What Are Stressors?

Stressors are any physical, chemical or biological parameters or entities that directly or indirectly result in biotic responses of concern. Proximate stressors (or causal agents) are directly responsible for these responses. Other stressors may be indirectly responsible for these responses via their effects on proximate stressors.

There currently are thirteen (13) stressor-based modules in CADDIS. They are:

• Ammonia
• Dissolved Oxygen
• Flow Alteration
• Herbicides
• Insecticides
• Ionic Strength
• Metals
• Nutrients
• pH
• Physical Habitat
• Sediments
• Temperature
• Unspecified Toxic Chemicals

How Do Stressors Relate to Candidate Causes?

A candidate cause is a hypothesized cause of a specific environmental impairment, sufficiently credible to be analyzed in a causal assessment.

A candidate cause can be simply a proximate stressor, or the stressor directly responsible for the observed biological response (e.g., low dissolved oxygen concentration). However, a candidate cause also may include more detailed information about the causal pathway.

This information may include what led to the proximate stressor (e.g., increased nutrients associated with stormwater runoff) or how that proximate stressor produced the observed biotic response response (e.g., fish died due to asphyxiation). Including more detail when listing candidate causes may help identify ways to distinguish among different candidate causes in the assessment.

• Learn more about candidate causes under Tips for Listing Candidate Causes.