66 
conduct Dataflow monitoring from April through October in tidal fresh, oligohaline, 
and mesohaline segments and from March through November in polyhaline 
segments. These assessment periods for the water clarity criteria were based on the 
growing seasons for the salinity-based SAV plant communities (U.S. EPA 2003a). 
CONTINUOUS MONITORING COMPONENT 
Continuous monitoring data are collected to assess the variability of water quality 
parameters throughout the day. Temporally intensive data help explain the relation¬ 
ships and timing among algal blooms, low dissolved oxygen, and nutrient additions. 
Although previous convention suggested that shallow-water habitats did not experi¬ 
ence significant low dissolved oxygen levels, continuous monitoring data are 
proving otherwise. The lowest dissolved oxygen levels often occur between 4:00 and 
6:00 a.m. when, historically, little information has been collected. 
The continuous monitoring program component employs automated YSI 6600 EDS 
water quality data sondes. Maryland and Virginia have agreed to use similar instru¬ 
ments, when possible, to ensure consistent methodology and comparability across 
Chesapeake Bay segments. The YSI 6600 sonde directly measures dissolved oxygen, 
fluorescence (an indication of chlorophyll a), turbidity (an indication of water 
clarity), temperature, salinity, and pH. The Maryland Department of Natural 
Resources Chesapeake Bay Shallow-water Monitoring Program Quality Assurance 
Project Plan (see page 32 in Maryland Department of Natural Resources 2006) docu¬ 
ments the YSI instrument parameters, range, resolution, units, and accuracy. 
Fluorescence is correlated to chlorophyll a , the measurement used for assessing 
attainment of the chlorophyll a criteria. Turbidity is correlated to K d (light attenuation 
coefficient), the measurement used to assess attainment of the water clarity criteria. 
The initial design recommended two shallow-water buoy deployments in each 
segment, but often, resources limit the number of buoys to one per site. The buoys 
are programmed to take measurements every 15 minutes for the six parameters listed 
above. They are deployed off piers or pylons, either 1-meter below the surface or at 
a fixed depth of 0.3 meters above the bottom, generally in waters of 2-meters or less 
in depth (Figure V1I-2). 
Instruments are exchanged every one to two weeks, depending on biofouling and 
following strict calibration protocols (Virginia Institute of Marine Science 2005). 
Field crews collect samples to calibrate fluorescence and turbidity instrument read¬ 
ings, respectively, with chlorophyll a and light attenuation. The monitors are 
positioned at representative sites both up- and down-river. 
Both Maryland and Virginia have rigorous shallow-water monitoring quality assur¬ 
ance/quality control (QA/QC) programs. The QA/QC protocols remain consistent 
between states; the Chesapeake Bay Program Quality Assurance Officer and the 
Chesapeake Bay Program’s Analytical Methods and Quality Assurance Workgroup 
have reviewed these protocols. 
chapter vii 
Shallow-water Monitoring and Application for Criteria Assessment 
