A review of mercury concentration and deposition in snow in eastern temperate North America

摘要

Most published research evaluating total (wet + dry) mercury (Hg) deposition in eastern North America has been conducted during the growing season. However, recent research indicates that winter throughfall Hg deposition can be significant. We reviewed and synthesized published and unpublished snow Hg concentration and deposition data collected at forested and open sites from 1989 to 2005 (14 studies) using various field methods. Mean snow Hg concentrations across years and locations ranged from 0.66 to 22.7 ng l~(-1) [standard deviation (SD): 15-99%]. Snow Hg deposition and concentration were consistently highest in conifer throughfall and lowest at open sites (no vegetation cover). These results suggest that the range of snow Hg deposition can be bracketed by sampling at two extremes: under conifer canopies and in open sites. Ratios of Hg in snowpack under tree canopies versus open sites were 3.4: 1 (conifers) and 2.1:1 (all forest types). Ratios of event throughfall to wet-only collections were 5.0: 1 (conifers) and 3.8 : 1 (all forest types), exceeding the previously reported overall average of throughfall to wet-only for the growing season. Future research should standardize snow Hg sampling methods to address volatilization and dry deposition. Mechanisms contributing to variability in snow Hg deposition could be assessed by measuring particulate Hg and examining interannual and spatial patterns.