ALBERT

Description: Methane plays an important role in the Earth’s atmospheric chemistry and radiative balance being the most important greenhouse gas after carbon dioxide. It has recently been established that geogenic gases contribute significantly to the natural CH4 flux to the atmosphere (Etiope et al., 2008). Volcanic/geothermal areas contribute to this flux, being the site of widespread diffuse degassing of endogenous gases (Chiodini et al., 2005). In such an environment soils are a source rather than a sink for atmospheric CH4 (Cardellini et al., 2003; Castaldi and Tedesco, 2005; D’Alessandro et al., 2009; 2011; 2013). Due to the fact that methane soil flux measurements are laboratory intensive, very few data have been collected until now in these areas. Preliminary studies (Etiope et al., 2007) estimated a total CH4 emission from European geothermal and volcanic systems in the range 4-16 kt a-1. This estimate was obtained indirectly from CO2 or H2O output data and from CO2/CH4 or H2O/CH4 values measured in the main gaseous manifestations. Such methods, although acceptable to obtain order-of-magnitude estimates, completely disregard possible methanotrophic activity within the soil. At the global scale, microbial oxidation in soils contributes for about 3-9% to the total removal of methane from the atmosphere. But the importance of methanotrophic organisms is even larger because they oxidise the greatest part of the methane produced in the soil and in the subsoil before its emission to the atmosphere. Environmental conditions in the soils of volcanic/geothermal areas (i.e. low oxygen content, high temperature and proton activity, etc.) have been considered inadequate for methanotrophic microrganisms. But recently, it has been demonstrated that methanotrophic consumption in soils occurs also under such harsh conditions due to the presence of acidophilic and thermophilic Verrucomicrobia. These organisms were found in Italy at the Solfatara di Pozzuoli (Pol et al., 2007), in New Zealand at Hell’s Gate (Dunfield et al., 2007) and in Kamchatka, Russia (Islam et al., 2008). Both the Italian and the Hellenic territories are geodynamically very active with many active volcanic and geothermal areas. Here we report on methane flux measurements made at Pantelleria (Italy) and at Sousaki and Nisyros (Greece). The total methane output of these three systems is about 10, 19 and 1 t a-1, respectively (D’Alessandro et al., 2009; 2011; 2013). The total emissions obtained from methane flux measurements are up to one order of magnitude lower than those obtained through indirect estimations. Clues of methanotrophic activity within the soils of these areas can be found in the CH4/CO2 ratio of the flux measurements which is always lower than that of the respective fumarolic manifestations, indicating a loss of CH4 during the travel of the gases towards earth’s surface. Furthermore laboratory methane consumption experiments made on soils collected at Pantelleria and Sousaki revealed, for most samples, CH4 consumption rates up to 9.50 µg h-1 and 0.52 µg h-1 respectively for each gram of soil (dry weight). Only few soil samples displayed no methane consumption activity. Finally, microbiological and molecular investigations allowed us to identify the presence of methanotrophic bacteria belonging to the Verrucomicrobia and to the Alpha- and Gamma-Proteobacteria in the soils of the geothermal area of Favara Grande at Pantelleria. While the presence of the former was not unexpected due to the fact that they include acidophilic and thermophilic organisms that were previously found in other geothermal environments, the latter are generally considered not adapted to live in harsh geothermal environments. Their presence in the soils of Pantelleria could be explained by the fact that these soils do not have extremely low pH values (〉5). Indeed thermotollerant methanotrophic Gamma-proteobacteria, have been previously found in the sediments of thermal springs in Kamchatka (Kizilova et al., 2012). Such species could find their niches in the shallowest part of the soils of Favara Grande were the temperatures are not so high and they thrive on the abundant upraising hydrothermal methane.

Description: Published

Description: Patras, Greece

Description: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Description: open

Description: Emissions of volcanoes and their depositions do have an immediate impact on their surrounding environment. In the present study, emissions and depositions of the active volcanic and geothermal system Vulcano (Italy) were investigated by active moss biomonitoring (Fig. 1) in the spring of 2012. Sphagnum moss bags were exposed for periods of 3 days, 3, 6 and 9 weeks. Soil and rainwater samples as well as meteorological data were also collected. After exposure, mosses were oven-dried, grinded and each sample was extracted either in deionized water or HNO3 (with H2O2). Extraction solutions were analyzed by ICP-MS for total concentrations of Li, Mg, Sr, Ba, Cr, Mn, S, Fe, Co, Cu, Zn, Mo, W, Tl, As, Sb, Bi, I, and Se. Soil and rain water samples were analyzed for the same trace elements. For elements such as As and Tl, deionized water extracts showed comparable concentrations to HNO3 extracts, indicating either the absence of particles or the presence of water-soluble particles. Elements such as Pb, Ba, Se and Sr were only dissolved to about 10 % or less in deionized water, indicating a significant share of water-insoluble particle formation. Distribution patterns of emissions and depositions over the whole island of Vulcano allowed classifying all investigated elements into four groups based on their origin (Fig. 2). Lithium was found ubiquitously on the island thus likely is of either marine or geogenic origin (group a in Fig. 2). The elements Mg, Fe, Sr, Mn, Zn, Co, and W were found predominantly on the crater where bare soil was present, and were grouped as “soilborne elements” (group b). These elements are characterized by deposition close to their source of origin. Elements with higher concentrations at the fumarolic field were grouped according to their transport characteristics. The elements I, Se, Tl, Bi, Sb, As, and S were considered as true volatiles (group c) being found also further away from the fumarolic field than Pb, Cr, Mo, and Ba which were interpreted to be predominantly emitted as particles (group d). Moss-bag biomonitoring proved to be an effective tool for the study of emission and deposition processes in active volcanic areas which also allows a classification of elements accumulated on the moss by their origin and distribution patterns.

Description: Published

Description: Patras, Greece

Description: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Description: open