Tidal Water Quality Monitoring
The Chesapeake Bay tidal monitoring program is designed to represent the complexities of the nation's largest estuary, with more than 100 tidal stations monitored at least once a month.
Chesapeake Bay Mainstem and Tributary Monitoring Quality Assurance
The Maryland Department of Natural Resources (DNR) and the Virginia Department of Environmental Quality (DEQ) 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 one- to two-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 Chesapeake Bay Program Data Integrity Workgroup is charged with the standardization of methods and the use of comparable methods for all Bay Program water quality monitoring programs. Methods are documented in standard operating procedures that follow the Bay Program's Methods and Quality Assurance for Chesapeake Bay Water Quality Monitoring Programs. 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: Bay Program Coordinated Split Sample Programs, Bay Program Blind Audit Program and 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:
- Work/Quality Assurance Project Plan for (Virginia) Chesapeake Bay Mainstem Water Quality Monitoring Program
- Quality Assurance Project Plan for the Maryland Chesapeake Bay Water Quality Monitoring Program - Chemical and Physical Properties
- Virginia Tributary Monitoring Program Quality Assurance/Quality Control Project Plan
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 nine 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. Three of the sites are part of the National Estuarine Research Reserve monitoring system. The locations and data from the Maryland sites are available from Eyes On the Bay; information and data from the Virginia sites are available from Virginia Estuarine and Coastal Observing System.
The QAPPs and standard operating procedures for Shallow Water Monitoring Programs are:
- Quality Assurance Project Plan for the Maryland Chesapeake Bay Shallow Water Monitoring Program
- Quality Assurance Project Plan for the Virginia Chesapeake Bay Shallow Water Monitoring Program
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 the Data Integrity Workgroup, Virginia and Maryland laboratories have conducted numerous comparability studies to demonstrate the equivalency of Bay Program methods and procedural modifications, many of which are listed below.
- Methodological Comparisons for Nitrogen and Chlorophyll Determinations in Estuarine Water Samples (1986)
- Results of Comparative Studies of Preservation Techniques for Nutrient Analysis on Water Samples (1986)
- Nitrogen and Phosphorous Determinations in Estuarine Waters: A Comparison of Methods Used in Chesapeake Bay Monitoring (1987)
- Estuarine Nutrient Analyses: A Comparison of Sample Handling Techniques and the Analyses of Carbon, Nitrogen, Phosphorus and Chlorophyll a (1990)
- A Comparison of Two Methods of Measuring Dissolved Organic Carbon (1992)
- The Advantages of Measurement of Particulate Carbon, Nitrogen and Phosphorous by Direct Analysis (1993)
- Comparison Study of Five Instruments Measuring Dissolved Organic Carbon for the Chesapeake Bay Monitoring Program (1994)
- A Comparison of Preservation Techniques for Dissolved Nutrient Analyses (1995)
- Dissolved Organic Carbon: Data Variability and Procedural Recommendations Report for AMQAW (1996)
- Immediate Filtration Processing of Water Samples to Separate Particulate and Dissolved Nutrient Parameters: What is the Critical Time Interval between Sample Collection and Filtration? (1997)