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 of Water Pollution
Causes of unhealthy and polluted water are pretty well outlined in this diagram:
Click image to enlarge
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
Acid rain is caused by compounds such as sulfur dioxide and nitrogen oxides that are released into the air. They can rise very high into the atmosphere and react with the environment to form more pollutants. These acidic polutants fall out and produce an acid rain. Sulfur dioxide and nitrogen oxides dissolve easily in water and can be spread very far by the wind. These compounds become part of the rain and snow. Human activities, primarily manufacturing, are the main cause of acid rain.
What Happens to Our Fresh Water?
First published: 2006