Question

when fertilizers run off farmland into streams and ponds, the nitrogen content of the water increases. this can lead to rapid growth of algae in a process called eutrophication. how can this process affect other organisms in the water? d. the extra nitrogen provides additional food for the other organisms, increasing their population. b. the water becomes better able to support aerobic organisms. a. oxygen is used up as algae is decomposed, reducing the amount available to other organisms. c. the algae provide food for fishes and other organisms, leading to decreased algae populations.

Explanation:

During eutrophication, when algae die and decompose, bacteria break them down. These bacteria use oxygen in the process of decomposition, leading to oxygen - depletion in water. This lack of oxygen can harm other aerobic organisms. Option A correctly describes this oxygen - using process during algae decomposition. Option B is incorrect as eutrophication usually leads to oxygen depletion rather than making water better for aerobic organisms. Option C is wrong because while algae can be food for some organisms, eutrophication often causes algal blooms that lead to negative impacts rather than a balanced food - source situation. Option D is incorrect as the extra nitrogen mainly causes algal over - growth and oxygen depletion rather than providing beneficial food for other organisms in a positive way.

Answer:

A. Oxygen is used up as algae is decomposed, reducing the amount available to other organisms.