DEFORESTATION AND CULTIVATION MOBILIZE MERCURY FROM TOPSOIL

Terrestrial biomass and soils are a primary global reservoir of mercury (Hg) derived from natural and anthropogenic sources. Relatively little is known about the fate and stability of Hg in the surface soil reservoir and its susceptibility to change from deforestation and cultivation. We are measuring concentrations of Hg, lead and organic matter in soils of southwestern Ohio, upper peninsula of Michigan, and northeastern Wisconsin to better understand how land use, particularly deforestation and cultivation, affect the surface soil Hg reservoir. In all three areas, soil was sampled from old- and new-growth forest stands. Soil also was sampled from agricultural fields in Ohio, a deforested field in Wisconsin, and deciduous and coniferous forests in Michigan. Mercury concentrations in surficial soils were significantly greater in old-growth than new-growth forests, and forested soils had greater Hg concentrations than their non-forested counterparts. As predicted, soil Hg concentrations and organic content were significantly less in coniferous forests than deciduous forests. Mercury:organic content ratios were greatest in old-growth forest, and different between the three sampling areas. A decrease in soil Hg concentrations from old- to new-growth forest to deforested landscape suggests that deforestation has resulted in surface soils being a source of Hg actively cycling in the environment. Our results suggest deforestation and cultivation exacerbate Hg mobilization from soil and its cycling in the environment.