Watersheds may be contaminated by fertilizers and other pollutants. when these substances enter a waterway, they can cause algal blooms, which are rapid overgrowths of algae.
when the algae die, the decay uses up a large portion of dissolved oxygen.
declining oxygen levels can then cause large die-offs of animals in the waterway.
what will an algal bloom in a watershed
most likely cause?

a. an increase in the watershed’s genetic diversity, which would reduce it’s ability to supply clean and safe drinking water.

b. a decrease in the watershed’s biodiversity, which would reduce it’s ability to supply clean and safe drinking water.

c. an increase in the watershed’s species diversity, which would improve it’s ability to supply large volumes of water.

d. a decrease in the watershed’s ecosystem diversity, which would improve it’s ability to supply large volumes of water.

and d is the wrong answer