More than half of the original wetlands in the United States have been drained or otherwise destroyed, mostly due to encroachment by agriculture, logging, industrial development and housing. Approximately 60,000 acres continue to be destroyed annually. Even where wetlands are protected, they are often subject to industrial pollution and agricultural runoff. Because they tend to be low-flow environments, they can retain pollutant can be retained in wetland ecosystems for extended periods of time. These pollutants poison individual species and disrupt reproduction.
According to the U.S. Fish and Wildlife Service, approximately 43 percent of threatened species rely on wetlands for survival. Because the wetlands are among the most biologically diverse ecosystems on the planet, their degradation and destruction can result in significant loss of biodiversity. Wetlands serve as stopover sites and nesting sites for migratory birds and as spawning sites for numerous fish species. Destruction of wetlands can lead to degradation of ecosystems across broad surrounding geographical areas, along with the loss of habitat for numerous mammal, fish, bird and amphibian species.
Wetlands play an important role in the broader environment that surrounds them. Therefore, problems affecting wetlands also affect a broad range of ecosystems. Wetlands act as natural filters, with plants and animals processing water, extracting excess nutrients and breaking down pollutants. By holding water in place, wetlands also allow underground aquifers to recharge, moderating river flows in the process and reducing opportunities for flooding. When located at the margins of large bodies of water, wetlands reduce erosion of shorelines. When wetlands are drained, the environmental consequences can include more downstream pollution, reduced freshwater resources, increased flooding and increased erosion.
Signifying their productivity, wetlands hold between 10 and 20 percent of the world's terrestrial carbon. When they are destroyed, the carbon held in plant matter decomposes and is released into the environment as carbon dioxide. But when they are healthy, wetlands act as a carbon sink, absorbing atmospheric carbon and reducing the greenhouse effect. Maintaining viable wetlands is a key step toward reducing the effects of global warming.