Fertilizer runoff has a negative impact on aquatic ecosystems because
a. it causes plants and algae to grow quickly, suffocating organisms in the water
b. phosphorus is not found in nature
c. phosphorus is poisonous to living organisms
d. living organisms do not require phosphorus in order to survive

The answer is a. it causes plants and algae to grow quickly, suffocating organisms in the water. The rapid growth of organisms due to fertilizer runoff leads to a process called eutrophication. When the vegetation dies, the process of decomposition leads to the formation of excessive amounts of carbon dioxide, which in turn suffocates aquatic animals.

The answer should be c.