Expanded study investigating potential bias in bioassessment tools for intermittently flowing streams

Posted May 6, 2024
Researchers are investigating if statewide stream condition scoring tools are biased against intermittently flowing streams, such as this reference site in the San Gabriel Mountains, above. Already, researchers have found that tools like the California Stream Condition Index are biased against intermittent streams in the San Francisco Bay Area, but not in the San Diego region.

SCCWRP and its partners have kicked off the next phase of an ongoing study investigating if a set of bioassessment scoring tools for evaluating the health of California streams is potentially biased against intermittently flowing streams – an investigation that could help determine if the bioassessment thresholds for these streams may need to be lowered for certain regions of the state.

The expanded study, which kicked off earlier this year, follows prior work that found that the California Stream Condition Index (CSCI) and Algal Stream Condition Index (ASCI) may need to be applied to intermittent streams differently in different geographic regions of California.

In the San Francisco Bay Area, researchers found that bioassessment scores are depressed at the reference sites of intermittent streams, meaning that even the healthiest intermittent streams in this region do not score as high as the healthiest streams for other stream types. By contrast, a similar analysis of the San Diego region found that CSCI and ASCI scores are not disproportionately depressed for intermittent streams, meaning that the tools are not biased against the region’s intermittent streams and thus there is no scientific basis for changing bioassessment thresholds for this region.

The expanded study is focusing on multiple regions of California, including the Los Angeles region. The Santa Ana region is expected to be the focus of a future study phase.

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