As stressor-response relationships are determined, research will be directed towards developing 
diagnostic approaches (box 3a), which will provide tools (box 3b) for building a decision support 
system. Resource managers then can use the system to assess the condition of a water body, 
diagnose the causes of any demonstrated impairment, and predict the results of any corrective 
actions that might be needed. 
Stressor-response relationships can be specific to different classes of systems. Thus, research 
also will focus on developing ecosystem classification approaches (boxes 4a,b) that allow for 
reasonable extrapolations of diagnostic approaches and stressor-response models. Classifying 
ecosystems is valuable for two primary reasons: 1) grouping ecosystems according to similar 
criteria and 2) spatially classifying ecosystems that are connected via stressor actions to facilitate 
an effective means for managing the consequences of stressors. Since little is known about scale 
relative to ecosystem classification, effects research also will provide guidance about the most 
appropriate scale for various ecosystem classification approaches, up to and including the 
watershed scale. 
At the same time, research identified in boxes la-4a will result in methods and approaches for 
deriving criteria (boxes 5a,b) for protecting aquatic ecosystems. Existing approaches, based on 
laboratory tests, have focused on individual aquatic life and wildlife species. However, much 
uncertainty is associated with extrapolating data to predict safe levels for populations and 
communities exposed to individual and multiple stressors (physical and/or chemical). Therefore, 
we need to improve current criteria, methods, or approaches for some stressors where major 
uncertainty exists, or develop them for others where little information is known (see Sections 4- 
8). In some cases, research will lead to relatively short-term fixes (1-2 years) to existing 
guidance. In others, research conducted over the longer term (3-6 years) will result in methods or 
models useful for deriving criteria with associated uncertainties. 
All aquatic stressor research elements (boxes 1-5) thus combine to help improve the tools 
available to managers for meeting designated uses (boxes 6a,b). It is important to recognize that 
NHEERL research on aquatic stressors supports the development of protective criteria, although 
actual criteria and management strategies fall beyond the research responsibilities of NHEERL. 
A discussion on a decision support system for using the products of this research follows. 
Decision Support System 
A general approach that a resource manager might follow for managing water bodies is outlined 
in the left side of Figure 2. The assessment of the condition of an aquatic resource to support 
ecological use designations first requires ecological criteria and a reference condition with which 
to compare those criteria. As shown in the right side of Figure 2, GPRA Goals 2 and 8 research 
products will support the development of both chemical and biological criteria that can assist 
managers in determining if designated uses are met. 
If designated uses are not met, managers will require a means of identifying the stressors causing 
the impairment. EPA’s Stressor Identification (SI) workgroup has developed an example of a 
"diagnostic tree" approach for SI that can be used by resource managers (EPA 2000b). NHEERL 
research will contribute by determining stressor-response relationships and specific diagnostic 
5 
