B014-06
Forestry and mercury: Site specific factors that influence the catchment sensitivity to forest harvest
Tuesday, 8 December 2020: 04:20
Virtual
Karin Josefina Eklöf1, Heleen De Wit2, Chris Eckley3, Collin Eagles-Smith4, Rob Mackereth5, Ulf Skyllberg6, Liisa Ukonmaanaho7, Matti Verta8, Craig J Allan9, Karen Kidd10, Carl P J Mitchell11, John Munthe12, Joel Segersten1, Susan L Eggert13, Tapani Sallantaus8, Randall K Kolka13, Erik Emilson14, Stephen Sebestyen13, Ulf Sikström15, Therese Zetterberg16 and Andrea Garcia Bravo17, (1)SLU Swedish University of Agricultural Sciences Uppsala, Uppsala, Sweden, (2)Norwegian Institute for Water Research, Catchment processes, Oslo, Norway, (3)Environmental Protection Agency Seattle, Seattle, WA, United States, (4)USGS Forest and Rangeland Ecosystem Science Center, Corvallis, United States, (5)Ontario Minitry of the Environment, Center for Northern Forest Ecosystem Research, Thunder Bay, Canada, (6)Swedish University of Agricultural Sciences, Umeå, Sweden, (7)Natural Resources Institute Finland, Helsinki, Finland, (8)Finnish Environment Institute, Helsinki, Finland, (9)University of North Carolina at Charlotte, Geography and Earth Sciences, Charlotte, NC, United States, (10)McMaster University, Hamilton, Canada, (11)University of Toronto, Physical and Environmental Sciences, Toronto, ON, Canada, (12)IVL Swedish Environmental Research Institute, Stockholm, Sweden, (13)USDA Forest Service, Grand Rapids, United States, (14)Natural Resources Canada, Great Lakes Forestry Centre, Sault Ste. Marie, Canada, (15)The Forestry Research Institute of Sweden - Skogforsk, Uppsala, Sweden, (16)SLU Swedish University of Agricultural Sciences, Uppsala, Sweden, (17)Spanish National Research Council, Barcelona, Spain
Abstract:
Forestry operations has been found to mobilize mercury (Hg) from soils to aquatic habitats and promote the transformation of inorganic Hg to the highly neurotoxic and bioaccumulative methyl-Hg (MeHg) species. However, available studies of forestry-related disturbance, mainly clear cutting, reveal great variation in the effects on Hg mobilization, especially regarding MeHg – from little or no mobilization to manifold concentration increases. By synthesizing the results and findings of previous studies and by performing supplementary field measurements, the aim of this study is to identify factors influencing site specific sensitivity to forest harvest in regards to total Hg (THg) and MeHg export. Based on our results, this study establishes a basis for mitigation measures during harvest operations to prevent increases of THg and MeHg in runoff water.
The synthesis is based on 13 publications involving 26 forest harvested catchments from the United States, Canada, Norway, Sweden and Finland. We related site-specific variables in each of the catchments to the forestry induced changes in THg and MeHg concentrations reported in previous publications. Information on site specific characteristics in the catchments was collected by sampling, observations, Geographic Information System mapping, and from documentation obtained from project leaders of the original studies.
Preliminary results show that variables increasing the risk of compaction and rutting, such as a high wetness index and low bearing capacity in the harvested area, increase the risk of elevated MeHg formation in soils, but not necessarily MeHg in runoff. Instead, the combination of MeHg formation in soils and hydrological connectivity to the streams dictate the risk of forest harvesting induced increase of MeHg in runoff. Steeper slopes generally had higher hydrological connectivity. In the steepest catchments, however, harvest did not increase MeHg formation in soils, so MeHg in runoff did not increase. Riparian buffers and natural wetlands along streams generally buffered the effects of forest harvesting and the transport of Hg to streams. This synthesis study also identified striking differences among sites in the performance of mitigation strategies related to forest machinery operation, with resulting effects on THg and MeHg.
