Which contaminant is considered the most concerning for surface runoff and why?

Phosphorus is considered the most concerning contaminant for surface runoff primarily due to its ability to bind to soil particles and subsequently be transported to water bodies during rainfall or snowmelt events. When phosphorus is present in surface runoff, it can lead to nutrient pollution, which is a significant factor in the eutrophication process. This process results in excessive algal blooms in aquatic ecosystems, consuming oxygen and producing toxins that can harm aquatic life and disrupt entire ecosystems. The transport of phosphorus in runoff is particularly problematic because it can have immediate and widespread impacts on water quality, creating conditions that degrade aquatic habitats. This characteristic makes phosphorus a key target in efforts to manage surface water quality.