Metrics and Models: River Thermal Regimes over Time and on the Snoqualmie River Network

Riverine thermal regimes cannot be captured, understood, or managed through mean temperatures or single-point measurements. We now understand that thermal regimes include minute-by-minute, day-to-night, and season-to-season fluctuations in water temperature at every location within the stream network.  A great deal of research has focused on human-induced changes in water temperature; however, human activities, e.g., dams, land-use, and climate change, impact the variability and complexity of water temperature regimes as well.  We apply network models to map variability at multiple time scales; explore spatial pattern across metrics and over time; and conceptualize which aspects of temporal variance are driven by within network versus out-of-network processes.  Using data collected every 30-min across the Snoqualmie River, WA, we demonstrate, for example, that while the spatial distribution of mean temperature over the stream network varies little between summer and winter, the spatial distribution of variance varies tremendously between summer and winter.  Changes in variance have the potential for dramatic sub-lethal effects on food web dynamics, species phenology, and community composition.  Understanding the drivers and patterns of thermal complexity as well as their impacts on biota are essential for effective management of aquatic systems.