1 / 21

MeHg Concerns in SF Bay and Wetlands: Understanding Production and Degradation

Learn about methylmercury in SF Bay and wetlands, its formation by bacteria, and the factors influencing its degradation and production. Explore research findings, methodologies, and the significance of Total Nitrogen and Redox in MeHg concentrations. Discover the implications and possible solutions to reduce MeHg levels and ensure ecosystem health in the region.

blackpamela
Download Presentation

MeHg Concerns in SF Bay and Wetlands: Understanding Production and Degradation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Methylmercury and Mercury in SF Bay & Wetlands

  2. What- MeHg Worry? • Most bioaccumulative form of mercury… • Formed by sulfate reducing bacteria under anoxic conditions • But is subject to degradation- • Microbial • Abiotic (photolytic)

  3. More MeHg Worries? • Horvat et al., 2003- MeHg higher collected under N2- why? • Less degradation? Or more production? (~4 hrs field to lab)

  4. Puckett & Bloom 2000 Calfed study Samples frozen in field vs overnight chilled shipping No correlation in MeHg analyses of samples generate MeHg degrade MeHg Random Number Generator v1

  5. Heim et al (2003) Samples collected October to December 1999 Frozen in field 0-0.5cm sediments Primarily bay margins MeHg mostly < 1ng/g dry weight SF Bay MeHg (Calfed)

  6. What (Not) to Do? • Yes • Freeze, ASAP • Minimal thawing before analysis • No • repeated freeze-thaw (Horvat et al 1992) • Separate small samples as replicates • processing in air (but maybe not an issue if frozen quickly)?

  7. RMP Methodology (& Mistakes?) • RMP ~50 stratified random sites • van Veen grab, top 5 cm • Composite of 2-3 grabs • Homogenized on board (In air) • ~40 minutes, 1st grab to last jar in freezer • Analyzed months to years later

  8. MeHg for RMP • July & August 2002- 2004 (2002-3 shown here) • 0-5cm sediments • Mix of shallow & deep sites • MeHg range ~0-2ng/g dry weight • Hg, TOC, TN, grainsize, • Redox starting 2003

  9. Hg & MeHg – Random Number Generator v2?

  10. Hg Necessary, Not Sufficient • Literature correlations over many orders of magnitude • 95% of RMP Hg within 10x (0.04-0.35 mg/kg) • [MeHg] = +production –degradation -uptake ±transport • Need reducing conditions for methylating bacteria • Other important parameters? • TOC, TN, grainsize, Eh (redox potential)

  11. Dominant Factors: TN, Redox

  12. Redox Does Matter

  13. TOC and MeHg

  14. (Total) Nitrogen  TOC?

  15. Why TN and ORP? • TN = biologically active organic matter (TOC includes refractory material) • Low ORP = anoxia, measure of net status • Metal sulfides (black) visually apparent • Field meter measurement

  16. Conclusions • Surface (0-5cm) sediment MeHg similar range to previously found 0-0.5cm concentrations • MeHg poorly/un-correlated to total Hg, TOC • MeHg better correlated to TN, Redox • Consistent w/ indicators of active microbes • Relationships match expectations despite possibly compromised handling

  17. What Can Be Done? • Reduce reducing environments? • Prevent eutrophication & anoxia • May run counter to other ecosystem goals (Bay & wetland productivity & habitat) • Decrease sediment Hg? • May need total Hg <0.2 mg/kg to see impact on MeHg

  18. Schollenberger Park Water treatment plant Petaluma Marsh North Petaluma Marsh South Black John Slough Toy Marsh Carl’s Marsh Greenpoint Future Directions • RMP Sampling • Unmixed site replicates • Rapidly homogenized splits • Sediment Hg speciation • Petaluma River Wetlands CBDA • MeHg processes in fresh/brackish to saline tidal marshes • Food web studies in channel/low marsh, and high marsh plain • SFEI, Avocet Assoc., USGS (MP, Wi, BRD)

  19. Hg ~Constant Among Wetlands • Similar sources- air deposition, tidally mixed waters

  20. Sediment MeHg Varies Among Wetlands • MeHg produced within wetlands- mid salinity maximum?

  21. Black Rail MeHg Varies Among Wetlands • Sediment  invertebrates  birds

More Related