Spatial variation in aquatic invertebrate and riparian songbird mercury exposure across a river-reservoir system with a legacy of mercury contamination
Mercury (Hg) loading and methylation in aquatic systems causes a variety of deleterious effects for fish and wildlife populations. Relatively little research has focused on Hg movement into riparian food webs and how this is modulated by habitat characteristics. This study characterized differences in Hg exposure in aquatic invertebrates and riparian songbirds across a large portion of the Willamette River system in western Oregon, starting at a Hg-contaminated Superfund site in the headwaters (Black Butte Hg Mine) and including a reservoir known to methylate Hg (Cottage Grove Reservoir), all downstream reaches (Coast Fork and Willamette River) and off-channel wetland complexes (Willamette Valley National Wildlife Refuge Complex). After accounting for year, date, and site differences in a mixed effects model, MeHg concentrations in aquatic invertebrates varied spatially among habitat categories and invertebrate orders. Similarly, THg in songbird blood varied by among habitat categories and bird species. The highest Hg concentrations occurred near the Hg mine, but Hg did not decline linearly with distance from the source of contamination. Birds were consistently elevated in Hg in habitats commonly associated with enhanced MeHg production, such as backwater or wetlands. We found a positive but weak correlation between aquatic invertebrate MeHg concentrations and songbird THg concentrations on a site-specific basis. Our findings suggest that Hg risk to riparian songbirds can extend beyond point-source contaminated areas, highlighting the importance of assessing exposure in surrounding habitats where methylmercury production may be elevated, such as reservoirs and wetlands.
KeywordsMethylmercury Willamette Black Butte Songbird Aquatic invertebrate
Funding for this work was provided by the U.S. Geological Survey Contaminant Biology Program. A.K.J. was funded by an Oregon State University Provost Distinguished Graduate Fellowship, Savery Outstanding Doctoral Student Award, David B. and Georgia Leupold Marshall Wildlife Graduate Scholarship, Mastin Wildlife Travel Scholarship, P.F. & Nellie Buck Yerex Graduate Fellowship, Coombs-Simpson Memorial Fellowship, and Munson Wildlife Graduate Scholarship. A.K.J. would like to thank her coadvisor Dr. W. Douglas Robinson and her entire dissertation committee: Dr. Anita Morzillo, Dr. David Evers, Dr. Daniel Cristol and Dr. Sarah Henkel. We would like to thank a variety of organizations for access to the field sites: USEPA, Army Corp of Engineers, Cottage Grove, USFWS, Oregon Parks Department, Benton County, City of Corvallis, City of Albany, City of Salem. Field support was provided by an amazing undergraduate field crew including (2013) Jim Randolph, Mason Wagner, Jessica Greer, Danielle Aquilar, Amanda Wasserman, (2014) Michael Brawner, Noelle Moan, Melanie Holte, Danielle Ramsden. This manuscript was made better by the help of two anonymous reviewers. Laboratory support was provided by James Willacker and John Pierce. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All samples were collected under authority of appropriate scientific collection permits, including both State (invertebrates: Oregon DFW# 17648; birds: Oregon DFW# 062-13) and Federal (USFWS MBTA# MB28361A; USGS Banding # 20786) agencies. All birds were handled under approved animal care and use protocols (Oregon State University ACUP # 4408).
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