Nonpoint source (NPS) pollution is
water pollution affecting a water body from diffuse sources, such as polluted
runoff from
agricultural areas draining into a river, or wind borne debris blowing out to sea. Nonpoint source pollution can be contrasted with
point source pollution, where discharges occur to a water body at a single location, such as discharges from a chemical factory, or from ships at sea.
NPS may derive from many different sources with no specific solution to rectify the problem, making it difficult to regulate. According to the U.S. Environmental Protection Agency (EPA), nonpoint source pollution is the leading cause of water pollution in the United States today, with polluted runoff from agriculture the primary cause.[1] [2]
Other significant sources of runoff include hydrological and habitat modification, stormwater runoff, and silviculture (forestry).[3] [4] Another important cause of NPS pollution is urban runoff of items like oil, fertilizers, and lawn chemicals. As rainfall or snowmelt moves over and through the ground, it picks up and carries away natural and human-made pollutants. These pollutants are eventually deposited into bodies of water, such as lakes, rivers, wetlands, coastal waters, and underground sources of drinking water.
Nitrogen is most often transported by water as nitrate (NO3). The nitrogen is usually added to a watershed as organic-N or ammonia (NH3), so nitrogen stays attached to the soil until oxidation converts it into nitrate. Since the nitrate is generally already incorporated into the soil, the water traveling through the soil is the most likely to transport it. Instead of surface runoff being the primary transporter, interflow and tile drainage.
