Finding a Needle in the Haystack – Finding the Cause of Reduced Biological Integrity in a Large Northern California Urban Stream
Currently the State of California is developing a Biological Integrity Policy (Policy) that will provide guidance to Regional Water Quality Control Boards on the use of biological assessment information in regulatory programs. Many municipal stormwater programs currently conduct bioassesments in receiving waters using benthic macroinvertebrates. Bioassessments are generally conducted to characterize the biological integrity of a water body and assess if beneficial uses are supported. As a result of the Policy, when bioassessment results indicate that the biological integrity of a creek, stream, or river may be reduced, municipalities may soon be required to conduct causal assessments to determine the extent of the problem and to assist in identifying the stressor and/or source of the impact. Very few case studies, however, have been conducted to-date in California and as a result limited guidance on causal assessment methodologies is currently available to assist municipalities identifying the causes of beneficial use impacts. This presentation will describe the methodologies recently used to conduct a causal assessment in Coyote Creek, a large northern California urban creek in Santa Clara County. We will present the process the Santa Clara Valley Urban Runoff Program (in collaboration with the Santa Clara Valley Water District and the City of San Jose) successfully used to develop and conduct the causal assessment study, including project results, conclusions and lessons learned, and evaluation of the ability to identify a specific stressor in an urban creek. The information presented will provide municipalities and stormwater programs throughout California with tangible and practical recommendations to consider when designing and conducting causal assessment studies triggered by bioassessment data.