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CADDIS Volume 2: Sources, Stressors & Responses


What are stressors?

Stressors are any physical, chemical, or biological parameters or entities that directly or indirectly result in one or more 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 13 stressor-based modules on CADDIS (which you can access using the navigation bar, at left): Ammonia, Dissolved Oxygen, Flow Alteration, Herbicides, Insecticides, Ionic Strength, Metals, Nutrients, pH, Physical Habitat, Sediments, Temperature, and Unspecified Toxic Chemicals. Additional stressor-based modules currently under development include endocrine-disrupting chemicals and polycyclic aromatic hydrocarbons.

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, such as 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 included in the assessment.

What are sources, and how do they relate to candidate causes?
What are responses, and how do they relate to candidate causes?

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