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Quality Assurance: Tidal Water Quality
Monitoring ProgramsMaryland Department of Natural Resources and Virginia Department of Environmental Quality are responsible for monitoring water quality of the Chesapeake Bay and its tidal tributaries. These agencies use a combination of in-house staff and other state institutions to accomplish their work. Each of the agencies below use the same procedures for sample collection, field measurements and laboratory analyses.
Mainstem and Tributary MethodsMaryland and Virginia have monitored 100 tidal, mid-channel stations at least once a month for almost 20 years. At each station, a hydrographic profile is made by measuring temperature, salinity, and dissolved oxygen at approximately 1 to 2 meter intervals. Discrete samples for nutrients, solids and chlorophyll a are collected from the surface and bottom layers, and if there is stratification, a sample above and a sample below the pycnocline. Samples are filtered on-board, frozen and sent to the laboratory for the following analyses:
Analytical Methods
Methods are documented in several ways. Each institution has standard
operating procedures that follow Chesapeake
Bay Program Guidelines for Sampling and Analysis Shallow Water MethodsThe Chesapeake Bay Program uses in-situ monitoring technologies to provide more accurate estimates of turbidity, chlorophyll a and dissolved oxygen levels in shallow, nearshore waters. Very detailed “maps” of these parameters are obtained from DATAFLOW instrumentation. As a small vessel speeds along the shoreline, surface water is pumped on-board and flows across YSI multi-parameter sensors that automatically record measurements every 25 feet. Sensors are calibrated before and after each cruise. At eight stops, field crew measure light attenuation (PAR and secchi depth) and collect discrete samples for chlorophyll a, dissolved oxygen, suspended solids and nutrients analyses. Discrete sample data are then correlated with the in-situ measurements. Data collected using this system show gradients and "hot-spots" that could not be detected with traditional fixed station monitoring. DATAFLOW cruises are scheduled once a month in the spring and summer. YSI multi-parameter sensors are also installed underwater in 33 shallow water locations. Sensors remain at the sites for up to 9 months, recording data every 15 minutes. Once a week field crew calibrate the sensors, download the data, measure light attenuation and collect discrete samples. Data are carefully checked for accuracy and then published on the internet. Seven of the sites are part of the National Estuarine Research Reserve (NERR) monitoring system, the data from which are available on the NERR website. Also See: NERRS Centralized Data Management Operations Manual Quality ControlField
and laboratory staff introduce quality control samples into the sampling and analytical
stream to check that procedures are performing properly. Blank, replicate and
spiked samples measure the amount of bias and imprecision in the data. QC sample
procedures and performance limits are specified in Chapter II, Sections D &
E of Recommended
Guidelines for Sampling and Analyses in the Chesapeake Bay Monitoring Program
Detection LimitsMethod detection limit (MDL) values are calculated as 3 times the standard deviation of seven replicate measurements/analyses of the same sample. A calculated MDL may or may not be in the concentration range covered by the lowest calibration standard. Tidal Water Quality Data Analysis Methods
Publications (CBP)
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(74 MB) 
In the 1980's,
Bay Program scientists developed laboratory
methods to accurately detect low concentrations of nitrogen and phosphorus in seawater.
Comparability studies showed that field filtering of nitrogen, phosphorus, and
chlorophyll is necessary to prevent changes in concentration en route to the lab.
Virginia and Maryland use the same field and laboratory methods. The 
