title: Eutrophication Increases Phytoplankton Methylmercury Concentrations in a Coastal Sea-A Baltic Sea Case Study.
abstract: Eutrophication is expanding worldwide, but its implication for production and bioaccumulation of neurotoxic monomethylmercury (MeHg) is unknown. We developed a mercury (Hg) biogeochemical model for the Baltic Sea and used it to investigate the impact of eutrophication on phytoplankton MeHg concentrations. For model evaluation, we measured total methylated Hg (MeHgT) in the Baltic Sea and found low concentrations (39 ± 16 fM) above the halocline and high concentrations in anoxic waters (1249 ± 369 fM). To close the Baltic Sea MeHgTbudget, we inferred an average normoxic water column HgIImethylation rate constant of 2 × 10-4d-1. We used the model to compare Baltic Sea's present-day (2005-2014) eutrophic state to an oligo/mesotrophic scenario. Eutrophication increases primary production and export of organic matter and associated Hg to the sediment effectively removing Hg from the active biogeochemical cycle; this results in a 27% lower present-day water column Hg reservoir. However, increase in organic matter production and remineralization stimulates microbial Hg methylation resulting in a seasonal increase in both water and phytoplankton MeHg reservoirs above the halocline. Previous studies of systems dominated by external MeHg sources or benthic production found eutrophication to decrease MeHg levels in plankton. This Baltic Sea study shows that in systems with MeHg production in the normoxic water column eutrophication can increase phytoplankton MeHg content.
authors.affiliation: Stockholm University , Department of Environmental Science and Analytical Chemistry, Stockholm SE-106 91, Sweden.
authors.forename: Anne L
authors.initials: AL
authors.lastname: Soerensen
authors.affiliation: Harvard University , John A. Paulson School of Engineering and Applied Sciences, Cambridge Massachusetts 02138, United States.
authors.forename: Amina T
authors.initials: AT
authors.lastname: Schartup
authors.affiliation: Stockholm University , Baltic Nest Institute, Baltic Sea Centre, Stockholm SE-106 91, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Gustafsson
authors.affiliation: Stockholm University , Baltic Nest Institute, Baltic Sea Centre, Stockholm SE-106 91, Sweden.
authors.forename: Bo G
authors.initials: BG
authors.lastname: Gustafsson
authors.affiliation: Stockholm University , Department of Environmental Science and Analytical Chemistry, Stockholm SE-106 91, Sweden.|Stockholm University , Baltic Nest Institute, Baltic Sea Centre, Stockholm SE-106 91, Sweden.
authors.forename: Emma
authors.initials: E
authors.lastname: Undeman
authors.affiliation: Umeå University , Department of Chemistry, Umeå SE-901 87, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Björn
mesh_terms: D004784:Environmental Monitoring; D005068:Eutrophication; D008628:Mercury; D008767:Methylmercury Compounds; D010839:Phytoplankton; D014874:Water Pollutants, Chemical
chemical_list: D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D008628:Mercury