Pre-Construction Biogeochemical Analysis of Mercury in Wetlands Bordering the Hamilton Army Airfield (HAAF) Wetlands Restoration Site. Part 2

With funding from the Long Term Management Strategy team, the U.S. Army Corps of Engineers (USACE) is working with the San Francisco Basin Regional Water Board, California State Coastal Conservancy, and San Francisco Bay Conservation and Development Commission to reconstruct wetlands at the former Hamilton Army Airfield (HAAF) on San Pablo Bay. This 203-ha site will provide tidal habitat to endangered species such as the clapper rail and the saltmarsh harvest mouse. Because HAAF has subsided well below mean sea level, it will require 8.1 million cubic meters of material to elevate the site to the point where emergent marsh vegetation can become established. This is a critical process that will reestablish natural sediment trapping, marsh building, and physical dynamics. However, wetlands are generally considered a source of monomethylmercury (MeHg) production, and the association of mercury with gold mining legacies of the Bay Basin raises particular concerns. HAAF represents only 203 ha of the additional 26,325 ha of wetlands to be established around the bay between 2005 and 2055. Means to mitigate MeHg magnification in bay aquatic food webs are needed not only for HAAF but other SF Bay restoration sites as well. Those means are currently unknown. This interim technical report describes studies primarily performed in 2004 and 2005 and completed in the first half of 2006. Work during this period focused on (1) site-specific rates of methylation and demethylation, as well as characterizations of sedimentary microbial communities; (2) mercury dynamics in decomposing plant litter; (3) mercury dynamics in food webs; and (4) bioavailability of sediment-associated mercury of existing marsh sediments to macrobenthos. A new time-integrative method for measuring and monitoring mercury cycle-related biogeochemical parameters in marshes was developed, and the role of marsh vegetation as a vector in mercury species transport was quantified.

See ADA439941 for earlier report, dated Sep 2005. Prepared in collaboration with Trent University, Department of Chemistry, Ontario, Canada and Applied Research Associates, Vicksburg, MS. The original document contains color images.