Algal Blooms and Phosphate Eutrophication of Inland Water Ecosystems with Special Reference to India

Abstract

Algal blooms lead to hypoxia resulting in the mortality of fish and other aquatic animals in inland as well as marine waters. A number of reports on fish mortality in lakes and river waters due to hypoxia are available in India. The main cause of algal blooms is reported to be the eutrophication of inland and marine waters with plant nutrients, of which phosphate is the most important. Phosphate is added to inland and marine waters from run-offs from agricultural fields receiving phosphate fertilizers. Phosphate is also added to the waters from untreated human solid waste and sewage in the river and lake waters from nearby towns and cities. An N:P ratio of less than 10:1 is reported to encourage bloomer phytoplankton. Causes other than hypoxia, responsible for the mortality of fish and other aquatic animals include the production of neurotoxins and methanol by phytoplankton, heavy metals from industrial effluents and residues of pesticides from agricultural fields.