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Rethinking the longitudinal stream temperature paradigm: region-wide comparison of thermal infrared imagery reveals unexpected complexity of river temperatures
Fullerton, A., C. Torgersen, J. Lawler, R. Faux, E. Steel, Beechie, Joe Ebersole, AND S. Leibowitz. Rethinking the longitudinal stream temperature paradigm: region-wide comparison of thermal infrared imagery reveals unexpected complexity of river temperatures. Hydrological Processes. John Wiley & Sons, Ltd., Indianapolis, IN, , 19, (2015).
An important cornerstone of managing for stream and river water temperatures protective of salmon and other cold-water taxa is the understanding that the region’s streams and rivers were naturally thermally diverse. Loss of thermal complexity has likely contributed to declines of salmonid populations, particularly in warmer streams and rivers. Highly diverse thermal patterns in rivers and streams and the cold-water habitats they retain may promote resilience of aquatic biota to climate change. This paper describes spatial diversity in Pacific Northwest river temperatures, and characterizes relationships between environmental variables and water temperature patterns. This understanding will help improve predictions about future water temperatures and resultant impacts to aquatic biota. Without this spatial context, models may incorrectly estimate loss of thermally suitable habitat under future climate change.
We used an extensive dataset of remotely sensed summertime river temperature to compare longitudinal profiles (temperature versus distance) for 54 rivers in the Pacific Northwest. We evaluated (1) how often profiles fit theoretical expectations of asymptotic downstream warming, and (2) correlations between water temperature and climate, hydrology, and landscape variables in rivers with different profile shapes. Profile shapes were diverse and scattered in space, with 80% of rivers not matching theoretical expectations. For at least 22% (and up to 44%) of sampled rivers, profile shapes were complex, exhibiting multiple discontinuities. Relationships between river temperature and environmental variables differed by profile pattern. These highly diverse thermal patterns may promote resilience of aquatic biota to climate change by providing complex thermal habitats. Furthermore, knowledge about relationships between environmental variables and water temperature patterns can improve predictions about future water temperatures. Without this spatial context, models may incorrectly estimate loss of thermally suitable habitat.