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Integrated Field Lysimetry and Porewater Sampling for Evaluation of Chemical Mobility in Soils and Established Vegetation
Published on: July 4, 2014
Unsaturated zone arsenic distribution and implications for groundwater contamination
Robert C Reedy1, Bridget R Scanlon, Jean-Philippe Nicot
1John A. and Katherine G. Jackson School of Geosciences, Bureau of Economic Geology, The University of Texas, University Station, Box X, Austin, Texas 78713-8924, USA. bob.reedy@beg.utexas.edu
Environmental Science & Technology
|November 13, 2007
Summary
Agricultural arsenic applications in Texas cotton fields did not contaminate the Ogallala aquifer. Soil analyses show arsenic accumulation in the upper meter, linked to fertilizers, not groundwater contamination.
Area of Science:
- Environmental Science
- Geochemistry
- Agricultural Science
Background:
- Arsenic compounds have been globally applied to land surfaces as pesticides in agriculture.
- The Ogallala aquifer in the Southern High Plains (SHP), Texas, faces contamination, with 36% of wells exceeding the EPA's 10 microg/L standard.
- Understanding the fate of agricultural arsenic is crucial for assessing its impact on groundwater quality.
Purpose of the Study:
- To evaluate the fate of anthropogenic arsenic applications from agriculture.
- To investigate potential linkages between agricultural arsenic use and Ogallala aquifer contamination in the SHP.
- To differentiate between geogenic and anthropogenic arsenic sources in agricultural soils.
Main Methods:
- Collection and analysis of unsaturated zone soil samples from boreholes beneath natural ecosystems (control) and cotton cropland in the SHP.
- Analysis of water-extractable arsenic, vanadium, phosphate, chloride, and nitrate in soil samples.
- Geographic Information System (GIS) analyses to correlate groundwater arsenic with land use, nitrate, and water table depth.
Main Results:
- Arsenic concentrations in natural ecosystems were high at depth, attributed to a geologic source.
- Cotton cropland soils showed elevated arsenic in the upper meter, correlating with phosphate and attributed to anthropogenic application.
- High arsenic concentrations below 1 meter in cropland soils were geogenic, predating agricultural applications.
- GIS analyses revealed poor correlations between groundwater arsenic and cultivated land, nitrate, or water table depth.
Conclusions:
- Anthropogenic arsenic from agricultural practices is primarily retained in the shallow subsurface (upper meter) of cotton fields.
- Geologic arsenic sources contribute to higher concentrations at greater depths in both natural and agricultural soils.
- Agricultural arsenic applications in the studied region are not linked to the contamination of the underlying Ogallala aquifer.
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