A Statewide Assessment of Mercury Dynamics in North Carolina Water Bodies and Fish

Abstract

Mercury contamination of aquatic systems has received much attention recently because of potential health effects on humans and wildlife. Although the factors affecting mercury deposition, its conversion to biologically active methylmercury, and its bioaccumulation in aquatic systems have been identified, equivocal results for particular species and systems have hampered policy making. Our study addresses this problem through a comprehensive, statewide synthesis of the available data on fish mercury contamination in North Carolina and the environmental factors associated with methylmercury formation and transport through aquatic food webs. Using data collected by the North Carolina Department of Environment and Natural Resources, the U.S. Environmental Protection Agency, and others, we examined the relationships between a suite of biotic and abiotic factors and tissue mercury concentrations in fish from North Carolina water bodies. Multivariate tests were conducted to create predictive models relating environmental variables to mercury levels in fish, and Akaike's information criterion was used to examine the relative strengths of the candidate models. The best model in our analyses (R 2 ¼ 0.81) included species, fish trophic status, ecoregion, and pH. Other important drivers of mercury accumulation were land use patterns (the percentage of the subbasin that is agricultural) and site type (swamps versus lakes, rivers, and bays). Although previous investigations have indicated similar individual relationships, our study is unique in that we examined the relative importance of a large number of biotic and abiotic variables across a range of environments, ecosystems, and species. The results of these analyses should help policymakers in making risk assessment decisions and serve as a template for future investigations.

Bottom‐up nutrient and top‐down fish impacts on insect‐mediated mercury flux from aquatic ecosystems

“…The p values from the test of simple main effects are reported in Supplemental Data, Table S2. with MeHg concentrations in biota [15,16,[40][41][42][43]. The hypothesized mechanism for the observed positive relationship between MeHg concentration and productivity is the stimulation of MeHg production by microbial communities.…”

“…The bottom-up effects of nutrients potentially influence the flux of MeHg from aquatic systems by regulating productivity and emergent insect biomass [10][11][12]. Nutrients may also alter the flux of MeHg by affecting the concentrations of MeHg of insects as has been shown for other consumers [13][14][15][16]. The top-down influence of predation by fish could affect MeHg flux by reducing the biomass and altering the taxonomic composition of larval and emergent insects [11,12,[17][18][19].…”

Does proximity to coal-fired power plants influence fish tissue mercury?

“…Bluegill exist at the intermediate trophic level, foraging on a mix of zooplankton, plant material, and benthic invertebrates (Werner and Hall 1988). Power analyses based on a previous dataset (Sackett et al 2009) suggested that collections of five individuals of a restricted size range per species (i.e., 10 fish per system) would be sufficient to confidently quantify differences in fish tissue Hg among lakes. Largemouth bass collections were limited to individuals that were 300-400 mm total length (TL) and bluegill collections were limited to 150-200 mm TL.…”

“…Ravichandran 2004), geographic region (e.g. Sackett et al 2009), and chlorophyll a (e.g. Lange et al 1993).…”

Evaluation of Species-Specific Dissimilarities in Two Marine Fish Species: Mercury Accumulation as a Function of Metal Levels in Consumed Prey

“…Moreover, some investigators support the idea that the commonly positive relationship between fish size and Hg concentration is frequently due to exposure time and to increased Hg in prey for larger fish rather than to variations in growth (Trudel and Rasmussen 2006). In addition, Hg accumulation and distribution patterns depend on the species, specific tissue, and environmental degree of contamination (Maury-Brachet et al 2006;Sackett et al 2009). However, D. labrax and L. aurata, which have different biological and ecological traits (e.g., metabolism, reproduction, activity levels, lipid content), demonstrated similar patterns of Hg distribution in their tissues (both T-Hg and O-Hg).…”