Previous Year Question

Statement 1 is correct. Eutrophication is the process in which excessive enrichment of nutrients occurs in a Water Body, such as a lake, pond, or river. The principal nutrients responsible are Nitrogen and Phosphorus, which enter water in the form of Nitrates and Phosphates. Their major sources include Agricultural Runoff containing fertilizers, domestic Sewage, and industrial wastewater. Excessive nutrient availability accelerates the growth of algae and aquatic vegetation.

Statement 2 is also correct. Excess nutrients promote excessive algal growth, known as an Algal Bloom. Dense algal growth can reduce the penetration of sunlight into water, affecting Photosynthesis in submerged aquatic plants. When algae and other aquatic plants die, Aerobic Bacteria consume large amounts of Dissolved Oxygen (DO) during their Decomposition. Consequently, the availability of oxygen in water decreases.

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 algae and other organic material can increase BOD, resulting in declining DO levels. When dissolved oxygen becomes excessively low, the condition is called Hypoxia. The near-complete absence of oxygen is known as Anoxia. These conditions can cause the death of fish and other aquatic organisms and lead to the formation of Dead Zones.

Eutrophication occurs through both natural and human-induced processes. Natural Eutrophication develops through the gradual accumulation of nutrients in water bodies over long periods, whereas human-induced or Cultural Eutrophication is accelerated by agricultural, domestic, and industrial wastes. Important control measures include Wastewater Treatment, balanced fertilizer application, and limiting the flow of nitrogen and phosphorus into water bodies.