甚麼叫nonpoint source (NPS) pollution?

Virginia is a water rich state. But plenty of water doesn't necessarily mean having abundant usable water. As with all natural resources, we must use water wisely. We need clean water for drinking, food production, jobs, transportation, recreation, beauty and habitat for some of the most unique natural environs in the world. One of those is among the world's most productive estuaries, the Chesapeake Bay.

Preventing water pollution is difficult, however, because water is dynamic -- it flows freely from property to property, from locality to locality, even from the surface to underground. How water is used upstream can and does affect its quality downstream.

Nonpoint Source Pollution

There's a type of pollution that degrades some of our state's waterways. Its called nonpoint source (NPS) pollution because it doesn't come from a single source, or point, such as a sewage treatment plant or an industrial discharge pipe.

NPS pollution occurs mainly through stormwater runoff. When it rains, runoff from farmland, city streets, construction sites, and suburban lawns, roofs and driveways enters our waterways. This runoff often contains harmful substances such as toxics, excess nutrients and sediments. NPS pollutions effects seldom show up overnight -- they often go unnoticed for years. This characteristic makes it all the more difficult to control.

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發電廠的煙囪, 大型污水渠等是定點排污， 因為污物由一易辨定的地點放出。
排放量大， 集中。

路上汽車廢氣， 農業區污水是不定點排放，因為排放點多， 而分散， 但每個排放的量又不多。