Trees,
shrubs, and grasses filter out much of the nitrate and atrazine residues before
they reach water supplies. Source: Iowa State University, 1993. Trees,
shrubs, and grasses filter out much of the nitrate and atrazine residues before
they reach water supplies. Source: Iowa State University, 1993.
Loss of part of an ecosystem affects everything else in that system. This can be seen with the disappearance of natural riparian zones, which has resulted in increased non-point source (NPS) pollution of surface and ground water, streams that are wide, deep and flood-prone, and loss of wildlife habitat throughout the Midwest. This loss of buffer protection contributes to serious environmental problems.
Increased water pollution
NPS pollution does not come from a specific source such as a sewage lagoon outlet pipe or a smokestack. Instead, NPS pollution is a general presence of pollutants, such as soil sediment, fertilizers, pesticides, and herbicides, whose specific source is difficult to pinpoint. This type of pollution is a serious concern in the Midwest because water in many streams is unfit for human consumption, livestock, or recreational use, and these streams cannot support fish or other aquatic life that they once did. Studies have shown that more than 60 percent of the nation's water pollution is NPS pollution. Estimates may be even higher in the Midwest due to its largely rural population and few heavy industries.
Sediment. Sediment in stream water is produced by storm runoff from fields, collapsed streambanks, or "dust" blown in from adjacent fields. According to the U.S. Department of Agriculture, 64 percent of sediment found in streams is from crop and range land. A large amount of sediment entering a stream can kill aquatic plants, an important food source, by blocking sunlight. It can disrupt feeding and reproduction of many fish species by covering the natural gravel stream bed. Heavy sediment loads gradually fill the channel, which contributes to increased flooding. Sediment also must be removed from drinking water.
Fertilizers. An excess of nitrogen or phosphorous may cause accelerated growth of algae and other aquatic plants, producing algae blooms in surface waters. This dense plant growth reduces oxygen available to other aquatic life. Nitrate, the form of nitrogen that moves most easily from agricultural fields into streams, also is dangerous to human and animal health. When dissolved in drinking water, nitrate is converted to nitrite, which makes hemoglobin cells in the blood unable to carry oxygen. This condition causes brain damage and death by suffocation in babies under six months of age and newborn livestock.
Because of these problems, the U.S. Environmental Protection Agency (EPA) has established 10 parts per million (ppm) as the allowable limit for nitrate in drinking water. This level often is exceeded in Midwestern states, especially during late spring and summer months. Field tile lines, a major source of high nitrate water, often have nitrate concentrations of 15 to 25 ppm, and have been measured as high as 80 to 90 ppm during the growing season.
Usually phosphorus is attached to soil particles and, thus, enters streams with eroded soil from surface runoff. It is not found in field tile water in significant amounts.
Pesticides and herbicides. Pesticides and herbicides are poisons that disrupt natural biological processes and they are effective in controlling unwanted pests and weeds. After application, many pesticides and herbicides are bound to soil particles, thus, if soil erodes from a field and enters a stream, the pollutant also will enter. Their presence in a water system can be lethal and is difficult to predict or trace. A 1985 study found eight pesticides in groundwater that supplies public wells in 31 Iowa counties. Another survey showed 53 percent of Iowa wells had detectable pesticide residues.