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

Abstract:

We measured total mercury (Hg <inf>T</inf>) 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 Hg <inf>T</inf> (U-Hg <inf>T</inf>) concentrations in groundwater (2.2-5.9 pM) and seawater (3.3-5.2 pM) decreased during a falling tide, with groundwater U-Hg <inf>T</inf> concentrations typically lower than seawater concentrations. Despite the low Hg <inf>T</inf> 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 <inf>T</inf> (F-Hg <inf>T</inf>) concentrations in seawater increased approximately 7-fold during low tide (from 0.5 to 3.6 pM). These elevated seawater F-Hg <inf>T</inf> concentrations exceeded those in filtered and unfiltered groundwater during low tide, but were similar to seawater U-Hg <inf>T</inf> concentrations, suggesting that enhanced SGD altered mercury partitioning and/or solubilization dynamics in coastal waters. Finally, we estimate that the SGD Hg <inf>T</inf> 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. © 2012 American Chemical Society.

Año de publicación:

2012

Keywords:

Fuente:

scopus