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Few studies have examined both long-term and fine-scale spatial variations in water quality of small streams in the Pacific Northwest. As such, a case study was conducted to determine if current physical and chemical properties of water in three streams located in the Oregon Coast Range differed from historically measured conditions, taking differences in past management regimes into account. In addition, this research provides an assessment of spatial and temporal variability in nitratenitrogen (N) concentrations and summer stream temperatures within each catchment. The three research catchments were part of the Alsea Watershed Study (1959- 1973), where effects of forest management practices were examined using a pairedwatershed study design. One catchment, Needle Branch, was clear-cut with no protection provided to the stream. Harvesting in Needle Branch was followed by an intense broadcast burn to remove logging slash. Another catchment, Deer Creek, was patch-cut in three small units resulting in a 25% harvest of the total catchment area, but buffers were retained along fish-bearing streams. The third catchment, Flynn Creek, was used as a control. In this revisit to the Alsea Watersheds, measurements were conducted continuously (discharge, turbidity), intermittently (suspended sediments), and at regular intervals (nitrate-N) for one year between October 2005 and September 2006. Summertime stream temperature was also measured every half-hour from mid-June to mid-September. Comparisons of recent data with historic data show no detectable changes over time for streamflow characteristics (annual runoff volume, peak flow discharges, and number of low-flow days), annual sediment yield, or summer maximum stream temperatures. Current nitrate-N export was similar to historically measured values for Flynn Creek and Deer Creek; however, export at Needle Branch was increased over past levels. This observation may be caused by dense colonization of the riparian area with red alder (Alnus rubra), a N-fixing species, following the 1966 harvest. Patterns of nitrate-N concentration varied throughout each catchment and are likely influenced by the current distribution of red alder stands. Synoptically measured stream temperatures were variable along each stream's longitudinal profile. The ability to meet Oregon's water quality standard for temperature was dependent on measurement location and method of analysis. Evaluating individual sampling points as discrete records resulted in each stream exceeding the standard for at least one measurement location, whereas evaluating the criteria based on the mean of all data collected within the mainstem stream excluded Flynn Creek and Needle Branch from violation. These results highlight the physical and chemical variability of stream water draining Oregon Coast Range headwater catchments and provide insight as to where future work should be focused to gain a more thorough understanding of these dynamic systems.
Streamflow variability can provide valuable information for nonpoint source pollution monitoring program planning. The research papers presented in this thesis examine selected properties of streamflow variability in Oregon to advance its application in regional planning of water quality monitoring programs. The products of this research depict Oregon streams by their relative streamflow variability and evaluate factors that may influence that variability. The three manuscripts examine the application of streamflow variability in the context of regional strategic planning by addressing three related questions: 1.) What is the relationship in Oregon between streamflow variability and watershed size, which is often described as a proxy for streamflow variability?, 2.) What geographic factors in Oregon influence streamflow variability, and are regionalscale factors adequate to efficiently predict streamflow variability on ungaged streams?, and 3.) How is streamflow variability in Oregon affected by seasonal climatic variation? Examination of these questions regarding the behavior of streamflow variability of river systems in Oregon is used to assist in the design of regional and local water quality monitoring programs. Data are from historical records of established US Geological Survey gaging stations. Simple linear regression depicts the relationship of streamflow variability to basin size on a statewide basis and stratified by ecoregions. The results indicate that basin area is not an appropriate indicator of streamflow variability. Multiple regression is used to develop regional models of streamflow variability. Three models are developed for natural flow streams and streams with upstream diversions. Regional and watershed scale variables are evaluated for their potential contributions to the models. Watershed scale variables do not increase the predictive capacity of the models; therefore, the regional scale is appropriate for efficiently modeling streamflow variability. Seasonal investigation of streamflow variability in Oregon develops its application for seasonal monitoring programs. Spatial and temporal analysis reveal a weak relationship between annual and monthly streamflow variability, indicating potential for refined application of the variability index. Streamflow variability is an accessible tool for developing water quality monitoring programs. The regional scale distribution of streamflow variability in Oregon demonstrates the ease at which streamflow variability may be estimated on ungaged streams.