Question

what effect can fertilizer runoff have on an aquatic ecosystem?
a. increased plant growth leading to a decrease in fish populations
b. increased plant growth leading to an increase in fish populations
c. decreased plant growth leading to a decrease in fish populations
d. decreased plant growth leading to an increase in fish populations

please select the best answer from the choices provided

○ a
○ b
○ c
○ d

Explanation:

Fertilizer runoff adds nutrients (like nitrogen, phosphorus) to aquatic ecosystems. This causes increased plant (e.g., algae) growth. Excessive plant growth can deplete oxygen in water (through decomposition after overgrowth or blocking light for other plants that produce oxygen), leading to hypoxia. Fish need oxygen, so low oxygen levels decrease fish populations. Option a says increased plant growth (from fertilizer nutrients) leads to decreased fish populations, which matches this process. Option b is wrong because increased plant growth often harms fish (via oxygen depletion). Options c and d are wrong as fertilizer runoff increases, not decreases, plant growth.

Answer:

A. Increased plant growth leading to a decrease in fish populations