Because of water-saturation and poor drainage, wetland soils tend to be poor in oxygen. Because of the lack of oxygen, dead plants do not entirely decay and may accumulate as peat . Typically, peat contains a lot of water and carbon, and may be burned as a fuel after drying. If buried deeply, peat may be converted to coal over geologic time. The Florida Everglades, one of largest salt marshes in the world, covers 13,000 km 2 .
Wetlands are also common in northern Minnesota, Wisconsin and Michigan.
Along with rainforests, wetlands are very productive in plant production, which is important in supporting the food chain for many different types of wildlife. Traditionally, wetlands have provided fruits, grains, and fish for humans. Wetlands are also important in absorbing floodwater and biodegrading pesticides and other organic contaminants. Specifically, cities in California, Maryland and Louisiana have found that wetlands are cheap and effective alternatives to sewage treatment plants. In attempts to save wetlands, the Federal government passed laws in 1985 and 1990 to provide incentives for farmers to conserve wetlands.