Minimal data collection for maxima results, combining geospatial modeling and a heat flux approach to the thermal regimes of headwater streams in a humid, hardwood forest.

Stream temperature monitoring programs and models provide valuable information and insights about stream temperature patterns and processes. Traditional approaches require time and resources for data collection and analyses, and for most headwater streams there is little information available. Often a stream's potential response to a specific environmental change is inferred from studies of other systems. With advances in measurement sensors, computational power, data availability and high-resolution geospatial analysis and modeling, new approaches requiring fewer resources can be used to provide information on stream temperatures. We investigated whether a simple heat flux approach, requiring minimal field data collection, combined with high-resolution GIS models could explain observed summer stream temperatures in forested first and second order streams within the Coweeta Basin of the Southern Appalachian Mountains. Water temperature was logged at the outlets of three north and two south facing streams over five and seven weeks of two summers. Local climatic and continuous discharge data were available, but field measurements were also collected for comparison in heat flux calculations. An open source GIS was used to delineate streams and estimate solar insolation using a high resolution bare-earth solar radiation model and a subcanopy solar radiation model (based on public airborne LiDAR data). Differences in the magnitude and timing of the daily peak temperature and net temperature gain were observed between north and south facing streams, indicating solar radiation was the dominant heat flux. Estimates of solar irradiation along the stream channels varied with differences in topography (bare-earth model) and vegetative shading (subcanopy model) and cumulative totals suggested that differences in temperature gain and peak temperature timing were related to solar gain. A full deterministic heat flux model of stream temperature is being implemented for a north and south facing watershed pair. However, our preliminary results suggest minimal stream temperature and discharge measurements, combined with a geospatial model of solar radiation, may provide useful information about stream thermal regimes and heat fluxes to managers and researchers with reduced monitoring or modeling effort.