The effects of alterations in temperature and flow regime on organic carbon dynamics in Mediterranean river networks

It is only recently that freshwaters have been identified as important quantitative components of the carbon (C) cycle at global and regional scales. To date there are no studies that quantitatively predict the effects of alterations in temperature and flow regimes, individually, or in concert, on organic C dynamics in streams. To address this need, we applied a mechanistic model to simulate organic C dynamics in Mediterranean river networks under 27 different scenarios of altered temperature and flow regimes. We predict that the organic C dynamics in freshwaters in the Mediterranean, as well as in other semiarid regions, will be highly sensitive to global climate change owing to major increases in the degree of intermittency as well as in flood frequency and magnitude. Results indicate that flow regime alterations increase C export rates, whereas temperature alterations increase instream metabolism of organic C. However, flow regime alterations exhibit a much greater influence on C dynamics than do changes in the temperature regime. Reservoirs partly counteract the effects of flow extremes on C export rates, and their role in the C dynamics increases with increasing flow variability. The present study is one of the first studies to quantify the complex interactions between the flow and the temperature regime on C dynamics, emphasizing the key role of extreme events such as dry periods and floods, compared with overall trend effects. This information is pivotal in understanding the impact of future climate change on global C dynamics.