Previous Year Question

Eutrophication is the process in which the concentration of nutrients increases excessively in a Water Body, such as a lake, pond, or river. The principal nutrients responsible are Nitrogen and Phosphorus, which occur in water in forms such as Nitrate and Phosphate. Agricultural Runoff containing fertilizers, domestic Sewage, industrial wastewater, and certain detergents are major sources of these nutrients. Their excessive accumulation causes abnormal growth of algae and aquatic plants.

Algal Bloom is a major consequence of eutrophication. Excess nutrients can cause rapid growth of Algae and Cyanobacteria. Dense algal growth may cover the water surface and reduce sunlight reaching submerged aquatic plants, thereby affecting Photosynthesis. When these algae and other aquatic plants die, Aerobic Bacteria involved in their Decomposition consume Dissolved Oxygen (DO) from the water. Consequently, the concentration of dissolved oxygen begins to decline.

Biochemical Oxygen Demand (BOD) represents the amount of oxygen required by microorganisms to decompose organic matter present in water. During eutrophication, the accumulation of dead organic material can increase BOD and reduce dissolved oxygen levels. Severe oxygen deficiency is called Hypoxia, while the near-complete absence of oxygen is called Anoxia. Under these conditions, fish, molluscs, and other aquatic organisms face difficulties surviving. Severely oxygen-depleted aquatic regions are also known as Dead Zones.

Eutrophication can occur through both natural and human-induced processes. Natural Eutrophication involves the gradual accumulation of nutrients and organic matter over long periods, whereas human-induced or Cultural Eutrophication is accelerated by agricultural fertilizers, untreated sewage, and other human activities. Important control measures include proper wastewater treatment, balanced fertilizer application, and limiting the entry of nitrogen and phosphorus into water bodies.