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Mercury and Dissolved Organic Matter in Delta Wetlands
Project
Chief: Brian Bergamaschi and Jacob Fleck
Between 1860 and 1914, hydraulic mining activities sent more than 800,000,000
cubic yards of mercury-laden sediment into the Delta altering the landscape,
water flows, and contributing to the leveeing and reclamation of the Delta's
marshes. Transport of mercury from historic mining areas continues today.
The sedimentary supply of mercury to the Delta and in Delta sediments
(cinnabar, metacinnabar, and elemental Hg) typically are insoluble, but
will pose an environmental hazard if they are (1) solubilized and (2)
methylated in Delta and Estuary wetlands. The relative roles of dissolved
organic matter (DOM) and reduced sulfur in facilitating mercury solubilization
are elucidated, and the net export of Hg and MeHg off tidal wetlands are
quantified. The net export represents the integrated effect of site-specific
processes such as solubilization, oxidant supply, physical dynamics, microbial
rates, atmospheric and sedimentary loss, as well as other variables. The
specific effects of some of these processes are under active study by
others. In close collaboration with these ongoing process, level studies
of Hg methylation rates and food web incorporation, we propose to measure
net Hg and MeHg export from representative tidal wetlands to help assess
the contribution of tidal wetlands to Hg concentrations in the Delta,
and compare the Hg concentrations predicted by process-level rate studies
with the observed net wetland fluxes. In collaboration with ongoing Delta
Mercury studies, two specific elements of Hg cycling in the Delta, not
currently addressed by other studies, are addressed. The two specific
objectives are to: (1) Quantify the capability of DOM from representative
Delta wetlands to solubilize the major sedimentary forms of mercury in
the Delta, cinnabar (HgS), metacinnabar, and elemental Hg, and (2) Determine
the dissolved and particulate fluxes of Hg and monomethyl-Hg at representative
wetland sites in the Delta. The results of this study will provide knowledge
and insights helpful for guiding restoration of wetlands in such a way
that MeHg production and export are minimized to the extent possible.
Contact Information
Brian Bergamaschi and Jacob Fleck
Office phone: 916-278-3000
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