Conceptualizing Influences on Stream Temperature: A Framework-Based Approach to Decision-Making

Human alteration of riparian and upland habitats throughout the U.S. has often resulted in increased stream temperature, which is an ecologically important and highly variable water quality parameter.  From the mid-1900s to present, land managers have undertaken conservation measures to better manage our aquatic resources, such as maintaining vegetated riparian buffers and grassed waterways.  However, growing populations and climate change increase the need for science-based approaches to support societal needs while protecting environmental resources.  We developed a conceptual model to describe basin- and reach-scale processes and factors that influence stream temperature, and we provide a decision framework for understanding direct and indirect effects of land use on stream temperature.  The conceptual model shows how five functionally related variables (climate, organisms, relief/topography, parent material, and time) drive basin hydrology and sediment transport, and channel and valley reach morphology to influence stream temperature.  The decision framework addresses multiple stream sizes and environments (e.g. rangelands, prairies, forests, urban areas, and agricultural areas).  We present an approach for assessing land management risks using the decision framework.  As an example, we use this approach to evaluate potential effects of riparian forest thinning on stream temperature in a mountain stream in the western Cascades, Oregon (USA).