Perchlorate (ClO4−) 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 local-scale distribution of shallow-soil (0–30 cm) ClO4− 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 [Larrea tridentata (Sessé & Moc. ex DC.) Coville] ClO4−; and (iii) atmospheric (wet plus dry, including dust) deposition of ClO4− in relation to soil and plant reservoirs and cycling. Soil ClO4− ranged from 0.3 to 5.0 μg kg−1. Within settings, valley floor ClO4− was 17× less near shrubs due in part to enhanced leaching, whereas shoulder and footslope values were ∼2× greater near shrubs. Hillslope regression models (soil, R2 = 0.42; leaf, R2 = 0.74) identified topographic and soil effects on ClO4− deposition, transport, and cycling. Selective plant uptake, bioaccumulation, and soil enrichment were evidenced by leaf ClO4− concentrations and Cl−/ClO4− molar ratios that were ∼8000× greater and 40× less, respectively, than soil values. Atmospheric deposition ClO4− flux was 343 mg ha−1 yr−1, ∼10× that for published southwestern wet-deposition fluxes. Creosote bush canopy ClO4− (1310 mg ha−1) was identified as a previously unrecognized but important and active reservoir. Nitrate δ18O analyses of atmospheric deposition and soil supported the leaf-cycled–ClO4− input hypothesis. This study provides basic data on ClO4− distribution and cycling that are pertinent to the assessment of environmental impacts in desert ecosystems and broadly transferable to anthropogenically contaminated systems.
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Soil, plant, and terrain effects on natural perchlorate distribution in a desert landscape