Lars Lambertsson

The Effects of Forest Harvest Operations on Mercury and Methylmercury in Two Boreal Streams: Relatively Small Changes in the First Two Years prior to Site Preparation

Abstract Forest harvest is hypothesized to increase the mercury (Hg) load in aquatic ecosystems. The Balsjö paired catchment study examined the outputs of methylmercury (MeHg) and total mercury (Hgtot) from two boreal catchments during the 2 y following forest harvest but prior to site preparation. This enabled us to separate the effect of the two operations that followed best management practices. Hgtot concentrations increased by approximately 15%, and fluxes by 20–30%. The MeHg concentrations and fluxes either declined or increased by up to 60%, depending on whether annual MeHg peaks during summer low flows were considered to have been influenced by forest harvest. The lack of a severalfold increase in Hg outputs after forest harvest, as reported from other sites, may be the result of minimal soil disturbance during the winter forest harvest operations. If so, there may be a greater Hg response after soil scarification to prepare for planting.

Net Methylmercury Production as a Basis for Improved Risk Assessment of Mercury- contaminated Sediments

Abstract Sediments contaminated by various sources of mercury (Hg) were studied at 8 sites in Sweden covering wide ranges of climate, salinity, and sediment types. At all sites, biota (plankton, sediment living organisms, and fish) showed enhanced concentrations of Hg relative to corresponding organisms at nearby reference sites. The key process determining the risk at these sites is the net transformation of inorganic Hg to the highly toxic and bioavailable methylmercury (MeHg). Accordingly, Hg concentrations in Perca fluviatilis were more strongly correlated to MeHg (p < 0.05) than to inorganic Hg concentrations in the sediments. At all sites, except one, concentrations of inorganic Hg (2–55 μg g−1) in sediments were significantly, positively correlated to the concentration of MeHg (4–90 ng g−1). The MeHg/Hg ratio (which is assumed to reflect the net production of MeHg normalized to the Hg concentration) varied widely among sites. The highest MeHg/Hg ratios were encountered in loose-fiber sediments situated in southern freshwaters, and the lowest ratios were found in brackish-water sediments and firm, minerogenic sediments at the northernmost freshwater site. This pattern may be explained by an increased MeHg production by methylating bacteria with increasing temperature, availability of energy-rich organic matter (which is correlated with primary production), and availability of neutral Hg sulfides in the sediment pore waters. These factors therefore need to be considered when the risk associated with Hg-contaminated sediments is assessed.

Assessment of the spatial distributions of total- and methyl-mercury and their relationship to sediment geochemistry from a whole-lake perspective

The aim of this study was to determine the spatial variability for total-and methylmercury in surface sediments (0-2 cm) across a single whole-lake basin, and to relate this variability to the sedi ...