Agricultural runoff
Agricultural runoff is water flowing from farmland into waterways while carrying soil, nutrients, pesticides, or other materials.
Surface runoff: Water that flows over land rather than infiltrating into soil or evaporating. It is the overland flow that carries contaminants off fields.
Eutrophication: The enrichment of water with nutrients, often causing excessive plant or algal growth. Runoff nitrogen and phosphorus can trigger nutrient enrichment in lakes and coastal waters.
Riparian buffer: A strip of vegetation beside a waterway that intercepts sediment, nutrients, and other pollutants. Buffers slow field runoff and capture pollutants before they enter streams.
Haber–Bosch process: An industrial method for synthesizing ammonia from nitrogen and hydrogen. Its fertilizer supply expanded crop production and the potential for nitrogen losses from fields.
Nonpoint source pollution: Pollution entering water from diffuse sources rather than a single identifiable discharge point. Agricultural runoff is difficult to regulate because it usually comes from many dispersed fields.
Soil erosion: The detachment and movement of soil by water, wind, ice, or gravity. Runoff transports eroded soil and the nutrients or chemicals attached to it.
Harmful algal bloom: A rapid growth of algae or cyanobacteria that harms organisms or people. Nutrient-rich runoff can fuel blooms that produce toxins or deplete oxygen.
Cover crop: A crop grown mainly to protect and improve soil between or alongside cash crops. Cover crops reduce bare soil, erosion, and nutrient losses during wet seasons.
Green Revolution: A mid-twentieth-century expansion of crop yields through improved varieties, irrigation, and inputs. Greater fertilizer use increased the scale of nutrient runoff concerns.
Nutrient trading: A system that allows regulated sources to meet nutrient limits by purchasing reductions elsewhere. Trading may fund farm nutrient reductions, but measuring their water-quality benefits remains challenging.