Is there a universal temperature dependence of aquatic ecosystem respiration?

Background/Question/Methods

Temperature is a fundamental control of ecological communities and ecosystem function. As the climate warms, it is increasingly critical to consider how temperature controls carbon cycling processes such as ecosystem respiration because of the potential for positive feedbacks to climate warming.  However, there is uncertainty about whether the temperature sensitivity of ecosystem respiration is governed by a universal temperature dependence or is system-specific, reflecting characteristics such as thermal history, resource abundance and quality, especially in aquatic ecosystems.  Here we use a combination of mesocosm and open channel estimates of aquatic ecosystem metabolism to evaluate the temperature sensitivity of ecosystem respiration rates among individual streams in the Wood River watershed in Southwest Alaska.   

Results/Conclusions

We find that temperature sensitivity is highly variable among streams and that resource quality causes the temperature dependence of respiration to deviate from the predicted universal temperature dependence.  We show that respiration based on more recalcitrant C sources (e.g., from wetlands) has higher temperature sensitivity than respiration based on labile C sources (e.g., autochthonous production). We show that this variation is strongly related to watershed geomorphic features, such that temperature sensitivity is linearly related to watershed slope (respiration in flatter watersheds is 3x that of steep watersheds).  We suggest that a universal temperature sensitivity value masks important variation in how aquatic ecosystems will respond to climate warming and that watershed geomorphic features influence the ultimate fate of carbon in a river network.