Summary of suspended-solids concentration data, Central and South San Francisco Bays, California, water years 1992 and 1993

Abstract

Suspended-solids concentration data were collected in Central and South San Francisco Bays during water years 1992 and 1993. Optical backscatterance sensors were used to monitor suspended solids at three sites in South San Francisco Bay and at two sites in Central San Francisco Bay. Sensors were positioned at two depths at each site, mid-depth and near-bottom. Water samples were collected periodically and were analyzed for concentrations of suspended solids. The results of the analyses were used to calibrate the electrical output of the optical backscatterance sensors. This report presents the data-collection methods used and summarizes the suspended-solids concentration data collected from December 1991 through September 1993. Calibration plots and edited data for each sensor also are presented. which limits photosynthesis and primary production (Cloem, 1987; Cole and Cloem, 1987), and deposit in ports and shipping channels, which require dredging (U.S. Environmental Protection Agency, 1992). The U.S. Geological Survey (USGS), in cooperation with the San Francisco Regional Water Quality Control Board (South Bay) and the U.S. Army Corps of Engineers (Central Bay), is studying the factors that affect suspended-solids concentrations in San Francisco Bay. Purpose and Scope This report summarizes suspended-solids concentration data collected by the USGS in Central and South San Francisco Bays in water years 1992 and 1993. Complete data are available from the files of the USGS in Sacramento. Suspended-solids concentrations were monitored at two sites in Central San Francisco Bay and at three sites in South San Francisco Bay. INTRODUCTION Sediments are an important component of the San Francisco Bay estuarine system. Potentially toxic substances, such as metals and pesticides, adsorb to sediment particles (Kuwabara and others, 1989; Domagalski and Kuivila, 1993). The sediments on the bottom of the bay provide the habitat for benthic communities that can ingest these substances and introduce them into the food web (Luoma and others, 1985). The bottom sediments are also a reservoir of nutrients that contribute to the maintenance of estuarine productivity (Hammond and others, 1985). The transport and fate of suspended sediment is an important factor in determining the transport and fate of the constituents adsorbed on the sediment. Suspended sediments also limit light availability in the bay, Study Area Tides in San Francisco Bay (fig. 1) are semidiurnal with a range of about 6.5 ft at the Golden Gate and Central Bay that increases to about 10 ft in South Bay. The tides also have a 14-day spring-neap cycle. Typical tidal currents range from 0.6 ft/s in shallow water to more than 3 ft/s in deep channels (Smith, 1987). Winds are typically strongest during the summer when there is an afternoon sea breeze. Most precipitation occurs from late fall to early spring and freshwater discharge into the bay is greatest in the spring due to snowmelt. About 90 percent of the discharge is from the Sacramento-San Joaquin River Delta, which drains the Central Valley of California (Smith, 1987). The delta discharge contains 83 to 86 percent of the fluvial sediments that enter San Fran-