LAKE ECOLOGY

Unit 1: Module 2/3 Part 1- IntroductionJanuary 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. 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: 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 qualityThe 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

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

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 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

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

Tt = V / QV = volume

Q = inflow

T50 = ?

T1 = ?

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 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)

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