PUB00012

• Year: 1999
• Title: Sustainability of Ground-Water Resources: U.S. Geological Survey Circular 1186
• CWCB Section: Interstate & Federal
• Author: William M. Alley, Thomas E. Reilly, O. Lehn Franke
• Description: Illustration of the hydrologic, geologic, and ecological concepts to assure wise and sustainable use of ground-water resources
• Publications - Doc Type: Historical

Wetlands

Wetlands are present wherever topography
and climate favor the accumulation or retention
of water on the landscape. Wetlands occur in
widely diverse settings from coastal margins
to flood plains to mountain valleys. Similar
to streams and lakes, wetlands can receive
ground-water inflow, recharge ground water,
or do both. Wetlands are in many respects ground-
water features.
Public and scientific views of wetlands
have changed greatly over time. Only a few
decades ago, wetlands generally were considered
to be of little or no value. It is now recognized that
wetlands have beneficial functions such as wildlife
habitat, floodwater retention, protection of the
land from erosion, shoreline protection in coastal
areas, and water-quality improvement by filtering
of contaminants.
The persistence, size, and function of
wetlands are controlled by hydrologic processes
(Carter, 1996). For example, the persistence of
wetness for many wetlands is dependent on a rela-
tively stable influx of ground water throughout
changing seasonal and annual climatic cycles. Char-
acterizing ground-water discharge to wetlands and
its relation to environmental factors such as mois-
ture content and chemistry in the root zone of

wetland plants is a critical but difficult to charac-
terize aspect of wetlands hydrology (Hunt and
others, 1999).

Wetlands can be quite sensitive to the
effects of ground-water pumping. Ground-water
pumping can affect wetlands not only as a result
of progressive lowering of the water table, but
also by increased seasonal changes in the altitude
of the water table. The amplitude and frequency
of water-level fluctuations through changing
seasons, commonly termed the hydroperiod, affect
wetland characteristics such as the type of vegeta-
tion, nutrient cycling, and the type of inverte-
brates, fish, and bird species present. The effects
on the wetland environment from changes to the
hydroperiod may depend greatly on the time of
year at which the effects occur. For example, lower
than usual water levels during the nongrowing
season might be expected to have less effect on the
vegetation than similar water-level changes
during the growing season. The effects of
pumping on seasonal fluctuations in ground-
water levels near wetlands add a new dimension
to the usual concerns about sustainable develop-
ment that typically focus on annual withdrawals
(Bacchus, 1998).

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