HR: 1340h
AN: H33E-1692    [Abstracts]
TI: Perchlorate Mobilization Related to Land Use Change in the Southern High Plains, USA
AU: Scanlon, B R
EM: bridget.scanlon@beg.utexas.edu
AF: Jackson School of Geosciences, The University of Texas at Austin, 10100 Burnet Rd., Bldg. 130, Austin, TX 78758, United States
AU: * Reedy, R C
EM: bob.reedy@beg.utexas.edu
AF: Jackson School of Geosciences, The University of Texas at Austin, 10100 Burnet Rd., Bldg. 130, Austin, TX 78758, United States
AU: Jackson, W A
EM: andrew.jackson@ttu.edu
AF: Civil Engineering Dept., Texas Tech University, 10th and Akron, Lubbock, TX 79409, United States
AU: Rao, B
AF: Civil Engineering Dept., Texas Tech University, 10th and Akron, Lubbock, TX 79409, United States
AB: Perchlorate, derived from precipitation and dry fallout, has accumulated in the unsaturated zone in semiarid regions, similar to chloride. Potential impacts of these perchlorate reservoirs on groundwater contamination depend on mobilization. The purpose of this study was to evaluate mobilization of perchlorate reservoirs related to land-use change from natural to agricultural ecosystems based on data from the southern High Plains where large perchlorate concentrations (<e; 60 ppb in groundwater) have been found in the Ogallala aquifer. Boreholes were drilled and sampled beneath natural ecosystems and beneath rainfed and irrigated agricultural ecosystems. Large inventories of perchlorate were found beneath natural grassland and shrubland ecosystems, similar to those found in previous studies in this region (234-1050 g perchlorate per ha; 2.5-7.2 ppb perchlorate in soil pore water). Perchlorate concentrations in these natural profiles is highly correlated with chloride concentrations, suggesting a similar source (precipitation and dry fallout) and evapotranspirative enrichment process over up to ~ 30,000 yr in some profiles. Profiles beneath rainfed agriculture show downward displacement of perchlorate bulges to a maximum depth of 8.3 m in the sampled profiles. High correlations between perchlorate and chloride concentrations in profiles beneath rainfed agriculture indicate that chloride profiles can be used to predict perchlorate mobility. Chloride profiles indicate the perchlorate should be completely flushed through the unsaturated zone in the southeastern part of the study area and partially flushed in other regions of the southern High Plains. Profiles beneath irrigated agriculture are variable. Chloride was completely flushed and there was no detectable perchlorate in one of the profiles, indicating that irrigation return flow had mobilized chloride and perchlorate to the aquifer in this setting. The other profiles did not extend deep enough to determine the fate of the natural salt bulges; however, chloride and perchlorate bulges near the root zone are attributed to more recent deficit irrigation within the last couple of decades that is causing soil salinization. Groundwater perchlorate contamination is likely to increase in the future with more widespread flushing of naturally occurring perchlorate beneath cultivated regions.
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1813 Eco-hydrology
DE: 1831 Groundwater quality
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: 2007 Fall Meeting