Which of the following events might lead to an algal bloom

a) nitrogen rich fertilizer washes off of field into the ocean

b) oxygen is removed from ocean water by decomposition

c)new sewage plants removed from wastes from discharge

d) the population of baleen whales increases

The correct answer is option A

The Nitrogen rich fertilizer washes off Field into the ocean and leads to the formation of algal bloom in the ocean.

Algal blood forms is formed by the the excess of nutrients in the water. The excess of nutrient allows the growth of algae and they keep on growing and trapping the sunlight and making the lower part of water oxygen deficient.

Algal bloom grows due to nitrogen rich fertilizers which comes into the water bodies by run off.