Question

The formation of a dead zone in a water body takes place because of the events which occur in the order of
I. Oxygen depletion
II. Algal bloom
III. Excess decomposition
IV. Nutrient runoff

• A. II, I, III and IV
• B. II, IV, III and I
• C. III, II, IV and I
• D. IV, I, II and III
• E. IV, II, III and I

Answer 1

The correct option is E IV, II, III and I

Dead zones are the hypoxic areas in the oceans and lakes where the oxygen level is very low. The low oxygen concentration in these areas leads to suffocation and death of the marine life or they tend to move away from such hypoxic areas. The formation of the dead zone is the result of eutrophication - when the water body receives too many nutrients such as phosphorous and nitrogen. The excess of these nutrients which run off the land in the form of wastewater into the rivers and oceans stimulate an overgrowth of algae which sinks into the water. The excess decomposition resulting from the algal bloom results in consumption of oxygen and depletion of the available oxygen levels making it difficult for the survival of the marine life.