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Mercury Dynamics in a San Francisco Estuary Tidal Wetland: Assessing Dynamics Using In Situ Measurements |
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| Authors: | Brian A Bergamaschi Jacob A Fleck Bryan D Downing Emmanuel Boss Brian A Pellerin Neil K Ganju David H Schoellhamer Amy A Byington Wesley A Heim Mark Stephenson Roger Fujii |
| Institution: | 1. United States Geological Survey California Water Science Center, 6000 J Street, Sacramento, CA, 95819-6129, USA 2. University of Maine School of Marine Sciences, Orono, ME, 04469, USA 3. United States Geological Survey Woods Hole Science Center, 384 Woods Hole Road, Woods Hole, MA, 02543-1598, USA 4. Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA, 95039, USA 5. California Department of Fish and Game Marine Pollution Studies Laboratory, 7544 Sandholdt Rd, Moss Landing, CA, 95039, USA |
| 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 filter-passing 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?C2006. 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 particle-associated, 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. |
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