Article

Estuaries and Coasts

, Volume 35, Issue 4, pp 1036-1048

Open Access This content is freely available online to anyone, anywhere at any time.

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

  • Brian A. BergamaschiAffiliated withUnited States Geological Survey California Water Science Center Email author 
  • , Jacob A. FleckAffiliated withUnited States Geological Survey California Water Science Center
  • , Bryan D. DowningAffiliated withUnited States Geological Survey California Water Science Center
  • , Emmanuel BossAffiliated withUniversity of Maine School of Marine Sciences
  • , Brian A. PellerinAffiliated withUnited States Geological Survey California Water Science Center
  • , Neil K. GanjuAffiliated withUnited States Geological Survey Woods Hole Science Center
  • , David H. SchoellhamerAffiliated withUnited States Geological Survey California Water Science Center
  • , Amy A. ByingtonAffiliated withMoss Landing Marine Laboratories
  • , Wesley A. HeimAffiliated withMoss Landing Marine Laboratories
    • , Mark StephensonAffiliated withCalifornia Department of Fish and Game Marine Pollution Studies Laboratory
    • , Roger FujiiAffiliated withUnited States Geological Survey California Water Science Center

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, 2005–2006. 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 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.

Keywords

Mercury Tidal wetlands San Francisco Bay Sacramento River Delta Mercury flux Sediment flux Rivers Wetlands Estuaries Wetland restoration