Evidence of possible enhanced peat burning by deep-origin methane in the Po River delta plain (Italy).

A burning peat site in the Po Valley (Italy) has been investigated for the first time. Beyond the smoke resulting from smouldering combustion of peat, there are carbonatic concretions and huge amounts of methane in the soil (>60% v/v), leading to fluxes to the atmosphere of the order of 102-103 mgm-2d-1. A wide set of analyses, (gas composition, stable isotopes of CH4 and CaCO3, methane radiocarbon), has been performed in order to understand whether methane is produced by peat layers or seeps from deeper natural gas reservoirs. The quasi-fossil character of CH4, methane-derived carbonates, methane stable isotopic compositions related to marine carbonates reduction, the presence of helium and a fault in correspondence with the burning site, all converge to indicate that methane mainly ascends from deep horizons. Such methane seepage is likely to feed the peat combustion, explaining the long-lived combustion phenomena and the large outbursts of historical gas emission events.