Continued Strengthening of the Clean Water Act
Reflects the Public's Concern for Clean Water
The Water Pollution Control Act of 1948 or "Clean Water Act" and its subsequent amendments through 1987 demonstrate strong congressional determination to improve the quality of our water resources. These laws have done much to clean up point source contaminants by requiring states to establish and enforce water quality standards, by requiring specifications and licensing for the discharge of effluents, and by funding the installation of municipal sewage treatment plants. As a result of the cleanup of concentrated pollution from specific sites, nonpoint source pollutants, which are typically dispersed in origin, have increased in relative importance and now account for more than 50% of the pollution in our nation's waters. Nonpoint source pollutants include sediment, nutrients, pesticides, animal wastes and other substances which enter our water supply as components of runoff and groundwater flow.
Excess Nitrogen and Phosphorous Spur Algal Growth, Deplete Oxygen and Kill Fish
Aquatic plants, like their terrestrial counterparts, require nutrients to grow and reproduce. The growth of algae and other vegetation in water bodies is usually controlled by the nutrient whose supply is most limited. This concept, first described by Justis Liebig in 1840, is known as "Liebig's Law of the Minimum". Phosphorous is usually the limiting nutrient in brackish or freshwater, while nitrogen is usually the limiting nutrient in saltwater. When excess nutrients applied to the land in the form of manure or commercial fertilizer find their way into the water, blooms or overabundant growth of algae and other aquatic plants can result. Algal blooms at the surface can interfere with photosynthesis of submerged plants by blocking sunlight, causing them to die. When this happens, dissolved oxygen levels near the bottom drop abruptly because oxygen because oxygen demand by decomposing bacteria is great while little or no oxygen is being produced by the dying plants. The problem is compounded when organisms which flourish in oxygen starved environments release hydrogen sulfide and methane. These substances are toxic to fish and other aquatic life.
Photo upper right: Dense algal growth from excess nutrients blocks sunlight, causing submerged plants to die.
Excessive algal growth in estuaries can result in decline of Eelgrass and the loss of shellfish beds. Shellfish die and the beds fail to recolonize when thick layers of algae prevent animals such as oysters from pumping water through their bodies to provide adequate food and oxygen. Eelgrass, a submerged grass eaten by many waterfowl, is lost when floating algal mats and or phytoplankton in the water reduce light penetration and interfere with photosynthesis.
Photo right: Aquatic grasses are important to the food web.
Some species of fish, as well as other animals lower in the food chain, are very sensitive to low levels of oxygen or food and generally die. The loss of species simplifies the food chain of an ecosystem and makes it more vulnerable to further destruction.
Many species, including fish, are sensitive to low oxygen levels and die as a result.
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