Question

question #12
fertilizer runoff containing nitrogen and phosphorous flows from agricultural fields into a lake. these chemicals encourage the rapid growth of algae in the lake, and the algae block sunlight. when algae die, their decomposition by bacteria consumes oxygen and depletes the dissolved oxygen content of the lake.
what will be the most likely consequence of the decomposition process?
a the amount of water in the lake will increase.
b the numbers of aquatic plants in the lake will increase.
c the populations of fish in the lake will decrease.
d the amount of carbon dioxide in the lake will decrease.

Explanation:

• Option A: Decomposition of algae doesn't increase the amount of water in the lake. The process described is about oxygen consumption and algal growth, not water volume change. So A is incorrect.
• Option B: Algae block sunlight, which is needed for aquatic plants to photosynthesize. With less sunlight, aquatic plants are likely to decrease, not increase. So B is incorrect.
• Option C: Fish need dissolved oxygen to survive. The decomposition of algae by bacteria consumes oxygen, depleting the dissolved oxygen in the lake. This lack of oxygen will harm fish, leading to a decrease in their population. So C is correct.
• Option D: Bacterial decomposition of organic matter (algae) produces carbon dioxide. So the amount of carbon dioxide in the lake should increase, not decrease. So D is incorrect.

Answer:

C. The populations of fish in the lake will decrease.