biogeochemical cycling of Hg in forests: alternative methods for quantifying total deposition and soil emission

A biogeochemical cycling approach to the Hg cycle is explored using existing data from the literature in order to begin to identify important processes that might be studied in detail and extrapolated to a regional scale. If it is assumed that all foliar Hg is taken up from the atmosphere, then estimates of total Hg deposition are rather easily made from measurements of leaf litterfall and throughfall. This assumption needs absolute verification before such an extrapolation can be made, however, because litterfall is a major Hg flux to the forest floor. Hg super(o) evolution from soils can be an important process and needs to be measured in more ecosystems. The diffusion model for soil gaseous efflux may be useful in this regard and deserves testing. There is a critical need for a systematic analysis of Hg cycles using common protocols so as to minimize artifacts associated with sampling methodology (i.e., soil Hg efflux). This should be done in several soil and forest types, given the high degree to which Hg transformations in and emissions from soils are dependent upon soil organic matter content, redox potential, and temperature.