Which statement correctly describes an over-fertile (eutrophic) lake?

Concept

Eutrophication is nutrient enrichment of a water body, chiefly by compounds of nitrogen and phosphorus. The added nutrients stimulate excessive growth of algae and aquatic plants.

When this biomass dies, microbial decomposition consumes dissolved oxygen. Low oxygen, harmful algal blooms, and habitat degradation can stress or kill aquatic organisms.

Application

An over-fertile lake is therefore nutrient-rich and biologically overproductive. Its algal biomass tends to increase, while decomposition tends to lower dissolved oxygen; these conditions can damage fish health and reduce the quality of fish produced.

Contrast

• A decrease in nitrate does not describe the nutrient enrichment that drives eutrophication.

• A decrease in algal productivity is opposite to the usual initial response to excess nutrients.

• A persistent increase in dissolved oxygen is inconsistent with the oxygen demand created by decomposition of abundant biomass.

• Impaired fish quality follows from oxygen stress, harmful algal toxins, and degraded habitat.

Thus, an over-fertile lake can produce fish of impaired quality.