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From
Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
2004 GSA Annual Meeting, Denver, Colorado, November 7–10, 2004 Impact
of Land-Use Change on Groundwater Recharge Bridget R. Scanlon, Robert C. Reedy, and David A. Stonestrom Abstract: Recharge is a critical component of the water cycle for assessing sustainable water resources. Most recharge studies have focused on natural ecosystems; however, humans have exerted large-scale changes on terrestrial ecosystems in the last century, primarily through agricultural activities. The purpose of this study was to evaluate the effect of land use and land-use change on groundwater recharge using data from natural ecosystems, nonirrigated cultivated (dryland) ecosystems, and irrigated cultivated ecosystems in the Amargosa Desert, Nevada and the Southern High Plains, Texas. Matric-potential and environmental-tracer data from the vadose zone were used as archives of past changes in recharge. The results
of the study indicate that recharge is highly correlated with land use:
negligible recharge beneath natural ecosystems, moderate recharge beneath
dryland ecosystems, and augmented but variable recharge beneath irrigated
ecosystems. Low matric potentials, upward potential gradients, and accumulations
of chloride and nitrate indicate little or no recharge beneath large areas
of native vegetation. High matric potentials, low chloride and nitrate
concentrations, and rising groundwater tables indicate induced recharge
beneath areas of dryland agriculture. High matric potentials and low to
moderate chloride and nitrate concentrations indicate substantially augmented
recharge beneath areas of irrigated agriculture according to type and
amount of irrigation. Conversion of native vegetation to irrigated agriculture
is accompanied by increases in matric potential and downward displacement
of accumulated chloride and nitrate. Induced recharge can flush accumulated
chloride and nitrate to underlying aquifers, impacting water quality.
The varied approaches of this study, which analyzed water-table fluctuations,
matric-potential profiles, and environmental and applied tracers, complement
each other in providing time-integrated and time-resolved information
on the linkages between land use and groundwater recharge. Understanding
these linkages is critical for optimal management of groundwater quantity
and quality in the southwestern United States. |