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Mercury and Methylmercury Processes in North SF Bay Tidal Wetland Ecosystems

Mercury and Methylmercury Processes in North SF Bay Tidal Wetland Ecosystems. San Francisco Estuary Institute USGS BRD WERC Vallejo, CA USGS WRD Menlo Park, CA USGS WRD Middleton, WI Avocet Research Associates. Background: The Good?. Tidal wetland restoration plans

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Mercury and Methylmercury Processes in North SF Bay Tidal Wetland Ecosystems

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  1. Mercury and Methylmercury Processes in North SF Bay Tidal Wetland Ecosystems San Francisco Estuary Institute USGS BRD WERC Vallejo, CA USGS WRD Menlo Park, CA USGS WRD Middleton, WI Avocet Research Associates

  2. Background: The Good? • Tidal wetland restoration plans • Adding 12,000+ acres North Bay • Tidal wetlands • Habitat for threatened & other wildlife • Wetland restoration = good but…

  3. x The Bad? • Mercury (Hg) already in Bay-Delta biota @ levels of concern • human & wildlife health • Hg in biota correlates to watershed % wetlands • Mostly freshwater systems • Similar in tidal marshes? • Attractive nuisance? • Wildlife check in, but …?

  4. The Ugly? • Not just a matter of reducing Hg…

  5. What (Me)Hg Worry? • Not just Hg, need to worry about reducing methylmercury (MeHg) • Most bioaccumulative form • Formed by sulfate reducing bacteria under reducing conditions • But is subject to degradation- • Microbial • Abiotic (photolytic)

  6. Ask Questions First • (Me)Hg in wetlands: where, when, how much? • What influences (Me)Hg distribution & production? • How does (Me)Hg accumulate in tidal wetland food webs? • How does (Me)Hg get there: wetlands to bay (or vice versa)?

  7. Approach: General • Spatial distribution of (Me)Hg (water, sediments, biota) • Differences in (Me)Hg concentrations • Differences in (de)methylation processes • Temporal distribution • Seasonal differences in methylation rates and concentrations

  8. Spatial Distribution • 3 wetlands along Petaluma River Gambinini Ranch (Mid-)Petaluma Marsh Black John Slough Salinity gradient along Petaluma main stem

  9. Spatial Distribution • Within wetlands: habitat elements • Medium channels (2nd-3rd order) • High marsh plain • Transect composites (some grabs) • Replicates of habitat elements

  10. Food Web • Charismatic Critter: California Black Rail (USGS-BRD CA) - capture, tag, track • Identify distribution, habitat use, range, diet

  11. Bioaccumulation Examine (Me)Hg in biota: • High marsh food web: • Hg in California Black Rails (blood, feathers) • (Me)Hg in probable/potential diet items • Channel biota food web • Channel fish and invertebrates to compare

  12. MeHg Processes • Sediment processes (USGS-Menlo Park CA) • (De)Methylation rates in channel and high marsh • Lab incubations of sediment composites • Microbially available (reactive) Hg • Sediment quality (sulfur, carbon) • Water processes (USGS-Middleton WI) • Demethylation rates • Photo-incubation experiments

  13. Results: Hg Distribution • Sediment Hg similar @ all sites • >>ancient Hg levels • comparable to Bay sediments • High marsh < channel

  14. Sediment MeHg Distribution • High marsh • Highest at mid-Petaluma • Channel MeHg • Opposite of salinity gradient • < high marsh

  15. Vertical MeHg Distribution • MeHg highest in high marsh surface layers Gambinini MidPetaluma Black John

  16. MeHg in Sediments • Net = methylation - demethylation • Sediment MeHg parallels sulfate reduction

  17. What Drives Sediment MeHg? • Sulfate reducing bacteria need food!

  18. (Me)Hg in Water • Water MeHg similar to channel sediments • MeHg lowest near Bay end of Petaluma • MeHg & Hg mostly (80%+) in particulate phase

  19. Where do Biota Fit? • Are black rails in areas w/ high MeHg? • Small ranges (avg .24ha) in spring Black John Slough Mid Petaluma

  20. Habitat Usage • Primarily in high marsh pickleweed

  21. 9 8 High Marsh Slough 7 6 5 MeHg (ng/g) 4 3 2 1 0 BJS MP GAM Does It Add Up? • High Marsh sediment MeHg ~2x higher Mid-Petaluma • MeHg is bioaccumulative form of Hg

  22. Black Rail (Feather) Hg • Black rails reside and feed in high marsh, therefore… Rail Hg differs among wetlands (Mid-Petaluma ~2x)

  23. Implications for Management • MP feather Hg up to 10ng/g, is it bad? • Other birds “background” in feather ~1-5ng/g • Can we do anything about it? • Less (or more) reducing conditions? • Less organic matter? • Other goals and priorities? • (Me)Hg not the only factor • Newer marsh Hg < ancient marsh (problem in 2000 years?)

  24. Closing Credits Funding:CBDA Ecosystem Restoration Program grant ERP-02D-P62 Site Access:CDFG, the Phelans Project Partners: SFEI: (Don Yee), Josh Collins, Letitia Grenier, S. Pearce USGS WRD-CA: Mark Marvin-DiPasquale, Jennifer Agee, Le Kieu, Nick Ladizinski, Lisa Windham USGS WRD-WI: Dave Krabbenhoft, Shane Olund, Tom Sabin USGS BRD- John Takekawa, Isa Woo, Danika Tsao-Melcer Avocet Associates: Jules Evens

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