Improving Water Quality and Hydrology

Wetlands are valuable to us because they greatly influence the flow and quality of water. They help improve water quality, including that of drinking water, by intercepting surface runoff and removing or retaining inorganic nutrients, processing organic wastes, and reducing suspended sediments before they reach open water. For example, as the runoff water passes through wetlands, they retain or process excess nitrogen and phosphorus, decompose organic pollutants, and trap suspended sediments that would otherwise clog waterways and affect fish and amphibian egg development.

In performing this filtering function, wetlands save us a great deal of money. A 1990 study showed that, the Congaree Bottomland Hardwood Swamp in South Carolina, removes a quantity of pollutants that would be equivalent to that removed annually by a $5 million waste water treatment plant. Another study at a 2,500 acre wetland in Georgia, indicated that it saves $1 million in water pollution abatement costs annually. Wetlands also reduce environmental problems, such as algal blooms, dead zones, and fish kills, that are generally associated with excess nutrient loadings. However, the capacity of wetlands to function this way is not unlimited, and too much surface runoff carrying sediments, nutrients, and other pollutants can degrade wetlands and thus the societal services they provide.

In addition to improving water quality through filtering, some wetlands maintain stream flow during dry periods; others replenish groundwater. Many Americans, of course, depend on groundwater for drinking. The Floridian aquifer system, for instance, is one of the more productive ground water sources in the United States. It occurs across the entire state of Florida, and into southern Georgia, and portions of South Carolina and Alabama. This huge subsurface reservoir produces some of the cleanest water in the nation. Its primary source is rainwater that filters through hundreds of feet of sand and rock. One calculation for 5-acre Florida cypress swamp recharging groundwater was that, if 80 percent of swamp was drained, available ground water would be reduced by an estimated 45 percent.