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LAKE ECOLOGY
Unit 1: Module 2/3 Part 1- IntroductionJanuary 2004
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-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.
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-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
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s4
1. Introduction - Major Themes
Lakes reflect their watersheds (soils, vegetation, landuses) and climates
Morphometry (shape, depth, size) and hydrology (flushing rate) are important determinants of how lakes function
Lakes are very patchy - they are not homogeneous well-stirred bathtubs as they often appear to be - they exhibit great variability which creates large and small habitats
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s5
3 main factors determine a lake’s trophic state(its biological productivity)
Watershed, climate & morphometry
Rate of nutrient supply (from watershed & airshed) Bedrock geology, soils, vegetation, land uses,
atmospheric deposition Climate
Sunlight, temperature, precipitation and hydrology Morphometry
Depth (mean and max), size (volume/area), “roundness” (shoreline convolutions)
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s6
Watersheds – extensively covered in Module 1 and will be further discussed in Modules 4/5
EVERYONE lives in a watershed!
Watershed - the area of land draining to a particular lake, wetland or stream
Everything that happens on the land affects its water qualityThe City of Duluth is made up of
many watersheds, all connected together like the pieces of a puzzle
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s7
Climate
Climate: rain, snow, wind, air temperature, flows, seasonality play a role in determining a lake’s trophic state.
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s8
Watershed: Lake Surface Area Ratio
HighLow
How big is the watershed compared to the size of the lake?
Ratio = Watershed Area = Aw:Ao
Lake Area
Higher ratio = higher productivity; often poorer water quality
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s9
Nutrient loading and Watershed area
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s10
Maximum length (fetch)Maximum
width
Z max
Morphometry
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s11
Morphometry Elevation = 390 km
(1279 ft MSL) Lake area (Ao) = 16.6 ha (41 acres) Watershed area (Aw) = 85.4 ha (211 acres) Aw:Ao = 5:1 Maximum depth (Zmax) = 16.1 m Lake volume (V) = 1.6 x 106 m3 Shoreline length = 1.6 km Littoral area = 32 % Hydraulic residence time (HRT) = 2.6 ± 0.9 yrs (30 yr
record)
Morphometric (and watershed) characteristics for Ice Lake
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s12
Retention time = lake volume outflow
Longer retention time:
• Lake is flushed less often
• Slower to respond
• Pollutants stay put longer
How long does it take for the lake to get “flushed?”
What is retention time?
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s13
Turnover and flushing
Tt = V / QV = volume
Q = inflow
T50 = ?
T1 = ?
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s14
Retention times
Turnover times for the Laurentian Great Lakes (approximate retention times) :
Lake Superior 191 years Lake Michigan 99 years Lake Huron 22 years Lake Ontario 6.0 years Lake Erie 2.6 years
Turnover times for some WOW lakes (approximate):
Grindstone Lake, MN 4 yrs Ice Lake, MN 3 years Lake Washington, WA 2.3 yrs Shagawa Lake, MN 1 yr Lake Onondaga, NY 0.25 yrs
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s15
Conceptual framework for lake water quality
GEOCHEMISTRY
LAND USEWATERSHED
INPUT
ATMOSPHERIC DEPOSITION
SHORELINE DEVELOPMENT
INDUSTRIAL-MUNICIPAL EFFLUENTS
NATURAL NUTRIENTS
ANTHROPOGENIC
NUTRIENTS
HYDROLOGY
LAKE
MORPHOMETRY
ALGAL BIOMASSALGAL BIOMASS
(chlorophyll-a)(chlorophyll-a)
HYPOLIMNETIC & WINTER HYPOLIMNETIC & WINTER
OO22 - depletion - depletion
WATER CLARITYWATER CLARITY
(secchi depth, turbidity)(secchi depth, turbidity)
(Adapted from Hutchinson 1991)
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s16
More about lake variability (patchiness)
physical : waves, currents, temp, light, sediments
chemistry: major, minor and micronutrients, gases, in the water and sediments
biology : biomass (structure) & growth rates (function)
spatial features: in-lake horizontal & vertical variations
time (daily, seasonal, weather events)
The natural variability of these properties defines different habitats which are optimal for different organisms
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Developed by: R.Axler and C. Hagley Draft Updated: January 13 , 2004 U1-m2/3Part 1-s17