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Hydrological controls on methylmercury distribution and flux in a tidal marsh

May 14, 2014

The San Francisco Estuary, California, contains mercury (Hg) contamination originating from historical regional gold and Hg mining operations. We measured hydrological and geochemical variables in a tidal marsh of the Palo Alto Baylands Nature Preserve to determine the sources, location, and magnitude of hydrological fluxes of methylmercury (MeHg), a bioavailable Hg species of ecological and health concern. Based on measured concentrations and detailed finite-element simulation of coupled surface water and saturated-unsaturated groundwater flow, we found pore water MeHg was concentrated in unsaturated pockets that persisted over tidal cycles. These pockets, occurring over 16% of the marsh plain area, corresponded to the marsh root zone. Groundwater discharge (e.g., exfiltration) to the tidal channel represented a significant source of MeHg during low tide. We found that nonchannelized flow accounted for up to 20% of the MeHg flux to the estuary. The estimated net flux of filter-passing (0.45 μm) MeHg toward estuary was 10 ± 5 ng m–2 day–1 during a single 12-h tidal cycle, suggesting an annual MeHg load of 1.17 ± 0.58 kg when the estimated flux was applied to present tidal marshes and planned marsh restorations throughout the San Francisco Estuary.

Citation Information

Publication Year 2014
Title Hydrological controls on methylmercury distribution and flux in a tidal marsh
DOI 10.1021/es500781g
Authors Hua Zhang, Kevan B. Moffett, Lisamarie Windham-Myers, Steven M. Gorelick
Publication Type Article
Publication Subtype Journal Article
Series Title Environmental Science & Technology
Index ID 70129259
Record Source USGS Publications Warehouse
USGS Organization National Research Program - Western Branch