Surface Water (pgs 29-32)

Lake Turnover

Lakes change as the seasons change. For example, the water is warmer in the summer than in the winter. Temperature changes through a year cause water to sink and rise in lakes. In the fall, the water mixes and spreads nutrients through a lake. This refreshes the lake so organisms in a lake can use the nutrients.

Eutrophication

This process occurs over a long period of time (years). Nutrients build up in a lake which causes algae to grow over the surface of a lake. Plants under the algae do not get enough sunlight for photosynthesis, so they die. The animals that eat those plants die too. Dead material fills up the lake, making it shallower. After a long time, the lake dies and a grassy field takes over.