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Watershed-Scale approach to Understanding Fecal Source Input in an Estuarine Watershed
Citation:
Zimmer-Faust, A., C. Brown, AND T Chris Mochon Collura. Watershed-Scale approach to Understanding Fecal Source Input in an Estuarine Watershed. American Society for Microbiology (ASM) Microbe 2019, San Francisco, CA, June 20 - 24, 2019.
Impact/Purpose:
Tillamook Bay, a National Estuary Program site, is located on the northwest coast of Oregon. The Bay is one of Oregon’s leading producers of shellfish for human consumption. However, high levels of fecal indicator bacteria that exceed state water quality standards often result in shellfish harvesting area closures leading to potential public health and economic burdens. In this study, we demonstrate the utility of combining microbial source tracking marker results with mixing models. The catchment-scale approach applied in this study provided insight into which sites and sources should be prioritized for remediation from the perspective of improving downstream water quality.
Description:
Tillamook Bay, a National Estuary Program site, is one of Oregon’s leading producers of shellfish for human consumption. However, high levels of fecal indicator bacteria that exceed state water quality standards often result in shellfish harvesting area closures leading to potential public health and economic burdens. Microbial source tracking (MST) efforts have previously been completed and are described elsewhere evaluating tributary water quality; however, catchment-wide dynamics have not been described and are harder to capture due to complicated estuarine dynamics including flushing from ocean waters and uncertainty regarding the fate, transport, and delivery of watershed-sourced microbial contaminants. In this study, MST analysis was used to characterize spatial and temporal trends in sources of fecal bacteria in Tillamook Bay (receiving waters) and in each of the five major river systems draining into Tillamook Bay. Water samples were collected above and below potential anthropogenic pollution sources on each river system draining into the Bay, along with six sites within Tillamook Bay itself over a two-year period. Moreover, to estimate freshwater contributions of microbial sources to downstream estuarine waters, tributary MST marker levels were normalized based on river flow and used to develop mixing models that predicted freshwater contributions to Tillamook Bay. Overall, host-associated qPCR genetic markers targeting human (HF183/BacR287 and HumM2), ruminant (Rum2Bac), cattle (CowM2 and CowM3), canine (DG3), and avian (GFD) fecal pollution sources were measured frequently in Tillamook Bay tributary and bay waters: 24% (CowM2), 43% (CowM3), 79% (Rum2Bac), 42% (HF183/BacR287), 19% (HumM2), and 74% (GFD) detection frequencies in water samples. Separate and unlinked temporal patterns were initially observed when comparing tributary and receiving water marker levels. However, trends in receiving waters were reflective of tributary marker levels when marker levels were normalized based on river flow. In addition, conservative mixing models were able to explain variability in Bay marker levels (Rum2Bac and HF183) during the wet season. Findings demonstrate the utility of combining flow measurements and mixing models to provide context for MST marker results in estuarine watersheds. The catchment-scale approach applied in this study provided insight into which sites and sources should be prioritized for remediation from the perspective of improving downstream water quality.