Methylmercury in Bay and Wetland Sediments of the San Francisco Bay Region Don Yee, SFEI RMP 2008 Hg Coordination Meeting San Francisco Estuary Institute UC Santa Cruz USGS WRD Menlo Park CA, Middleton WI, BRD Vallejo CA

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

Ongoing SF Bay Hg Sources SFBRWQCB TMDL

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

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

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

Hydro-Biological Interactions Overbank events recharge groundwater table Marsh plain interiors drain slowly Redox swings with O 2 supply and respiration

Bay Hg and MeHg

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

SF Bay MeHg vs Total Hg Sediment concentrations poorly correlated

Wetland MeHg vs Total Hg Sediment MeHg vs Hg also poorly correlated

What Drives MeHg? Plenty of Hg, SO 4, bacteria need food!

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

Wetland Devegetation Effects organic = reduced reduction

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

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

SF Bay MeHg vs Redox OM substrate -> reduction -> methylation

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

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

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 202 Hg 1% of total Hg overall but 6% of vegetation Hg within 15 weeks

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

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