Paper No. 16
Presentation Time: 9:00 AM-6:30 PM


ANDRASKI, Brian J.1, JACKSON, W. Andrew2, WELBORN, Toby L.1, STONESTROM, David A.3 and BOHLKE, J.K.4, (1)US Geological Survey, 2730 N Deer Run Rd, Carson City, NV 89701, (2)Department of Civil Engineering, Texas Tech University, Lubbock, TX 79409-1023, (3)US Geological Survey, 345 Middlefield Road MS-420, Menlo Park, CA 94025, (4)U.S. Geological Survey, 431 National Center, 12201 Sunrise Valley Dr, Reston, VA 20192,

Growing concern about perchlorate (ClO4) contamination of drinking water and food has heightened the need for improved understanding of its natural occurrence. Natural ClO4 is being studied at the USGS Amargosa Desert Research Site to determine factors and processes that control its distribution in a desert-shrub landscape. Total atmospheric deposition measured approximately quarterly over 6 yr had an average ClO4 concentration of 608 ng L−1 and the flux was 300 mg ha−1 yr−1. Comparisons between total deposition results and previous work on wet deposition indicated that dry deposition could be an important contributor to the occurrence of ClO4 in arid environments. Feature-based sampling was used to evaluate the effects of landscape setting (shoulder slope, footslope, and valley floor) and plant proximity (far versus near) on shallow (0-30 cm) soil ClO4. Soil-ClO4 concentrations and Cl/ClO4 molar ratios ranged from 0.26–5.00 μg kg−1 and 3300–84,300 mol mol1, respectively. Valley floor concentrations showed a large (~20 fold) decrease near plants, but those for the shoulder and footslope increased (~2 fold) near plants. These increases were attributed to a reduction in near-plant soil leaching and increased accumulation of ClO4 from a bioconcentrated-leaf source. Bioaccumulation was indicated by high leaf-ClO4 concentrations (14,000–60,000 μg kg−1) and low leaf-Cl/ClO4 molar ratios (60–180 mol mol1). Grid-based sampling was used to assess soil, plant, and terrain influences on soil and leaf ClO4 concentrations across a 9-ha hillslope. Soil and leaf concentrations ranged from 0.82–11.81 μg kg−1 and 9700–59,000 μg kg−1, respectively. Regression results for soil ClO4 identified elevation and slope gradient as significant variables that explained 42% of the variation; both variables are suggestive of processes affecting deposition and transport of ClO4 by wind or water. For leaf ClO4, 74% of the variation was explained by elevation, soil CO3-C, soil total-organic C, and aspect. The soil variables indicated caliche and organic matter influences on ClO4 uptake, and aspect was related to shrub growth and ClO4 bioaccumulation. This study provides a framework for improved understanding of the interactive factors and processes that control the distribution of ClO4 in a desert landscape.