Quantification and source determination of CO2 exchanges measured over a carbonate ecosystem using the eddy covariance technique and stable carbon isotopes

Net CO2 fluxes in different terrestrial ecosystems and their determinant processes are keys to characterizing the global carbon cycle and to assessing global warming effects on ecosystems. Over carbonate ecosystems biological processes interact with geochemical and ventilation processes in the ecosystem behaviour related with the carbon cycle and can, at least temporarily, dominate the terrestrial carbon exchange with the atmosphere. Here we used the eddy covariance technique together with stable carbon isotopes and soil CO2 fluxes and meteorological measurements to characterize the underlying processes. The carbonate ecosystem acted as a net source or sink of CO2 according to differences in meteorological variables. Under optimal conditions of temperature and water the isotopic composition of the CO2 (delta C-13) reached minimum values suggesting a major contribution of biological processes. During dry periods and extremely high temperatures the contribution of such biological processes decreases substantially. Ventilation processes can contribute in the measured CO2 exchange due to similar values of delta C-13 in the external air and the cavity.