The Effects of Soil Properties and Vegetation On Mercury Accumulation in Upland Forest Soils Across the Northeastern United States.

As humans continue to emit greater amounts of mercury (Hg), understanding its distribution and cycling in soils is an essential area of research. The Hg in upland forest soils is a large, potential source to aquatic ecosystems. Thus, characterizing the mechanisms responsible for the accumulation of Hg in upland forest soils is important. To deduce the Hg distribution in upland forest soils, samples were collected at three depths at 18 long-term montane forest sites across the northeastern United States, from northwestern Pennsylvania to central New Hampshire. Concentrations in the mineral soil ranged from 8 to 200 µg Hg per kg of soil. The accumulation of Hg in the mineral soil was significantly correlated with water-extractable chloride concentrations, latitude, and longitude with R2 values of 0.71, 0.55, and 0.44, respectively. There was no correlation between Hg concentrations and soil clay (< 2 µm) content. X-ray diffraction of the clay-sized fraction revealed spatial mineralogical differences. The vertical distribution of Hg was significantly affected by vegetation and soil type. Hg concentration in the A horizons of the Inceptisols were significantly greater than the E horizons of Spodosols. Conversely, Hg concentrations were significantly greater in the Bs horizons compared with the Bw horizons. Coniferous dominated stands had significantly less Hg in the upper soil horizons compared to the lower soil horizons. Deciduous dominated stands did not exhibit a vertical change in Hg distribution. This occurred because conifer stands were generally underlain with Spodosols while deciduous stands were primarily on Inceptisols. These patterns warrant further investigation into the effects of vegetation, soil mineralogy and chemistry on Hg accumulation and retention in forest soils.