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Lake Zonation by Biological Production of Organic Matter MP 2.3 Oligotrophic Lakes • Low productivity with a small surface area compared to depth • Little decomposition because it is so cold so oxygen is plentiful • Bottom sediments low in decomposable material (detritus) • Shortage of nutrients limits photosynthesis • Very clear water Eutrophic Lakes • Nutrient-rich have a small surface area compared to depth • Have much detritus on the bottom that supports high rates of photosynthesis. • High decomposition rate uses up much of the oxygen in the pond. Mesotrophic Lakes • Have an intermediate level of productivity, less than eutrophic but more than oligotrophic lakes. Stream Ecology MP 2.4 Streams and Rivers • Defined is a body of water that is moving continuously in one direction • At the headwaters the water is usually cold and clear (except for glacier streams) with little minerals or nutrients • Rivers pick up minerals and nutrients as they head downstream. Turbidity • Becomes more and more turbid (carrying sediment) downstream • There is a frequently a visible line where a clear stream enters a turbid one (or vice versa), called the line of turbidity • Turbulence stirs up water adding oxygen, slow flowing rivers have less oxygen Animal Adaptations • Animals that live in and around rivers have evolved hydrodynamic body shapes to handle current or live on the downstream side of rocks. Point Source Pollution • Rivers have been a dumping ground for pollutants for centuries because they carry it away from the local area • Downstream in a river system pollution accumulates increasing as it moves toward the sea. Water Quality • Ecologists measure water quality by counting the diversity of invertebrates • The better the water quality the greater the invertebrate species richness (number of species)