Mercury Cycling in Stream Ecosystems. 3. Trophic Dynamics and Methylmercury Bioaccumulation

时间：2009-04-19  阅读：    我要评论:

Lia C. Chasar*^†, Barbara C. Scudder^‡, A. Robin Stewart^§, Amanda H. Bell^‡ and George R. AikenU.S. Geological Survey, Florida Integrated Science Center, 2639 North Monroe Street, Suite A-200,Tallahassee, Florida 32303, U.S. Geological Survey, Wisconsin Water Science Center, 8505 Research Way, Middleton, Wisconsin 53562, U.S. Geological Survey, National Research Program, 345 Middlefield Road, Menlo Park, California 94025, and U.S. Geological Survey, National Research Program, 3215 Marine Street, Suite E-127, Boulder, Colorado 80303Environ. Sci. Technol., 2009, 43 (8), pp 2733–2739DOI: 10.1021/es8027567Publication Date (Web): March 11, 2009Copyright This article not subject to U.S. Copyright. Published 2009 by the American Chemical Society * Corresponding author phone: 850-553-3649; e-mail: lchasar@usgs.gov., †

USGS, Tallahassee, FL.

, ‡

USGS, Middleton, WI.

, §

USGS, Menlo Park, CA.

,

USGS, Boulder, CO.

Abstract

Trophic dynamics (community composition and feeding relationships) have been identified as important drivers of methylmercury (MeHg) bioaccumulation in lakes, reservoirs, and marine ecosystems. The relative importance of trophic dynamics and geochemical controls on MeHg bioaccumulation in streams, however, remains poorly characterized. MeHg bioaccumulation was evaluated in eight stream ecosystems across the United States (Oregon, Wisconsin, and Florida) spanning large ranges in climate, landscape characteristics, atmospheric Hg deposition, and stream chemistry. Across all geographic regions and all streams, concentrations of total Hg (THg) in top predator fish and forage fish, and MeHg in invertebrates, were strongly positively correlated to concentrations of filtered THg (FTHg), filtered MeHg (FMeHg), and dissolved organic carbon (DOC); to DOC complexity (as measured by specific ultraviolet absorbance); and to percent wetland in the stream basins. Correlations were strongest for nonurban streams. Although regressions of log[Hg] versus δ¹⁵N indicate that Hg in biota increased significantly with increasing trophic position within seven of eight individual streams, Hg concentrations in top predator fish (including cutthroat, rainbow, and brown trout; green sunfish; and largemouth bass) were not strongly influenced by differences in relative trophic position. Slopes of log[Hg] versus δ¹⁵N, an indicator of the efficiency of trophic enrichment, ranged from 0.14 to 0.27 for all streams. These data suggest that, across the large ranges in FTHg (0.14−14.2 ng L⁻¹), FMeHg (0.023−1.03 ng L⁻¹), and DOC (0.50−61.0 mg L⁻¹) found in this study, Hg contamination in top predator fish in streams likely is dominated by the amount of MeHg available for uptake at the base of the food web rather than by differences in the trophic position of top predator fish.

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