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Temperature is often considered a master variable controlling many chemical reactions and biological processes. Research efforts have begun address how temperature affects whole stream nutrient uptake rates, but little has attention has been paid to the influence of temperature on nutrient uptake versus concentration kinetics. In this study, we investigated 1) how ambient nutrient uptake rates and 2) nutrient uptake kinetics vary along a thermal gradient established by an altitudinal gradient in the Rocky Mountains, Colorado, USA. Instantaneous nutrient additions were performed at 15 streams within three adjacent drainage basins in the Colorado Rocky Mountains to test these questions. Ambient uptake metrics were estimated using multiple approaches and quantitatively related to variation in ambient temperatures and long-term thermal regimes. We found no relationship among nutrient uptake velocities and temperature. However, NH4+ uptake rates significantly increased with temperature whereas NO3- uptake rates decreased with temperature, though the significance differed by estimation approach and component of thermal regime examined. Response in uptake to increased nutrient availability was also estimated for each stream, where response in NO3- uptake was found to increase with increasing temperatures. In summary, temperature partially accounted for variation in nutrient uptake rates observed in this study. However, background nutrient concentrations and other stream characteristics also exert control on uptake dynamics and I surmise those controls dampen the role of temperature in controlling uptake rates in these streams.
Advisor: Steven A. Thomas