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Phosphorus can encourage excessive growths of plants and algae and contribute to eutrophication. If a river discharges into a lake or reservoir phosphate can be mobilised year after year by natural processes. In the summer time, lakes stratify so that warm oxygen rich water floats on top of cold oxygen poor water.
It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or phosphorus, stimulate algal growth. [1] Sources of nutrient pollution include surface runoff from farm fields and pastures, discharges from septic tanks and feedlots, and emissions from combustion.
Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water. [1] [2] Eutrophication may occur naturally or as a result of human actions.
A eutrophic water body, commonly a lake or pond, has high biological productivity. Due to excessive nutrients, especially nitrogen and phosphorus, these water bodies are able to support an abundance of aquatic plants. Usually, the water body will be dominated either by aquatic plants or algae. When aquatic plants dominate, the water tends to be ...
Lake ecosystems are a prime example of lentic ecosystems (lentic refers to stationary or relatively still freshwater, from the Latin lentus, which means "sluggish"), which include ponds, lakes and wetlands, and much of this article applies to lentic ecosystems in general.
If a lake is eutrophic and has a high sediment oxygen demand, the hypolimnion in dimictic lakes can become hypoxic during summer stratification, as often seen in Lake Erie. During summer stratification, most lakes are observed to experience internal waves due to energy input from winds.
Gradual environmental changes through eutrophication or global warming can cause major oxic-anoxic regime shifts. Based on model studies this can occur abruptly, with a transition between an oxic state dominated by cyanobacteria , and an anoxic state with sulfate-reducing bacteria and phototrophic sulfur bacteria .
The superabundance of phosphorus in the lake has been linked to nonpoint source pollution such as urban and agricultural runoff as well as point source pollution that includes sewage and wastewater treatment plants. [46] The zone was first noticed in the 1960s amid the peak of eutrophication occurring in the lake. [47]