Water pollution
From open-encyclopedia.com - the free encyclopedia.
Water pollution has many sources and characteristics. Humans and other organisms produce bodily wastes which enter rivers, lakes, oceans, and other surface waters; in high concentrations these wastes result in bacterial contamination and excessive nutrient loading. Industries discharge a variety of toxic compounds and heavy metals, and industrial process wastewater may also be too hot or too low in dissolved oxygen to support life. Silt-bearing runoff from construction sites and farms can inhibit the penetration of sunlight through the water column, and hampers water organisms in their search for food.
Ground water pollution is more difficult to clean up than surface pollution, because ground water can move hundreds of miles through unseen aquifers. Porous, fine grained aquifers, such as sands and sandstones naturally purify water of bacteria by simple filtration, but have no effect on chemical contaminants such as the components of gasoline. Ground water that moves through cracks and caverns is not filtered and can have organic pollution just as easily as surface water. In fact this can be aggravated by the human tendency to use sinkholes in Karst topography areas as dumps.
Causes
The causes of water pollution can be divided into two groups: anthropogenic sources of pollution are those due to human choices, and natural sources are those resulting from forces intrinsic to the environment. Anthropogenic sources include:
- discharge of poorly-treated or untreated sewage;
- runoff from construction sites, farms, or paved and other impervious surfaces;
- discharge of contaminated and/or heated water used on industrial processes
- acid rain caused by industrial discharge of sulfur dioxide (by burning high-sulfur fossil fuels)
Natural sources include:
- seasonal turnover of lakes and embayments;
- siltation due to floods;
- eutrophication of lakes due to seasonal changes
- acid rain caused by natural volcanic discharges
- acid pollution of rivers and lakes by runoff from naturally acid soils
- carbon dioxide discharges and runoff, volcanic or mineral
Contaminants
The Drinking Water Equivalent Level (DWEL) is the concentration (in mg/mL) of a chemical contaminant in water that is deemed safe (in other words, the risk of poisoning is 10^-6).
Contaminants may include organic and inorganic substances. Organic water pollutants include:
- bacteria, as from sewage or livestock operations;
- fertilizers, in runoff from agricultural fields or forestry;
- food processing waste;
- tree and brush debris from logging operations
Inorganic pollutants include:
- metals;
- acid mine drainage;
- silt in stormwater runoff from cleared land
- acid rain caused by industrial or volcanic discharges
- acid pollution of lakes by runoff from acid soils
- carbon dioxide discharges and runoff, volcanic or mineral
- chemical waste factory byproduct
Sources
- U.S. Environmental Protection Agency Homepage, http://www.epa.gov/
- Kentucky Division of Water Homepage, http://water.ky.gov/
Mercury in zooplankton (copepods) in the open ocean off New York and Atlantic City USA New Jersey
Oxygen depletion as a consequence of too much nutrient input
zh:水污染
