Limnetica 33

Small water bodies, such as temporary ponds, have a high carbon processing potential. Nevertheless, despite the global occurrence of these systems, the carbon effluxes from such water bodies have been largely overlooked. In this study, we examined the intra- and intersystem variability of carbon dioxide (CO₂) effluxes from a set of Mediterranean temporary ponds during the flooding phase, a hot-spot for biogeochemical cycling in temporary systems. The CO₂ effluxes showed higher variability among the various sections of each pond (i.e., inundated, emerged-unvegetated and emerged-vegetated) than among the ponds. The emerged-vegetated sections showed the highest CO₂ effluxes per unit area and tended to drive the total effluxes at the whole-ecosystem scale. The mean CO₂ efflux (121.3 ± 138.1 mmol m^-2 d^-1) was in the upper range for freshwater ecosystems. The CO₂ effluxes were not related to catchment properties but rather to the organic content of the sediments, especially in the emerged sections of the ponds. Our results indicate that temporary ponds, especially their emerged sections, are important sources of CO₂ to the atmosphere, highlighting the need to include the dry phases of these and other temporary aquatic systems in regional carbon budgets.