86 
Figure VII-12. Locations of the Virginia Chesapeake Bay Shallow- 
water Monitoring Program calibration stations. In each location, a 
circle indicates that no significant difference occurs between the in 
situ chlorophyll measures and the in vitro chlorophyll measures. A 
square indicates that the in situ measures are less than the in vitro 
measures. An X indicates that in-situ measures are greater than the 
in-vitro measures. 
Source: Virginia Institute of Marine Science—www2.vims.edu/vecos. 
in situ chlorophyll might be biased low during the day because of this measurement 
problem. A special study was conducted at the Jug Bay station on the tidal Patuxent 
River collecting hourly calibration samples for 24 hours. One set of samples was 
collected monthly from March to December in 2005. Analysis of the in situ/in vitro 
difference shows a very slight diel pattern in these data, but this variability became 
trivial when compared to other sources of variance. 
Collection Agency 
The two principal agencies collecting these data—the Maryland Department of 
Natural Resources and the Virginia Institute of Marine Sciences—have devoted 
considerable effort to maintaining comparable shallow-water monitoring program 
field collection methodologies, instrumentation, and QA/QC procedures. Even so, 
because the two agencies work in geographically distinct regions, comparing results 
between agencies to determine if these data can be combined to estimate calibration 
curves should prove useful. Initial data evaluations indicate that no more variation 
exists between Maryland and Virginia data than among the tidal tributaries in Mary¬ 
land. These evaluations suggest that any differences between Maryland and Virginia 
data may actually result from variations among the tidal tributaries and not from 
dissimilarities between the data-collecting agencies. 
chapter vii • Shallow-water Monitoring and Application for Criteria Assessment 
