1. Unit 1: Module 2/3 Part 1- Introduction January 2004
LAKE ECOLOGY
Unit 1: Module 2/3 Part 1- Introduction January 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.
Goal: Provide a practical introduction to lake ecology. This is not a comprehensive limnology course. Rather, it is a “crash course” to be integrated with other tool-oriented WOW modules for initial training in technical areas related to water resource management.
Lecture time: 2-3 weeks of classroom instruction with weekly lab/field experience.
Slides Divided into 6 subtopics. Note – Subtopics 4-6 use WOW data and visualization tools first introduced in Subtopic 4 – the density stratification discussion. Also, the module introduces lake biota before discussing physical and chemical data, although some instructors may want to reverse this order.
Status (Jan 2004)
Lecture – WOW staff review in progress; a few more slides are in prep; some graphic design needed
Lab – in prep; focus will be on “traditional” field surveys comparing local ponds/lakes to each other and to WOW lakes.

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
A 2 week module can only highlight the basics of limnology. Students should be referred to the variety of introductory and advanced limnology texts now available. Some of these include:
Cole, G.A Textbook of limnology. 4th edition.
Dodds, W.K Freshwater Ecology: Concepts and environmental applications. Academic Press, San Diego, CA. USA.
Horne, A. J. and C.R. Goldman Limnology. 2nd Edition. McGraw-Hill, Inc. New York.
Hutchinson, G.E volumes . A treatise on limnology. John Wiley & Sons, New York.
Mason, C.F Biology of freshwater pollution. 3rd edition. Longman House Publ., Essex, UK.
McComas, S Lake Smarts: The first lake maintenance handbook. Terrene Institute, Washington, D.C., USA.
Monson, B.A A primer on limnology (2nd edition). Water Resources Center, University of Minnesota, St. Paul, MN, USA.
Moss, , B., J. Madgwick and G. Phillips A guide to the restoration of nutrient-enriched shallow lakes. W.W.Hawes, UK.
NALMS Lake and reservoir guidance manual. North American Lake Management Society, Madison , WI (
Schmitz, R.J An introduction to water pollution biology. Gulf Publ. Co., Houston, TX, USA.
Welch, E.B Ecological effects of wastewater: Applied limnology and pollutant effects. 2nd edition. Chapman & Hall, London, UK.
Wetzel, R.G Limnology 3rd Edition. Academic Press, San Diego, CA.
Wetzel, R.G. and G.E. Likens Limnological analyses. 3rd edition. Springer-Verlag, NY,NY, USA.

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
If the lake was a well mixed tub of water with little variation from one point to another, we’d expect its organisms to be equally dispersed throughout. It’s not. Physical and chemical properties vary across the lake, with depth and with time- all over many different spatial and time scales.
These differences structure the lake into different zones that represent different habitats to aquatic organisms. The metabolic and ecological activities of these organisms, in turn, further modifies the properties of these habitat zones.
A famous paper was written by the eminent limnologist G. Evelyn Hutchinson (a man by the way) that was titled “The Paradox of the Plankton” (1961. American Naturalist 95: ) asked the question “Why are there so many species” of phytoplankton (and zooplankton) since classical ecological competition and predation theory at that time basically assumed the organisms that existed were there because of “survival of the fittest”. If so, how can there be dozens of species present in a bottle of water grabbed at any time of year ?
Excellent website about lakes :

5. Rate of nutrient supply (from watershed & airshed)
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)
The Bottom–Up Model states that a lake’s productivity is driven by it’s physical and chemical properties. The Top-Down Model is states that a lake’s productivity is driven by the consumers (i.e., big fish eat planktivorous fish, that eat herbivorous zooplankton, that eat phytoplankton).

6. EVERYONE lives in a watershed!
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.
The hydrologic cycle is covered in Module 1.

8. Watershed: Lake Surface Area Ratio
How big is the watershed compared to the size of the lake?
Ratio = Watershed Area = Aw:Ao
Lake Area
High
Low
The higher watershed to lake area ratio means that precipitation falling on the watershed has, on average, more contact with watershed soils and impervious surfaces than in the system with a lower Aw:Ao ratio. In general this means higher nutrient loads and therefore higher productivity. Where there are disturbed soils and high percentages of impervious surfaces, this can lead to greatly increased nutrient loads and therefore, degraded water quality.
Higher ratio = higher productivity; often poorer water quality

9. Nutrient loading and Watershed area

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

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. Tt = V / Q T50 = ? T1 = ? Turnover and flushing V = volume Q = inflow
T50 = 5 minutes (300 seconds) and represents a deep lake with a relatively long flushing time. It is slower to respond to a pollutant addition because of dilution by its large volume but it retains a pollutant longer – unless it degrades or settles to the sediments.
The faster flushing system represents a shallow lake which may respond to a pollutant more quickly because because of reduced dilution, but for a shorter time because it can be flushed downstream more quickly. Shallow systems may also have reduced loss to the sediments because of wind resuspension and little density (i.e. thermal) stratification.
Observe how Halsteds Bay in Lake Minnetonka, which is relatively shallow (zmax ~ 8-9m), responds to wind mixing from late summer storms each year (GO TO DATA and use the DxT tool to examine the temperature and oxygen depth profiles).
How would Ice Lake, L. Washington, L. Mead, L. Onondaga and Medicine Lake be affected by a tanker truck with 5000 L of a persistent pesticide falling off a bridge and spilling into the lake ?

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. Conceptual framework for lake water quality
GEOCHEMISTRY
LAND USE
WATERSHED
INPUT
HYDROLOGY
IN-LAKE
NUTRIENTS
NATURAL NUTRIENTS
ATMOSPHERIC DEPOSITION
SHORELINE DEVELOPMENT
ANTHROPOGENIC
NUTRIENTS
INDUSTRIAL-MUNICIPAL EFFLUENTS
HYPOLIMNETIC & WINTER
O2 - depletion
LAKE
MORPHOMETRY
Slide adapted from Hutchinson, N
This schematic is a version of a classic diagram adapted from Dr. Jack Vallentyne’s paper entitled “The Algal Bowl” . This paper provides an excellent discussion of the factors and issues relating to natural versus cultural eutrophication
The Algal Bowl- A Faustian View of Eutrophication, (by J.R. Vallentyne, 1972, Federation Proceedings, Vol 32 (7), pp American Society of Biological Chemists Symposium on Man and his Environment at the 56th Annual Meeting of the Federation of American Societies for Experimental Biology, Atlantic City, NJ, USA, April 10, 1972).
The schematic assumes that algal biomass and hypolimnetic oxygen depletion are driven by in-lake nutrient levels that in turn depend upon the rate of nutrient delivery from the surrounding watershed. This is also referred to as a “bottom up” conceptual model of lake productivity
Deficiencies:
1. The model ignores bottom down effects due to grazers. A relatively new school of thought has shown that in some situations where nutrients are high, algal biomass may not be as high as expected due to intense grazing by cladoceran zooplankton (usually Daphnia sp.). These zooplankters are relatively large and also have a rapid growth rate which together yields a higher grazing rate on phytoplankton than other members of the zooplankton community. However, they are also relatively slow moving and this fact, coupled with their large body size, makes them highly vulnerable to planktivorous fish (minnows, sunfish, rough-fish, and young of the year for many species).
2. High nutrient influx may also be accompanied by high levels of suspended sediment which may cloud the lake (turbidity) enough to light-limit algal photosynthetic growth.
3. High nutrients may occur in conjunction with high macrophyte growth which may also act to light-limit open water phytoplankton. This is a shallow lake phenomenon and one can often find lakes with luxuriant water weed growth where the water itself is quite clear and free of suspended algae.
This top-down effect has given rise to a lake management tool called biomanipulation that will be discussed in more detail in Unit_6__ Module _24__ (Lake Restoration). Briefly it is based on the removal of planktivorous fish to promote the development of high densities of Daphnids that regulate algal biomass even when nutrient supply is high. This is usually accomplished by some combination of chemical poisoning (rotenone), intensive netting, or stocking with predators, often coupled with a lake drawdown at some point to concentrate the undesirable fish.
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)
Physical properties – basin and watershed shape and size; lake morphometry (size, shape, depth); hydrology (water budget, flushing rate or retention time); in-lake spatial variability (horizontally and vertically)
Chemistry - gases, nutrients, sediment-water interactions
The natural variability of these properties defines different habitats which are optimal for different organisms

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