GROUND
WATER RECHARGE
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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