How does sulphur dioxide affect aquatic ecosystems?

Sulphur dioxide has significant environmental effects, particularly in aquatic ecosystems, primarily through the process of acidification. When sulphur dioxide enters the atmosphere, it can combine with water vapor to form sulfuric acid. This acid can then fall as acid rain, which lowers the pH of rivers and lakes, making the water more acidic.

One of the critical impacts of this increased acidity is that it leaches aluminium from the soil and surrounding rocks into the water bodies. Elevated levels of aluminium in water can be toxic to fish and other aquatic organisms. It interferes with gill function in fish and can lead to increased mortality rates. Moreover, aluminium can disrupt the reproductive processes of aquatic life, thereby negatively impacting populations over time.

The other choices do not accurately reflect how sulphur dioxide impacts aquatic ecosystems. It does not increase fish populations or improve water clarity; instead, it creates conditions that are harmful to aquatic life. Additionally, it does not reduce water temperature; rather, it affects water chemistry and the overall health of the ecosystem. Hence, the leaching of aluminium due to increased acidity from sulphur dioxide is the most significant and accurate reflection of its impact on aquatic environments.