CADDIS: Helping Scientists Identify the Causes of Biological Impairments

These two photographs show stream reaches that look very different - one is flowing through an industrialized area and appears to have been channelized; the other is flowing through woods. However, both were found to be biologically impaired. The state of Connecticut used the Stressor Identification process (the basis for CADDIS) to successfully identify the cause of the biological effects observed in these two streams.

Thousands of water bodies in the United States are listed by states as biologically impaired. For many of these, the cause of the impairment is reported as "unknown". Before the TMDL process can be used to formulate an appropriate management action, the cause of the biological impairment must be determined. Defensible causal analyses require knowledge of the mechanisms, symptoms, and stressor-response relationships for various specific stressors as well as the ability to use that knowledge to draw appropriate conclusions.

CADDIS is an online application that helps scientists and engineers in the Regions, States and Tribes find, access, organize, use and share information to conduct causal evaluations in aquatic systems. It is based on the U.S. Environmental Protection Agency Stressor Identification process which is a formal method for identifying causes of impairments in aquatic systems. Current features of this site include:

• The Step-by-Step Guide to conducting a causal analysis,
• Example worksheets,
• Introductory material on several commonly encountered candidate causes,
• A conceptual model library, and an interactive conceptual model for phosphorus,
• Advice on how to use specific data analysis methods, general advice on data handling and analysis in a causal assessment, and downloadable data analysis tools.
• Information sources including related links, glossary and acronyms list, databases of stressor-response information and a reference section.

Future plans include modules on deriving empirical stressor-response relationships, stressor-specific tolerance values, and databases and syntheses of relevant literature on sediments and toxic metals. Future versions will be developed incrementally and iteratively (updates to this site can be found on our recent additions page), and your input and feedback will be essential to the system's success.