CONICET | Buscador de Institutos y Recursos Humanos

Direct measurements of surface CO2 emissions (CO2 fluxes) represent an effective tool to estimate the contribution of greenhouse gases from individual sources to atmosphere. In this way, the determination of absolute CO2 fluxes to assess the actual contribution of C to the atmosphere requires the careful calibration of methods in laboratory. This work presents the quantification of CO2 fluxes from a Municipal Waste Final Disposition Site in Gualeguaychú, where the closed dynamic chamber method was applied. This method was calibrated in laboratory before field measurements. For this purpose, a system that simulates the process of CO2 diffusion through a porous soil was developed in order to compare measured to known CO2 fluxes. The deviations between measured and reference values were always smaller than 10%. CO2 flux was estimated from the increase of CO2 concentrations in time inside the chamber taking discrete sequential lectures. These concentrations were determinated by an infrared gas analyzer. Under specific experimental conditions linear fits with R2 ≥ 0.99 were obtained. These reliable measurements allowed the quantification of the CO2 fluxes that ranged from 31 g m-2 day-1 to 331 g m-2 day-1. Using statistical analysis three different populations were distinguished: background soil gases (averaging, 0,017 T m-2 day-1) and anomalous values (averaging, 0,040 T m-2 day-1and 0,098 T m-2 day-1). Likewise, a soil gas probe (placed to a depth of 20 cm), coupled with a battery pump was used for sampling CO2, CH4, N2 and O2. The CO2 (< 10%V), CH4 (< 1%V), N2 (~78%V) and O2 (~21%V) concentrations, the time and depth of waste emplacement, the non compacted materials and the meteorological conditions, suggested that the study site could be mainly at the final stage of waste biodegradation. The water table degassing flux was estimated coupling water table geochemistry with hydrogeological data. The resulting average rate of CO2 production was 0,005 T m-2 year-1. Following the downstream direction, the dissolved inorganic carbon increased when the water table crossed through the site. The δ13C (-35 to -18) of the CO2 extracted with the gas probe as well as the δ13C of dissolved inorganic carbon of water samples (-15 to 4) showed that the present process fluctuate between aerobic and anaerobic oxidation phases. The total CO2 gas emissions from the site were calculated in 0,160 T m-2 year-1 (0,043 T m-2 year-1of C).