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Q.An aquatic ecosystem having luxurious growth of cyanobacteria (Algal bloom) leads to eutrophication.

a) What kind of pollutants cause algal bloom to colonize the aquatic ecosystem?
b) What are the consequences of eutrophication?
Kerala DhseKerala DHSE Plus Two Board 2015Subjective· 2mImportance★★★★★
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Eutrophication is the excessive enrichment of a water body with nutrients — mainly from fertiliser runoff and sewage — that fuels algal blooms, and it ultimately suffocates the aquatic ecosystem by depleting oxygen.

a) Pollutants causing the algal bloom: The excessive growth of cyanobacteria/algae is driven by an oversupply of plant nutrients, chiefly nitrates and phosphates. These enter aquatic ecosystems from agricultural fertiliser runoff, discharge of untreated or partially treated domestic sewage, and phosphate-rich detergents. This nutrient enrichment of the water body is called eutrophication, and the resulting excessive algal/cyanobacterial growth on the surface is the visible 'algal bloom'.

b) Consequences of eutrophication:

  • The dense algal mat blocks sunlight from reaching submerged aquatic plants, reducing their photosynthesis.
  • When the algae die, their decomposition by aerobic bacteria consumes large amounts of dissolved oxygen, causing hypoxia (oxygen depletion) in the water.
  • This oxygen depletion leads to large-scale death of fish and other aquatic organisms. …

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