The process whereby oxygen is depleted by the growth of microorganisms due to excess nutrients in aquatic systems is called
dead zoning
eutrophication
retrophication
depletion

Eutrophication.

Explanation:

Eutrophication may be defined as the process of over expression of nutrient and mineral in the aquatic system. The example of eutrophication is algal bloom.

This eutrophication causes the depletion of oxygen in the aquatic system due to the excess nutrients. The release of phosphates and detergents in the water body is the main cause of eutrophication.

Thus, the correct answer is option (2).

a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.