title: Mercury speciation and transport via submarine groundwater discharge at a southern California coastal lagoon system.
abstract: We measured total mercury (Hg(T)) and monomethylmercury (MMHg) concentrations in coastal groundwater and seawater over a range of tidal conditions near Malibu Lagoon, California, and used (222)Rn-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 Hg(T) (U-Hg(T)) concentrations in groundwater (2.2-5.9 pM) and seawater (3.3-5.2 pM) decreased during a falling tide, with groundwater U-Hg(T) concentrations typically lower than seawater concentrations. Despite the low Hg(T) 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 Hg(T) (F-Hg(T)) concentrations in seawater increased approximately 7-fold during low tide (from 0.5 to 3.6 pM). These elevated seawater F-Hg(T) concentrations exceeded those in filtered and unfiltered groundwater during low tide, but were similar to seawater U-Hg(T) concentrations, suggesting that enhanced SGD altered mercury partitioning and/or solubilization dynamics in coastal waters. Finally, we estimate that the SGD Hg(T) 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.
authors.affiliation: Earth and Planetary Sciences, University of California, Santa Cruz, California, United States. pganguli@ucsc.edu
authors.forename: P M
authors.initials: PM
authors.lastname: Ganguli
authors.forename: C H
authors.initials: CH
authors.lastname: Conaway
authors.forename: P W
authors.initials: PW
authors.lastname: Swarzenski
authors.forename: J A
authors.initials: JA
authors.lastname: Izbicki
authors.forename: A R
authors.initials: AR
authors.lastname: Flegal
mesh_terms: D002140:California; D004784:Environmental Monitoring / Q000706:statistics & numerical data*; D019015:Geologic Sediments / Q000737:chemistry; D060587:Groundwater / Q000737:chemistry*; D008628:Mercury / Q000032:analysis*; D008767:Methylmercury Compounds / Q000032:analysis*; D011886:Radon; D054712:Salinity; D012623:Seawater / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013696:Temperature; D014872:Water Movements
chemical_list: D008767:Methylmercury Compounds; D008628:Mercury; D011886:Radon