1. Lake stratification (and chemistry) Water column is all the same temperature Complete circulation of the water column

2. Lake stratification (and chemistry) Bottom water is cold, isolated, and stagnant Circulation of only the surface water

3. Lake stratification (and chemistry) Warm, mixed Cold, stagnant CO 2 + H 2 O  CH 2 O + O 2 (photosynthesis, shorthand) Note temperature profile: surface water is warmer, less dense, and doesn’t mix with bottom water Complete circulation of the water column

4. Lake stratification (and chemistry) As the weather cools in autumn, surface water cools and becomes more dense...

5. Lake stratification (and chemistry)... and wind energy is able to mix the lake completely.

7. Some lakes never turn over. If bottom water is very dense (due to salt, for instance), temperature doesn’t matter and the bottom water remains permanently cut off from the atmosphere – and anoxic. High levels of dissolved solids = high density