Mercury in the San Francisco Estuary - Reviews of Environmental Contamination and Toxicology - page 43

(2006) contrasted the accumulation of additions of inorganic Hg(II) and MMHg from
the dissolved phase and from invertebrate food by mosquitofish ( Gambusia affinis )
and redear sunfish ( Lepomis microlophus ) using water types collected from the delta
with different DOC concentrations. Bioaccumulation and retention of MMHg in fish
was substantially higher than that of inorganic mercury and differed by both fish spe-
cies and water type. Based on biokinetic modeling of the observed fish concentra-
tions, Pickhardt et al. concluded that high assimilation efficiencies and slow loss of
MMHg from dietary sources are the principal determinants of mercury burdens, but
that further research is needed to address the effects of DOC on its bioavailability
at lower levels of the food web in aquatic ecosystems.

B Untangling Biomagnification: Food Webs and

Environmental Effects

There are marked spatial and temporal variations in mercury concentrations in
higher trophic level organisms in San Francisco Estuary, which confounds efforts
to resolve processes governing bioaccumulation and biomagnification (Brookens
et al. 2007; Greenfield et al. 2005). Interannual variation in sportfish in the estuary
has been explained by factors ranging from variation in fish movement patterns,
diet, and populations sampled, or, alternatively, variation in freshwater discharge
causing increases of bioavailable mercury in the estuary (Greenfield et al. 2005).
Models of food chains need to be delineated within different regions and seasons
in the estuary, and these modeling efforts are being complicated by ongoing stressors
to the estuary (e.g., invasive species, climate change, water diversions and regula-
tion, and wetland management and restoration). Although algal blooms have now
been shown to have a bloom dilution effect on MMHg concentrations at the base of
planktonic food chains in the estuary (Luengen 2007), what effect the new phenom-
enon of increasing phytoplankton blooms in the estuary (Cloern et al. 2006) will
have on MMHg cycling in the estuary is unknown. These and other unknowns need
to be addressed by first making accurate measurements of concentrations and speci-
ation at different trophic levels and in different food chains within the estuary.

VI Management and Restoration

A History of Mercury Management in the Estuary

The history of mercury management in San Francisco Estuary begins with the wide-
spread recognition of the environmental problem in the 1970s (D'Itri 1972). Measures
resulting from litigation in the late 19th and early 20th century, such as the 1884
Sawyer Injunction and the 1893 Caminetti Act, sought to regulate the transport of