Hydrological controls on methylmercury distribution and flux in a tidal marsh.
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.
Environmental Earth System Science, Stanford University , Stanford, California 94305-2115, United States.
Hua
H
Zhang
Kevan B
KB
Moffett
Lisamarie
L
Windham-Myers
Steven M
SM
Gorelick
D002140:California; D004784:Environmental Monitoring; D063366:Estuaries; D060587:Groundwater / Q000737:chemistry; D062070:Hydrology; D008628:Mercury / Q000032:analysis; D008767:Methylmercury Compounds / Q000032:analysis*; D008906:Mining; D010944:Plants / Q000378:metabolism; D016062:Porosity; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis; D053833:Wetlands
D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D008628:Mercury