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Hydrological intermittency affects sediment biogeochemistry, organic carbon (OC) metabolism and carbon dioxide (CO 2 ) emission but the study of the effects of drying is generally confined to natural ecosystems. Agricultural canals are artificial, widespread elements in irrigated floodplains, and regularly subjected to water level fluctuations. The aim of this study was to quantify the CO 2  emissions along water saturation gradients in artificial canals to understand the environmental factors regulating these fluxes. CO 2  measurements were performed in five replicated canals within the Po River basin (Northern Italy). In each canal we analysed three sites: (i) a spot with exposed, dry sediments; (ii) a spot with inundated, saturated sediments and (iii) a spot with an intermediate level of saturation. Besides dark CO 2  flux measurements, net potential nitrification and denitrification rates were measured as proxies of sediment redox potential and due to their CO 2  sink and source role, respectively. We hypothesized a site-specific regulation of CO 2  emission, depending on the interplay among water saturation, sediment oxidation and organic matter content. Our results suggest that desiccation stimulates mineralization processes and CO 2  fluxes, that were mainly dependant on water and organic matter content and correlated with microbial N transformations. CO 2  emissions tended to increase along the considered water saturation gradients, almost tripling rates from inundated, saturated (158.2 ± 24.1 mmol CO 2  m −2  days −1 ) to dry, exposed sediments (416.5 ± 78.9 mmol CO 2  m −2  days −1 ). Results also suggest that net potential nitrification and denitrification allow tracing the effects of drying on N microbial communities involved in CO 2  fluxes. Net potential nitrification rates produce little effects on CO 2  fluxes, but is a good proxy of oxygen (O 2 ) availability, whereas potential denitrification may be responsible for variable fractions (up to 100%) of CO 2  production, in wetter sediments.

Regulation of CO2 fluxes along gradients of water saturation in irrigation canal sediments