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1.
In the eastern edge of the Ordos Basin, the coalbed methane (CBM) development has not made substantial progress in the past 20 years, and the origin of gas can be used to guide the CBM block-selecting and development. Based on the 37 sets of carbon isotope data, the origin of the gas was determined and the origin mechanism was studied in this work. The δ 13CPDB of methane ranges from ?70.5‰ to ?36.19‰ in the eastern edge in the Ordos Basin and the value becomes heavier from the north to the south. The secondary biogenic gas and the thermogenic gas are mixed in the shallow area and the thermogenic gas occurs in the medium and deep levels. The phenomenon is controlled mainly by the distribution of coal rank and hydrodynamics. Firstly, based on the relationship between China coal rank and methane δ 13CPDB, the medium rank coal is dominant in the eastern edge of the Ordos Basin, and the mixture of the secondary biogenic gas and the thermogenic gas is formed in the coal of vitrinite reflectant ratio (R max) between 0.5% and 2.0% if there is appropriate hydrodynamics; at the same time, because of the shallow burial depth, and the well-developed coal outcrop, meteoric water and other surface water carrying bacteria recharge the coal reservoir, metabolize the organic compounds at a relatively low temperature, and generate methane and carbon dioxide. Wherever the trapping mechanisms occur in the coal, such as Liulin and Hancheng, modern gas content should be high.  相似文献   

2.
Three carbon components are evident in eleven analyzed mid-oceanic basalts: carbon on sample surfaces (resembling adsorbed gases, organic matter, or other non-magmatic carbon species acquired by the glasses subsequent to their eruption), mantle carbon dioxide in vesicles, and mantle carbon dissolved in the glasses. The combustion technique employed recovered only reduced sulfur, all of which appears to be indigenous to the glasses. The dissolved carbon concentration (measured in vesicle-free glass) increases with the eruption depth of the spreading ridge, and is consistent with earlier data which show that magma carbon solubility increases with pressure. The total glass carbon content (dissolved plus vesicular carbon) may be controlled by the depth of the shallowest ridge magma chamber. Carbon isotopic fractionation accompanies magma degassing; vesicle CO2 is about 3.8‰ enriched in 13C, relative to dissolved carbon. Despite this fractionation, δ13CPDB values for all spreading ridge glasses lie within the range ?5.6 and ?7.5, and the δ13CPDB of mantle carbon likely lies between ?5 and ?7. The carbon abundances and δ13CPDB values of Kilauea East Rift glasses apparently are influenced by the differentiation and movement of magma within that Hawaiian volcano. Using 3He and carbon data for submarine hydrothermal fluids, the present-day mid-oceanic ridge mantle carbon flux is estimated very roughly to be about 1.0 × 1013 g C/yr. Such a flux requires 8 Gyr to accumulate the earth's present crustal carbon inventory.  相似文献   

3.
Hydrocarbon compositions and δ13C values for methane of fourteen natural seep gases and four underwater vents in the northwestern Gulf of Mexico are reported. The C1/(C2 + C3) ratios of the seep gas samples ranged from 68 to greater than 1000, whereas δPDB13C values varied from ?39.9 to ?65.5‰. Compositions suggest that eleven of the natural gas seeps are produced by microbial degradation whereas the remaining three have a significant thermocatalytically produced component. Contradictions in the inferences drawn from molecular and isotopic compositions make strict interpretation of the origins of a few of the samples impossible.  相似文献   

4.
The stable carbon isotope values of coalbed methane range widely, and also are gener- ally lighter than that of gases in normal coal-formed gas fields with similar coal rank. There exists strong carbon isotope fractionation in coalbed methane and it makes the carbon isotope value lighter. The correlation between the carbon isotope value and Ro in coalbed methane is less obvious. The coaly source rock maturity cannot be judged by coalbed methane carbon isotope value. The carbon isotopes of coalbed methane become lighter in much different degree due to the hydrodynamics. The stronger the hydrodynamics is, the lighter the CBM carbon isotopic value becomes. Many previous investigations indicated that the desorption-diffusion effects make the carbon isotope value of coalbed methane lighter. However, the explanation has encountered many problems. The authors of this arti- cle suggest that the flowing groundwater dissolution to free methane in coal seams and the free methane exchange with absorbed one is the carbon isotope fractionation mechanism in coalbed methane. The flowing groundwater in coal can easily take more 13CH4 away from free gas and com- paratively leave more 12CH4. This will make 12CH4 density in free gas comparatively higher than that in absorbed gas. The remaining 12CH4 in free gas then exchanges with the adsorbed methane in coal matrix. Some absorbed 13CH4 can be replaced and become free gas. Some free 12CH4 can be ab- sorbed again into coal matrix and become absorbed gas. Part of the newly replaced 13CH4 in free gas will also be taken away by water, leaving preferentially more 12CH4. The remaining 12CH4 in free gas will exchange again with adsorbed methane in the coal matrix. These processes occur all the time. Through accumulative effect, the 12CH4 will be greatly concentrated in coal. Thus, the stable carbon isotope of coalbed methane becomes dramatically lighter. Through simulation experiment on wa- ter-dissolved methane, it had been proved that the flowing water could fractionate the carbon isotope of methane, and easily take heavy carbon isotope away through dissolution.  相似文献   

5.
The Ediacaran Yangtze platform in South China, which represents depositional settings ranging from coastal to basinal, provides valuable information for understanding climate changes and animal evolution during the Ediacaran Period. Although the shallower settings have been investigated, research on the basinal sections has been limited. This has hampered efforts to establish stratigraphic correlations and understand the oceanographic setting of the Yangtze platform. In this paper, the chemostratigraphy of a basinal section at Fengtan, Hunan Province, is reported based on analyses of stable carbon isotope profiles in carbonates (δ13Ccarb), organic matter (δ13Corg), total organic carbon, 87Sr/86Sr ratios, and Mn, Rb, and Sr concentrations. The basinal section of the Doushantuo Formation, which is represented at Fengtan, provides data supporting regional correlations and oceanography. Three intervals in the Doushantuo Formation are correlated with the Three Gorges: (i) a negative δ13Ccarb anomaly with stable δ13Corg values and altered 87Sr/86Sr ratios in the lower section can be correlated to the boundary between Doushantuo Members 2 and 3 (Interval A); (ii) a relatively high δ13Ccarb anomaly with unaltered 87Sr/86Sr ratios (up to 0.7086) in the middle section corresponding to the lower part of Doushantuo Member 3 (Interval B); and (iii) a negative δ13Ccarb anomaly with lowered δ values in the upper section can be correlated to the long interval of negative δ13Ccarb (Interval C). The Gaskiers glaciation is likely represented in Interval A, and Interval C corresponds to the Shuram excursion reported for other Ediacaran localities. Our correlations confirm the depth gradient of δ13Ccarb in the Yangtze platform and imply that reductive conditions prevailed in the basinal section from the Early to Middle Ediacaran. Under such conditions, anaerobic degradation of organic carbon or methane perturbed the inorganic carbon isotopic compositions and was at least partly responsible for the depth gradient of δ13Ccarb.  相似文献   

6.
The origin and the chemical and isotopic evolution of dissolved inorganic carbon (DIC) in groundwater of the Okavango Delta in semi-arid Botswana were investigated using DIC and major ion concentrations and stable oxygen, hydrogen and carbon isotopes (δD, δ18O and δ13CDIC). The δD and δ18O indicated that groundwater was recharged by evaporated river water and unevaporated rain. The river water and shallow (<10 m) groundwater are Ca–Na–HCO3 type and the deep (≥10 m) groundwater is Na–K–HCO3 to HCO3–Cl–SO4 to Cl–SO4–HCO3. Compared to river water, the mean DIC concentrations were 2 times higher in shallow groundwater, 7 times higher in deep groundwater and 24 times higher in island groundwater. The δ13CDIC indicate that DIC production in groundwater is from organic matter oxidation and in island groundwater from organic matter oxidation and dissolution of sodium carbonate salts. The ionic and isotopic evolution of the groundwater relative to evaporated river water indicates two independent pools of DIC.  相似文献   

7.
We measured the concentrations of dissolved inorganic carbon (DIC) and major ions and the stable carbon isotope ratios of DIC (δ13CDIC) in two creeks discharging from carbonate‐rich sulphide‐containing mine tailings piles. Our aim was to assess downstream carbon evolution of the tailings discharge as it interacted with the atmosphere. The discharge had pH of 6.5–8.1 and was saturated with respect to carbonates. Over the reach of one creek, the DIC concentrations decreased by 1.1 mmol C/l and δ13CDIC increased by ~4.0‰ 200 m from the seep source. The decrease in the DIC concentrations was concomitant with decreases in the partial pressure of CO2(aq) because of the loss of excess CO2(aq) from the discharge. The corresponding enrichment in the δ13CDIC is because of kinetic isotope fractionation accompanying the loss of CO2(g). Over the reach of the other creek, there was no significant decrease in the DIC concentrations or notable changes in the δ13CDIC. The insignificant change in the DIC concentrations and the δ13CDIC is because the first water sample was collected 160 m away from the discharge seep, not accessible during this research. In this case, most of the excess CO2(aq) was lost before our first sampling station. Our results indicate that neutral discharges from tailings piles quickly lose excess CO2(aq) to the atmosphere and the DIC becomes enrich in 13C. We suggest that a significant amount of carbon cycling in neutral discharges from tailings piles occur close to the locations where the discharge seeps to the surface. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

8.
Aquatic plants are essential for maintaining the diversity and stability of a lake ecosystem. Stable carbon isotopes (δ13C) of macrophytes have been widely used as a powerful tool to study ecological processes and paleoenvironmental evolution in lakes. Varying results are obtained when using the δ13C of macrophytes to study the changes in the lake environment at different spatio-temporal scales. Thus, sample preparation and subsequent laboratory analyses are crucial for studying environmental changes using the isotopic signal retained in the macrophytes, and are essential for the interpretation of isotope-environment relationships. This study analyzed the δ13C of different tissue components of macrophytes in three lakes of the lower Yangtze River basin, and a correlation analysis was performed on aquatic environments influencing the δ13C values in the different tissue components of macrophytes. The test results showed the difference between the δ13C values of the whole sample and cellulose. Relative analyses indicated that the major factors contributing to the δ13C variability in macrophytes were pH and the concentration of dissolved inorganic carbon (DIC). The δ13C of α-cellulose (δ13CAC) is more sensitive to environmental variables than that of the whole sample (δ13CW) and holocellulose (δ13CHC). The results of this study imply that extraction of α-cellulose is a prerequisite for research on the changes in lake environment using δ13C of macrophytes. This study aims to provide theoretical and data basis for further research on the environmental and ecological change using stable carbon isotopes of aquatic plants.  相似文献   

9.
Dissolved inorganic carbon isotope (δ13CDIC) is an important tool to reveal the carbon cycle in lake systems. However, there are only few studies focusing on the spatial variation of δ13CDIC of closed lakes. Here we analyze the characteristics of δ13CDIC of 24 sampled lakes (mainly closed lakes) across the Qiangtang Plateau (QTP) and identify the driving factors for its spatial variation. The δ13CDIC value of these observed lakes varies in the range of ? 15·0 to 3·2‰, with an average value of ? 1·2‰. The δ13CDIC value of closed lakes is close to the atmospheric isotopic equilibrium value, much higher than that in rivers and freshwater lakes reported before. The high δ13CDIC value of closed lakes is mainly attributed to the significant contribution of carbonate weathering in the catchment and the evasion of dissolved CO2 induced by the strong evaporation of lake water. The δ13CDIC value of closed lakes has a logarithmic correlation with water chemistry (TDS, DIC and pCO2), also suggesting that the evapo‐concentration of lake water can influence the δ13CDIC value. The δ13CDIC value shows two opposite logarithmic correlations with lake size depending on the δ13CDIC range. This study suggests that the δ13C in carbonates in lacustrine sediments can be taken as an indicator of lake volume variation in closed lakes on QTP. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

10.
Graphite comprises about 2% of some of the 3.8-AE metamorphosed sedimentary rocks of Isukasia, west Greenland. δ13CPDB of carbon in this graphite ranges from ?16.0 to ?9.3‰. For those samples that contain both graphite and siderite, Δcarbonate-graphite is about 6; this fractionation is consistent with an inorganic equilibrium between siderite and graphite at roughly 400–500°C. It is likely that graphite found in these rocks formed by the reaction: 6FeCO3 = 2Fe3O4 + 5CO2 +C in which case it is of little help in determining whether or not organisms were active 3.8 AE ago. The presence of quartz-magnetite-cummingtonite-iron formation in the Isukasia metasedimentary sequence may, ultimately, be one of the most powerful environmental indicators remaining in these rocks.  相似文献   

11.
Stable isotopic signatures (δ13C and δ15N) and C/N ratios of suspended particulate organic matter (POM) were investigated from the surface water of Daya Bay during summer and winter of 2015. The relatively high δ13CPOM values suggested the input of 13C-depleted terrigenous organic matter was low in Daya Bay. There were significant correlations between δ13CPOM values and chlorophyll a concentrations both during summer and winter, suggesting the δ13CPOM values were mainly controlled by the phytoplankton biomass in the surface water. The distribution of δ15NPOM values was more complicated than that of δ13CPOM and displayed low values in the outer bay and the Dan'ao River estuary. 15N-depleted ammonia originating from industrial wastewater might have strongly influenced the water quality and stable isotopic signatures of POM near the Dan'ao River estuary. The δ13CPOM and δ15NPOM values strongly reflect the influences of anthropogenic activity and eutrophication in Daya Bay.  相似文献   

12.
Horizontal drilling and hydraulic fracturing have enhanced unconventional hydrocarbon recovery but raised environmental concerns related to water quality. Because most basins targeted for shale‐gas development in the USA have histories of both active and legacy petroleum extraction, confusion about the hydrogeological context of naturally occurring methane in shallow aquifers overlying shales remains. The Karoo Basin, located in South Africa, provides a near‐pristine setting to evaluate these processes, without a history of conventional or unconventional energy extraction. We conducted a comprehensive pre‐industrial evaluation of water quality and gas geochemistry in 22 groundwater samples across the Karoo Basin, including dissolved ions, water isotopes, hydrocarbon molecular and isotopic composition, and noble gases. Methane‐rich samples were associated with high‐salinity, NaCl‐type groundwater and elevated levels of ethane, 4He, and other noble gases produced by radioactive decay. This endmember displayed less negative δ13C‐CH4 and evidence of mixing between thermogenic natural gases and hydrogenotrophic methane. Atmospheric noble gases in the methane‐rich samples record a history of fractionation during gas‐phase migration from source rocks to shallow aquifers. Conversely, methane‐poor samples have a paucity of ethane and 4He, near saturation levels of atmospheric noble gases, and more negative δ13C‐CH4; methane in these samples is biogenic and produced by a mixture of hydrogenotrophic and acetoclastic sources. These geochemical observations are consistent with other basins targeted for unconventional energy extraction in the USA and contribute to a growing data base of naturally occurring methane in shallow aquifers globally, which provide a framework for evaluating environmental concerns related to unconventional energy development (e.g., stray gas).  相似文献   

13.
In the process of methane oxidation by nitrite ion, the latter, when in high concentration, inhibits the oxidation process. The effect of inhibition is incorporated in the proposed model, describing the dynamics of anaerobic oxidation of methane and its heavy fractions δ13CH4 and δC2H1H3 by nitrite ion. Two substrates—methane and nitrite—are considered in a modified Monod function, describing the oxidation rate. The model is calibrated against experimental data given in [8]. The dynamic behavior of the system under a deficiency of methane or nitrite ion is described. The dynamics of δ13CH4 and δC2H1H3 are shown to be governed by the oxidation dynamics of total methane CH4. By contrast to the conventional opinion that Rayleigh equation corresponds to 1st-order kinetics in terms of substrate concentration, this study shows that Rayleigh equation can be derived from dynamic equations for methane with heavy isotopes (13C and 2H), whatever the kinetic type of total methane oxidation.  相似文献   

14.
Immediately before the extinction of the end‐Guadalupian (Middle Permian; ca 260 Ma), a significant change to the global carbon cycle occurred in the superocean Panthalassa, as indicated by a prominent positive δ13C excursion called the Kamura event. However, the causes of this event and its connection to the major extinction of marine invertebrates remain unclear. To understand the mutual relationships between these changes, we analyzed the sulfur isotope ratio of the carbonate‐associated sulfate (CAS) and HCl‐insoluble residue, as well as the carbon isotope ratio of bulk organic matter, for the Middle‐Upper Permian carbonates of an accreted mid‐oceanic paleo‐atoll complex from Japan, where the Kamura event was first documented. We detected the following unique aspects of the stable carbon and sulfur isotope records. First, the extremely high δ13C values of carbonate (δ13Ccarb) over +5 ‰ during the Capitanian (late Guadalupian) were associated with large isotopic differences between carbonate and organic matter (Δ13C = δ13Ccarb ? δ13Corg). We infer that the Capitanian Kamura event reflected an unusually large amount of dissolved organic matter in the expanded oxygen minimum zone at mid‐depth. Second, the δ34S values of CAS (δ34SCAS) were inversely correlated with the δ13Ccarb values during the Capitanian to early Wuchiapingian (early Late Permian) interval. The Capitanian trend may have appeared under increased oceanic sulfate conditions, which were accelerated by intense volcanic outgassing. Bacterial sulfate reduction with increased sulfate concentrations in seawater may have stimulated the production of pyrite that may have incorporated iron in pre‐existing iron hydroxide/oxide. This stimulated phosphorus release, which enhanced organic matter production and resulted in high δ13Ccarb. Low δ34SCAS values under high sulfate concentrations were maintained and the continuous supply of sulfate cannot by explained only by the volcanic eruption of the Emeishan Trap, which has been proposed as a cause of the extinction. The Wuchiapingian δ34SCAS–δ13Ccarb correlation, likely related to low sulfate concentration, may have been caused by the removal of oceanic sulfate through the massive evaporite deposition.  相似文献   

15.
We present a time series of carbon and oxygen stable isotope records of the last 30?000 14C years throughout the last glacial-postglacial cycle from western Qinghai-Xizhang (Tibet) Plateau. A 20-m core drilled in the south basin of Zabuye Salt Lake was analyzed for inorganic and organic carbon and total sulfur contents, δ13C and δ18O values of carbonates. Our results indicate that climatic changes have led to a drastic negative shift of stable isotope ratios at the transition between the Last Full Glacial and the postglacial phase during Later Pleistocene times (∼16.2 kyr BP), and a rapid positive shift at the transition from Pleistocene to Holocene (∼10.6 kyr BP). The first shift is marked by the drop of δ18Ocarb values of about 10‰ (from +2 to −8‰) and δ13Ccarb values of about 3‰ (from 5 to 2‰). The second shift which occurred at the transition from Pleistocene to Holocene was of similar magnitude but in the opposite direction. Isotope data, combined with total organic and inorganic carbon contents and the lithological composition of the core, suggest this lake was an alluvial pre-lake environment prior to ca. 28 14C kyr BP. During ca. 28-16.2 14C kyr BP, Zabuye Lake was likely a moderately deep lake with limited outflow. The cool and arid glacial climate led the lake level to drop drastically. Extended residence time overwhelmed the lower temperature and caused a steady increase of δ13Ccarb and δ18Ocarb values and total inorganic carbon content in the sediments. During ca. 16.2-10.6 14C kyr BP, this lake probably overflowed and received abundant recharge from melting glaciers when the deglaciation was in its full speed. A spike of markedly enhanced δ13Ccarb and δ18Ocarb is seen at ∼11.5 kyr BP, probably due to the isotopic effects left behind by the short but severe Younger Dryas (YD) event. After ca. 10.6 14C kyr BP, Zabuye Lake probably closed its surface outflow, due to strong desiccation and drastic climate warming. The Early and Middle Holocene were characterized by unstable climatic conditions with alternating warmer/cooler episodes as indicated by the severe fluctuations of total organic carbon, δ13C and δ18O values. A hypersaline salt lake environment was finally formed at Zabuye after ∼5 14C kyr BP when the mirabilite and halite concentrations steadily increased and became the dominant minerals in the sediments. Severe imbalance of inflow/outflow resulted in the drastic increase of total sulfur, δ13Ccarb and δ18Ocarb values and dominance of halite in the lake since ca. 3.8 kyr BP to present.  相似文献   

16.
The Flin Flon Belt of Canada contains Paleoproterozoic volcanic–sedimentary sequences that are related to the Trans‐Hudson Orogeny. The sequences include island arc volcanic and volcaniclastic rocks (Amisk Group) that are unconformably overlain by subaerial sedimentary rocks (Missi Group), and younger deep facies sediments. In the Flin Flon area, several north–south trending faults divide the sequences into blocks and obscure the depositional environment of the deep facies sediments. Locally, within the Flin Flon area, the Embury Lake Formation is in fault contact with island arc volcanic–sedimentary sequences of the Amisk and Missi Groups. To identify the depositional environment of the Embury Lake Formation, we used lithologic and geochemical approaches. Here, we report carbon isotopic values in organic matter (δ13Corg) and sulfur isotopes (δ34S), as well as total organic carbon and total sulfur measurements for the black shale in the formation. Samples were taken from a drill core that contains alternating bands of sandstone and black shale. Pyrite in the black shale is divided into four textural types: euhedral, vein‐type, elliptical, and microcrystalline. Microcrystalline pyrite is typically generated by microbially mediated sulfate reduction. An extremely low S/C ratio (avg. = 0.04) is consistent with lacustrine deposition. The ranges of δ13Corg (?36 ‰ to ?27 ‰) and δ34S (+3.0 ‰ to +7.7 ‰) values can be explained by bacterial photosynthesis that involved Calvin cycle and acetyl CoA pathways, and sulfate reduction in a low‐sulfate environment. Considering the depositional age reported in a previous study of < 1.84 Ga, the Embury Lake Formation was likely emplaced in a lacustrine setting during the Trans‐Hudson Orogeny.  相似文献   

17.
According to gas compositional and carbon isotopic measurement of 114 gas samples from the Kuqa depression, accumulation of the natural gases in the depression is dominated by hydrocarbon gases, with high gas dryness (C1/C1–4) at the middle and northern parts of the depression and low one towards east and west sides and southern part. The carbon isotopes of methane and its homologues are relatively enriched in 13C, and the distributive range of δ 13C1, δ 13C2 and δ 13C3 is ?32‰–?36‰, ?22‰–?24‰ and ?20‰–?22‰, respectively. In general, the carbon isotopes of gaseous alkanes become less negative with the increase of carbon numbers. The δ 13 \(C_{CO_2 } \) value is less than ?10‰ in the Kuqa depression, indicating its organogenic origin. The distributive range of 3He/4He ratio is within n × 10?8 and a decrease in 3He/4He ratio from north to south in the depression is observed. Based on the geochemical parameters of natural gas above, natural gas in the Kuqa depression is of characteristics of coal-type gas origin. The possible reasons for the partial reversal of stable carbon isotopes of gaseous alkanes involve the mixing of gases from one common source rock with different thermal maturity or from two separated source rock intervals of similar kerogen type, multistages accumulation of natural gas under high-temperature and over-pressure conditions, and sufficiency and diffusion of natural gas.  相似文献   

18.
Closely spaced samples (285 in number) of varved sediments from the Upper Permian in Delaware Basin, Texas, have been analyzed for δ13Ccarb, δ13Corg, δ18Ocarb, Corg, Ccarb, and calcite/dolomite. δ13C records a dramatic rise from ?2.8 to +5.7‰ in only 4400 years, detected in three sections across the basin, extrapolating smoothly through a 600-year interruption by a local (west side of the basin) fresh-water inflow evidenced by low δ18O. This continuity and low Corg within the basin, both indicate that the excess net deposition of Corg, necessary to generate the rise in δ13C, took place in the ocean external to the Delaware Basin. Correlation with similar records from the Zechstein Basin suggest that the event was world-wide, although this poses obvious difficulties for the carbon cycle. The rate of rise of δ13C, and its sustained high level, must imply conversions of oxidized carbon to reduced carbon that are very large depending on which reservoirs were involved.  相似文献   

19.
In regions where aquifers sustain rivers, the location and quantification of groundwater discharge to surface water are important to prevent pollution hazards, to quantify and predict low flows and to manage water supplies. 222Rn is commonly used to determine groundwater discharge to rivers. However, using this isotopic tracer is challenging because of the high diffusion capacity of 222Rn in open water. This study illustrates how a combination of isotopic tracers can contribute to an enhanced understanding of groundwater discharge patterns in small rivers. The aim of this paper is to combine 222Rn and δ13CDIC to better constrain the physical parameters related to the degassing process of these tracers in rivers. The Hallue River (northern France) was targeted for this study because it is sustained almost exclusively by a fractured chalk aquifer. The isotopes 222Rn, δ13CDIC, δ2H and δ18O were analysed along with other natural geochemical tracers. A mass balance model was used to simulate 222Rn and δ13CDIC. The results of δ2H and δ18O analyses prove that evaporation did not occur in the river. The calibration of a numerical model to reproduce 222Rn and δ13CDIC provides a best‐fit diffusive layer thickness of 3.21 × 10?5 m. This approach is particularly useful for small rivers flowing over carbonate aquifers with high groundwater DIC where the evolution of river DIC reflects the competing processes of groundwater inflow and CO2 degassing. This approach provides a means to evaluate groundwater discharge in small ungauged rivers. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

20.
Biodegradation of organic compounds in groundwater can be a significant source of methane in contaminated sites. Methane might accumulate in indoor spaces posing a hazard. The increasing use of ethanol as a gasoline additive is a concern with respect to methane production since it is easily biodegraded and has a high oxygen demand, favoring the development of anaerobic conditions. This study evaluated the use of stable carbon isotopes to distinguish the methane origin between gasoline and ethanol biodegradation, and assessed the occurrence of methane in ethanol fuel contaminated sites. Two microcosm tests were performed under anaerobic conditions: one test using ethanol and the other using toluene as the sole carbon source. The isotopic tool was then applied to seven field sites known to be impacted by ethanol fuels. In the microcosm tests, it was verified that methane from ethanol (δ13C = −11.1‰) is more enriched in 13C, with δ13C values ranging from −20‰ to −30‰, while the methane from toluene (δ13C = −28.5‰) had a carbon isotopic signature of −55‰. The field samples had δ13C values varying over a wide range (−10‰ to −80‰), and the δ13C values allowed the methane source to be clearly identified in five of the seven ethanol/gasoline sites. In the other two sites, methane appears to have been produced from both sources. Both gasoline and ethanol were sources of methane in potentially hazardous concentrations and methane could be produced from organic acids originating from ethanol along the groundwater flow system even after all the ethanol has been completed biodegraded.  相似文献   

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