title: Optimizing stream water mercury sampling for calculation of fish bioaccumulation factors.
abstract: Mercury (Hg) bioaccumulation factors (BAFs) for game fishes are widely employed for monitoring, assessment, and regulatory purposes. Mercury BAFs are calculated as the fish Hg concentration (Hg(fish)) divided by the water Hg concentration (Hg(water)) and, consequently, are sensitive to sampling and analysis artifacts for fish and water. We evaluated the influence of water sample timing, filtration, and mercury species on the modeled relation between game fish and water mercury concentrations across 11 streams and rivers in five states in order to identify optimum Hg(water) sampling approaches. Each model included fish trophic position, to account for a wide range of species collected among sites, and flow-weighted Hg(water) estimates. Models were evaluated for parsimony, using Akaike's Information Criterion. Better models included filtered water methylmercury (FMeHg) or unfiltered water methylmercury (UMeHg), whereas filtered total mercury did not meet parsimony requirements. Models including mean annual FMeHg were superior to those with mean FMeHg calculated over shorter time periods throughout the year. FMeHg models including metrics of high concentrations (80th percentile and above) observed during the year performed better, in general. These higher concentrations occurred most often during the growing season at all sites. Streamflow was significantly related to the probability of achieving higher concentrations during the growing season at six sites, but the direction of influence varied among sites. These findings indicate that streamwater Hg collection can be optimized by evaluating site-specific FMeHg-UMeHg relations, intra-annual temporal variation in their concentrations, and streamflow-Hg dynamics.
authors.affiliation: U.S. Geological Survey, 425 Jordan Road, Troy, New York 12180, United States. krmurray@usgs.gov
authors.forename: Karen
authors.initials: K
authors.lastname: Riva-Murray
authors.forename: Paul M
authors.initials: PM
authors.lastname: Bradley
authors.forename: Barbara C
authors.initials: BC
authors.lastname: Scudder Eikenberry
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Knightes
authors.forename: Celeste A
authors.initials: CA
authors.lastname: Journey
authors.forename: Mark E
authors.initials: ME
authors.lastname: Brigham
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Button
mesh_terms: D000818:Animals; D004784:Environmental Monitoring / Q000379:methods*; D005399:Fishes; D020387:Food Chain; D008628:Mercury / Q000032:analysis* / Q000493:pharmacokinetics*; D008767:Methylmercury Compounds / Q000032:analysis; D008962:Models, Theoretical; D045483:Rivers; D017747:Seafood / Q000032:analysis; D012621:Seasons; D013997:Time Factors; D014481:United States; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D008628:Mercury