Mountains and surrounding regions do provide evidence of
cooler/wetter conditions around this time (Costin, 1972; Martin, 1986;1999). This is demonstrated in a
study conducted by Costin (1972), which found evidence of renewed periglacial action and geomorphic
instability between ~4,000 and 2,000 cal. yr BP, through identifying reactivation of solifluction terraces
and rubble layers in fen peats surrounding Club Lake. A later palynological study by Martin (1986)
interpreted cooler conditions during the same timeframe by identifying low values of the
Eucalyptus/Poaceae ratio. Subsequent pollen records by Martin (1999) presented further evidence of
a cooler climate through identifying a decline in Snow Gum (Eucalyptus pauciflora) between 5,200 and
1,900 cal. yr BP, as well as an increase in Poaceae pollen and a Eucalypt minimum between 4,000 to
1,900 cal. yr BP. More broadly, Marx, et al (2011) found a decrease in dust deposition from 4000 to
2000 cal. yr BP and Stanley & De Deckker (2003) presented reduced dust grain size between 4000 to
1500 cal. yr BP, each attributing these changes to wetter conditions in the Murray-Darling Basin (MDB),
the main source area of dust to the Snowy Mountains.
Consequently, the timing of proxy changes exhibited in the Blue Lake record are suggested to imply a
gradual change in climate from colder, wetter conditions before 3,500 cal. yr BP to drier, warmer
conditions after 3,500 cal. yr BP, whilst other studies conducted in the region have proposed that
cooler/wetter conditions continued until ~2,000 cal. yr BP (Costin, 1972; Martin, 1986;1999; Marx, et
al, 2011; Stanley & De Deckker, 2003). Considering this, it is questioned whether there may have
previously been an overestimation of the length of the cool period in the KNP.
The timing of periglacial activity presented by Costin (1972) is questionable since it was established
using some of the earliest radiocarbon dates undertaken in Australia, and occurred prior to advances
in sample preparation to improve the removal of contamination (Stromsoe, et al, 2016). It is therefore
reasonable to suggest that these dates may have been contaminated by younger carbon, which would
imply that the periglacial action occurred earlier than expected. Furthermore, the dust records
presented by Marx, et al (2011) and Stanley & De Deckker (2003) are suggested to broadly mirror the
hydrological regime and climate of the Snowy Mountains region, however, there is a possibility that the
MDB source region may have experienced a longer cool/wet period, or the alpine zone may have more
rapidly responded to a minor change in climate conditions. Alternatively, the dates obtained from the
BLUE01 core may have been contaminated by older carbon, which would bring the timing of the
63
proposed cooler climate more in line with other palaeoclimate evidence from the region. In either case,
the results suggest cooler conditions in the KNP climate at some point around 3,500 cal. yr BP.
5.1.2 An Extended Warm and Dry Period
Evidence of warmer and drier conditions in the Snowy Mountains between 3,000 and 2,000 cal. yr BP
has not previously been identified in research from the alpine zone, however, amelioration of the
climate in the Snowy Mountains around ~2,000 cal. yr BP has been suggested through pollen records
from Diggers Creek (Martin, 1999) as well as other works on the MDB palaeo-environment (Marx, et al,
2011; Harrison, 1993; Luly, 1993; Cupper, et al, 2000; Dodson, 1974; Bowler, 1981; De Deckker, 1981).
In particular, Martin (1999) suggested drier conditions in the Snowy Mountains during this time due to
a decline in wet sclerophyll species. For the MDB, Marx, et al (2011) interpreted a sharp increase in
dust deposition around 2000 cal. yr BP as a change to arid conditions, while Harrison (1993), Luly (1993)
and Cupper, et al (2000) also identified general drying in the lower MDB after this time. In addition, a
number of studies have suggested a change to drier conditions at Lake Keilambete in south-western
Victoria, due to evidence of reduced water level (Dodson, 1974; Bowler, 1981; De Deckker, 1982).
It is hypothesised that the dry episode proposed in this investigation reflects the same climatic episode
that has been interpreted in other studies from the surrounding region, despite the timing being
relatively inconsistent. This would again suggest that our C14 dates are slightly older than they should
be. Alternatively, the dates may be accurate and the length of the Blue Lake environmental response
to this episode may have been extended due to the alpine zone being more sensitive to changes in
climate. Either way, the proxy evidence does provide an indication of an environmental response to a
relatively warmer/drier climate in the Blue Lake environment around this time.
5.1.3 A Return to Wetter Conditions
The proxy records from the Blue Lake core present evidence for a change to a wetter climate after
~1500 cal. yr BP. These hypothesised conditions do broadly overlap with some other palaeo-evidence
from the surrounding region, for instance, the results of Mooney (1997) from Lake Keilambete in
Victoria are suggested to reflect an increase in moisture availability for a period around 1,600 and 1,300
cal. yr BP. Additionally, the influence of relatively wetter conditions for a period of this time also
compares with dust results of Marx, et al (2011), where a small increase in dust deposition around 1000
cal. yr BP was attributed to higher sediment supply to dust source areas in the MDB, caused by
increased river discharge. Marx, et al (2011) attributes this change to wetter conditions in the MDB to
increased penetration of south-westerly winds and rain bearing cold fronts (Marx, et al, 2011). On the
64
contrary, however, other research in the region has suggested this period was generally drier (Gingele,
et al, 2007; Bowler, 1981; Dodson, 1974). In particular, drier conditions during the earlier period
(between ~2,000 and 1,000 cal. yr BP) of this proposed episode is suggested by Marx, et al (2011). This
inconsistency could demonstrate that the climate of the south-east Australian region may have been
highly variable during this time. Alternatively, since the extent of the changes present within the Blue
Lake record are only small, there is also a strong possibility that the lake is not sensitive enough to
detect changes in climate at that scale, therefore the changes may not be reflective of palaeoclimatic
variability in the region at all.
5.1.4 Difficulties with Determining Evidence of the MWP and LIA Climatic Events
Unfortunately, inferences about both the Medieval Warm Period and the Little Ice Age phases cannot
be confidently determined from the results of this investigation due complexity of the age model
between ~700 to 140 cal yr BP (1200 to 1800 AD). This is because the discontinuity that is exhibited in
the age model between 14 cm and 18 cm depth implies a very low sedimentation rate, therefore makes
proxy changes difficult to be identified. It is expected that the discontinuity may have been caused by
something affecting the upper most 14C date. In particular, it is speculated that this date may be
anomalously early, possibly due to the dated charcoal specimen being sourced from a tree or plant
which had been burnt many years prior to being transported to the lake, or from a part of a tree which
had been standing for hundreds of years (Schiffer, 1984). This source of variability has been termed the
‘old wood’ problem (Schiffer, 1982), and may account for the significant change in sedimentation rate
that is exhibited in the Bayesian age/depth model. Alternatively, the region have been significantly
disturbed. Either way, this section of the core warrants further analysis so that a better understanding
this region can be obtained. This would entail obtaining extra radiocarbon dates from the region of
interest, as well as running additional 210Pb dating and caesium (137Cs) dating (Ritchie & McHenry, 1990)
for the top section of the core.
5.1.5 Evidence of Distinct Palaeoenvironmental ‘Episodes’ in the Late Holocene
There appears to be two distinct episodes of high mineral input (Fig. 16), slightly higher dry bulk density
(Fig. 13), lower grain size (Fig. 14), and a sharp decrease in organic content (Fig. 26, and 27) roughly
corresponding with the periods between ~3,200 and 3,000 cal. yr BP (Episode 1), and ~1,850 and 1620
cal. yr BP (Episode 2). For both periods, the scale of these changes, especially in the Itrax data, are
relatively significant compared with variations throughout the rest of the core. However, no other
research in the region has identified any major climatic events at the time corresponding with the
65
Episode 1, and there is generally disagreement about the conditions experienced in south-eastern
Australia at the time of Episode 2 (Martin, 1999; Mooney, 1997; Bowler & Hamada, 1971; Dodson,
1974). For instance, Martin (1999) interpreted a shift to warmer conditions during Episode 2 through
identifying a decrease in Poaceae pollen, and Mooney (1997) also proposed warmer conditions and
catchment instability at Lake Keilambete, due to increased microscopic charcoal concentrations,
magnetic susceptibility and minerogenic component of the sediment. This was interpreted because a
rise in microscopic charcoal is suggested to reflect an increased occurrence of fire from regional/extra-
regional source areas (Mooney & Tinner, 2010), while higher magnetic susceptibility and minerogenic
input are interpreted to imply an increase in erosion and transport from the catchment (Dearing, 1999).
On the other hand, Bowler & Hamada (1971) identified a major rise in lake levels at Lake Keilambete
around this time, which was suggested to imply wetter conditions. Similarly, results presented by
Dodson (1974) implied wetter conditions during this time in Lake Leake, South Australia, through an
increase in the pollen species, Myviophyllum and Triglochin, which have been associated with higher
water depth.
The proxy results from both episodes provide evidence of a change to wetter conditions in the KNP due
to the substantial increase in sediment delivery, however, a significant decline in the organic content
roughly corresponding with both periods is inconsistent with this interpretation. Considering this, it is
speculated that these periods might reflect local scale, in-basin processes, rather than a response to
climatic conditions. Overall, it is difficult to provide a clear explanation about these episodes based on
the evidence presented in this thesis or from other palaeoclimatic studies from the region. However,
the results, particularly the Itrax data, do provide evidence for a change in the erosional regime in the
Blue Lake catchment. Further investigation into this may involve delving more deeply into the
evaluation of geochemical changes, through quantitative analysis of bulk sediment chemistry.
5.1.6 Possible Influence of the ‘Freshwater Reservoir Effect’ on 14C Ages
As previously mentioned in section 5.1.4., it is speculated that the discontinuity demonstrated in the
Bayesian age/depth model (Fig. 14) may be caused by complex processes of carbon transfer to the lake.
What has not been suggested, however, is the possibility that some (if not all) of the dated specimens
may have been aquatic samples and therefore the resultant 14C ages may have been influenced by the
‘freshwater reservoir effect’ (FRE) (Phillippsen, 2013). More specifically, the FRE can result in
anomalously old radiocarbon ages in freshwater systems, most commonly due to the presence of
dissolved ancient carbonates which lead to the so-called ‘hardwater effect’ and a dilution of the 14C
concentration. This can cause a maximum FRE of one half-life of 14C, which is about 5,370 years
66
(Phillippsen, 2013). Considering this, it is speculated whether the 14C dates may have been influenced
by the FRE, and that the discontinuity exhibited in the age model may be an artefact of this. If that were
to be the case, this would imply that the age model is at least ~700 years too old. Importantly, this
would bring a number of the proposed palaeoclimatic ‘phases’ more in-line with existing palaeorecords
from the Snowy Mountains and south-east Australian region. For instance, the transition stage out of
the Neoglacial which has been proposed to have occurred around 3,500 to 3,00 cal. yr BP would be
revised to some-time between 2,800 and 2,300 cal. yr BP, and the dry episode which has originally been
proposed to have occurred between ~3,000 and 1,900 cal. yr BP would instead have taken place from
approximately 2,300 to 1,200 cal. yr BP. Both phases would be significantly more consistent with other
palaeoclimatic variability recorded in the region (Costin, 1972; Martin, 1986; Martin, 1999; Marx, et al,
2011; Harrison, 1993; Luly, 1993; Cupper, et al, 2000; Dodson, 1974; Bowler, 1981; De Deckker, 1981),
and therefore may indicate that the results presented in this study are reflective of recent
palaeoclimatic change.
67
5.2 Land Degradation in Kosciuszko National Park following European
Settlement
It is evident through synchronous changes within the proxy data that a substantial shift in the
sedimentological, ecological and geochemical function of the environment has occurred following
European settlement in Australia (~1800 AD to present). This change, which occurred within the top
14 to 15 cm of the Blue Lake core, represents the most significant perturbation recorded within the
3500 yr cal. BP history of the core. Historical accounts of post European settlement activity in KNP
provide a basis for interpreting the sedimentary record and for ascribing causes to some of the
observed changes. In particular; extensive summer grazing which took place in the alpine region from
the late 1820’s to 1940’s, the establishment of Pb mining in Australia from the 1840’s, the use of leaded
petrol from the 1930’s to 2000’s, and the expansion of wider agricultural practices in south-eastern
Australia are expected to have contributed to the changes which are evident within the proxies. These
human activities will be discussed further in the sections which follow.
5.2.1 Environmental Changes due to Grazing in the Alpine Zone
It is speculated that a number of the proxy results from this investigation provide evidence of an erosion
response in the KNP alpine zone after ~1860 AD. In particular, it is suggested that there has been an
increase in erosion and a shift from the erosion and supply of relatively unweathered catchment rock,
as is exposed as bedrock outcrops and talus around the cirque walls, to the preferential erosion of more
highly weathered soil and its deposition in the lake basin. A change to soil sediment erosion is implied
through a substantial increase in magnetic susceptibility, a decline in mean grainsize and a decrease in
organic content above ~10 cm depth in the BLUE01 core. Increasing magnetic susceptibility is thought
to reflect increasing soil delivery to the lake as the highly ferromagnetic mineral magnetite is formed
by weathering within the soil environment (Maher & Taylor, 1988; Maher, 2016). A decrease in mean
grainsize and organic content also generally imply increased influx of fine-grained (silty), minerogenic
material to the lake. The production of finer material is also indicative of weathering within soil profiles.
Most significantly, a change to increased supply of soil material to the lake supply is implied by a change
in the geochemistry of sediment deposited in the lake after European settlement. This is shown by an
increase in the Ti/Ca ratio after European settlement (Fig.30). This change reflects the fact that Ca is
likely to be depleted in the more highly weathered soils, compared with the unweathered rock outcrops
in the catchments. Similar results were previously reported in the top of Club Lake by Stromsoe, et al
(2013). In that study the Rb/Sr, Th/Ba, Ti/Ca and Nd/Sr were all found to decrease in the top of the core,
68
implying the input of more highly weathered material. That data suggested increasing then steadying
or decreasing supply of weathered material in the upper section of the Club Lake core (Fig. 29),
corresponding with the introduction and subsequent exclusion of grazing from the alpine zone.
Figure 29: Weathering index/age profiles for a core from Club Lake in the Snowy Mountains. Mobile elements (Ca, Sr, and Ba) are depleted during weathering. (Source: Stromsoe, et al, 2013)
Figure 30: Weathering index/age profile (Ti/Ca) of BLUE01 core.
0
2
4
6
8
10
12
14
16
4.0 6.0 8.0 10.0
Ti/Ca
154016401740
1840
1940
69
In addition to Ca loss, a general increase in the supply of lithogenic elements (Fe, Ti, Mn, K, and Rb) are
also interpreted to reflect changes in erosion at this time as they display a rapid increase from
approximately 1890, a peak around 1950 – 60, steady deposition between ~1980 and 2010 and then
a gradual decline to present (Fig.17). Additionally, an increase in charcoal concentration/sedimentation
rates from 1860 to present (Fig.20) is likely to reflect higher frequency of fire in the region at the time,
which would have been caused by graziers using burning of large areas of grassland to enhance growth
of alpine pasture (Scherrer & Pickering, 2001).
The results are suggested to closely tied with the timeline of grazing practices in the KNP because up
until the time when they were introduced in the region in the late 1820’s, the landscape and vegetation
of the alpine zone had not experienced trampling by heavy, hard-hoofed animals or apparently intense
fire activity (see Fig. 20). This therefore would have led to changes such as the observed accelerated
soil erosion, decrease in organic productivity and change in sediment composition that has also been
identified in several other previous works (Helms, 1893; Byles, 1932; Costin, 1954; 1958; Costin, et al,
1959; 1960; Bryant, 1971; Stromsoe, 2013; 2016). Furthermore, the subsequent decline in erosion
observed in the Blue Lake record corresponds well with when grazing was officially stopped in the
immediate alpine area of KNP (Worboys & Pickering, 2002) and soil conservation measures were
established (Clothier & Condon, 1968; Keane, 1977; Clark, 1992). This decline has also been identified
in Stromsoe, et al, (2016).
5.2.2 Pb Pollution due to Mining and Leaded-petrol
After European settlement (~200 years ago), Australia became rapidly industrialised, establishing
mining and production of metals on a wide scale (Marx, et al, 2010). These industries have largely been
associated with the perturbation of metals in the atmosphere (Nriagu & Pacyna, 1988; Pacyna &
Pacyna, 2001), as they are typically released in gas phase or as fine particulate, which can be
transported thousands of kilometres from their source (Macdonald, et al, 2000; Marx, et al, 2008). For
this reason, these activities are likely to be important sources of atmospheric metal pollution that have
since accumulated in the Australian environment (Marx, et al, 2010). One metal which has been found
to be enriched in the Blue Lake core after European Settlement is Pb. The contamination of Blue Lake
sediment with Pb is reasonably closely tied with Australian Pb production and, to a lesser extent, the
use of leaded petrol in cars. Importantly, the most notable source of Pb pollution within the Blue Lake
record is expected to be from the mines in the Broken Hill region and the associated Port Pirie smelters
in South Australia (where most of the Pb ore from Broken Hill was smelted). Both of these sources are
located upwind of the Snowy Mountains and within the mid-latitude westerlies, implying the Pb
70
enriched aerosols and dust are likely to be regularly transported over the Snowy Mountains (Marx, et
al, 2010). Enrichment of excess Pb in the Blue Lake core largely mirrors the pattern of Australian Pb
production, particularly the history of the Broken Hill mines, as a significant increase in the Pb/Ti ratio
is evident from approximately 1900 to ~1980 AD, followed by a general decline from 1980 AD to
present (Fig.18). However, the timing of the onset of Pb contamination is later than previously identified
in peat cores within the Snowy Mountains, that is approximately 1910 in this study versus 1890 in peat
cores (Marx, et al, 2010). This either reflects differences in resolution of age models between the two
studies, or may reflect the more subdued pattern recorded in lakes due to their greater relative
catchment input compared to atmospheric input (Stromsoe, et al, 2013).
The Pb, Ag and Zn mines of the Broken Hill region dominated global Pb production until the 1980’s,
after which, Mt Isa in northern-central Queensland was the major source of Pb production in Australia
until the 1990’s (Mudd, 2007). Consequently, the shift to Pb production in Mt Isa may have contributed
to the decline in Pb enrichment in the record as this emission source is less likely to have reached to
the Snowy Mountains (Marx, et al, 2010). In addition, advancements in smelting and improvements in
emission controls at the Port Pirie Smelters in the 1950’s and 60’s are also likely to have contributed to
the decline in Pb pollution (Green, 1977; Dawson, 1989) reaching Blue Lake.
In conjunction with Pb mining and smelting in Australia, the use of Pb-petrol is also speculated to have
enhanced the level of Pb pollution in the Blue Lake core after its introduction in Australia from the
1930’s (Cook & Gale, 2005). However, it is difficult to isolate its contribution in this context as it has
been shown by Marx, et al (2010) that the isotope composition of Pb-petrol sold in southern Australia
corresponded closely with the composition of the Broken Hill Ore. Nevertheless, studies have identified
it as a major source of pollutant Pb (Bollhӧfer & Rosman, 2000; Chiaradia, et al, 1997; Gulson, et al,
1983), therefore it is likely that it has contributed to Pb enrichment in the alpine landscape. In particular,
two spikes in the excess Pb concentration is evident during the early 1970’s and 80’s, corresponding
with the time when mainstream tourism in the Snowy Mountains became popular due to the
development of ski resorts within the subalpine and alpine areas (Scherrer & Pickering, 2001), as well
as when the Broken hill mines were at their peak Pb production. It is speculated that this spike may
reflect an increase in use of Pb-petrol fuelled heavy machinery and cars within the KNP area, therefore
bringing Pb emissions much closer to the remote alpine landscape.
Atmospheric Pb pollution that is evident within the Itrax record (Fig.18) is approximately 1.2 to 4.9
times that of pre-industrial levels. These values were calculated by finding the average of the
background Ti/Pb values (before 1885 AD), then taking the maximum and minimum values and dividing
them by the average. The enrichment values are quite variable compared with other estimates from
71
the Snowy Mountains, particularly one study by Marx, et al (2010), which analysed peat bogs from
remote alpine sites and concluded that atmospheric Pb pollution had been accumulating at
approximately 5x the natural rates recorded prior to European settlement. These values are also
slightly lower than the results of studies from other parts of the Southern Hemisphere, including
Australian dust deposited in New Zealand, where enrichment of Pb was calculated to be approximately
5.1 times that of background concentrations (Marx, et al, 2008); but higher than Antarctic snow
records, where Pb was 4 times the natural concentration (Wolff & Suttie, 1994). Importantly, these
enrichment values are fairly high compared with analysed metal accumulations from Club Lake in the
Snowy Mountains, where Pb enrichment was found to be approximately 1.1 to 1.3 times natural
concentrations (Stromsoe, et al, 2013). The discrepancy between these lake and peat Pb concentrations
could be due to lake sediments being more influenced by groundwaters and surface waters, while
ombrotrophic bogs are hydrologically isolated and therefore receive their inorganic solids exclusively
by atmospheric deposition (Shotyk, et al, 1996). Furthermore, it has been shown that the sensitivity of
a lake to increasing atmospheric metal emissions depends strongly on local conditions; conditions
which may either subdue (Martinez Cortizas, et al, 2002), amplify (Swain, et al, 1992), or accurately
reflect the direct (Dillon & Evans, 1982) atmospheric flux. Therefore, the difference evident between
the Blue Lake and Club lake records may be a function of specific catchment processes such as
catchment source, patterns of sediment storage, runoff regimes and the degree to which metals are
concentrated or diluted during transport to the lake. In the case of Club Lake, subdued concentrations
of atmospheric Pb pollution is suggested to be due to a larger amount of soil erosion being supplied to
the lake by that catchment, which would have resulted in dilution of the Pb pollution. This is plausible,
especially for the period when grazing took place in the alpine zone, because the area surrounding Club
Lake was extensively utilised for grazing practices during this time. Evidence of this is shown through
records of frequent fire activity (Sharp, 1992, cited by Zylstra, 2006) and soil erosion (Stromsoe, et al,
2013), as well as photographic evidence of grazing on the banks of the lake (Costin, 2000). Despite these
speculations, it is reasonable to assume that the results presented in Stromsoe, et al (2013) would more
accurately represent Pb accumulation in KNP lacustrine environments because the study has
quantitatively evaluated Pb pollution concentrations. In contrast, the Itrax data used to describe Pb
accumulation in this investigation is measured as counts rather than concentrations, therefore
quantitative analysis of bulk sediment chemistry would need to be applied to compare results properly
(Lӧwemark, et al, 2010).
72
5.2.3 The Effects of Agriculture Expansion on the Kosciuszko National Park Environment
A number of studies have recorded a substantial increase in aeolian dust deposition within the Snowy
Mountains environment since the late 1800’s, with the MDB suggested to be the main source of dust
supplied to the region (Stanley & De Deckker, 2003; Marx, et al, 2011; 2014). Whilst there are a number
of factors that may have contributed to the century of accentuated dust deposition after 1880,
introduction of European farming methods to the Australian landscape, and particularly the
establishment of land clearing and livestock grazing in the MDB have been highlighted as the
predominant cause (Marx, et al, 2011; 2014). Farming practices began in the MDB during the 1820’s
and rapidly expanded westward across the basin after 1830 (Pearson & Lennon, 2010). Expansion was
driven by a wool boom from 1875 to 1890, as well as by the discovery of ground water and the
construction of dams which facilitated agricultural practices in the semiarid lands of the MDB (Pearson
& Lennon, 2010). By the 1880’s, pastoralism was extensively developed within the entire MDB, and
then after railways became established, cropping practices overtook lands that had previously been
utilised for grazing (O’Gorman, 2013). Initially, cropping practices in the MDB used conventional tillage
which was suggested to have played a major role in the increase in wind erosion rates across the region
(Marx, et al, 2014).
In the Blue Lake core, an increase in the supply of dust to the Lake after European settlement is implied
by a shift in the Nd/K and Ta/Ti ratios in the core (Fig.19). This change suggests a shift in the lithology
of material in the core. Assuming a homogenous catchment chemistry, this change implies an addition
of material not derived from the catchment. Given that dust deposition is known to be a significant
process in KNP, this change likely represents an increasing dust component after 1800.
Soils of KNP are highly organic (Stromsoe, et al, 2016) and K can concentrate in organic material.
Therefore, the decreasing Nd/K may partially be related to the deposition of organic material for input
with higher K, i.e. it might not imply dust input alone. Despite this, the Ta/Ti ratio clearly implies an
addition of none catchment material, that is, dust.
Whilst changes in dust deposition cannot be specifically quantified using the Itrax records, it is
suggested that the aforementioned changes in the geochemistry of the sediment after 1800 AD provide
evidence of increased dust deposition within the Blue Lake environment. These correspond with the 2
to 10-fold increase in dust deposition recorded by Marx, et al (2011) and Marx, et al (2014).
In addition to geochemical changes, significant increases in the sedimentation rate (shown in the
Bayesian age/depth model) (Fig.11), MAR (Fig.12) and DBD (Fig.13) are expected to be partially related
to the onset of enhanced aeolian dust deposition in the KNP alpine environment. In particular, they
73
may provide evidence of the expansion of the spatial area supplying dust to the Snowy Mountains as
the changes correspond with the timing of expansion and intensification of agriculture in Australia, as
well as records of dramatic changes in erosion across the south-eastern region (McCulloch, et al, 2003;
Lewis, et al, 2007; Hughes, et al, 2009). Marx, et al (2014) highlighted that removal of native vegetation
for pastoral expansion into the semiarid Western Division of NSW, as well as cropping in the Riverina
region, would have enabled the exposure of previously stable soils to wind, thereby increasing wind
erosion of the soil from these sources. Marx, et al (2014) also suggested that agricultural practices such
as the introduction of hard-hoofed animals (and rabbits in the 1850’s) would have likely caused wind
erosion to be accentuated because of their effects on soil and vegetation, while wide spread land
clearing and alterations to the hydrological regime of the landscape would have further contributed to
increased erosion in broad areas of eastern Australia (Chassemi, et al, 1995).
Interestingly, in this context, the Blue Lake core is recording both increased dust and increased soil
input at the same time. In order to be able to see increased dust, within a period of enhance soil erosion,
requires that the input of dust is relatively significant compared to the soil erosion. Alternatively, the
soils of the KNP are considered to contain significant dust, implying that dust deposition is contributing
to soil formation (Costin, et al, 1952; Johnston, 2001; Marx et al, 2011). Therefore, the soils are already
overprinted with dust. Consequently, a significant component of the dust in Blue Lake after 1800 may
be secondary dust derived from the weathered soils which have been supplied to the lake.
74
5.3 The Impact of Recent Climate Change on Kosciuszko National Park
Since the advent of industrialisation in the mid 1800’s, global surface temperatures have risen by over
1° C (NASA/Goddard Institute for Space Studies, 2016) (Fig.31). All proxy results from the Blue Lake
record demonstrate dramatic changes corresponding with this time, with the sheer scale and extent of
these changes unmatched anywhere in the previous ~3,300 years of the record. While it is likely that
local and regional scale human activities have predominantly influenced these results, it is also
speculated that increasingly warmer conditions would be partially responsible for some of the changes
evident in the proxy data. Most notably, the increase in Chironomus species and decline in all other
Chironomid species (Fig.22) that is evident from ~1900 AD to present is suggested to be indicative of a
shift to warmer temperatures, since Chironomus are more tolerant of significant changes in
temperature and anoxic conditions than other midge species (Woodward, et al, 2017). This would imply
that they are more likely to survive when the lake undergoes inverse thermal stratification for an
extended period of time. More specifically, inverse stratification is when the water layer near the
surface of the lake (epilimnion) is cooler, and the layer below is warm (hypolimnion) (Raine, 1984).
Additionally, an anoxic layer at the bottom of the lake can also form under these conditions (Boehrer &
Schultze, 2006). A decline in all other species also fits with this hypothesis as Chironomids of the
Orthocladiinae and Diamesinae sub-families generally prefer cooler water (Lindegaard, 1995; Epler,
2001) and oxygenated environments (Parkin & Stahl, 1981), therefore a reduced abundance of these
species is likely to due to less mixing in the lake, therefore not oxygen rich, or it being too warm at
depth (i.e not thermally stratified).
Figure 31: The change in global surface temperature from 1880 to 2016 AD (Source: NASA/Goddard Institute for Space
Studies, 2016).
75
Considering the substantial changes that have been previously highlighted, it is suggested that results
presented here server as a baseline for the sensitivity of the alpine zone to change. With the
Intergovernmental Panel on Climate Change (IPCC) projecting global surface warming of up to 4°C by
2100 (IPCC, 2007), as well as with increased development in the surrounding regions, and increased
tourism in the park, it expected that the KNP alpine zone will continue to undergo further significant
change in the future. In order to assist in the preservation of KNP, additional conservation programs
and research conducted in the region will enable better documentation of changes in both the climate
and the ecosystem, as well as further highlight the impact of human activities on the fragile landscape.
76
Part 4 6. Conclusion and Recommendations:
6.1 Conclusion:
The primary aim of this thesis was to quantify the impact of recent climate change and human activity
on the KNP alpine zone, in order to expand upon the knowledge of the region’s palaeo-environment
and assist management for future planning. This was achieved through evaluating synchronous changes
in a series of biological, geochemical and sedimentary proxy records extracted from a core that was
obtained from Blue Lake, a lacustrine environment in the KNP alpine zone. With regard to the specific
objectives of this study, the following speculations about the recent environmental history of the KNP
have been made:
• Natural climate variability was identified from approximately 3,500 to 140 cal. yr BP, with the
region suggested to have initially experienced a relatively cool and wet period at the earliest
stages of the cores history (approximately 3,500 cal. yr BP), followed by a gradual transition to
a comparatively warm, dry period. After the dry episode, it is suggested conditions may have
become gradually wetter in the KNP alpine zone. In addition, there was some significant
climatic variability experienced during this time, especially at some-time around ~3,200 –
3,000 cal. yr BP, and ~1,850 – 1,620 cal. yr BP. These ‘episodes’ have not been previously
identified in other south-east Australian palaeoclimatic records, and therefore expected to be
evidence of some local-scale event.
• Whilst these changes are speculated to be reflected in the Blue Lake record with regard to the
age model that has been constructed, it is suggested that there may be three possible
conclusions about these climatic ‘phases’. These are; (1) the timing of the phases presented
are correct and could reflect a more sensitive response by the alpine environment to climatic
change by being significantly longer or shorter than previously thought, (2) due to the changes
being small, the Blue Lake record may not able to detect the sensitivity of the palaeoclimatic
changes, or (3) the record is detecting changes in climate but the timing is off due to possibly
being influenced by the ‘freshwater reservoir effect’. In light of this, it is recommended that the
changes in the age/model, and the possibility of a reservoir effect, be further explored.
77
• Unfortunately, the results of this study could not confidently infer any information about the
widely documented climatic events, the Medieval Warm Period or the Little Ice Age. This is also
expected to be due to complexity of the age model around this time.
• Human activities since European settlement (early 1800’s to present), particularly grazing
practices, the expansion of tourism in the Snowy Mountains, the development of industrial
activities and expansion of agriculture in the surrounding regions, have significantly changed
the ecological, sedimentological and geochemical function of the KNP alpine zone. Importantly,
these activities are expected to be partially responsible for an increase and change in
catchment erosion material, as well as dust deposition since the early 1800’s.
• A substantial (and sustained) change in all proxy records from the late 1880’s to present is
interpreted to imply a significant response to anthropogenic activity. In particular, a significant
increase in fire and both rock weathering and soil erosion has been detected in the Blue Lake
record. Furthermore, the changes also correspond with the >1°C increase in global surface
temperatures which has occurred since the beginning of the Industrial Revolution. The results
presented here therefore server as a baseline and show the sensitivity of the KNP alpine zone
to change. Considering this, it is likely that further changes to the alpine zone will continue to
take place in response to future climate change.
In light of these findings, it is evident that the KNP alpine environment has changed over time. However,
the scale and extent of the changes which have occurred since European settlement are unprecedented
compared with those of the previous 3,300 years. Considering this, it is concluded that the Kosciuszko
National Park is most sensitive to the impacts of modern human activities.
6.2 Recommendations for Future Work
Evaluation of the whole KNP alpine zone is difficult when only studying a single site. This study could be
greatly expanded and a more comprehensive view of the system obtained simply by the collection and
comparative analysis of lake cores from the other three alpine lakes (Club Lake, Lake Albina and Lake
Cootapatamba) in the region.
Additionally, the Itrax data provides an indication of an increase in weathered material, Pb and dust in
the core, however, it cannot be used to accurately quantify change in the geochemistry of the core.
78
Further evaluation through quantitative analysis of the geochemical changes would be needed to better
understand these patterns.
As previously mentioned, this study would also be enhanced by a more thorough evaluation of the age
model, particularly for the 210Pb dates and the discontinuous region between the lower most 210Pb date
and the upper most 14C date. It is recommended that additional 210Pb dates, and perhaps 137Cs analysis,
could be utilised to better understand recent ages, while a number of extra dated radiocarbon samples
would provide clearer evidence at the region of discontinuity.
Furthermore, lake records are expected to be relatively insensitive to small palaeoclimate changes
compared to peats, therefore analysis of a peat core from the region may enable a better
understanding about the palaeoclimate to be obtained. Alternatively, the proxies used in this study may
not be particularly sensitive to these changes, therefore alternate proxies, such as measuring stable
isotopes, may further test the palaeoclimate implication of this study.
79
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