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: Pantelleria is an active volcanic complex, at present in quiescent status, hosting a high enthalpy geothermal system. Explorative geothermal wells tapped exploitable water-dominated reservoirs at 600-800 m depth with maximum measured temperatures of 250°C. Five field campaigns for soil gas measurements were made in the period from July 2005 to October 2006. CO2 flux was measured with the accumulation chamber method at 807 sites, CO2 concentration and Rn activity in soil atmosphere were measured at 50 cm depth at 728 and 358 sites, respectively. The first campaign covered the whole island (about 83 km2) with an approximately sample density of 3.5 points per km2 for CO2 (flux and concentration) measurements and of 1.6 points per km2 for Rn measurements. The distribution of the sampling points was as far as possible evenly distributed. Only few limited areas resulted uncovered due to accessibility problems (inhabited areas, airport, steep or rough topography). In the following four surveys nine areas were studied with greater detail with sample densities of up to 100 points per km2. Flux measurements for the whole surveys gave values in the range 〈 0.1 - 4700 gCO2 m-2 day-1 (Fig. 1). Organic contribution could not be distinguished with statistical methods and in the present study was considered negligible above 30 g m-2 day-1. The sites displaying flux values above this threshold, representing about 32% of the total population, are almost all located within the 50 ka old caldera. The highest values correspond to the areas of Favara Grande and of the lake Specchio di Venere (Fig. 1), which have long been recognized as sites of anomalous degassing with the presence of active fumarolic vents with temperatures of about 100 °C in the former and thermal springs with abundant bubbling gases and a mofette in the latter. A new anomalous degassing area with very high output values has been identified on the southern flank of Mt. Grande (MGS in Fig. 1). In this area the vegetation cover strongly contrasts with that of the neighboring areas, consisting of scrubby low growing plants, mosses and bare land. Indeed, high CO2 flux values are always measured as long as such vegetation cover is found, abruptly decreasing when higher growing plants are present. The contrast is particularly evident in springtime and can be used as a good marker to individuate anomalous degassing areas. Further areas were studied in detail being sites of fumarolic manifestations. All of them are also sites of anomalous CO2 fluxes although of limited areal extension. The area of the last subaerial volcanic activity (Mursia) was also studied but the measurements were all far below the anomaly threshold. The total CO2 output of the anomalous degassing areas was estimated through geostatistical methods considering only values above the anomaly threshold. Results evidence that most of the output (87%) of the island is due to 3 of the anomalous degassing areas (Lake, MGS and Favare), the first of which accounts for more than 50%. Summing up the contribution of all anomalous areas we obtained a total output of about 0.3 kg s-1 (26 t day-1) over an area of about 0.58 km2. Concentrations of CO2 ranged from 0.039 (atmospheric value) up to 95 % (Fig. 1). The distribution of the values on a probability plot evidenced two statistically distinct populations with an inflection point at about 0.8 %. The values below the threshold (65 % of the population) can be considered as derived from organic activity while those above of magmatic/geothermal origin. The spatial distribution of the sites with anomalous concentrations closely resembles those of anomalous CO2 fluxes. Radon222 activity in the soil ranged from 〈 0.1 to 〉1000 kBq m-3 (Fig. 1). The distribution of the values on a probability plot evidenced three statistically distinct populations with inflection points at 40 and 400 kBq m-3. The lower population (74% of the entire population) probably corresponds to close to equilibrium values in soils with different contents of parent isotopes of the 238U decay chain and could be considered as background population. The values of the other two populations have to be considered anomalous and their high activity values have to be related either to sustained fluxes of a carrier gas (CO2) or/and to enhanced release from the soil due to fumarolic alteration. These anomalous values generally correspond to elevated CO2 flux values and are found close to active or fossil fumarolic areas. The close relationship with fumarolic alteration is confirmed by the contrasting behavior of two of the areas displaying the highest CO2 flux values, namely Favare and Lake. In the former area the high soil temperatures, testifying for anomalous fluxes of hydrothermal fluids, are reflected in a high percentage of anomalous values of soil 222Rn activity. On the contrary at the lake area, where the highest CO2 fluxes are measured, soil temperatures are much lower and consequently also soil 222Rn activity. The only high soil 222Rn activity values are measured along the southern shores of the lake where seeps of thermal water with about 60 °C are present. At Mursia, where recent basaltic lavas and scorias crop out, soil 222Rn activity is particularly low due to the low content of parent radioactive elements in these rocks. Finally, the present study evidenced a few areas were the gas hazard due to both CO2 and radon is elevated with either acute or chronic health issues for humans. These are the western shores of the lake and the village of Rekale the only inhabited area close to an anomalous degassing area.

Description: Published

Description: Patras, Greece

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

Description: open

Description: Volcanic emissions are considered one of the major natural sources of several trace metals (e.g. As, Cd, Cu, Pb, and Zn) to the atmosphere [Nriagu, 1989], and the geochemical cycles of these elements have to be considered strongly influenced by volcanic input. However, the accurate estimation of the global volcanic emissions of volatile trace metals into the atmosphere is still affected by a high level of uncertainty. The latter depends on the large variability in the emission of the different volcanoes, and on their changing stage of activity. Moreover, only few of the potential sources in the world have been directly measured [Hinkley et al. 1999]. Atmospheric deposition processes (wet and dry) are the pathways through which volcanic emissions return to the ground (soils, plants, aquifers), resulting in both harmful and beneficial effects [Baxter et al. 1982; Aiuppa et al. 2000; Brusca et al. 2001; Delmelle, 2003; Bellomo et al. 2007; Martin et al. 2009; Floor et al. 2011; Calabrese et al. 2011]. In the first part of this study we present the results of a literature review on trace metals emissions from active volcanoes around the world. In the second part, we present new data on the fluxes of the trace metals from Etna (Italy) and four active volcanoes in the world: Turrialba (Costarica), Nyiragongo (DRC), Mutnovsky and Gorely (Kamchatka). We found 27 publications (the first dating back to the 70’s), 13 of which relate to the Etna and the other include some of the world’s most active volcanoes: Mt. St. Helens, Erebus, Merapi, White Island, Kilauea, Popocatepetl, Galeras, Indonesian arc, Satasuma and Masaya. The review shows that currently there are very few data available, and that the most studied volcano is Mt. Etna. Using these data, we defined a range of fluxes for As, Ba, Bi, Cd, Cu, Fe, Mn, Pb, Se, V and Zn (Figure 1). To obtain new data we sampled particulate filters at the five above mentioned volcanoes. Filters were mineralized (acid digestion) and analyzed by ICP-MS. Sulphur to trace element ratios were related to sulphur fluxes to indirectly estimate trace elements fluxes. Etna confirms to be one of the greatest point sources in the world. The Nyiragongo results to be also a significant source of metals to the atmosphere, especially considering its persistent state of degassing from the lava lake. Also Turrialba and Gorely have high emission rates of trace metals considering the global range. Only Mutnovsky Volcano show values which are sometimes lower than the range obtained from the review, consistent with the fact that it is mainly a fumarolic field. This work highlights the need to expand the current dataset including many other active volcanoes for a better constraint of global trace metal fluxes from active volcanoes.

Description: Published

Description: Nicolosi (Catania)

Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive

Description: open

Description: Volcanic emissions represent one of the most relevant natural sources of trace elements to the troposphere, both during and between eruptions. Due to their potential toxicity they may have important environmental impacts from the local to the global scale. Mount Etna, the largest European volcano and one of the most active volcano in the world, covers an area of about 1250 km2 and reaches an altitude of about 3340 m. It has been persistently active during historical time, with frequent paroxysmal episodes separated by passive degassing periods. Atmospheric precipitation was collected approximately every two weeks, from April 2006 to December 2007, using a network of five rain gauges, located at various altitudes on the upper flanks around the summit craters of Etna Volcano. The collected samples were analysed for major (Ca, Mg, K, Na, F, SO4, Cl, NO3) and a large suite of trace elements (Ag, Al, As, Au, B, Ba, Be, Bi, Cd, Co, Cr, Cs, Cu, Fe, Hg, La, Li, Mn, Mo, Ni, Pb, Rb, Si, Sb, Sc, Se, Sr, Th, Ti, Tl, U, V, Zn) by using different techniques (IC, SPEC, ICP-MS and CV-AFS). The monitoring of atmospheric deposition gave the opportunity to occasionally sample volcanic fresh ashes emitted by the volcano during the paroxysmal events. This was possible because the network of five rain gauges were equipped with a filter-system to block the coarse material. In this way, more than twenty events of ashfall were collected. Unfortunately, only half of these samples were suitable for a complete chemical analysis, because of the small amount of sample. In order to obtain elemental chemical composition of ashes, powdered samples were analysed by a combination of methods, including X-ray Fluorescence Spectroscopy (XRF), total digestion followed by Inductively Coupled Plasma Emission Mass Spectrometry (ICP-MS), Instrumental Neutron Activation Analysis (INAA), and infrared detection (IR). The chemistry of rainwater reveals that most of the investigated elements have higher concentrations close to the emission vent of the volcano, confirming the prevailing volcanic contribution. Rainwater composition clearly reflects the volcanic plume input. Ash-normalised rainwater composition indicates a contrasting behaviour between volatile elements, which are highly-enriched in rainwater, and refractory elements, which have low rainwater/ash concentration ratios. The degree of interaction between collected ash and rainwater was variable, depending on several factors: (i) the length of the period in which tephra was present in the sampler (the ash fall may have occurred any day from the first to the last day of the rain collecting period); (ii) the amount of rainwater fallen on the collectors after the ash-fall event, and its acidity; (iii) the granulometry of the ash samples that was widely variable (from few centimetres to micrometric particles) increasing the interaction with decreasing dimensions of the grains; (iv) the distance of collector with respect to the craters. In order to investigate the role of volcanic ash on the evolution of the rainwater chemistry, absolute concentrations of rain and ash were plotted in binary plot diagrams (Figure 1). Each diagram corresponds to a single event, and pH and TDS of the solution collected is reported. The diagonal bars in the diagrams represent the rain/ash ratios (1:1 and 1:10000). The results confirm that sulphate and halide salt aerosols are adsorbed onto ash particles, and their rate of dissolution in rainwater depends on solubility. Moreover, rapid chemical weathering of the silicate glass by volcanic acid (SO2, HCl and HF) can also explain the enrichment of several refractory elements (Na, K, Ca, Mg, Si, Al, Fe, Ti, Sc). Our observations highlight how explosive activity can increase enormously the deposition rate of several chemical elements, up to several km away from the emission vents.

Description: Published

Description: Nicolosi (Catania)

Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive

Description: open