Characterizing spatial and temporal variations in CO2 fluxes from ground surface using three complimentary measurement techniques

Fluxes of CO2 from non-agricultural soil ecosystems, though globally important, are poorly characterized. Previously, we tested a dynamic closed chamber (DCC) method that was shown to accurately measure CO2 fluxes from ground surface to the atmosphere in mesocosms. In the current study, the DCC method was used to measure the CO2 efflux at a field site where conditions were similar to those used in the mesocosm tests. Fluxes measurements also were obtained using static closed chamber (SCC) and eddy covariance (EC) methods. The study site consisted of a large, flat-topped, waste pile at the Key Lake uranium mine, in northern Saskatchewan. The pile was constructed of uniform, fine to medium grain sand and was devoid of a soil zone and vegetative cover. Chamber-based measurements were used to characterize the spatial variability associated with the CO2 flux; whereas the EC method was used to characterize temporal variability. Results showed that the chamber-based (DCC and SCC) methods yielded comparable data, with a time-averaged CO2 flux of 171±54 mg CO2 m−2 h−1. Spatial variability associated with the flux was relatively small and no distinct spatial pattern was observed. Fluxes measured using the EC method tended to underestimate those measured using the chamber-based methods, with a time-averaged CO2 flux (150±35 mg CO2 m−2 h−1) that was about 12% lower than the average flux calculated from the chamber data. The greater temporal resolution provided by the EC method demonstrated that the CO2 flux exhibited a distinct diurnal pattern, but that long-term variations in the flux were relatively small (CV=23%). When used together, the chamber-based and EC methods provide information of a complementary nature that can greatly improve our understanding of the processes at work in unsaturated media.