Abstract
The U.S. Geological Survey (USGS) monitors water
quality and suspended-sediment transport in the San Francisco
Bay. The San Francisco Bay area is home to millions of people,
and the bay teems with both resident and migratory wildlife,
plants, and fish. Fresh water mixes with salt water in the bay,
which is subject both to riverine and marine (tides, waves,
influx of salt water) influences. To understand this environment,
the USGS, along with its partners,
has been monitoring the bay’s waters continuously since 1988.
Several water-quality variables are of particular importance
to State and Federal resource managers and are monitored
at key locations throughout the bay. Salinity, which
indicates the relative mixing of fresh and ocean waters in
the bay, is derived from specific conductance measurements.
Water temperature, along with salinity, affects the density of
water, which causes gravity driven circulation patterns and
stratification in the water column. Turbidity is measured using
light-scattering from suspended solids in water, and is used
as a surrogate for suspended-sediment concentration (SSC).
Suspended sediment often carries adsorbed contaminants;
attenuates sunlight in the water column; deposits on tidal
marsh and intertidal mudflats, which can help sustain these
habitats as sea level rises; and deposits in ports and shipping
channels, which can necessitate dredging. Dissolved oxygen,
which is essential to a healthy ecosystem, is a
fundamental indicator of water quality, and its
concentration is affected by water temperature,
salinity, ecosystem metabolism, tidal currents,
and wind. Tidal currents in the bay reverse four
times a day, and wind direction and intensity
typically change on a daily cycle: consequently,
salinity, water temperature, suspendedsediment
concentration, and dissolvedoxygen
concentration vary spatially and
temporally throughout the bay, and continuous
measurements are needed to observe these
changes. The purpose of this fact sheet is to
inform the public and resource managers of the
availability of these water-quality data.
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First posted September 24, 2014
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