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: The paper describes a case of a natural emission of methane from soil in an urban development area, generating a significant risk for the local population and buildings, due to gas explosiveness and asphyxiation potential. The site is located on the south-western margin of the East-European Platform in eastern Romania, in a hydrocarbon-prone area crossed by the Pericarpathian lineament and regional faults. Molecular composition of gas and stable isotopic analyses of methane (CH4〉90%, δ to the power of 13 C1: -49.4‰, δD1: -173.4‰) indicate a dominant thermogenic origin, with significant amounts of C2-C5 alkanes (~5%), likely migrating through faults from a deep reservoir. Possible candidates are the Saucesti and Secuieni gas fields, located in the same petroleum system. Two surface geochemical surveys, based on closed-chamber flux measurements, were performed to assess the degassing intensity and the extent of the affected area. Methane fluxes from soil reach orders of 10 to the power of 4 mg m to the power of -2 day to the power of -1. Gas seepage mainly occurs in one zone 30 000 m2 wide, and it is likely controlled by channeling along a fault and gas accumulation in permeable sediments and shallow subsoil. The estimated total CH4 emission is about 40 t year to the power of -1 CH4, of which 8–9 t year to the power of -1 are naturally released from soil and 30–35 t year to the power of -1 are emitted from shallow boreholes. These wells have likely channeled the gas accumulated in shallow alluvial sediment but gas flux from soil is still high and mitigation measures are needed to reduce the risk for humans and buildings.

Description: Published

Description: 311-320

Description: 3.8. Geofisica per l'ambiente

Description: JCR Journal

Description: reserved

Description: The Chimaera gas seep, near Antalya (SW Turkey), has been continuously active for thousands of years and it is known to be the source of the first Olympic fire in the Hellenistic period. New and thorough molecular and isotopic analyses including methane (approximately 87% v/v; δ to the power of 13 C1 from -7.9‰ to -12.3‰; δ to the power of 13 D1 from -119‰ to -124‰), light alkanes (C2 + C3 + C4 + C5 = 0.5%; C6+: 0.07%; δ to the power of 13 C2 from -24.2‰ to -26.5‰; δ to the power of 13 C3 from -25.5‰ to -27‰), hydrogen (7.5–11%), carbon dioxide (0.01–0.07%; δ to the power of 13 CCO2: -15‰), helium (approximately 80 ppmv; R/Ra: 0.41) and nitrogen (2–4.9%; δ to the power of 15 N from -2‰ to -2.8‰) converge to indicate that the seep releases a mixture of organic thermogenic gas, related to mature type III kerogen occurring in Palaeozoic and Mesozoic organic-rich sedimentary rocks, and abiogenic gas produced by low-temperature serpentinization in the Tekirova ophiolitic unit. Methane is not related to mantle or magma degassing. The abiogenic fraction accounts for about half of the total gas released, which is estimated to be well beyond 50 ton year to the power of -1. Ophiolites and limestones are in contact along a tectonic dislocation leading to gas mixing and migration to the Earth’s surface. Chimaera represents the biggest emission of abiogenic methane on land discovered so far. Deep and pressurized gas accumulations are necessary to sustain the Chimaera gas flow for thousands of years and are likely to have been charged by an active inorganic source.

Description: Published

Description: 263-273

Description: 3.8. Geofisica per l'ambiente

Description: JCR Journal

Description: reserved

Description: The study area is a 130 km long fast spreading graben in Central Greece. Its complex geodynamical setting includes both the presence at depth of a subduction slab responsible for the recent (Quaternary) volcanic activity in the area and the western termination of a tectonic lineament of regional importance (the North-Anatolian fault). Its high geothermal gradient is evidenced by the presence of many thermal springs with temperatures from 19 to 82 C, issuing along the normal faults bordering the graben. In the period 2004-2012 about 50 gas and water samples have been collected and their chemical and isotopic analysis revealed a wide range of compositions. Going from west to east the gas composition changes from CH4- to CO2-dominated passing through mixed N2- CH4 and N2-CO2 compositions, while at the same time the He isotopic composition goes from typical crustal values (0.05 R/Ra) up to 0.87 R/Ra (corrected for air contamination), showing in the easternmost sites a small but significant mantle input. Isotopic composition of CH4-C indicates a thermogenic origin for the CH4-rich samples and hydrothermal origin for the remaining samples. Positive 15N values indicate a contribution of crustal derived nitrogen for the N2-rich samples. The 13C values of most the CO2-enriched samples show a mixed origin (mantle and marine carbonates). Also the chemical composition of the waters shows differences along the graben and two main groups can be separated. The first, represented by dilute waters (E.C. 〈 600 S/cm), is found in the westernmost sites characterised by the presence of CH4-rich and mixed N2-CH4 gases. The remaining waters display higher salinities (E.C. from 12 to 56 mS/cm) due to the mixing with a modified marine component. Only the water composition of easternmost sites in the Giggenbach’s cation triangular graph plots in the field of the partially equilibrated waters giving estimated temperatures at depth of 150-160 C.

Description: Published

Description: Vienna, Austria

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

Description: open

Description: Temperate forest soils are often considered as an important sink for atmospheric carbon (C), thereby buffering anthropogenic CO2 emissions. However, the effect of tree species composition on the magnitude of this sink is unclear. We resampled a tree species common garden experiment (six sites) a decade after initial sampling to evaluate whether forest floor (FF) and topsoil organic carbon (Corg) and total nitrogen (Nt) stocks changed in dependence of tree species (Norway spruce—Picea abies L., European beech—Fagus sylvatica L., pedunculate oak—Quercus robur L., sycamore maple—Acer pseudoplatanus L., European ash—Fraxinus excelsior L. and small‐leaved lime—Tilia cordata L.). Two groups of species were identified in terms of Corg and Nt distribution: (1) Spruce with high Corg and Nt stocks in the FF developed as a mor humus layer which tended to have smaller Corg and Nt stocks and a wider Corg:Nt ratio in the mineral topsoil, and (2) the broadleaved species, of which ash and maple distinguished most clearly from spruce by very low Corg and Nt stocks in the FF developed as mull humus layer, had greater Corg and Nt stocks, and narrow Corg:Nt ratios in the mineral topsoil. Over 11 years, FF Corg and Nt stocks increased most under spruce, while small decreases in bulk mineral soil (esp. in 0–15 cm and 0–30 cm depth) Corg and Nt stocks dominated irrespective of species. Observed decadal changes were associated with site‐related and tree species‐mediated soil properties in a way that hinted towards short‐term accumulation and mineralisation dynamics of easily available organic substances. We found no indication for Corg stabilisation. However, results indicated increasing Nt stabilisation with increasing biomass of burrowing earthworms, which were highest under ash, lime and maple and lowest under spruce. Highlights We studied if tree species differences in topsoil Corg and Nt stocks substantiate after a decade. The study is unique in its repeated soil sampling in a multisite common garden experiment. Forest floors increased under spruce, but topsoil stocks decreased irrespective of species. Changes were of short‐term nature. Nitrogen was most stable under arbuscular mycorrhizal species.

Description: Deutsche Forschungsgemeinschaff (DFG)

Description: Little research attention has been given to validating clusters obtained from the groundwater geochemistry of the waterworks' capture zone with a prevailing lake‐groundwater exchange. To address this knowledge gap, we proposed a new scheme whereby Gaussian finite mixture modeling (GFMM) and Spike‐and‐Slab Bayesian (SSB) algorithms were utilized to cluster the groundwater geochemistry while quantifying the probability of the resulting cluster membership against each other. We applied GFMM and SSB to 13 geochemical parameters collected during different sampling periods at 13 observation points across the Barnim Highlands plateau located in the northeast of Berlin, Germany; this included 10 observation wells, two lakes, and a gallery of drinking production wells. The cluster analysis of GFMM yielded nine clusters, either with a probability ≥0.8, while the SSB produced three hierarchical clusters with a probability of cluster membership varying from 〈0.2 to 〉0.8. The findings demonstrated that the clustering results of GFMM were in good agreement with the classification as per the principal component analysis and Piper diagram. By superimposing the parameter clustering onto the observation clustering, we could identify discrepancies that exist among the parameters of a certain cluster. This enables the identification of different factors that may control the geochemistry of a certain cluster, although parameters of that cluster share a strong similarity. The GFMM results have shown that from 2002, there has been active groundwater inflow from the lakes towards the capture zone. This means that it is necessary to adopt appropriate measures to reverse the inflow towards the lakes.

Description: Article impact statement: The probability of cluster membership quantified using an algorithm should be validated against another probabilistic‐based classifier.

Description: Federal Ministry of Education and Research http://dx.doi.org/10.13039/501100002347