Temperature sensitivity of community respiration rates in streams is associated with watershed geomorphic features

Aquatic ecosystems play an important role in the global carbon (C) cycle and represent substantial source of greenhouse gases to the atmosphere. However, little attention has been paid to quantifying how aquatic community respiration (CR), a major source of CO2, will respond to warming temperatures expected under climate change, and whether landscape features affect temperature modulation of CR. We quantified how temperature sensitivity of CR varied among streams in southwestern Alaska, a region with one of the fastest warming trends globally. We incubated sediments from streams spanning a geomorphic gradient and estimated the degree to which CR responded to increased water temperature as described by Arrhenius kinetics. As expected, CR increased with temperature across all streams, and the average temperature sensitivity was similar to theoretical predictions for heterotrophic metabolism. However, temperature sensitivity was significantly higher in streams with higher quantity but lower quality organic C substrates, conditions that were strongly associated with watershed geomorphic characteristics. These results suggest that basic geomorphic features of landscapes will control the rates at which C is lost or sequestered from watersheds under new climate regimes.