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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology
The United States has about 39.9 million acres of lakes (excluding the Great Lakes). Of the 18 million acres assessed by the states in 1992, 35 percent failed to meet designated use criteria at times, 9 percent frequently failed to meet designated use criteria, and less than 1 percent of the lakes could not be used at all due to irreversible natural conditions or human activity. Metals and nutrients are the most common causes of nonsupport. An example of metal problems is the accumulation of excessive amounts of mercury in top predator game fish in lakes throughout the Northern Hemisphere. More than 33 states have issued fish consumption advisories because of elevated concentrations of mercury in game fish.
Nutrient problems were reported widely by states. Forty-five states reported that agricultural runoff is the leading source of pollutants, impairing more lake acres than any other source. Agricultural runoff includes nutrients, organics, and pesticides. Thirty states reported that siltation impaired lakes and reservoirs. Priority organic chemicals, such as PCBs (polychlorinated biphenyls), were reported as significant in the number of lake acres they impaired (ranking eighth).
Another indicator of water quality problems in lakes is the growth of organizations such as the North American Lake Management Society (NALMS) that resonate a strong societal concern. By 1994, NALMS had 20 state chapters comprised of local citizens interested in solving or preventing lake water quality problems. NALMS has actively promoted the involvement of citizens in lake sampling under the umbrella of government environmental agencies. The number of volunteers trained in lake sampling is impressive: 600 in Wisconsin, 3,000 in Texas, and 1,500 in Florida.
When European settlers first arrived in America, about 89 million hectares of wetlands existed in what would eventually become the conterminous states. Today, more than half of the original wetlands have been destroyed by filling, draining, polluting, channelizing, clearing, and other modifications resulting from human activities. In their water quality assessments for the Clean Water Act, 27 states listed agriculture and commercial development as the leading cause of wetland loss. Of 14 states that identified sources of pollutants that degrade wetlands, 11 ranked agriculture as the number one source. Agricultural runoff includes excessive levels of nutrients, organic matter, and pesticides. A U.S. Fish and Wildlife Service study of wetland loss found that 1.1 million hectares of wetlands were lost over a nine-year period (mid-1970s to mid-1980s), or about 117,000 hectares per year. Although this is a seemingly unacceptable rate of loss, it is an improvement compared with the 1950s to 1970s,