Wetlands such as marshes, swamps and artificial wetlands, have been shown to remove selected pollutants from urban stormwater runoff and treated municipal wastewaters. Wetlands have produced reduction in BOD, pathogens, and some hydrocarbons, and excel in nitrogen removal. They have been reported to act as sinks for trace metals, phosphorus and suspended solids. Physical pollutant removal mechanisms in wetlands include sedimentation, coagulation, chemical filtration, volatilization, adsorption and chelation. Vegetative mechanisms include absorption through roots, stems and leaves, filtration and chemical transformations in the plants. Although individual plant species have been studied for their pollutant removal properties, the interaction of numerous plant and animal species in pollutant removal in a wetland is not well understood.