46 
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 
observed K d 
Figure C-3. A comparison of the two estimates against values calculated at validation 
points (n = 99) in the lower tidal James River Polyhaline Chesapeake Bay Program segment 
(JMSPH) (9/14/2005 cruise). 
At least for the three selected cruisetracks, the two methods produced similar esti¬ 
mates, though there is a suggestion that the method used for the 2008 assessment 
predicts with less error. The methods come with their own advantages, however. The 
2007 U.S. EPA guidance method is faster and easier to do as there are fewer steps 
involved. The 2008 assessment method is difficult to do without either Arclnfo or 
Arc Spatial Analyst, but it allows one to visualize spatial patterns, particularly areas 
of uncertainty, in the individual components of K d . 
LITERATURE CITED 
U.S. Environmental Protection Agency. 2007. Ambient Water Quality Criteria for Dissolved 
Oxygen , Wlater Clarity' and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries 
- 2007 Addendum. EPA 903-R-07-003 Region III Chesapeake Bay Program Office, 
Annapolis, MD. 21403. 
appendix c 
A Comparison of Methods for Estimating K , d 
