Geochemistry of gases and waters discharged by the mud volcanoes at Paternò, Mt. Etna (Italy)

 Approximately 20 km south of Mt. Etna craters, at the contact between volcanic and sedimentary formations, three mud volcanoes discharge CO₂-rich gases and Na–Cl brines. The compositions of gas and liquid phases indicate that they are fed by a hydrothermal system for which temperatures of 100–150  °C were estimated by means of both gas and solute geothermometry. The hydrothermal system may be associated with CO₂-rich groundwaters over a large area extending from the central part of Etna to the mud volcanoes. Numerous data on the He, CH₄, CO₂ composition of the gases of the three manifestations, sampled over the past 5 years, indicate clearly that variations are due to separation processes of a CO₂-rich gas phase from the liquid. The effects of these processes have to be taken into account in the interpretation of the monitoring data collected for the geochemical surveillance of Etna volcano. Received: 4 September 1995 / Accepted: 14 February 1996     

三峡水库CO2、CH4通量监测分析研究

自成库以来,三峡水库CO₂、CH₄等温室气体通量较蓄水前发生明显改变。如何科学认识和客观评估三峡水库修建及运行对其CO₂、CH₄等温室气体通量的影响备受关注。本文简要回顾了自2009年以来在三峡水库开展CO₂、CH₄等温室气体通量监测与分析工作,综述认为,现阶段三峡水库温室气体排放以水-气界面扩散释放为主要途径。陆源输入的有机碳是主导三峡水库CO₂、CH₄产生的主要碳源,但在局部区段或时段自源性有机碳的贡献亦十分显著。同蓄水前相比,三峡水库碳排放量呈现为净增加,淹没效应约占水库C净增量的20%,库区内点面源污染负荷并未对CO₂排放的净增量产生显著贡献,阻隔效应和生态系统重建效应对三峡水库碳排放的净增量产生显著贡献。近10年来,监测方法比对、监测点位优化等工作在一定程度上完善了三峡水库温室气体通量监测体系。新方法、新技术的引入也为三峡水库温室气体通量监测分析提供了有利支撑和保障,但复杂水文环境...     

Continuous monitoring of distal gas emanations at Vulcano,southern Italy

The increasing activity of Vulcano Island (Italy) since 1985 led to the initiation of continuous geochemical monitoring of the lateral soil gas emissions. On the basis both of their relative geochemical characteristics and of local considerations, three gaseous components were selected for monitoring, namely CO₂, He and ²²²Rn. Monitoring has been performed by means of specific analysers. Gases extracted from a water well located at the foot of the active cone were selected for monitoring, on the basis of their geochemical and isotopic characters that indicate their genetic link with central high temperature fumarolic gases emitted at the crater. Very strong variations of gas composition can be observed within one day (from 1 to about 94% for CO₂). Some variations display a daily character and can be correlated with that of atmospheric pressure. The three monitored gases are highly correlated, suggesting very high kinetics of gas transfer in the system. Because of these considerable variations of chemical composition, bulk concentrations obviously are not suitable for monitoring at Vulcano. However, the evolution with time of ratios such as ²²²Rn/CO₂ and He/CO₂ (the latter being corrected for atmospheric contamination) supplies numerical parameters that the expected to characterize the intensity of the degassing process. A new input of magmatic gases, that would lead to an increase in the ²²²Rn/CO₂ and He/CO₂ ratios, should therefore be detected by such a monitoring station.     

Molecular simulation of the CH4/CO2/H2O adsorption onto the molecular structure of coal

Clarification of the molecular mechanism underlying the interaction of coal with CH₄, CO₂, and H₂O molecules is the basis for an in-depth understanding of the states of fluid in coal and fluid-induced coal swelling/contraction. In terms of instrumental analysis, molecular simulation technology based on molecular mechanics/dynamics and quantum chemistry is a powerful tool for revealing the relationship between the structure and properties of a substance and understanding the interaction mechanisms of physical-chemical systems. In this study, the giant canonical ensemble Monte Carlo (GCMC) and molecular dynamics (MD) methods were applied to investigate the adsorption behavior of a Yanzhou coal model (C₂₂₂H₁₈₅N₃O₁₇S₅). We explored the adsorption amounts of CH₄, CO₂, and H₂O onto Yanzhou coal, the adsorption conformation, and the impact of oxygen-containing functional groups. Furthermore, we revealed the different adsorption mechanisms of the three substances using isosteric heat of adsorption and energy change data. (1) The adsorption isotherms of the mono-component CH₄, CO₂, and H₂O were consistent with the Langmuir model, and their adsorption amounts showed an order of CH₄<CO₂<H₂O. In addition, high temperatures were non-conducive to adsorption. When the three components of CH₄/CO₂/H₂O were mixed (at a molar ratio of 1:1:1) for adsorption, only the adsorption curve of H₂O was consistent with the Langmuir model. (2) The mean values of the isosteric heat of adsorption of CH₄, CO₂, and H₂O were 22.54, 36.90, and 37.82 kJ/mol, respectively; that is, H₂O>CO₂>CH₄. In addition, at higher temperatures, the isosteric heat of adsorption decreased; pressure had no significant effect on the heat of adsorption. (3) CH₄ molecules displayed an aggregated distribution in the pores, whereas CO₂ molecules were cross arranged in pairs. Regarding H₂O molecules, under the influence of hydrogen bonds, the O atom pointed to surrounding H₂O molecules or the H atoms of coal molecules in a regular pattern. The intermolecular distances of the three substances were 0.421, 0.553, and 0.290 nm, respectively. The radial distribution function (RDF) analysis showed that H₂O molecules were arranged in the most compact fashion, forming a tight molecular layer. (4) H₂O molecules showed a significantly stratified distribution around oxygen-containing functional groups on the coal surface, and the bonding strength showed a descending order of hydroxyl> carboxyl>carbonyl. In contrast, CO₂ and CH₄ showed only slightly stratified distributions. (5) After the adsorption of CH₄, CO₂, and H₂O, the total energy, the energy of valence electrons, and the non-bonding interaction of the system in the Yanzhou coal model all decreased. The results regarding the decrease in the total energy of the system indicated an order of H₂O>CO₂>CH₄ in terms of the adsorption priority of the Yanzhou coal model. The results regarding the decrease in the energy of valence electrons showed that under certain geological conditions, a pressure-induced “coal strain” could lead to a structural rearrangement during the interaction of coal with fluid to form a more stable conformation, which might be the molecular mechanism of coal swelling resulting from the interaction between fluid and coal. An analysis of the contribution of Van der Waals forces, electrostatic interactions and hydrogen bonds to the decrease in non-bonding interactions revealed the mechanism underlying the interactions between coal molecules and the three substances. The interaction between coal molecules and CH₄ consisted of typical physical adsorption, whereas that between coal molecules and CO₂ consisted mainly of physical adsorption combined with weak chemical adsorption. The interaction between coal molecules and H₂O is physical and chemical.     

Impacts of Methane on Carbon Dioxide Storage in Brine Formations

In the context of geological carbon sequestration (GCS), carbon dioxide (CO₂) is often injected into deep formations saturated with a brine that may contain dissolved light hydrocarbons, such as methane (CH₄). In this multicomponent multiphase displacement process, CO₂ competes with CH₄ in terms of dissolution, and CH₄ tends to exsolve from the aqueous into a gaseous phase. Because CH₄ has a lower viscosity than injected CO₂, CH₄ is swept up into a ‘bank’ of CH₄‐rich gas ahead of the CO₂ displacement front. On the one hand, this may provide a useful tracer signal of an approaching CO₂ front. On the other hand, the emergence of gaseous CH₄ is undesirable because it poses a leakage risk of a far more potent greenhouse gas than CO₂ if the cap rock is compromised. Open fractures or faults and wells could result in CH₄ contamination of overlying groundwater aquifers as well as surface emissions. We investigate this process through detailed numerical simulations for a large‐scale GCS pilot project (near Cranfield, Mississippi) for which a rich set of field data is available. An accurate cubic‐plus‐association equation‐of‐state is used to describe the non‐linear phase behavior of multiphase brine‐CH₄‐CO₂ mixtures, and breakthrough curves in two observation wells are used to constrain transport processes. Both field data and simulations indeed show the development of an extensive plume of CH₄‐rich (up to 90 mol%) gas as a consequence of CO₂ injection, with important implications for the risk assessment of future GCS projects.     

Measuring Concentrations of Dissolved Methane and Ethane and the 13C of Methane in Shale and Till

Baseline characterization of concentrations and isotopic values of dissolved natural gases is needed to identify contamination caused by the leakage of fugitive gases from oil and gas activities. Methods to collect and analyze baseline concentration‐depth profiles of dissolved CH₄ and C₂H₆ and δ¹³C‐CH₄ in shales and Quaternary clayey tills were assessed at two sites in the Williston Basin, Canada. Core and cuttings samples were stored in Isojars^® in a low O₂ headspace prior to analysis. Measurements and multiphase diffusion modeling show that the gas concentrations in core samples yield well‐defined and reproducible depth profiles after 31‐d equilibration. No measurable oxidative loss or production during core sample storage was observed. Concentrations from cuttings and mud gas logging (including IsoTubes^®) were much lower than from cores, but correlated well. Simulations suggest the lower concentrations from cuttings can be attributed to drilling time, and therefore their use to define gas concentration profiles may have inherent limitations. Calculations based on mud gas logging show the method can provide estimates of core concentrations if operational parameters for the mud gas capture cylinder are quantified. The δ¹³C‐CH₄ measured from mud gas, IsoTubes^®, cuttings, and core samples are consistent, exhibiting slight variations that should not alter the implications of the results in identifying the sources of the gases. This study shows core and mud gas techniques and, to a lesser extent, cuttings, can generate high‐resolution depth profiles of dissolved hydrocarbon gas concentrations and their isotopes.     

Acoustic emission and volumetric strain induced in coal by the displacement sorption of methane and carbone dioxide

The aim of this study was to assess whether acoustic emission (AE) could carry information on preferential sorption/desorption of CH₄ or CO₂ in coal. AE and expansion/contraction of two nearly identical cylindrical coal samples were continuously monitored during displacement sorption experiments. One sample was subjected to presorption of CH₄, followed by sorption of CH₄/CO₂ mixture. With the other one, presorption of CO₂ preceded sorption of the mixture. The results obtained are the following: first, AE and stain kinetics show that the affinity of the coal tested is higher for CO₂ than for CH₄; second, methane is preferentially desorbed after presorption of CH₄ — sorption of mixture of CH₄ and CO₂; third, during displacement sorption, kinetics of AE and sample swelling/shrinkage bring out the importance of presorption and the sorbate used. It matters whether the coal is first exposed to CH₄ or to CO₂. The present study has demonstrated that injection of CO₂ into the coal previously exposed to CH₄ causes considerable swelling of the coal. On desorption after CH₄/CO₂ exchange sorption, initial shrinkage is followed by swelling of the coal. These results could have implications for the sequestration of CO₂ in coal seams and CH₄ recovery from coalbeds (ECBM). Swelling/shrinkage of the coal matrix should be included in models used to predict coal permeability and gas flow rates. They also show that the AE technique can give more insights into coal matrix-gas interactions.     

Structural pattern and CO2–CH4 degassing of Ustica Island,Southern Tyrrhenian basin

Brittle tectonics and ground degassing, including fracture-field, soil–gas and exhalation flux analyses of CO₂ and CH₄, were studied at Ustica Island, a Pleistocene volcanic complex in the Southern Tyrrhenian Sea. The mesoscopic fracture pattern perfectly fits an E–W-trending left-lateral strike–slip master fault, in agreement with the main morpho-structural submarine alignment including Ustica Island and Anchise Seamount. Along the SW–NE high-angle normal Arso Fault, geological evidence of reactivation with different kinematics (left- to right-lateral displacements) was recognised. Major CO₂ and CH₄ degassing (with fluxes up to 93,750 and 20 t km⁻² a⁻¹, respectively, and soil–gas concentrations of 11.3% and 5.7 ppm) occur over the Arso Fault. Although this fault is mapped just in the SW sector of the island, soil–gas CO₂ anomalies point out its clear continuation up to the NE margin of the island. These data, together with those of previous geophysical and geochemical results from off-shore Ustica, suggest that the Arso Fault is the local evidence of a more important active, gas-bearing structure. This tectonic feature is interpreted as a reactivation of a preexistent SW–NE trend, inherited as a second-order structure of the E–W deep shear zone. The reactivation is related to the interplay among different structures of the Southern Tyrrhenian basin.     

Geochemistry of the Submarine Gaseous Emissions of Panarea (Aeolian Islands, Southern Italy): Magmatic vs. Hydrothermal Origin and Implications for Volcanic Surveillance

The marine sector surrounding Panarea Island (Aeolian Islands, South Italy) is affected by widespread submarine emissions of CO₂ -rich gases and thermal water discharges which have been known since the Roman Age. On November 3^rd, 2002 an anomalous degassing event affected the area, probably in response to a submarine explosion. The concentrations of minor reactive gases (CO, CH₄ and H₂) of samples collected in November and December, 2002 show drastic compositional changes when compared to previous samples collected from the same area in the 1980s. In particular the samples collected after the November 3^rd phenomenon display relative increases in H₂ and CO and a strong decrease in the CH₄ contents, while other gas species show no significant change. The interaction of the original gas with seawater explains the variable contents of CO₂, H₂S, N₂, Ar and He which characterize the different samples, but cannot explain the large variations of CO, CH₄ and H₂ which are instead compatible with changes in the redox, temperature and pressure conditions of the system. Two models, both implying an increasing input of magmatic fluids are compatible with the observed variations of minor reactive species. In the first one, the input of magmatic fluids drives the hydrothermal system towards atypical (more oxidizing) redox conditions, slowly pressurizing the system up to a critical state. In the second one, the hydrothermal system is flashed by the rising high-T volcanic fluid, suddenly released by a magmatic body at depth. The two models have different implications for volcanic surveillance and risk assessment: In the first case, the November 3^rd event may represent both the culmination of a relatively slow process which caused the overpressurization of the hydrothermal system and the beginning of a new phase of quiescence. The possible evolution of the second model is unforeseeable because it is mainly related to the thermal, baric and compositional state of the deep magmatic system that is poorly known.     

Impact of Hurricane Irene and Tropical Storm Lee on riparian zone hydrology and biogeochemistry

Although riparian zones are well known to reduce nitrogen (N) and phosphorus (P) runoff to streams, they also have the potential to affect greenhouse gas (CO₂, N₂O, and CH₄) fluxes to the atmosphere. Following large storms, soil biogeochemical conditions often become more reduced, especially in oxbow depressions and side channels, which can lead to hot moments of greenhouse gas production. Here, we investigate the impact of the remnants of Hurricane Irene and Tropical Storm Lee on riparian zone hydrology (water table: WT), and biogeochemistry (oxidation‐reduction potential [ORP], dissolved oxygen [DO], NO₃^?, PO₄^3?, CO₂, N₂O, CH₄). Results indicate that large storms have the potential to reset WT levels for weeks to months. Overbank flooding at our site following Irene and Lee led to the infiltration of well‐oxygenated water at depth (higher DO and ORP) while promoting the development of anoxic conditions within soil aggregates near the soil surface (increased N₂O and CH₄ fluxes). A short‐term increase in CO₂ emission was observed following Irene at our site where aerobic respiration was water‐limited. Over a 2‐year period, an oxbow depression exhibited higher WT, higher N₂O and CH₄ fluxes (hot moment), higher CO₂ fluxes (seasonal), and lower NO₃^? concentrations (seasonal) than the rest of the riparian zone. However, neither Irene, nor Lee, nor the oxbow depression significantly impacted PO₄^3?. Dissolved organic carbon, ORP, and DO data illustrate the time‐lag (>20 years) between the creation of an oxbow depression and the development of reducing conditions despite clear differences in riparian zone and oxbow WT dynamics.     

大型水库分层期和混合期溶存温室气体空间变化及排放通量

水库作为温室气体的重要来源,对区域气候变化有不可忽略的影响。然而,目前对水库溶存温室气体的空间异质性及垂向特征的认知仍然欠缺。为了揭示水库分层期和混合期溶存温室气体空间特征及排放通量,也为厘清水库温室气体产生和排放的关键过程提供重要支撑。研究选择东北地区大型水库——汤河水库为对象,于2021年7—9月和10月(分别代表水库分层期和混合期)对水库不同位置(坝前、库中和库尾)开展溶存温室气体垂向分层监测。研究结果显示,水库CH₄排放通量变化范围为0.018～0.174 mmol/(m²·d),是大气CH₄的源,空间分布为库尾>库中>坝前;CO₂通量为-4.91～58.77 mmol/(m²·d),除分层期东支库尾,其余点位均表现为大气CO₂的源,空间分布为坝前>库中>库尾。时间上,分层期CH₄排放通量(0.071±0.044 mmol/(m²·d))高于混合期((0.027±0.008) mm...     

Aqueous volatiles in hydrothermal fluids from the Main Endeavour Field, northern Juan de Fuca Ridge: temporal variability following earthquake activity

The Main Endeavour Field, northern Juan de Fuca Ridge, experienced intense seismic activity in June 1999. Hydrothermal vent fluids were collected from sulfide structures in September 1999 and July 2000 and analyzed for the abundance of H₂, H₂S, CH₄, CO₂, NH₃, Mg and Cl to document temporal and spatial changes following the earthquakes. Dissolved concentrations of CO₂, H₂, and H₂S increased dramatically in the September 1999 samples relative to pre-earthquake abundances, and subsequently decreased during the following year. In contrast, dissolved NH₃ and CH₄ concentrations in 1999 and 2000 were similar to or less than pre-earthquake values. Aqueous Cl abundances showed large decreases immediately following the earthquakes followed by increases to near pre-earthquake values. The abundances of volatile species at the Main Endeavour Field were characterized by strong inverse correlations with chlorinity. Phase separation can account for 20-50% enrichments of CO₂, CH₄, and NH₃ in low-chlorinity fluids, while temperature- and pressure-dependent fluid-mineral equilibria at near-critical conditions are responsible for order of magnitude greater enrichments in dissolved H₂S and H₂. The systematic variation of dissolved gas concentrations with chlorinity likely reflects mixing of a low-chlorinity volatile-enriched vapor generated by supercritical phase separation with a cooler gas-poor hydrothermal fluid of seawater chlorinity. Decreased abundances of sediment-derived NH₃ and CH₄ in 1999 indicate an earthquake-induced change in subsurface hydrology. Elevated CO₂ abundances in vent fluids collected in September 1999 provide evidence that supports a magmatic origin for the earthquakes. Temperature-salinity relationships are consistent with intrusion of a shallow dike and suggest that the earthquakes were associated with movement of magma beneath the ridge crest. These data demonstrate the large and rapid response of chemical fluxes at mid-ocean ridges to magmatic activity and associated changes in subsurface temperature and pressure.     

三峡水库澎溪河水-气界面CO2、CH4扩散通量昼夜动态初探

三峡水库温室气体效应近年来备受关注.为揭示三峡水库典型支流澎溪河水-气界面CO₂和CH₄通量的昼夜动态规律,明晰短时间尺度下该水域温室气体释放的影响因素,在2010年6月至2011年5月的一个完整水文周年内,选择4个具有代表性的时段(2010年8、11月和2011年2、5月)对澎溪河高阳平湖水域开展昼夜跟踪观测.结果表明:2010年8、11月和2011年2、5月4次采样的CO₂日总通量值分别为-8.34、73.94、28.13和-20.12 mmol/(m²·d),相应的CH₄日总通量值分别为2.22、0.11、0.32和7.16 mmol/(m²·d),不同时期昼夜变化明显.研究水域CO₂和CH₄通量过程不具同步性:CO₂昼夜通量变化可能更显著地受到水柱光合/呼吸过程的影响,但瞬时气象过程(水汽温差、瞬时风速等)在高水位时期亦可对CO₂通量产生显著影响;CH₄昼夜通量变化与水温条件改变更为密切.     

A magmatic source for fumaroles and diffuse degassing from the summit crater of Teide Volcano (Tenerife, Canary Islands): a geochemical evidence for the 2004–2005 seismic–volcanic crisis

The present work reports the results of 15 studies of diffuse CO₂ degassing performed at Teide Volcano crater (Canary Island, Spain) and the chemical and isotopic compositions of fluids discharged from a fumarolic field located at the top of the volcano as measured between 1991 and 2010. A higher contribution of magmatic gases accompanied by enhanced total diffuse CO₂ emissions were observed in relation with a seismic crisis that occurred in Tenerife Island between 2001 and 2005, with the main peak of seismic activity between April and June 2004. A significant pulse in total diffuse CO₂ emission was observed at the crater of Teide (up to 26.3?t day^?1) in 2001. In December 2003, the chemical composition of the Teide fumarole changed significantly, including the appearance of SO₂, an increase in the HCl and CO concentrations and in the C₂H₆/C₂H₄ and C₃H₈/C₃H₆ ratios, and a decrease in the H₂S, CH₄, and C₆H₆ concentrations and in the gas/steam ratio. A few months after a drastic decrease in seismic activity, the SO₂, HCl, and CO concentrations and the C₂H₆/C₂H₄ and C₃H₈/C₃H₆ ratios strongly decreased, whereas the CH₄ and C₆H₆ concentrations and the gas/steam ratios increased. According to the trends shown by both the geochemical parameters and the seismic signals late in the observation period, the risk of a rejuvenation of volcanic activity at Teide is considered to be low. The associated temporal changes in seismic activity and magmatic degassing indicate that geophysical and fluid geochemistry signals in this system are related. Future monitoring programs aimed at mitigating volcanic hazard on Tenerife Island should involve coupled geophysical and geochemical studies.     

Variations in dissolved CO2 and CH4 in a first‐order stream and catchment: an investigation of soil–stream linkages

Spatial and seasonal variations in CO₂ and CH₄ concentrations in streamwater and adjacent soils were studied at three sites on Brocky Burn, a headwater stream draining a peatland catchment in upland Britain. Concentrations of both gases in the soil atmosphere were significantly higher in peat and riparian soils than in mineral soils. Peat and riparian soil CO₂ concentrations varied seasonally, showing a positive correlation with air and soil temperature. Streamwater CO₂ concentrations at the upper sampling site, which mostly drained deep peats, varied from 2·8 to 9·8 mg l^?1 (2·5 to 11·9 times atmospheric saturation) and decreased markedly downstream. Temperature‐related seasonal variations in peat and riparian soil CO₂ were reflected in the stream at the upper site, where 77% of biweekly variation was explained by an autoregressive model based on: (i) a negative log‐linear relationship with stream flow; (ii) a positive linear relationship with soil CO₂ concentrations in the shallow riparian wells; and (iii) a negative linear relationship with soil CO₂ concentrations in the shallow peat wells, with a significant 2‐week lag term. These relationships changed markedly downstream, with an apparent decrease in the soil–stream linkage and a switch to a positive relationship between stream flow and stream CO₂. Streamwater CH₄ concentrations also declined sharply downstream, but were much lower (<0·01 to 0·12 mg l^?1) than those of CO₂ and showed no seasonal variation, nor any relationship with soil atmospheric CH₄ concentrations. However, stream CH₄ was significantly correlated with stream flow at the upper site, which explained 57% of biweekly variations in dissolved concentrations. We conclude that stream CO₂ can be a useful integrative measure of whole catchment respiration, but only at sites where the soil–stream linkage is strong. Copyright © 2004 John Wiley & Sons, Ltd.     

Transfer of carbon dioxide and methane through the soil‐water‐atmosphere system at Mer Bleue peatland,Canada

Surface waters associated with peatlands, supersaturated with CO₂ and CH₄ with respect to the atmosphere, act as important pathways linking a large and potentially unstable global repository of C to the atmosphere. Understanding the drivers and mechanisms which control C release from peatland systems to the atmosphere will contribute to better management and modelling of terrestrial C pools. We used non‐dispersive infra‐red (NDIR) CO₂ sensors to continuously measure gas concentrations in a beaver pond at Mer Bleue peatland (Canada); measurements were made between July and August 2007. Concentrations of CO₂ in the surface water (10 cm) reached 13 mg C l^?1 (epCO₂ 72), and 26 mg C l^?1 (epCO₂ 133) at depth (60 cm). The study also showed large diurnal fluctuations in dissolved CO₂ which ranged in amplitude from ～1·6 mg C l^?1 at 10 cm to ～0·2 mg C l^?1 at 60 cm depth. CH₄ concentration and supersaturation (epCH₄) measured using headspace analysis averaged 1·47 mg C l^?1 and 3252, respectively; diurnal cycling was also evident in CH₄ concentrations. Mean estimated evasion rates of CO₂ and CH₄ over the summer period were 44·92 ± 7·86 and 0·44 ± 0·25 µg C m^?2s^?1, respectively. Open water at Mer Bleue is a significant summer hotspot for greenhouse gas emissions within the catchment. Our results suggest that CO₂ concentrations during the summer in beaver ponds at Mer Bleue are strongly influenced by biological processes within the water column involving aquatic plants and algae (in situ photosynthesis and respiration). In terms of carbon cycling, soil‐stream connectivity at this time of year is therefore relatively weak. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermal Monitoring of Natural Source Zone Depletion

Natural depletion of subsurface petroleum liquids releases energy in the form of heat. The rate of natural source zone depletion (NSZD) can be derived from subsurface temperature data. An energy balance is performed to resolve NSZD‐generated energy in terms of W/m². Biodegradation rates are resolved by dividing the NSZD energy by the heat of reaction in joules/mol. Required temperature data are collected using data loggers, wireless connections, and automated data storage and analysis. Continuous thermal resolution of monthly NSZD rates at a field site indicates that apparent monthly NSZD rates vary through time, ranging from 10,000 to 77,000 L/ha/year. Temporal variations in observed apparent NSZD rates are attributed to processes governing the conversion of CH₄ to CO₂, as opposed to the actual rates of NSZD. Given a year or more of continuous NSZD rate data, it is anticipated that positive and negative biases in apparent NSZD rates will average out, and averaged apparent NSZD rates will converge to true NSZD rates. An 8.4% difference between average apparent NSZD rates over a 31‐month period using the thermal monitoring method and seven rounds of CO₂ efflux measurements using CO₂ traps supports the validity of both CO₂ trap and thermal monitoring methods. A promising aspect of thermal monitoring methods is that continuous data provide a rigorous approach to resolving the true mean NSZD rates as compared to temporally sparse CO₂ trap NSZD rate measurements. Overall, a vision is advanced of real‐time sensor‐based groundwater monitoring that can provide better data at lower costs and with greater safety, security, and sustainability.     

三峡澎溪河水-气界面温室气体模型估算及其敏感性分析

模型估算法是水-气界面温室气体通量监测的主要方法,所得成果也不胜枚举.然而监测过程中诸多环境因素会对最终结果产生不确定的影响.结合三峡库区澎溪河背景条件,利用模型估算法进行水-气界面温室气体通量(以CO_2为例)估算,并且采用修正Morris筛选法尝试分析模型估算法中各个参数对温室气体扩散通量(以CO_2为例)的局部敏感性.研究结果表明:利用模型估算法计算三峡澎溪河流域水-气界面温室气体通量具有较高的可行性和可靠性;风速、水温以及pH值会对监测结果产生影响,且风速越强、水温越高、pH值越小,CO_2扩散通量就越大;pH值是高灵敏参数,风速和水温是灵敏参数.在三峡库区澎溪河监测过程中更应注意pH值的精确性,每次采样前需校正仪器.     

Long-time variation of soil CO2 fluxes at the summit crater of Vulcano (Italy)

Here, we report the first continuous data of geochemical parameters acquired directly from the active summit crater of Vulcano. This approach provides a means to better investigate deep geochemical processes associated with the degassing system of Vulcano Island. In particular, we report on soil CO₂ fluxes from the upper part of Vulcano, a closed-conduit volcano, from September 2007 to October 2010. Large variations in the soil CO₂ and plume SO₂ fluxes (order of magnitude), coinciding with other discontinuous geochemical parameters (CO₂ concentrations in fumarole gas) and physical parameters (increase of shallow seismic activity and fumarole temperatures) have been recorded. The results from this work suggest new prospects for strengthening geochemical monitoring of volcanic activity and for improving the constraints in the construction of a “geochemical model”, this being a necessary condition to better understand the functioning of volcanic systems.     

Chaotic behaviour of acoustic emission induced in hard coal by gas sorption-desorption

This paper presents study of non-linear dynamics of acoustic emission (AE) generated in coal samples subjected to gas sorption-desorption. Carbon-dioxide and methane were used as sorbats. Experimental facilities used in high pressure sorption of CO₂ and/or CH₄ on coal comprised a pressure vessel and associated pressurisation and monitoring systems. Tests were conducted on medium-rank coal obtained from the Upper Silesia Basin. Several approaches to the treatment of experimental results are proposed in order to detect and characterize deterministic chaos: (1) analysis of fractal/multifractal character of AE energy rate, using fractal generalised dimensions D _q (q); (2) analysis of temporal changes of AE energy rate and its fractal correlation dimension D ₂; and (3) evaluation of attractor dimension within the reconstructed phase space from experimental time series. It was shown that AE generated during CO₂ sorption on medium-rank coal is a more heterogeneous and lower dimensional process in comparison with AE induced by CO₂ desorption. Yet, the AE associated with desorption of CO₂ exhibits higher heterogeneity than the AE generated during desorption of CH₄. There are certain similarities between changes of D₂ during desorption of CO₂ as well desorption of CH₄. However, dynamics of these changes and character of time distributions of D₂ differ, depending on a sorbate. We do not know the precise reason for observed differences, but we presume that the carbon-dioxide molecules dissimilarity to methane molecules can account for them.