Assessing Mercury Exposure and Effects to American Dippers in Headwater Streams near Mining Sites |
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Authors: | Email author" target="_blank">Charles?J?HennyEmail author James?L?Kaiser Heidi?A?Packard Robert?A?Grove Michael?R?Taft |
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Institution: | (1) USGS-Forest and Rangeland Ecosystem Science Center, 3200 SW Jefferson Way, Corvallis, OR 97331, USA |
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Abstract: | To evaluate mercury (Hg) exposure and possible adverse effects of Hg on American dipper (Cinclus mexicanus) reproduction, we collected eggs and nestling feathers and the larval/nymph form of three Orders of aquatic macroinvertebrates
(Ephemeroptera, Plecoptera and Trichoptera = EPT) important in their diet from three major headwater tributaries of the upper
Willamette River, Oregon in 2002. The Coast Fork Willamette River is contaminated with Hg due to historical cinnabar (HgS)
mining at the Black Butte Mine; the Row River is affected by past gold-mining operations located within the Bohemia Mining
District, where Hg was used in the amalgamation process to recover gold; and the Middle Fork Willamette River is the reference
area with no known mining. Methyl mercury (MeHg) concentrations (geometric mean) in composite EPT larvae (111.9 ng/g dry weight
dw] or 19.8 ng/g wet weight ww]), dipper eggs (38.5 ng/g ww) and nestling feathers (1158 ng/g ww) collected from the Coast
Fork Willamette were significantly higher than MeHg concentrations in EPT and dipper samples from other streams. Total mercury
(THg) concentrations in surface sediments along the same Hg-impacted streams were investigated by others in 1999 (Row River
tributaries) and 2002 (Coast Fork). The reported sediment THg concentrations paralleled our biological findings. Dipper breeding
territories at higher elevations had fewer second clutches; however, dipper reproductive success along all streams (including
the lower elevation and most Hg-contaminated Coast Fork), was judged excellent compared to other studies reviewed. Furthermore,
MeHg concentrations in EPT samples from this study were well below dietary concentrations in other aquatic bird species, such
as loons and ducks, reported to cause Hg-related reproductive problems. Our data suggest that either dipper feathers or EPT
composites used to project MeHg concentrations in dipper feathers (with biomagnification factor of 10–20×) may be used, but
with caution, to screen headwater streams for potential Hg-related effects on dippers. When actual feather concentrations
or projected feather concentrations are equal to or lower than concentrations reported for the Coast Fork, dippers are expected
to reproduce well (assuming adequate prey and suitable nest sites). When Hg concentrations are substantially higher, more
detailed investigations may be required. Birds feeding almost exclusively on fish (e.g., osprey Pandion haliaetus]) and usually found further downstream from the headwaters would not be adequately represented by dippers given the higher
MeHg concentrations in fish resulting from biomagnification, compared to lower trophic level invertebrates. |
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Keywords: | mercury American dipper mining feathers eggs production rates macroinvertebrates biomagnification |
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