HR: 0800h
AN: H21F-1100    [Abstracts]
TI: Impact of Land use Change From Natural to Agricultural Ecosystems on Groundwater Recharge
AU: * Scanlon, B R
EM: bridget.scanlon@beg.utexas.edu
AF: Jackson School of Geosciences, Bur. of Econ. Geol., Univ. of Texas at Austin, 10100 Burnet Rd, Austin, TX 78758
AU: Reedy, R C
EM: bob.reedy@beg.utexas.edu
AF: Jackson School of Geosciences, Bur. of Econ. Geol., Univ. of Texas at Austin, 10100 Burnet Rd, Austin, TX 78758
AU: Stonestrom, D A
EM: dastones@usgs.gov
AF: U.S. Geological Survey, Water Resources Division, Bldg. 15, McKelvey Building 345 Middlefield Road, Menlo Park, CA 94025-3591
AB: Recharge is a critical component of the water cycle for groundwater resources. The purpose of this study was to evaluate the impact of land use changes from natural to agricultural ecosystems on groundwater recharge in the Amargosa Desert, Nevada and Southern High Plains, Texas. A variety of approaches were used to evaluate groundwater recharge, including noninvasive electromagnetic induction, matric potential monitoring, and chloride and nitrate profiles. The results of the study indicate that recharge is highly correlated with land use: negligible recharge beneath natural ecosystems, moderate recharge beneath nonirrigated agricultural ecosystems, and augmented but variable recharge beneath irrigated agricultural 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 nonirrigated 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 in the Amargosa Desert. However, lower irrigation application rates result in negligible drainage below the root zone beneath center pivot irrigation systems in the Southern High Plains as shown by matric potential monitoring. Noninvasive EM induction proved useful in distinguishing subsurface flow beneath natural and nonirrigated agricultural areas and may be used as a reconnaissance tool to map the effects of agriculture on subsurface water movement. The point data from the vadose zone are consistent with regional increases in groundwater levels of 10 - 20 m during the last 30 to 50 yr beneath nonirrigated agricultural regions in the Southern High Plains. Degradation of groundwater quality over that time may be attributed to flushing of salts into the underlying aquifer. Combining different approaches for estimating groundwater recharge provides a more comprehensive understanding of the impacts of land use change on groundwater recharge over different space and time scales. Understanding forcings and feedbacks between land use change and recharge is critical for optimal management of groundwater quantity and quality in the southwestern United States.
DE: 1803 Anthropogenic effects
DE: 1829 Groundwater hydrology
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting