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Wetlands outside of the floodplain can affect the hydrology of a watershed by influencing more than just the flow rates of surface waters. Functioning in very much the same manner as floodplain wetlands, some of these upland wetlands help regulate water levels in aquifers. Maintenance of these aquifers is critical to ensure there is an adequate sustainable groundwater supply for human use (Illinois Department of Natural Resources 1997 and Mitsch and Gosselink 1986).

Many aquifers in Illinois are confined, which means they can not be recharged by surface water sources. The relative thickness of the loess soils generally does not allow water to penetrate down to, or percolate up from, the water table. As a result, a large number of upland wetlands are not associated with groundwater, and only affect surface waters (Admiraal et al. 1997 and Illinois Department of Natural Resources 1994).

Some aquifers in Illinois, however, are unconfined. Consequently, there are wetlands that are strongly associated with groundwater supplies. Wetlands associated with groundwater sources can serve either as recharge zones or discharge zones. Recharge zones are areas where the substrate is permeable enough to allow an aquifer to be refilled by surface waters. Discharge zones are areas where the substrate is permeable enough to allow water from an aquifer to escape and be added to the surface water supply (Admiraal et al. 1997 and Illinois Department of Natural Resources 1994).

Wetlands located above recharge zones are responsible for filling aquifers with filtered, clean water. When these strategically located wetlands are eliminated, the rate at which aquifers are recharged decreases and the quality of water they contain declines. If the pumping exceeds the recharge rate, a process known as overdrafting, the aquifer will eventually be depleted. In Illinois, however, the topography, hydrology, and soil types of the state dictate that wetlands outside of the floodplain are more likely to be discharge areas for groundwater supplies than recharge areas (Admiraal et al. 1997).

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

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