75 
were granted the highest priority for shallow-water monitoring (see Figures VII-4 
and VII-5). 
DISSOLVED OXYGEN CRITERIA ASSESSMENTS 
USING SHALLOW-WATER MONITORING DATA 
The Chesapeake Bay Shallow Water Monitoring Program has provided unprece¬ 
dented volumes of spatially and temporally intensive Chesapeake Bay, tidal 
tributary, and embayment data to assess water quality criteria attainment. This 
wealth of data, however, provides new and unique analytical challenges within the 
regulatory framework. In the case of dissolved oxygen criteria, these challenges 
include: temporal variation of water quality parameters, spatial interpolations, and 
scaling and interpolation issues. Specific procedures for evaluation of the 7-day, 1- 
day, and instantaneous minimum open-water and deep-water dissolved oxygen 
criteria have not been fully developed at this time. 
The assessment of the 30-day mean dissolved oxygen criteria for open-water desig- 
nated-use habitats will rely on mid-channel fixed station data combined with 
Dataflow and Dataflow calibration profile data. As noted previously, the Dataflow 
vessel stops at five to eight locations throughout a segment to collect calibration 
measurements. Dissolved oxygen is measured from the surface to the bottom at these 
sites using the same procedure as the mid-channel data collection. The dissolved 
oxygen calibration data will provide an additional day of dissolved data each month, 
at five locations instead of one or two. The dissolved oxygen Dataflow and the corre¬ 
sponding Dataflow dissolved oxygen calibration data will be interpolated and 
analyzed, along with fixed-station dissolved oxygen data, using the Chesapeake Bay 
Program's interpolator and the CFD approach described in Chapter 2. 
TEMPORAL VARIATION 
Dataflow cruises collect between 3,000 and 10,000 points over several hours in a 
segment. Data are normally collected between 7:00 a.m. and 5:00 p.m. with the boat 
traversing open and shallow waters on one side of a tidal tributary or embayment and 
repeating the process on the opposite side. The measurements can be interpolated to 
produce a continuous surface of data that can be evaluated for the percentage area of 
a segment that fails the applicable criterion. 
The diel patterns of surface dissolved oxygen are well documented in both the liter¬ 
ature and continuous monitoring data (www.eyesonthebay.net). In summer, 
dissolved oxygen normally declines to its lowest level during the early morning 
hours (3:00 a.m.) when algal and plant communities have been respiring throughout 
the night; it reaches its peak in mid-afternoon (3:00 p.m.) following photosynthetic 
activity. In some cases, this diel fluctuation can reach more than 15 mgliter' 1 
chapter vii 
Shallow water Monitoring and Application for Criteria Assessment 
