Abstract
Inputs of anthropogenic mercury (Hg) to the environment have led to accumulation of Hg in terrestrial and aquatic ecosystems, contributing to fish Hg concentrations well above the European Union standards in large parts of Fennoscandia. Forestry operations have been reported to increase the concentrations and loads of Hg to surface waters by mobilizing Hg from the soil. This summary of available forestry effect studies reveals considerable variation in treatment effects on total Hg (THg) and methylmercury (MeHg) at different sites, varying from no effect up to manifold concentration increases, especially for the bioavailable MeHg fraction. Since Hg biomagnification depends on trophic structures, forestry impacts on nutrient flows will also influence the Hg in fish. From this, we conclude that recommendations for best management practices in Swedish forestry operations are appropriate from the perspective of mercury contamination. However, the complexity of defining effective policies needs to be recognized.
Highlights
High mercury (Hg) concentrations in freshwater fish are observed in many regions, including Sweden
There are more studies on the effects of forestry on MeHg in surface waters, the magnitude of that forestry effect is still uncertain. This is partly due to the high variation between different forestry effect studies, and partly due to the fact that forestry’s influence on mercury in fish goes beyond just mobilizing mercury to altering the aquatic foodwebs that structure the bioaccumulation of high mercury (Hg) which eventually reaches fish
The earlier estimate of 9–23 % of Hg in Swedish freshwater fishes arising from forestry (Bishop et al 2009) may be too narrow and high, missing some sites that have recently been reported where there is a low degree of influence after forest harvest operations
Summary
High mercury (Hg) concentrations in freshwater fish are observed in many regions, including Sweden. Forestry activities have been found to increase mobilization of Hg (both MeHg and the total Hg (THg) which can later be methylated) from soils to surface waters and to create environments of high Hg methylation.
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