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1.
Methane hydrate is a crystalline compound with methane molecules enclosed in cages formed by hydrogen-bonded water molecules. Understanding the mechanism of nucleation and crystal growth from methane vapour and liquid water is important for all hydrate applications. However, processes near the water/methane interface are still unclear. In this work, we focused on the crystal growth of methane hydrate seeds located near the water/methane interface. We performed molecular dynamics (MD) simulation and analysed the crystal growth of the hydrate seed at the interface. New cages formed in the liquid water phase were stabilised when they shared faces with the hydrate seed. We also investigated the crystal growth rate as the time development of the number of methane molecules trapped in hydrate cages, based on the trajectory of the MD simulation. The calculated growth rate in the direction that covers the interface was 1.38 times that in the direction towards the inside of the water phase. 相似文献
2.
Taoufik Saleh Ksiksi Shaijal Babu Thru Ppoyil Abdul Rasheed Palakkott 《Physiology and Molecular Biology of Plants》2018,24(2):251-259
Water stress has been reported to alter morphology and physiology of plants affecting chlorophyll content, stomatal size and density. In this study, drought stress mitigating effects of CO2 enrichment was assessed in greenhouse conditions in the hot climate of UAE. Commercially purchased maize (Zea mays L.) and alfalfa (Medicago sativa L.) were seeded in three different custom-built cage structures, inside a greenhouse. One cage was kept at 1000 ppm CO2, the second at 700 ppm CO2, and the third at ambient greenhouse CO2 environment (i.e. 435 ppm). Three water stress treatments HWS (200 ml per week), MWS (400 ml per week), and CWS (600 ml per week) were given to each cage so that five maize pots and five alfalfa pots in each cage received same water stress treatments. In maize, total chlorophyll content was similar or higher in water stress treatments compared to control for all CO2 concentrations. Stomatal lengths were higher in enriched CO2 environments under water stress. At 700 ppm CO2, stomatal widths decreased as water stress increased from MWS to HWS. At both enriched CO2 environments, stomatal densities decreased compared to ambient CO2 environment. In alfalfa, there was no significant increase in total chlorophyll content under enriched CO2 environments, even though a slight increase was noticed. 相似文献
3.
J. Elizabeth Corbett Malak M. Tfaily David J. Burdige William T. Cooper Paul H. Glaser Jeffrey P. Chanton 《Biogeochemistry》2013,114(1-3):327-340
Although methanogenic pathways generally produce equimolar amounts of carbon dioxide and methane, CO2 concentrations are often reported to be higher than CH4 concentrations in both field and laboratory incubation studies of peat decomposition. In field settings, higher pore water concentrations of CO2 may result from the loss of methane by: (1) ebullition due to the low solubility of methane in pore water and (2) vascular-plant transport. Higher CO2 concentrations may also be caused by: (1) production of additional CO2 by high-molecular weight (HMW) organic matter (OM) fermentation and/or (2) respiration from non-methanogenic pathways. In this study of a peatland where advection and transverse dispersion were the dominant pore water solute transport mechanisms, an isotope-mass balance approach was used to determine the proportions of CO2 formed from non-fractionating OM respiration and HMW fermentation relative to CO2 production from methanogenesis. This approach also allowed us to estimate the loss of CH4 from the belowground system. The pathways of CO2 production varied with depth and surface vegetation type. In a Carex-dominated fen, methane production initially produced 40 % of the total CO2 and then increased to 90–100 % with increasing depth. In a Sphagnum-dominated bog, methanogenesis resulted in 60 % of total CO2 production which increased to 100 % at depth. Both bogs and fens showed 85–100 % of methane loss from pore waters. Our results indicate that the isotopic composition of dissolved CO2 is a powerful indicator to allow partitioning of the processes affecting peat remineralization and methane production. 相似文献
4.
In this study, we perform grand canonical Monte Carlo simulations to evaluate the hydrogen storage capacity of structure I (sI) hydrogen hydrates at pressures up to 500 MPa. Initially, we calculate the upper limit of H2 content of sI hydrates by studying the hypothetical sI hydrate, where H2 is the single guest component. It is found that the storage capacity of the hypothetical pure H2 sI hydrate could reach 3.5 wt% at 500 MPa and 274 K. Depending on pressure, the large cavities of the pure H2 hydrate can accommodate up to three H2 molecules while the small ones are singly occupied at most, even at pressures as high as 500 MPa, without any double occupancy being observed. Subsequently, the binary H2–ethylene oxide (EO) hydrate is examined. In this case, the large cavities are occupied by a single EO molecule while the small cavities can accommodate at most a single H2 molecule. Such configuration results in a maximum H2 content of only 0.37 wt%. The hydrogen storage capacity does not improve significantly even in case when EO is replaced by a component with smaller molecular weight. 相似文献
5.
The dissociation processes of methane and carbon dioxide hydrates were investigated by molecular dynamics simulation. The simulations were performed with 368 water molecules and 64 gas molecules using NPT ensembles. The TraPPE (single-site) and 5-site models were adopted for methane molecules. The EPM2 (3-site) and SPC/E models were used for carbon dioxide and water molecules, respectively. The simulations were carried out at 270 K and 5.0 MPa for hydrate stabilisation. Then, temperature was increased up to 370 K. The temperature increasing rates were 0.1–20 TK/s. The gas hydrates dissociated during increasing temperature or at 370 K. The potential models of methane molecule did not much influence the dissociation process of methane hydrate. The mechanisms of dissociation process were analysed with the coordination numbers and mean square displacements. It was found that the water cages break down first, then the gas molecules escape from the water cages. The methane hydrate was more stable than the carbon dioxide hydrate at the calculated conditions. 相似文献
6.
Dong-Hyuk Chun 《Molecular simulation》2013,39(9):837-844
The hydrogen capacity of the binary THF–H2 sII hydrate is determined by the cage occupancy and by the selectivity of guest molecules. Grand canonical Monte Carlo (GCMC) simulation is used to study the cage occupancy and selectivity of guest molecules from the equilibrium configuration of the binary sII hydrate. The cage framework is regarded as a rigid body and the number of guest molecules is varied to preserve the grand canonical ensemble. The occupancy and selectivity were investigated at a temperature of 270 K for pressures ranging from 0.1 to 200 MPa. It was found that most large cages select THF as guest molecules while small cages include only hydrogen molecules. Multiple occupancy of hydrogen, up to four molecules in large cages and two molecules in small cages, was found as the pressure increases. GCMC results show that the hydrogen capacity is approximately 1.1 wt% at 200 MPa. 相似文献
7.
Carbon dioxide and methane emissions from interfluvial wetlands in the upper Negro River basin, Brazil 总被引:1,自引:0,他引:1
Extensive interfluvial wetlands occur in the upper Negro River basin (Brazil) and contain a mosaic of vegetation dominated by emergent grasses and sedges with patches of shrubs and palms. To characterize the release of carbon dioxide and methane from these habitats, diffusive and ebullitive emissions and transport through plant aerenchyma were measured monthly during 2005 in permanently and seasonally flooded areas. CO2 emissions averaged 2193 mg C m?2 day?1. Methane was consumed in unflooded environments and emitted in flooded environments with average values of ?4.8 and 60 mg C m?2 day?1, respectively. Bubbles were emitted primarily during falling water periods when hydrostatic pressure at the sediment?Cwater interface declined. CO2 and CH4 emissions increased when dissolved O2 decreased and vegetation was more abundant. Total area and seasonally varying flooded areas for two wetlands, located north and south of the Negro River, were determined through analysis of synthetic aperture radar and optical remotely sensed data. The combined areas of these two wetlands (3000 km2) emitted 1147 Gg C year?1 as CO2 and 31 Gg C year?1 as CH4. If these rates are extrapolated to the area occupied by hydromorphic soils in the upper Negro basin, 63 Tg C year?1 of CO2 and 1.7 Tg C year?1 as CH4 are estimated as the regional evasion to the atmosphere. 相似文献
8.
L. S. Shirokova O. S. Pokrovsky S. N. Kirpotin C. Desmukh B. G. Pokrovsky S. Audry J. Viers 《Biogeochemistry》2013,113(1-3):573-593
Active processes of permafrost thaw in Western Siberia increase the number of soil subsidencies, thermokarst lakes and thaw ponds. In continuous permafrost zones, this process promotes soil carbon mobilisation to water reservoirs, as well as organic matter (OM) biodegradation, which produces a permanent flux of carbon dioxide (CO2) to the atmosphere. At the same time, the biogeochemical evolution of aquatic ecosystems situated in the transition zone between continuous permafrost and permafrost-free terrain remains poorly known. In order to better understand the biogeochemical processes that occur in thaw ponds and lakes located in discontinuous permafrost zones, we studied ~30 small (1–100,000 m2) shallow (<1 m depth) lakes and ponds formed as a result of permafrost subsidence and thaw of the palsa bog located in the transition zone between the tundra and forest-tundra (central part of Western Siberia). There is a significant increase in dissolved CO2 and methane (CH4) concentration with decreasing water body surface area, with the largest supersaturation with respect to atmospheric CO2 and CH4 in small (<100 m2) permafrost depressions filled with thaw water. Dissolved organic carbon (DOC), conductivity, and metal concentrations also progressively increase from large lakes to thaw ponds and depressions. As such, small water bodies with surface areas of 1–100 m2 that are not accounted for in the existing lake and pond databases may significantly contribute to CO2 and CH4 fluxes to the atmosphere, as well as to the stocks of dissolved trace elements and organic carbon. In situ lake water incubation experiments yielded negligible primary productivity but significant oxygen consumption linked to the mineralisation rate of dissolved OM by heterotrophic bacterioplankton, which produce a net CO2 flux to the atmosphere of 5 ± 2.5 mol C m2 year?1. The most significant result of this study, which has long-term consequences on our prediction of aquatic ecosystem development in the course of permafrost degradation is CO2, CH4, and DOC concentrations increase with decreasing lake age and size. As a consequence, upon future permafrost thaw, the increase in the number of small water bodies, accompanied by the drainage of large thermokarst lakes to the hydrological network, will likely favour (i) the increase of DOC and colloidal metal stocks in surface aquatic systems, and (ii) the enhancement of CO2 and CH4 fluxes from the water surface to the atmosphere. According to a conservative estimation that considers that the total area occupied by water bodies in Western Siberia will not change, this increase in stocks and fluxes could be as high as a factor of ten. 相似文献
9.
10.
Carbon cycling within the sulfate-methane-transition-zone in marine sediments from the Ulleung Basin 总被引:1,自引:0,他引:1
Wei-Li Hong Marta E. Torres Ji-Hoon Kim Jiyoung Choi Jang-Jun Bahk 《Biogeochemistry》2013,115(1-3):129-148
The significance of the various carbon cycling pathways in driving the sharp sulfate methane transition zone (SMTZ) observed at many locations along continental margins is still a topic of debate. Unraveling these processes is important to our understanding of the carbon cycle in general and to evaluate whether the location of this front can be used to infer present and past methane fluxes from deep reservoirs (e.g., gas hydrate). Here we report the pore water data from the second Ulleung Basin Gas Hydrate Expedition and on the results of a box model that balances solute fluxes among different carbon pools and satisfies the observed isotopic signatures. Our analysis identifies a secondary methanogenesis pathway within the SMTZ, whereby 25–35 % of the dissolved inorganic carbon (DIC) produced by the anaerobic oxidation of methane (AOM) is consumed by CO2 reduction (CR). To balance this DIC consumption, a comparable rate of organic matter degradation becomes necessary, which in turn consumes a significant amount of sulfate. The fraction of sulfate consumed by AOM ranges from 70 to 90 %. Whereas a simple mass balance would suggest a one to one relationship between sulfate and methane fluxes; our isotopic considerations show that methane flux estimates based solely on sulfate data may be in error by as much as 30 %. Furthermore, the carbon cycling within the SMTZ is fueled by a significant contribution (10–40 %) of methane produced by CR just below the SMTZ. Therefore sulfate gradient cannot necessarily be used to infer methane contributions from gas hydrate reservoirs that may lay tens to hundreds of meters below the SMTZ. 相似文献
11.
Influence of weather variables on methane and carbon dioxide flux from a shallow pond 总被引:5,自引:0,他引:5
Sivakiruthika Natchimuthu Balathandayuthabani Panneer Selvam David Bastviken 《Biogeochemistry》2014,119(1-3):403-413
Freshwaters are important sources of the greenhouse gases methane (CH4) and carbon dioxide (CO2) to the atmosphere. Knowledge about temporal variability in these fluxes is very limited, yet critical for proper study design and evaluating flux data. Further, to understand the reasons for the variability and allow predictive modeling, the temporal variability has to be related to relevant environmental variables. Here we analyzed the effect of weather variables on CH4 and CO2 flux from a small shallow pond during a period of 4 months. Mean CH4 flux and surface water CH4 concentration were 8.0 [3.3–15.1] ± 3.1 mmol m?2 day?1 (mean [range] ± 1 SD) and 1.3 [0.3–3.5] ± 0.9 µM respectively. Mean CO2 flux was 1.1 [?9.8 to 16.0] ± 6.9 mmol m?2 day?1. Substantial diel changes in CO2 flux and surface water CH4 concentration were observed during detailed measurements over a 24 h cycle. Thus diel patterns need to be accounted for in future measurements. Significant positive correlations of CH4 emissions with temperature were found and could include both direct temperature effects as well as indirect effects (e.g. related to the growth season and macrophyte primary productivity providing organic substrates). CO2 flux on the other hand was negatively correlated to temperature and solar radiation, presumably because CO2 consumption by plants was higher relative to CO2 production by respiration during warm sunny days. Interestingly, CH4 fluxes were comparable to ponds with similar morphometry and macrophyte abundance in the tropics. We therefore hypothesize that CH4 and CO2 summer emissions from ponds could be more related to the morphometry and dominating primary producers rather than latitude per se. Data indicate that CH4 emissions, given the system characteristic frameworks, is positively affected by increased temperatures or prolonged growth seasons. 相似文献
12.
We report a molecular simulation study to investigate the decomposition of CH4 hydrate. The decomposition is revealed to be stepwise from the outer to inner layers. Upon decomposition, the number of 51262 cages drops faster than that of 512 cages. CH4 molecules are released, dissolved in water, then enter gas phase; meanwhile, CH4 bubbles may form particularly at a high temperature. Based on the variations of potential energy, order parameter, cage number and density profile of CH4 at different temperatures (300, 330, 345 and 360 K) and NaCl concentrations (0, 0.6 and 1.8 M), the effects of temperature and salt are comprehensively examined. With increasing temperature, the decomposition in pure water is accelerated, whereas two opposite effects are observed in NaCl solution. At 330 K, the decomposition is retarded at a higher NaCl concentration, as attributed to the reduced CH4 solubility in NaCl solution and the participation of ions in cage formation; at 360 K, however, the decomposition is accelerated when NaCl concentration increases due to bubble formation. This simulation study provides microscopic insights into hydrate decomposition, which might be useful towards the optimisation of operating conditions for CH4 production from CH4 hydrate. 相似文献
13.
Philippe Ungerer Aurélie Wender Grégoire Demoulin Émeric Bourasseau Pascal Mougin 《Molecular simulation》2013,39(10):631-648
The design of improved processes for producing hydrogen sulphide (H2S)-rich natural gases faces a general scarcity of experimental data, because of the high toxicity and corrosive character of H2S. We present here a prospective application of Monte Carlo simulation to predict desired fluid properties. A first step was the selection of intermolecular potentials for water, H2S, carbon dioxide (CO2) and methane on the basis of pure component properties (vapour pressures, vapourisation enthalpies, liquid densities, supercritical densities at high pressure). A second step involved the prediction of phase diagrams of binary and ternary mixtures of the methane–H2S–water system, using two-phase and three-phase Gibbs ensemble simulations. In a third step the density and excess enthalpy of the CO2–H2S system were computed for a large range of pressure, temperature and compositions. Comparison with available experimental data showed that all investigated properties could be consistently predicted without needing parameter calibration on binary data. The results also provided a qualitative understanding of water solubility in H2S-rich fluids based on molecular self-association. 相似文献
14.
Summary Anaerobic phenol degrading consortia were selected in sewage sludge and culture conditions were improved to allow maximum degradation rates of 0.9 g/l·d. Phenol had to be added in two portions of 0.45 g/l at intervals of 12 h to keep the fermentation at stable conditions. From U-14C-phenol little benzoate and acetate were formed as intermediates under a N2:CO2 gas phase. Final products were methane and CO2. When methanogenesis was inhibited by BESA, less labeled methane and CO2 were formed and labeled acetate remained undegraded. Turnover rates of phenol were significantly reduced in the presence of a H2:CO2 gas atmosphere and benzoate was formed from phenol and CO2. Acetate did not accumulate remarkably. After the H2:CO2 was converted to methane or was exchanged by N2:CO2 the accumulated benzoate was further degraded to methane and CO2. Elevated pools of acetate in sewage sludge led also to a reduction of the phenol degradation rates and presumably to an increased concentration of benzoate. In fresh sewage sludge benzoate degradation proceeds immediately, while the degradation of phenol starts only after a lag-phase of 3–10 days. 相似文献
15.
A three-dimensional model of CO2 transport in airspaces and mesophyll cells of a silver birch leaf 总被引:3,自引:2,他引:1
A realistic numerical three‐dimensional (3D) model was constructed to study CO2 transport inside a birch leaf. The model included chloroplasts, palisade and spongy mesophyll cells, airspaces, stomatal opening and the leaf boundary layer. Diffusion equations for CO2 were solved for liquid(mesophyll) and gaseous(air) phases. Simulations were made in typical ambient field conditions varying stomatal opening, photosynthetic capacity and temperature. Doubled ambient CO2 concentration was also considered. Changes in variables caused non‐linear effects in the total flux, especially when compared with the results of double CO2 concentration. The reduction in stomatal opening size had a smaller effect on the total flux in doubled concentrations than ambient CO2. The reduced photosynthetic capacity had a similar effect on the flux in both cases. The palisade and spongy mesophyll cells had unequal roles mainly due to the light absorption profile. Results from the 3D simulation were also compared to the classical one‐dimensional resistance approach. Liquid and gas phase resistances were estimated and found strongly variable according to changes in temperature and degree of stomatal opening. For the birch leaves modelled, intercellular airspace resistance was small (2% of the total resistance in saturating irradiance conditions at 25 °C at stomatal opening diameter of 4 µm) whereas the liquid phase resistance was significant (23% for mesophyll and chloroplasts in the same ‘base case’). The absorption of CO2 into water at cell surfaces caused additional (strongly temperature dependent) resistance which accounted for 36% of the total resistance in the base case. 相似文献
16.
The transfer of carbon (C) from Amazon forests to aquatic ecosystems as CO2 supersaturated in groundwater that outgases to the atmosphere after it reaches small streams has been postulated to be an important component of terrestrial ecosystem C budgets. We measured C losses as soil respiration and methane (CH4) flux, direct CO2 and CH4 fluxes from the stream surface and fluvial export of dissolved inorganic C (DIC), dissolved organic C (DOC), and particulate C over an annual hydrologic cycle from a 1,319-ha forested Amazon perennial first-order headwater watershed at Tanguro Ranch in the southern Amazon state of Mato Grosso. Stream pCO2 concentrations ranged from 6,491 to 14,976 ??atm and directly-measured stream CO2 outgassing flux was 5,994 ± 677 g C m?2 y?1 of stream surface. Stream pCH4 concentrations ranged from 291 to 438 ??atm and measured stream CH4 outgassing flux was 987 ± 221 g C m?2 y?1. Despite high flux rates from the stream surface, the small area of stream itself (970 m2, or 0.007% of watershed area) led to small directly-measured annual fluxes of CO2 (0.44 ± 0.05 g C m2 y?1) and CH4 (0.07 ± 0.02 g C m2 y?1) per unit watershed land area. Measured fluvial export of DIC (0.78 ± 0.04 g C m?2 y?1), DOC (0.16 ± 0.03 g C m?2 y?1) and coarse plus fine particulate C (0.001 ± 0.001 g C m?2 y?1) per unit watershed land area were also small. However, stream discharge accounted for only 12% of the modeled annual watershed water output because deep groundwater flows dominated total runoff from the watershed. When C in this bypassing groundwater was included, total watershed export was 10.83 g C m?2 y?1 as CO2 outgassing, 11.29 g C m?2 y?1 as fluvial DIC and 0.64 g C m?2 y?1 as fluvial DOC. Outgassing fluxes were somewhat lower than the 40?C50 g C m?2 y?1 reported from other Amazon watersheds and may result in part from lower annual rainfall at Tanguro. Total stream-associated gaseous C losses were two orders of magnitude less than soil respiration (696 ± 147 g C m?2 y?1), but total losses of C transported by water comprised up to about 20% of the ± 150 g C m?2 (±1.5 Mg C ha?1) that is exchanged annually across Amazon tropical forest canopies. 相似文献
17.
Four common pure fluids were chosen to elucidate the reliability of reactive force fields in estimating bulk properties of selected molecular systems: CH4, H2O, CO2 and H2. The pure fluids are not expected to undergo chemical reactions at the conditions chosen for these simulations. The ‘combustion’ ReaxFF was chosen as reactive force field. In the case of water, we also considered the ‘aqueous’ ReaxFF model. The results were compared to data obtained implementing popular classic force fields. In the gas phase, it was found that simulations conducted using the ‘combustion’ ReaxFF formalism yield structural properties in reasonable good agreement with classic simulations for CO2 and H2, but not for CH4 and H2O. In the liquid phase, ‘combustion’ ReaxFF simulations reproduce reasonably well the structure obtained from classic simulations for CH4, degrade for CO2 and H2, and are rather poor for H2O. In the gas phase, the simulation results are compared to experimental second virial coefficient data. The ‘combustion’ ReaxFF simulations yield second virial coefficients that are not sufficiently negative for CH4 and CO2, and slightly too negative for H2. The ‘combustion’ ReaxFF parameterisation induces too strong an effective attraction between water molecules, while the ‘aqueous’ ReaxFF yields a second virial coefficient that is in reasonable agreement with experiments. The ‘combustion’ ReaxFF parameterisation yields acceptable self-diffusion coefficients for gas-phase properties of CH4, CO2 and H2. In the liquid phase, the results are good for CO2, while the self-diffusion coefficient predicted for liquid CH4 is slower, and that predicted for liquid H2 is about nine times faster than those expected based on classic simulations. The ‘aqueous’ ReaxFF parameterisation yields good results for both the structure and the diffusion of both liquid and vapour water. 相似文献
18.
The magnitude of greenhouse gas (GHG) flux rates may be important in wet and intermediate wet forest soils, but published estimates are scarce. We studied the surface exchange of methane (CH4) and nitrous oxide (N2O) from soil along toposequences in two temperate deciduous forest catchments: Strødam and Vestskoven. The soil water regime ranged from fully saturated to aerated within the catchments. At Strødam the largest mean flux rates of N2O (15 μg N2O-N m?2 h?1) were measured at volumetric soil water contents (SWC) between 40 and 60% and associated with low soil pH compared to smaller mean flux rates of 0-5 μg N2O-N m?2 h?1 for drier (SWC < 40%) and wet conditions (SWC > 80%). At Vestskoven the same response of N2O to soil water content was observed. Average CH4 flux rates were highly variable along the toposequences (?17 to 536 μg CH4-C m?2 h?1) but emissions were only observed above soil water content of 45%. Scaled flux rates of both GHGs to catchment level resulted in emission of 322 and 211 kg CO2-equivalents ha?1 year?1 for Strødam and Vestskoven, respectively, with N2O contributing the most at both sites. Although the wet and intermediate wet forest soils occupied less than half the catchment area at both sites, the global warming potential (GWP) derived from N2O and CH4 was more than doubled when accounting for these wet areas in the catchments. The results stress the importance of wet soils in assessments of forest soil global warming potentials, as even small proportions of wet soils contributes substantially to the emissions of N2O and CH4. 相似文献
19.
A. P. Schrier-Uijl A. J. Veraart P. A. Leffelaar F. Berendse E. M. Veenendaal 《Biogeochemistry》2011,102(1-3):265-279
Shallow fresh water bodies in peat areas are important contributors to greenhouse gas fluxes to the atmosphere. In this study we determined the magnitude of CH4 and CO2 fluxes from 12 water bodies in Dutch wetlands during the summer season and studied the factors that might regulate emissions of CH4 and CO2 from these lakes and ditches. The lakes and ditches acted as CO2 and CH4 sources of emissions to the atmosphere; the fluxes from the ditches were significantly larger than the fluxes from the lakes. The mean greenhouse gas flux from ditches and lakes amounted to 129.1 ± 8.2 (mean ± SE) and 61.5 ± 7.1 mg m?2 h?1 for CO2 and 33.7 ± 9.3 and 3.9 ± 1.6 mg m?2 h?1 for CH4, respectively. In most water bodies CH4 was the dominant greenhouse gas in terms of warming potential. Trophic status of the water and the sediment was an important factor regulating emissions. By using multiple linear regression 87% of the variation in CH4 could be explained by PO4 3? concentration in the sediment and Fe2+ concentration in the water, and 89% of the CO2 flux could be explained by depth, EC and pH of the water. Decreasing the nutrient loads and input of organic substrates to ditches and lakes by for example reducing application of fertilizers and manure within the catchments and decreasing upward seepage of nutrient rich water from the surrounding area will likely reduce summer emissions of CO2 and CH4 from these water bodies. 相似文献
20.
Seasonal variability of methane in the rivers and lagoons of Ivory Coast (West Africa) 总被引:2,自引:0,他引:2
We report a data-set of dissolved methane (CH4) in three rivers (Comoé, Bia and Tanoé) and five lagoons (Grand-Lahou, Ebrié, Potou, Aby and Tendo) of Ivory Coast (West Africa), during the four main climatic seasons (high dry season, high rainy season, low dry season and low rainy season). The surface waters of the three rivers were over-saturated in CH4 with respect to atmospheric equilibrium (2221–38719%), and the seasonal variability of CH4 seemed to be largely controlled by dilution during the flooding period. The strong correlation of CH4 concentrations with the partial pressure of CO2 (pCO2) and dissolved silicate (DSi) confirm the dominance of a continental sources (from soils) for both CO2 and CH4 in these rivers. Diffusive air–water CH4 fluxes ranged between 25 and 1187 μmol m?2 day?1, and annual integrated values were 288 ± 107, 155 ± 38, and 241 ± 91 μmol m?2 day?1 in the Comoé, Bia and Tanoé rivers, respectively. In the five lagoons, surface waters were also over-saturated in CH4 (ranging from 1496 to 51843%). Diffusive air–water CH4 fluxes ranged between 20 and 2403 μmol m?2 day?1, and annual integrated values were 78 ± 34, 338 ± 217, 227 ± 79, 330 ± 153 and 326 ± 181 μmol m?2 day?1 in the Grand-Lahou, Ebrié, Potou, Aby and Tendo lagoons, respectively. The largest CH4 over-saturations were observed in the Tendo and Aby lagoons that are permanently stratified systems (unlike the other three lagoons), leading to anoxic bottom waters favorable for a large CH4 production. In addition, these two stratified lagoons showed low pCO2 values due to high primary production, which suggests an efficient transfer of organic matter across the pycnocline. As a result, the stratified Tendo and Aby lagoons were respectively, a low source of CO2 to the atmosphere and a sink of atmospheric CO2 while the other three well-mixed lagoons were strong sources of CO2 to the atmosphere but less over-saturated in CH4. 相似文献