What impact does decomposition of aquatic plants have?

The correct answer identifies the impact of decomposition of aquatic plants as being detrimental to oxygen levels in the water. When aquatic plants die and decompose, the process consumes dissolved oxygen that is critical for the survival of aquatic life, such as fish and invertebrates. Microorganisms responsible for breaking down the organic matter use a significant amount of oxygen in this process, leading to a situation known as hypoxia, where oxygen levels drop below what is necessary to support life. Therefore, this can create an imbalance in the aquatic ecosystem, negatively affecting fish populations and potentially leading to fish kills.

The other options suggest benefits or a positive impact from the decomposition of aquatic plants, which are misleading in this context. For example, while plant decomposition may eventually contribute organic matter that could enhance nutrients for new plant growth over time, the immediate impact is negative due to the rapid depletion of oxygen during the breakdown process.