o- o Percentage of Area/Volume Exceeding the Criteria 
Figure VI-15. Initial attempt at developing a dissolved oxygen criteria reference curve for 
migratory, spawning and nursery habitat designated use areas using the 6 mg liter 1 7-day 
mean criterion assessed as a 30-day mean. 
Figure VI-16. Dissolved oxygen criteria reference curve for defining criteria attainment in 
open-water designated use habitats. 
were identified based on assessments of surface and above-pycnocline concentra¬ 
tions of four parameters: total nitrogen, total phosphorus, chlorophyll a and total 
suspended solids (see Appendix F for details). Cumulative frequency distribution 
reference curves for migratory spawning and nursery designated use habitats from 
February through May (Figure VI-15) and for open-water designated use habitats in 
summer (Figure VI-16) were derived using dissolved oxygen concentration data 
from these segments. 
The Chesapeake Bay Program’s Tidal Monitoring and Analysis Workgroup devel¬ 
oped a procedure to assess relative status for cases in which an absolute point of 
reference for a water quality parameter is not available (Alden and Perry 1997). That 
procedure uses the logistic distribution of a parameter in a ‘benchmark’ data set as a 
chapter vi • Recommended Implementation Procedures 
