Temperature dependence of stream benthic respiration in an Alpine river network under global warming

1. Global warming has increased the mean surface temperature of the Earth by 0.6 degrees C in the past century, and temperature is probably to increase by an additional 3 degrees C by 2100. Water temperature has also increased, which in turn can affect metabolic rate in rivers. Such an increase in metabolic rate could alter the role of river networks in the global C cycle, because the fraction of allochthonous organic C that is respired may increase. 2. Laboratory-based incubations at increasing water temperature were used to estimate the temperature dependence of benthic respiration in streams. These experiments were performed on stones taken from seven reaches with different thermal conditions (mean temperature ranging 8-19 degrees C) within the pre-alpine Thur River network in Switzerland, June-October 2007. 3. The activation energy of respiration in different reaches along the river network (0.53 +/- 0.12 eV, n = 94) was similar, indicating that respiration was constrained by the activation energy of the respiratory complex (E = 0.62 eV). Water temperature and the thickness of the benthic biofilm influence the temperature dependence of respiration and our results suggest that an increase of 2.5 degrees C will increase river respiration by an average of 20 +/- 1.6%.