Oregon Department of Environmental Quality
Date of Award
Professional Science Master in Environmental Science and Management
Environmental Science and Management
Johnson Creek Watershed (Clackamas County and Multnomah County, Or.), Water -- Pollution -- Total maximum daily load, Escherichia, Bacterial pollution of water, Watershed management
Like many other waterbodies in the United States, Johnson Creek, a tributary of the Lower Willamette River is water quality limited for bacteria. Escherichia coli (E. coli), a member of the fecal coliform bacteria group, has been found to have a high association with human pathogens and the occurrences of gastrointestinal illnesses in waters used for contact recreation; E. coli is commonly used as an indicator of fecal contamination. In the State of Oregon water contact recreational standards for fecal exposure is assessed by measuring in stream levels of E. coli. Because Johnson Creek is water quality limited for bacteria the Oregon Department of Environmental Quality (ODEQ) developed a Total Maximum Daily Load (TMDL) document to address the re-attainment of water quality standards. ODEQ designated management agencies (DMAs) within the Johnson Creek Watershed to adopt best management practices (BMPs) to meet required bacterial loading conditions called for by the TMDL. In this study the status and trends of E. coli over the last two decades were assessed (1996-2016) by analyzing loading conditions for different flow regimes before and after implementation of the TMDL. In addition, management actions utilized by DMAs within the watershed were observed, the effectiveness of structural BMPs were assessed, and recommendations were made to better evaluate progress towards meeting the TMDL.
Four sampling sites were selected in this study to evaluate bacterial water quality within the watershed. The study sites spanned from the upper watershed near where Johnson Creek enters the City of Gresham to the mouth of the watershed in the City of Milwaukie. Two of the four study sites, located in subwatersheds dominated by urban development, showed progress towards meeting water quality standards, while the other two sites, which were in subwatersheds where rural and agricultural land use predominated, did not show progress. The strength of the conclusions in this study were hampered by inconsistent temporal spacing and sparse data which rendered trend and loading analyses largely un-interpretable.
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Gala, John, "Johnson Creek Bacteria TMDL Implementation: Status and Trend Analysis Study" (2017). Environmental Science and Management Professional Master's Project Reports. 32.