Effects of the Canterbury

Effects of the Canterbury earthquakes on Avon-Heathcote Estuary / Ihutai macroalgae Report No. R12/91 ISBN: 978-1-927222-46-1 (print) 978-1-927222-47-8 (web) Report prepared for Environment Canterbury and Christchurch City Council by

Neill Barr1

John Zeldis2

Catherine Gongol2

Laura Drummond2

Kristin Scheuer3

1 NIWA, Wellington 2 NIWA, Christchurch 3 University of Canterbury, Christchurch September 2012

Report No. R12/91 ISBN: 978-1-927222-46-1 (print) 978-1-927222-47-8 (web)

24 Edward Street, Lincoln PO Box 345 Christchurch 8140 Phone (03) 365 3828 Fax (03) 365 3194 75 Church Street PO Box 550 Timaru 7940 Phone (03) 687 7800 Fax (03) 687 7808 Website: www.ecan.govt.nz Customer Services Phone 0800 324 636

Effects of the Canterbury earthquakes on Avon-Heathcote Estuary / Ihutai macroalgae

Final Report

Prepared for Environment Canterbury and Christchurch City Council

September 2012

© All rights reserved. This publication may not be reproduced or copied in any form without the permission of the copyright owner(s). Such permission is only to be given in accordance with the terms of the client’s contract with NIWA. This copyright extends to all forms of copying and any storage of material in any kind of information retrieval system.

Whilst NIWA has used all reasonable endeavours to ensure that the information contained in this document is accurate, NIWA does not give any express or implied warranty as to the completeness of the information contained herein, or that it will be suitable for any purpose(s) other than those specifically contemplated during the Project or agreed by NIWA and the Client.

Authors/Contributors: Neill Barr1 John Zeldis2 Catherine Gongol2

Laura Drummond2 Kristin Scheuer3 1 NIWA, Wellington 2 NIWA, Christchurch 3 University of Canterbury, Christchurch

For any information regarding this report please co ntact:

Neill Barr Algal eco-physiologist, NIWA +64-4-38080 7980 [email protected] National Institute of Water & Atmospheric Research Ltd 301 Evans Bay Parade, Greta Point Wellington 6021 Private Bag 14901, Kilbirnie Wellington 6241 New Zealand Phone +64-4-386 0300 Fax +64-4-386 0574

NIWA Client Report No: CHC2012-072 Report date: September 2012 NIWA Project: ENC11527

Effects of the Canterbury earthquakes on Avon-Heathcote Estuary / Ihutai macoalgae 3

Contents

1 Introduction ...................................... ........................................................................... 6

1.1 Context ................................................................................................................ 6

1.2 Scope ................................................................................................................... 6

2 Methods ........................................... ............................................................................ 7

2.1 Background algal monitoring ................................................................................ 7

2.2 River sites and collections .................................................................................... 8

2.3 Algal nitrogen status indices ............................................................................... 10

2.3.1 Tissue nitrogen and nitrogen isotopes .................................................. 10

2.3.2 Tissue chlorophyll and free amino acid content .................................... 10

2.4 Water quality parameters ................................................................................... 10

2.4.1 Nutrients ............................................................................................... 10

2.4.2 Isotopes of dissolved inorganic nitrogen ............................................... 10

3 Results ........................................... ............................................................................ 12

3.1 Long-term Algal Monitoring ................................................................................ 12

3.2 Algal responses to earthquake derived nitrogen ................................................. 15

3.2.1 Algal tissue nitrogen indices - Rivers .................................................... 15

3.2.2 Algal responses to changes in DIN-δ15N isotopes - Rivers .................... 17

3.2.3 Nitrogen loading in the Heathcote and Avon rivers ............................... 19

3.2.4 Algal tissue nitrogen indices - Estuary .................................................. 20

3.2.5 Nitrogen loading – Estuary ................................................................... 22

4 Discussion ........................................ ......................................................................... 24

4.1.1 Responses of macroalgae to the Christchurch wastewater diversion and the Christchurch earthquakes ......................................... 24

4.1.2 Isotopic sources of nitrogen affecting the Avon-Heathcote estuary ....... 25

4.1.3 Other potential earthquake effects on macroalgae ................................ 26

5 Conclusions ....................................... ........................................................................ 27

6 Acknowledgements .................................. ................................................................. 27

7 References ........................................ ......................................................................... 28

Appendix A ....................................... ............................................................................... 30

Appendix B ....................................... ............................................................................... 31

Appendix C ....................................... ............................................................................... 32

Appendix D ....................................... ............................................................................... 33

4 Effects of the Canterbury earthquakes on Avon-Heathcote Estuary / Ihutai macoalgae

Tables Table 2-1: Site locations and collection dates for algal bioindicator and water quality at

monitoring stations located in lower reaches of the Avon River and the Heathcote River. 9

Figures Figure 2-1: Avon-Heathcote Estuary showing nominal locations of existing algal

sampling stations where regular collections have been made since November 2009. 7

Figure 2-2: Avon-Heathcote Estuary showing nominal locations of test-algal stations at the Avon River and Heathcote river study sites. 8

Figure 2-3: In situ algal culture chamber and frame. 9

Figure 3-1: Changes in seawater dissolved inorganic nitrogen concentrations and tissue chlorophyll content in Ulva at the Humphreys Drive and Heron Street sites. 12

Figure 3-2: Changes in Ulva tissue-δδδδ15N from long-term monitoring sites from the Avon-Heathcote Estuary. 14

Figure 3-3: Comparison of changes intissue-N and tissue-δδδδ15N in Ulva grown at test-algae monitoring stations on the Avon and Heathcote rivers over the period of this study. 16

Figure 3-4: Comparison of changes in NH4+-δδδδ15N, NO3

--δδδδ15N and NO3--δδδδ18O in water

samples collected from monitoring stations on the Avon and Heathcote rivers over the period of this study. 18

Figure 3-5: Comparison of changes in mixed source DIN-δδδδ15N river samples collected in the Avon and Heathcote rivers over the period of this study and changes in Ulva tissue-δδδδ15N from long term monitoring sites at Heron and Humphreys from the Avon-Heathcote Estuary. 19

Figure 3-6: Daily nitrogen loading rates in the Heathcote and Avon rivers since 2007. 20

Figure 3-7: Comparison of three tissue nitrogen status indices in Ulva averaged for summer periods at two sites in the Avon-Heathcote estuary. 21

Figure 3-8: Comparison of water column nutrient levels averaged for summer periods at two sites in the Avon-Heathcote estuary. 22

Reviewed by Approved for release by

Wendy Nelson Julie Hall Frontispiece: Typical peak season biomass of Ulva and Gracilaria in the Avon-Heathcote Estuary. (photo: Neill Barr, Ebbtide Street 2002).


Executive summary This report describes a 12-month study on the effects of nitrogen derived from earthquake-driven wastewater overflows on nuisance algae growing in the Avon-Heathcote Estuary. The two rivers that enter the estuary, the Avon and the Heathcote, have received considerable but variable wastewater overflows of raw effluent resulting from damage caused by the Christchurch earthquakes, particularly from those on 22nd February and 13th June, 2011. To examine the influence of changes in river-sourced nutrients on macroalgae growing in the estuary, test-algae were grown in chambers deployed in the lower reaches of the Avon and the Heathcote rivers. Algal tissue and river water samples were collected monthly between March 2011 and April 2012. Tissue nitrogen status indices (including tissue-nitrogen, chlorophyll, free amino acids) and tissue nitrogen isotopic composition (tissue-δ15N) in these algae were compared to those of naturally occurring algae growing in the estuary in relation to changes seen in nitrogen (N)-loading resulting from the earthquakes.

Research conducted since the beginning of 2009 had been investigating the use of algal nitrogen status indices and tissue-δ15N values (derived from the ratio of naturally abundant nitrogen isotopes; 14N / 15N) as indictors of both amount and source, respectively, of nitrogen in the Avon-Heathcote estuary. While high values of nitrogen status indices in algae can indicate high N availability in estuarine environments, tissue-δ15N values can indicate the different sources of N available in these environments. Typically high tissue-δ15N in algae (> 9 ‰) can indicate the influence of N from tertiary-treated wastewater while low values (< 6 ‰) can indicate the presence of N from raw, or less treated sewage effluent. In addition to evaluating changes seen in algal tissue-δ15N indices over the period of this study, riverine and marine sources of stable nitrogen isotopes dissolved in water entering the estuary were investigated.

Based on nitrogen status indices and tissue-δ15N isotopic composition of algae growing in both the rivers and in the estuary, there was a measurable contribution of raw effluent derived nitrogen to algae growing in the estuary. However the contributions of dissolved inorganic nitrogen (DIN) as a result of the earthquake were probably relatively minor compared to the positive effect of reduced N-loading by ~ 90% with the diversion of the Christchurch Wastewater Treatment Plant (CWTP) discharge away from the estuary in March 2010. In addition, based on water nutrient values recorded since 2007, the background N-loading from both the Avon and Heathcote rivers to the estuary also appears to have been more important than the contribution of nutrients resulting from the earthquakes. Moreover, the bulk of additional earthquake derived nitrogen that was detected in algal tissues, which may have influenced algal growth in the estuary, occurred over autumn and winter months when growth was more likely to be limited by light and temperature. Historically proliferations of nuisance algae in the estuary occur under summer conditions when elevated N concentrations drive growth.

In addition to evaluating the effects of the Christchurch earthquakes on algae growing in the estuary it is envisaged that this investigation will help inform future management of riverine contributions in relation to growth of nuisance macroalgae in the Avon and Heathcote Estuary.


1 Introduction

1.1 Context Historically, massive Ulva and Gracilaria blooms in the eutrophic Avon-Heathcote Estuary (Christchurch, New Zealand) have significantly affected both the estuary’s aesthetic value and its ecosystem function. Frondose Ulva species (e.g., U. pertusa, U. lactuca or U. rigida) are the dominant bloom forming macroalgal group in the estuary. With the diversion of Christchurch Wastewater Treatment Plant (CWTP) discharge away from the estuary in March 2010 it was expected there would be a significant (~90%) reduction in nitrogen (N)-loading (predominantly as ammonium), which in turn promised a reduction in algal biomass within the estuary. A three-year MSI-funded partnership between NIWA and University of Canterbury had been investigating, amongst other ecosystem components, background monitoring of macroalgal nitrogen indictors in relation to changes in seawater N-loading resulting from the wastewater diversion.

Since September 4th 2010, Canterbury has been subjected to an earthquake sequence unprecedented in its human history. The most intense earthquakes local to Christchurch occurred on 22nd February 2011, with violent ground accelerations, resulting in significant damage to municipal wastewater reticulation infrastructure. This resulted in the re-introduction of sewage derived nitrogen into the estuary from overflows of raw effluent directly into the estuary via drains and the Avon and Heathcote rivers. Peaks in estimated total overflow volumes occurred immediately after the February earthquake (85,400 m3 per day) and after the 13th June earthquake (67,600 m3 per day). At the commencement of the study the influence of increased nitrogen loading from river-borne sewage on nuisance algae in the estuary was unknown. It was therefore possible that enhancement of growth in ‘new’ macroalgal beds could occur with a resupply of wastewater derived nutrients to the estuary at some point in the future, particularly if it coincided with growth peak season (summer). Gaining information to separate the presumably short term effects of the earthquakes from the long term effects of remediation by the CWTP diversion was therefore a priority of Environment Canterbury and Christchurch City Council.

1.2 Scope This report describes algal biochemical/isotopic responses to river contamination effects as a consequence of the September 2010, February 2011 and June 2011 Canterbury earthquakes. The project is a collaborative research effort between the University of Canterbury and NIWA and is commissioned by Environment Canterbury and the Christchurch City Council (CCC).

The study employs a system of field cultured ‘test-algae’ to examine the likely influence of nutrients derived from sewage overflows to the Avon and Heathcote rivers. Specifically it seeks to examine changes in nitrogen status indices and tissue nitrogen isotopic composition within the algae and relate these to dissolved inorganic nitrogen (DIN) loading and DIN-δ15N from wastewater, rivers and ocean sources over the period of the earthquakes (e.g., nitrogen in the Avon and the Heathcote rivers, and in wastewater effluent and marine water). We evaluate how the algal nitrogen status indices and tissue nitrogen isotopic composition inform managers about nutrient pollution sources to the Avon-Heathcote estuary.


2 Methods

2.1 Background algal monitoring Prior to the Christchurch earthquakes an existing algal monitoring programme was tracking changes in biochemical responses of several algal populations to nitrogen (N)-loading in the estuary (see Figure 2-1). Two algal collection areas adjacent to Heron Street and Humphreys Drive represent the main ‘sentinel’ collection sites for this study (Figure 2-1). The primary aim of this research was to evaluate algal responses for the purpose of developing macroalgae as cost effective indicators of N-loading and to study their responses to the diversion of the CWTP wastewater to the ocean outfall. The primary motivation for this work was the recognition of the limitations of conventional water quality monitoring, which is typically expensive, often highly variable and subject to the effects of tidal aliasing, therefore not necessarily reflecting all sources of nitrogen available to primary producers. The diversion of the CWTP wastewater away from the estuary provided an ideal opportunity to test and validate the responses algal indicators to N-loading.

Discharge

Humphreys Drive

Heron Street

Pukeko Street

McCormacks Causeway

Avon

Figure 2-1: Avon-Heathcote Estuary showing nominal locations of existing algal sampling stations where regular collections have been made since November 2009. The Heron Street and Humphreys Drive sites represent areas of the estuary that historically have suffered the highest biomass of blooming seaweeds. Photo from Google Earth, prior to the September earthquake.


2.2 River sites and collections In May 2011, two months after the most damaging earthquake on February 22nd, we began collecting algae and bulk water samples from two sites, one each in the lower reaches of the Avon and the Heathcote rivers (Figure 2-2). Initially, naturally occurring algae were sampled but the distribution of the algae was sparse and unreliable for regular collections. Therefore a system of moored culture chambers was employed as described by Barr (2007) to house Ulva (and Gracilaria) as ‘test-algae’ at each of the two river sites (Figure 2-3). Each site had four stations which were located within approximately 100 m of each other. Site locations, sampling dates and samples collected are further detailed in Table 2.1. In addition to collecting low-tide water samples from the rivers, incoming seawater was also collected from a site at Beachville Road (Figure 2-2) to reflect the oceanic end-member for isotopic comparison with river water isotopic data. While algal growth and recovery was generally successful at the Heathcote River, success was variable at the Avon River site with Ulva being recovered only in the second half of this study. Gracilaria was later added to culture chambers in both rivers to bolster algal collections, particularly those from the Avon River.

Heathcote River stations

Avon River stations

Beachville Road

Humphreys Drive

Heron Street

Figure 2-2: Avon-Heathcote Estuary showing nominal locations of test-algal stations at the Avon River (1577685 E, 5181000 N) and Heathcote (1576380 E, 5176855 N) river study sites. Also shown are the locations Beachville Road for tidal incoming seawater collections, and the Heron and Humphreys algal monitoring sites where monthly collections have been made since November 2009. (Photo from Google Earth, accessed prior to the September earthquake).


Figure 2-3: In situ algal culture chamber and frame as described by Barr (2007).

Table 2-1: Site locations and collection dates for algal bioindicator and water quality at monitoring stations located in lower reaches of the Avon River and the Heathcote River. Coordinates are approximate and are given as Eastings and Northings. Growth chambers along with test-Ulva and/or Gracilaria were deployed on the 24th May with test-Ulva collected and redeployed at monthly intervals. Where no Ulva was recovered in the chambers this is noted.

Date Avon River WQ samples Heathcote River WQ samples

14th April 2011 Native Ulva Nil

5th May 2011 Native Ulva Nil

24th May 2011 Chambers deployed 3 L Chambers deployed 3 L

16th June 2011 Ulva 3 L Nil 3 L

6th July 2011 Ulva Nil

26th August 2011 Ulva 3 L Nil 3 L

23th September 2011 Ulva, Grac Ulva, Grac

12th October 2011 Ulva, Grac 3 L Ulva, Grac 3 L

9th November 2011 Ulva, Grac Grac

6th December 2011 Ulva 3 L Nil 3 L

4th January 2012 Ulva Grac

9th February 2012 Ulva 3 L Ulva 3 L

6th March 2012 Ulva Ulva

10th April 2012 Ulva 3 L Ulva 3 L


At each river site:

1. Four algal culture chambers were deployed at surface moorings and test-algae housed and maintained from May 2011. Sampling has continued on a monthly basis since then. Tissue samples were stored at -80 °C at NIWA, Christchurch for later determination of tissue biochemical indices.

2. Opportunistic collections were also made of naturally occurring algae in the vicinity of these sites where possible.

3. Water samples (3 x 1 L) were collected for determination of the river isotopic end-members. These were filtered through 1 µm GFC filters to preserve the particulate fraction in water samples as soon as possible after collection. The bulk water sample and filters have been stored at -80 °C for later analysis of dissolved nutrients and of both the particulate and dissolved fractions of δ15N.

Seawater samples (3 x 1L) were also collected at the Beachville Road site from the incoming tide for determination of the oceanic isotopic end-member for the estuary.

2.3 Algal nitrogen status indices

2.3.1 Tissue nitrogen and nitrogen isotopes For all algae collected from river and estuary sites, tissue-N and tissue-δ15N were determined from stored (frozen at -80 °C) samples. Samples were dried at 60 ˚C for 48 hours and then ground to a fine powder for analyses of algal tissue-N and tissue-δ15N content. These were determined on an automated Europa Scientific 20/20 isotope analyser at the Waikato Isotope Unit along with appropriate reference standards.

2.3.2 Tissue chlorophyll and free amino acid conten t Tissue chlorophyll and free amino acids were extracted and determined as described by Barr and Rees (2003).

2.4 Water quality parameters

2.4.1 Nutrients In most cases nutrient data derived from Environment Canterbury’s on-going water quality monitoring programme were used to examine long-term trends in nutrient loading to the rivers and estuary. Nitrogen loading rates were calculated using 13-day median values for river flow data, centred on days when water quality samples were collected for rivers.

2.4.2 Isotopes of dissolved inorganic nitrogen Changes in the isotopic composition of dissolved inorganic nitrogen (DIN) in Avon and Heathcote river water were examined for the period between December 2009 and April 2012.

The nitrogen (15N/14N) and oxygen (18O/16O) isotopic compositions of nitrate (NO3-) were

determined using the denitrifier method (Sigman et al. 2001 and Casciotti et al. 2002) at the University of California, Riverside Facility for Isotope Ratio Mass Spectrometry (FIRMS). The denitrifier method is based on the isotopic analysis of nitrous oxide (N2O) reduced from NO3

- by denitrifying bacteria (Pseudomonas aureofaciens) that lack the N2O-reductase


enzyme. NO3- -δ15N denotes a difference measurement made relative to the international

reference standard, atmospheric dinitrogen (N2) and NO3- -δ18O denotes a difference

measurement made relative to Vienna Standard Mean Ocean Water (VSMOW). Prior to the isotope measurements the concentration of NO3

- -N in the water samples was measured by ion chromatography. While the NO3

- concentrations can be interpreted as nitrate and nitrite (NO2

-), there was no NO2- measured above the 0.1 µmol l-1 detection limit.

The nitrogen (15N/14N) isotopic composition of ammonium (NH4+) was determined at NIWA

using the recently developed ammonia diffusion method (Chen and Dittert, 2008) and as such presented several analytical challenges. In this technique, ammonia (NH3) released from a water sample mixed with a strong base (sodium hydroxide) is diffused through a PTFE membrane onto an acid trap. The total nitrogen and the 15N/14N ratio on the acid trap filter papers were analysed by continuous-flow direct combustion and mass spectrometry at NIWA’s Isotope Ratio Mass Spectrometry (IRMS) facility. Before applying the method to the Avon and Heathcote river water samples, the diffusion procedure was carried out on a series of test water samples with N content ranging from 20 to 200 µg N. The ideal N content per sample volume was found to be 100 µg N, and isotopic values were less precise below 50 µg N. Prior to the river isotope measurements the concentration of NH4

+ -N in the water samples was determined by spectrometry according to the method of Koroleff (1983). Taking into account the concentration of NH4

+ in each sample, the volume of water used in each diffusion measurement was calculated so that the predicted amount of N on the filters would be greater than 50 µg N.

A mixed source dissolved inorganic nitrogen (DIN)-δ15N value for each water sample was calculated from the estimated NO3

- -δ15N and NH4+-δ15N values using a two-source mixing

model (derived from Fry 2006) as shown below:

δmixed source = (δsource 1 × f source 1) + (δsource 2 × f source 2)

Where, δsource 1 and δsource 2 are the δ15N values (‰), and f source 1 and f source 2 are the relative fractions of nitrate and ammonium in dissolved inorganic nitrogen.


3 Results

3.1 Long-term Algal Monitoring Shown below is an example of the recent historical changes in seawater N-loading from 2007 through to May 2012, and also corresponding changes that have occurred in nitrogen status indices in frondose Ulva populations from the Heron and Humphreys ‘sentinel’ collection sites (Figure 3-1). Similar responses were also observed for tubular Ulva forms (e.g., U. intestinalis and U. compressa) and also Gracilaria collected from these sites over the same period. One of the clearest trends seen in algal nitrogen status indices can be seen

1 2 3 54

A) Humphreys Drive

B) Heron Street

0

2

4

6

8

10

12

14

16

18

20

0

50

100

150

200

Jan-

07

Jul-0

7

Jan-

08

Jul-0

8

Jan-

09

Jul-0

9

Jan-

10

Jul-1

0

Jan-

11

Jul-1

1

Jan-

12

Chl

orop

hyll

a +

b (

mg

⋅ g D

W-1

)

0

2

4

6

8

10

12

14

16

18

20

Sea

wat

er in

orga

nic

nitr

ogen

(µM

)

0

50

100

150

200

Figure 3-1: Changes in seawater dissolved inorganic nitrogen concentrations (blue squares) and tissue chlorophyll content in Ulva (green and yellow round symbols, yellow symbols indicate summer values from November to February) at the (A) Humphreys Drive and (B) Heron Street sites. Five significant events affecting the estuary are denoted on both plots by numbers and arrows. (1) Wastewater diversion from the estuary on the 4th March 2010, and the four main Christchurch earthquakes; (2) 4th September 2010, (3) 22nd February 2011, (4) 13th June 2011 and (5) 23rd December 2011. Nutrient data are derived from Environment Canterbury water quality monitoring sites in the estuary; Penguin Street (SQ32575), being the nearest site to the Heron collection site, and Humphreys Drive (SQ32819).


in Ulva chlorophyll content which tracks changes also seen in dissolved inorganic nitrogen (DIN) concentration in the estuary over the period beginning February 2009 when the algal collections began. In the six months following the diversion of the wastewater loading from the estuary in March 2010 there was a decline in seawater DIN concentration and a corresponding reduction in chlorophyll content in Ulva growing at these sites (Figure 3-1). However, seawater DIN concentration increased again with the onset Christchurch earthquake series (4th September 2010, 22nd February 2011, 13th June 2011 and 23rd December 2011) which resulted in overflows of raw effluent to the estuary predominantly via the two rivers. Increases in DIN concentration and Ulva chlorophyll content occurred at the Humphreys site just after the September 2010 earthquake but also for both sites for the period beginning with the 22nd February earthquake through the 13th June earthquake. Concentrations decreased towards November 2011 when the last of overflows to the two rivers were repaired (Bourke 2012). It was estimated during this time that up to 30 % of Christchurch city’s wastewater was being discharged as raw effluent overflows into the two rivers and various drains that lead to the estuary (Bolton-Richie, 2012).

In addition to the changes seen in algal nitrogen status indices over the course of the algal monitoring program (which also include total tissue-N and free amino acid content which will be discussed later) it was also evident that there had been a shift in nitrogen isotopic (δ15N) composition recorded in algal tissues through the times series beginning in the summer before the CWTP diversion in March 2012 (Figure 3-2). These changes occurred in Ulva from the various collection sites around the estuary (Figure 3-3, A) but are most clearly seen at the two sentinel sites at Heron Street and Humphreys Drive (Figure 3-3, B). In the summer before the diversion there was a noticeable variability in tissue-δ15N composition. While pre-diversion Ulva at the Humphreys Drive site typically had only higher (> 8.8 ‰) tissue-δ15N values, the Heron Street sites, along with the discharge and Avon River sites produced Ulva with both higher (> 8.8 ‰) and lower (< 6.6 ‰) tissue-δ15N in early summer November / December 2009. These low tissue-δ15N values coincided with very elevated NH4

+ : NO3-

ratios recorded in the main discharge oxidation pond (Pond 6, see the red trace in Figure 3-3, A). The increase in NH4

+ : NO3- apparently resulted from the intentional diversion of

ammonium-rich effluent from earlier in the processing sequence into oxidation ponds to control chironomid larvae (Feary, 2012). The relative increase of ammonium, which probably carried a lighter isotopic signature typical of raw or less processed effluent (Rogers 1999, 2003; Bedard-Haughn et al. 2003; Barr et al. 2012), over nitrate would probably have been reflected in lighter tissue-δ15N in Ulva growing during this time. The peak of the second pulse observed on 18th February occurred 3 days after algal collections on the 15th February and is possibly why this second event was not recorded in algae tissues at this time. The next algal collection on the 15th March occurred after the diversion of discharge effluent to the ocean outfall on the 4th March 2010 (Bourke, 2012).

In the six months following the diversion there was a consistent decrease both terms of tissue-δ15N variability and also in absolute values of tissue-δ15N in Ulva at both Heron and Humphreys sites with values then tending towards the oceanic baseline levels (6.6 – 8.8 ‰) previously recorded for Ulva growing in clean coastal situations around New Zealand (Barr 2007; Barr et al. 2012). The generally higher tissue-δ15N values seen in Ulva at these sites prior to the diversion was almost certainly associated with the higher δ15N isotopic signatures of the CWTP discharge (Drake and Stewart, 2008) and typical of other (Dudley, 2007) tertiary treated wastewater discharges with effluent denitrification. In addition, effluent


samples collected between December 2009 and April 2012 from the main discharge oxidation pond (Pond 6) and analysed for dissolved fraction of NH4

+ -δ15N and NO3--δ15N

indicated a mean DIN -δ15N value of 11.9 ± 1.0 ‰ (Appendix B).

Apart from the spike in DIN concentration and Ulva tissue chlorophyll at Humphreys Drive in September, the only other possible indication of some influence on algae from the September earthquake was a subtle increase in tissue-δ15N in Ulva from Humphreys Drive after first September earthquake. It is not known what caused this increasing tissue-δ15N trend in Ulva but it was probable that the destructive effects of the February earthquake initiated the shift to lower Ulva tissue-δ15N presumably reflecting new raw effluent being delivered to the estuary.

1 2 3 4

B) Heron and Humphreys only

A) All sites

0

2

4

6

8

10

12

14

16

18

NH

4+ :

NO

3- ra

tio in

Oxi

datio

n P

ond

6

0

200

400

600

800

1000

Nov

-09

Dec

-09

Jan-

10

Feb

-10

Mar

-10

Apr

-10

May

-10

Jun-

10

Jul-1

0

Aug

-10

Sep

-10

Oct

-10

Nov

-10

Dec

-10

Jan-

11

Feb

-11

Mar

-11

Apr

-11

May

-11

Jun-

11

Jul-1

1

Aug

-11

Sep

-11

Oct

-11

Tis

sue-

δ15N

(‰

)

0

2

4

6

8

10

12

14

16

18

HeronHumphreysPukekoAvonDischargeOxidation Pond 6

Figure 3-2: Changes in Ulva tissue-δ15N from long-term monitoring sites from the Avon-Heathcote Estuary. The shaded blue shaded region represents the expected coastal marine baseline levels for tissue-δ15N in Ulva (from Barr 2007, also see Appendix D). The red trace in plot A indicates changes in the ammonium : nitrate (NH4

+ : NO3-) ratio from discharge oxidation pond (Pond 6). Four significant

events affecting the estuary are denoted on both plots by numbers and arrows. (1) Wastewater diversion from the estuary on the 4th March 2010, and the three main Christchurch earthquakes; (2) 4th September 2010, (3) 22nd February 2011 and (4) 13th June 2011.


3.2 Algal responses to earthquake derived nitrogen

3.2.1 Algal tissue nitrogen indices - Rivers For the duration of the river study Ulva grown in the Heathcote River had tissue-N levels that were saturated (~ 4 %), with levels possibly supersaturated (> 5 %) in the second half of the study (from November to April 2012) (Figure 3-3, A). Tissue-δ15N levels in Heathcote River Ulva, on the other hand, declined from 6.6 ‰ in April to close to 0 ‰ three days after the June earthquake. These levels then increased again to reasonably stable levels mostly just above marine baseline (6.6 ‰ to 8.8 ‰) by November after current overflows at that time had been repaired (Figure 3-1, B). In general the shift to lower levels of tissue-δ15N in the Heathcote Ulva coincided with elevated total inorganic nitrogen (TIN) concentrations peaking at around 160 µM in June and also with an increasing ammonium contribution to the river inferred from higher ammonium : nitrate ratios at that time (Figure 3-3, C).

Ulva was successfully recovered from the Avon River site only during the second half of this study but during this period, from September onwards, showed the same saturating responses as in the Ulva from the Heathcote River. Tissue-δ15N values in Ulva in the Avon River were similar to Heathcote Ulva over the last six months with values mostly within or just above the coastal marine baseline for Ulva. Similarly to the Heathcote River, Avon DIN concentrations peaked at around 160 µM but in July. There were also generally higher ammonium : nitrate ratios in the Avon over most of this study also probably indicating ammonium contributions from overflows (Figure 3-3, C).


A

B

C

1 2

Tis

sue-

N (

%)

0

1

2

3

4

5

6

Heathcote River Ulva Avon River Ulva

Tis

sue−

δ15N

(‰

)

-2

0

2

4

6

8

10

12

14

16

18

Heathcote River Ulva Avon River Ulva

Apr

-11

May

-11

Jun-

11

Jul-1

1

Aug

-11

Sep

-11

Oct

-11

Nov

-11

Dec

-11

Jan-

12

Feb

-12

Mar

-12

Apr

-12

May

-12

Dis

solv

ed in

orga

nic

nitr

ogen

(µM

)

0

20

40

60

80

100

120

140

160

180

NH

4+ :

NO

3-

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Heathcote River DINAvon River DINHeathcote NH4

+ : NO3-

Avon NH4+ : NO3

-

Figure 3-3: Comparison of changes in (A) tissue-N and (B) tissue-δ15N in Ulva grown at test-algae monitoring stations on the Avon and Heathcote rivers over the period of this study. Also changes in (C) dissolved inorganic nitrogen (DIN) and the ratios of ammonium (NH4

+) : nitrate (NO3-) over the

course of the study are shown. The shaded blue shaded region in plot A represents the approximate seasonal range of values for Ulva grown in non-polluted estuaries and in plot B the expected coastal marine baseline levels for tissue-δ15N in Ulva (derived from Barr et al. 2012, also see Appendix D). Nutrient concentrations are derived from Environment Canterbury river water quality monitoring sites at Ferrymead Bridge (SQ30548) for the Heathcote River and at Bridge Street (Sth Brighton) Bridge (SQ30597) for the Avon River. The red arrow and vertical dotted line indicate the 13th June earthquake while the blue arrow and dotted line indicate the repair of overflows in 25th October.


3.2.2 Algal responses to changes in DIN- δδδδ15N isotopes - Rivers Changes in isotopic fractions of dissolved inorganic nitrogen (DIN) in river water were also examined for the period December 2009 to April 2012. There was significant variability in ammonium-δ15N (NH4

+ -δ15N) values measured in water samples from both rivers, but particularly those from the Heathcote river over the period of this study (Figure 3-4, A). For the period leading up to June 2011 NH4

+ -δ15N values in both rivers were mostly positive and in the range of -1.6 to 28 ‰., but from June 2011 values tended to decline to a minimum of close to -10 ‰ in December 2011 and then increase again. Some of the observed variability in values from the Heathcote river may have been related to three values from this site (indicted by asterisks in Figure 3-4, A) which were also reported as results with poor chromatography.

In contrast to variability in NH4+ -δ15N, nitrate-δ15N (NO3

- -δ15N) values were both reasonably constant over time and distinctly different between the two rivers, with mean NO3

- -δ15N values of 5.2 ± 0.1 ‰ and 10.0 ± 0.4 ‰ for the Avon and Heathcote rivers, respectively (Figure 3-4, B. See also Appendix A). Qualitatively the same was also true for oxygen isotopes in nitrate-δ18O (NO3

- -δ18O) measured in river samples with mean NO3- -δ18O values

of 1.4 ± 0.4 ‰ and 4.4 ± 0.3 ‰ for the Avon and Heathcote rivers, respectively (Figure 3-4, C. Also see Appendix A). There was no apparent effect of either the wastewater diversion or the subsequent earthquake events on NO3

- -δ15N or NO3- -δ18O values over time, however

there was slight peak in their values in December 2011, coinciding with the minimum in NH4+

-δ15N values for both rivers (Figure 3-4, B and C. See also Appendix A).

From the δ15N isotope values above, and their respective concentrations at the time of sampling (see Appendix A), a two-source mixing model was used to estimate the mixed source DIN -δ15N for river water. Two notable features were the difference in DIN -δ15N mean values between the two rivers and the decline values between June 2011 to October 2011, particularly in water samples from the Avon River (Figure 3-5, A). The mixed source DIN -δ15N theoretically represents what would be reflected in algal tissue grown in the rivers and was compared with tissue-δ15N values for Ulva and Gracilaria grown in the rivers (Figure 3-5, B). Also included in this comparison were all long term Ulva tissue-δ15N data currently available from the Heron and Humphreys sentinel sites in the estuary (Figure 3.5, B). As well as broadly corresponding with decease in mixed source DIN -δ15N in river water, the low δ15N values recorded in both Ulva and Gracilaria tissues suggested that the main influence of earthquake driven N-loading began shortly after the February 2011 earthquake but was predominantly centred around the winter months of 2011.


*

**

A

B

C

ΝΟ

3− − δ

15N

(‰

)

-20

-10

0

10

20

30

Nov

-09

D

ec-0

9

Jan-

10

Feb

-10

M

ar-1

0

Apr

-10

M

ay-1

0

Jun-

10

Jul-1

0

Aug

-10

S

ep-1

0

Oct

-10

N

ov-1

0

Dec

-10

Ja

n-11

F

eb-1

1

Mar

-11

A

pr-1

1

May

-11

Ju

n-11

Ju

l-11

A

ug-1

1

Sep

-11

O

ct-1

1

Nov

-11

D

ec-1

1

Jan-

12

Feb

-12

M

ar-1

2

Apr

-12

M

ay-1

2

ΝΟ

3− −δ18

O (

‰)

-20

-10

0

10

20

30

NH

4+ −δ15

N (

‰)

-20

-10

0

10

20

30

Avon River waterHeathcote River water

1 2 3 4 65

Figure 3-4: Comparison of changes in (A) NH4+-δ15N, (B) NO3

--δ15N and (C) NO3--δ18O in water

samples collected from monitoring stations on the Avon and Heathcote rivers over the period of this study. Six significant events affecting the estuary are denoted on both plots by numbers and arrows. (1) Wastewater diversion from the estuary on the 4th March 2010, the earthquakes on (2) 4th September 2010, (3) 22nd February 2011, (4) and 13th June 2011, (5) the repair of last sewage overflows on 25th October and the earthquake on (6) 23rd December 2011.


1 2 3 4 65

Heron (Ulva)Humphreys (Ulva)Avon River (Ulva)Heathcote River (Ulva)Avon River (Gracilaria)Heathcote River (Gracilaria)

A

B

*

**

Mix

ed s

ourc

e-δ15

N (

‰)

0

2

4

6

8

10

12

14

16

18

Avon River waterHeathcote River water

Nov

-09

D

ec-0

9

Jan-

10

Feb

-10

M

ar-1

0

Apr

-10

M

ay-1

0

Jun-

10

Jul-1

0

Aug

-10

S

ep-1

0

Oct

-10

N

ov-1

0

Dec

-10

Ja

n-11

F

eb-1

1

Mar

-11

A

pr-1

1

May

-11

Ju

n-11

Ju

l-11

A

ug-1

1

Sep

-11

O

ct-1

1

Nov

-11

D

ec-1

1

Jan-

12

Feb

-12

M

ar-1

2

Apr

-12

M

ay-1

2

Tis

sue-

δ15N

(‰

)

0

2

4

6

8

10

12

14

16

18

Figure 3-5 : Comparison of changes in (A) mixed source DIN-δ15N river samples collected in the Avon and Heathcote rivers over the period of this study and (B) changes in Ulva tissue-δ15N from long term monitoring sites at Heron (green symbols) and Humphreys (pink symbols) from the Avon-Heathcote Estuary, and also Ulva and Gracilaria from the Avon and Heathcote rivers. The dashed brown and grey lines in plot A represents the mean mixed source DIN-δ15N value in the Avon and Heathcote rivers, respectively. The shaded blue shaded region in plot B represents the expected coastal marine baseline levels for tissue-δ15N in Ulva (from Barr 2007). Six significant events affecting the estuary are denoted on both plots by numbers and arrows. (1) Wastewater diversion from the estuary on the 4th March 2010, the earthquakes on (2) 4th September 2010, (3) 22nd February 2011, (4) and 13th June 2011, (5) the repair of last sewage overflows on 25th October and the earthquake on (6) 23rd December 2011.

3.2.3 Nitrogen loading in the Heathcote and Avon ri vers For the period since January 2007 mean daily values of dissolved inorganic N-loading were calculated for both the Heathcote and Avon rivers. These were typically slightly higher for the Avon River with a crude mean value (calculated for the whole available time period) of 156 kg · day-1 compared with 102 kg · day-1 for Heathcote River. However, winter peaks for both rivers were often similar, exceeding 300 kg · day-1. Due largely to variability of nutrient loading data the only clearly discernible contribution associated with the earthquake series was in slightly elevated ammonium concentrations in the Avon River during the period from February 2011 to December 2012 (Figure 3-6).


Jan-

07

Jul-0

7

Jan-

08

Jul-0

8

Jan-

09

Jul-0

9

Jan-

10

Jul-1

0

Jan-

11

Jul-1

1

Jan-

12

Mea

n di

ssol

ved

N-lo

adin

g (k

g ·

day-1

)

0

100

200

300

400

500

0

100

200

300

400

500

AmmoniumNitrate + NitriteTotal Inorganic NitrogenTotal Nitrogen

2 3 4 6

B) Avon River

A) Heathcote River

1 5

Figure 3-6: Daily nitrogen loading rates in the (A) Heathcote and (B) Avon rivers since 2007. Rates are calculated using daily mean river flow rates derived from Gloucester Street NIWA Hydro-station [66602] for the Avon River and from Buxton Terrace NIWA Hydro-station [66612] for the Heathcote River. Flow rates are calculated from 13-day median values centred on days when nutrient samples were collected from Environment Canterbury river water quality monitoring sites at Ferrymead Bridge (SQ30548) for the Heathcote River and at Bridge Street (Sth Brighton) Bridge (SQ30597) for the Avon River. Six significant events affecting the estuary are denoted on both plots by numbers and arrows. (1) Wastewater diversion from the estuary on the 4th March 2010, the earthquakes on (2) 4th September 2010, (3) 22nd February 2011, (4) and 13th June 2011, (5) the repair of last sewage overflows on 25th October and the earthquake on (6) 23rd December 2011.

3.2.4 Algal tissue nitrogen indices - Estuary The possible enhancing influence of earthquake driven N-loading on algae during peak seasonal conditions, relative to the possible limiting influence resulting from cessation of wastewater derived-N to the estuary in March 2010, was examined. This was done by comparing algal nitrogen status indices during peak seasonal (summer; November to February) conditions, when increased N-loading is likely to drive algal blooms, for the summer period pre-diversion (09/10) and the earthquake affected post-diversion summer periods (10/11 and 11/12). For both the Heron and Humphreys sites there were significant reductions in tissue nitrogen, chlorophyll and free amino acid content in Ulva in the post-diversion summers (10/11 and 11/12), compared to pre-diversion levels (Figure 3-7). Tissue-N in Ulva showed a post-diversion (summer 10/11) reduction of 28 % and 33 % at the Heron


and Humphreys sites, respectively (Figure 3.7, A). However chlorophyll in Ulva was reduced by 51 % and 46 %, and free amino acids pools by much as 62% and 43% at the Heron and Humphreys sites, respectively, in summer 10/11 compared with summer 09/10 (pre-diversion) (Figure 3-7, B and C). At both sites all three algal nitrogen status indices in summer 11/12 showed slight increases again relative to summer 10/11, but were still lower than pre-diversion levels. All pre- and post-diversion levels of algal nitrogen status indices were higher than those recorded for Ulva from non-polluted sheltered sites by Barr 2007.

Tot

al ti

ssue

-N(%

)

0

1

2

3

4

5

Chl

orop

hyll

a +

b

(µg

⋅ g D

W-1

)

0

2

4

6

8

10

12

HE

09/

10

HE

10/

11

HE

11/

12

HU

09/

10

HU

10/

11

HU

11/

12

Fre

e am

ino

acid

s (µ

mol

N ⋅

g D

W-1

)

0

50

100

150

200

250

↓ 51 %↓ 39 % ↓ 46 %

↓ 36 %

↓ 28 % ↓ 33 %

↓ 62 % ↓ 56 % ↓ 43 %↓ 28 %

A

B

C

↓ 22 %↓ 19 %

Figure 3-7: Comparison of three tissue nitrogen status indices in Ulva averaged for summer periods at two sites (Heron Street, green bars and Humphreys Drive, pink bars) in the Avon-Heathcote estuary; Pre-diversion 09/10 and Post-diversion 10/11 and 11/12. Summer values are means and standard errors calculated from monthly samples collected in November, December, January and February. Values and arrows above the histogram bars indicate the magnitude and direction of change in Ulva tissue nitrogen status indices in the two post-diversion summers (10/11 and 11/12) relative to pre-diversion summer levels (09/10). Bold red values above the histogram bars indicate significant differences (P < 0.005) in post-diversion summer levels (10/11 and 11/12) relative to pre-diversion summer levels (09/10) (according to the Holm-Sidak method for multiple comparisons versus pre-diversion levels). Dashed lines in each plot represent mean values of tissue nitrogen status indices in Ulva from non-polluted sheltered rural sites in summer 2002 (from Barr 2007).


3.2.5 Nitrogen loading – Estuary Water column total inorganic nitrogen (TIN) concentrations showed pronounced (70 to 80 %) declines at both Heron Street and Humphreys Drive in the two post diversion summers (November to February) (10/11 and 11/12) relative to pre-diversion summer (November to February) concentrations that were close to those predicted (90%) before the diversion (Figure 3-8). However, DIN concentrations at Humphreys Drive were over four-fold higher than at the Heron Street algal monitoring site. Total reactive phosphorus (TRP) also showed similar (~ four-fold) pre-diversion differences in concentrations between the two sites, and

Tot

al R

eact

ive

Pho

spho

rus

(µΜ

)

0

2

4

6

8

10

Tot

al In

orga

nic

Nitr

ogen

(µΜ

)

0

20

40

60

80

100

HE

09/

10

HE

10/

11

HE

11/

12

HU

09/

10

HU

10/

11

HU

11/

12

Nitr

ogen

: P

hosp

horu

s

0

5

10

15

20

25

↓ 53 % ↓ 37 % ↓ 82 % ↓ 80 %

↓ 78 %

↓ 84 %

↓ 16 %

↓ 57 %

↑ 20 %

A

B

C

↓ 72 %

↓ 71 %

↓ 8 %

Figure 3-8: Comparison of water column nutrient levels averaged for summer periods at two sites (Heron Street, green bars and Humphreys Drive, pink bars) in the Avon-Heathcote estuary; Pre-diversion 09/10 and Post-diversion 10/11 and 11/12. Summer values are means and standard errors calculated from monthly samples collected in November, December, January and February. Values and arrows in the histogram bars indicate the magnitude and direction of change in nutrient levels and the N : P ratio in the two Post-diversion summers (10/11 and 11/12) relative to Pre-diversion summer levels (09/10). Nutrient data are derived from Environment Canterbury water quality monitoring sites nearest to algal sampling sites; Heron Street (SQ32575) and Humphreys Drive (SQ32819). Dashed lines in each plot represent mean values of seawater nitrogen and phosphorus parameters from non-polluted sheltered rural sites in summer 2002 (from Barr 2007).


also similar declines in the two post-diversion summers (10/11 and 11/12) relative to pre-diversion concentrations. Dissolved N : P (DIN : TRP) ratios although highly variable tended to be similar across pre- and post-diversion summers with values less than 10 for the Heron Street site while at the Humphreys Drive site tended to be higher (> 10) and again similar across pre- and post-diversion summers. However due to the variability in DIN : TRP values it is likely that the differences were not significantly, both between sites and between pre- and post-diversion levels (Figure 3-8).


4 Discussion

4.1.1 Responses of macroalgae to the Christchurch w astewater diversion and the Christchurch earthquakes

The influence of reintroduced nitrogen from earthquake driven overflows on algae in the estuary appears to have been relatively minor, and sporadically driven by the main earthquake events, compared to the 90 % reduction in N-loading that occurred with the cessation of the wastewater discharge to the estuary in March 2010. From the responses of all nitrogen status indices in Ulva there was clear evidence of a response to reduced N-loading with the diversion (also see Appendix D to compare tissue nitrogen indices in Ulva from environments with contrasting nitrogen loading), and also to increases in earthquake driven N-loading, as evidenced from changes in levels of chlorophyll in Ulva at the two sites over time. In addition, there was a qualitative shift in N source, reflected in increasing concentrations of ammonium (relative to nitrate) in the rivers and reduced levels of tissue-δ15N (< 6.6 ‰) recorded in algae grown in the two rivers, together indicating the presence of N derived from raw effluent. Moreover decreasing tissue-δ15N was also seen in algae growing at the two long-term Heron and Humphreys algal monitoring sites, particularly during the period from June through to November 2011. Given the worst earthquake effects on sewage overflows were centred around the winter months of 2011, it is probable that any influence of earthquake driven nitrogen on algal growth during this time would have been largely overridden by lower light and temperature conditions.

While the wastewater diversion resulted in a pronounced reduction seen in water-column N (and P loading) that was more or less consistent with the predicted (90 %) values, this change was not proportionally reflected in the internal N concentration of Ulva. Moreover, while there were substantial differences in DIN concentrations recorded in water column samples between the Heron and Humphreys sites during the summer pre-diversion, nitrogen status indices in Ulva were similar between these sites. This may have been because snapshot water column samples taken near these sites may have either under-represented biologically assimilated N concentrations in Ulva at Heron, or even over-represented in that at Humphreys Drive. Some of the differences between the sites might be attributable to tidal aliasing due to timing of water column sampling relative to the tidal state. The fact that Heron algae recorded two low values of tissue-δ15N during the pre-diversion summer would tend to suggest that algae at this site was being influenced by effluent derived N that may not necessarily be captured in water samples given the lower DIN concentrations typically recorded here. Note that water quality sampling in the Avon-Heathcote estuary was historically designed to capture the discharge effluent parcel on the outgoing tide (Bolton-Richie and Main 2005) with samples from Penguin Street (SQ32575), the nearest Environment Canterbury water quality monitoring site to the Heron Street algae site, typically collected an average of 1.3 hours after high tide while those from Humphreys Drive (SQ32819) were taken an average 2.3 hours after high tide.

In addition to the issues relating to interpretation of snapshot water samples above, it is also probable that pre-diversion water column DIN concentrations were in saturating supply for nitrogen storage pools in Ulva tissues, particularly at the Humphreys Drive sites. The responses of nitrogen status indices in Ulva (e.g., tissue-N) tend to saturate at higher DIN (either as nitrate or ammonium) concentrations averaging in the range of 10 – 30 µM for Ulva


(Caves et al. 2012, Barr et al. 2012, Barr, 2007 and Dudley et al. 2008) and for Gracilaria (Wilcox et al. 2006). This is also supported by tissue-N being supersaturated (> 4 %, but see also Appendix D for values of tissue nitrogen status indices in Ulva from nitrogen enriched environments) in Ulva from both the Avon and Heathcote rivers indicating that DIN was excess to growth requirements for the algae. For the duration of test-algae deployments DIN concentrations in both rivers was in saturating supply for Ulva nitrogen requirements, with average DIN concentrations of 80.5 µM ± 10.2 [1.1 mg/L ± 0.1] and 90.1 µM ±10.7 [1.3 mg/L ± 0.1] for the Avon and Heathcote rivers, respectively. It was also clear that N-loading in both rivers was typically high with the effects of the earthquakes resulting in fairly minor increases. Although it is not known what contribution the 6 city drains entering the estuary made to overflow derived N-loading in the estuary, it is likely to have been significant given that there were detectable changes in N-loading and algal N-indices seen in the estuary over the time of the earthquake series.

During spring/summer peak growth when N supply is in excess of growth requirements it tends to accumulate in tissue nitrogen status indices (e.g., free amino acids). However, in addition to responding to external N concentration, tissue nitrogen status indices in Ulva are also affected to differing degrees by seasonal changes in light and temperature, and can also be a function of growth rate. When comparing algal tissue nitrogen status indices in summer (e.g., Figure 3-8), a time when growth is less likely to be limited by light (and low temperature), higher levels of these indices would tend to reflect high N availability (Barr et al. 2012). Furthermore, when light and temperature are optimal for growth, tissue-N content can be used as a predictor of potential growth rate (Barr, 2007) when growth is limited by nitrogen. Summer tissue-N content for Ulva at Humphreys and Heron monitoring sites had post-diversion summer tissue-N quotients of over 2 % (Figure 3-7). In principle, tissue-N levels greater than about 1.5 to 2 % would be sufficient for growth that is not N-limited (de Winton, 1998; Barr, 2007; Caves et al. 2012). It is anticipated that in next summer (12/13) it will be possible to properly assess whether algal growth has become N-limited, assuming there are no confounding effects such as further earthquakes.

4.1.2 Isotopic sources of nitrogen affecting the Av on-Heathcote estuary From this study we observed that the Heathcote River had consistently higher DIN-δ15N levels than the Avon River and this was driven by its higher NO3

--δ15N as opposed to differences in NH4

+ -δ15N levels between the rivers. We observed a relatively constant difference between the rivers with respect to NO3

--δ15N and NO3--δ18O in water samples and

therefore the rivers appear to have very distinct nitrate source pools. The nitrate source pools are influenced by differences in the catchment land uses and hydrology. Whereas the Avon River has a predominately urban catchment, the Heathcote River has a catchment influenced by both urban and agricultural sources (Bolton-Ritchie and Main 2005). The Heathcote River has a higher mean concentration of nitrogen than the Avon River, but the Avon River contributes more N bearing water to the Avon-Heathcote estuary as a consequence of the higher flow (see Figure 3-6 and also Bolton-Ritchie and Main 2005). The flows of both rivers are dominated by groundwater sources with stormwater runoff making up a smaller portion of the total flow (Bolton-Ritchie and Main 2005). Denitrification often favours the lighter isotope δ14N and in areas with high rates of denitrification this can result in a nitrate pool enriched in δ15N (Fry 2006). In the current study, the Heathcote River had higher NO3

--δ15N enrichment suggesting that denitrification may be more significant in its nitrate-enriched source spring waters compared to the Avon River where groundwater source is primarily derived from the


Waimakariri River (White, 2009 and Stewart, 2012). The higher NO3--δ15N in the Heathcote

River could also be the result of fractionation during benthic denitrification in the river itself.

Sources of naturally abundant nitrogen isotopes can vary widely depending on a variety of chemical, physical and biological processes operating in watersheds and their receiving riverine and estuarine environments (e.g., Bedard-Haughn et al. 2003, also see Appendix C for selected δ15N signatures of nitrogen sources in water). Specifically nitrogen assimilation, nitrification, denitrification and mineralisation are all processes that affect the expression of DIN-δ15N in water. Consequently, the isotopes of NH4

+ and NO3- in water samples may not

necessarily have the same δ15N value, but they mix in the receiving environment giving a DIN-δ15N value representing all the combined DIN sources. With the diversion of the ammonium dominated wastewater discharge away from the estuary in March 2010, the two rivers became the dominant source of terrestrial nitrate to the estuary. Presumably with the cessation of further perturbations to the estuary algal tissue-δ15N will increasingly reflect the mixed contribution of nitrate derived from the two rivers (5.2 ± 0.1 ‰ and 10.2 ± 0.4 ‰ for the Avon and the Heathcote rivers, respectively) and marine derived nitrate probably represented in samples from Beachville road (6.9 ± 0.7 ‰) (see Appendices A and B). To what extent nitrate from the rivers drives algal growth in estuaries in the future has yet to be determined.

4.1.3 Other potential earthquake effects on macroal gae Other potential effects that warrant consideration are the changes in bed heights in different parts of the estuary that occurred with the February and June 2011 earthquake (Measures et al. 2011. NIWA Client Report No: CHC2011-066). Lidar survey results indicate close to a 0.5m subsidence in the northern, Avon end, of the estuary and a 0.5m uplift of Humphreys Basin (historically a significant area of Ulva and Gracilaria biomass accumulation). The uplift of Humphreys Basin is likely to impinge on algal growth here over the summer months as a result of increased tidal desiccation (because of longer periods of exposure). In addition, liquefaction occurred after the main earthquake events resulting in exhumed sediment smothering significant portions of existing algal beds. These events are very likely to impact on the growth and distribution of seaweeds growing in the estuary, at least in the short term.

Finally the results from this study complement the algal biochemical patterns observed so far in the long-term monitoring programme of the estuary that commenced in November 2009 (pre-sewage diversion) in the MSI-funded research. We anticipate that continuation of the current algal and water quality monitoring programmes will enable us to further separate the effects of earthquake from the on-going remediation effects resulting from the CWTP wastewater diversion.


5 Conclusions 1) There was a reduction in tissue nitrogen status indices (tissue-N, chlorophyll and free

amino acid-N content) in the two post-diversion summers (10/11 and 11/12), relative to pre-diversion summer levels. This indicated a reduction in nitrogen availability to Ulva in the estuary after the diversion of wastewater from the estuary in March 2010, despite the effects of the earthquakes on N-loading.

2) Over the period of the February and June earthquakes there was a clear shift in nitrogen source, inferred from isotopic (tissue-δ15N) composition, suggesting that there was at least some influence of raw effluent derived-N on algae growing in the estuary linked to effects of the earthquakes.

3) Background levels of river nitrogen loadings (and concentrations) are high with only minor detectable inputs of ammonium resulting from earthquake driven overflows.

4) Physical changes in the estuary (e.g., uplift of Humphreys Basin) as a result of the earthquakes may have a long-term impact on growth and distribution of some algal beds.

5) Given the original long-term monitoring study was designed to study the effects of the CWTP diversion we still have yet to see the final equilibrium levels of algal tissue-N indices in the estuary, without the effects of the earthquakes.

6 Acknowledgements This work was carried out in Environment Canterbury / Christchurch City Council-funded earthquake response contracts in combination with Ministry of Science and Innovation-funded University of Canterbury/NIWA research. We thank the numerous University of Canterbury staff and students and NIWA staff who assisted with these surveys often under hazardous conditions: Stephanie McCall, Stephanie Fry, Michael Greer, Rosanne Homewood, Jen Skilton, Jess Hill, Jan McKenzie, Stacie Lilley, Chris Cunningham, Allison Brownlee, Helena Campbell, Mark Gall, Donna Sutherland, Paul South, Kerry O’Connell, and David Schiel. We also thank the staff, including Sarah Bury, Julie Brown, Anna Kilimnik and Thomas Max at the NIWA Isotope Ratio Mass Spectrometry (IRMS) facility for their work in analysing the NH4

+-δ15N of the water samples and advice regarding their results.


7 References Barr, N.G. (2007). Aspects of nitrogen metabolism in the green alga Ulva;

Developing an indicator of seawater nitrogen loading. PhD Thesis, University of Auckland Research Space. URL: http://hdl.handle.net/2292/2522

Barr, N.G.; Rees, T.A.V. (2003). Nitrogen status and metabolism in the green seaweed Enteromorpha intestinalis: an examination of three natural populations. Marine Ecology Progress Series 249: 133–144.

Barr, N.G.; Dudley, B.D.; Rogers, K.R. and Cornelisen, C.D. (2012). Broad-scale patterns of tissue- δ15N and tissue-N indices in Ulva; Developing a national baseline indicator of nitrogen-loading for coastal New Zealand. Marine Pollution Bulletin, Accepted June 2012.

Barr, N.G.; Kloeppel, A.; Rees, T.A.V.; Scherer, C.; Taylor, R.B.; Wenzel, A. (2008). Wave surge increases rates of growth and nutrient uptake in the green seaweed Ulva pertusa maintained at low bulk flow velocities. Aquatic Biology 3: 179–186.

Bedard-Haughn, A.; van Groenigen, J.W.; van Kessel, C. (2003). Tracing 15N through landscapes: potential uses and precautions. Journal of Hydrology 272: 175–190.

Bolton-Richie, L. (2012). Senior Water Quality Scientist- Coastal. Environment Canterbury. Personal Communication.

Bolton-Richie, L.; Main, M. (2005). Nutrient water quality Avon-Heathcote Estuary/Ihutai; Inputs, concentrations and potential effects. Environment Canterbury. Report No. U05/71.

Casciotti, K.L.; Sigman, D.M.; Galanter Hastings, M.; Bohlke, J.K.; Hilkert, A. (2002). Measurement of the oxygen isotopic composition of nitrate in seawater and freshwater using the denitrifier method. Analytical Chemistry 74: 4905–4912.

Chen, R.R.; Dittert, K. (2008). Diffusion technique for 15N and inorganic N analysis of low-N aqueous solutions and kjeldahl digests. Rapid Communications in Mass Spectrometry 22: 1727–1734.

Conley, D.J.; Paerl, H.W.; Howarth, R.W.; Boesch, D.F.; Seitzinger, S.P.; Havens, K.E.; Lancelot, C. and Likens, G.E. (2009). Controlling eutrophication: nitrogen and phosphorus. Science Magazine 323(5917): 1014–1015.

Drake, D.; Stewart, S. (2008). A baseline description of nitrogen sources and food webs prior to large-scale restoration in Te Ihutai, Avon-Heathcote Estuary New Zealand. Unpublished report held at NIWA Christchurch.

Dudley, B.D. (2007). Quantitative ecological impact assessments using natural abundance carbon and nitrogen stable isotope signatures. PhD thesis, Victoria University of Wellington, Wellington, New Zealand.

Dudley, B.D.; Shima, J.S. (2010). Algal and invertebrate bioindicators detect sewage effluent along the coast of Titahi Bay, Wellington, New Zealand. New Zealand Journal of Marine and Freshwater Research 44: 39–51.


Dudley, B.D.; Barr, N.G.; Shima, J.S. (2010). Influence of light intensity and nutrient source on δ13C and δ15N signatures in Ulva pertusa. Aquatic Biology 9: 850–93.

Feary, J. (2012). Water and Wastewater Treatment Manager at Christchurch City Council. Personal Communication.

Measures, R.; Hicks, M.; Shankar, U.; Bind, J. and Arnold, J. (2011). Mapping earthquake induced topographical change and liquefaction in the Avon-Heathcote Estuary. NIWA Client Report No: CHC2011-066.

Miyaka, Y.; Wada, E. (1967). The abundance ratio of 15N/14N in marine environments. Records of Oceanographic works, Japan 9: 37–53.

Rogers, K.M. (1999). Effects of sewage contamination on macro-algae and shellfish at Moa Point, New Zealand using stable carbon and nitrogen isotopes. New Zealand Journal of Marine and Freshwater Research 33: 181–188.

Rogers, K.M. (2003). Stable carbon and nitrogen isotope signatures indicate recovery of marine biota from sewage pollution at Moa Point, New Zealand. Marine Pollution Bulletin 46: 821–827.

Sigman, D.M.; Casciotti, K.L.; Andreani, M.; Barford, C.; Galanter, M. and Bohlke, J.K. (2001). A bacterial method for the nitrogen isotopic analysis of nitrate in seawater and freshwater. Analytical Chemistry 73: 4145–4153.

Stewart, M.K. (2012). A 40-year record of carbon-14 and tritium in the Christchurch groundwater system, New Zealand: Dating of young samples with carbon-14. Journal of Hydrology 430-431: 50–68.

Wada, E.; Kadonaga, T. and Matsuo, S. (1975). 15N abundance in nitrogen of naturally occurring substances and global assessment of denitrification from isotopic viewpoint. Geochemical Society of Japan 9: 139–148.

White, P.A. (2009). Avon River springs catchment, Christchurch City, New Zealand. Australian Journal of Earth Sciences 56: 61–70.

Wilcox, S.J.; Barr, N.G.; Broom, J.; Furneaux, R.H.; Nelson, W.A. (2006). Using gigartinine to track the distribution of an alien species of Gracilaria in New Zealand. Journal of Applied Phycology 19: 313–323. DOI 10.1007/s10811-006-9138-3.


Appendix A Dissolved nitrate and ammonium concentrations and isotope values (with means and standard errors in parentheses) determined from water samples collected at the Avon River and Heathcote River monitoring sites. The mixed source values calculated from the nitrate and ammonium fractions are also included.

Collection date NH4+– N (µM) NO3

-– N (µM) NH4+– δ15N (‰) NO3

-– δ15N (‰) NO3-– δ18O (‰) NH4

+ Fraction NO3- Fraction Mixed source δ15N

(‰)

Avon River 1-Dec-09 17.8 73.6 0.9 5.2 2.8 0.19 0.81 4.4

29-Apr-10 8.3 71.6 6.6 5.2 2.0 0.10 0.90 5.4 22-Jul-10 10.1 53.8 3.1 5.0 2.8 0.16 0.84 4.7 15-Apr-11 21.1 69.6 7.5 4.6 0.7 0.23 0.77 5.3 16-Jun-11 42.5 23.8 1.3 4.8 1.5 0.64 0.36 2.5 30-Aug-11 28.0 18.7 -1.9 5.3 -0.1 0.60 0.40 1.0 12-Oct-11 9.4 31.7 -2.1 5.4 0.7 0.23 0.77 3.7 6-Dec-11 4.7 39.2 -8.4 5.5 2.7 0.11 0.89 4.0 9-Feb-12 5.6 42.7 -3.7 5.8 0.6 0.12 0.88 4.7 10-Apr-12 7.0 50.0 1.0 5.3 0.4 0.12 0.88 4.7 Mean (SE) 15.4 (3.8) 47.5 (6.3) 0.4 (1.5) 5.2 (0.1) 1.4 (0.3) 0.25 (0.06) 0.75 (0.06) 4.1 (0.4)

Heathcote River

1-Dec-09 13.1 87.9 9.4 8.7 4.7 0.13 0.87 8.8 29-Apr-10 11.0 114.1 -1.6 10.0 4.4 0.09 0.91 8.9 22-Jul-10 12.0 72.2 28.3* 9.5 4.5 0.14 0.86 12.2 15-Apr-11 25.9 95.0 5.1* 9.9 4.3 0.21 0.79 8.9 16-Jun-11 97.8 79.4 2.6 10.0 3.6 0.55 0.45 5.9 30-Aug-11 29.8 50.0 9.5* 9.6 3.2 0.37 0.63 9.6 12-Oct-11 17.4 34.3 -3.2 10.1 4.6 0.34 0.66 5.6 6-Dec-11 4.3 40.5 -12.2 13.3 6.3 0.10 0.90 10.9 9-Feb-12 6.4 50.0 -0.03 11.2 4.2 0.11 0.89 9.9 10-Apr-12 16.3 24.4 4.1 10.2 4.7 0.40 0.60 7.8 Mean (SE) 23.4 (8.6) 64.8 (9.3) 4.2 (3.3) 10.2 (0.4) 4.4 (0.3) 0.24 (0.05) 0.76 (0.05) 8.8 (0.6)

*Poor chromatography. Use NH4

+–δ15N data with caution.


Appendix B Dissolved nitrate and ammonium concentrations and isotope values (with means and standard errors in parentheses) determined from water samples collected at the Beachville Road and Oxidation Pond (6) monitoring sites. The mixed source values calculated from the nitrate and ammonium fractions are also included.

Collection date NH4+– N (µM) NO3

-– N (µM) NH4+– δ15N (‰) NO3

-– δ15N (‰) NO3-– δ18O (‰) NH4

+ Fraction NO3- Fraction Mixed source δ15N

(‰)

Beachville Road

30-Apr-10 5.2 0.6 2.4 6.2 -4.7 0.89 0.11 2.8 20-Jul-10 2.9 1.2 -18.8* 11.1 10.0 0.71 0.29 -10.2 15-Apr-11 5.3 0.4 -1.4* 5.9 1.8 0.93 0.07 -0.8 25-Jun-11 8.7 1.4 -0.5* 6.3 0.7 0.86 0.14 0.5 1-Sep-11 96.5 4.2 -1.7 5.0 1.1 0.96 0.04 -1.4 17-Oct-11+ 1.6 <0.1 6-Dec-11 4.2 <0.1 -8.3 6.8 2.5 1.00 <0.01 -8.3 12-Feb-12 13.5 0.8 5.9 6.1 0.5 0.94 0.06 5.9 10-Apr-12 2.5 0.1 -3.9 8.0 0.8 0.95 0.05 -3.3 Mean (SE) 15.6 (10.2) 1.1 (0.5) -3.3 (2.7) 6.9 (0.7) 1.6 (1.4) 0.90 (0.03) 0.10 (0.03) -1.9 (1.9)

Oxidation Pond 6

1-Dec-09 1057 17.0 14.4 -5.4 -7.6 0.98 0.02 14.1 29-Apr-10 1249 16.6 10.8 -5.8 -12.6 0.99 0.01 10.6 22-Jul-10 1854 13.2 9.9 0.9 -1.6 0.99 0.01 9.8 15-Apr-11 1369 2.5 12.7 -1.8 -9.6 1.00 <0.01 12.6 Mean (SE) 1383 (169) 12.3 (3.4) 11.9 (1.0) -3.0 (1.6) -7.9 (2.3) 0.99 (<0.01) 0.01 (<0.01) 11.8 (1.0)


+–δ15N data with caution. +The concentration of NH4

+ and NO3- were too low to measure an isotope value.


Appendix C Selected examples of values of isotopic dissolved inorganic and particulate organic nitrogen from various marine and terrestrial water sources. Water source NH4

+ δ

15N (‰) NO3- -δ15N (‰) DIN -δ15N (‰) PON -δ15N (‰) Source

Seawater

5.8 (1.6)

Wada et al. 1975 Northeastern Pacific 5.1 to 7.0 Miyaki and Wada 1967 Central North Pacific 5.0 to 6.0 Wada et al. 1975 Seawater estimate 6.7 Gartner et al. 2002

Groundwater nitrate 0.0 to 20.0 Bedard-Haughn et al. 2003 Ammonium fertiliser -4.0 to 4.0 Bedard-Haughn et al. 2003

Nitrate fertiliser ~ 0.0 to 4.0 Bedard-Haughn et al. 2004 Primary effluent - Moa Point, Wellington 2.3 (0.3) Rogers 1999 Tertiary effluent - Tetahi Bay, Wellington 23.4 (2.1) Dudley & Shima 2010

Beachville tidal inflow (April 11 - April 12) -3.3 (2.7) * 6.9 (0.7) -1.9 (1.9) * Current study Avon River (April 11 - April 12) 0.4 (1.5) 5.2 (0.1) 4.1 (0.4) Current study Heathcote River (April 11 - April 12) 4.2 (3.4) 10.2 (0.4) 8.8 (0.6) Current study Retention pond 6 (Dec 09 - April 11) 12.1 (1.0) -3.0 (1.6) 12.1 (1.0) Current study


+–δ15N data with caution.


Appendix D Seawater nutrient concentrations and Ulva tissue nitrogen indices recorded from five environmental categories at 27 locations around New Zealand, in summer and winter 2002 (from Barr 2007). Values are means with standard errors in brackets. SUMMER Sheltered rural Exposed rural Sheltered urban Expos ed urban Enriched urban Seawater nutrients (n = 2) (n = 7) (n = 5) (n = 6) (n = 5) DIN (µM) 2.2 (1.7) 4.0 (1.9) 4.3 (1.2) 1.3 (0.7) 38.2 (19.3) TRP (µM) 0.6 (0.1) 0.6 (0.2) 0.5 (0.2) 0.5 (0.1) 7.0 (3.9) N : P 4.2 (3.4) 5.3 (1.1) 11.1 (4.3) 2.9 (1.6) 12.2 (7.1)

Nitrogen indices in Ulva Chlorophyll a + b (µg · g DW-1) 1.5 (0.3) 3.9 (0.5) 3.7 (0.9) 3.1 (0.6) 7.3 (1.5) Free amino acids (µmol N · g DW-1) 19.8 (5.2) 46.5 (5.9) 64.4 (14.7) 61.8 (25.8) 173.7 (14.5)

Tissue-N (%) 1.0 (0.2) 2.3 (0.2) 1.7 (0.2) 1.6 (0.2) 3.1 (0.2) Tissue-δ15N (‰) 7.5 (0.3) 7.8 (0.2) 8.3 (0.5) 8.7 (0.5) 10.2 (1.6)

WINTER Sheltered rural Exposed rural Sheltered urban Expos ed urban Enriched urban Seawater nutrients (n = 3) (n = 8) (n = 5) (n = 6) (n = 5) DIN (µM) 0.7 (0.2) 3.7 (2.3) 1.9 (0.4) 1.4 (0.3) 17.8 (4.3) TRP (µM) 0.5 (0.1) 0.3 (0.1) 0.4 (0.0) 0.4 (0.1) 3.3 (1.0) N : P 1.7 (0.5) 21.7 (11.9) 4.4 (0.8) 3.8 (0.8) 7.7 (2.0)

Nitrogen indices in Ulva Chlorophyll a + b (µg · g DW-1) 3.6 (0.1) 6.4 (0.6) 4.5 (0.7) 7.3 (1.4) 9.7 (0.6) Free amino acids (µmol N · g DW-1) 58.5 (5.1) 168.3 (31.3) 144.9 (28.5) 200.7 (43.6) 225.0 (39.3)

Tissue-N (%) 1.8 (0.3) 3.5 (0.2) 2.4 (0.4) 3.4 (0.5) 3.7 (0.2) Tissue-δ15N (‰) 7.7 (0.8) 7.6 (0.2) 7.7 (0.2) 8.6 (0.3) 8.8 (1.7)

Documents

Effects of the Canterbury