Total CO2 output and carbon origin discharged from Rincón de Parangueo Maar (México)

Abstract

A geochemical survey was carried out (May 2016) in the Rincón de Parangueo maar in Valle de Santiago, México. The challenge was to measure CO2 and CH4 fluxes discharged from soil and to investigate the chemical and isotopic compositions of interstitial soil gases and remaining vents at the bottom of maars system subjected to critical and high rate drawdown aquifer. Total CO2 flux calculated by sequential Gaussian simulation is 10.6 ton d−1 (±2.1 ton d−1) over the entire crater maar area. Two degassing groups were recognized: Group A (background degassing) with values lower than 10 g m−2 d−1 (40% of the total measurements) and Group B with values ranging between 10 and 347.1 g m−2 d−1 (60% of the total amount of measurements). CH4 flux ranges from 2.1 to 1577 g m−2 d−1. CH4/CO2 flux mean ratio is ~20.51 while CH4/CO2 concentration ratios are 78 and 119 for bubbling gases and 8.4 for interstitial gases. The δ13C-CH4 values are ~65 per mil vs V-PDB indicating a biogenic origin of methane in bubbling and interstitial gases. The δ13C-CO2 values, ranging from −10.6 to −27.6 and −1.9 per mil vs V-PDB for bubbling gases and the interstitial gases, respectively, suggest secondary CO2 consumption within the soil.