title: Impact of forestry on total and methyl-mercury in surface waters: distinguishing effects of logging and site preparation.
abstract: Forestry operations can increase the export of mercury (both total and methyl) to surface waters. However, little is known about the relative contribution of different forestry practices. We address this question using a paired-catchment study that distinguishes the effects of site preparation from the antecedent logging. Runoff water from three catchments, two harvested and one untreated control, was sampled biweekly during one year prior to logging, two years after logging, and three years after site preparation. The logging alone did not significantly increase the concentrations of either total or methyl-mercury in runoff, but export increased by 50-70% in one of the harvested catchments as a consequence of increased runoff volume. The combined effects of logging and site preparation increased total and methyl-mercury concentrations by 30-50% relative to preharvest conditions in both treated catchments. The more pronounced concentration effect after site preparation compared to logging could be related to site preparation being conducted during summer. This caused more soil disturbance than logging, which was done during winter with snow covering the ground. The results suggest that the cumulative impact of forest harvest on catchment mercury outputs depends on when and how forestry operations are implemented.
authors.affiliation: Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences , Box 7050, SE-75007, Uppsala, Sweden.
authors.forename: Karin
authors.initials: K
authors.lastname: Eklöf
authors.forename: Jakob
authors.initials: J
authors.lastname: Schelker
authors.forename: Rasmus
authors.initials: R
authors.lastname: Sørensen
authors.forename: Markus
authors.initials: M
authors.lastname: Meili
authors.forename: Hjalmar
authors.initials: H
authors.lastname: Laudon
authors.forename: Claudia
authors.initials: C
authors.lastname: von Brömssen
authors.forename: Kevin
authors.initials: K
authors.lastname: Bishop
mesh_terms: D016468:Forestry; D005618:Fresh Water / Q000032:analysis*; D062070:Hydrology; D008628:Mercury / Q000032:analysis*; D008767:Methylmercury Compounds / Q000032:analysis*; D013696:Temperature; D014197:Trees; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D008628:Mercury