APM 2B FY05 Application of coastal watershed and estuarine/lacustuary classification 
schemes to predict probability of impairment based on Great Lakes and Gulf of Mexico 
regional case studies (GED, MED). 
APM 2C FY05 Guidance on and user-friendly interfaces for derivation of diagnostic 
indicators for individual stressors (MED, AED). 
APG 3 FY07 Provide diagnostic methods and technical support documents for determining the 
relative significance of multiple stressors in 303(d) listed waters. 
APM 3A FY02 Case studies of multivariate approaches to community data analysis to 
apportion cause among stressors. (AED, MED). 
APM 3B FY06 Simulation of key stressor interactions with generic ecosystem models 
using sensitivity analysis to define the range of stressors and stressor combinations under 
which nonadditive interactive effects will occur (MED, AED). 
APM 3C FY07 Decision-support system(s), including forecasting of future cause-effect 
relationships (MED). 
Critical Path 
The relationship of the diagnostic APGs to each other and to the research of other ORD 
laboratories (NERL, NRMRL) is defined in the critical path diagram (Figure 12). The steps in 
the critical path are described as follows: 
Step 1. Develop a conceptual framework (APG 1 FY03). 
This APG includes the development of conceptual models illustrating stressor-response 
relationships for single and multiple stressors and development of appropriate classification 
frameworks at the habitat, water body, watershed, and regional scales. Development of 
hierarchical classification frameworks involves the determination of which types of habitats, 
water bodies, watersheds, and regions are expected to behave similarly in response to a given 
level of stressor or loading. Thus, classification helps establish regional, watershed, or habitat- 
specific criteria and the range across which model extrapolations (including empirical stressor- 
response curves) are appropriate. At this stage, the nature of significant interactions among 
stressors also will be defined based on the expected modes of action. 
Step 2. Development of single-stressor methods and models (APG 2 FY05). 
Methods and models for diagnosis of the predominant source of impairment from single stressors 
are needed. Significant input is required at this stage from other research areas (Sections 4-7). 
Step 3. Development of multiple-stressor methods and models (APG 3 FY07). 
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