title: Surface-air mercury fluxes across Western North America: A synthesis of spatial trends and controlling variables.
abstract: Mercury (Hg) emission and deposition can occur to and from soils, and are an important component of the global atmospheric Hg budget. This paper focuses on synthesizing existing surface-air Hg flux data collected throughout the Western North American region and is part of a series of geographically focused Hg synthesis projects. A database of existing Hg flux data collected using the dynamic flux chamber (DFC) approach from almost a thousand locations was created for the Western North America region. Statistical analysis was performed on the data to identify the important variables controlling Hg fluxes and to allow spatiotemporal scaling. The results indicated that most of the variability in soil-air Hg fluxes could be explained by variations in soil-Hg concentrations, solar radiation, and soil moisture. This analysis also identified that variations in DFC methodological approaches were detectable among the field studies, with the chamber material and sampling flushing flow rate influencing the magnitude of calculated emissions. The spatiotemporal scaling of soil-air Hg fluxes identified that the largest emissions occurred from irrigated agricultural landscapes in California. Vegetation was shown to have a large impact on surface-air Hg fluxes due to both a reduction in solar radiation reaching the soil as well as from direct uptake of Hg in foliage. Despite high soil Hg emissions from some forested and other heavily vegetated regions, the net ecosystem flux (soil flux+vegetation uptake) was low. Conversely, sparsely vegetated regions showed larger net ecosystem emissions, which were similar in magnitude to atmospheric Hg deposition (except for the Mediterranean California region where soil emissions were higher). The net ecosystem flux results highlight the important role of landscape characteristics in effecting the balance between Hg sequestration and (re-)emission to the atmosphere.
authors.affiliation: US Environmental Protection Agency, Region-10, Seattle, WA 98101, USA. Electronic address: eckley.chris@epa.gov.
authors.forename: Chris S
authors.initials: CS
authors.lastname: Eckley
authors.affiliation: US Geological Survey, Middleton, WI 53562, USA.
authors.forename: Mike T
authors.initials: MT
authors.lastname: Tate
authors.affiliation: Center for Advances on Water and Air quality, Lamar University, Beaumont, TX 77710, USA.
authors.forename: Che-Jen
authors.initials: CJ
authors.lastname: Lin
authors.affiliation: Department of Natural Resources & Environmental Science, University of Nevada, Reno, NV 89557, USA.
authors.forename: Mae
authors.initials: M
authors.lastname: Gustin
authors.affiliation: CDM Smith, Portland, OR 97205, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Dent
authors.affiliation: US Geological Survey, Corvallis, OR 97331, USA.
authors.forename: Collin
authors.initials: C
authors.lastname: Eagles-Smith
authors.affiliation: US Geological Survey, Middleton, WI 53562, USA.
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Lutz
authors.affiliation: US Geological Survey Boulder, CO 80303, USA.
authors.forename: Kimberly P
authors.initials: KP
authors.lastname: Wickland
authors.affiliation: US Geological Survey, Anchorage, AK 99508, USA.
authors.forename: Bronwen
authors.initials: B
authors.lastname: Wang
authors.affiliation: US Geological Survey, Denver, CO 80225, USA.
authors.forename: John E
authors.initials: JE
authors.lastname: Gray
authors.affiliation: Department of Environment and Geography, Macquarie University, North Ryde, NSW 2109, Australia.
authors.forename: Grant C
authors.initials: GC
authors.lastname: Edwards
authors.affiliation: US Geological Survey, Middleton, WI 53562, USA.
authors.forename: Dave P
authors.initials: DP
authors.lastname: Krabbenhoft
authors.affiliation: US Geological Survey, Denver, CO 80225, USA.
authors.forename: David B
authors.initials: DB
authors.lastname: Smith
keywords: Deposition; Dynamic flux chamber; Emission; Mercury; Western North America