Wetlands are sometimes called the "kidneys of the landscape." They serve as natural filters, removing pollution from waters flowing through them, while purifying and recharging aquifers below. Water is cleansed as wetland soils and vegetation trap sediments, heavy metals and pathogenic microbes. Wetlands also sift out nutrients such as nitrogen and phosphorus that cause eutrophication - the increased production of organic matter that can degrade water quality and threaten fisheries. The economic value of this natural filtering is immense, reducing the need for costly water purification facilities.
Aquatic plants such as water hyacinths are adept at absorbing pollutants and nutrients, although they can interfere with navigation if allowed to spread unchecked. A study that evaluated a proposal to use Florida's cypress swamps for treating domestic wastewater concluded that 98 percent of all nitrogen and 97 percent of all phosphorous was removed from the waste stream before it entered groundwater supplies. Although this research highlights the impressive water-cleansing abilities of wetlands, that does not mean that beautiful cypress swamps should be converted, as a matter of course, into sewage treatment facilities.
Flood control is yet another important service provided by wetlands. Coastal marshes absorb the main brunt of ocean storms, serving as giant buffers that protect shorelines from wave erosion. Inland wetlands act like sponges, sopping up water from rain and overflowing rivers and storing it in temporary reservoirs, thereby retarding the flow of floodwaters. Since most flood damage is caused by peak flows, wetlands help by changing sharp runoff peaks into slower discharges. One study showed that draining 8600 acres of floodplain wetlands along the Charles River Basin in Massachusetts would increase flood damages by $17 million per year. Those numbers need to be revised dramatically upward, given that the analysis was performed almost 30 years ago. Another study found that restoration of 13 million acres of wetlands along the Mississippi river (at an unknown cost) could have prevented $15.7 billion in flood damages in 1993.
During dryer periods, wetlands perform the opposite role: They can mitigate droughts by storing water during the wettest times of the year and slowly releasing it during the driest times.
Astronomers investigating the possibility of life on other planets are well aware of the importance of water for supporting life as we know it. But on this planet, wetlands are unrivaled in their ability to regulate the flow of this precious liquid, insure its quality and make it available to a vast number of users.
More than half of the wetlands in the United States have been lost to human activities and as much as 90 percent of the wetlands in states such as California and Ohio have been wiped out.