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Impact of flow diversion by run‐of‐river dams on American dipper diet and mercury exposure
Author(s) -
Silverthorn Veronica M.,
Bishop Christine A.,
Jardine Timothy,
Elliott John E.,
Morrissey Christy A.
Publication year - 2018
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1002/etc.3961
Subject(s) - mercury (programming language) , methylmercury , streams , environmental science , invertebrate , environmental chemistry , dipper , river ecosystem , fish migration , benthic zone , feather , periphyton , ecology , ecosystem , fishery , bioaccumulation , biology , chemistry , habitat , algae , computer network , ambulatory blood pressure , computer science , blood pressure , programming language , endocrinology
Abstract Run‐of‐river dams produce lower greenhouse gas emissions than large hydropower projects, but there is a paucity of research on their potential ecotoxicological impacts through disruption of natural flow regimes. We used stable isotopes (δ 13 C, δ 15 N, δ 34 S) to reconstruct diet and trace methylmercury in a predatory river‐resident passerine, the American dipper ( Cinclus mexicanus ), at 7 regulated and 6 free‐flowing mountain streams in coastal British Columbia, Canada. Assimilated diets were comparable among regulated and unregulated streams, dominated by benthic macroinvertebrates and resident freshwater fish, with negligible contributions from anadromous Pacific salmon. Although invertebrates at unregulated streams were isotopically similar along their gradient, dippers and invertebrates sampled below dams on regulated streams had 34 S‐depleted tissues, suggesting increased activity of sulfate‐reducing bacteria and more Hg methylation below the dams. Mercury concentrations in dipper blood (417.6 ± 74.1 standard error [SE] ng/g wet wt at regulated streams, 340.7 ± 42.7 SE ng/g wet wt at unregulated streams) and feathers (1564 .6 ± 367.2 SE ng/g dry wt regulated, 1149.0 ± 152.1 SE ng/g dry wt unregulated), however, were not significantly different between stream types. Relative to other passerines across western North America, dippers in these densely forested mountain streams experienced high mercury exposure; and one recently regulated stream supported dippers with mercury concentrations of potential toxicity concern (up to 8459.5 ng/g dry wt in feathers and 1824.6 ng/g wet wt in whole blood). Elevated mercury in dippers is likely attributable to the birds’ relatively high trophic position and high regional inorganic mercury deposition; however, biogeochemical conditions in reservoirs of some regulated streams may be contributing to methylmercury production. Environ Toxicol Chem 2018;37:411–426. © 2017 SETAC