87 
Figure VIM3. Locations of the Maryland Chesapeake Bay Shallow-water 
Monitoring Program continuous monitors. In each location, a circle indicates 
that no significant difference exists between the in situ chlorophyll measures 
and those for in situ chlorophyll. A square indicates that the in situ measures 
are less than the in vitro measures. 
Source: Department of Natural Resources-www2.eyesonthebay.net. 
Background Fluorescence 
In some Bay areas, the background fluorescence constitutes a significant component 
of the total fluorescence signal due to freshwater input from blackwater streams. 
Background fluorescence is the fluorescence measured on filtered water. This study 
will identify those areas where background fluorescence requires measurement and 
develop an algorithm to adjust for background fluorescence. Analysis indicates that 
background fluorescence is not significant in the systems assessed to date. 
Ancillary Data 
While conventional wisdom holds that in vitro methods produce more accurate 
measures of chlorophyll than in situ methods, both are still subject to error. Using 
data collected independently of either type, the relative accuracy of the two method¬ 
ologies will be assessed. For example, measurements taken as part of the nutrient 
suite (e.g., particulate nitrogen, total nitrogen, etc.) have some predictive power for 
chlorophyll. In cases where the in situ and in vitro measurements differ by more than 
expected due to sampling error, these ancillary data may resolve which is more reliable. 
Often a time series of both in situ and in vitro chlorophyll will show that the two 
measurements compare quite well for much of the data record, with occasional large 
discrepancies. Because these large discrepancies are most problematic from a 
chapter vii • Shallow-water Monitoring and Application for Criteria Assessment 
