Causal Analysis/Diagnosis Decision Information System (CADDIS)

• Common Candidate Causes
• Interactive Conceptual Models

Candidate causes are stressors that could be responsible for causing the biological impairment that you are investigating. The pages in this section review basic information on several commonly encountered causes as identified in the navigation box on the right.  We also refer readers to aquatic ecology text books such as Allan (1995), Dodds (2002) and Wetzel (2001).  The stressors we discuss here appear frequently on U.S. EPA’s 303(d) list of impaired water bodies. We plan to include material for more candidate causes in the future.  In particular, we plan to add a module on physical habitat structure.  So, please contact us with suggestions for additions.

Most of the currently available features in this module are relevant to Step 2: List Candidate Causes. If you already know the Stressor Identification (SI) process and have defined your case, you are ready to list candidate causes. If you are new to SI, we recommend that you review the entire SI process before proceeding.

The sections on “What to Consider When Determining if a Candidate Cause Should be Included” can help you:

• Choose what to include in your list of candidate causes based on sources, site information, and observed biological effects,

• Justify your choice to include some candidate causes and defer others,

• Write your report by providing supporting text you can copy and modify to explain the source-to-impairment pathways for your site, and

• Make useful site observations when you are in the field.

The “Ways to Measure” sections are useful for:

• Knowing what measurements to look for when listing candidate causes. Some stressors are measured and reported in multiple ways with potentially unfamiliar names or units. For example, both total suspended solids and Secchi depth are measures of suspended sediment,

• Knowing what to measure if a causal analysis includes generation of new data, and

• Operationally defining the candidate cause. The definition of a stressor is often unclear until the measurements are specified.

The “Literature Reviews" are useful for:

• Saving time in finding good general reviews of the stressor and its effects, and

• Finding levels of the stressor that cause effects and exposure-response relationships. These may be used to determine whether the stressor occurs at levels sufficient to cause effects in other places (see Step 4.2: Evaluate Data from Elsewhere). At this time CADDIS points to reviews only for metals, sediments, and toxic chemicals with Ambient Water Quality Criteria.  

Allan, JD. (1995) Stream ecology: structure and function of running waters. London, UK: Chapman and Hall Publishers.

Dodds, WK. (2002) Freshwater Ecology: Concepts and Environmental Applications. San Diego, CA: Academic Press.

Wetzel, RG. (2001) Limnology, 3rd edition. San Diego, California: Academic Press.

First candidate cause