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 (eutrophication). Industries discharge a variety of toxic compounds and heavy metals, and wastewater from industrial process 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, hampering water organisms in their ability to photosynthesize.

Groundwater pollution is more difficult to clean up than surface pollution because groundwater 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. Groundwater that moves through cracks and caverns is not filtered and can be polluted just as easily as surface water. In fact this can be aggravated by the human tendency to use sinkholes in areas of Karst topography 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 for industrial processes
• acid rain caused by industrial discharge of sulfur dioxide (by burning high-sulfur fossil fuels)
• excess nutrients added by runoff containing large amounts of detergeants or fertilizers

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

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

See also

• Water quality

Sources

• U.S. Environmental Protection Agency Homepage, http://www.epa.gov/
• Kentucky Division of Water Homepage, http://water.ky.gov/