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Lake Ecology. Unit 1: Modules 2/3 Part 6 – Management January 2004. Modules 2/3 overview. Goal – Provide a practical introduction to limnology Time required – Two weeks of lecture (6 lectures) and 2 laboratories - PowerPoint PPT Presentation
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Lake Ecology
Unit 1: Modules 2/3 Part 6 – ManagementJanuary 2004
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s2
Modules 2/3 overview
Goal – Provide a practical introduction to limnology
Time required – Two weeks of lecture (6 lectures) and 2 laboratories
Extensions – Additional material could be used to expand to 3 weeks. We realize that there are far more slides than can possibly be used in two weeks and some topics are covered in more depth than others. Teachers are expected to view them all and use what best suits their purposes.
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s3
Modules 2/3 outline
1. Introduction2. Major groups of organisms; metabolism3. Basins and morphometry4. Spatial and temporal variability – basic
physical and chemical patchiness (habitats)5. Major ions and nutrients 6. Management – eutrophication and water
quality
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s4
6. Management topics
Trophic status Eutrophication Water quality
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s5
Nutrients most limiting to algal growth
Phosphorus Essential for growth PO4
-3 is primary dissolved form
PO4-3 sticks to soil and
sediment particles Usually key nutrient for
triggering excess plant growth
Must be reduced to control eutrophication
1 lb (kg) P can yield 500 lbs (kg) fresh algae
Nitrogen Essential for growth NO3
-, NH4+, and N2 are
primary biological forms NO3
- soluble in water May limit algal growth in
some circumstances More difficult to remove
from wastewater than P Some forms are toxic or
disease-causing to fish and mammals (including humans)
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s6
Limiting nutrients – demand versus supply
Nitrogen and phosphorus are typically in extremely short supply in water relative to plant demand
The “Redfield ratio” is the average composition of elements in phytoplankton
Ratio – 100DW:40C:7N:1P
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s7
The concept of limiting nutrients
Liebig’s Law of the Minimum (~1840): An organism’s total biomass yield is proportional to the
lowest concentration of nutrient relative to the requirements of that organism (paraphrased).
Lake managers are interested in limiting nutrients because: An increase might change water quality or food
webs. Restoration often requires a strategy for
reducing nutrient loading and predictions of the consequences of specific actions.
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s8
Limiting nutrients – a conceptual example
The following set of slides were developed to illustrate more specifically what is meant by “limiting nutrients” in the context of eutrophication studies
This may be appropriate for a lab exercise in which different combinations of N and P are added to lake water
Lake Superior was used as an example because we can see it out our window and because it is the biggest lake in the world and the cleanest of the Laurentian Great Lakes, so it is important to understand
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s9
Example – loosely based on Lake Superior
•Dave Hansen
•Minnesota Sea Grant
•Dave Hansen
•Dave Hansen
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s10
Conceptual nutrient limitation bioassay – 1
This example is loosely based on Lake Superior
1. Algal composition is approximately:
500 g wet weight : 100 g dry weight : 40 g C : 7 g N : 1 g P
Remember that the ratio of C:N:P is called the “Redfield ratio” and approximates the composition of algae!
40:7:1 by weight100:16:1 by atoms
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s11
Conceptual nutrient limitation bioassay – 2
2. Mid-summer bioavailable water chemistry: Dissolved inorganic carbon (DIC):
~ 10,000 µg C/L (as carbon dioxide and bicarbonate)
Dissolved inorganic nitrogen (DIN): ~ 300 µg N/L (95% as nitrate, with very low
ammonium) Dissoved inorganic phosphorus (ortho-P, DIP):
~ 0.5 µg P/L
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s12
Conceptual nutrient limitation bioassay – 3
3. Assume: Algal biomass = B0 ~ 200 µg C/L (particulate) Algal maximum growth rate ~ 20% per day
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s13
Conceptual nutrient limitation bioassay – 4
4. Run a nutrient enrichment experiment to estimate the limiting nutrient by doubling each nutrient: Set up 4 liter bottles of lake water in triplicate:
Incubate for 1 day and re-measure algal
biomass (Bf)
Control + Carbon+ Nitrogen+ PhosphorusAdd nothing + 0.5 µg P/L + 300 µg N/L + 10,000 µg C/L
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s14
Conceptual nutrient limitation bioassay – 5
5. What happens? After 1 day – algae grow 20% X 200 µg C/L = +
40 µg C/L Apply the “Redfield Ratio” to estimate nutrient
needs
Is there sufficient DIC to support this much growth? Is there sufficient DIN to support this much growth? Is there sufficient DIP to support this much growth?
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s15
Conceptual nutrient limitation bioassay – 6
6. What happened? 40 µg C/L of new growth would require:
40 µg DIC/L + 7 µg DIN/L + 1 µg DIP/L
+0 control treatment: 10,000 µg DIC/L is much more than enough 300 µg DIN/L is more than enough (293 excess) 0.5 µg DIP/L is half of what is needed
Therefore growth is 50% of maximum: = +20 µg C/L
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s16
Conceptual nutrient limitation bioassay – 6
6. What happened? 40 µg C/L of new growth would require:
40 µg DIC/L + 7 µg DIN/L + 1 µg DIP/L
+N treatment: 10,000 µg DIC/L is much more than enough 600 µg DIN/L is more than enough (593 excess) 0.5 µg DIP/L is half of what is needed
Therefore growth is 50% of maximum = +20 µg C/L
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s17
Conceptual nutrient limitation bioassay – 6
6. What happened? 40 µg C/L of new growth would require:
40 µg DIC/L + 7 µg DIN/L + 1 µg DIP/L
+C treatment: 20,000 µg DIC/L is much more than enough 300 µg DIN/L is more than enough (293 excess) 0.5 µg DIP/L is half of what is needed
Therefore growth is 50% of maximum = +20 µg C/L
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s18
Conceptual nutrient limitation bioassay – 6
6. What happened? 40 µg C/L of new growth would require:
40 µg DIC/L + 7 µg DIN/L + 1 µg DIP/L
+P treatment: 10,000 µg DIC/L is much more than enough 300 µg DIN/L is more than enough (293 excess) 1.0 µg DIP/L is just what is needed
Therefore growth is 100% of maximum = +40 µg C/L
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s19
An enrichment of only 0.5 µg P/L doubled algal growth
It would take a depletion of 43 µg P/L to deplete the 300ug DIN/L, based on the 7:1 ratio
The DIC is virtually inexhaustible in all lakes. It may “briefly” limit algal growth in
hypereutrophic sewage oxidation ponds The data suggest strong P-limitation for Lake
Superior
100 %
200 %
0 %
+C +P+N+0
Nutrient bioassay – summary and plot
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s20
Nutrient limitation bioassay responses•In progress, 10/20/03
Theory
Real data from the epilimnia of pristine northern Minnesota lakes
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s21
Halsteds Bay late summer mixing events
What might this mean for phosphorus levels in the water column?
Why?
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s22
Medicine Lake– Algal blooms & mixing events - 1
Background:
• Medicine Lake is extremely productive because of historically high nutrient enrichment from its watershed
(go to http://lakeaccess.org/lakedata/lawnfertilizer/mainlawn.htm)
• Major blooms of algae can be detected in the RUSS data set as:
• supersaturated O2 (why ?)
• increased pH (why ?)
• increased chlorophyll-a or turbidity (why ?)
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s23
Medicine Lake – Algal blooms & mixing events-2
STRATIFY RE- STRATIFY
MIX MIX
SundaySunday
ThursdayThursday
Friday-Friday-midnightmidnight
SaturdaySaturdayColor = O2
Line = pH
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s24
Halsteds Bay – Algal blooms & mixing events- 3
Why did the phosphorus in the bottom water drop so dramatically in August 1999 in Halsteds Bay ?
P levels drop
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s25
Halsteds Bay – Algal blooms & mixing events- 4
First, focus on the ice-free season water quality• relatively high epilimnion (surface)TP ~ 75-150 ugP/L• chlor-a (algae ) builds up steadily to levels > 50 ug/L
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s26
Halsteds Bay – Algal blooms & mixing events- 5
See how secchi drops as chlorophyll increases ?
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s27
Halsteds Bay – Algal blooms & mixing events- 6
Now see how much TP is in the hypolimnion
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s28
Halsteds Bay – Algal blooms & mixing events- 7Summary slide without animation
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s29
Medicine Lake: Storm mixing events
•This sequence runs from 1-5 from Aug 29-30, 1999
C
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s30
Trophic status classification
• This topic will be developed further in Module 22 (Regulations and Compliance Monitoring - Lake Biocriteria)
• Managers need to classify lakes to set water quality standards and prioritize monitoring, research, and restoration $$.
• Lake productivity, as indicated by its production of algal biomass, is a useful classification in regard to water quality issues as well as fisheries management
• Trophic status indices usually assume that nutrient levels (e.g. total-P) control algal biomass (measured by chlorophyll-a) which in turn regulates lake clarity (Secchi disk transparency)
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s31
Trophic Status
• Carlson trophic state index (TSI)- most widely used• based on log transformation of Secchi disk values as a measure of algal biomass on a scale from 0 – 110
• 10 units = doubling of algal biomass• TSI’s also developed for chlor-a and total-P based on their relationships to secchi for a set of midwestern lakes
• TSI useful for comparing lakes within a region and for assessing changes in trophic status over time
• Time period: usually summer; often set at June 15 – Sep 15 but it is rarely a good idea to restrict data acquisition without a good reason – especially Volunteer secchi data
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s32
Carlson TSI equations
•TSI-S = 60 - 14.41 ln [Secchi disk, m]
•TSI-C = 9.81 ln [Chlor-a, µg/L] + 30.6
•TSI-P = 14.42 ln [TP, µg/L] + 4.15
• Average TSI = [TSI-P + TSI-C + TSI-S] / 3
• If the 3 TSI values are not similar to each other, it is likely that:
• algae may be light- or nitrogen-limited instead of P-limited, or
• secchi is affected by erosional silt rather than by algae, or something else. One should look deeper into the data!
• Note that Dr. Carlson recommended not averaging the 3 values to avoid obscuring important differences
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s33
Carlson TSI vs water quality
<40 Oligotrophic; clear water; high hypolimnetic O2 year-round but possible anoxia in the deeper hypolimnion part of year
40-50 Mesotrophic; moderately clear water; possible hypolimnetic anoxia in summer and/or under ice. Fully supportive of all swimmable /aesthetic uses; possible cold-water fishery
50-60 Mildly eutrophic; decreased secchi; anoxic hypolimnion; possible macrophyte “problems”; warm-water fishery; supportive of all swimmable /aesthetic uses but “threatened”
60-70 blue-green algal dominance with scums possible; extensive macrophyte problems; not supportive of all beneficial uses
>70 Heavy blooms and scums in summer likely; dense “weed” beds; hypereutrophic; possible fish kills; fewer plant beds due to high algae; not supportive of many beneficial uses
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s34
TSI (Carlson) - graphical
Oligotrophic Mesotrophic Eutrophic Hypereutrophic
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s35
What are Ecoregions ?
Areas with similar: Climate Landuse Soils Topography “Potential” natural vegetation
Minnesota has seven major ecoregions Four ecoregions contain most of the lakes Water quality varies greatly from south to north
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s36
Minnesota’s Ecoregions
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s37
1.6-3.3 ft5-11 ft
1.0-3.3 ft
8-15 ft
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s38
Comparison of trophic indicators in Minnesota
TP (ug/L)
Chlor-a(ug/L)
Secchi(m)
TSI(Carlson)
Trophic Status O M E O M E O M E O M E
Standard Criteria <11
11- 24
>24 <3 3- 7>7 >4.0 4.0- 2.2<2.2 <35 40-55 >55
NLF 14 - 27 < 10 2.4 - 4.6 41 - 52
NCHF 23-50 5 - 22 1.5 – 3.2 49 - 66
WCB 65 - 150 30 - 80 0.5 – 1.0 67 - 77
NGP 130 - 250 30 - 55 0.3 – 1.0 67 - 73
O: oligotrophic; M: mesotrophic; E: eutrophic; see slide notes and accompanying slide for Minnesota Ecoregions map and code names; “General” values from Axler et al. 1994.
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s39
TSI Trends in Minneapolis, MN area WOW Lakes
Note importance of flagging which TSI is plotted and leaving space for missing years
Solid bars:TSI average for TP, chlor and secchi; striped: secchi only
How would you determine how well the TSI- secchi alone (stripes) predicts average TSI or TSI- chlor ?
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s40
Chlor-a - TP and Secchi – TP relationships in MN
Log chlor-a vs Log TP scatterplot for Minnesota’s ecoregion reference lakes (summer mean surface values)
Secchi transparency vs TP for Minnesota’s ecoregion reference lakes (summer mean surface values)
Data from Minnesota Pollution Control Agency Year 2000 Lake Assessment report (www.pca.state.mn.us)
Notice that lake clarity is much more sensitive to
increased phosphorus at the low end of the scale.
Why ?
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s41
Ex: Halsteds Bay late summer mixing events
• Run the color mapper from April 1999 through 2002 focusing on storm events in mid August 1999 and 2000
• START with MAP = TEMP and plot =DO to show variable stratification
• Then switch to MAP = DO and PLOT = TEMP to show anoxic events and discuss the release of P from sediments that swamps annual P-inflow from the watershed
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s42
Hypolimnion responses to increasing productivity
Trophic Status O2 PO4
-3 NH4+ H2S
Fe+2
(ferrous)
OligotrophicHigh
(mostly)Low Low Absent Absent
MesotrophicLow; partly anoxic
Low High if anoxic
Moderate High if anoxic
AbsentPresent where anoxic
Eutrophic Anoxic High High High High
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s43
Hypolimnion responses to anoxia
As the hypolimnion becomes O2 –depleted:
• NH4+ accumulates
• increased organic matter is decomposing
• cannot be converted to NO3- without 2 (bacterial nitrification)
• not much algal uptake (its dark and anoxic)
• Insoluble oxidized Fe+3 (ferric) at sediment surface is reduced to Fe +2
(ferrous) that is soluble; the phosphate adsorbing layer dissolves
• PO4-3 diffusion from the sediments increases dramatically
• Increasing decomposition leads to strong reducing conditions that favor bacterial reduction of sulfate to sulfide - producing rotten egg gas (H2S)
• Mixing adds lots of available N + P to the sunlit zone = ALGAE !!
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s44
Eutrophication and water quality
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s45
Trophic (feeding metabolism) terminology
Oligotrophic – low nutrients and “productivity;” usually high clarity
Mesotrophic – moderate nutrients, “productivity” and clarity
Eutrophic – high nutrients and “productivity;” low clarity
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s46
Eutrophication – Excess fertility leading to excessive plant growth
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s47
• excess algae: scums, noxious blue-greens, taste/odor/smell
• excess macrophyte (“weed”) growth- loss of open water; favors exotic species (EWM); sediment destabilization
• loss of clarity (secchi depth); aesthetic loss;
Water Quality Impacts- Eutrophication (some of them)
• O2 depletion; loss of fish habitat
• game fish impacts
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s48
• loss of native macrophytes from algal shading; loss of fish & waterfowl habitat and food; reduced shoreline & bottom stabilization, increased erosion
• lower bottom O2: increased sediment nutrient release: loss of fish habitat
• excess organic matter: smothers eggs and bugs
Water Quality Impacts- Eutrophication (…and some more)
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s49
Eutrophication – natural vs cultural
Natural filling by mineral and organic sediment – leads to lower V and larger Aw:A0 and A0:V
Lake to wetland conversion
Time scale > 103 years (if at all)
Irreversible
Human-caused from excess nutrient inputs and poor land-use management
Water quality degraded; loss of beneficial uses
Time scale < decades
Reversible loading
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s50
Eutrophication – the sad Lake Tahoe story
Data courtesy of C.R. goldman and J.E. Reuter, Tahoe Reesrach Group, U. of California-Davis,
http://www.news.ucdavis.edu/tahoetv/
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s51
Other regulators of lake productivity - Grazing
Top-down Model
High rates of nutrient driven algal growth is removed by intense zooplankton grazing pressure (usually cladoceran Daphnids)
Fishless lakes with low zooplankton predation
Lakes where planktivorous fish are regulated by predatory fish (game fish) –usually by intensive control
In these cases, algae are not nutrient limited
management tool = biomanipulation
Bottom-up Model
• Nutrient inputs drive algal growth
• Classic Pyramid
N+P
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s52
Potential Top-down effects on food chains
Low Secchi
O2 stress high pH ??
Low Predators
HIGH Planktivores
Low Zoops
HIGH Algae
HIGH Predators
Low Planktivores
HIGH Zoops
Low Algae
Higher Secchi less O2 stress lower pH ??
Smaller Zoops less grazing
= Larger Zoops more grazing =
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s53
Biomanipulation – fish management
Fish control • Intensive netting• Rotenone (poison)
• Stock increased #’s of piscivorous fish
• Selective catch or catch restrictions
• Control conditions for fish and zoop growth and survival
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s54
Biomanipulation- Summary
Summary:• Considered experimental • Requires complex knowledge of food
web processes (shallow lakes are particularly poorly understood)
• Herbivores may not consume certain blue-greens
• May be more successful in lakes without large-bodied zooplankton
• May require external loading to also be controlled
• Currently considered only a management tool- not a restoration technique
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s55
Lake Mendota Biomanipulation Project
Lake Mendota –large, urban, Lake Mendota –large, urban, limnologically “famous” lake limnologically “famous” lake in Madison, WIin Madison, WI
• Eutrophic with blooms of blue-green algae
• Sewage effluents diverted out of basin entirely by 1971
• Continued nonpoint pollution from agricultural and urban runoff
• 1987: attempt to control blooms by a massive stocking of walleye to reduce planktivorous fish
1988 – hot summer causes summerkill of Ciscos, the major planktivore zoops increase and algae decrease for few years Ciscos recover, anglers hammer the walleye, zoops decrease and algae are back
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s56
Other lake productivity regulators – light shading
Nutrients aren’t always the whole story Shallow lake research
Aquatic plants vs algae Over a wide range of nutrients there are alternative
stable states of dominance Plants shade phytoplankton creating clearwater Phytoplankton turbidity shades plants and restricts
growth to nearshore Periphyton mats and mucky sediments hinder plant
rooting High densities of grazers regulate periphyton on
leaves
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s57
PWC at ~ negative 5 m depth
Water transparency – clear vs turbid state
depth 5 m & secchi >5 m
Water transparency – clear vs turbid state
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s58
Water transparency – clear vs turbid state -2Water transparency – clear vs turbid state -2
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s59
Shallow lakes vs deeper lakes - “switches”
Usually more productive – higher Aw:Ao ratio Plants vs algae
Natural predominance of macrophytes over algae. Human impacts can switch them from clearwater-plants to turbid water-algae state maintained by
Poor fish management (carp, exotics, …) Inadequate shoreline protection of emergent veg Boat damage Pesticide and nutrient runoff (fish, grazers, plants)
Susceptible to very obnoxious algal blooms Difficult to reestablish clearwater-macrophyte state
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s60
Photosynthesis (PPr) & respiration (Rn) effects on routine water quality parameters – examples
Temperature: no effect generally. High rates of respiration can increase the temperature in bottom waters over long periods of time (>decades) but this is unusual and associated with “meromixis”
DO: High rates of photosynthesis (= primary productivity = PPr) produce O2 and can lead to supersaturation (>100%)
EC25: EC increases in the hypolimnion during stratified periods due to mostly to the accumulation of bicarbonate ions (HCO3
- ) from
respired CO2 that dissolves in the water at moderate pH (~6-9). The pH is usually lowered as well.
pH: High rates of PPr increase pH due to the removal of CO2 and HCO3
- from the water (essentially removing carbonic acid);
repiration does the opposite as noted above for EC25.
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s61
PPr & Rn effects in relation to density layering
Ice L., MN 6/14/99 Grindstone L., MN 6/20/99
•The line plots are dissolved-O2
•PPr – O2 “bump” •Rn – O2 “dip”
•Rn – O2 decline & anoxia
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s62
More about Onondaga in 2003
Here’s DO
Run the color mapper – set EC to 1200-2200 uS/cm and DO to % saturation
• DO > 150% from 0-3m and then <10% down to the bottom !
• pH drops >1 unit from 3 down to 5 m
•EC jumps up and down by 400 uS/cm !
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s63
Lake Washington tidbits… Apr- Oct 2002
Apr: high chlor – Is it real ?
Sep: low chlorophyll; low metalimnion DO - Is it real ?
Oct: high chlorophyll; - Is it real ?
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s64
Water Quality – What is it ?
Water quality is actually a subjective term that is used to describe the condition of a water body in relation to the needs of humans (beneficial uses in regulatory parlance), or the needs of aquatic organisms
Water quality is not an absolute since different user groups may have different expectations and values
Water quality protection involves both human health and environmental health risk assessments and management
Water quality regulatory standards alone may be met yet the “patient may die”. For this reason biocriteria have become an important new aspect of water resource protection
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s65
Water Quality – What’s a high value ?
Protection: environmental health vs human healthBeneficial use: fishable & swimmable vs drinkable
Lake-P : 100 ppb = hyper-eutrophic Cola-P : 1000's ppb = tasty Drinking water-P = no limit (Duluth adds 1000 ppb to
control lead leaching from old pipes) Lake-N : >500 ppb = high Drinking water : OK if < 10,000 ppb Nitrate-N Lake Hg < ~ 3 ppt vs DW < 2,000,000 ppt Lake fish PCB’s< 50 ppb vs Baby food < 2000 ppb
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s66
Water quality depends on many factors
Characteristics of the ecoregion Type and size of the watershed Precipitation patterns and surface water
hydrology Groundwater influences Lake size, shape, and retention time Number of people and land uses in the
watershed
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s67
Minnesota Ecoregions
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s68
1.6-3.3 ft5-11 ft
1.0-3.3 ft
8-15 ft
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s69
Other important factors affecting the health and economic sustainability of lake resources
Non-water quality impacts shoreline attached algae & aquatic plants shoreline woody debris & aquatic habitat exotic species (invasive plants & animals) noise pollution light pollution sight pollution
Developed by: Axler, Hagley Draft Updated: January 13 , 2004 U1-m2/3part6-s70