Nutrient Pollution

1 Key excerpts on "Nutrient Pollution"

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  eBook - ePub

  Pollution

  Causes, Effects and Control

  • R M Harrison(Author)
  • 2015(Publication Date)
  • Royal Society of Chemistry

    (Publisher)

  Alongside this dramatic increase in nitrogen in freshwater systems, the global phosphorus cycle has been amplified by around 400% by human activities. 21 It has already been described how the release of nutrients during the breakdown of organic matter stimulates the growth of aquatic plants. This addition of nutrients to a waterbody is known as eutrophication. Nitrogen and phosphorus are the two nutrients most implicated in eutrophication and, because growth is normally limited by phosphorus rather than nitrogen, it is the increase in phosphorus which stimulates excessive plant production in freshwaters. Beyond agricultural fertilizers, the main sources of excess nutrients to surface waters include phosphorus from STW, the washing of manure from intensive farming units into water, the burning of fossil fuels which increases the nitrogen content of rain and the felling of forests which causes increasing erosion and run-off. 4.3.1 Nutrient Pollution in Lakes The concentrations of nitrate and phosphate in the water of Ardleigh Reservoir, a eutrophic waterbody in East Anglia, are shown in Figure 4.2. 22 Note that the concentration of nitrate increases during the late winter when fertilizer is applied to growing crops and is washed into streams feeding the reservoir in large amounts. By contrast, the concentration of phosphate peaks in late summer, when low flows in the feeder streams consist largely of treated sewage effluent while, at this time of year, much phosphate is released from the reservoir sediments into the water. 22 Figure 4.2 Concentrations (mg l −1) of nitrate and phosphate in Ardleigh Reservoir, eastern England, over two years. 22 Table 4.2 lists the guidelines for assessing the trophic status of a waterbody. Peak phosphorus concentrations in Ardleigh Reservoir were some 250 times the minimum concentration for assigning a waterbody as eutrophic, while peak concentrations of nitrogen were 10 times the minimum

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