Microbial Source Tracking in CA Watersheds: The CA Source ID Manual, a Case Study in Santa Barbara, and Current Research
Pathogens are among the most common pollutants on California’s 303(d) list of impaired waterbodies. Total maximum daily loads (TMDLs) have either been established or are being developed to address bacterial impairments in many watersheds. Conventional assessments have been of pathogen indicators: fecal indicator bacteria including total and fecal coliforms, Escherichia coli, and enterococci. However, microbial source tracking (MST) can identify sources of fecal contamination contributing to bacterial exceedances of water quality criteria, and is therefore increasingly being implemented in California watersheds. The “California Microbial Source Identification Manual", published in 2013, was generated as part of a collaborative study to guide practitioners in the use of advanced MST tools for the identification of fecal sources. This presentation will highlight the steps and tools that are recommended in the Manual, as well as lessons learned during its development. The tiered approach to MST will be described, which includes the use of traditional source tracking tools such as dye testing and televising of sewers prior to the use of more advanced approaches involving DNA-based markers for specific fecal sources. Information on recommended MST markers for the identification of human, dog, gull, cow, and other animal fecal sources will be presented. Results of an MST case study at Arroyo Burro Beach in Santa Barbara, CA, employing the methods in the Manual including use of specific markers for discriminating human, dog and gull fecal sources, will then be discussed. A takeaway message from this study is the impact that pet waste can have on water quality in urbanized areas and how management actions can have an immediate effect. This study showed how, in addition to the identification of fecal sources, MST can be used to demonstrate the effectiveness of source control best management practices. To engage the audience, a survey will be conducted on dog waste disposal practices, serving to both gain information from a water quality conscious audience and raise awareness to this issue. Finally, current research into the environmental degradation of sewage-related MST markers in relation to indicator bacteria and pathogens will be discussed. Knowledge of the stability of MST markers compared to indicators could assist with interpreting MST markers in relationship to indicator bacteria levels. Additionally, information on the relative stability of pathogens such as Campylobacter jejuni and Salmonella in environmental waters will be useful in determining if MST marker detections can reliably indicate risks to human health. Overall, this presentation will show that MST is an effective tool for identifying fecal sources, which will increasingly be used to make a difference in California’s stormwater quality.