Scientific Approach 
Case studies are a useful vehicle for developing and testing conceptual models, classification 
systems, diagnostic tools and models, and stressor-response relationships. Furthermore, case 
studies focused on specific places or issues of interest to the Agency provide an excellent 
mechanism to address high priority environmental problems, including the development of 
TMDLs. Diagnostic case studies will provide a mechanism for developing, testing, and applying 
methods and models for distinguishing among single aquatic stressors and allocating cause 
among multiple stressors. Case studies will be performed to incorporate the habitat, ecosystem, 
watershed, and regional spatial scales as well as the organismal, population, community, and 
ecosystem levels of biological organization. 
Case studies will be selected based on the following critical attributes: 
• Sites will be selected from those already designated as impaired (or threatened) based on 
the 305(b) or 303(d) reporting process, representing a range of degrees of impairment, a 
range of stressor combinations, multiple stressors with interaction potential, and common 
stressor-resource class combinations. 
• Sites will be selected to represent specific region-watershed-water body classes, such that 
results can be extrapolated using a regional or nationwide classification system. 
• Coastal systems will be selected, to include both watershed(s) and receiving waters. 
• Methods and information management will be coordinated across case studies. 
Additional desired attributes of regional case studies include the following: 
• Data have already been collected and/or analyzed in time series or at multiple time points. 
• Studies will involve cross-Agency collaboration. 
• Sites will have well-organized stakeholder groups [e.g.. National Estuarine Reserve 
Program, National Estuary Program, Areas of Concern or Lakewide Management Plan 
(LaMP) committees for Great Lakes]. 
• Studies will not duplicate assessments of well-studied systems. 
• Representative models exist. 
• Research or monitoring at the sites is ongoing. 
• Sites are in logistical proximity to an Ecology Division. 
Each case study will include the following elements: 
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