Polluted runoff comes in various forms and causes a series of problems. Soil sediment from sources such as plowed fields and construction sites can destroy fish habitat and kill aquatic life. Pesticides swept from fields and lawns into water bodies can increase the risks of cancer and birth defects in human beings. Excess nutrients, such as nitrogen and phosphorus from fertilizers applied to lawns and crops, feed algae blooms that can prevent people from swimming and can kill fish and other aquatic life by robbing the water of oxygen. Heavy metals such as lead and copper, which can come from mining and industrial processes, along with bacteria and pathogens from various sources also make their way into waterways through polluted runoff where they can cause a variety of human health problems.
Wetlands are a vital line of defense in protecting water quality from polluted runoff.
Because of their crucial position between water and land, wetlands function as a buffer zone that intercepts and filters polluted runoff before it can degrade rivers, lakes, and coastal areas. Dense wetland vegetation improves the clarity and health of receiving waters by trapping sediment and pollutants. Wetland microorganisms and plants remove excess nutrients from water and store them in cell tissue, which ultimately decomposes into soil rich in organic matter, or return them to the atmosphere as harmless gas. Wetlands also filter pesticides and heavy metals from water, and microbial action taking place on wetland bottoms can reduce water-borne bacterial contamination significantly. By filtering these pollutants from America's waters, wetlands help to safeguard drinking water sources.