Characterization of CO2 exchanges in deep soils and caves and their role in the net ecosystem carbon balance

Abstract

This Thesis arises to response to the anomalous CO2 fluxes detected by the Eddy towers located on two carbonate and semiarid sites in the south-east of Spain. In the soil-atmosphere CO2 exchanges in both El Llano de los Juanes in the Sierra de Gádor and also Balsa Blanca located in the Natural Park of Cabo de Gata-Nijar (Almeria province), significant CO2 emissions to the atmosphere were detected. These emissions could only come from the soil and not from the vegetation, occurring as they did mainly during the summer, with senescent vegetation. For this reason, this Thesis focuses on monitoring and characterization of the soil, distinguishing which are the main factors implicated in CO2 exchanges with the atmosphere. For the characterization and monitoring of subterranean CO2 soil CO2 profiles were established in both experimental sites with sensors installed at three different depths (0.15, 0.5 and 1.5 m). Furthermore, in El Llano de los Juanes sensors were installed at 0.25 m depth and in a borehole of 7 m depth, which was sealed from the surface to simulate a karst cave. With the first CO2 data obtained from the borehole, we realized that the deep soil could store large amounts of CO2, because in the first 7 meters we recorded values of up to 18000 ppm. Since we were interested in determining the factors involved in CO2 ventilation from soils and particularly in karstic areas containing numerous cavities, we launched an examination of the literature regarding cave ventilation.