Question

Which one of the following statements is NOT correct?

• A. Algal blooms caused by excess of organic matter in water in water improve water quality and promote fisheries
• B. Water hyacinth grows abundantly in eutrophic water bodies and leads to an imbalance in the ecosystem dynamics of the water body
• C. The amount of some toxic substances of industrial waste water increases the organisms at successive trophic levels
• D. The micro-organisms involved in the biodegradation of organic matter in a sewage polluted water body consume a lot of oxygen causing the death of aquatic organisims

Answer 1

The Correct Option is A

Correct Answer: Option 1 – Algal blooms caused by excess of organic matter in water improve water quality and promote fisheries

This question tests your understanding of aquatic pollution, eutrophication, and the ecological impacts of excessive organic matter. Let’s analyze each statement to identify the one that is NOT correct.

Option 1: This is the incorrect statement and thus the correct answer to the question. Algal blooms are caused by the excess of nutrients, particularly nitrates and phosphates from sewage, agricultural runoff, and detergents. These blooms do not improve water quality; instead, they:

• Block sunlight from reaching aquatic plants
• Reduce dissolved oxygen levels when algae die and decompose
• Lead to the death of aquatic life such as fish and invertebrates

Algal blooms create hypoxic (low oxygen) conditions, degrading water quality and harming fisheries rather than promoting them.

Option 2: This is a true statement. Water hyacinth is an invasive species that proliferates in nutrient-rich (eutrophic) water bodies. It disrupts the aquatic ecosystem by blocking sunlight, depleting oxygen, and crowding out native species.

Option 3: This is also true. Toxic substances from industrial waste (like heavy metals and pesticides) accumulate in organisms through the food chain, a process known as biomagnification. This increases toxicity at higher trophic levels, including fish, birds, and even humans.

Option 4: This is another true statement. When sewage containing organic matter enters a water body, microorganisms decompose it. This process consumes a significant amount of oxygen, leading to oxygen deficiency (hypoxia) and causing the death of aquatic organisms — a major problem in sewage-polluted water bodies.

Conclusion: While algal blooms are often mistaken as a sign of productivity, in reality, they severely disrupt aquatic ecosystems. Therefore, Option 1 is not correct and is the right choice for this question. Understanding the consequences of eutrophication and organic pollution is crucial for NEET, board exams, and environmental science awareness.