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•  Leaching of mineral nutrients from agricultural land into rivers causes eutrophication and leads to increased

    biochemical oxygen demand

Eutrophication is the enrichment of an ecosystem (typically aquatic) with chemical nutrients (nitrates, phosphates, etc.)

  • The nutrients can be introduced via leaching from soil by rainfall or released as part of sewage
  • Eutrophication is common around agricultural lands where the use of artificial fertilisers are prevalent

An increase in nutrient supply within waterways will result in several ecological consequences:

  • A rapid growth in algal populations will occur (algal blooms) as a result of the increased availability of nutrients
  • As the algae die, there will be a subsequent spike in the numbers of saprotrophic microbes (decomposers)
  • The high rate of decomposition will result in an increased biochemical oxygen demand (BOD) by saprotrophic bacteria
  • The saprotrophs will consume available quantities of dissolved oxygen, leading to deoxygenation of the water supply
  • Eutrophication will also increase the turbidity of the water, which will reduce oxygen production by photosynthetic seaweeds
  • This will stress the survival of marine organisms, potentially leading to a reduction in biodiversity within the ecosystem