27 January, 2010 ESSC Brown Bag/Climate Dynamics Seminar

Characterization of stream temperatures across Pennsylvania

Christa Kelleher
Civil Engineering, Penn State

Abstract: Stream temperature is an important characteristic of both water quality and ecosystem health. It directly affects the geographic distribution of aquatic species, and controls many vital biotic and abiotic processes. Climate and land use changes threaten to alter stream temperatures, thereby endangering habitat for aquatic organisms dependent on particular temperature regimes. This effect is especially pronounced in Pennsylvania, where the combined effect of high water temperatures and low flows may render many once cold-water streams uninhabitable for cold and cool water aquatic species in the future. In order to determine how aquatic ecosystems will be affected by environmental change and how water temperature varies across a region, we need to understand what controls water temperature sensitivity. To investigate both controls on and sensitivity of stream temperature, we define ‘thermal elasticity’ to quantify the sensitivity of a given stream to environmental change. Thermal elasticity was shown to vary from near zero to one across Pennsylvania, and controls were identified to be stream size (stream order), shading (shading factor) and groundwater contribution (baseflow index). Controls were strongest within the Susquehanna basin and weakest in the Delaware River Basin. Analysis of historical trends in water temperature, used to indicate the extent to which Pennsylvania’s streams have already been impacted by environmental change, also suggest that warming has occurred over the past decade for monthly averaged daily maximum, minimum, and average values for sites within the Delaware River Basin. The work indicates that stream temperatures are already being affected by environmental change, and that their sensitivity to change, as a function of size, groundwater, and shading, also poses a risk to habitat for sensitive aquatic species.