title: Influence of Cladophora-Quagga Mussel Assemblages on Nearshore Methylmercury Production in Lake Michigan.
abstract: Recent spread of invasive mussels in Lake Michigan has altered primary productivity in the nearshore zone, resulting in proliferation of filamentous benthic green algae (Cladophora glomerata). In areas of dense Cladophora and quagga mussel (Dreissena bugensis) assemblages, as well as in regions where sloughed Cladophora accumulates, methylmercury (MeHg) production is enhanced. A shoreline transect from a river mouth through waters overlying Cladophora/quagga-rich zones showed that aqueous MeHg concentrations increased, despite river dilution. Cladophora, as primary producers, ranged from 0.6 to 7.5 ng g(-1) MeHg [4-47% of total mercury (Hg) as MeHg], and were higher than MeHg concentrations in offshore-collected seston. Concentrations of MeHg in decaying Cladophora accumulated onshore ranged from 2.6 to 18.0 ng g(-1) MeHg (18-41% as MeHg) and from 0.1 to 3.0 ng g(-1) MeHg (2-21% as MeHg) in deposits of recently sloughed and accumulated Cladophora in a nearshore topographical depression. Relative to offshore open waters, interstitial waters within decaying Cladophora from onshore and nearshore deposits were elevated in MeHg concentration, 1000- and 10-fold, respectively. Percent Hg as MeHg was also elevated (65-75% and 9-19%, respectively for onshore interstitial water and nearshore interstitial water, compared to 0.2-3.3% as MeHg for open water). Quagga mussels collected within growing Cladophora beds in the nearshore zone were significantly higher in MeHg than offshore counterparts. Our combined results suggest that recent changes in nearshore primary production contributes to MeHg production and bioaccumulation in Lake Michigan.
authors.affiliation: †Department of Civil and Environmental Engineering, Environmental Chemistry and Technology Program, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.
authors.forename: Ryan F
authors.initials: RF
authors.lastname: Lepak
authors.affiliation: ‡Wisconsin Water Science Center, United States Geological Survey, Middleton, Wisconsin 53562, United States.
authors.forename: David P
authors.initials: DP
authors.lastname: Krabbenhoft
authors.affiliation: ‡Wisconsin Water Science Center, United States Geological Survey, Middleton, Wisconsin 53562, United States.
authors.forename: Jacob M
authors.initials: JM
authors.lastname: Ogorek
authors.affiliation: ‡Wisconsin Water Science Center, United States Geological Survey, Middleton, Wisconsin 53562, United States.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Tate
authors.affiliation: §School of Freshwater Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53204, United States.
authors.forename: Harvey A
authors.initials: HA
authors.lastname: Bootsma
authors.affiliation: †Department of Civil and Environmental Engineering, Environmental Chemistry and Technology Program, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.|∥University of Wisconsin Aquatic Sciences Center, Madison, Wisconsin 53706, United States.
authors.forename: James P
authors.initials: JP
authors.lastname: Hurley
mesh_terms: D000818:Animals; D000460:Chlorophyta / Q000502:physiology*; D049875:Dreissena / Q000502:physiology*; D017753:Ecosystem; D058865:Introduced Species; D060106:Lakes; D008628:Mercury / Q000032:analysis / Q000378:metabolism; D008767:Methylmercury Compounds / Q000378:metabolism*; D008824:Michigan; D045483:Rivers
chemical_list: D008767:Methylmercury Compounds; D008628:Mercury