Hydrological Controls on Methylmercury Distribution and Flux in a Tidal Marsh

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• 作者：Hua Zhang ; Kevan B. Moffett ; Lisamarie Windham-Myers ; Steven M. Gorelick
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：June 17, 2014
• 年：2014
• 卷：48
• 期：12
• 页码：6795-6804
• 全文大小：522K
• 年卷期：v.48,no.12(June 17, 2014)
• ISSN：1520-5851

文摘

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 渭m) MeHg toward estuary was 10 卤 5 ng m^鈥? day^鈥? during a single 12-h tidal cycle, suggesting an annual MeHg load of 1.17 卤 0.58 kg when the estimated flux was applied to present tidal marshes and planned marsh restorations throughout the San Francisco Estuary.