WATER QUALITY

The presence of riparian hydrophytic vegetation, along with the storage capacity of floodplain wetlands, has a number of effects on not only the flow rates of floods but also on the affects floods have on streams themselves and their surrounding environment. Vegetation in floodplain wetlands increases resistance to flood waters which reduces flood velocity. This slowing of flood waters causes suspended sediment particles to settle out onto the floodplain, reducing sediment loads carried by the main stream. The reduction of sediment loads carried by streams is crucial to maintaining healthy stream ecology, providing clean water supplies, maintaining the ability of the river to scour itself, and extending the longevity of navigation channels and downstream dams. Reducing sediment loads through this process not only efficiently improves the quality and condition of streams, it also enriches the riparian floodplains by depositing fresh silt upon which additional hydrophytic plants may grow (Illinois Department of Natural Resources 1994 and Mitsch and Gosselink 1986).

In wetlands, chemicals become entrapped and broken down by microorganisms living in the sediment while wetland vegetation uses any available excess nutrients to enhance their growth. Various studies have concluded different wetland types can filter out as much as 80-90 percent of dissolved nutrients such as phosphorous and nitrogen. By removing and utilizing excess nutrients, chemicals, and particulate matter from runoff and flood waters, wetlands act as nutrient sinks and settling ponds. In fact, the purifying effects of wetlands are so effective that some inland marshes are used as tertiary treatment for sewage treatment facilities, and many "artificial" wetlands are being created, to perform similar treatment functions for industrial processes (Illinois Department of Natural Resources 1994, Mitsch and Gosselink 1986, and U.S. Environmental Protection Agency 1993).

[ Introduction | Biological Functions | Threatened & Endangered Species | Hydrological Functions |  Water Quality | Ground Water Recharge | Terrestrial Functions | Aesthetics & Recreation   |  Economics | Conclusion ]

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