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1.
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.  相似文献   

2.
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.  相似文献   

3.
M. F. Billett  T. R. Moore 《水文研究》2008,22(12):2044-2054
Carbon dioxide (CO2) and methane (CH4) concentrations and evasion rates were measured in surface waters draining Mer Bleue peatland (Ontario, Canada) between spring and autumn 2005. All sites exhibit a consistent pattern of supersaturation throughout the year, which is broadly related to hydrological and temperature changes between spring snowmelt and autumn freezing. Both measurements and estimates of CO2 and CH4 evasion from open water to the atmosphere suggest that parts of the catchment (including beaver dams) are significant degassing hot spots. We present data showing how vertical gaseous carbon fluxes compare with lateral carbon fluxes and make an initial estimate of the importance to the overall carbon budget of CO2 and CH4 evasion to the atmosphere from water surfaces at Mer Bleue. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

4.
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.  相似文献   

5.
煤岩吸附二氧化碳气体的CT实验研究   总被引：1，自引：0，他引：1  
利用工业CT技术及应变测量研究不同气压下煤岩的二氧化碳气体吸附性质。研究发现：煤样的应变随吸附时间和气体压力的增加而增加,且在不同方向是不同的,吸附气体导致煤样孔隙率增加;煤样CT图像的灰度均值和灰度标准差随吸附时间和气体压力的增长都表现出增加的趋势。结果表明：吸附二氧化碳导致煤样总体发生膨胀变形,这为吸附提供更多的孔隙表面积而使吸附气体量增加,含气煤样的密度也因此而增大;气体吸附导致的煤样密度均值增加的效应大于体积膨胀导致的煤样密度均值减小的效应;吸附使煤样内部物质分布不均匀程度增加。  相似文献   

6.
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.  相似文献   

7.
Estimates of greenhouse gas evasion from rivers have been refined over the past decades to constrain their role in global carbon cycle processes. However, despite 55% of the human population living in urban areas, urban rivers have had limited attention. We monitored carbon dynamics in an urbanized river (River Kelvin, 331 km2, UK) to explore the drivers of dissolved carbon lateral and vertical export. Over a 2-year sampling period, riverine methane (CH4) and carbon dioxide (CO2) concentrations were consistently oversaturated with respect to atmospheric equilibria, leading to continual degassing to the atmosphere. Carbon stable isotopic compositions (δ13C) indicated that terrestrially derived carbon comprised most of the riverine CH4 and dissolved CO2 (CO2*) load while dissolved inorganic carbon (DIC) from groundwater was the main form of riverine DIC. The dynamics of CH4, CO2*, and DIC in the river were primarily hydrology-controlled, that is, [CH4] and [CO2*] both increased with elevated discharge, total [DIC] decreased with elevated discharge while the proportion of biologically derived DIC increased with increasing discharge. The concentration of dissolved organic carbon (DOC) showed a weak relationship with river hydrology in summer and autumn and was likely influenced by the combined sewer overflows. Carbon emission to the atmosphere is estimated to be 3.10 ± 0.61 kg C·m−2·yr−1 normalized to water surface area, with more than 99% emitted as CO2. Annual carbon loss to the coastal estuary is approximately 4.69 ± 0.70 Gg C yr−1, with annual DIC export approximately double that of DOC. Per unit area, the River Kelvin was a smaller carbon source to the atmosphere than natural rivers/streams but shows elevated fluxes of DIC and DOC under comparable conditions. This research illustrates the role urban systems may have on riverine carbon dynamics and demonstrates the potential tight link between urbanization and riverine carbon export.  相似文献   

8.
We characterize and quantify volatile emissions at Hot Spring Basin (HSB), a large acid-sulfate region that lies just outside the northeastern edge of the 640 ka Yellowstone Caldera. Relative to other thermal areas in Yellowstone, HSB gases are rich in He and H2, and mildly enriched in CH4 and H2S. Gas compositions are consistent with boiling directly off a deep geothermal liquid at depth as it migrates toward the surface. This fluid, and the gases evolved from it, carries geochemical signatures of magmatic volatiles and water–rock reactions with multiple crustal sources, including limestones or quartz-rich sediments with low K/U (or 40?Ar/4?He). Variations in gas chemistry across the region reflect reservoir heterogeneity and variable degrees of boiling. Gas-geothermometer temperatures approach 300 °C and suggest that the reservoir feeding HSB is one of the hottest at Yellowstone. Diffuse CO2 flux in the western basin of HSB, as measured by accumulation-chamber methods, is similar in magnitude to other acid-sulfate areas of Yellowstone and is well correlated to shallow soil temperatures. The extrapolation of diffuse CO2 fluxes across all the thermal/altered area suggests that 410 ± 140 t d− 1 CO2 are emitted at HSB (vent emissions not included). Diffuse fluxes of H2S were measured in Yellowstone for the first time and likely exceed 2.4 t d− 1 at HSB. Comparing estimates of the total estimated diffuse H2S emission to the amount of sulfur as SO42− in streams indicates ~ 50% of the original H2S in the gas emission is lost into shallow groundwater, precipitated as native sulfur, or vented through fumaroles. We estimate the heat output of HSB as ~ 140–370 MW using CO2 as a tracer for steam condensate, but not including the contribution from fumaroles and hydrothermal vents. Overall, the diffuse heat and volatile fluxes of HSB are as great as some active volcanoes, but they are a small fraction (1–3% for CO2, 2–8% for heat) of that estimated for the entire Yellowstone system.  相似文献   

9.
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...  相似文献   

10.
A systematic approach was used to characterize the biosorption of copper(II) onto two biosorbents, Posidonia oceanica and peat, focusing on the interaction mechanisms, the copper(II) sorption–desorption process and the thermal behavior of the biosorbents. Sorption isotherms at pH 4–6 were obtained and the experimental data were fitted to the Langmuir model with a maximum uptake (qmax) at pH 6 of 85.78 and 49.69 mg g?1, for P. oceanica and peat, respectively. A sequential desorption (SD) with water, Ca(NO3)2, and EDTA was applied to copper‐saturated biosorbents. Around 65–70% copper(II) were desorbed with EDTA, indicating that this heavy metal was strongly bound. The reversibility of copper(II) sorption was obtained by desorption with HCl and SD. Fourier transform IR spectroscopy (FTIR) analysis detected the presence of peaks associated with OH groups in aromatic and aliphatic structures, CH, CH2, and CH3 in aliphatic structures, COO? and COOH groups and unsaturated aromatic structures on the surface of both biosorbents, as well as peaks corresponding to Si? O groups on the surface of peat. The results of SEM‐EDX and FTIR analysis of copper‐saturated samples demonstrated that ion exchange was one of the mechanisms involved in copper(II) retention. Thermal analysis of biosorbent samples showed that copper(II) sorption–desorption processes affected the thermal stability of the biosorbents.  相似文献   

11.
This paper focuses on the chemical and isotopic features of dissolved gases (CH4 and CO2) from four meromictic lakes hosted in volcanic systems of Central–Southern Italy: Lake Albano (Alban Hills), Lake Averno (Phlegrean Fields), and Monticchio Grande and Piccolo lakes (Mt. Vulture). Deep waters in these lakes are characterized by the presence of a significant reservoir of extra-atmospheric dissolved gases mainly consisting of CH4 and CO2. The δ13C-CH4 and δD-CH4 values of dissolved gas samples from the maximum depths of the investigated lakes (from ?66.8 to ?55.6?‰ V-PDB and from ?279 to ?195?‰ V-SMOW, respectively) suggest that CH4 is mainly produced by microbial activity. The δ13C-CO2 values of Lake Grande, Lake Piccolo, and Lake Albano (ranging from ?5.8 to ?0.4?‰ V-PDB) indicate a significant CO2 contribution from sublacustrine vents originating from (1) mantle degassing and (2) thermometamorphic reactions involving limestone, i.e., the same CO2 source feeding the regional thermal and cold CO2-rich fluid emissions. In contrast, the relatively low δ13C-CO2 values (from ?13.4 to ?8.2?‰ V-PDB) of Lake Averno indicate a prevalent organic CO2. Chemical and isotopic compositions of dissolved CO2 and CH4 at different depths are mainly depending on (1) CO2 inputs from external sources (hydrothermal and/or anthropogenic); (2) CO2–CH4 isotopic exchange; and (3) methanogenic and methanotrophic activity. In the epilimnion, vertical water mixing, free oxygen availability, and photosynthesis cause the dramatic decrease of both CO2 and CH4 concentrations. In the hypolimnion, where the δ13C-CO2 values progressively increase with depth and the δ13C-CH4 values show an opposite trend, biogenic CO2 production from CH4 using different electron donor species, such as sulfate, tend to counteract the methanogenesis process whose efficiency achieves its climax at the water–bottom sediment interface. Theoretical values, calculated on the basis of δ13C-CO2 values, and measured δ13CTDIC values are not consistent, indicating that CO2 and the main carbon-bearing ion species (HCO3 ?) are not in isotopic equilibrium, likely due to the fast kinetics of biochemical processes involving both CO2 and CH4. This study demonstrates that the vertical patterns of the CO2/CH4 ratio and of δ13C-CO2 and δ13C-CH4 are to be regarded as promising tools to detect perturbations, related to different causes, such as changes in the CO2 input from sublacustrine springs, that may affect aerobic and anaerobic layers of meromictic volcanic lakes.  相似文献   

12.
三峡水库澎溪河消落区土-气界面CO2和CH4通量初探   总被引：1，自引：0，他引：1  
李哲  张利萍  王琳  郭劲松  高旭  方芳  蒋滔 《湖泊科学》2013,25(5):674-680
水库近岸湿地(消落区)温室气体(CO2、CH4)产汇是水库温室气体效应问题的重要组成部分.本文以三峡水库支流澎溪河的白家溪、养鹿两处大面积消落区为研究对象,于2010年6 9月水库低水位运行期间,对近岸消落区土-气界面CO2、CH4通量进行监测.白家溪消落区土-气界面CO2通量均值为12.38±2.42 mmol/(m2·h);CH4通量均值为0.0112±0.0064 mmol/(m2·h).养鹿消落区CO2、CH4通量均值分别为10.54±5.17、0.14±0.16 mmol/(m2·h).总体上,6 9月土-气界面CO2通量呈增加趋势,而CH4通量水平呈现显著的递减趋势.消落区土地出露后植被恢复,在一定程度上促进了土壤有机质含量的增加,使得6 9月CO2释放通量的总体趋势有所增加.消落区退耕后,其甲烷氧化菌的活性得到恢复,加之在土地出露曝晒过程中土壤透气性增强,使得消落区土壤对大气中CH4吸收氧化潜势增强.尽管如此,仍需进一步的研究以明晰消落区土-气界面CO2、CH4产汇的主要影响因素.  相似文献   

13.
In the Whitehall Forest of Georgia during the 1985-86 non-growing season soil CO2 varied with soil depth, varied spatially at constant depth, and varied temporally with changing environmental conditions. Variations with depth in the upper 1.4 m of the soil were of greater magnitude than temporal variations and spatial differences at 30 cm depth were of lesser magnitude. Mean soil CO2 in evergreen forest was higher (0.207 per cent) than in deciduous and mixed forest (0.157 per cent). There were no trends in soil CO2 along hillslopes or with changes in soil texture, bulk density, moisture content, or temperature. Soil CO2 did increase near trees possibly due to increased root densities and/or more numerous pockets of microbial activity. For CO2 at 30 cm depth, two variables–the mean daily temperature range in the month before measurement and actual evapotranspiration in the week before measurement (AET7)–explained 76 per cent of the variation in mean soil CO2. At the profile site, where soil CO2 was measured at five depths, 66 per cent of the variability in CO2 was explained by soil depth, AET7, and the average daily temperature range in the two months before measurement.  相似文献   

14.
This study investigated CO2 degassing and related carbon isotope fractionation effects in the Wiesent River that drains a catchment in the karst terrain of the Franconian Alb, Southern Germany. The river was investigated by physico‐chemical and stable isotope analyses of water and dissolved inorganic carbon during all seasons along 65‐km long downstream transects between source and mouth. Calculated pCO2 values at the source were 21 400 ± 2400 µatm. The pCO2 rapidly decreased in the river water and dropped to an average of 1240 ± 330 µatm near the mouth. About 90% of this decrease occurred within the first 6 km of the river. The river was supersaturated with respect to CO2 over its entire course and must have acted as a continuous year‐round CO2 source to the atmosphere. The average CO2 flux from the karst river was estimated with 450 mmol m?2 day?1 with higher fluxes up to 5680 mmol m?2 day?1 at the source. At the source, δ13CDIC values showed no seasonal variations with an average of ?14.2 ± 0.2‰. This indicated that groundwater retained high pCO2 mainly from soil CO2. The contribution of soil CO2 to dissolved inorganic carbon was estimated at 65% to 72%. The downstream CO2 loss caused a positive shift in δ13CDIC values of 2‰ between source and mouth because of the preferential loss of the 12C isotope during degassing. Considering the findings of this study and the fact that carbonate lithology covers a significant part of the earth's surface, CO2 evasion from karst regions might contribute notably to the annual carbon dioxide release from global freshwater systems. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

15.
Soils release more carbon, primarily as carbon dioxide (CO2), per annum than current global anthropogenic emissions. Soils emit CO2 through mineralization and decomposition of organic matter and respiration of roots and soil organisms. Given this, the evaluation of the effects of abiotic factors on microbial activity is of major importance when considering the mitigation of greenhouse gases emissions. Previous studies demonstrate that soil CO2 emission is significantly affected by temperature and soil water content. A limited number of studies have illustrated the importance of bulk density and soil surface characteristics as a result of exposure to rain on CO2 emission, however, none examine their relative importance. Therefore, this study investigated the effects of soil compaction and exposure of the soil surface to rainfall and their interaction on CO2 release. We conducted a factorial laboratory experiment with three soil types after sieving (clay, silt and sand soil), three different bulk densities (1·1 g cm–3, 1·3 g cm–3, 1·5 g cm–3) and three different exposures to rainfall (no rain, 30 minutes and 90 minutes of rainfall). The results demonstrated CO2 release varied significantly with bulk density, exposure to rain and time. The relationship between rain exposure and CO2 is positive: CO2 emission was 53% and 42% greater for the 90 minutes and 30 minutes rainfall exposure, respectively, compared to those not exposed to rain. Bulk density exhibited a negative relationship with CO2 emission: soil compacted to a bulk density of 1·1 g cm–3 emitted 32% more CO2 than soil compacted to 1·5 g cm–3. Furthermore we found that the magnitude of CO2 effluxes depended on the interaction of these two abiotic factors. Given these results, understanding the influence of soil compaction and raindrop impact on CO2 emission could lead to modified soil management practices which promote carbon sequestration. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

16.
Carbon dioxide is one of the first gases to escape the magmatic environment due to its low solubility in basaltic magmas at low pressures. The exsolved CO2 gas migrates towards the surface through rock fractures and high permeability paths. If an aquifer is located between the magmatic environment and the surface, a fraction of the CO2 emitted is dissolved in the aquifer. In this paper, an estimation of the water mass balance and the CO2 budget in Las Cañadas aquifer, Tenerife, Canary Islands, is presented. Magmatic CO2 is transported by groundwater and discharged through man-made sub-horizontal drains or galleries that exist in this island, and by the flow of groundwater discharged laterally towards other aquifers or to the ocean. In addition, the pCO2 at the gallery mouth (or entrance) and at the gallery bottom (internal and deepest discharge point where the gallery starts) are calculated and mapped. The total CO2 advectively transported by groundwater is estimated to range from 143 to 211 t CO2 d?1. Considering that the diffuse soil emission of CO2 for the same area is 437 t d?1, the diffuse/dissolved CO2 flux ratio varies between 2 and 3. The high dissolved inorganic carbon content of groundwater explains the ability of this low temperature hydrothermal water to dissolve and transfer magmatic CO2 at volcanoes, even during quiescence periods.  相似文献   

17.
采用室内培养的方法,以富营养化湖泊太湖为例,研究了沉积物有机质矿化过程中碳、氮、磷的迁移特征.结果表明,在沉积物中的有机质矿化过程中,碳以溶解性无机碳释放至水中,同时以CH4和CO2形式释放至大气中,培养结束时,CH4和CO2累积排放含量分别为1492.21和498.96 mg/g(dw),其中CH4占气态碳的89.16%(以C质量计);此外,大量的氮、磷营养盐释放至上覆水体,水中总氮、总磷和铵态氮的最高浓度分别是初始浓度的62.16、28.16和139.45倍,而硝态氮浓度在整个培养过程中逐渐下降,培养末期浓度是初期的0.21倍;厌氧条件下,沉积物有机质的矿化,不仅可以生成大量的CH4、CO2气体,还能够促使沉积物中铵态氮和磷的释放;而沉积物有机质矿化释放的碳、氮、磷营养元素又能加剧湖泊富营养化程度,促进湖泊水体的初级生产力,从而增加湖泊沉积物有机质输入.这样的循环方式可能是湖泊富营养化自维持的重要机制之一.  相似文献   

18.
The atmospheric carbon dioxide (CO2) concentration has been consistently increasing each year throughout the world. Internal combustion (IC) engines are significant contributors to CO2 emissions. This study explores the possibility of employing effective biomass-based adsorbents to mitigate CO2 from a diesel engine exhaust. As a first step, two distinct agro-wastes, namely, i) corn cob and ii) sugarcane bagasse, are used to prepare inexpensive and efficient activated carbons. The two main steps in the activated carbon preparation are a) carbonization and b) activation. The derived activated carbons are subjected to discrete analytical techniques to examine their structural and textural characteristics, surface functional groups, and physical, chemical, and adsorptive properties. As a second step, the exhaust treatment chamber unit is filled with the adsorbents one by one and is connected to the exhaust of the constant pressure heat addition engine. A single-cylinder, four-stroke, naturally-aspirated, air-cooled, direct injection (DI) compression ignition (CI) engine is used in the experimental investigations. The essential findings show that ≈68 and 60% of CO2 emissions are adsorbed in the test engine by utilizing corn cob and sugarcane bagasse adsorbents, respectively. The results show that during the D100 and JME20 operations, the prospective adsorbents can curb more than 40% of overall CO2 emissions.  相似文献   

19.
Gravel bars (GBs) contribute to carbon dioxide (CO2) emissions from stream corridors, with CO2 concentrations and emissions dependent on prevailing hydraulic, biochemical, and physicochemical conditions. We investigated CO2 concentrations and fluxes across a GB in a prealpine stream over three different discharge‐temperature conditions. By combining field data with a reactive transport groundwater model, we were able to differentiate the most relevant hydrological and biogeochemical processes contributing to CO2 dynamics. GB CO2 concentrations showed significant spatial and temporal variability and were highest under the lowest flow and highest temperature conditions. Further, observed GB surface CO2 evasion fluxes, measured CO2 concentrations, and modelled aerobic respiration were highest at the tail of the GB over all conditions. Modelled CO2 transport via streamwater downwelling contributed the largest fraction of the measured GB CO2 concentrations (31% to 48%). This contribution increased its relative share at higher discharges as a result of a decrease in other sources. Also, it decreased from the GB head to tail across all discharge‐temperature conditions. Aerobic respiration accounted for 17% to 36% of measured surface CO2 concentrations. Zoobenthic respiration was estimated to contribute between 4% and 8%, and direct groundwater CO2 inputs 1% to 23%. Unexplained residuals accounted for 6% to 37% of the observed CO2 concentrations at the GB surface. Overall, we highlight the dynamic role of subsurface aerobic respiration as a driver of spatial and temporal variability of CO2 concentrations and evasion fluxes from a GB. As hydrological regimes in prealpine streams are predicted to change following climatic change, we propose that warming temperatures combined with extended periods of low flow will lead to increased CO2 release via enhanced aerobic respiration in newly exposed GBs in prealpine stream corridors.  相似文献   

20.
Two soil CO2 efflux surveys were carried out in September 1999 and June 2002 to study the spatial distribution of diffuse CO2 degassing and estimate the total CO2 output from Showa-Shinzan volcanic dome, Japan. Seventy-six and 81 measurements of CO2 efflux were performed in 1999 and 2002, respectively, covering most of Showa-Shinzan volcano. Soil CO2 efflux data showed a wide range of values up to 552 g m-2 d-1. Carbon isotope signatures of the soil CO2 ranged from -0.9‰ to -30.9‰, suggesting a mixing between different carbon reservoirs. Most of the study area showed CO2 efflux background values during the 1999 and 2002 surveys (B = 8.2 and 4.4 g m-2 d-1, respectively). The spatial distribution of CO2 efflux anomalies for both surveys showed a good correlation with the soil temperature, indicating a similar origin for the extensive soil degassing generated by condensation processes and fluids discharged by the fumarolic system of Showa-Shinzan. The total diffuse CO2 output of Showa-Shinzan was estimated to be about 14.0–15.6 t d-1 of CO2 for an area of 0.53 km2.  相似文献   

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