Karst hydrosystems represent one of the largest global drinking water resources, but they are extremely vulnerable to pollution. Climate change, high population density, intensive industrial, and ...agricultural activities are the principal causes of deterioration, both in terms of quality and quantity, of these resources. Samples from 172 natural karst springs were collected in the whole territory of Greece. To identify any geogenic contamination and/or anthropogenic pollution, analyses of their chemical compositions, in terms of major ions and trace elements, were performed and compared to the EU limits for drinking water. Based on chloride content, the collected karst springs were divided into two groups: low-chloride (< 100 mg L
) and high-chloride content (> 100 mg L
). An additional group of springs with calcium-sulfate composition was recognised. Nitrate concentrations were always below the EU limit (50 mg L
), although some springs presented elevated concentrations. High contents in terms of trace elements, such as B, Sr, As, and Pb, sometimes exceeding the limits, were rarely found. The Greek karst waters can still be considered a good quality resource both for human consumption and for agriculture. The main issues derive from seawater intrusion in the aquifers along the coasts. Moreover, the main anthropogenic pollutant is nitrate, found in higher concentrations mostly in the same coastal areas where human activities are concentrated. Finally, high levels of potentially harmful trace elements (e.g. As, Se) are very limited and of natural origin (geothermal activity, ore deposits, etc.).
We report on the results of an extensive geochemical survey of fluids released in the Vardar zone (central‐western Serbia), a mega‐suture zone at the boundary between Eurasia and Africa plates. ...Thirty‐one bubbling gas samples are investigated for their chemical and isotopic compositions (He, C, Ar) and cluster into three distinct groups (CO2‐dominated, N2‐dominated, and CH4‐dominated) based on the dominant gas species. The measured He isotope ratios range from 0.08 to 1.19 Ra (where Ra is the atmospheric ratio), and reveal for the first time the presence of a minor (<20%) but detectable regional mantle‐derived component in Serbia. δ13C values range from −20.2‰ to −0.1‰ (versus PDB), with the more negative compositions observed in N2‐dominated samples. The carbon‐helium relationship indicates that these negative δ13C compositions could be due to isotopic fractionation processes during CO2 dissolution into groundwater. In contrast, CO2‐rich samples reflect mixing between crustal and mantle‐derived CO2. Our estimated mantle‐derived He flux (9.0 × 109 atoms m−2 s−1) is up to 2 orders of magnitude higher than the typical fluxes in stable continental areas, suggesting a structural/tectonic setting favoring the migration of deep‐mantle fluids through the crust.
Key Points
Chemical and isotopic composition of natural gas manifestations along the Serbian Vardar zone are controlled by mixing processes and fraction during water‐gas‐rock interactions in shallow crustal layers
Mantle‐derived He flux of 2 orders of magnitude higher than normally found in stable continental areas are estimated
Mantle volatiles and heat are sourced directly from the mantle supporting the asthenosphere up‐rise and delamination processes at the mantle‐crust boundary recognized in the studied area
Duvalo “volcano” is a site of anomalous geogenic degassing close to Ohrid (North Macedonia) not related to volcanic activity, despite its name. CO2 flux measurements made with the accumulation ...chamber (321 sites over ∼50,000 m2) showed fluxes up to nearly 60,000 g m−2 d−1, sustaining a total output of ∼67 t d−1. Soil gas samples were taken at 50 cm depth from sites with high CO2 fluxes and analyzed for their chemical and isotope composition. The gas is mainly composed by CO2 (>90%) with significant concentrations of H2S (up to 0.55%) and CH4 (up to 0.32%). The isotope compositions of He (R/RA 0.10) and of CO2 (δ13C ∼ 0‰) exclude significant mantle contribution, while δ13C‐CH4 (∼−35‰) and δ2H‐CH4 (∼−170‰) suggest a thermogenic origin for CH4. The area is characterized by intense seismic activity and Duvalo corresponds to an active tectonic structure bordering the Ohrid graben. The production of H2S within the stratigraphic sequence may be explained by thermochemical reduction of sulfate. The uprising H2S is partially oxidized to sulfuric acid that, reacting with carbonate rocks, releases CO2. The tectonic structure of the area favors fluid circulation, sustaining H2S production and oxidation, CO2 production and allowing the escape of the gases to the atmosphere. In the end, Duvalo represents a tectonic‐related CO2 degassing area whose gases originate mostly, if not exclusively, in the shallowest part of the crust (<10 km). This finding highlights that even systems with trivial mantle contribution may sustain intense CO2 degassing (>1,000 t km−2 d−1).
Plain Language Summary
The carbon cycle is an important piece of the puzzle of the present climate change. While anthropogenic sources of atmospheric carbon are reasonably constrained, geological sources are much less. Among the latter, carbon release to the atmosphere in seismically active areas, though known from decades, is less studied. Here we estimate the total emission of carbon dioxide from Duvalo, an area near Ohrid (North Macedonia). The obtained value (67 metric tons per day) is comparable with some active volcanic areas in the region. Although local inhabitants call this area Duvalo volcano, no recent volcanic activity is recognized here. The composition of the gas released by this system seems also to rule out geothermal activity or deep contributions from the Earth's mantle. This study shows that natural degassing systems with relatively shallow crustal sources (few kilometers), may sustain intense gas emissions from the soil.
Key Points
The total CO2 output from Duvalo “volcano” has been estimated for the first time
Gas compositions rule out significant mantle contributions or recent volcanic activity while geothermal activity is improbable
An active fault system favors indirect gas production and upflow to the Earth's surface
Samples of efflorescences and encrustations of hydrothermal origin were collected at Sousaki (Greece) and analysed for their mineralogical (XRD) and chemical composition. Solutions obtained both from ...mineralization with HNO3 and from leaching with deionised water were analysed for major (ICP-OES), minor and trace metals (ICP-MS) and sulfate contents (IC). Results evidence the dependence of the chemical and mineralogical composition on micro-environmental conditions i.e. humidity, oxygen-rich or -poor environment, exposed or sheltered from meteoric agents. In fact, the presence of highly soluble sulfate minerals with elevated contents of many metals (e.g. Mg, Al, Fe, Mn, Cr, Ni, etc.) further underscores the important influence of hydrothermal activity on elements' mobility, whilst the sometimes very high concentrations in toxic elements like Al, Cr, Ni suggest also possible environmental impacts.
•The ultramafic rock composition of the area is reflected in the chemistry of the efflorescences and incrustations.•Fumarolic alteration products temporarily stores high quantities of highly soluble elements.•Flushes after dry periods may transport high levels of harmful toxic contaminants.
Nisyros Island (Greece) is an active volcano hosting a high-enthalpy geothermal system. During June 2013, an extensive survey on Hg concentrations in different matrices (fumarolic fluids, atmosphere, ...soils, and plants) was carried out at the Lakki Plain, an intracaldera area affected by widespread soil and fumarolic degassing. Concentrations of gaseous elemental mercury (GEM), together with H2S and CO2, were simultaneously measured in both the fumarolic emissions and the atmosphere around them. At the same time, 130 samples of top soils and 31 samples of plants (Cistus creticus and salvifolius and Erica arborea and manipuliflora) were collected for Hg analysis. Mercury concentrations in fumarolic gases ranged from 10,500 to 46,300 ng/m3, while Hg concentrations in the air ranged from high background values in the Lakki Plain caldera (10-36 ng/m3) up to 7100 ng/m3 in the fumarolic areas. Outside the caldera, the concentrations were relatively low (2-5 ng/m3). The positive correlation with both CO2 and H2S in air highlighted the importance of hydrothermal gases as carrier for GEM. On the other hand, soil Hg concentrations (0.023-13.7 μg/g) showed no significant correlations with CO2 and H2S in the soil gases, whereas it showed a positive correlation with total S content and an inverse one with the soil pH, evidencing the complexity of the processes involving Hg carried by hydrothermal gases while passing through the soil. Total Hg concentrations in plant leaves (0.010-0.112 μg/g) had no direct correlation with soil Hg, with Cistus leaves containing higher values of Hg with respect to Erica. Even though GEM concentrations in the air within the caldera are sometimes orders of magnitude above the global background, they should not be considered dangerous to human health. Values exceeding the WHO guideline value of 1000 ng/m3 are very rare (<0.1%) and only found very close to the main fumarolic vents, where the access to tourists is prohibited.
Abstract
Duvalo “volcano” is a site of anomalous geogenic degassing close to Ohrid (North Macedonia) not related to volcanic activity, despite its name. CO
2
flux measurements made with the ...accumulation chamber (321 sites over ∼50,000 m
2
) showed fluxes up to nearly 60,000 g m
−2
d
−1
, sustaining a total output of ∼67 t d
−1
. Soil gas samples were taken at 50 cm depth from sites with high CO
2
fluxes and analyzed for their chemical and isotope composition. The gas is mainly composed by CO
2
(>90%) with significant concentrations of H
2
S (up to 0.55%) and CH
4
(up to 0.32%). The isotope compositions of He (
R
/
R
A
0.10) and of CO
2
(δ
13
C ∼ 0‰) exclude significant mantle contribution, while δ
13
C‐CH
4
(∼−35‰) and δ
2
H‐CH
4
(∼−170‰) suggest a thermogenic origin for CH
4
. The area is characterized by intense seismic activity and Duvalo corresponds to an active tectonic structure bordering the Ohrid graben. The production of H
2
S within the stratigraphic sequence may be explained by thermochemical reduction of sulfate. The uprising H
2
S is partially oxidized to sulfuric acid that, reacting with carbonate rocks, releases CO
2
. The tectonic structure of the area favors fluid circulation, sustaining H
2
S production and oxidation, CO
2
production and allowing the escape of the gases to the atmosphere. In the end, Duvalo represents a tectonic‐related CO
2
degassing area whose gases originate mostly, if not exclusively, in the shallowest part of the crust (<10 km). This finding highlights that even systems with trivial mantle contribution may sustain intense CO
2
degassing (>1,000 t km
−2
d
−1
).
Plain Language Summary
The carbon cycle is an important piece of the puzzle of the present climate change. While anthropogenic sources of atmospheric carbon are reasonably constrained, geological sources are much less. Among the latter, carbon release to the atmosphere in seismically active areas, though known from decades, is less studied. Here we estimate the total emission of carbon dioxide from Duvalo, an area near Ohrid (North Macedonia). The obtained value (67 metric tons per day) is comparable with some active volcanic areas in the region. Although local inhabitants call this area Duvalo volcano, no recent volcanic activity is recognized here. The composition of the gas released by this system seems also to rule out geothermal activity or deep contributions from the Earth's mantle. This study shows that natural degassing systems with relatively shallow crustal sources (few kilometers), may sustain intense gas emissions from the soil.
Key Points
The total CO
2
output from Duvalo “volcano” has been estimated for the first time
Gas compositions rule out significant mantle contributions or recent volcanic activity while geothermal activity is improbable
An active fault system favors indirect gas production and upflow to the Earth's surface
The present study is aimed at evaluating the possibility to predict bread specifications, for an industrial bread-making process, on the basis of the properties of flour employed in production. The ...flour delivered at the production plant, of which rheological and chemical properties were available, were analysed by means of Near Infrared Spectroscopy (NIRS). Based on the flour properties and NIR signals, multivariate control charts were constructed in order to detect flour batches leading to a bread with non-optimal behaviour. The results show that it is possible to distinguish flour batches leading to a product with a particularly negative performance, by modelling the properties commonly measured on flours and the acquired Near Infrared signals. In spite of the absence of monitoring of process variables, which could have offered a more sound basis for the interpretation, especially when false positives and negatives are detected, these results are of particular interest from the point of view of raw material evaluation in process monitoring. Also, the potentiality of Near Infrared Spectroscopy allows considering this approach for an on-line implementation in the control of incoming raw materials in this industrial process.
Nonlinear microwave response of different ceramic MgB2 samples has been investigated by the technique of second-harmonic emission. The second-harmonic signal has been investigated as a function of ...temperature, DC magnetic field and input microwave power. The attention has mainly been devoted to the response at low magnetic fields, where nonlinear processes arising from motion of Abrikosov fluxons are ineffective. The results show that different mechanisms are responsible for the nonlinear response in the different ranges of temperature. At low temperatures, the nonlinear response is due to processes involving weak links. At temperatures close to Tc, a further contribution to the harmonic emission is present; it can be ascribed to modulation of the order parameter by the microwave field and gives rise to a peak in the temperature dependence of the harmonic signal.
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