Graduate Thesis Or Dissertation
 

The Thermal Response of Small Streams to Atmospheric Heat Waves in the Oregon Coast Range

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/ws859q393

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  • Streams across the Pacific Northwest have shown diverse temperature responses to increasing air temperatures. However, there is a knowledge gap in how short term events, such as atmospheric heat waves (AHWs), impact stream temperatures. This study focuses on how four small streams in the Oregon Coast Range respond to atmospheric heat waves. Stream temperatures at each site were autocorrelated up to nine days. During the study period, there were on average 18 spring AHWs, 11 summer AHWs, 14 fall AHWs, and 14 winter AHWs. The average air temperature during seasonal AHWs at each site was 14.8°C in the fall, 19.4°C in the spring, 22.4°C in the summer, and 12.0°C in the winter. Stream temperatures were found to be significantly elevated at all sites in all seasons during AHWs. The post-atmospheric heat wave period (post-AHW), defined as the 7-14 days after an AHW event, had significantly elevated stream temperatures in the fall (October – December) at all sites. Thermal sensitivity, defined as the slope of the linear regression between stream temperature and air temperature, was used to assess the seasonal empirical relationship between stream temperature and air temperature. Between each site, the thermal sensitivity ranged from 0.32°C/°C – 0.68°C/°C in the spring, 0.37°C/°C – 0.66°C/°C in the summer, 0.43°C/°C – 0.51°C/°C in the fall, and 0.17°C/°C – 0.34°C/°C in the winter. Beaver Creek, the smallest site, had lower thermal sensitivities in each season while the West Fork of the Smith, the largest site, had the highest thermal sensitivities in each season. Despite AHWs being associated with significantly elevated stream temperatures, fall and winter AHWs did not cause discernable patterns or shifts in coho salmon redd construction timing. Overall, these results show that AHWs in all seasons are associated with significant increases in stream temperature. Other factors, such as riparian shading, groundwater inputs, and stream size should be examined and included in future studies of AHWs and stream temperature to ascertain the specific role of each of those factors in the stream’s energy budget during these atmospheric events. Studies such as this should be expanded into other geographies and basin types (transient & snow-dominated) to develop a deeper understanding of the interaction between AHWs and stream temperature.
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