Explain How Nutrient-Rich Runoff Can Cause Waters to Become Hypoxic

Explain how nutrient-rich runoff can cause waters to become hypoxic.

A) Algae and cyanobacteria flourish on the nutrients in the run-off. Heterotrophic microbes then flourish on the organic molecules produced by these organisms, using oxygen in the process. This consumption of oxygen leads to a hypoxic state in the area. Larger animals cannot survive in the hypoxic area.
B) Algae and cyanobacteria flourish on the nutrients in the run-off, using oxygen in the process. This consumption of oxygen leads to a hypoxic state in the area. Larger animals cannot survive in the hypoxic area.
C) The nutrients in the run-off often include chemicals that spontaneously oxidize in the presence of oxygen. As such, they tend to deplete the amount of oxygen present in an area simply by being present themselves. This consumption of oxygen leads to a hypoxic state in the area. Larger animals cannot survive in the hypoxic area.
D) It doesn't. This claim is a scare tactic used by environmental extremists to prevent farmers and individuals from fertilizing their crops and lawns. There is no induction of a hypoxic state in bodies of water where run-off occurs.