Soil, Plant, and Terrain Effects on Natural Perchlorate Distribution in a Desert Landscape

Abstract

980Perchlorate (ClO 4 -) is a contaminant that occurs naturally throughout the world, but little is known about its distribution and interactions in terrestrial ecosystems. The objectives of this Amargosa Desert, Nevada study were to determine (i) the localscale distribution of shallow-soil (0-30 cm) ClO 4 -with respect to shrub proximity (far and near) in three geomorphic settings (shoulder slope, footslope, and valley floor); (ii) the importance of soil, plant, and terrain variables on the hillslope-distribution of shallow-soil and creosote bush [ -distribution and cycling that are pertinent to the assessment of environmental impacts in desert ecosystems and broadly transferable to anthropogenically contaminated systems.

Global patterns and environmental controls of perchlorate and nitrate co-occurrence in arid and semi-arid environments

“…Elevated ClO 4 À concentrations also have been reported in the clay hills near Death Valley Lybrand et al, 2013), subsurface salt accumulations in the southwestern U.S. (Rao et al, 2007), surface soils of the Dry Valleys of Antarctica (Kounaves et al, 2010), and surface soils in northeastern China (Ye et al, 2013) and the Amargosa Desert (Andraski et al, 2014). These occurrences have been interpreted to be of natural origin based on the distribution and age of the accumulations and /or the stable isotopic composition of the ClO 4 À and coexisting NO 3 À .…”

“…À is largely produced in the atmosphere and deposited in dry and wet deposition (Rajagopalan et al, 2009;Andraski et al, 2014). It is abiotically stable in most near-surface environments but can be irreversibly reduced biologically under anoxic conditions.…”

“…ClO 4 À is deposited at the Earth's surface by wet and dry atmospheric deposition. Modern ClO 4 À wet deposition rates measured in North America averaged 64 mg/ha-year (Rajagopalan et al, 2009) and total deposition rates measured in the Amargosa Desert (southwestern Nevada) over a 6-year period averaged 343 mg/ha-year (Andraski et al, 2014). Accumulations of ClO 4 À (93-1050 g/ha) have been observed in deep unsaturated-zone salt bulges throughout the southwestern United States (U.S.) that accumulated during the late Quaternary, roughly over the last 100,000-10,000 years based on Cl À deposition rates and inventories (Rao et al, 2007).…”

“…leaves) Voogt and Jackson, 2010), and do not generally appear to transform it substantially (Tan et al, 2006;Seyfferth et al, 2008), although this may occur in some cases (Van Aken and Schnoor, 2002). Bioaccumulated ClO 4 À can be returned to the environment by senescence and leaching of plant tissue (Tan et al, 2004b(Tan et al, , 2006Andraski et al, 2014).…”

“…Ratios for wet deposition include 18 sites located across the conterminous U.S., as well as Alaska, and Puerto Rico for weekly samples over a three year period Rajagopalan et al (2009). The total deposition ratio (green line) represents the 6 year average of quarterly samples Andraski et al (2014). landscape) to the tussock steppe grasslands of the Western Andes Cordillera (4200 m) (Fig.…”