Relative to seawater, groundwater typically has low salinity, is oxygen-depleted, and contains high nutrient concentrations [1]. As a result, the groundwater-seawater interface is characterized by redox and geochemical gradients that can influence mercury bioavailability and toxicity through the microbial production of MMHg. Our work has shown that MMHg is generated in coastal aquifers and can be transported to the ocean via submarine groundwater discharge (SGD) along the coastal margin [2]. Furthermore, this discharge may be the predominant source of mercury species in some nearshore environments, with loadings comparable to, or greater than atmospheric deposition or benthic fluxes [2-5]. Field results also suggest enhanced SGD, which includes both terrestrial groundwater and recirculated seawater, can alter mercury partitioning and/or solubility in seawater and potentially influence Hg(II) bioavailability [2]. This phenomenon warrants further investigation, as does the observation that coastal groundwater temperature varies in concert with MMHg concentrations, possibly due to changes in bacterial activity [6]. We will explore these hypotheses through laboratory experiments and by detailing site-specific changes in mercury speciation and partitioning in groundwater and seawater over tidal, diurnal and seasonal cycles.
[1] Moore, W.S., The effect of submarine groundwater discharge on the ocean. Annual
Review of Marine Science, 2010. 2:
p. 59-88.
[2] Ganguli, P.M., C.H. Conaway, P.W. Swarzenski,
J.A. Izbicki, and A.R. Flegal, Mercury speciation and transport via submarine groundwater discharge at a Southern
California coastal lagoon system. Environmental Science & Technology,
2012. 46(3): p. 1480-1488.
[3] Cook, J., Woods Hole Oceanographic Institution. Researchers find substantial amount of mercury entering the ocean through groundwater: New pathway for pollution may change views of how much mercury is lingering in coastal waters. http://www.whoi.edu/page.do?pid=83318&tid=3622&cid=24446&c=2
[4] Black, F.J., A. Paytan, K.L. Knee, N.R. De Sieyes, P.M. Ganguli, E. Gary, and A.R. Flegal, Submarine Groundwater Discharge of Total Mercury and Monomethylmercury to Central California Coastal Waters. Environmental Science & Technology, 2009. 43(15): p. 5652-5659.monomethylmercury production and transport in nearshore surface water and groundwater: Younger Lagoon, California. in prep.
[5] Ganguli, P.M., P.W. Swarzenski, H. Dulaiova,
C.R. Glenn, and A.R. Flegal, Mercury
dynamics in a coastal aquifer: Maunalua Bay, O'ahu, Hawai'i. Estuarine,
Coastal and Shelf Science, 2014. 140:
p. 52-65.
[6] Ganguli, P.M., P.W. Swarzenski, N.T. Dimova, A.T. Fisher,
C.H. Conaway, R.A. Hohn, J. Merckling, N.C. Kehrlein, C.M. Richardson, C.D.
Johnson, C.H. Lamborg, and A.R. Flegal, Driving
mechanisms for monomethylmercury production and transport in nearshore surface
water and groundwater: Younger Lagoon, California. in prep.
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