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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 EcologyMP 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)