Submarine Groundwater Discharge of Total Mercury and Monomethylmercury to Central California Coastal Waters

Abstract

Fluxes of total mercury (Hg(T)) and monomethylmercury (MMHg) associated with submarine groundwater discharge (SGD) at two sites onthe central California coast were estimated by combining measurements of Hg(T) and MMHg in groundwater with the use of short-lived, naturally occurring radium isotopes as tracers of groundwater inputs. Concentrations of Hg(T) were relatively low, ranging from 1.2 to 28.3 pM in filtered groundwater, 0.8 to 11.6 pM in filtered surface waters, and 2.5 to 12.9 pM in unfiltered surface waters. Concentrations of MMHg ranged from < 0.04 to 3.1 pM in filtered groundwater, < 0.04 to 0.53 pM in filtered surface waters, and 0.07 to 1.2 pM in unfiltered surface waters. Multiple linear regression analysis identified significant (p < 0.05) positive correlations between dissolved groundwater concentrations of Hg(T) and those of NH4+ and SiO2, and between dissolved groundwater concentrations of MMHg and those of Hg(T) and NH4+. However, such relationships did not account for the majority of the variability in concentration data for either mercury species in groundwater. Fluxes of Hg(T) via SGD were estimated to be 250 +/- 160 nmol day m(-1) of shoreline at Stinson Beach and 3.0 +/- 2.0 nmol m(-2) day(-1) at Elkhorn Slough. These Hg(T) fluxes are substantially greater than net atmospheric inputs of Hg(T) reported for waters in nearby San Francisco Bay. Calculated fluxes of MMHg to coastal waters via SGD were 10 +/- 12 nmol day(-1) m(-1) of shoreline at Stinson Beach and 0.24 +/- 0.21 nmol m(-2) day at Elkhorn Slough. These MMHg fluxes are similar to benthic fluxes of MMHg out of surface sediments commonly reported for estuarine and coastal environments. Consequently, this work demonstrates that SGD is an important source of both Hg(T) and MMHg to coastal waters along the central California coast.

Groundwater dynamics in subterranean estuaries of coastal unconfined aquifers: Controls on submarine groundwater discharge and chemical inputs to the ocean

“…Black et al [2009] found that monomethyl-Hg (MMHg) fluxes from SGD were similar to those from fine grained surface sediments of a coastal Californian embayment; Lee et al [2011] reported a similar result for a Korean volcanic island. These examples are noteworthy because MMHg is the major Hg-species that is known to bio-accumulate through the food web and can lead to dangerous levels of Hg in fish that are harvested for human consumption.…”

Mass balance of mercury for the Yellow Sea downwind and downstream of East Asia: the preliminary results, uncertainties and future research priorities

“…In this estimate, the riverine Hg input to the YS is estimated by the concentrations of dissolved and particulate Hg levels and the amount of water and particulate load. Groundwater discharge may also represent an important contribution of Hg and other substances to the adjacent oceans (e.g., Rahman et al 2013;Peterson et al 2008;Waska and Kim 2011;Black et al 2009). However, in the past three decades the excessive exploitation of groundwater in the coastal region of the YS (particularly in China) has led to the seawater intrusion (Liu 2004).…”

Mercury Reduction and Methyl Mercury Degradation by the Soil Bacterium Xanthobacter autotrophicus Py2

“…It was long thought that Hg was relatively immobile in the subsurface due to sorption on sediment components such as iron oxides (1), but this assumption has come under scrutiny, since Hg has been unexpectedly found in groundwater at numerous sites, such as the Kirkwood-Cohansey aquifer in New Jersey (15,16), the Waquoit Bay near Cape Cod, MA (17), and the coasts of California, northern France, and South Korea (18)(19)(20)(21). One attractive hypothesis to explain the mobilization of Hg in the subsurface is that bacteria reduce sediment-bound Hg(II) to Hg(0), possibly catalyzed by MerA.…”