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)