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United States Department of Agriculture

Agricultural Research Service


item Morrison, Matthew
item Shanks, Orin
item Bonta, James - Jim
item Field, Katharine

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/17/2006
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The Tillamook Bay Watershed, located in northwest Oregon, covers approximately 572 square miles and contains five major rivers. The Miami, Kilchis, Trask, Wilson and Tillamook Rivers originate in the coastal mountains and their drainages include significant amounts of forest and agricultural land. In addition to these natural resources, the Tillamook Bay Watershed fishery contains productive, but threatened, populations of chinook, coho chum and steelhead salmon. In June 2001, the Oregon Department of Environmental Quality developed a TMDL analysis for temperature and bacteria that covers the entire Tillamook Bay Watershed. Land use impacts on water quality and beneficial uses in the watershed include dairy agriculture, CAFOs, and timber harvesting in the forested uplands, while point sources and urban areas contribute to impairment in the coastal zone. The Tillamook Bay Watershed TMDL analysis provides a comprehensive assessment of land use distribution in the watershed, and estimates loading for probable bacterial source areas. Recent data provides additional information on fecal indicator bacteria concentrations within the Tillamook Bay Watershed, coupled with fecal source tracking (FST) assays. The FST data markers include both human and ruminant source-specific primers, and indicate that bacterial loading in the watershed is linked more strongly to ruminant sources (i.e., dairy operations and CAFOs) than to human sources. The current study combines bacteria concentration and fecal source tracking data with a duration curve approach, which can be used to separate point and nonpoint source loading based on river discharge. The objective of the research is to demonstrate the utility of FST and the duration curve approach in the examination of source-specific loading and allocation within a TMDL framework.

Last Modified: 06/23/2017
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