Interpreting B-IBI Scores

The B-IBI is a measure of a stream's biological condition (i.e., health). Each of the individual metrics reflect the condition of important biological components. These components provide insight and clues about the types of degradation responsible for changes within the biological community of benthic macroinvertebrates.

A value close to 50 (or 25 for 5 Metric B-IBI) indicates that the stream's biology is equivalent to what would be found in a "natural" stream of that area. A value close to 10 (or 5) indicates a poor biotic condition within the stream. Most likely, however, a score will be somewhere in between these two extremes. Listed below are cut off values for the B-IBI scores and the qualitative interpretation.

It is important to not only look at the final B-IBI score, but to look at the individual metric scores for clues to the types of impacts affecting the final score. For example: Is there a high percentage of pollution tolerant taxa? Were long lived taxa present? Were sediment tolerant taxa present? The individual metrics, the original data set, and notes on the land uses surrounding the site will help you understand the processes occurring within and around the sampling site.

Interpreting Stream Condition/Health Scores

Graphing Your Results

Stream surveys of the surrounding land uses can help interpret the metric results. A useful way of interpreting IBI scores is to plot the final IBI score against a gradient of human influence expected. Scores lower than the general plotted trend may occur when surrounding or upstream human impacts (e.g., new development, leaking septic systems, new clearcuts, etc.) are present. Conversely, monitoring sites may plot higher than the trend in the presence of wetlands, protected riparian corridors, and other biological conducive conditions.

Saturday, 16-Dec-2000 15:00:04 PST