Water Quality of San Francisco Bay Database Glossary

Terms are listed in the same order as they appear in the data query table.

Detailed methods information can be found in Water quality measurements in San Francisco Bay by the U.S. Geological Survey, 1969–2015.

Date: Date of water quality sampling in YYYY-MM-DD format.
Julian Date: The date as expressed in the format YYYYDDD, with DDD being the three-digit number of days since the start of the year. For example: 1994001=January 1, 1994 and 1994365=December 31, 1994.
Time: Local time (either Pacific Standard or Pacific Daylight) of water quality sample collection in 24h format (HH:MM).
Station: Numeric identifier of the fixed geographic location where sample collection occurred. See the Sampling Locations page for description, map, and table of station locations.
Distance from Sta 36 (km): Distance from Station 36, the southernmost Station. The distance values increase from Station 36 along the sampling track with the maximum value at the farthest Station, 657. This location information is provided for data plotting.
Depth (m): Depth in the water column where sample collection occurred. For sensor data, values are means of all measurements made from approximately 0.5 m above to 0.5 m below the reported Depth.
Discrete Chlorophyll-a (µg/L): Laboratory-analyzed concentration of chlorophyll-a in water samples. Chlorophyll-a measurements began in 1977, with methods altered as new instrumentation and widely accepted standard methods emerged.
Discrete Chlorophyll-Pheopigment Ratio: Ratio calculated as Discrete Chlorophyll-a/ (Discrete Chlorophyll-a+pheopigments). Pheopigments are chlorophyll degradation products measured during chlorophyll analysis.
Calculated Chlorophyll-a (µg/L): Estimated chlorophyll-a concentration, calculated from a linear regression of the chlorophyll fluorometer sensor output and Discrete Chlorophyll-a. Regressions were conducted for each cruise and sub-embayment to account for spatial and temporal variability in phytoplankton communities.
Discrete Oxygen (mg/L): Concentration of oxygen dissolved in water analyzed in the laboratory using the Winkler method.
Oxygen (mg/L): Concentration of dissolved oxygen as measured with a sensor (2017 – present). Prior to 2017, Oxygen values were calculated using linear regression between sensor output and Discrete Oxygen. Previously called "Calculated Oxygen".
Oxygen Percent Saturation: Percent oxygen concentration in the water relative to complete saturation at the in-situ temperature and pressure. Oxygen Percent Saturation is calculated from Oxygen, Depth, and Temperature measurements using formulas of Gnaiger and Forstner (1983).
Discrete SPM (mg/L): Laboratory-analyzed concentration of suspended particulate matter (SPM) in water samples.
Calculated SPM (mg/L): Estimated concentration of suspended particulate matter (SPM) calculated from a linear regression of the optical backscatter sensor output and Discrete SPM. Regressions were conducted for each cruise and sub-embayment to account for spatial and temporal variability in suspended sediment optical properties.
Extinction Coefficient (1/m): The light extinction coefficient is derived from vertical profiles of photosynthetically active radiation (PAR). It is calculated as the slope of the linear regression of ln(PAR) against water depth. Extinction Coefficient data are listed on the station's surface depth line, usually 1m. Previously called "Measured Extinction Coefficient".
Salinity: A nondimensional measure of dissolved salts in the water, calculated from conductivity, temperature, and pressure sensor measurements in accordance with the Practical Salinity Scale 1978.
Temperature (°C): Water temperature as measured with a submersible sensor.
Sigma-t (kg/m3): A measure of the density of the water as a function of Salinity and Temperature at standard atmospheric pressure. Sigma-t calculations began in November 1987.
Nitrite (µM): Concentration of nitrite (NO2) in water samples.
Nitrate+Nitrite (µM): Concentration of nitrate plus nitrite (NO32) in water samples.
Ammonium (µM): Concentration of ammonium (NH4) in water samples.
Phosphate (µM): Concentration of dissolved inorganic phosphorus as PO4 in water samples.
Silicate (µM): Concentration of dissolved silica as SiO2 in water samples.

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