watershed, and region. Some classification schemes already exist for systems at each of the 
above levels of organization (Cowardin et al. 1979, Omemik 1987, McKee et al. 1992, Brinson 
1993, Maxwell et al. 1995, Frissell et al. 1986, Rosgen 1996, Detenbeck et al. 2000). To be 
useful in diagnoses, classification systems must be based on differences in the spectrum of 
forcing functions that result in differences in the behavior of systems among classes, (e.g., fluvial 
versus lagoonal geomorphology of a water body). The key to the viability of a classification 
system at any of these hierarchical levels is that the classes identified behave differently under 
the influence of the stressor of concern. Once classes have been identified based on existing or 
new classification systems, an initial screening of the stressor-response data at all four levels of 
organization will determine if research should proceed further on a specific stressor/class 
combination. 
Existing classification frameworks and necessary elements of an integrated classification strategy 
will be reviewed by a work group consisting of representatives from all Ecology Divisions, from 
each of the Aquatic Stressors research areas, and from experts on classification at each of the 
scales of interest. Representation will be requested from other ORD Laboratories and Centers, 
other Federal agencies, EPA Program Offices, and non-govemmental organizations as 
appropriate. Logical collaborators on this task include the Landscape Sciences Branch at NERL- 
Las Vegas, the Watershed Restoration planning group in NRMRL, OW [(OWOW), Office of 
Science and Technology (OST)], USGS (under NAWQA), FWS, NOAA, and the Nature 
Conservancy. Recent work on classification approaches within or outside of NFIEERL is 
summarized in Table 4. 
The classification workgroup will work towards the following goals: 
• Identification of key factors (forcing functions) controlling sensitivity of response to 
different classes of toxic and nontoxic (non-point source) stressors. 
• Identification of key factors determining sensitivity of response across multiple stressors 
to facilitate development of a comprehensive classification scheme rather than multiple 
schemes. 
• Development of national and regional classification frameworks. 
• Coordination of opportunities for testing classification strategies in a systematic fashion. 
Efforts of this workgroup will be supplemented by the extramural grants STAR program. The 
STAR grants program has an existing request for proposals (RFP) on aquatic ecosystem 
classification, and might add an RFP on watershed classification strategies in the future. 
Alternative strategies for classification will be tested through regional case studies (project 3). 
Regional case studies will be based on multiple-scale classification schemes, with coordination 
across Divisions to bring together appropriate areas of expertise. In particular, stressor-response 
relationships will be compared among regional/watershed/water-body classes. 
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