With ~2000 t CO2 per day, the Mefite site, located in the Ansanto Valley (Campania, Italy), represents the most significant natural, non-volcanic source of low-temperature, CO2-rich gases on Earth. The area features a prominent sulfurous pond, locally referred to as “Lake Mefitis”, situated at the base of a landslide deposit. This bubbling mud pool, lacking surrounding vegetation due to intense gas exposure, marks the primary degassing zone. Gas emissions emerge from multiple vents and boiling mud basins across the site, likely linked to active fault systems that have historically generated major seismic activity in the region. The chemical composition of the emitted gases is dominated by CO2 (~98%), with minor constituents including non-atmospheric nitrogen (1.3%), hydrogen sulfide (0.33%), and methane (0.23%). Under low wind, the dense gas accumulates and flows downslope through a natural channel, forming an invisible, continuous plume that is lethal due to hypoxia and toxicity. Its impact extends up to 3 km, causing high soil acidity, oxygen depletion, and severe vegetation stress. These unique geochemical and ecological features make the Mefite site an exceptional natural laboratory for investigating the long-term biological and physico-chemical responses of the soil system to extreme gaseous exposure. To do that, topsoil (0-10 cm) samples were collected at a distance of 30 m (zone A), 80 m (zone B) and 120 m (zone C) from the river/lake. Sediment samples were also taken from the lake. All samples were characterized for pH and electrical conductivity, major and trace elements (XRF), main mineral phases (XRD), and organic carbon, total nitrogen and sulphur content (CHNS). Enzymatic activities, including β-glucosidase (EC), urease and N-acetylglucosaminidase (EN) and phosphomonoesterase (EP), were also assessed. Standardized major axis regression confirmed a relationship between soil EC and EN (R2 = 0.15, p<0.05) as well as between soil EC and EP (R2 = 0.34, p<0.001). The slope test performed after the regression showed a metabolic imbalance between EC and EN (p<0.001). The vector analysis indicated differences at metabolic level both between soil and sediment, and between soil collected at different distances. In particular, soils from zone A were characterised by a deficiency of N, which decreased with increasing distance from the lake, whereas those from zone C (pH>7) and sediments (pH~2; avg S > 50%) showed a P deficiency. Carbon use efficiency in relation to N and P confirmed this result. Although soil stoichiometric ratios C:N and C:P are not statistically different between zones, redundancy analysis identified them, together with pH (ranging from 2.5 to 7.9), as main environmental drivers of metabolic changes. Mefite is therefore confirmed as a site of extreme interest not only from the geological point of view, but also chemically and biologically.
Soil and enzyme stoichiometry in the extreme environment of Mefite d’Ansanto (Southern Italy)
Zaccone C.
2025-01-01
Abstract
With ~2000 t CO2 per day, the Mefite site, located in the Ansanto Valley (Campania, Italy), represents the most significant natural, non-volcanic source of low-temperature, CO2-rich gases on Earth. The area features a prominent sulfurous pond, locally referred to as “Lake Mefitis”, situated at the base of a landslide deposit. This bubbling mud pool, lacking surrounding vegetation due to intense gas exposure, marks the primary degassing zone. Gas emissions emerge from multiple vents and boiling mud basins across the site, likely linked to active fault systems that have historically generated major seismic activity in the region. The chemical composition of the emitted gases is dominated by CO2 (~98%), with minor constituents including non-atmospheric nitrogen (1.3%), hydrogen sulfide (0.33%), and methane (0.23%). Under low wind, the dense gas accumulates and flows downslope through a natural channel, forming an invisible, continuous plume that is lethal due to hypoxia and toxicity. Its impact extends up to 3 km, causing high soil acidity, oxygen depletion, and severe vegetation stress. These unique geochemical and ecological features make the Mefite site an exceptional natural laboratory for investigating the long-term biological and physico-chemical responses of the soil system to extreme gaseous exposure. To do that, topsoil (0-10 cm) samples were collected at a distance of 30 m (zone A), 80 m (zone B) and 120 m (zone C) from the river/lake. Sediment samples were also taken from the lake. All samples were characterized for pH and electrical conductivity, major and trace elements (XRF), main mineral phases (XRD), and organic carbon, total nitrogen and sulphur content (CHNS). Enzymatic activities, including β-glucosidase (EC), urease and N-acetylglucosaminidase (EN) and phosphomonoesterase (EP), were also assessed. Standardized major axis regression confirmed a relationship between soil EC and EN (R2 = 0.15, p<0.05) as well as between soil EC and EP (R2 = 0.34, p<0.001). The slope test performed after the regression showed a metabolic imbalance between EC and EN (p<0.001). The vector analysis indicated differences at metabolic level both between soil and sediment, and between soil collected at different distances. In particular, soils from zone A were characterised by a deficiency of N, which decreased with increasing distance from the lake, whereas those from zone C (pH>7) and sediments (pH~2; avg S > 50%) showed a P deficiency. Carbon use efficiency in relation to N and P confirmed this result. Although soil stoichiometric ratios C:N and C:P are not statistically different between zones, redundancy analysis identified them, together with pH (ranging from 2.5 to 7.9), as main environmental drivers of metabolic changes. Mefite is therefore confirmed as a site of extreme interest not only from the geological point of view, but also chemically and biologically.
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