Relationship between diffuse carbon dioxide emissions and soil types of the Xalapa Monogenetic Volcanic Field (XMVF)

Carbon dioxide (CO2), along with other gases, is classified as a greenhouse gas, being the main contributor, accounting for around 60% of global emissions that produce the greenhouse effect. The emissions into the atmosphere are the result of anthropogenic activities, mainly derived from the burning of fossil fuels. However, CO2 is also generated by natural processes, of biogenic origin and non-biogenic origin, which is divided into volcanic and non-volcanic degassing. CO2 outgassing can occur with visible manifestations, such as fumaroles, or invisibly, known as diffuse emissions, with CO2 being the main component and present in all soils. In the context of carbon dynamics on Earth, soil hold significant importance, as it functions as a reservoir and as a source of CO2 to the atmosphere. Soil stores twice as much carbon as the atmosphere (only after the oceans), and contributes approximately with 20% of total emissions to the atmosphere. The soil emissions are influenced by numerous processes and exhibit a high spatial and temporal variability, which are affected by various factors, such as soil temperature, humidity, pH, texture, and organic matter content. Currently, in geothermal and volcanic areas, diffuse emissions, are studied to detect changes in volcanic activity, temporary degassing variations, diffuse degassing structures, estimate the energy released from a system, among others. The main objective of this work is to study diffuse CO2 emissions of soils and its relationship with soil physicochemical parameters in the Xalapa Monogenetic Volcanic Field (XMVF), to study relationship between CO2 flux and the soil types and their physical and chemical properties. The methodology consisted of 4 main activities: 1) selection of the study area; 2) fieldwork; 3) laboratory work; and, 4) statistical processing. As our main results, more than 300 points of diffuse CO2 emissions were measured at XMVF, in the range of 0.26 – 275.19 g m-2d-1 ±5% and a total flux of ~29,260 ton d-1. These measurements covered 4 soil types: Phaeozems, Andosols, Leptosols and Luvisols, in the range of 8.9 - 86.17 g m-2d-1, 0.25 - 275.19 g m-2d-1, 6.85 - 49.46 g m-2d-1 and 6.33 - 90.66 g m-2d-1 respectively, all with less than 10% uncertainty. Soil properties were obtained in field, such as temperature, pH and humidity. Additionally, soil samples were analyzed in the laboratory in order to obtain other physical parameters, such as true density, bulk density, porosity, humidity, texture and chemical parameters (C, N). Subsequently, statistical work was carried out to assess potential relationships between flux and the obtained soil parameters. This work aims to enhance understanding of degassing in the XMVF and the influence of soil properties on these processes. Acknowledgments: I would like to thank Dra. Lucy Natividad Mora Palomino of Experimental Edaphology laboratory at Geology Institute, UNAM. I would also like to express my gratitude to Lic. Brenda Caldera Osorio, for her support in the work field. Additionally, for the fund PAPIIT-UNAM, Project No. IA102123 “Exploración avanzada en Los Baños, Veracruz, para usos directos de la energía geotérmica”, that made this work possible.