2. What is a lake? A lake is a topographic depression (basin) in the landscape that collects water Lakes can be made by shifting tectonic plates, volcanism, glacial activity, and man.

3. Structure of a Lake Littoral Zone: shallowest water along lake shore where rooted aquatic plants grow Limnetic Zone: open part of the lake Epilimnion: warm water surface layer Metalimnion: aka thermocline, temp. drops 1 degree Celsius every meter. Hypolimnion: cold and dark water that usually lacks dissolved oxygen

4. Lakes! Lake coloration can vary from blue to brownish-red. Color largely depends on the chemistry and biology of that particular lake. Shallow lake + Phytoplankton + large quantities of nutrients = deep green Deep lake + low quantities of nutrients + low Phytoplankton counts = clear blue The world average for salinity for freshwater is 120 mg per liter. Lakes become thermally stratified as they heat!

5. Overturn of a body of water  Overturn of the water is mostly fueled by the temperature/density relationship  As the temp drops, the stratification that separated the water breaks down  The cooler temp causes the surface water to become slightly denser and sink until it reaches water of the same density.  As the season progresses this process repeats until the density and temp of the body of water is the identical from top to bottom.

6. Oligotrophic vs. Eutrophic

7. Lake Flora

8. Lake Fauna

9. Human Influences Humans usually have a negative impact on the ecology of lakes. Most lakes attract people causing the populations around them to rise. For example Lake Erie went from 2.5 million in 1880 to over 13 million in 1980 ! Due to massive populations lots of excess nutrients and toxic wastes seeped into Lake Erie. These events turned a healthy fish filled lake into a algal soup where only the most tolerant species could survive. Pollution is not the only impact that humans have had on the ecology of lakes. Many invasive species wind up hitching free rides on boats or are intentionally put into an area where they have no natural predators and wind up outcompeting the native species!