Spatial and vertical distribution of mercury in upland forest soils across the northeastern United States

•Mercury in the forest floor and mineral soil was quantified at 17 sites.•Concentrations and amounts were regressed with regional factors and soil properties.•Forest floor Hg was most explained by soil organic matter, pH, and precipitation.•Mineral soil Hg was explained by latitude, Fe concentration, and soil organic matter.•Mineral soil Hg was greatest in Bs horizons of Spodosols due to podzolization.

Assessing current Hg pools in forest soils of the northeastern U.S. is important for monitoring changes in Hg cycling. The forest floor, upper and lower mineral horizons were sampled at 17 long-term upland forest sites across the northeastern U.S. in 2011. Forest floor Hg concentration was similar across the study region (274 ± 13 μg kg−1) while Hg amount at northern sites (39 ± 6 g ha−1) was significantly greater than at western sites (11 ± 4 g ha−1). Forest floor Hg was correlated with soil organic matter, soil pH, latitude and mean annual precipitation and these variables explained approximately 70% of the variability when multiple regressed. Mercury concentration and amount in the lower mineral soil was correlated with Fe, soil organic matter and latitude, corresponding with Bs horizons of Spodosols (Podzols). Our analysis shows the importance of regional and soil properties on Hg accumulation in forest soils.