52 
Predicting the Lowest 1 Percent Concentration From The Mean 
Down the left side of Figure V-l are plots of the 1 percent measured dissolved 
oxygen concentration versus the measured monthly mean concentration for each 
designated use (all buoy records parsed by month and pooled within designated use). 
Down the right side of Figure V-l are plots of the same sets of measurements only 
for an individual segment, CB4MH as an example, where multiple buoys or records 
including multiple months were available. Both solid circles and open triangles are 
displayed on the plots. The circles are the observed 1 percent concentration data; the 
triangles are concentrations predicted by a simple regression model including the 
observed monthly mean and the coefficient of variation. In these examples, the 
prediction model does pretty well because of the relative large number of observa¬ 
tions and thus the very good estimate of the monthly mean and 1 percent 
concentrations, as well as the close relationship of each observation to the next. As 
the number of available continuous buoy data records increases for a wider array of 
segments and designated uses, the Chesapeake Bay Program partners should be in a 
position to develop a more generalized model for designated uses by segment that 
would enable the user to predict the 1 percent concentration from the monthly means 
obtained from the long-term fixed-station monitoring data. 
One question still under investigation is how well those observed monthly means 
compare to the means obtained from the continuous buoy data records. Figure V-2, 
which shows the fixed station twice monthly monitoring data and semi-continuous 
buoy data plotted together, provides some current insights into answering this ques¬ 
tion. Down the left side of Figure V-2 are plots of the observed 1 percent 
concentrations versus observed monthly mean dissolved oxygen concentrations 
(June-September) obtained from fixed station monitoring data and plotted for open- 
water, deep-water and deep-channel designated uses in segment CB4MH. Down the 
right side of Figure V-2 are the plots from the continuous buoy data for CB4MH. The 
vertical and horizontal reference lines cutting each graph into 4 quadrants represent 
the 30-day mean and instantaneous minimum dissolved oxygen criteria concentra¬ 
tions. Again, a regression model using the mean and coefficient of variation of the 
monitoring data has been used to predict the 1 percent concentration. As illustrated 
in Figure V-l, solid circles represent the observed concentrations and open triangles 
represent the predicted concentrations. As expected from the fixed station moni¬ 
toring data, the fit of predicted to observed is not as tight as with the buoy data. These 
regression models can be improved with the addition of more explanatory variables. 
The point is that in some, possibly many segments, the relationship of the monthly 
mean with the 1 percent concentration evidenced in monitoring data is similar to that 
found in the buoy data records. The regression models output illustrated in Figures 
V-l and V-2 can be improved by including other explanatory variables to better 
predict the variability detected and quantified in the buoys. 
Figure V-3 shows similar plots of the 1 percent concentration versus the monthly 
mean obtained from monitoring data in various other example segments. Note how 
tight the relationship is in segment BOHOH (Bohemia River) in contrast to the 
chapter v 
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 
