PARENT SESSION
Organized Oral Session 5: Mercury cycles: Sources, mass balances, bioaccumulation, and options to manage affected systems
Organizer(s): EPH Best, JG Wiener, and D Planas
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 511 C, Level 5, Palais des congrès de Montréal

Net production and incorporation of methylmercury in the base of the San Pablo Bay (CA) salt marsh food web.

Best, Elly^*,1, Fredrickson, Herbert¹, Hintelmann, Holger², ¹ U.S. Army Engineer Research & Development Center, Environmental Laboratory, Vicksburg, Mississippi, USA² Trent University, Peterborough, Ontario, Canada

ABSTRACT- Restoration of wetland habitat around San Francisco Bay must be evaluated in the context of the potential impact of adding methylmercury to the Bay-Delta ecosystem. Little quantitative data are currently available on the factors that control net methylmercury production in salt marshes and on the processes and rates at which methylmercury bioaccumulates at different trophic levels. Dredged material is to be used to raise a 203 ha site at the formerly used defense site, Hamilton Army Airfield (HAAF) on San Pablo Bay, to an elevation that will support submerged and emergent aquatic macrophytes in a salt marsh environment. This beneficial use of dredged material would be a win - win situation as large volumes of fill are needed to restore the wetlands and costs of transporting the dredged material to more distant disposal sites can be avoided. Due to past mercury and gold mining, the watersheds draining into the San Francisco Bay system contain elevated levels of total mercury (THg) and methylmercury (MeHg). Atmospheric sources have also been shown to be important in other mercury impacted aquatic ecosystems. The significant sources of mercury for methylation and the potential for saltmarshes around the Bay to export MeHg into the Bay have yet to be determined. The potential for coastal wetlands to act as a source or sink for MeHg has to be assessed and management measures to minimize net MeHg production evaluated. We collected pre-construction data in an existing wetland bordering the HAAF site and in a nearby, established, reference wetland, China Camp. We measured the concentrations of THg and MeHg in the sediments and in biota representing major functional groups, and determined the on-site methylation and demethylation rates using stable Hg isotopes. Based on the collected data we calculated a mass balance for the HAAF. This study will provide site-specific information, needed as a basis for wetland design and management in the San Francisco Bay area.

Key words: mercury, mass, biomagnification, management