水体富营养化英文.ppt

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Eutrophication of water
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Definition
Eutrophication is one of the water pollution .It is mainly caused by human activities.
When a large amount of nutrients , such as nitrogen and phosphorus ,are discharged into large lakes, estuaries, bays and other water bodies which flow slowly, it will cause a phenomenon that algae and other plankton in water multiply rapidly, dissolved oxygen decreases , water quality deteriorates and a large number of fish and other organisms die.
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Mechanism
Excess nutrients(N、P)
Autotrophic organisms (especially blue-green algae and red algae) grow quickly
Other algae species gradually reduce
Plankton and other small organisms die
Be decomposed by aerobic microorganism
consume dissolved oxygen in water
Fish and other aquatic life die
Or be decomposed by anaerobic microorganism
Produce hydrogen sulfide and other gases
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Identification index
Nitrogen content ≧~ ppm
Biochemical oxygen demand(BOD) ≧ 10 ppm
Phosphorus content ≧ ~ ppm
The number of bacteria is more than 100000 in per ml of water(pH=9~10)
The content of chlorophyll–a in characterized algae ≧ 10μmg/L
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Source
Excess nitrogen and phosphorus in the water body mainly come from
industrial waste water and domestic sewage, organic waste, livestock and poultry manure and agricultural chemical fertilizer.
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