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Mercury Cycling and Bioaccumulation in Streams

This study examines mercury levels and bioaccumulation in streams in Oregon, Wisconsin, and Florida. Factors controlling mercury levels in fish and sediment are investigated, along with the impact of urbanization on mercury loading. The study also analyzes the relationship between methylmercury (MeHg) concentrations and sediment characteristics.

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Mercury Cycling and Bioaccumulation in Streams

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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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