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A Glossary of Terms and Acronyms
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Attenuation Coefficient: |
| A measure of the rate at which light disappears
with depth in Bay waters; large attenuation coefficients occur in turbid
waters, and small attenuation coefficients occur in clear water |
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Biomass: |
| The quantity of a living community or population, such as the
phytoplankton; for example, phytoplankton biomass is often measured as
chlorophyll concentration |
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Calibration: |
| The process of converting electrical signals from
instruments into measured quantities that describe water quality. For
example, the relative concentration of dissolved oxygen can be measured with
an electrode. These relative concentrations are then converted into real
concentrations by making true measurements of oxygen concentration in a set
of water samples, and then relating these to the concentrations estimated
with the electrode |
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Chlorophyll: |
| The green pigment of plants, including phytoplankton, which
absorbs sunlight energy and converts it to chemical energy used in the
process of photosynthesis. We report chlorophyll a in units of milligrams per cubic meter (i.e.,
the weight of chlorophyll contained in each cubic meter of water). Milligrams per cubic meter is equivalent to micrograms
per liter. |
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Conductivity: |
| A measure of the resistance of water to electrical flow;
this resistance is a direct measure of the salinity of water,
and it can be measured accurately with a conductivity sensor |
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CTD: |
| An instrument package that measures
Conductivity, Temperature, and
Depth as the package is lowered through the water. Additional sensors for
measuring oxygen concentration, chlorophyll, suspended solids, and light
penetration are integrated with the CTD instrument-computer package. |
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Delta Outflow (Index): |
| An estimate of the flow of freshwater from the
Sacramento-San Joaquin River Delta into San Francisco Bay; units of
measurement are cubic meters per second |
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Dissolved Oxygen: |
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| The concentration of oxygen dissolved in Bay waters;
this is often measured in units of milligrams per liter, or as percent
saturation (the measured concentration divided by the concentration that
would occur if dissolved oxygen was determined only by exchanges with the
atmosphere -- i.e., in the absence of biological processes of oxygen
consumption and production) |
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DO: |
| Dissolved Oxygen |
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Fluorometer: |
| An instrument that measures the relative concentration of
chlorophyll, by sending a beam of blue light into the water and measuring
the production of red light (fluorescence) by the chlorophyll contained in
phytoplankton cells;
chlorophyll concentration is proportional to fluorescence |
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Hypersaline: | -
| A condition in which the salinity
of the Bay becomes higher
than the salinity of the ocean; this occurs during prolonged periods of
drought (such as in 1977), when freshwater inputs are smaller than losses of
water to evaporation |
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Inorganic: | -
| An inorganic compound refers to chemical compounds that do not contain carbon (C) e.g. nitrate (NO3-). |
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Light Penetration: |
| A general term describing the absorbance of sunlight
by Bay waters; usually, sunlight penetrates only a few meters below the
water surface because waters of San Francisco Bay have high concentrations
of suspended solids that absorb and reflect light (they are a source of
turbidity). Low light penetration results in a high attenuation coefficient. |
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Limiting Factor: |
| A parameter (e.g. light, temperature, nutrients) that controls the rate of a specific process. For example in SF Bay, light is frequently the limiting factor controlling phytoplankton production and growth. |
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Longitudinal Axis: |
| The spatial dimension of an estuary, such as San
Francisco Bay, that extends from the landward to the seaward domains; the
USGS makes water quality measurements along the longitudinal axis of the
Bay-Delta, from the Sacramento River, to the Central Bay, and into the South Bay |
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Longitudinal Profile: |
| The distribution of a constituent, such as salinity
or dissolved oxygen, along the longitudinal axis of the Bay-Delta |
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OBS: |
| Optical Backscatter Sensor |
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Nitrogen: |
| Nitrogen (N) is a critical nutrient for phytoplankton growth.
In marine ecosystems the most abundant form of inorganic N available for organisms is
typically nitrate, followed by ammonium. We measure nitrate plus nitrite (NO3- +
NO2-) and ammonium (NH4+) in micromoles N per liter (molecular weight of N
per liter of water). Typically, in marine ecosystems nitrogen is the limiting nutrient on phytoplankton production and growth. Consequently, nitrogen dynamics in the estuary are crucial to our understanding of phytoplankton dynamics. |
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Nutrients: |
| Chemical elements or compounds necessary for or contributing to an organism’s metabolism, growth or function. Nutrients provide energy and are used as molecular building blocks in the biosynthesis of cellular structures. Nitrogen (N) and phosphorous (P) are critical nutrients for phytoplankton, thus their growth can be limited by the availability of these nutrients when light and temperature are adequate. |
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Optical Backscatter Sensor: |
| An instrument that measures the abundance of
small particles suspended in water; it sends a beam of infrared light into
the water, and measures the amount of light reflected off the particles
(higher reflected light means higher concentrations of suspended solids);
used to measure TSS |
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Organic Material: |
| An organic compound refers to a large class of chemical compounds that contain carbon (C). |
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Oxygen Electrode: |
| A sensor that produces an electrical current that is
proportional to the amount of oxygen dissolved in water; used to measure
dissolved oxygen |
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Phosphorous: |
| Phosphorous (P) is an essential nutrient for all living organisms.
Although it is not needed in as great abundances as oxygen, carbon, nitrogen or hydrogen, phosphorus is
one of the major nutrients known to limit phytoplankton production in certain fresh and marine
ecosystems. We measure phosphate (PO4-3) in micromoles P per liter (molecular weight of P
per liter of water). |
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Photosynthesis: |
| The set of reactions in plant cells (including
phytoplankton) that use sunlight energy to convert carbon dioxide into food
(carbohydrates) and oxygen |
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Phytoplankton: |
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| The diverse community of microscopic suspended algae
(single-celled plants); in San Francisco Bay this community represents the
largest component of living biomass; phytoplankton
photosynthesis is a
source of oxygen and phytoplankton biomass is an important food resource for the small animals that
live in the Bay |
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Phytoplankton Bloom: |
| Period of explosive population growth of the
phytoplankton community; a recurrent event that occurs every spring in South
San Francisco Bay |
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Primary Production: |
| The process of producing organic compounds from carbon dioxide (CO2), principally through photosynthesis. The organisms responsible for this process are called primary producers and make up the base of most food chains e.g. phytoplankton are primary producers. |
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Quantum Sensor: |
| A sensor that measures the instantaneous quantity of
sunlight (number of light photons) hitting a surface, such as the surface of
the Bay ; used to measure light penetration and the
attenuation coefficient,
by measuring the quantity of sunlight at different depths as it is lowered
into the water |
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Respiration: |
| Metabolic processes of organisms or communities that consume
oxygen |
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Salinity: |
| A measure of the salt content of water, which can be estimated
accurately from measures of conductivity and temperature; salinity is
measured in practical salinity units (psu), and the salinity of river water
is often about 0.1 psu while the salinity of coastal Pacific Ocean water is
about 33-34 psu; measures of salinity in the Bay tell the relative
proportions of river water and ocean water at different locations |
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Salinity Stratification: |
| Condition where the salinity of the surface
waters is lower than the salinity of deeper waters; this condition acts to
slow the rate of mixing between surface and bottom waters |
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Silica: |
| Silica (Si) is an important nutrient particularly for diatoms. Diatoms
are one of the most common types of phytoplankton and use silicate to cover their cells and
form their cell wall called a frustule. Dissolved silica (DSi) is measured in micromoles Si per liter (molecular weight
of Si per liter of water). |
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Suspended Sediments: |
| the small mineral (mostly clay) particles suspended
in Bay waters |
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Suspended Solids: |
| The small suspended particles contained in a water
sample; in San Francisco Bay, most suspended solids are sediment particles,
so 'suspended solids' and 'suspended sediments' are nearly synonymous; the
concentration of suspended solids is measured with an OBS, in units of
milligrams per liter (i.e., the weight of all solids contained in each liter
of water). On this website, the terms Total Suspended Solids (TSS) and Suspended
Particulate Matter (SPM) are used interchangeably. |
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Temperature Gradient: |
| A pattern in which water temperature varies
spatially, such as along the longitudinal axis of the Bay-Delta or in a
vertical profile |
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Trophic Level: |
| Position that an organism occupies in a food chain, determined by the number of energy transfer steps to that level e.g. primary producer, primary consumer, secondary consumer, tertiary consumer. |
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TSS: |
| Total suspended solids
contained in a water sample |
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Turbidity: |
| A general term describing the clarity of water; turbidity is
caused by dissolved colored substances in water and by the suspended
particles that absorb and reflect sunlight |
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Vertical Profile: |
| The distribution of a constituent, such as salinity or
dissolved oxygen, from the surface of the water to the seafloor |
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U.S. Department of the Interior |
U.S. Geological Survey