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LAKE ECOLOGY

LAKE ECOLOGY. Unit 1: Module 2/3 Part 1- Introduction January 2004. Modules 2/3 overview. Goal – Provide a practical introduction to limnology Time required – Two weeks of lecture (6 lectures) and 2 laboratories

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LAKE ECOLOGY

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  1. LAKE ECOLOGY Unit 1: Module 2/3 Part 1- IntroductionJanuary 2004

  2. 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.

  3. Modules 2/3 outline • Introduction • Major groups of organisms; metabolism • Basins and morphometry • Spatial and temporal variability – basic physical and chemical patchiness (habitats) • Major ions and nutrients • Management – eutrophication and water quality

  4. 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

  5. 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)

  6. 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 quality The City of Duluth is made up of many watersheds, all connected together like the pieces of a puzzle

  7. Climate Climate: rain, snow, wind, air temperature, flows, seasonality play a role in determining a lake’s trophic state.

  8. High Low Watershed: Lake Surface Area Ratio 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

  9. Nutrient loading and Watershed area

  10. Maximum length (fetch) Maximum width Z max Morphometry

  11. Morphometric (and watershed) characteristics for Ice Lake • 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)

  12. What is retention time? How long does it take for the lake to get “flushed?” Retention time = lake volume outflow Longer retention time: • Lake is flushed less often • Slower to respond • Pollutants stay put longer

  13. Turnover and flushing Tt = V / Q V = volume Q = inflow T50 = ? T1 = ?

  14. 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

  15. IN-LAKE NUTRIENTS Conceptual framework for lake water quality GEOCHEMISTRY LAND USE WATERSHED INPUT HYDROLOGY NATURAL NUTRIENTS ATMOSPHERIC DEPOSITION SHORELINE DEVELOPMENT ANTHROPOGENIC NUTRIENTS INDUSTRIAL-MUNICIPAL EFFLUENTS HYPOLIMNETIC & WINTER O2 - depletion LAKE MORPHOMETRY WATER CLARITY (secchi depth, turbidity) ALGAL BIOMASS (chlorophyll-a) (Adapted from Hutchinson 1991)

  16. 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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