Mercury in the San Francisco Estuary - Reviews of Environmental Contamination and Toxicology - page 30

Bay: The Ecosystem (Hollibaugh 1996). In addition, articles are available on the
characteristics and circulation patterns in the estuary (Conomos et al. 1985), temporal
fluctuation and time scales of variability of estuarine parameters (Cloern and Nichols
1985; Thomson-Becker and Luoma 1985), and anthropogenic modification of the estu-
ary over time (Nichols et al. 1986). Some recent studies have covered water circulation,
salinity, and nutrients (Kimmerer 2002; Monismith et al. 2002; Smith and Hollibaugh
2006); suspended sediment (Ganju et al. 2005; McKee et al. 2006; Ruhl et al. 2001;
Schoellhamer 2002); organic carbon (Lesen 2006; Murrell and Hollibaugh 2000;
Stepanauskas et al. 2005); marsh formation (Watson 2004); and sedimentation
(Foxgrover et al. 2004; Jaffe and Foxgrover 2006; Jaffe et al. 1998).
San Francisco Estuary is a truly unique setting (Fig. 1). It is a natural, semien-
closed body of water created by right-lateral movement on the San Andreas fault
system (Hedgpeth 1979). It is the largest estuary on the California coast and is heav-
ily urbanized (Nichols et al. 1986). Its circulation is controlled by tidal currents and
freshwater flow, which is dominated by the distinctly Mediterranean climate in the
region—dry summers and wet winters (Kimmerer 2002). San Francisco Estuary can
be divided into two geochemically distinct subestuaries, the northern and southern
reaches, which join in the Central Bay and connect to the Pacific Ocean via the
Golden Gate (Flegal et al. 1991). The system has further been divided into six hydro-
graphically distinct regions: Tributaries, Southern Sloughs, South Bay, Central Bay,
Northern Estuary, including San Pablo Bay and Suisun Bay, and River-Delta
(Conaway et al. 2007). Ninety percent of the annual freshwater inflow to the estuary
enters via the northern reach through the delta formed by the convergence of the
Sacramento-San Joaquin drainage basins, which includes most of the Coast Ranges,
the Central Valley of California, and the western Sierra Nevada (Conomos et al.
1985). The Napa and Petaluma Rivers, which also drain to the northern reach, pro-
vide local drainage from the Coast Ranges, but their discharges are relatively small
in comparison. In contrast, the southern reach receives only a small amount of fresh-
water input (<10% of the total freshwater input to the estuary), mostly from the
Guadalupe River, Coyote Creek, and other small tributaries that locally drain the
Coast Ranges and the Santa Clara Valley. Onto this physically and chemically com-
plex system is superimposed an ecologically and biogeochemically complex mer-
cury contamination issue, which has been the focus of many studies reviewed here.

II Issues Related to Mercury Contamination

in San Francisco Estuary

Concerns about mercury in San Francisco Estuary center on human health and
ecological effects on birds. The San Francisco Bay Regional Water Quality Control
Board (SFRWQCB), which is tasked with the preservation of beneficial uses of the
estuary, has determined that the estuary is impaired for mercury, in part because of
the reported concentrations of mercury in fish tissue and bird eggs (SFRWQCB
2006). Studies on fish and ecotoxicological effects on birds both support this regu-
latory statement and highlight concerns of mercury toxicity.