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Methylmercury in Bay and Wetland Sediments of the San Francisco Bay Region

This study examines the distribution and drivers of methylmercury (MeHg) in the sediments of the San Francisco Bay and its wetlands. It explores the sources of MeHg, the impacts of wetland vegetation, and the implications for management and restoration efforts. Funding for this project was provided by the SF Estuary Regional Monitoring Program and the CBDA Ecosystem Restoration Program.

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Methylmercury in Bay and Wetland Sediments of the San Francisco Bay Region

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  1. Methylmercury in Bay and Wetland Sediments of the San Francisco Bay RegionDon Yee, SFEIRMP 2008 Hg Coordination Meeting San Francisco Estuary Institute UC Santa Cruz USGS WRD Menlo Park CA, Middleton WI, BRD Vallejo CA

  2. San Francisco Hg Sources • Anthropogenic sources dating to Gold Rush USBM/USGS

  3. Ongoing SF Bay Hg Sources SFBRWQCB TMDL

  4. Bay Sampling Locations • Regional Monitoring Program • survey Bay1993- • summer (annual) • 49 sediment sites • random stratified • 5 bay segments + rivers

  5. Wetland Sampling Locations City of Petaluma • 3 wetlands along Petaluma River • Gambinini Ranch • Mid-Petaluma Marsh • Black John Slough • Gradient of increasing salinity/Bay influence < Gambinini Marsh < Mid Petaluma Black John Slough > San Pablo Bay

  6. Wetland Site Distribution • Habitat elements • medium channels • small channels • high marsh edge • high marsh interior • Composites (transects or clusters) • Replicates of habitat elements a c b d

  7. Hydro-Biological Interactions • Overbank events recharge groundwater table • Marsh plain interiors drain slowly • Redox swings with O2 supply and respiration

  8. Bay Hg and MeHg 2002-2006

  9. Intersegment Differences San Pablo Bay (SPB) Hg high but MeHg low

  10. SF Bay MeHg vs Total Hg • Sediment concentrations poorly correlated

  11. Wetland MeHg vs Total Hg • Sediment MeHg vs Hg also poorly correlated

  12. What Drives MeHg? • Plenty of Hg, SO4, bacteria need food!

  13. Wetland Plant Processes • (Windham will give details) • Compare untreated vs devegetated areas

  14. Wetland Devegetation Effects •  organic =  reduced reduction

  15. SF Bay MeHg vs TOC • Not all carbon is good bacterial food

  16. SF Bay MeHg vs Total N • N better proxy for labile organic matter?

  17. SF Bay MeHg vs Redox • OM substrate -> reduction -> methylation

  18. Linkage to Biota • Biota Hg concentrations mirror ambient MeHg • matrix linked to nearest food web element • e.g. Slotton water MeHg vs fish in Sacramento Delta

  19. Summary • New(ish): Total Hg not limiting MeHg in SF Bay (both wetlands & subtidal) • MeHg generally < 1% of total Hg • Legacy loads, ongoing inputs >> sufficient for all MeHg production • Q1 (what “hot” spots) & Q2 (what processes): high Sediment MeHg linked to OM/ redox • Less reduction  less methylation, more demethylation

  20. Management Implications • Q3 (how might we manage) even small Hg inputs could support a major portion of standing MeHg pool • 1 week air input = water MeHg pool • 2 years input = sediment MeHg pool top 5cm • Might some Hg be more manageable? • e.g. METAALICUS new 202Hg 1% of total Hg overall but 6% of vegetation Hg within 15 weeks

  21. Management Implications • More productivity = more OM  more MeHg? • Will wetland restoration exacerbate Hg problem? • Competing goal of more wildlife habitat • Indirect management levers • MeHg control by-product of nutrient TMDL? • Need better understanding of • Relative availability of Hg loads • MeHg transport and uptake into food web

  22. Closing Credits Funding: SF Estuary Regional Monitoring Program, CBDA Ecosystem Restoration Program Sampling, Site Access: USBR Endeavor, CA DFG, R.Phelan & S.Brand Project Partners: AMS: P.Salop, B.Bemis, C.Dominik, B.Hajduczek SFEI: J.Collins, L.Grenier, J.Hunt, S.Pearce, C.Striplen, S.Shonkoff, S.Bezalel, N.David, A.Franz,M.Williams UCSC : A.R.Flegal, S. Hibdon USGS WRD-CA: M.Marvin-DiPasquale, J.Agee, L.Kieu, N.Ladizinski, L.Windham USGS WRD-WI: D.Krabbenhoft, T.Sabin, J.DeWild USGS BRD- J.Takekawa, I.Woo, D.Tsao-Melcer, Photo: D.Gaube, E.Lindgren, B.Hill

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