Addressing Magnitude, Duration, Frequency, Space and Time.148 
Developing the Cumulative Frequency Distribution.152 
Step 1. Interpolation of water quality monitoring data.152 
Step 2. Comparison of interpolated water quality 
monitoring data to the appropriate criterion value.155 
Step 3. Identification of interpolator cells that 
exceed the criterion value'.156 
Step 4. Calculation of the cumulative probability 
of each spatial extent of exceedance .156 
Step 5. Plot of spatial exceedance vs. the cumulative frequency ... 159 
Diagnosing the Magnitude of Criteria Exceedance.164 
Defining the Reference Curve .166 
Strengths and limitations.166 
Approaches to defining reference curves .167 
Reference curves for dissolved oxygen criteria.168 
Reference curves for water clarity criteria.171 
Reference curves for chlorophyll a criteria.174 
Reference curve implementation.174 
Monitoring to Support the Assessment of Criteria Attainment.176 
Shallow-water monitoring .176 
Dissolved oxygen criteria assessment.177 
Water clarity criteria assessment .185 
Chlorophyll a criteria assessment .191 
Evaluation of Chesapeake Bay Water Quality Model Output.194 
Chesapeake Bay Watershed Model .195 
Chesapeake Bay Water Quality Model .196 
Integration of Monitoring and Modeling for Criteria Assessment ..196 
Literature Cited.197 
VII. Diagnostic Procedures for Natural Processes and 
Criteria Nonattainment .201 
Addressing Natural Exceedance of the Chesapeake Bay Criteria .. .201 
Natural excursions of low dissolved oxygen conditions.202 
Natural reductions in water clarity levels .206 
Natural elevated chlorophyll a concentrations.209 
