42 
NON-SUMMER OPEN-WATER DISSOLVED OXYGEN 
CRITERIA REFERENCE CURVE 
The default reference curve, illustrated in Figure II-4 in Chapter 2, should be used in 
the assessment of the 30-day mean, open-water dissolved oxygen criteria during the 
non-summer months (January 1 through May 31 and October 1 through December 
31). The necessary biological indices and data were not available to support deriva¬ 
tion of a biologically based reference curve for open-water habitats during the 
non-summer months. 
Figure IV-4. Chesapeake Bay deep-channel dissolved oxygen criterion biological reference 
curve. 
ASSESSMENT OF DEEP-CHANNEL INSTANTANEOUS 
MINIMUM DISSOLVED OXYGEN CRITERIA 
The April 2003 Chesapeake Bay water quality criteria document provides conflicting 
guidance in the use of reference curves for assessing attainment of the four instanta¬ 
neous minimum dissolved oxygen criteria. Pages 170 to 173 in U.S. EPA 2003a 
display and discuss reference curves for migratory spawning and nursery, open- 
water, deep-water, and deep-channel criteria attainment assessment. All four sets of 
designated-use specific criteria include a use-specific instantaneous minimum crite¬ 
rion. With the exception of the deep-channel criteria (page 173 in U.S. EPA 2003a), 
none of these sections specifically describe whether a reference curve should be 
chapter iv 
Refinements to the Chesapeake Bay Dissolved Oxygen Criteria Assessment Procedures 
