Biological monitoring and assessment methods have become indispensable tools for evaluating the condition of aquatic and terrestrial
ecosystems. When an undesirable biological condition is observed (e.g., a depauperate fish assemblage), its cause (e.g., toxic
substances, excess fine sediments, or nutrients) must be determined in order to design appropriate remedial management actions.
Causal analysis challenges environmental scientists to bring together, analyze, and synthesize a broad variety of information
from monitoring studies, models, and experiments to determine the probable cause of ecological effects. Decision-support systems
can play an important role in improving the efficiency, quality and transparency of causal analyses.
CADDIS (
http://www.epa.gov/caddis) is an on-line decision framework for identifying the stressors responsible for undesirable biological conditions in aquatic
systems. CADDIS was developed in response to requirements under the U.S. Clean Water Act to develop plans for restoring impaired
aquatic systems. CADDIS is based on U.S. EPA’s 2000 Stressor Identification Guidance document, and draws from multiple types
of eco-epidemiological evidence. A major update in 2007 added summaries of commonly encountered causes of biological impairment:
metals, sediments, nutrients, flow alteration, temperature, ionic strength, low dissolved oxygen, and toxic chemicals. These
reviews are designed to help practitioners choose which causes to consider, based on sources, site information, and observed
biological effects. A series of conceptual models illustrates connections between sources, stressors and effects. Another
major new section provides advice and tools for analyzing data and interpreting results as causal evidence; these tools help
quantify associations between any cause and any biological impairment using innovative methods such as species-sensitivity
distributions, biological inferences, conditional probability analysis, and quantile regression analysis.
An essential part of the development strategy for CADDIS has been the use of case studies to test the process and tools in
different regions, and with different causal factors. Case studies have been conducted in streams on the urbanized east coast
and the agriculturally-dominated mid-west to the arid west, and have considered causes including low dissolved oxygen, increased
temperature, toxic substances, altered food resources and fine sediments. Lessons learned from the case studies include the
importance of a structure for organizing the large variety of evidence that is often available, the need for well-matched
reference sites for comparison, the benefits of iterative and directed data collection, and the frequency of surprising results.
The case studies illustrate the promise of CADDIS: by building on the foundation of biological monitoring, we can provide
a powerful means for improving the health of our aquatic systems.