Mercury Dynamics in a San Francisco Estuary Tidal Wetland: Assessing Dynamics Using In Situ Measurements

Abstract

We used high-resolution in situ measurements of turbidity and fluorescent dissolved organic matter (FDOM) to quantitatively estimate the tidally driven exchange of mercury (Hg) between the waters of the San Francisco estuary and Browns Island, a tidal wetland. Turbidity and FDOM-representative of particle-associated and filterpassing Hg, respectively-together predicted 94 % of the observed variability in measured total mercury concentration in unfiltered water samples (UTHg) collected during a single tidal cycle in spring, fall, and winter, [2005][2006]. Continuous in situ turbidity and FDOM data spanning at least a full spring-neap period were used to generate UTHg concentration time series using this relationship, and then combined with water discharge measurements to calculate Hg fluxes in each season. Wetlands are generally considered to be sinks for sediment and associated mercury. However, during the three periods of monitoring, Browns Island wetland did not appreciably accumulate Hg. Instead, gradual tidally driven export of UTHg from the wetland offset the large episodic on-island fluxes associated with high wind events. Exports were highest during large spring tides, when ebbing waters relatively enriched in FDOM, dissolved organic carbon (DOC), and filter-passing mercury drained from the marsh into the open waters of the estuary. On-island flux of UTHg, which was largely particleassociated, was highest during strong winds coincident with flood tides. Our results demonstrate that processes driving UTHg fluxes in tidal wetlands encompass both the dissolved and particulate phases and multiple timescales, necessitating longer term monitoring to adequately quantify fluxes.

Concurrent photolytic degradation of aqueous methylmercury and dissolved organic matter

“…DOM strongly binds with the reactive inorganic form Hg II (Han et al, 2006;Lamborg et al, 2003;Ravichandran, 2004) and MeHg (Hintelmann et al, 1997;Khwaja et al, 2010;Qian et al, 2002). Because of this DOM plays a role in the cycling and bioavailability of both Hg II (Bergamaschi et al, 2012;Brigham et al, 2009;Dittman et al, 2010;Gorski et al, 2008;Gerbig et al, 2011;Graham et al, 2012;Schuster et al, 2011) and MeHg (Bergamaschi et al, 2011;Pickhardt and Fisher, 2007;Tsui and Finlay, 2011). DOM also binds with other radical-forming constituents that may participate in photochemical processes (Gu et al, 2011;Gao and Zepp, 1998).…”

“…Furthermore, optical properties can be measured in situ at time-scales relevant to natural processes (Romera-Castillo et al, 2011). Recently, optical proxies have been used successfully to determine temporal variability in THg and MeHg concentration in dynamic hydrologic settings (Bergamaschi et al, 2011(Bergamaschi et al, , 2012Dittman et al, 2009).…”

Optically based quantification of fluxes of mercury, methyl mercury, and polychlorinated biphenyls (PCBs) at Berry's Creek tidal estuary, New Jersey

“…These optical signatures may describe particle composition (e.g., Twardowski et al ; Sullivan et al ; Chang et al ), size distribution (e.g., Boss et al , b ; Agrawal and Mikkelsen ; Briggs et al ), and/or concentration (Babin et al ) including for colored dissolved organic matter (CDOM) (Coble et al ); therefore optical measurements provide a potential means to quantify the concentration of COCs. Bergamaschi et al (, , b ) successfully developed and validated statistical models for the derivation of mercury and methyl mercury concentration from in situ optical properties and used the optically based results to quantify mass flux of mercury and methyl mercury throughout several different tidal estuaries. To the authors’ knowledge, no previous studies have quantified concentrations of PCBs using in situ optical properties.…”

Recent Advances in Understanding Flow Dynamics and Transport of Water-Quality Constituents in the Sacramento–San Joaquin River Delta

“…Elevated concentrations of mercury in suspended sediments have been reported (Domagalski et al 2004;Roth et al 2001). The concern is that these sediments will be deposited in reducing environments such as wetlands (Bergamaschi et al 2012) where the mercury will be transformed into its organic and more toxic form: methylmercury ).…”

“…Optical sensors invented in the 1980s were first deployed in the Delta in the late 1990s to continuously measure suspended-sediment concentration (Wright and Schoellhamer 2005). Optical sensors that continuously measure carbon and nutrients were first deployed in the Delta in the 2000s (Bergamaschi et al 2012;Downing et al 2009;Pellerin et al 2013). When these instruments are deployed with sufficient density to enable several channels or locations to be observed simultaneously, continuous data streams that include all tidal fluctuations can be collected, and these data have led to improved understanding of flow and constituent transport in the Delta.…”