ALBERT

Description: Methane is a major contributor to the greenhouse effect, its atmospheric concentration being more than doubled since the XIX century. Every year 22 Tg of methane are released to the atmosphere from several natural and anthropogenic sources. Natural sources include geothermal/volcanic areas but the estimation of the total methane emission from these areas is currently not well defined since the balance between emission through degassing and microbial oxidation within the soils is not well known. Microbial oxidation in soils contributes globally for about 3-9% to the removal of methane from the atmosphere and recent studies evidenced methanotrophic activity also in soils of volcanic/geothermal areas despite their harsh environmental conditions (high temperatures, low pH and high concentrations of H2S and NH3). Methanotrophs are a diverse group of bacteria that are able to metabolize methane as their only source of carbon and energy and are found within the Alpha and Gamma classes of Proteobacteria and within the phylum Verrucomicrobia. Our purpose was to study the interaction between methanotrophic communities and the methane emitted from the geothermally most active site of Pantelleria island (Italy), Favara Grande, whose total methane emission has been previously estimated in about 2.5 t/a. Laboratory incubation experiments with soil samples from Favara Grande showed methane consumption values of up to 9500 ng g-1 dry soil per hour while soils collected outside the geothermal area consume less than 6 ng g-1 h-1. The maximum consumption was measured in the shallowest part of the soil profile (1-3 cm) and high values (〉100 ng g-1 h-1) were maintained up to a depht of 15 cm. Furthermore, the highest consumption was measured at 37 C, and a still recognizable consumption (〉20 ng g-1 h-1) at 80 C, with positive correlation with the methane concentration in the incubation atmosphere. These results can be considered a clear evidence of the presence of methanotrophs that were investigated by culturing and culture-independent techniques. The diversity of proteobacterial methanotrophs was investigated by creating a clone library of the amplified methane mono-oxygenase encoding gene, pmoA. Clone sequencing indicates the presence of Gammaproteobacteria in the soils of Favara Grande. Enrichment cultures, on a mineral medium in a CH4-enriched atmosphere, led to the isolation of different strains that were identified as Methylocistis spp., which belong to the Alphaproteobacteria. The presence of Verrucomicrobia was detected by amplification of pmoA gene using newly designed primers. Soils from Favara Grande show therefore the largest spectrum of methanotrophic microorganisms until now detected in a geothermal environment. While the presence of Verrucomicrobia in geothermal soils was predictable due to their thermophilic and acidophilic character, the presence of both Alpha and Gamma proteobacteria was unexpected. Their presence is limited to the shallowest part of the soil were temperatures are lower and is probably favored by a soil pH that is not too low (pH 5) and their contribution to biological methane oxidation at Pantelleria is significant. Understanding the ecology of methanotrophy in geothermal sites will increase our knowledge of the role of soils in methane emissions in such environments.

Description: Published

Description: Vienna, Austria

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

Description: open

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: Volcanic and geothermal systems emit endogenous gases by widespread degassing from soils, including CH4, a greenhouse gas twenty-five times as potent as CO2. Recently, it has been demonstrated that volcanic or geothermal soils are not only a source of methane, but are also sites of methanotrophic activity. Methanotrophs are able to consume 10–40 Tg of CH4 a−1 and to trap more than 50% of the methane degassing through the soils. We report on methane microbial oxidation in the geothermally most active site of Pantelleria (Italy), Favara Grande, whose total methane emission was previously estimated at about 2.5Mga−1 (t a−1). Laboratory incubation experiments with three top-soil samples from Favara Grande indicated methane consumption values of up to 59.2 nmol g−1 soil d.w. h−1. One of the three sites, FAV2, where the highest oxidation rate was detected, was further analysed on a vertical soil profile, the maximum methane consumption was measured in the topsoil layer, and values greater than 6.23 nmol g−1 h−1 were still detected up to a depth of 13 cm. The highest consumption rate was measured at 37 C, but a still detectable consumption at 80 C (〉1.25 nmol g−1 h−1) was recorded. The soil total DNA extracted from the three samples was probed by Polymerase Chain Reaction (PCR) using standard proteobacterial primers and newly designed verrucomicrobial primers, targeting the unique methane monooxygenase gene pmoA; the presence of methanotrophs was detected at sites FAV2 and FAV3, but not at FAV1, where harsher chemical–physical conditions and negligible methane oxidation were detected. The pmoA gene libraries from the most active site (FAV2) pointed to a high diversity of gammaproteobacterial methanotrophs, distantly related to Methylocaldum-Metylococcus genera, and the presence of the newly discovered acido-thermophilic Verrucomicrobia methanotrophs. Alphaproteobacteria of the genus Methylocystis were isolated from enrichment cultures under a methane-containing atmosphere at 37 C. The isolates grow at a pH range of 3.5 to 8 and temperatures of 18–45 C, and consume 160 nmol of CH4 h−1 mL−1 of culture. Soils from Favara Grande showed the largest diversity of methanotrophic bacteria detected until now in a geothermal soil. While methanotrophic Verrucomicrobia are reported as dominating highly acidic geothermal sites, our results suggest that slightly acidic soils, in high-enthalpy geothermal systems, host a more diverse group of both culturable and uncultivated methanotrophs.

Description: Published

Description: 5865–5875

Description: 4V. Vulcani e ambiente

Description: JCR Journal

Description: open

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 is released to the atmosphere by a wide number of sources, both natural and anthropogenic, with the latter being twice as large as the former. It has recently been established that significant amounts of geological methane, produced within the Earth’s crust, are currently released naturally into the atmosphere. Active or recent volcanic-geothermal areas represent one of these sources of geological methane. Due to the fact that methane flux measurements are laboratory intensive, very few data have been collected until now and the contribution of this source has been often indirectly estimated. Both the Italian and the Hellenic territories are geodynamically very active with many volcanic and geothermal areas. Here we report on methane flux measurements made at Pantelleria (Italy), Sousaki and Nisyros (Greece). The total outputs of these three systems are about 10, 19 and 2 t a-1 respectively. These figures are up to one order of magnitude lower than those obtained through indirect estimations. At the global scale, microbial oxidation in soils contributes to the total removal of methane from the atmosphere. Environmental conditions in the soils of volcanic/geothermal areas (i.e. low pH, high temperature, 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 thermo-acidophilic Verrucomicrobia. Here we present the results of laboratory incubation experiments on soil samples collected at the main exhalative areas that highlighted methanotrophic activity also at Pantelleria and Sousaki. Soil metagenomic DNA was extracted from some of the Pantelleria samples and analysed using Temporal Temperature Gradient Electrophoresis (TTGE) of the amplified Bacterial 16S rRNA gene in order to evaluate the total bacterial diversity. Soil DNA amplification with primers targeting Proteobacterial and Verrucomicrobial methane monooxygenase genes (pmmo) revealed the presence of methanotrophs affiliated to both phyla up to a depth of 11 cm and a temperature of 80°C. The diversity of proteobacterial methanotrophs was investigated by creating a clone library of the amplified methane mono-oxygenase encoding gene, pmmoA. The clone sequences are close to those of uncultured type I methanotrophic proteobacteria. An attempt to isolate methanotrophs was carried out on soils from Pantelleria, sampled at different depths, by enrichment cultures on a mineral medium in a methane-enriched atmosphere. No isolates were obtained from enrichments carried out at 65°C while incubation at 37°C allowed to isolate a few methanothropic strains that were identified as Methylocystis spp.

Description: Published

Description: Kagoshima, Japan

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

Description: open

Description: Volatiles are transported from the deep crust or mantle to the surface in geodynamically active areas where seismic, volcanic and geothermal activity is present; the circulation of hydrothermal fluids in the crust is enhanced. In such areas, faults may act as preferential pathways for advective gas-carrying fluid transport. Towards the surface, pressure decrease allows the gases to escape from the fluids into soil gas and eventually into the atmosphere (King, 1986). The migration of carbon-bearing crustal and mantle fluids contributes to Earth’s carbon cycle (Berner & Kothavala 2001). However, till now, the mechanisms, magnitudes and time variations of carbon transfer from depth to the surface remain the least understood parts of the global carbon budget. Carbon dioxide and methane are the main contributors of the total amount of C-degassing from geological (volcanic and non-volcanic) sources. From the beginning of the last century, high attention has been paid to the reservoirs of CO2 and CH4 in the atmosphere because they represent the most dangerous species in terms of global warning. The increased amount of carbon dioxide and methane in the atmosphere has important implications for the energy balance and the chemical composition of the atmosphere. Mörner and Etiope (2002) calculated that 102-103 Mt of CO2 are presumably involved in the carbon cycle every year. This estimation though, is affected by high uncertainty as a number of sources and C-degassing environments that account for this high leakage were not taken into consideration. Greece belongs to the most geodynamically active regions of the world and as such, it has to be considered an area of intense geogenic degassing. Regarding carbon, the territory is characterized by the high hydrothermal and volcanic activity of the South Aegean Active Volcanic Arc (SAAVA), and by widespread geological seeps of buried carbon dioxide and methane. In the present work, we present more than 700 literature data of free gases spread along the whole Hellenic territory to get insight on geographic distribution and composition of the released fluids. Moreover, we review all the published studies on CO2 and/or CH4 output of high degassing areas of Greece that are mainly concentrated along the SAAVA in a first attempt to estimate the total geologic output of the nation. Helium isotope data propose that the highest mantle contribution (50 to 90%) is found along the SAAVA, whereas the lowest in continental Greece (0-20%), with the atmospheric contribution being mostly negligible. Based on the geographical distribution of the gases, it is evident that the R/RA ratios and CO2 concentrations increase in areas characterized by: i) thin crust; ii) elevated heat flow values; iii) recent (Pleistocene-Quaternary) volcanic activity; and iv) deep routed extensional or transtensional regional faults. The highest values are therefore found along the SAAVA and the lowest in the western part of Greece where CH4 emission is prevailing. Furthermore, it was noticed that the majority of the samples present a prevailing limestone C component, whilst only few samples have a prevailing mantle C component (Sano and Marty, 1995). It seems barely possible though to distinguish CO2 deriving from crustal and slab-related limestones. Additionally, due to the complex geodynamic history, the mantle C isotope composition could be affected by subduction-related metasomatism and, similarly to the nearby Italian area (Martelli et al., 2008), the C isotope composition could be more positive. In this case, the mantle contribution is probably underestimated. In terms of geogenic carbon degassing, the best studied and most exhaling area is the SAAVA, which releases 104,090 t/a of CO2 and 20.26 t/a of CH4. Continental Greece on the contrary, is much less studied but may release CO2 in the same order of magnitude in its eastern-central and northern part. The western and south-western parts of Greece are conversely the main area of methane and higher hydrocarbon degassing. Methane output of Greece is much less constrained but the presence on its territory of one of the biggest thermogenic gas seepages of Europe releasing about 200 t/a of CH4 to the atmosphere underscores its potentially high contribution. Approximately 114,310 t/a of CO2 and 221 t/a of CH4 are released from the whole Hellenic territory (Daskalopoulou et al., submitted). This estimation though, should be considered minimum as there are processes and sources that have not been taken into consideration yet. More specifically, in the submarine manifestations found at greater depths, gases cannot reach the sea surface due to the dissolution process that takes place along the water column; this is especially true for CO2 that is more soluble in water respect to other gases (eg. Milos - Dando et al., 1995; Kolumbo - Rizzo et al., 2016 etc). Moreover, the geological and geodynamic regime can contribute in the formation of CO2 reservoirs. This is the case of Florina Basin (Pearce et al., 2004) where more than one CO2 reservoirs were created, with one of them being exploited by the company Air Liquide Greece. It is worth noting that this reservoir, found at a depth of approximately 300 m, produces 30,000 t/a of CO2 (Pearce et al., 2004). Moreover, in the same area, water is also used for water supply and irrigation purposes. This water though contains a great amount of dissolved CO2 great part of which is released to the atmosphere when the water is pumped to the surface. Another source that should be underscored is the quantification of geogenic CO2 dissolved in big karstic aquifers. Chiodini et al. (1999, 2000) demonstrated that the relatively high solubility of CO2 in water plays an important role in the quantification of carbon. This approach was proved for central Italy and it might be the case for continental Greece due to the similar geodynamic history. Finally, in ophiolitic sequences where serpentinization takes place, if and when the conditions are adequate (i.e. presence of effective catalysts – Etiope and Ionescu, 2015) an abiogenic origin for CH4 seems to be favored even at low temperatures. Ophiolitic sequences crop out widely in Greece along two N-S trending belts, whilst more hyperalkaline springs or dry seeps may be present. However, their flux in generally is very low and therefore their contribution to the total natural CH4 output has probably to be considered negligible.

Description: Published

Description: Athens, Greece

Description: 6A. Geochimica per l'ambiente e geologia medica

Description: Shallow submarine gas vents in Levante Bay, Vulcano Island (Italy), emit around 3.6t CO2 per day providing a natural laboratory for the study of biogeochemical processes related to seabed CO2 leaks and ocean acidification. The main physico-chemical parameters (T, pH and Eh) were measured at more than 70 stations with 40 seawater samples were collected for chemical analyses. The main gas vent area had high concentrations of dissolved hydrothermal gases, low pH and negative redox values all of which returned to normal seawater values at distances of about 400 m from the main vents. Much of the bay around the vents is corrosive to calcium carbonate; the north shore has a gradient in seawater carbonate chemistry that is well suited to studies of the effects of long-term increases in CO2 levels. This shoreline lacks toxic compounds (such as H2S) and has a gradient in carbonate saturation states.

Description: Published

Description: 485–494

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

Description: JCR Journal

Description: restricted

Description: In a volcanic area, the composition of air is influenced by the interaction between fluids generated from many different environments (magmatic, hydrothermal, meteoric, and marine). Any physical and chemical variation in one of these subsystems is able to modify the outgassing dynamic. The increase of natural gas hazard, related to the presence of unhealthy components in air, may depend on temporary changes both in the pressure and chemical gradients that generate transient fluxes of gases and can have many different causes. Sometimes, the content of unhealthy gases approaches unexpected limits, without clear warning. In this case, an altered composition of the air can be only revealed after accurate sampling procedures and laboratory analysis. The investigations presented here are a starting point to response to the demand for a new monitoring program in the touristic area of Baia di Levante at Vulcano Island (Aeolian archipelago, Italy). Three multiparametric geochemical surveys were carried in the touristic area of Baia di Levante at Vulcano Island (Aeolian archipelago, Italy) in 2011, 2014, and 2015. Carbon dioxide (CO2) and hydrogen sulfide (H2S) are the main undesired components, usually present at the local scale. Anomalous CO2 and H2S outputs from soil and submarine bubbling vents were identified; the thermal anomaly of the ground was mapped; atmospheric concentrations of CO2 and H2S were measured in the air 30 cm above the ground surface. Atmospheric concentrations above the suggested limits for the wellbeing of human health were retrieved in open areas where tourists stay and where CO2 can accumulate under absence of wind.

Description: INGV-DPCN (Italian National Institute of Geophysics and Volcanology-Italian National Department for Civil Protection) volcanic surveillance program of Vulcano Island Ob-Fu 02.5.

Description: Published

Description: 478

Description: 6A. Geochimica per l'ambiente e geologia medica

Description: JCR Journal