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This study is focused on the (micro)biogeochemical features of two close geothermal sites ( FAV1 and FAV2), both selected at the main exhalative area of Pantelleria Island, Italy. A previous biogeochemical survey revealed high CH4 consumption and the presence of a diverse community of methanotrophs at FAV2 site, whereas the close site FAV1 was apparently devoid of methanotrophs and recorded no CH4 consumption. Next-Generation Sequencing ( NGS) techniques were applied to describe the bacterial and archaeal communities which have been linked to the physicochemical conditions and the geothermal sources of energy available at the two sites. Both sites are dominated by Bacteria and host a negligible component of ammonia-oxidizing Archaea (phylum Thaumarchaeota). The FAV2 bacterial community is characterized by an extraordinary diversity of methanotrophs, with 40% of the sequences assigned to Methylocaldum, Methylobacter (Gammaproteobacteria) and Bejerickia (Alphaproteobacteria); conversely, a community of thermo-acidophilic chemolithotrophs ( Acidithiobacillus, Nitrosococcus) or putative chemolithotrophs ( Ktedonobacter) dominates the FAV1 community, in the absence of methanotrophs. Since physical andchemical factors of FAV1, such as temperature and pH, cannot be considered limiting for methanotrophy, it is hypothesized that the main limiting factor for methanotrophs could be high NH4+ concentration. At the same time, abundant availability of NH4+ and other high energy electron donors and acceptors determined by the hydrothermal flux in this site create more energetically favourable conditions for chemolithotrophs that outcompete methanotrophs in non-nitrogen-limited soils. [ABSTRACT FROM AUTHOR]

Abstract: 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 CO2 flux measurements from the soils were made with the accumulation chamber method in an area of about 0.015km2 within the main fumarolic area of the island (Favara Grande). The 23 measurements range from −34 to 3550mgm−2 d−1 for CH4 and from 0.6 to 379gm−2 d−1 for CO2. The relationships between CH4 and CO2 fluxes and the CH4/CO2 ratios in the gases collected between the depths of 25 and 100cm provide evidence for methanotrophic processes within the soils. Methane output for the surveyed area was calculated to be 2.5ta−1 and extrapolated to about 5–10ta−1 for the entire volcanic/hydrothermal system of the island. Previous higher estimates of the CH4 output at Pantelleria (Etiope et al., 2007, J. Volcanol. Geotherm. Res., 165, 76–86) were based on soil CO2 output and CH4/CO2 ratios in fumarolic gases; the present work provides the first direct CH4 flux data and it suggests that methanotrophic activity in the soil could be substantial in reducing the CH4 emission to the atmosphere. [Copyright &y& Elsevier]

Hydrological and geochemical studies performed on Lake Specchio di Venere on Pantelleria island (Italy) indicate that this endorheic basin has been formed through upwelling of the water table, and that it is continuously fed by the thermal springs situated on its shores. The lake is periodically stratified both thermally and in salinity, albeit this stratification is rather unstable over time, since meteorological events such as strong rain or wind can determine the mixing of its waters. Periodical analyses of the lake water chemistry show large variations of the salt content due to the yearly evaporation-rain dilution cycle. These processes are also responsible for the saline stratification during steady meteorological conditions. The mineralogical characterisation of the bottom sediments shows the almost exclusive presence of neoformation minerals, mainly carbonates, formed in response to the pH gradient between spring- (pH ≈ 6) and lake-waters (pH ≈ 9). Finally, the CO2 partial pressures in the lake water slightly exceeding the atmospheric one, are due to the large amounts of CO2 brought to the lake through the bubbling free gas phase of the thermal springs. Nevertheless the high pH value of the lake water, its small volume and its periodical mixing prevent dangerous built up of this gas. [ABSTRACT FROM AUTHOR]