Data Series 282
U.S. GEOLOGICAL SURVEY
Data Series 282
Sediments are an important component of the San Francisco Bay estuarine system. Bottom sediments provide habitat for benthic organisms and are a reservoir for nutrients that contribute to estuarine productivity (Hammond and others, 1985). Potentially toxic substances, such as metals and pesticides, can adsorb to sediment particles (Kuwabara and others, 1989; Domagalski and Kuivila, 1993; Flegal and others, 1996). Benthic organisms can then ingest these substances and introduce them into the food web (Luoma and others, 1985; Brown and Luoma, 1995; Luoma, 1996). Large tidal-induced current velocities and wind waves in shallow water are capable of resuspending bottom sediments (Powell and others, 1989; Schoellhamer, 1996).
The mobilization, resuspension and deposition of suspended sediments are important factors in determining the transport and fate of sediment-associated contaminants. In Suisun Bay, the maximum suspended-sediment concentration (SSC) typically marks the position of the turbidity maximum—a crucial ecological zone where suspended sediments, nutrients, phytoplankton, zooplankton, larvae, and juvenile fish accumulate (Peterson and others, 1975; Arthur and Ball, 1979; Kimmerer, 1992; Jassby and Powell, 1994; Schoellhamer and Burau, 1998; Schoellhamer, 2001).
Suspended sediments limit the penetration of light into San Francisco Bay, which affects photosynthesis and primary phytosynthetic carbon production (Cole and Cloern, 1987; Cloern, 1987, 1996). Sediments also are deposited in ports and shipping channels, which then require dredging in order to remain navigable (U.S. Environmental Protection Agency, 1992). The U.S. Geological Survey (USGS), in cooperation with the CALFED Bay-Delta Authority, and the U.S. Army Corps of Engineers, is studying the factors that affect SSC in San Francisco Bay.
This report summarizes SSC data collected by the USGS in San Francisco Bay during water year (WY) 2005 and is the latest in a series of reports that present the data collected beginning in WY 1992 (Buchanan and Schoellhamer, 1995, 1996, 1998, 1999; Buchanan and others, 1996; Buchanan and Ruhl, 2000, 2001; Buchanan and Ganju, 2002, 2003, 2004, 2005; and Buchanan and Lionberger, 2006). Collection of SSC data in San Francisco Bay required development of monitoring methods and calibration techniques that are presented in this report. SSC were monitored at two sites in Suisun Bay, three sites in San Pablo Bay, two sites in Central San Francisco Bay, and three sites in South San Francisco Bay. SSC data from WY 1992 through WY 2005 were used to help determine the factors that affect SSC in San Francisco Bay (Schoellhamer and others, 2003; for the current bibliography of reports see U.S. Geological Survey, accessed February 26, 2007). Numerical SSC data for WY 1992 through 2005 are available from the U.S. Geological Survey (accessed February 26, 2007).
San Francisco Bay (fig. 1) comprises several major subembayments: Suisun Bay, San Pablo Bay, Central San Francisco Bay (Central Bay), and South San Francisco Bay (South Bay). In San Francisco Bay, tides are semidiurnal (two high and two low tides per day) and have a range of about 5.5 feet (ft) in Suisun Bay, 6.5 ft at the Golden Gate and Central Bay, and about 10 ft in South Bay. The tides also follow a 14-day spring-neap cycle. Typical tidal currents range from 0.6 foot per second (ft/s) in shallow water to more than 3 ft/s in deep channels (Cheng and Gartner, 1984; Smith, 1987). The strongest winds typically are sea breezes that blow onshore during summer afternoons. Most precipitation occurs from late autumn to early spring. Freshwater discharge into San Francisco Bay is greatest in the spring as a result of runoff from snowmelt. About 90 percent of the discharge into the Bay is from the Sacramento-San Joaquin River Delta, which drains the Central Valley of California (Smith, 1987).
Typically, discharge from the Delta contains about 60 percent of the fluvial sediments that enter the Bay (McKee and others, 2006), though this percentage varies from year to year. During wet winters, turbid plumes of water from the Delta have extended into South Bay (Carlson and McCulloch, 1974). The bottom sediments in South Bay and in the shallow water areas (about 12 ft or less) of Central, San Pablo, and Suisun Bays are composed mostly of silts and clays. Silts and sands are present in the deeper parts of Central, San Pablo, and Suisun Bays and in Carquinez Strait (Conomos and Peterson, 1977).
The authors gratefully acknowledge Gregory Brewster, Brad Sullivan and Heather Ramil of the USGS for their assistance with sample collection and maintenance of the data-collection network. The authors also wish to acknowledge the U.S. Coast Guard (USCG), the National Park Service, California Department of Transportation, California Department of Water Resources (DWR), EAI International, and the City of Vallejo for their permission and assistance in establishing the monitoring sites used in this study.
The project was done in cooperation with the CALFED Bay–Delta Authority, and the U.S. Army Corps of Engineers, as part of the San Francisco Estuary Regional Monitoring Program for Trace Substances. Additional funding was supplied by the USGS Priority Ecosystem Science Program.
U.S. Department of the Interior | U.S. Geological Survey
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