Methane seepage dynamics and ground heating phenomena in the southern Po Valley: the case study of Santa Maria Nuova (Italy)

Natural reservoirs that release CH4 can substantially increase atmospheric greenhouse gas levels, posing environmental and safety risks. Degassing phenomena in the Emilia-Romagna region (Italy) have been documented across a variety of fluids and reservoir types, with a focus on their origin and evolution. This study combines ground measurements and satellite data analysis to explore the relationships between CH4 seepage, thermal anomalies, and vegetation stress at the Santa Maria Nuova (SMN) site in southern Po Valley. The explosion of a CH4-saturated water well in July 2021 prompted a two-year investigation in the adjacent cultivated field (1.5 ha), revealing significant spatial and temporal variations in diffuse CH4 fluxes (ranging from 0 to 917 g m−2 d−1) and corresponding CO2 fluxes (1.9–466 g m−2 d−1). Soil temperature measurements and thermal imaging identified localised ground heating, attributed to methanotrophic exothermic oxidation of CH4 to CO2. These hotspots correspond to areas of visibly stressed vegetation, marked by reduced vitality and barren areas. Satellite-derived Ratio Vegetation Index (RVI) data confirmed persistent vegetation stress over the anomaly site from 2017 to 2024. Geochemical analysis of soil gases indicated a primarily biogenic origin of CH4, supported by isotopic signatures (δ13C–CH4 values < −60 ‰ V-PDB) and the presence of shallow Pleistocene carbonate deposits beneath the site, which can generate CH4 seepage. These findings demonstrate the utility of integrating ground-based and remote sensing techniques for monitoring CH4 seepage and its environmental impacts.