Mercury speciation and transport via submarine groundwater discharge at a southern California coastal lagoon system

Environmental Science & Technology
By: , and 



We measured total mercury (HgT) and monomethylmercury (MMHg) concentrations in coastal groundwater and seawater over a range of tidal conditions near Malibu Lagoon, California, and used 222Rn-derived estimates of submarine groundwater discharge (SGD) to assess the flux of mercury species to nearshore seawater. We infer a groundwater-seawater mixing scenario based on salinity and temperature trends and suggest that increased groundwater discharge to the ocean during low tide transported mercury offshore. Unfiltered HgT (U-HgT) concentrations in groundwater (2.2–5.9 pM) and seawater (3.3–5.2 pM) decreased during a falling tide, with groundwater U-HgT concentrations typically lower than seawater concentrations. Despite the low HgT in groundwater, bioaccumulative MMHg was produced in onshore sediment as evidenced by elevated MMHg concentrations in groundwater (0.2–1 pM) relative to seawater (∼0.1 pM) throughout most of the tidal cycle. During low tide, groundwater appeared to transport MMHg to the coast, resulting in a 5-fold increase in seawater MMHg (from 0.1 to 0.5 pM). Similarly, filtered HgT (F-HgT) concentrations in seawater increased approximately 7-fold during low tide (from 0.5 to 3.6 pM). These elevated seawater F-HgT concentrations exceeded those in filtered and unfiltered groundwater during low tide, but were similar to seawater U-HgT concentrations, suggesting that enhanced SGD altered mercury partitioning and/or solubilization dynamics in coastal waters. Finally, we estimate that the SGD HgT and MMHg fluxes to seawater were 0.41 and 0.15 nmol m–2 d–1, respectively – comparable in magnitude to atmospheric and benthic fluxes in similar environments.

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Publication type Article
Publication Subtype Journal Article
Title Mercury speciation and transport via submarine groundwater discharge at a southern California coastal lagoon system
Series title Environmental Science & Technology
DOI 10.1021/es202783u
Volume 46
Issue 3
Year Published 2012
Language English
Publisher American Chemical Society.
Contributing office(s) California Water Science Center, National Research Program - Western Branch
Description 9 p.
First page 1480
Last page 1488
Country United States
State California
Other Geospatial Southern California Coastal Lagoon System
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