Hydrothermal methane fluxes from the soil at Pantelleria island (Italy)

摘要

Chemical and isotopic analyses of the main gas manifestations of the island of Pantelleria (Italy) were used to gain insight on the origin of the released methane. Results indicate that the most probable origin is through abiogenic reactions within the hydrothermal system. Methane and CO_2 flux measurements from the soils were made with the accumulation chamber method in an area of about 0.015 km~2 within the main fumarolic area of the island (Favara Grande). The 23 measurements range from - 34 to 3550 mg m~(-2) d~(-1) for CH_4 and from 0.6 to 379 gm~(-2)d~(-1) for CO_2. The relationships between CH_4 and CO_2 fluxes and the CH_4/CO_2 ratios in the gases collected between the depths of 25 and 100 cm provide evidence for methanotrophic processes within the soils. Methane output for the surveyed area was calculated to be 2.5 t a~(-1) and extrapolated to about 5-10 t a~(-1) for the entire volcanic/hydrothermal system of the island. Previous higher estimates of the CH_4 output at Pantelleria (Etiope et al., 2007, J. Volcanol. Geotherm. Res., 165,76-86) were based on soil CO_2 output and CH_4/ CO_2 ratios in fumarolic gases; the present work provides the first direct CH_4 flux data and it suggests that methanotrophic activity in the soil could be substantial in reducing the CH_4 emission to the atmosphere.