Phosphorus pollution can lead to which ecological consequence?

• A. Increased salinity.
• B. Oxygenation of deep waters.
• C. Decreased phytoplankton growth.
• D. Eutrophication and dead zones.

Answer: (D)

Excess phosphorus acts as a nutrient that fuels algae and aquatic plant growth in water bodies. When phosphorus pollution enters lakes or rivers, it often triggers algal blooms. As these blooms expand, they shade other aquatic life and, once they die, their organic matter is decomposed by bacteria, which consumes large amounts of dissolved oxygen. The resulting drop in oxygen creates hypoxic or anoxic conditions—dead zones where most aquatic life cannot survive. This sequence—nutrient-driven eutrophication leading to oxygen depletion and zone formation—is why eutrophication and dead zones are the expected consequence of phosphorus pollution.

Increased salinity isn’t driven by nutrient loading, deep-water oxygenation isn’t a typical result of phosphorus pollution (it usually involves oxygen depletion), and phosphorus tends to increase, not decrease, phytoplankton growth.