The process whereby oxygen is depleted by the growth of microorganisms due to excess nutrients in aquatic systems is called

$a$. dead zoning

$b$. eutrophication

$c$. retrofication

$d$. depletion

Dead zoning is a term used to describe zones or places in aquatic systems that are devoid of oxygen due to excessive pollution created by humans and their activities, rather than due to excessive microorganism development.

Retrofication is the process of altering something after it has been created, and it has nothing to do with the depletion of oxygen in aquatic systems caused by microbe growth.

Depletion occurs when a specific nutrient is present in extremely low concentrations, however, it does not apply to the process of oxygen depletion in aquatic systems caused by the proliferation of microbes.

The incorrect answer is$a,c,d$

Eutrophication is the process in which runoff of nutrients causes excessive growth of microorganisms leading to depletion in the levels of oxygen in aquatic systems like saltwater and freshwater systems which leads to the killing of the fauna of that ecosystem.