An oxygen sag occurs most often
A) In estuaries closest to a pollution source
B) Immediately downstream from a pollution source
C) Immediately upstream from a pollution source
D) After the water recovers from the pollution source
E) At any of these places

Question

Quizplus · Accepted Answer

An oxygen sag occurs most often immediately downstream from a pollution source. This is because pollutants, especially biodegradable ones, increase the demand for dissolved oxygen as microorganisms break them down, leading to a decrease in oxygen levels in the water.

An Oxygen Sag Occurs Most Often