Functioning in very much the same manner as floodplain wetlands, some of these upland wetlands help regulate water levels in aquifers. 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. 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.
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.