title: Impact of Beaver Pond Colonization History on Methylmercury Concentrations in Surface Water.
abstract: Elevated concentrations of methylmercury (MeHg) in freshwater ecosystems are of major environmental concern in large parts of the northern hemisphere. Beaver ponds have been identified as a potentially important source of MeHg. The role of beavers might be especially pronounced in large parts of Europe, where beaver populations have expanded rapidly following near-extirpation. This study evaluates the role of the age and colonization history (encompassing patterns of use and reuse) of ponds constructed by the Eurasian beaver Castor fiber in regulating MeHg concentrations in Swedish streams. In 12 beaver systems located in three regions, we quantified MeHg concentrations together with other relevant parameters on five occasions per year in 2012-2013. Five were pioneer systems, inundated for the first time since beaver extirpation, and seven were recolonized, with dams reconstructed by newly recolonizing beavers. MeHg concentrations in pioneer but not in recolonized beaver systems were up to 3.5 fold higher downstream than upstream of the ponds, and varied between seasons and years. Our results show that pioneer inundation by beavers can increase MeHg concentrations in streams, but that this effect is negligible when dams are reconstructed on previously used ponds. We therefore expect that the recovery and expansion of beavers in the boreal system will only have a transitional effect on MeHg in the environment.
authors.affiliation: Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, (SLU) , Box 7050, SE-750 07 Uppsala, Sweden.
authors.forename: Oded
authors.initials: O
authors.lastname: Levanoni
authors.affiliation: Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, (SLU) , Box 7050, SE-750 07 Uppsala, Sweden.|Department of Earth Sciences, Air Water and Landscape Sciences, Villavägen 16, Uppsala University , SE-752 36 Uppsala, Sweden.
authors.forename: Kevin
authors.initials: K
authors.lastname: Bishop
authors.affiliation: Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, (SLU) , Box 7050, SE-750 07 Uppsala, Sweden.
authors.forename: Brendan G
authors.initials: BG
authors.lastname: Mckie
authors.affiliation: Department of Ecology, Swedish University of Agricultural Sciences, (SLU) , Box 7050, SE-750 07 Uppsala, Sweden.
authors.forename: Göran
authors.initials: G
authors.lastname: Hartman
authors.affiliation: Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, (SLU) , Box 7050, SE-750 07 Uppsala, Sweden.
authors.forename: Karin
authors.initials: K
authors.lastname: Eklöf
authors.affiliation: Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, (SLU) , Box 7050, SE-750 07 Uppsala, Sweden.|Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, (SLU) , SE-901 83 Umeå, Sweden.
authors.forename: Frauke
authors.initials: F
authors.lastname: Ecke
mesh_terms: D000818:Animals; D017753:Ecosystem; D004777:Environment; D005060:Europe; D005618:Fresh Water; D008767:Methylmercury Compounds / Q000032:analysis*; D061005:Ponds; D012377:Rodentia; D012621:Seasons; D013548:Sweden; D014867:Water; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D014867:Water