Contextualizing changes of both local land use and global climate within the directional, dendritic structure of stream networks is essential in understanding their relative consequence from location to location, and in making basin-wide assessments of water quality. With stream temperature’s notable influence on the overall health of aquatic ecosystems, warming trends impact the viability of cold-water species’ habitats and confound efforts to conserve them without a spatial appreciation of these connections. Land managers often use results of region-scale geostatistical models such as NorWeST to understand thermal dynamics of watersheds. However, neighboring watersheds’ atmospheric, landscape and in-stream variables can act on stream temperatures with dissimilar degrees of spatial autocorrelation and at discrete scales of influence, adding caution to interpretations of these results. In this study, we collected stream temperature data in the mostly undeveloped, rain-snow transient Clackamas River Basin and the nearby, rapidly urbanizing rain-dominated Tualatin River Basin in Oregon to derive geostatistical spatial stream network (SSN) models using a novel pool of stream temperature covariate datasets derived at three spatial scales. This poster presentation will demonstrate how variables such as air temperature, land cover and topography work together differently from basin to basin to influence stream temperature and affect the reliability of predicted thermal regimes throughout river basins using SSNs. Modeled thermal changes within the Clackamas River Basin can be attributed to variables from which effects predictably accumulate as a percent of total upstream area, whereas the Tualatin River Basin’s relatively disjointed thermal patterns appear to stem from variables with more distinct local influence. We will highlight how locally informed approaches to stream sampling and selection of variables are needed to reliably model stream temperatures in basins with different levels of disturbance (e.g., wildfire) and land cover heterogeneity. Finally, we will discuss the implications of scaled influential factors to resource managers’ future efforts to conserve and restore riverscapes.
