GLACIAL VERSUS GEOMORPHIC CONTROLS ON STREAM TEMPERATURE AND CONDUCTIVITY IN A TEMPERATE WATERSHED

Climate change is impacting mountain systems worldwide with far ranging consequences including increasing air temperature and altered precipitation patterns. These changes result in cascading effects including shrinking glaciers, and changing timing and amount of water delivered to, and the movement of water through alpine stream networks and groundwater systems. Stream temperatures and chemistry are expected to change along with this but the drivers of those changes are complex, making it difficult to predict the direction and degree of change for these parameters. In glacier-dominated systems, previous studies have focused on the distance from glaciers as the primary control on stream temperature and chemistry. However, many other watershed attributes such as the interaction with groundwater, presence of lakes, topography and vegetation also have a strong impact. Here we aimed to take a more holistic approach to determine the combination of watershed properties that most influence stream temperature and specific conductivity, a bulk measure of the ionic strength of the water, and how they change over a summer season. To do so, we used spatially distributed 15-min observations of stream temperature and conductivity in the Dinwoody Creek watershed, located on the east side of the Wind River Range in western Wyoming. We coupled this with geospatial analysis and spatial stream network statistical modeling to identify the primary landscape characteristics that explain the most variability in the daily mean and range of stream temperature and conductivity over the summer. We found that while the amount of perennial ice and snow was an important predictor for all variables, it was most important early and late in the season (June, July, and September), but it was never significant in August for temperature or conductivity. However, the percent of the watershed with gneiss bedrock was a significant predictor of mean temperature in July and August. Further, the terrain ruggedness near the stream channel was a significant predictor of stream daily mean and range of conductivity in June and July. Combined, these results indicate that the major drivers of alpine water quality parameters are variable over a summer season. Additionally, while perennial ice (glaciers) and snow are important the lithology and terrain ruggedness, both indicators of the amount of surface water-groundwater interaction, also influence stream temperature and conductivity. These findings are a first step towards, and highlight the need for, a broad understanding of how the landscape mosaic influences critical water quality parameters in rapidly changing mountain ecosystems.