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U.S. Department of the Interior U.S. Geological Survey

Mercury cycling and bioaccumulation in streams in Oregon, Wisconsin, and Florida Mark E. Brigham 5 th National Monitoring Conference San José, California May 7-11, 2006. U.S. Department of the Interior U.S. Geological Survey.

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U.S. Department of the Interior U.S. Geological Survey

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  1. Mercury cycling and bioaccumulation in streams in Oregon, Wisconsin, and FloridaMark E. Brigham5th National Monitoring ConferenceSan José, CaliforniaMay 7-11, 2006 U.S. Department of the Interior U.S. Geological Survey

  2. Mercury: A leading water-quality impairmentData source: EPA 303(d) list(http://oaspub.epa.gov/waters/national_rept.control) Mercury: ~ 6,000 Metals impairments ~ 2,100 Fish consumption advisories >8,100 impaired waters

  3. Factors that control mercury levels in fish Hg(II)  MeHg After: Mumley & Abu-Saba, WEF National TMDL Science and Policy Conference Proceedings, Nov. 13-16, 2002

  4. USGS NAWQA mercury study areas Western Lake Michigan Drainages Hudson River Basin Willamette Basin Long Island-New Jersey Lake Erie Basin Santee Basin Georgia-Florida Coastal Plain Reference stream Urban stream

  5. Sites span gradient of wet Hg deposition

  6. Urban sites Presumed higher loading; proximity to many sources Not targeted to point sources! Enhanced runoff Disturbed ecosystems Reference sites Low-moderate Hg loading Not “control” for urban sites Natural runoff pathways Minimally disturbed ecosystems Settings

  7. Comparison of Basin Sizes

  8. Reference settings: streams range from high-topographic gradient / low organic carbon…

  9. …to low-gradient, high-carbon streams

  10. Main study components: THg, MeHg, and related measures in: Precipitation Stream water filtered & particulate phases Sediment & pore water aquatic food web Hg+2 MeHg

  11. Aqueous methylmercury (MeHg) is a major control on mercury bioaccumulation Hg in forage fish (μg/g wet wt.) [mean of N≈24 at each site] Aqueous MeHg (ng/L) [mean of N ≈ 35 at each site]

  12. Stream sediment geochemistry • Characterize channel substrate. • Detailed geochemical measures: Concentrations: MeHg, THg, carbon, S, etc. Rates: • Methylation: Hg(II)  MeHg • Demethylation: MeHg  Hg(II), Hg° • Sulfate reduction: SO4-2 S-2

  13. Sediment methylation rate and MeHg concentration strongly relate to texture & organic content 250 Evergreen y = 4.36x + 9.7 R2 = 0.95 Oak Creek 200 Pike Creek 150 Methylation rate (from 203Hg experiment) (ng • g dry sed-1 • d-1) 100 50 0 0 10 20 30 40 50 60 Loss On Ignition (% dry weight)

  14. Substrate characterization sampling points Stream sediment characterization Mixed sand & fines Fines Sand Gravel & cobble Simplified channel cross section

  15. Sediment & porewater geochemistry sampling Transect Sand Sand & fine mixture Fines

  16. Large range in dominant channel substrate(grain size; organic content) 100 90 80 70 60 50 Low organic - Fine Percent of channel substrate High organic - Fine 40 High org-Sand/Fine 30 Sand 20 Larger than sand 10 0 L. Wekiva Santa Fe Lookout Evergreen St. Mary's Beaverton Oak Cr. Pike R.

  17. Note extremes MeHg in sediment (spatially weighted) unrelated to stream-water MeHg 9 Oregon sites Florida sites Wisc. sites 0.4 8 7 0.3 6 5 Sediment MeHg (ng/g dry sed) Mean aqueous MeHg (ng/L) 0.2 4 3 0.1 2 1 0 0 St Marys L Wekiva Santa Fe Pike Evergr. Oak Cr Lookout Beaver.

  18. Fluvial MeHg yield (μg/m2/year) Sediment methylation rate (spatially weighted; potential rate from 203Hg experiment, μg/m2/year) Fluvial MeHg yield unrelated to stream-sediment methylation rate

  19. Summary & Implications (1) • Aqueous MeHg is strongly related to fish-Hg concentrations. • Therefore, efforts to better understand MeHg production and transport are important for ecosystem management

  20. Summary & Implications (2) • Sediment MeHg unrelated to fluvial MeHg concentration and yield. • Evidence suggests stream sediments play weak role in MeHg mass balance • Demethylation – high in sandy sediments. • Methylation – high in organic-rich sediments. • Difficult to scale isotope experiments to mass-balance context. • It’s the watershed—Thursday’s presentation.

  21. Acknowledgments USGS: Dennis Wentz, Barb Scudder, Lia Chasar, Amanda Bell, Michelle Lutz, Dave Krabbenhoft, Mark Marvin-DiPasquale, George Aiken, Robin Stewart, Carol Kendall, Bill Orem, Rod DeWeese, Jeff Isely, and many others… USGS: NAWQA and several other programs USEPA: support for periphyton study MDN site support: Wisconsin DNR, Oregen DEQ, Forest Service, US Fish & Wildlife Service, St. John’s River Water Management District (Florida), USGS NAWQA Menomonie Indian Tribe of Wisconsin

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