An area where water covers the soil or is present at or near the surface for all or part of the year, supporting hydrophytic vegetation and hydric soils. Wetlands provide critical ecosystem services including flood storage, water filtration, and biodiversity habitat.
A wetland is an ecosystem characterized by the presence of water at or near the land surface for a sufficient duration to develop hydric soils (saturated, anaerobic conditions), support hydrophytic vegetation (plants adapted to wet conditions), and drive distinctive biogeochemical processes. Wetland types include marshes (herbaceous vegetation), swamps (forested), bogs (acidic, peat-accumulating, precipitation-fed), and fens (alkaline, groundwater-fed). Wetlands occupy roughly 5-8% of the Earth's land surface and provide ecosystem services disproportionate to their area, including flood peak reduction (a single acre of wetland can store up to 1.5 million gallons of floodwater), water quality improvement through sediment trapping, nutrient uptake, and pollutant transformation, shoreline stabilization, groundwater recharge, carbon sequestration, and habitat for a third of all threatened and endangered species in the United States. Despite their value, approximately 53% of the original wetland area in the conterminous United States was lost between the 1780s and 1980s, primarily due to agricultural conversion and urban development. The Clean Water Act Section 404 regulates the discharge of dredged and fill material into wetlands, requiring permits from the U.S. Army Corps of Engineers. Wetland mitigation banking and in-lieu fee programs provide mechanisms for compensating unavoidable wetland losses, though the ecological equivalency of created or restored wetlands to natural ones remains debated.