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Quality Assurance: Tidal Water Quality Monitoring

Chesapeake Bay Mainstem and Tributary Monitoring Quality Assurance

The Maryland Department of Natural Resources and the Virginia Department of Environmental Quality are responsible for the collection and quality assurance of water quality monitoring data in the Chesapeake Bay and its tidal tributaries. The tidal monitoring program is designed to represent the complexities of the estuary, with over 100 tidal mid-channel stations monitored at least once a month. At each station, a hydrographic profile is made by measuring temperature, salinity and dissolved oxygen at approximately 1 to 2 meter intervals through the water column.

Standardized sampling and analytical methods are used to detect low levels of nutrients, chlorophyll and particulates; these methods were approved by EPA in 1986 and are still used today. The CBP Analytical Methods and Quality Assurance Workgroup (AMQAW) is charged with the standardization of methods and the use of comparable methods for all CBP water quality monitoring programs. Methods are documented in standard operating procedures (SOPs) that follow the Chesapeake Bay Program Recommended Guidelines for Sampling and Analysis (1.4 MB). Chapter IV, Mainstem and Tributary Field Procedures contains the most recent guidelines for sample collection and field measurements in the tidal waters of the Chesapeake Bay.

Field and laboratory personnel continually check for random and systematic errors with quality control samples during the collection and analysis of water samples. Blank, duplicate and spiked samples, and known standards are processed in the field and/or laboratory to monitor bias and imprecision in the data. The accuracy and comparability of laboratory data are externally evaluated up to 12 times a year using several types of inter-laboratory performance testing and comparison samples: a) CBP Coordinated Split Sample Programs, b) CBP Blind Audit Program and c) USGS Standard Reference Samples.

Maryland DNR and Virginia DEQ have EPA-approved Quality Assurance Project Plans (QAPPs) that describe in detail the methods and quality assurance activities for this program. The following QAPPs cover the Maryland and Virginia Chesapeake Bay Mainstem and Tributary Monitoring Programs.

Shallow Water Monitoring Quality Assurance

The 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 surface concentrations 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 five or more stops, field crews measure light attenuation (PAR and secchi depth) and collect discrete samples for chlorophyll a, dissolved oxygen and suspended solids analyses. Discrete sample data are then correlated with the in-situ measurements.

Data collected using this system show the gradients and "hot-spots" that could not be detected with traditional fixed station monitoring. DATAFLOW cruises are conducted once a month in the spring and summer.

Semi-permanent installations of YSI multi-parameter sensors are installed in shallow waters of selected tributaries of the Bay. Sensors remain at the sites for up to 9 months, recording data every 15 minutes. Once every two weeks field crews 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 (NERRS) monitoring system. The locations and data from the Maryland sites are available on the www.eyesonthebay.net; information and data from the Virginia sites are available from www.vecos.org.

The QAPPs and SOPs for Chesapeake Bay Shallow Water Monitoring Programs are:

Analytical Method Equivalency Studies

In the 1980s, Bay Program scientists developed analytical methods sensitive enough to detect the low levels of nitrogen and phosphorus in saline waters. The methods were approved by EPA Region 3 at that time and later validated and published by EPA's National Exposure Research Laboratories in the document Methods for the Determination of Chemical Substances in Marine and Estuarine Environmental Matrices - 2nd Edition. Through AMQAW, Virginia and Maryland laboratories have conducted numerous comparability studies to demonstrate the equivalency of CBP methods and procedural modifications, many of which are listed below.

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