Using a transient storage model to characterize habitat and biological conditions in urban streams of the Pacific Northwest, USA

Urban development can affect the health of stream ecosystems through mechanisms that alter in-stream habitats. The relation between land-use changes accompanying urbanization and changes in streamflow patterns and their impact on in-stream habitat are often difficult to address based on traditional habitat measures collected at varying scales. To address these limitations, a One-Dimensional Transport with Inflow and Storage (OTIS) transient storage model of dye tracer injections was performed at 21 urban and rural streams in the Pacific Northwest. The model was utilized to better understand how urbanization influences stream habitat conditions.  The OTIS model was used to generate hydrologic storage metrics for each stream. The changes in transient storage model metrics were consistent with urban development and were found to generally decrease with increases in hydraulic alteration. In addition, OTIS model metrics were significantly related to the number and location of road crossings upstream of the study sites as well as with macroinvertebrate metrics and a biotic index developed for the study area. The results of this study demonstrate how a transient storage model (OTIS) can be used to characterize ecologically relevant in-stream habitat conditions and how these results can be used to identify potential watershed scale perturbations.