Accumulation chamber measurements of methane fluxes from natural environments and landfills

Direct measurement of present day CH4 diffuse degassing from the soil represents an effective tool to better estimate
the degassing rate of individual sources and to calibrate global Earth degassing estimates. While many data exist on
CH4 emissions from ecosystems, agricultural soils and landfills, few estimates of CH4 emissions from volcanic-geothermal
areas have been performed. The authors report results and discuss applications of accumulation-chamber
measurements of soil CH4 and CO2 flux from Solfatara of Pozzuoli (Naples), Vulcano Island and Poggio dell’Olivo
(Viterbo) volcanic-geothermal areas, and the Palma Campania landfill (Naples). Volcanic-geothermal study areas are
characterised by vent discharges of fluids with different CH4/CO2 ratios (from 4.7X1E-5 to 7.5X1E-5, 4.7X1E-4 and
2.5X1E-3 by weight, for Solfatara of Pozzuoli, Vulcano island, and Poggio dell’Olivo areas, respectively). Soil CH4
fluxes range from 0.003 to 48 g m-2 day-1 in the volcanic-geothermal areas and from 0.0021 to 936 g m-2 day-1 in the
landfill, with high spatial variability observed in all areas. Using statistical methods different flux populations were
distinguished (i.e. background soil gases and deeply derived gases) and the total gas emissions from study sites calculated.
The results of this work show that CH4/CO2 ratios of deep fluids, fumarolic fluids in the case of the volcanicgeothermal
environment and biogas in landfills, are roughly maintained in the gas phase diffusely degassed by the soil.
Due to high spatial variability, a large number of flux measurements and appropriate statistical methods are needed to
estimate total gas discharge from study areas. Furthermore, the simultaneous measurement of diffuse CH4 and CO2
fluxes represents a strong constraint for interpretative models of deep processes associated with soil degassing.

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