How does stormwater run-off generally affect aquatic ecosystems?

Stormwater runoff can significantly impact aquatic ecosystems, often leading to nutrient loading and an increase in pest growth. When rainwater flows over urban and agricultural surfaces, it gathers a variety of pollutants such as fertilizers, pesticides, oils, and heavy metals. These pollutants can be delivered in high concentrations into nearby water bodies as part of the runoff.

The introduction of excess nutrients, particularly nitrogen and phosphorus—often found in fertilizers—can lead to eutrophication. This process stimulates algal blooms, which may initially seem beneficial as they provide food for some aquatic organisms. However, these blooms can quickly become detrimental. They often deplete oxygen levels in the water as they die off and decompose, leading to hypoxic conditions that can harm or kill fish and other aquatic life.

Additionally, these nutrient-rich conditions can promote the growth of pest species—such as certain types of algae, invasive aquatic plants, and other organisms—that can outcompete native species for resources, further disrupting the ecosystem balance. Hence, the statement regarding the potential for nutrient-loading and increased pest growth accurately reflects one of the key detrimental effects of stormwater runoff on aquatic ecosystems.