title: Terrestrial discharges mediate trophic shifts and enhance methylmercury accumulation in estuarine biota.
abstract: The input of mercury (Hg) to ecosystems is estimated to have increased two- to fivefold during the industrial era, and Hg accumulates in aquatic biota as neurotoxic methylmercury (MeHg). Escalating anthropogenic land use and climate change are expected to alter the input rates of terrestrial natural organic matter (NOM) and nutrients to aquatic ecosystems. For example, climate change has been projected to induce 10 to 50% runoff increases for large coastal regions globally. A major knowledge gap is the potential effects on MeHg exposure to biota following these ecosystem changes. We monitored the fate of five enriched Hg isotope tracers added to mesocosm scale estuarine model ecosystems subjected to varying loading rates of nutrients and terrestrial NOM. We demonstrate that increased terrestrial NOM input to the pelagic zone can enhance the MeHg bioaccumulation factor in zooplankton by a factor of 2 to 7 by inducing a shift in the pelagic food web from autotrophic to heterotrophic. The terrestrial NOM input also enhanced the retention of MeHg in the water column by up to a factor of 2, resulting in further increased MeHg exposure to pelagic biota. Using mercury mass balance calculations, we predict that MeHg concentration in zooplankton can increase by a factor of 3 to 6 in coastal areas following scenarios with 15 to 30% increased terrestrial runoff. The results demonstrate the importance of incorporating the impact of climate-induced changes in food web structure on MeHg bioaccumulation in future biogeochemical cycling models and risk assessments of Hg.
authors.affiliation: Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden.; Umeå Marine Sciences Centre, Umeå University, SE-910 20 Hörnefors, Sweden.
authors.forename: Sofi
authors.initials: S
authors.lastname: Jonsson
authors.affiliation: Umeå Marine Sciences Centre, Umeå University, SE-910 20 Hörnefors, Sweden.; Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Agneta
authors.initials: A
authors.lastname: Andersson
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Mats B
authors.initials: MB
authors.lastname: Nilsson
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Ulf
authors.identifier: 0000-0001-6939-8799
authors.initials: U
authors.lastname: Skyllberg
authors.affiliation: Umeå Marine Sciences Centre, Umeå University, SE-910 20 Hörnefors, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Lundberg
authors.affiliation: Department of Environmental Sciences, Rutgers University, New Brunswick, NJ 08901, USA.
authors.forename: Jeffra K
authors.initials: JK
authors.lastname: Schaefer
authors.affiliation: Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden.
authors.forename: Staffan
authors.initials: S
authors.lastname: Åkerblom
authors.affiliation: Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Björn
mesh_terms: D000818:Animals; D058448:Biota; D020387:Food Chain; D008767:Methylmercury Compounds / Q000378:metabolism*; D008954:Models, Biological; D015048:Zooplankton / Q000254:growth & development*
chemical_list: D008767:Methylmercury Compounds
keywords: bioaccumulation; methylmercury; pelagic food web; terrestrial discharge; trophic shift