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The Wetlands & Water Resources

The waters in wetlands generally aren't quite deep enough to support large-scale transportation, don't host great game fisheries and move so slowly they seem to just stand there growing weeds, muck, bugs and reptiles. They're known by names like "swamp," "marsh," "bog" and "drowned lands." Until the last quarter of the 20th century, the general impulse was to drain them and try to recover their open expanses for agriculture. In the last decades, however, the world has discovered that wetlands play vital roles in retaining and purifying water resources, especially when they stand between agricultural land use and rivers, lakes and seas.

Water for the Birds
- The U.S. Geological Survey has documented the exemplary history of the Horicon Marsh in Wisconsin, which was dammed and flooded in 1846 to create a 56-square-mile lake that supported commercial transportation and fishing for a quarter of a century. It was returned to swamp in 1869, but its value was measured in waterfowl hunted there and fur-bearing animals trapped. In the early 20th century, the marsh was partially drained for agriculture, but the plan fell apart when the Horicon couldn't be completely drained. Beginning in the 1920s and culminating in 1990, the area has been preserved as wetlands, but for its value as bird habitat.
Collecting Sediment
- The slow pace at which water moves through wetlands provides time for silt and mud from upstream to settle out. This improves the quality of the water that leaves the wetland and eventually enters larger bodies of water with more plants and animals that depend on light and oxygen coming through those waters. If the wetlands are near the edges of larger bodies, their entrapment of silt also slows erosion of the shorelines.
Filtering Human Pollution
- When people add chemical nutrients to farmland, irrigation water carries excess downstream. If these extra plant nutrients make it all the way to larger bodies of water, they can make the waters unsuitable to support anything but algae by depleting the water of oxygen. If the water passes through wetlands, however, the slow pace allows the nutrients to settle out with the silt and to be captured by wetland plants and microbes that are already adapted to oxygen deprivation. Because the soil under a wetland is saturated with water for more of the year than other soils, it contains less oxygen.
Storing Water
- The slowdown of water passing through wetlands, spreading the flow of a narrow stream or river out across a wider area, can lessen the effects of flooding. This can work with water coming downstream or a storm surge heading upstream from a hurricane or tropical storm. A typical wetland can accommodate an extra three feet of water across its acres, which could be surging over the banks of a river. Water slowed down as it crosses wetlands also has the time to seep into groundwater stores under the wetland and then into aquifers.

Nature