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Preconstruction Biogeochemical Analysis of Mercury in Wetlands Bordering the Hamilton Army Airfield (HAAF) Wetlands Restoration Site. Part 3
ENGINEER RESEARCH AND DEVELOPMENT CENTER VICKSBURG MS ENVIRONMENTAL LAB
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The U.S. Army Corps of Engineers USACE is working to reconstruct wetlands at the former Hamilton Army Airfield HAAF on San Pablo Bay SPB. This 203-ha site will provide tidal habitat to endangered species such as the clapper rail and the saltmarsh harvest mouse. Means to mitigate MeHg magnification in bay aquatic food webs are needed not only for HAAF but for other Bay restoration sites as well. This interim technical report describes studies primarily performed in 2006. A field study was conducted in San Pablo Bay focusing on site-specific rates of mercury methylation and demethylation, and biogeochemical parameters related to the mercury cycle as measured by both conventional and emerging methods, including Diffusive Gradient in Thin Film DGT and Diffusional Equilibration in Thin Film DET techniques. Experiments on MeHg accumulation by clams, fish, and DGTs were conducted under laboratory conditions to test the ability of the DGT technique to mimic MeHg bioaccumulation. The multiple source mixing models SOURCE and STEP were used to quantify food web sources and trophic structure using multiple stable isotopes, and, thus, contribute to elucidating the trophic relationships leading to MeHg bioaccumulation. Use of these models showed that macrophytic primary producers of the salt marsh formed important food sources of consumers. Consumers in the nearshore bay were found to be largely benthivorous and fed partly on higher plant fragments andor bay-POM, of which the relative contributions decreased with increasing trophic level. A data gap exists on food chain structure, components, bioaugmentation mechanisms and MeHg accumulated in the biota associated with San Francisco Bay wetlands. Additional field, experimental, and modeling research was recommended to decrease the uncertainty of these early model outcomes.
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