Variability of Salinity and Temperature In San Francisco Bay

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The USGS has been collecting specific conductance (salinity) and water temperature data in San Francisco Bay (SF Bay) since 1990. Data are typically collected at 5-10 fixed locations throughout the bay, every fifteen minutes, every minute of the day.

Estuary and bird

Photo of the San Francisco Bay Estuary.

Gaps that appear in the resulting record are most often due to environmental fouling of the sensors that occur. The resulting data are first posted to https://waterdata.usgs.gov/nwis in provisional form, and are then switched to approved status once reviewed and approved.

The data are used for both regulatory purposes and to reveal changes and trends in water quality that can have impacts on ecology and sediment transport.

During critical low flow periods, an understanding of the relative importance of forcing mechanisms such as fresh water flow, meteorology, and climate can help managers determine the significance of alteration of freshwater flow on salinity and temperature. Four specific questions are often addressed: What are the trends in the salinity and temperature in SF Bay? What are the relative contributions of the different forcing mechanisms (for example, freshwater flow or meteorology) to variability in salinity and temperature? Do small changes in freshwater discharge affect the salinity and temperature throughout the Bay during low flow periods? How can we improve the monitoring network?

Two examples of results based on these datasets are shown in a tab on this page. These documents focus on record-high values observed during recent drought conditions.

Since salinity and water temperature are key estuarine habitat variables, understanding their variability is critical to understanding changes in an ecosystem. Knowing the relative importance of forcing mechanisms such as freshwater flow, meteorology, and climate can help managers determine the significance of alteration of freshwater flow, especially for low flow conditions.