How can water quality be affected by agricultural runoff?

Agricultural runoff significantly impacts water quality primarily by introducing pesticides and nutrients into waterways. When rain falls on agricultural land, it can wash away fertilizers, herbicides, and insecticides that have been applied to crops. These substances can then enter streams, rivers, and lakes, resulting in pollution that can harm aquatic ecosystems.

Nutrients, particularly nitrogen and phosphorus from fertilizers, can lead to eutrophication, which is the excessive growth of algae in water bodies. This process depletes oxygen in the water, harming fish and other aquatic life and creating dead zones. On the other hand, pesticides can be toxic to various organisms and can disrupt the food chain, further contributing to ecological imbalance.

While increasing sediment levels in rivers is indeed a concern associated with runoff, it is more directly related to soil erosion rather than the chemicals used in agriculture. Lowering groundwater levels, as well as promoting drought conditions, are consequences of broader water management practices, climate factors, or over-extraction of resources rather than solely agricultural runoff itself. Thus, introducing pesticides and nutrients is the most direct way agricultural runoff affects water quality.