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Life in Freshwater

Oxygen in Ponds and Lakes

The lower the temperature the higher the saturation of oxygen. Conversely the warmer the water gets the lower the amount of oxygen that can dissolve in it. Oxygen is essential for most of the life in freshwater. Some will be able to live anaerobically in the mud. They may either be permanent anaerobes, e.g. some types of bacteria, whilst others may be able to survive short periods without oxygen, e.g. chironomid larvae. But the majority of organisms need a steady supply of oxygen and if the temperatures rises this will be a problem. Even when it is fully saturated water contains little oxygen. At 5 degrees (and at normal air pressure) one litre of water contains only 8.9 cc oxygen and at 20 degrees it contains 6.4 cc. At higher altitudes this lessens but the lowering level of oxygen may be compensated for by the reduction in temperature that allows a higher amount to saturate the water. The amount of oxygen consumed by animals will increase as temperature rises.

The rate of decomposition within the benthos will be determined by the amount of oxygen present. In oligotrophic lakes the oxygen levels may well be moderately high in the benthos compared to eutrophic ones that can be deoxygenated.

Abiotic factors:


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