What are the major sources of nutrient pollution in surface waters?

Nutrient pollution in surface waters primarily stems from sources that contribute significant amounts of nutrients, particularly nitrogen and phosphorus. The correct choice highlights agricultural runoff, sewage discharge, and stormwater runoff as major contributors.

Agricultural activities often involve the use of fertilizers, which are rich in nutrients. When it rains, these fertilizers can wash off fields and into nearby rivers and lakes, leading to an excess of nutrients in the water. Sewage discharge, especially from wastewater treatment plants that may not fully remove nitrogen and phosphorus, also plays a critical role in introducing these nutrients into surface water bodies. Additionally, stormwater runoff collects various pollutants, including those from urban areas, and can further contribute to nutrient loads in rivers and lakes.

Understanding these sources is crucial for managing and mitigating nutrient pollution, as they are the main pathways through which excess nutrients enter aquatic ecosystems, potentially leading to harmful algal blooms and other ecological issues. Alternative sources, such as industrial discharge, rainwater, and natural sedimentation, play lesser roles in nutrient loading compared to the highlighted sources, thus reinforcing the importance of focusing on agricultural, sewage, and stormwater influences in surface water management.