title: A synthesis of terrestrial mercury in the western United States: Spatial distribution defined by land cover and plant productivity.
abstract: A synthesis of published vegetation mercury (Hg) data across 11 contiguous states in the western United States showed that aboveground biomass concentrations followed the order: leaves (26μgkg(-1))~branches (26μgkg(-1))>bark (16μgkg(-1))>bole wood (1μgkg(-1)). No spatial trends of Hg in aboveground biomass distribution were detected, which likely is due to very sparse data coverage and different sampling protocols. Vegetation data are largely lacking for important functional vegetation types such as shrubs, herbaceous species, and grasses. Soil concentrations collected from the published literature were high in the western United States, with 12% of observations exceeding 100μgkg(-1), reflecting a bias toward investigations in Hg-enriched sites. In contrast, soil Hg concentrations from a randomly distributed data set (1911 sampling points; Smith et al., 2013a) averaged 24μgkg(-1) (A-horizon) and 22μgkg(-1) (C-horizon), and only 2.6% of data exceeded 100μgkg(-1). Soil Hg concentrations significantly differed among land covers, following the order: forested upland>planted/cultivated>herbaceous upland/shrubland>barren soils. Concentrations in forests were on average 2.5 times higher than in barren locations. Principal component analyses showed that soil Hg concentrations were not or weakly related to modeled dry and wet Hg deposition and proximity to mining, geothermal areas, and coal-fired power plants. Soil Hg distribution also was not closely related to other trace metals, but strongly associated with organic carbon, precipitation, canopy greenness, and foliar Hg pools of overlying vegetation. These patterns indicate that soil Hg concentrations are related to atmospheric deposition and reflect an overwhelming influence of plant productivity - driven by water availability - with productive landscapes showing high soil Hg accumulation and unproductive barren soils and shrublands showing low soil Hg values. Large expanses of low-productivity, arid ecosystems across the western U.S. result in some of the lowest soil Hg concentrations observed worldwide.
authors.affiliation: Desert Research Institute, Division of Atmospheric Sciences, 2215 Raggio Parkway, Reno, NV 89512, United States. Electronic address: daniel.obrist@dri.edu.
authors.forename: Daniel
authors.initials: D
authors.lastname: Obrist
authors.affiliation: Desert Research Institute, Division of Hydrologic Sciences, 2215 Raggio Parkway, Reno, NV 89512, United States.
authors.forename: Christopher
authors.initials: C
authors.lastname: Pearson
authors.affiliation: Civil, Environmental and Architectural Engineering, University of Colorado at Boulder (UCB), 428, Boulder, CO 80309, United States.
authors.forename: Jackson
authors.initials: J
authors.lastname: Webster
authors.affiliation: U.S. Geological Survey, National Research Program, 3215 Marine St., Boulder, CO 80303, United States.
authors.forename: Tyler
authors.initials: T
authors.lastname: Kane
authors.affiliation: Department of Civil and Environmental Engineering, Lamar University, Beaumont, TX 77710, United States.
authors.forename: Che-Jen
authors.initials: CJ
authors.lastname: Lin
authors.affiliation: U.S. Geological Survey, National Research Program, 3215 Marine St., Boulder, CO 80303, United States.
authors.forename: George R
authors.initials: GR
authors.lastname: Aiken
authors.affiliation: U.S. Geological Survey, California Water Science Center, 6000 J Street, Placer Hall, Sacramento, CA 95819, United States.
authors.forename: Charles N
authors.initials: CN
authors.lastname: Alpers
mesh_terms: D004784:Environmental Monitoring; D008628:Mercury / Q000032:analysis* / Q000378:metabolism*; D015205:Northwestern United States; D010944:Plants / Q000378:metabolism*; D012989:Soil Pollutants / Q000032:analysis*; D015206:Southwestern United States
chemical_list: D012989:Soil Pollutants; D008628:Mercury
keywords: Landscape gradients; Plant pump; Soil pollution; Trace metals; Western North American mercury synthesis; Wnams