Question

dead zones in the oceans are generally caused by

heavy metals in the water
excess sediments in the water
excess nutrients in the water
pharmaceuticals in the water

Explanation:

Define ocean dead zones

Ocean dead zones are hypoxic (low-oxygen) areas in the world's oceans and large lakes, where most marine life cannot survive due to lack of oxygen.

Identify the primary cause

These zones are primarily caused by nutrient pollution, particularly nitrogen and phosphorus, which is a major form of Water Pollution.

Explain the biological process

Excess nutrients stimulate rapid growth of algae (algal blooms). When the algae die and sink, bacteria decompose them, consuming dissolved oxygen in the process.

Evaluate the given options

• Heavy metals: Toxic to organisms but do not directly cause widespread oxygen depletion.
• Excess sediments: Block light and clog gills, but do not drive the massive oxygen depletion cycle.
• Excess nutrients: Directly fuel algal blooms and subsequent oxygen depletion (eutrophication).
• Pharmaceuticals: Chemical pollutants with physiological effects, but not the primary cause of dead zones.

Answer:

• Heavy metals in the water
• Excess sediments in the water
• Excess nutrients in the water (Correct answer)
• Pharmaceuticals in the water