LAKE ECOLOGY Unit 1: Module 2/3 Part 1- Introduction January 2004

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.

Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 1-s3 Modules 2/3 outline 1. Introduction 2. Major groups of organisms; metabolism 3. Basins and morphometry 4. Spatial and temporal variability – basic physical and chemical patchiness (habitats) 5. Major ions and nutrients 6. Management – eutrophication and water quality

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

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)

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

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.

Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 1-s8 Watershed: Lake Surface Area Ratio High Low How big is the watershed compared to the size of the lake? Ratio = Watershed Area = A w :A o Lake Area Higher ratio = higher productivity; often poorer water quality

Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 1-s9 Nutrient loading and Watershed area

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

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 10 6 m 3  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

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?

Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 1-s13 Turnover and flushing T t = V / Q V = volume Q = inflow T 50 = ? T 1 = ?

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

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 USE WATERSHED INPUT ATMOSPHERIC DEPOSITION SHORELINE DEVELOPMENT INDUSTRIAL-MUNICIPAL EFFLUENTS NATURAL NUTRIENTS ANTHROPOGENIC NUTRIENTS HYDROLOGY LAKE MORPHOMETRY ALGAL BIOMASS (chlorophyll-a) HYPOLIMNETIC & WINTER O 2 - depletion WATER CLARITY (secchi depth, turbidity) (Adapted from Hutchinson 1991)

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

Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 1-s17