Soil Gas Research Articles

Measurement of radon concentration in soil gas and radon exhalation rate from soil samples along and across the Main Central Thrust of Garhwal Himalaya, India.

The present study focuses on measuring radon concentrations in soil gas at various depths, radon exhalation rate (surface and mass) from soil samples, and gamma dose rate along and across the Main Central Thrust of Garhwal Himalaya, India. Radon concentration in soil gas, surface, and mass exhalation rates was measured using a portable SMART radon monitor (RnDuo). Furthermore, the gamma dose rate was measured using a pocket radiation monitor. The soil gas radon concentration varied from 15 ± 4 to 579 ± 82Bqm-3 at a depth of 25cm, 10 ± 2 to 533 ± 75Bqm-3 at a depth of 30cm, and 9 ± 1 to 680 ± 95Bqm-3 at a depth of 35cm. The surface and mass exhalation rates were found 3 ± 0.7 to 98 ± 3Bqm-2h-1 (with AM ± SD = 36 ± 28Bqm-2h-1) and 1 ± 0.2 to 95 ± 2mBqkg-1h-1 (with AM ± SD = 30 ± 22mBqkg-1h-1), respectively. The gamma dose rate for the present study area varies from 0.11 ± 0.05 to 0.28 ± 0.05µSvh-1 with a mean value of 0.17 ± 0.05µSvh-1. The correlation analysis between the exhalation rates (mass and surface) and radon concentration of soil gas at various depths was carried out in the current study.

Indoor Air Quality in Homes

Indoor air pollution is an international health concern because people spend a majority of their time indoors. Children are at a higher risk of health problems from pollutant exposure, especially because air in the child breathing zone is more polluted than it is in the adult breathing zone. Pollutants of concern include biological contaminants, combustion pollutants, volatile organic compounds, and radon and other soil gases. Humans have a history with lead and asbestos that goes back thousands of years to the ancient Romans and Egyptians. These two pollutants are still problems in older homes and apartments. All of these toxicants can be minimized or abated. Awareness of these issues is a critical first step in improving air quality in places where people live. These factors are of particular concern when examining indoor air quality because most people in the U.S. spend about 90% of their time indoors with some groups such as infants, the elderly, and infirm persons spending nearly all of their time indoors [1]. A number of conditions contribute to typically higher levels of indoor pollutants than corresponding levels outdoors [2]. The U.S. Environmental Protection Agency has reported that pollutant levels can be higher indoors than outdoors. By one estimate, pollutant levels can be 10 to 100 times higher inside than outside [3].

Soil geochemistry of hydrogen and other gases along the San Andreas fault

Natural hydrogen has generated great interest as a potential clean and renewable energy source. To understand the occurrence of natural hydrogen, 103 1-m deep soil gas samples were acquired near the San Andreas Fault at Jasper Ridge and Portola Valley, California, USA. The gas samples were analyzed for hydrogen, helium, carbon dioxide, light hydrocarbons, and fixed gas concentrations. Statistical data analysis was carried out to group samples, reveal their spatial distribution, and understand possible sources of the gases.High concentrations of hydrogen up to 20.3 ppmv and 17.3 ppmv occur in Jasper Ridge and Portola Valley, respectively, ∼30–35 times greater than the atmospheric concentration. Most samples with high hydrogen concentrations fall on or near faults, suggesting an origin by serpentinization or geomechanical activation of catalytic sites in minerals, although a deep-seated primordial origin cannot be excluded. Elevated concentrations of carbon dioxide resulted from aerobic microbial degradation of organic matter and elevated concentrations of light hydrocarbons likely resulted from thermal cracking of organic matter.

Land inclination controls CO2 and N2O fluxes, but not CH4 uptake, in a temperate upland forest soil

Abstract. Inclination and spatial variability in soil and litter properties influence soil greenhouse gas (GHG) fluxes and thus ongoing climate change, but their relationship in forest ecosystems is poorly understood. To elucidate this, we explored the effect of inclination, distance from a stream, soil moisture, soil temperature, and other soil and litter properties on soil–atmosphere fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) with automated static chambers in a temperate upland forest in eastern Austria. We hypothesised that soil CO2 emissions and CH4 uptake are higher in sloped locations with lower soil moisture content, whereas soil N2O emissions are higher in flat, wetter locations. During the measurement period, soil CO2 emissions were significantly higher on flat locations (p<0.05), and increased with increasing soil temperature (p<0.001) and decreasing soil moisture (p<0.001). The soil acted as a CH4 sink, and CH4 uptake was not significantly related to inclination. However, CH4 uptake was significantly higher at locations furthest away from the stream as compared to at the stream (p<0.001) and positively related to litter weight and soil C content (p<0.01). N2O fluxes were significantly higher on flat locations and further away from the stream (p<0.05) and increased with increasing soil moisture (p<0.001), soil temperature (p<0.001), and litter depth (p<0.05). Overall, this study underlines the importance of inclination and the resulting soil and litter properties in predicting GHG fluxes from forest soils and therefore their potential source-sink balance.

Advances in Hydrocarbon Speciation for Soil Gas Analysis

In the field of contaminated site remediation, risk analyses can be carried out by the use of appropriate mathematical models, based on simplified hypotheses of real sites. The possibility to have shared and accurate analytical methods is an important challenge for both routine laboratories and supervisory institutions. Although official methods (e.g., APH2009) are already available, they are lacking in some aspects, such as applicability to all the different sampling and analysis media and ease of use in routine analysis. Here, we report our recent advances in the implementation of an empirical method for hydrocarbon speciation in an air matrix, previously developed by the authors and published in 2015. The validation results led to a coefficient of variation (CV%) between 10–15% for the hydrocarbon fractions investigated (C5-C8 aliphatic, C9-C12 aliphatic, C9-C10 aromatic and C11-C12 aromatic) and recovery of ≤20%, in agreement with the required characteristics for the analytical methods. Several real samples were analyzed by the proposed method and the results were compared to those obtained by the official approach. The comparison led to an average bias (that is, the difference between the results from the developed method and those from the conventional one) of about 10%, confirming that the innovative approach is robust, accurate and can be applied to all the analytical media used for air sampling, such as soil gas.

Mechanisms of the effects of the biochar application rate and time on farmland water, heat and gas environments during soil thawing in seasonally frozen soil areas: A two-year field trial

Biochar has shown great potential in improving the soil environment and alleviating greenhouse gas (GHG) emissions. However, the biochar effect in seasonally frozen soil areas remains unclear due to the complexity of the freezethaw cycle processes. To effectively regulate the soil waterheatgas environment, three treatments, a single high-dose application (BL), two low-dose applications (BS), and no biochar application (CK), were established in a two-year field experiment. The characteristics of soil GHG emissions under the different treatments and their response relationships to soil water, heat and air permeability were explored. The results indicated that the average water content under BL and BS treatments increased by 10.78 % and 7.05 %, respectively, relative to the CK treatment in 2021, while the BS treatment exhibited the best performance in 2022. The temperature regulation effect under the different treatments showed similar trends, with the average temperature under the BS treatment in 2022 was 0.62 °C and 1.38 °C higher, respectively, than that under the BL and CK treatments. The two-year cumulative CO2 emission flux under the BL and BS treatments was 9.36 % and 2.98 % higher, respectively, than that under the CK treatment. Biochar increased soil macropores (>75 µm) and promoted soil gas circulation. Resulting in increased pmoA and nosZ gene abundance and inhibited CH4 and N2O fluxes in soil. The two-year global warming potentials (GWPs) under the BL and BS treatments were 65.7 and 113.17 kg CO2 hm-2 lower, respectively, than that under the CK treatment. Overall, multiple low-dose biochar applications could comprise an efficient and sustainable application mode.

Using groundwater monitoring wells for rapid application of soil gas radon deficit technique to evaluate residual LNAPL

The application of the 222Radon (Rn) deficit technique using subsurface soil gas probes for the identification and quantification of light non-aqueous phase liquids (LNAPL) has provided positive outcomes in recent years. This study presents an alternative method for applying this technique in the headspace of groundwater monitoring wells. The developed protocol, designed for groundwater monitoring wells with a portion of their screen in the vadose zone, is based on the use of portable equipment that allows rapid measurement of the Rn soil gas activity in the vadose zone close to the water table (i.e., smear zone) where LNAPL is typically expected. The paper first describes the step-by-step procedure to be followed for the application of this method. Then, a preliminary assessment of the potential of the method was carried out at two Italian sites characterized by accidental gasoline and diesel spills into the subsurface from underground storage tanks. Although the number of tests conducted does not allow for definitive conclusions, the results obtained suggest that, from a qualitative point of view, Rn monitoring in the headspace of monitoring wells is a promising, fast, and minimally invasive screening method that could also potentially reduce the costs associated with field data acquisition. This method proves to be suitable for detecting the presence of LNAPL in both the mobile and residual phases with results consistent with the other lines of evidence available at the sites, such as groundwater and soil gas monitoring. Future efforts should be directed toward evaluating the accuracy of this method for a quantitative assessment of residual LNAPL saturations.

Exploring natural hydrogen hotspots: a review and soil-gas survey design for identifying seepage

Exploration for natural hydrogen seepages has grown rapidly, with surface seepages being seen as a primary indication of an underlying resource. While soil gas sampling has proven successful in detecting hydrogen in the soil, current understanding of hydrogen in the subsurface remains incomplete, with various potential sources of origin. This paper presents a selected review of published hydrogen hotspots around the world, examining their distribution with respect to two main features commonly associated with natural seepages: sub-circular depressions (SCD) and fault zones. Based on the findings, the paper proposes a conceptual soil-gas survey design for efficiently identifying potential hydrogen hotspots. The proposed scheme is tested on a SCD and a fault zone located in Western Australia. The study findings near the Perth Basin and the Yilgarn Craton highlight the presence of anthropogenic artifacts in hydrogen measurement, necessitating further investigation to constrain the possible sources of hydrogen generation. The study of the SCD in the Perth Basin supports the development of a statistical understanding of hydrogen distribution around surface features associated with hydrogen hotspots. Such a framework can guide soil-gas surveys and target areas with a higher likelihood of detecting natural hydrogen seepage. By addressing these points, prospective areas for natural hydrogen seepage can be better identified and evaluated, ultimately contributing to the development of hydrogen as a sustainable energy resource. Thematic collection: This article is part of the Hydrogen as a future energy source collection available at: https://www.lyellcollection.org/topic/collections/hydrogen

Soil respiration responses of moss and lichen biocoenoses to moderate and severe rain events after summer drought in a temperate early‐successional ecosystem

AbstractIt is commonly accepted that CO2 efflux increases with soil water content in aerated soils and that rewetting after periods of soil drying can result in respiration pulses. It has further been shown that soil pores may become water logged which can impede soil gas exchange. The present study aimed to quantify the carbon response of moss (Polytrichum piliferum) and lichen (Cladonia coniocraea) biocoenoses to different quantities of rain in an artificial catchment, which granted that the starting point of the development of both biocoenoses was the same. To address this aim, we conducted in situ soil moisture and soil respiration measurements, where soil respiration was hypothesised to emerge from a cryptogamic vegetation layer and from mineral soil beneath. We found that higher water‐holding capacity of the moss layer and higher accumulation of organic matter in the upper mineral soil under mosses result in higher amounts of water stored near the surface. As a consequence, evaporation of water as well as pulses of CO2 efflux after moderate rain following a period of drought were higher in the moss biocoenosis, where the upper mineral soil was of key importance. In contrast, the lichen biocoenosis facilitated penetration of rainwater into the deep soil. Superimposing rewetting pulses, near‐saturation of soil pores with water after severe rain resulted in gas exchange inhibition and diminished soil respiration until subsequent aeration in both biocoenoses.

Influence of soil-gas diffusivity on expansion of leaked underground natural gas plumes and application on simulation efforts

A proper understanding of subsurface gas migration patterns resulting from belowground natural gas (NG) infrastructure is essential for safe and efficient first responder operations and to improve leak repair actions. Subsurface migration of leaked gas occurs predominately by pressure-driven advection close to the leak. Far migration occurs by concentration-driven diffusion and eventually defines the plume’s edge. Therefore, proper formulation of the diffusion behavior in mathematical models of gas transport is critical to safety and response. This study evaluated six diffusivity parametric functions (DPFs) for an accurate representation of soil gas diffusivity through soils by comparing predicted and measured values for mineral, clay, and sand soils. DPFs were further tested by implementing them in a multiphase flow model previously developed for belowground NG transport. DPFs were also tested by comparing with field scale NG leakage experiments conducted in varying soil conditions (mineral soil, sand, and sand/clay) at controlled NG leak rates ranging from 5 to 21 slpm. Results showed that soil-type and structure-dependent DPFs performed better than soil-type and structure-independent DPFs in simulating the diffusive transport of NG. Further, results showed that DPF selection does not significantly influence NG migration simulations under dry soil conditions during the leak period. However, when the leak is terminated, simulation results followed the same trend of over- and under-predictions as of Dp/Do parameterization. Further, wet soil simulations show more than a 10% CH4 composition deviation and 2.5-day time differences among DPFs in reaching explosive limits. Unique to this work, the selection of a DPF can result in large differences in flux estimates in transport models, masking the effects of the gas behavior, especially in cases where gas diffusion to outer boundaries is of interest. The findings, therefore, support the idea that careful selection of DPFs based on soil-type, structure and moisture condition is essential to predict NG plume behavior during a leak event and after repair.

Detecting gas pipeline leaks in sandy soil with fiber-optic distributed acoustic sensing

Detecting pinhole leaks in long-haul buried gas pipelines is challenging due to weak leak signals and large spans. Fiber-optic distributed acoustic sensing (DAS) technology offers highly sensitive long-distance monitoring. This study evaluates DAS for detecting pinhole gas leaks in pipelines buried in sandy soil. Controlled experiments examined the effects of pipe-to-fiber distance, fiber position, leak direction, gas pressure, and leak diameter. Pressurized gas erodes the overlying soil, forming cavities and fissures that change soil morphology. Gas preferentially diffuses upward; an optical fiber above the pipe has the highest sensitivity regardless of leak direction and should be deployed above pipelines. Two mechanisms produce DAS-recorded leak vibration signals: dynamic soil straining and gas–fiber friction. Vibration energy from dynamic soil motion concentrates at 60–120 Hz while gas–fiber friction exhibits a broader spectral response. Increasing gas pressure or leak diameter increases detected vibration power but decreases peak frequency and proportion generated by soil strain, indicating a shift toward gas–fiber friction as the dominant mechanism. These results inform improved pinhole leak monitoring in buried gas pipelines using DAS technology.

Effect of Soil Volumetric Water Content on the CO2 Diffusion Coefficient

Purpose: The soil air diffusion coefficient (Ds) is particularly important for the study of soil gas diffusion movement, and there are still many uncertainties in the widely used methods; as such, a method was designed to in situ measure the soil gas diffusion coefficient. Methods: Four different soil media were selected and studied by means of a designed in situ measurement of soil gas diffusion coefficients, and these were compared and analyzed with the predictions of several commonly used prediction models. In addition, they were combined with gas transport models to validate the results of the empirical models that were obtained by the in situ measurements. Results: The results of the data indicate that increasing the volumetric soil moisture content decreases the soil gas diffusion coefficient, with changes in the soil gas diffusion coefficient for the small-grained quartz sand medium being similar to those predicted by the Buckingham model. The soil gas diffusion coefficients for the large-grained quartz sand were similar to the Millington and Quirk model predictions at low humidity; for increased humidity, it was instead similar to the Buckingham model predictions. The soil gas diffusion coefficients of the two active media were closer to those of the SWLR model with high Cm. In addition, the R2 of the measured data was verified, by empirical modeling, to be greater than 0.54, and inversion experiments were conducted to verify that the results were consistent with those of the SWLR model. Conclusion: When measuring relative diffusion coefficients in the field, we recommend the in situ measurement method, which is more reflective of the actual situation in natural environments and provides more accurate data support for soil carbon flux studies.

Interaction of Filth Flies and Epigeal Arthropods with Soil Nitrogen and Gas Emissions in Grazing Systems under a Legacy of Low Fertilization

During the summers of 2021 and 2022, we conducted a study in four Georgia Piedmont pastures to assess the effect of the presence of filth flies and epigeal arthropods on carbon and nitrogen emissions and soil nitrogen retention from lax rotational grazing systems under a legacy of low fertilization. Carbon dioxide (CO2), nitrous oxide (N2O), and ammonia (NH3) emissions were measured from dung on days 0, 4, 8, and 15 following depositions. Soil and manure samples were collected on days 0 and 16 and analyzed for ammonium (NH4+), nitrate (NO3−), plant-available nitrogen (PAN), and potentially mineralizable nitrogen (PMN). Manure samples were analyzed for total Kjeldahl nitrogen (TKN). The numbers of filth flies ovipositing and emerging from manure, fire ants, and epigeal arthropods around the manure were determined. Our results indicated that more than 12 ovipositing filth flies per manure pat can reduce PMN by up to 14.7 kg of nitrogen per hectare, while an increase in the biodiversity and abundance of predators may help to increase PAN and PMN in grazing systems, as well as decrease the number of emerging filth flies.

Natural hydrogen seeps or salt lakes: how to make a difference? Grass Patch example, Western Australia

Natural hydrogen exploration is picking up around the world while the geogenic hydrogen system is still a Frontier science. Natural hydrogen seepage can occur in the form of a sub-circular surface feature named by some authors “fairy circles.” Numerous hydrogen seep-alike surface features are visible from the sky in Australia but can be difficult to distinguish from the many salt lakes. In this study, we combined literature review, remote sensing, field and lab measurements (soil gas sampling, X-Ray diffraction, salinity) to uncover a potential hydrogen system and its differences with the salt lakes in the Grass Patch area in Western Australia. The local geology shows a good potential to generate hydrogen. Study of the surface geology and Digital Elevation Model showed that salt lakes are static old features influenced by the soil composition and long-term climatic trend whereas potential hydrogen seeps have recently appeared. This study soil-gas sampling method includes a monitoring procedure compatible with time series measurements via a portable gas analyser, getting rid of artificially produced hydrogen. Low hydrogen values (<30 ppm) have been measured. Those measurements are lower than measurements published along potential hydrogen seeps in Australia. Vegetation indexes are also less constructed than explored fairy circles in Namibia. Salinity and mineralogical results did not indicate any trend with the hydrogen but are coherent with what is found in salt lakes. A microbial system could be the source of the hydrogen but would also be linked to the soil behaviour, climatic parameters, and agricultural practices. This study underlines the need to monitor surface features over few weeks to better understand the evolution of the gas mix seeping above a structure and determine if the periodicity and variability of the leakage can be correlated with bacterial activity or a geogenic hydrogen source.

Co-application of biochar and organic amendments on soil greenhouse gas emissions: A meta-analysis

Biochar has been shown to reduce soil greenhouse gas (GHG) and increase nutrient retention in soil; however, the interaction between biochar and organic amendments on GHG emissions remain largely unclear. In this study, we collected 162 two-factor observations to explore how biochar and organic amendments jointly affect soil GHG emissions. Our results showed that biochar addition significantly increased soil CO2 emission by 8.62 %, but reduced CH4 and N2O emissions by 27.0 % and 23.9 %, respectively. Meanwhile, organic amendments and the co-application with biochar resulted in an increase of global warming potential based on the 100-year time horizon (GWP100) by an average of 18.3 % and 26.1 %. More importantly, the interactive effect of biochar and organic amendments on CO2 emission was antagonistic (the combined effect was weaker than the sum of their individual effects), while additive on CH4 and N2O emissions. Additionally, our results suggested that when biochar is co-applied with organic amendments, soil GHG emissions were largely influenced by soil initial total carbon, soil texture, and biochar feedstocks. Our work highlights the important interactive effects of biochar and organic amendments on soil GHG emissions, and provides new insights for promoting ecosystem sustainability as well as mitigating future climate change.

Understanding unsaturated sulfate saline soil in cold regions: A comprehensive hydraulic–thermal–air–salt–mechanical model with experimental research

The destruction of infrastructure built on saline soil in cold regions is closely related to water and salt migration, and soil deformation in foundations. Consequently, it is imperative to understand the mechanisms of heat and mass transfer, along with deformation in saline soil. Based on the unsaturated soil mechanics and porous media theory, a hydraulic–thermal–air–salt–mechanical (HTASM) coupled mathematical model for frozen unsaturated sulfate saline soil is proposed. The model incorporates the impact of ice-water phase change, sodium sulfate crystallization, and vapor flow on heat and mass transfer during the freezing process. Two parameters—salt crystallization pressure, and ice pressure—are introduced into the mechanical control equation to capture the effects of phase change on deformation. In addition, the relationship between the density of soil particles, water, ice and gas, and temperature and pressure is considered to reflect the dynamic change of density during freezing. Finally, the numerical simulation using the HTASM model is conducted and its efficacy is validated by comparing the numerical results with those obtained from indoor unidirectional freezing tests. The coupling effect of the HTASM model is revealed by analyzing the dynamic changes of temperature, water content, salt content, vapor flux and crystallization pressure in the soil column during freezing. The results show that the proposed HTASM model can well simulate the heat and mass transfer behavior in freezing unsaturated sulfate saline soil.

Mapping in a radon-prone area in Adamawa region, Cameroon, by measurement of radon activity concentration in soil.

The radon-prone area of the Adamawa region in Cameroon is characterized by high natural radiation background resulting from the high concentrations of radium-226, thorium-232, and indoor radon. To produce a radon-risk map, radon measurements in soil were carried out in the city of Ngaoundere. The radon activity concentration in soil gas ranged from 256 to 166kBqm-3 with a mean of 80kBqm-3 and a standard deviation of 38kBqm-3. The area is mostly classified as high risk (80%) according to the Swedish classification, and 20% as medium risk. A low-risk area was not observed. Granite-like geology sites were characterized by higher radon concentration. A ratio of about 295:1 was obtained for soil radon gas to indoor radon concentrations, with a positive correlation (R = 0.40), and a transfer factor of 3 per mil. These results demonstrate that in situ measurements of radon concentration in soil can provide accurate information on the level of indoor radon concentrations. Geostatistical and deterministic interpolation techniques have been used to obtain a radon map by comparing the suitability of ordinary kriging and inverse-distance-weighted (IDW) interpolation methods. It turned out that there is not much difference in the prediction errors of the two techniques (Root Mean Square Error = 34.4 for ordinary kriging and 34.3 for IDW). It is concluded that both methods give acceptable results. In situ measurements and geostatistical analysis allow assessment of expected indoor radon exposure in a given area at reduced costs and time required. However, for the investigated area, more research is needed to produce reliable radon-risk maps.

Source and migration patterns of heavy metals and human health risk assessment of heavy metals in soil-corn straw-flue gas system.

The process of rapid urbanization in Northeast China has resulted in severe heavy metal pollution in the environment. In this study, we investigated the characteristics of heavy metal pollution in soil-corn straw and its combustion flue gas system, and the health risks of heavy metal pollution. The results showed that Cu and Zn in soil were more easily absorbed by corn straw roots. Heavy metals in soil, corn straw and flue gas from corn straw burning all pose some health risk to humans, and are more harmful to children than adults. The concentrations of heavy metals in both soil and flue gas from corn straw burning have reached extremely high ecological risk. The main sources of heavy metal elements in soils are, in order, industrial production, agricultural production activities and metallurgical production. This study highlights the key issues of heavy metal contamination in soil-corn straw and its combustion flue gas system, provides an auxiliary guide for the next step in analyzing the transfer mechanisms, and suggests a rational approach to mitigate heavy metal contamination.

Sulfur origin and flux variations in fumarolic fluids of Vulcano Island, Italy

A sharp increase in volatiles, especially SO2 fluxes from the solfataric plume and diffuse CO2 from the soils of the La Fossa crater area, started in June 2021, and subsequently from the Levante Bay area, suggests renewed unrest at Vulcano Island, Italy. This event has encouraged monitoring activities and stimulated new research activities aimed at understanding the recent evolution of the volcanic system. In this study, the chemical and isotopic composition of fumaroles, thermal waters, and soil gases from the main degassing areas of Vulcano Island with a special focus on sulfur isotopes, are used to investigate the fluid transfer mechanism inside the volcano. Sulfur is one of the most abundant volatile elements present in magmas and volcanic fluids from the La Fossa crater, where it mostly occurs as SO2 and H2S at variable relative concentrations depending on oxygen fugacity and temperature. The isotope composition and the chemical ratio of sulfur species depict a complex hydrothermal-magmatic system. In addition, we utilize the installed SO2 monitoring network that measures the total outgassing of SO2 with the UV-scanning DOAS technique. The SO2 fluxes from the La Fossa crater fumaroles, coupled with the SO2/CO2 and SO2/H2O ratios, were measured to evaluate the total mass of fluids emitted by the shallow plumbing system and its relationship with the status of volcanic activity. Combining the whole chemical composition of fumaroles analyzed with a discrete, direct sampling of high-temperature fumaroles located on the crater summit, the output of discharged water vapor has been estimated (5,768 t·d−1). On the basis of the water output, we estimated the total thermal energy dissipated by the crater during the last enhanced degassing activity (167 MW). This strong and sharp increase in energy observed during the current crisis confirms the long-growing trend in terms of mass and energy recorded in recent decades, which has brought the surface system of Vulcano Island to a critical level that has never been recorded since the last eruptive event of 1888–91.

Effect of near-surface winds on the measurement of forest soil CO2 fluxes using closed air chambers

Forest soil CO2 flux measurements are important for studying global climate change. Current monitoring methods are based on closed gas chambers, which block the wind pumping effect of near-surface winds in the measurements, resulting in biased values. Therefore, in this study, the effects of near-surface winds on chamber-monitored fluxes were investigated. The CO2 flux was quantified using a designed flux reference system with different CO2 concentrations, and the monitoring performance of the closed chamber was studied. Wavelet coherence was used to analyze the response relationship between near-surface winds and soil gas, and was combined with a flux calculation model to explore the relevant factors influencing gas chamber measurement-produced bias. The data indicate that at near-surface wind speeds greater than 0.8 m·s−1, gas transport enhancement was significant and further increased the deviation of the gas chamber-monitored CO2 fluxes. The monitoring error of the flow chamber (NSF) increased from 7% to 30% in soils with low carbon content, but did not vary significantly (3–7%) in soils with high CO2 concentrations. The flux measurement bias of the non-flow chamber (NSNF) was positively correlated with the soil carbon content, with the measurement error expanding by 16–24% with increasing soil CO2 concentrations. The measurement errors of the exponential and linear models in a windless environment were 9.8% (Exp) and 18.7% (Lin), respectively. The estimation errors of both models were positively correlated with both the time of a single monitoring event and the wind-induced coefficient Dw. Therefore, flux calculation models should be improved by considering environments with wind disturbances to reduce the effect of wind on measured values, which will help improve the accuracy of ecosystem carbon budgets.