Wetlands remove 70% to 90% of the nitrogen from the water. Riparian forests can reduce the nitrogen by 90% and phosphorus by 50%. Scientists have estimated that the mean retention of phosphorus by wetlands is 45%. Wetlands with high concentrations of aluminum in the soil can remove 80% of total phosphorus from the water. Ranchers and watershed managers in the West are using beavers to improve water quality. The beavers create wetlands by building damns which can be extremely useful. Wetlands made by beavers retain 1000 times more nitrogen than streams that are not dammed by the beavers.
Suspended solids such as sediment and organic matter may enter wetlands through runoffs, as particulate litter fall. Sediment deposition depends on water velocity, flooding regime, area vegetation, and water retention time. The deposit of sediments in wetlands prevents a source of turbidity from entering downstream ecosystems. The vegetation in wetlands generally traps 80 to 90% of sediment runoff. 65% of the eroded sediment from upland watersheds is deposited in wetlands. .
Sediment runoff from parking lots, roads, and other urban structures may contain petroleum-based contaminants. Oils, gasoline, or grease are examples of petroleum-based runoffs. Agricultural area sediments may contain fertilizers, insecticides, and pesticides. The introduction of these sediments into a wetland may affect any of the following functions provided; water quality protection, flood storage, and hydrophytic vegetation.
Wetlands remove pathogens from the waters. Fecal coliform bacteria and protozoan are a threat to human health. These pathogens come from municipal sewage, urban storm water, leaking septic tanks, and agricultural runoff. Bacteria in the waters of wetlands attach to the suspend solids that are trapped in vegetation. Because these pathogens are out of their host organisms, degradation by sunlight, low pH of the water, protozoan consumption, and toxins excreted from the roots of some plants kills them.