1. 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

2. Mercury: A leading water-quality impairment Data 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 After: Mumley & Abu-Saba, WEF National TMDL Science and Policy Conference Proceedings, Nov. 13-16, 2002 Hg(II)  MeHg

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

5. Sites span gradient of wet Hg deposition

6. Settings 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

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: Stream water filtered & particulate phases Precipitation aquatic food web Hg +2 MeHg Sediment & pore water

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 1.Characterize channel substrate. 2.Detailed geochemical measures: Concentrations: MeHg, THg, carbon, S, etc. Rates: –Methylation: Hg(II)  MeHg –Demethylation: MeHg  Hg(II), Hg° –Sulfate reduction: SO 4 -2  S -2

13. Sediment methylation rate and MeHg concentration strongly relate to texture & organic content 0 50 100 150 200 250 0102030405060 Loss On Ignition (% dry weight) Methylation rate (from 203 Hg experiment) (ng g dry sed -1 d -1 ) y = 4.36x + 9.7 R 2 = 0.95 Evergreen Oak Creek Pike Creek

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

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

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

17. MeHg in sediment (spatially weighted) unrelated to stream-water MeHg 0 0.1 0.2 0.3 0.4 St MarysL WekivaSanta FePikeEvergr.Oak CrLookoutBeaver. Mean aqueous MeHg (ng/L) 0 1 2 3 4 5 6 7 8 9 Florida sitesWisc. sites Oregon sites Sediment MeHg (ng/g dry sed) Note extremes

18. Fluvial MeHg yield unrelated to stream-sediment methylation rate Fluvial MeHg yield (μg/m 2 /year) Sediment methylation rate (spatially weighted; potential rate from 203 Hg experiment, μg/m 2 /year)

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. Future directions: Move toward more complete mass balance: --Net role of sediments & periphyton --Dry deposition? Evasion? --Watershed retention / delivery / methylation Integrate with model development Intensive study area

22. 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