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Lakes

Lakes. Most of world’s freshwater resides in a few large lakes: Great Lakes contain 20% of freshwater in world. Structure:. Littoral Zone: Shallows Limnetic Zone: Open lake. Fig 3.37. Lakes. Vertical Distribution: Epilimnion: warm surface layers

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Lakes

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  1. Lakes • Most of world’s freshwater resides in a few large lakes: • Great Lakes contain 20% of freshwater in world Molles: Ecology 2nd Ed.

  2. Structure: Littoral Zone: Shallows Limnetic Zone: Open lake Fig 3.37 Molles: Ecology 2nd Ed.

  3. Lakes • Vertical Distribution: • Epilimnion: warm surface layers • Metalimnion: (Thermocline) – temp changes substantially with depth • Hypolimnion: – cold dark waters Fig 3.37 Molles: Ecology 2nd Ed.

  4. Lakes • Color: • Depends on light absorption and bio. activity • Stratification: • Become thermally stratified as they warm Molles: Ecology 2nd Ed.

  5. Molles: Ecology 2nd Ed. Fig 3.38

  6. Temperate lake Molles: Ecology 2nd Ed.

  7. Lakes • Nutrient Levels • Oligotrophic: low biological production, often well oxygenated • Eutrophic: high biological production, may be depleted of oxygen Molles: Ecology 2nd Ed.

  8. Oligotrophic lake = nutrient poor Little plant growth, deeper Molles: Ecology 2nd Ed.

  9. Eutrophic lake = nutrient richhigh plant growth, shallow Molles: Ecology 2nd Ed.

  10. Mesotrophic lakes:some plant growth • Life cycle of a glacial natural lake • Lake forms from glacial deposits or groundwater filling hole = oligotrophic Molles: Ecology 2nd Ed.

  11. Life cycle of a natural lake • Nutrients wash in from surrounding watershed, lake fills in some = mesotrophic Molles: Ecology 2nd Ed.

  12. Life cycle of a natural lake • Lake fills in further, nutrients wash in from surrounding watershed, heavy plant growth = eutrophic • Finally lake fills in completely Molles: Ecology 2nd Ed.

  13. Lakes • Human Populations have had profound, usually negative effects • Municipal and Agricultural Run-off • Eutrophic from nutrients • Toxins • Exotic Species – Zebra Mussels, round goby Molles: Ecology 2nd Ed.

  14. Molles: Ecology 2nd Ed.

  15. Index of Biotic Integrity • IBI score is method to evaluate streams • Compare biota to nearby undisturbed stream • Fish communities generally used Molles: Ecology 2nd Ed.

  16. IBI • 1. Number of species, kinds, tolerances • 2. Trophic compositions of species • Omnivores • Insectivores • Piscivores • 3. Fish abundance and condition Molles: Ecology 2nd Ed.

  17. Molles: Ecology 2nd Ed.

  18. Molles: Ecology 2nd Ed.

  19. Molles: Ecology 2nd Ed.

  20. Summary • Hydrologic Cycle exchanges water among different holding areas. • Biology of aquatic largely determined by physical and chemical factors. • Light, temp, salinity, oxygen, etc. Molles: Ecology 2nd Ed.

  21. Molles: Ecology 2nd Ed.

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