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Mercury Bioaccumulation

     Phytoplankton are the entry point for mercury in marine food webs [1,2], and subsequent mercury bioaccumulation in fish is the primary route of human exposure [3] . Yet despite the fact that phytoplankton form this critical link, their role in aquatic mercury dynamics is not clear, especially with respect to seasonal and geographic variability [2]. We are evaluating trends in mercury cycling in highly productive systems, with a focus on system response to algal blooms. Semi-enclosed ecosystems, such as coastal lagoons and terrestrial lakes, provide accessible natural laboratories with predictable algal blooms.

Are Coastal Lagoons Monomethylmercury (CH3Hg+) Hotspots?
     Urban and agricultural development increase the risk of nearshore eutrophication [4], which can enhance the
production of bioaccumulative monomethylmercury (CH3Hg+). Preliminary results
 suggest that coastal lagoons are monomethylmercury (CH3Hg+) hotspots, with concentrations in lagoon water up to 20-fold higher than
 in adjacent seawater [5,6,7]. This observation is of concern because these highly productive habitats have intricate food webs and serve as nurseries for a variety of organisms [8-10]. Processes that affect contaminant bioavailability in lagoons may therefore have a disproportionate impact on nearshore food web dynamics. Primary producers at the base of the food web represent the most significant step in mercury biomagnification, providing a mechanism to quantify biouptake [2]. We are therefore investigating the influence of phytoplankton bloom and die-off cycles on the biological uptake and fate of mercury in productive coastal lagoon systems by measuring the concentration and form of mercury in lagoon water, seawater, and phytoplankton at sites with a range of watershed attributes. We plan to complement our field investigations with laboratory experiments to assess Hg(II) and MMHg uptake  in cultured phytoplankton.

[1]  Black, F.J., C.H. Conaway, and A.R. Flegal, Mercury in the Marine Environment, in Mercury in the Environment: Pattern and Process, M.S. Bank, Editor 2012, Univ of California Press. p. 167-220.

[2]  Le Faucheur, S., P.G. Campbell, C. Fortin, and V.I. Slaveykova,
Interactions between mercury and phytoplankton: Speciation, bioavailability, and internal handling. Environmental Toxicology and Chemistry, 2014. 33(6): p. 1211-1224.

  Sunderland, E.M., Mercury exposure from domestic and imported estuarine and marine fish in the US seafood market. Environmental Health Perspectives, 2007. 115(2): p. 235-242.

[4]  Barnes, R.S.K., Coastal lagoons: the natural history of a neglected habitat. Cambridge Studies in Modern Biology. Vol. 1. 1980: Cambridge University Press. 106.

[5]  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.

[6]  Ganguli, P.M., C.H. Conaway, N.T. Dimova, P.W. Swarzenski, N.C. Kehrlein, and A.R. Flegal,
Seasonal variability in mercury speciation within select coastal lagoons of Central California. American Geophysical Union (AGU) Fall Meeting, San Francisco, CA, USA, 2011. Abstract No. B33H-0572.

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.

[8]  SFB RWQCB, Pescadero
Butano Watershed Sediment TMDL. 2013: p. 32.

[9]  Smith, J.J. and D.K. Reis,
Pescadero Marsh Natural Preserve salinity, tidewater goby and red-legged frog monitoring for 1995-1996. Report for the CA Department of Parks and Recreation, 1997: p. 76.

[10]  2NDNATURE,
Comparative Lagoon Ecological Assessment Project (CLEAP) for Santa Cruz County, California. 2006: p. 279.