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1.
The advection initiative ADVEX within CarboEurope-IP conducted advection experiments at three European coniferous sites in 2005 and 2006. All experiments shared the same geometry and instrumentation. Data of the ADVEX experiments were used to calculate advective fluxes of carbon dioxide and sensible heat using exactly the same method. However, the advective flux of sensible heat can be assessed more easily than the carbon dioxide flux with its associated complex measurements of gas concentrations. We explored the possibility to use advective fluxes of sensible heat as a proxy for the corresponding flux of carbon dioxide despite somewhat differing sinks and sources. On average, advective fluxes of sensible heat were of opposite sign in relation to the advective fluxes of carbon dioxide for the three investigated sites, especially during nighttime. Therefore, the respective gradients were of opposite sign, on average, for vertical and (to a lesser extent) horizontal direction. This is not as obvious for horizontal direction as for the vertical direction. A scheme is presented to explain the correlation of the respective gradients for different conditions. Based on the gained insights and regression statistics, two simple empirical models were tested to derive advective fluxes of carbon dioxide from advective fluxes of sensible heat. Our results suggest that the advective flux of sensible heat could be taken as an indicator concerning the presence and sign of carbon dioxide advection. However, the suitability of advective fluxes of sensible heat as a quantitative proxy for advective fluxes of carbon dioxide is more problematic because the representativeness including the magnitude of advection derived from advection measurements is not yet clarified. An inspection of the budget of sensible heat and carbon dioxide revealed considerable changes by advection. The results indicate that the budget of carbon dioxide might be generally more affected by the investigated non-turbulent advective fluxes than the budget of sensible heat.  相似文献   

2.
Internal loading is a critical component of the phosphorus (P) budget of aquatic systems that can control trophic conditions. While diffusion across the soil?Cwater interface is generally considered the dominant process controlling P load to the water column, advection due to water table fluctuations can also be significant. Our objective was to evaluate the role of diffusive and advective fluxes in relation to the total P (TP) loads entering and exiting an impacted wetland in the Lake Okeechobee drainage basin. The average diffusive flux of TP was 0.32?±?0.14 mg?m?2?day?1 and occurred for 240 days out of 314, while advective flux was 1.31?±?4.03 mg?m?2?day?1 and occurred for only 57 days. Phosphorus load to the wetland via internal modes was estimated to be 2.3 and 4.0 g?day?1 from diffusion and advection respectively, accounting for 18% of the total P input, while overland flow (51%) was the major input pathway to the wetland. Ditch flow and groundwater outflow accounted for 49% (18.0 g?day?1) and 14% (5.0 g?day?1) of the total P output, respectively. This study shows the importance of advective flux in addition to diffusive flux and that the former should not be neglected when estimating internal P load of transiently flooded isolated wetlands. The monthly P budget-based retention and release patterns were consistent with previous findings, showing that intermittent flooding and drying cycling significantly reduces the P retention capacity of a wetland.  相似文献   

3.
Gas transport in soils is usually assumed to be purely diffusive, although several studies have shown that non-diffusive processes can significantly enhance soil gas transport. These processes include barometric air pressure changes, wind-induced pressure pumping and static air pressure fields generated by wind interacting with obstacles. The associated pressure gradients in the soil can cause advective gas fluxes that are much larger than diffusive fluxes. However, the contributions of the respective transport processes are difficult to separate. We developed a large chamber system to simulate pressure fields and investigate their influence on soil gas transport. The chamber consists of four subspaces in which pressure is regulated by fans that blow air in or out of the chamber. With this setup, we conducted experiments with oscillating and static pressure fields. CO2 concentrations were measured along two soil profiles beneath the chamber. We found a significant relationship between static lateral pressure gradients and the change in the CO2 profiles (R2 = 0.53; p-value <2e-16). Even small pressure gradients between −1 and 1 Pa relative to ambient pressure resulted in an increase or decrease in CO2 concentrations of 8% on average in the upper soil, indicating advective flow of air in the pore space. Positive pressure gradients resulted in decreasing, negative pressure gradients in increasing CO2 concentrations. The concentration changes were probably caused by an advective flow field in the soil beneath the chamber generated by the pressure gradients. No effect of oscillating pressure fields was observed in this study. The results indicate that static lateral pressure gradients have a substantial impact on soil gas transport and therefore are an important driver of gas exchange between soil and atmosphere. Lateral pressure gradients in a comparable range can be induced under windy conditions when wind interacts with terrain features. They can also be caused by chambers used for flux measurements at high wind speed or by fans used for head-space mixing within the chambers, which yields biased flux estimates.  相似文献   

4.
Measurements of the horizontal and vertical fluxes of energy and mass were taken at a crop canopy edge and downwind of it to examine the effects of inhomogeneity on surface-atmosphere exchange, for the ideal case of flat uniform terrain. Energy balance closure was also examined and the effects of the often-neglected advection terms on the energy budget were evaluated. The results show that neither vertical nor horizontal advection should be neglected for moderate distances downwind from heterogeneous boundaries, with the energy budget closure near the leading edge improved by more than 20% with the inclusion of the horizontal and vertical advection of latent and sensible heat. Significant mean advective horizontal and vertical flux divergences of water vapor and temperature were found even in typical daytime conditions. In stable conditions horizontal advection can be responsible for more than 15% of the scalar (water vapor) transport 136 canopy heights downwind of a change in water vapor source density and surface roughness.  相似文献   

5.
Water balance, transpiration and canopy conductance in two beech stands   总被引：1，自引：0，他引：1  
Measurements of sap flow, vapour fluxes, throughfall and soil water content were conducted for 19 months in a young beech stand growing at low elevation, in the Hesse forest. This experiment is part of the Euroflux network, covering 15 representative European forests. Study of the radial variation of sap flow within tree trunks, showed a general pattern of sap flux density in relation to the depth below cambium. Among-tree variation of sap flow was also assessed, in order to determine the contribution of the different crown classes to the total stand transpiration. Stand sap flow and vapour flux, measured with eddy covariance technique, were well correlated, for half hourly as well for daily values, the ratios of the fluxes for both averaging periods being 0.77. A strong canopy coupling to the atmosphere was found, omega factor ranging between 0.05 and 0.20 relative to the windspeed. Canopy conductance variation was related to a range of environmental variables: global radiation, vapour pressure deficit, air temperature and soil water deficit. In addition to the effect of radiation and of vapour pressure deficit often found in various other tree species, here beech exhibited a strong reduction in canopy conductance when air temperature decreased below 17°C. The model of transpiration was calibrated using data measured in the Hesse forest and applied to another beech stand under mountainous conditions in the Vosges mountains (east France). Measured and modelled stand transpiration were in good agreement.  相似文献   

6.
Drained organic soils contribute substantial amounts of nitrous oxide to the global atmosphere, and we should be able to estimate this contribution. We have investigated when the fluxes of N2O from drained forested or cultivated organic soils could be determined by calculating the fluxes from the concentration gradients of the gas in soil or snow according to Fick's law of diffusion. A static chamber method was applied as a control technique for the gas gradient method. Concentrations of N2O in soil varied from 296 nl l?1 to 8534 nl l?1 during the snow‐free periods and were greatest in the early summer. Our results suggest that the gas gradient method can be used to estimate N2O emissions from drained organic soils. There was some systematic difference in the N2O fluxes measured with these two methods, which we attributed to the differences in weather between years 1996 and 1997. In the wet summer of 1996 the chamber method gave greater flux rates than the gas gradient method, and the reverse was true in the dry summer of 1997. In the forest the N2O fluxes measured with the two methods agreed well. The gas gradient is convenient and fast for measuring N2O emissions from fairly dry organic unfrozen soil. In winter the diffusion calculation based on the N2O gradients in snow and the chamber method gave fairly similar flux rates and provided adequate estimates of the fluxes of N2O in winter.  相似文献   

7.
One of the best ways to evaluate the coupled heat and mass transfer in soil is to measure the heat flux and water distribution simultaneously. For this purpose, we developed an apparatus for measuring the one‐dimensional steady‐state heat flux and water distribution in unsaturated soil under reduced air pressure. The system was tested using four samples with known thermal conductivity (0.6–8.0 W m?1 K?1). We confirmed that the system could measure the one‐dimensional steady‐state heat flux under a fixed temperature difference between ends of the samples over a wide range of thermal conductivity values. Time domain reflectometry was used to measure the water distribution with a repeatability of less than ± 1.0%. We used the apparatus to measure the soil heat flux and distribution of water content and temperature under steady‐state conditions with reduced air pressure. The initial volumetric water content, θini, of the soil samples was set at 0.20 and 0.40 m3m?3. For a θini of 0.20, the heat flux was not significantly affected by air pressure, and the water content on the hot side decreased whilst that on the cold side increased, i.e. a pronounced water content gradient was formed. For a θini of 0.40, the heat flux increased sharply with reduced air pressure, and the water content did not change, i.e. a homogeneous water distribution was observed. The increase in the heat flux with air pressure reduction is caused by the vapour transfer in soil pores. We found that a large vapour transfer took place in the soil with the homogeneous water distribution, and that the vapour transfer was less in the soil with the pronounced water content gradient. These experimental facts were entirely different from the traditional knowledge of vapour transfer in soil under temperature gradients. A lack of data on heat flux must have resulted in the previously incorrect conclusions. The new apparatus will serve to clarify the intricate phenomena of thermally induced vapour transfer in unsaturated soil in further experiments.  相似文献   

8.
Indirect emissions of the major greenhouse gas nitrous oxide (N2O) occurring from aquatic ecosystems are considered to be a highly uncertain component in the global N2O budget. In this study, we investigated the fate of N2O produced by denitrification in a sandy shallow aquifer in northern Germany. The experimental data from a previous 15N field study and site‐specific diffusion coefficients were used to simulate upward fluxes of groundwater‐derived (15N‐)N2O in the soil as well as its ultimate emission into the atmosphere. The one‐dimensional simulation model considered gas diffusion and gas retardation by dissolution in the water phase. The modelled concentration gradients and emissions were in good agreement with the experimental data, indicating that diffusion was the dominant transport process in the soil, and that our model approach was thus suitable for simulating N2O fluxes from the unsaturated zone to the atmosphere. Furthermore, the results revealed that there was no evidence for consumption of 15N‐N2O during upward diffusion from the surface groundwater to the atmosphere. Simulated concentrations and emissions of groundwater‐derived N2O were found to be very small and a negligible component of total N2O.  相似文献   

9.
The distribution of dissolved and particulate 234Th in the upper 200 m of the water column was obtained for three stations in the Ross Sea off Victoria Land and Terra Nova Bay. At site 24a, close to the retreating ice margin, all the sampled depths showed deficiencies in 234Th relative to the equilibrium with 238U. These are related to uptake of 234Th onto sinking particles. Residence times of 234Th in solution and of particulate 234Th were 130-247 days and 8.1-6.6 days, respectively. A high particle flux (1.23-5.03 g m-2 d-1) was calculated at this station. At the other two sites (11c and 15c), 234Th depth profiles are irregular, probably due to the release of dissolved 234Th by decomposing particles at certain depths, or to the contribution from lateral advection. Bulk mass fluxes measured by floating traps at stations 11c and 15c are very low (66-138 mg m-2 d-1). Also fluxes of organic carbon and nitrogen, and biogenic silica are reported for these two sites. The calculated fluxes are discussed with respect to methodologies and to the dynamics of the ice margin retreat.  相似文献   

10.
Soil aeration is a critical factor for oxygen-limited subsoil processes, as transport by diffusion and advection is restricted by the long distance to the free atmosphere. Oxygen transport into the soil matrix is highly dependent on its connectivity to larger pore channels like earthworm and root colonised biopores. Here we hypothesize that the soil matrix around biopores represents different connectivity depending on biopore genesis and actual coloniser. We analysed the soil pore system of undisturbed soil core samples around biopores generated or colonised by roots and earthworms and compared them with the pore system of soil, not in the immediacy of a biopore. Oxygen partial pressure profiles and gas relative diffusion was measured in the rhizosphere and drilosphere from the biopore wall into the bulk soil with microelectrodes. The measurements were linked with structural features such as porosity and connectivity obtained from X-ray tomography and image analysis. Aeration was enhanced in the soil matrix surrounding biopores in comparison to the bulk soil, shown by higher oxygen concentrations and higher relative diffusion coefficients. Biopores colonised by roots presented more connected lateral pores than earthworm colonised ones, which resulted in enhanced aeration of the rhizosphere compared to the drilosphere. This has influenced biotic processes (microbial turnover/mineralization or root respiration) at biopore interfaces and highlights the importance of microstructural features for soil processes and their dependency on the biopore's coloniser.  相似文献   

11.
Turbulence within open canopies is shown to undergo a dramatic change in character during the transition from convective to stable conditions. In convective conditions the flow within the canopy is coupled through turbulent exchange to the flow aloft. As the transition proceeds, the within- and above-canopy flows decouple and vertically coherent waves form within the canopy. The intensity of above-canopy turbulence is not a good indicator of flow decoupling. Within-canopy waves can lead to large random error in the measurement of the change of storage and the advection terms in the mass balance equation. More importantly, errors associated with sampling over incomplete wave cycles will inevitably be combined with true advective flux divergences at non-ideal sites. Quantitative estimates of likely errors on storage of heat and CO2 within the canopy are presented.  相似文献   

12.
A quasi steady state respiration test based on Fick’s law with a correction term for advective flux, for estimating petroleum hydrocarbon degradation rates, was evaluated in a full-scale (3,000 m3) biopile study. A contaminated clayey sand soil with an average TPH content of 1,421?±?260 mg kg?1 soil was treated in a biopile with a fixed venting and heating system. Temperature in the biopile ranged from 12.1 to 36.6°C and soil water content from 15.2 to 35.8 m3 H2O m?3 soil. Oxygen concentrations in the biopile showed a rapid decrease with depth, before venting and reached constant atmospheric concentration during venting. Measured oxygen consumption in the biopile ranged from ?0.04 to ?0.68 mol O2 m?3 soil day?1. Average oxygen consumption rates calculated with the quasi-steady-state method were significantly (P?<?0.05) lower then the oxygen consumption rates calculated with the transient method. It was suggested that the oxygen diffusion was underestimated by the diffusivity models used and that further research is needed to determine relative effective diffusion coefficients in biopiles. Although both respiration testing and petroleum hydrocarbon concentration showed a decrease of oxygen consumption in time, the estimated degradation rate was low compared to the actual decrease in petroleum hydrocarbon concentration. Additional work will have to be done to acquire a more precise knowledge of the relationship between respirometrically determined degradation rates and the actual change in petroleum hydrocarbon concentration in the soil.  相似文献   

13.
《Applied soil ecology》2011,48(3):160-166
We studied the effect of water table on CO2 and CH4 fluxes at different time scales in the littoral zone of Lake Obuchi, a brackish lake in northern Japan. The vegetation formed three distinct zones along the water table gradient, two dominated by emergent aquatic macrophytes (the Phragmites australis-dominated zone and the Juncus yokoscensis-dominated zone) and one dominated by terrestrial macrophytes (Miscanthus sinensis and Cirsium inundatum-dominated zone). To clarify the impact of variations in water table on monthly and yearly summed CO2 and CH4 fluxes, we examined the relationship between water table and the ratio of observed flux to calculated flux, whereby the calculated flux was based solely on the exponential relationship between flux and soil temperature for each gas. This study revealed that the impact of variations in water table on monthly and yearly summed CO2 and CH4 fluxes differed markedly between the vegetation zones. By taking the temporal change in water table into account in the estimation of both the CO2 and CH4 fluxes, the monthly summed CO2 and CH4 fluxes in the Phragmites-zone were markedly greater in every month of the year compared to estimation based on temperature alone. In the Juncus-zone, the effect of water table on monthly summed CO2 and CH4 fluxes differed between months. In addition, the magnitude of water-table effects controlling monthly summed CO2 and CH4 fluxes differed with atmospheric conditions, i.e., between the pressure-falling and low-pressure phase on the one hand and other pressure phases on the other hand. After weighting all the impacts of temporal changes in water table on fluxes, the yearly summed CO2 and CH4 fluxes showed a 1.26–6.64-fold increase compared with not taking water table effects into account, and the increase differed among the three vegetation zones.  相似文献   

14.
The increasing use of petroleum-derived fuels over the last few decades has subsequently augmented the risk of spills in the environment. Soil pollution with petroleum hydrocarbons (principally caused by leaks in pipelines and underground storage tanks) is one of the major sources of soil degradation. Once in soil, fuel hydrocarbons suffer from a wide variety of multiphase processes including transport (advection, diffusion, and dispersion) among and within phases (aqueous and non-aqueous liquid, gas, and soil solids), mass transfer among phases (volatilization, sorption, and solution), and other natural attenuation processes, such as biodegradation and plant uptake and metabolism. This review identifies and describes the major processes occurring in soil that have a significant influence on the environmental fate of petroleum hydrocarbons. The definition of the processes involved in pollutant migration and distribution in soil and the formulation of adequate equations using accurate parameters (e.g., diffusion coefficients, velocity of advective flows, and mass transfer coefficients) will allow prediction of the final fate of soil pollutants. In addition to transport and mass transfer processes, which are more widely studied, the incorporation of attenuation mechanisms driven by microorganisms and plants is essential to predict the final concentration of the pollutants in the whole multiphase scenario. This work underlines the importance of the determination of accurate parameters through the performance of laboratory and/or field-scale experiments to develop precise pollutant migration models.  相似文献   

15.
The determination of stomatal ozone fluxes is essential to assess the potential damage to plants due to ozone uptake. This parameter is not accessible directly with measurements, but can be deduced through algorithms using observational data. Total ozone fluxes and water vapour fluxes are generally used. Water vapour fluxes give an indication on stomatal aperture, which is the controlling factor of ozone uptake by vegetation. In this work, a series of observations made during the growing season over an onion field are used to show the equivalence of two algorithms found in the literature to derive ozone stomatal fluxes and both based on the similarity between ozone stomatal fluxes and water vapour stomatal fluxes. One of these algorithms uses the Penman-Monteith approach, where the water vapour pressure deficit is calculated using air temperatures; the second calculates, with another formulation, the water vapour deficit from the leaf temperature. The two approaches lead to the same results if applied properly, as shown in this work, both theoretically and numerically.  相似文献   

16.
In bioremediation, hydrocarbon biodegradation rates can be estimated from measured O2 and CO2 profiles in situ. Although Fick's law is typically used in calculating the respiration rates, its theoretical base is weak. We propose an adjusted Fick's law with a correction term for the advective flux. We evaluated the applicability of this model to simulate gas diffusion associated with passive degradation of petroleum hydrocarbons in a biopile by comparing the results of this model with the results of Fick's law and the Stefan–Maxwell equations. The deviations from the use of Fick's law depended strongly on the consumption rate of oxygen, the respiration quotient, the mineralization quotient and the volatility of the hydrocarbon. In the whole range of calculated CO2 concentration versus depth profiles, production rates of CO2 could be estimated by Fick's law with a maximum deviation of 6%. For the consumption rate of O2 the maximum deviation is 19%. However, when we used the adjusted Fick's law, the deviations from the results obtained with the Stefan–Maxwell equations were much smaller. The deviations amounted up to only 4%, when the respiration rate r was 1.5 or a hydrocarbon with volatility similar to benzene was present. If the presence of a hydrocarbon was neglected in the calculations, the deviations of the adjusted Fick's law from the results obtained with the Stefan–Maxwell equations were substantial for a hydrocarbon with volatility similar to benzene or toluene.  相似文献   

17.
Analytical air pollution advection and diffusion models   总被引：1，自引：0，他引：1  
A review of non-Gaussian analytical solutions of the advection diffusion equation is presented. Their utilization to mathematical models of air pollution diffusion is discussed and the application of a particular solution is suggested. The suggested KAPPAG model uses the Demuth's (1978) solution and can incorporate smoothed observed vertical wind and diffusion coefficient profiles. It is shown that Demuth's solution can represent the realistic situations of the diminishing vertical exchange coefficient at the top of boundary layer.  相似文献   

18.
Background, aim, and scope  Exploited gas fields and underground gasholders are specific sources of increasing methane concentration. Methane migrates into the soils by diffusion and convection through natural and technogenic cracks in geological structures and influences the function of the soils. Soil cover of gas-bearing area functions as a specific, bilateral, periodically penetrating, geomembrane. Soils shield, transform, and differentiate migrating fluxes of technogenic-allochthonous methane, preventing its emission to the atmosphere. Problems of methane’s emission are rather current at the present, as methane is the second in importance after CO2 greenhouse gas, since its concentration in the atmosphere annually grows by approximately 1%. By global estimations, methane emissions in the gas industry make about 8% of annual receipt to the atmosphere, equal on the average to 500 Тg per a year (Cicerone and Oremland, Global Biogeochem Cy 2:299–327, 1988). But these calculations are based on the account of the technological losses making 3–12% from the mining of natural gas. The contribution of migratory methane fluxes to the atmosphere, as a rule, is not considered. The need for research of soil cover functioning on gas-bearing areas is explained by the fact that processes of methane oxidation, its transformation in soils, and emission to the atmosphere at these objects are now practically not being studied. The aim of our study was to reveal specific processes of soil function and formation on gas-bearing areas by an example of underground gasholder. Materials and methods  The material was sampled in 1998–2003 at the territory of underground gasholder located in Albeluvisol’s zone in Russia. According to the comparative-geographical method, 51 soil profiles have been studied in similar litologically geomorphological conditions in various geochemical zones: in the industrial zone, in the zone of gas dissipation, and at the regional background. The total square of investigated territory is about 60 km2. Six soil profiles were investigated in seasonal dynamics. Samples of soils for physical, chemical, and microbiological analyses were taken from each horizon of soil profiles (202 samples). Samples of soil air for a definition of methane concentration were taken from depths of 20, 40, and 60 cm. Methane emission to the atmosphere was measured near soil’s cuts and, in addition, on all area of the investigated territory at knots of squares network through 700–1,000 m, in total at 32–42 points in May, July, and November. Years of investigation have been split by technological and hydrothermal conditions. The periods with the normal and lowered compression of gas in gasholder, dry and warm, and damp and cool years have been allocated. It has influenced the soil function processes and considered an interpretation of the data received. Results  The changes of functional parameters of soils at a gas-bearing area influenced by methane fluxes migrating from gas deposits, in comparison with background soils, are revealed. Such functional parameters are methane concentration in the soils, activity of its bacterial oxidation, methane emission to the atmosphere, and oxidation–reduction potential. Spatial and temporary dynamics of these parameters at gas-bearing and background territory are investigated. Discussion  Methane interaction with soil’s air is in its ascending (descending) and lateral diffusion and convection in soils. Methane fluxes dissipate in porous space of soils forming gas anomalies. The technogenic-allochthonous methane concentration strongly varies in soil’s air on gas-bearing area (1–10,500 ppm) and, on average, exceeds the autochthonous, microbiologically produced methane at background territories. Migratory methane is deposited on diffusion and sorption barriers. The capacity of diffusion barrier depends on effective coefficient of diffusion, the attitude of air and general porosity, and granulometric composition and sharply differs in auto-, semi-hydro-, and hydromorphic soils reaching maximum in hydromorphicity and among the soils with identical water content—in heavy soils. The capacity of the sorption barrier is defined by abiotic methane absorption and a specific surface of soils and grows with their increasing intensity in soils to a heavier granulometric composition or into soils with peat and gleyic horizons. The low sorption capacity leads to an increase of methane concentration in the soil’s air and decreases its utilization by microorganisms, in which its quantity depends on sorption properties. The central component of functioning that promotes a number of essential transformations in soils on gas-bearing areas is methane interaction with the biotic phase. The periods of methane deposition by diffusion and sorption barriers are used for biological methane oxidation and formation of biogeochemical barriers in soils. The activity of bacterial methane oxidation is characterized by spatial variability and depends on the entrance of methane, defined by granulometric composition, soil moisture, the attitude of air and general porosity, Eh, organic matter content, and salinization. During interaction between technogenic-allochthonous methane and soil on diffusion, sorption, and biogeochemical barriers, its transformation occurs, accompanied by a strengthening of variability of oxidation–reduction potential and formation of pedogenic, bacteriomorphic, and nanodispersic magnetic oxides of iron. Conclusions and perspectives  Specificity of soil functioning on a gas-bearing area is in interaction of technogenic-allochtonous methane with solid, liquid, gaseous, and living substance of the soil system. Spatial laws of soils functioning on gas-bearing area in the Albeluvisol’s zone are revealed. Distinctions of soil functions depending on litologically geomorphological conditions are shown. The greatest changes of parameters of functioning under the influence of technogenic-allochthonous methane occur in automorphic soils, and it is less in semi-hydromorphic soils. Activity of bacterial methane oxidation in soils, emission, and consumption from the atmosphere and their spatial laws are characterized by the time dynamics depending on hydrothermal and technological conditions of seasons and years. During oxidation in soils of gas-bearing areas, carbon of methane is concentrated on a biogeochemical barrier that is shown in the increase of methylotrophic microorganisms’ biomass and leads to a high variability and decrease of Eh and to the formation of magnetic oxides of iron. Recommendations  Results of research can be used for carrying out ecological monitoring and an estimation of tightness of objects of the gas industry. Activity of bacterial methane oxidation, Eh, and magnetic oxides of iron can be used as diagnostic parameters of soils on gas-bearing areas. This paper has been developed from a presentation at the conference SUITMA-4 (Soils in Urban, Industrial, Traffic, Mining and Military Areas) Nanjing, China, 2007  相似文献   

19.
Under favourable conditions, soil ingestion by earthworm populations can be equivalent to approximately 5–10% of the topsoil mass per year. This suggests that for contaminants that are strongly bound to soil, earthworm ‘bioturbation’ may be a more important transport mechanism than water‐borne advection dispersion. It is therefore quite surprising that few modelling studies to date have explicitly considered the effects of biological processes on contaminant transport in soil. In this study, we present a general model that incorporates the effects of both ‘local’ and ‘non‐local’ biological mixing into the framework of the standard physical (advective‐dispersive) transport model. The model is tested against measurements of the redistribution of caesium‐137 (137Cs) derived from the Chernobyl accident, in a grassland soil during 21 years after fallout. Three model parameters related to biological transport were calibrated within ranges defined by measured data and literature information on earthworm biomasses and feeding rates. Other parameters such as decay half‐life and sorption constant were set to known or measured values. A physical advective‐dispersive transport model based on measured sorption strongly underestimated the downward displacement of 137Cs. A dye‐tracing experiment suggested the occurrence of physical non‐equilibrium transport in soil macropores, but this was inadequate to explain the extent of the deep penetration of 137Cs observed at the site. A simple bio‐diffusion model representing ‘local’ mixing worked reasonably well, but failed to reproduce the deep penetration of Cs as well as a dilution observed close to the soil surface. A comprehensive model including physical advective‐dispersive transport, and both ‘local’ and ‘non‐local’ mixing caused by the activities of both endogeic and anecic earthworms, gave an excellent match to the measured depth profiles of 137Cs, with predictions mostly lying within confidence intervals for the means of measured data and model efficiencies exceeding 0.9 on all sampling occasions but the first.  相似文献   

20.
在2007年1月—2007年11月分4个航次对宁波南沙港养殖水域上覆水和表层沉积物间隙水中的溶解无机氮（DIN）和活性磷酸盐（PO4^3--P）浓度进行了现场调查,并应用Fick第一定理对该养殖水域沉积物-水界面DIN和PO4^3--P的扩散通量进行了估算。结果表明,南沙港养殖水域上覆水中NH4^＋-N、NO3^--N、NO2^--N和PO4^3--P的浓度变化范围分别为1.07～11.73、0.01～121.43、0.06～3.79μmol·L^-1和0.42～4.16μmol·L^-1;间隙水中NH4^＋-N、NO3^--N、NO2^--N和PO4^3--P浓度年变化范围分别为24.00～219.51、4.02～1250.41、0.45～8.70μmol·L^-1和3.41～41.87μmol·L^-1;DIN和PO4^3--P的扩散通量平均值分别为1520.73μmol·m^-2·d^-1和22.33μmol·m^-2·d-^1,扩散方向总体表现为从沉积物向上覆水扩散,每年向养殖系统中输入的DIN和PO4^3--P量分别约为9.87t和0.32t,表明沉积物是南沙港养殖水域水体氮磷营养盐,尤其是DIN的重要的输入源。  相似文献   

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