胶体作用下饱和土壤中Cd运移的数值模拟

通过室内土柱出流实验探讨了饱和壤砂土中Cd在SiO2胶体作用下的运移行为,并用对流-弥散方程(Convection-Dispersion Equation,CDE)对实验结果进行了数值模拟。结果表明,土壤中SiO2胶体的存在抑制了Cd的运移,土壤对Cd的吸附以动力学反应为主。耦合Freundlich等温吸附的单点非平衡模型(One Site Nonequilibrium Model,OSM)能较好地模拟Cd在壤砂土中的运移,模拟得到的吸附特性参数β较小,表明壤砂土吸附表面的不均一性较强。SiO2胶体的穿透时间较早,耦合沉淀-释放反应的CDE模型可以很好地描述SiO2胶体在壤砂土中的运移。胶体作用下的CDE模型成功地模拟了SiO2胶体存在时Cd的运移;同时,参数敏感性分析结果表明,胶体对Cd的吸附速率系数kamc、kaic越小,解吸速率系数kdmc、kdic越大,越有利于Cd的运移。     

胶体作用下饱和土壤中Cd运移的数值模拟

通过室内土柱出流实验探讨了饱和壤砂土中Cd在SiO2胶体作用下的运移行为,并用对流-弥散方程(Convection-Dispersion Equation,CDE)对实验结果进行了数值模拟.结果表明,土壤中SiO2胶体的存在抑制了Cd的运移,使Cd穿透时间较晚,出流浓度较低,土壤对Cd的吸附以动力学反应为主.耦合Freun-dlich等温吸附的单点非平衡模型(One Site Nonequilibrium Model,OSM)能较好地模拟Cd在壤砂土中的运移,模拟得到的吸附特性参数β较小,表明壤砂土吸附表面的不均一性较强.SiO2胶体的穿透时间较早,耦合沉淀-释放反应的CDE模型可以很好地描述SiO2胶体在壤砂土中的运移.胶体作用下的CDE模型成功地模拟了SiO2胶体存在时Cd的运移;同时,参数敏感性分析结果表明,胶体对Cd的吸附速率系数κamc、κaic越小,解吸速率系数κdmc、κdic越大,越有利于Cd的运移.     

不同类型微型蒸发器测定土壤蒸发的田间试验研究

利用微型蒸发器(Micro-Lysimeter,简称ML)测定土壤蒸发是一种简单、有效的方法,在中国西北旱区有很大的利用价值,但目前还没有统一的ML设计标准,所以寻求适合西北旱区使用的ML类型具有重要的现实意义。该文利用不同直径、不同长度、不同材料以及不同封底情况的ML在西北旱区进行了砂土和壤土的蒸发测量试验。研究结果表明：测得的土壤蒸发量随ML直径的增大而减小,不同直径ML测得的蒸发量在0.05的水平下有显著差异,测量砂土蒸发采用直径为15 cm的ML效果较好,壤土采用10 cm的较为理想。直径较小的情况下,ML的长度对蒸发量的影响显著,直径较大时则不显著,ML的长度以20c m为宜。ML的制作材料和是否封底对蒸发测量也有显著影响,在西北旱区,采用PVC不封底的ML较好。     

三峡水库消落带土壤胶体释放与迁移特征

三峡水库消落带是库区陆源污染物进入水库的最后屏障。高强度、周期性的干湿交替对消落带土壤理化性质、结构和可蚀性产生潜在影响,进而影响胶体颗粒的释放和迁移特征。探究消落带土壤胶体的释放与迁移行为是衡量胶体促进污染物迁移入库的重要前提。该研究对比消落带与非消落带土壤,通过原状土柱淋洗试验,研究饱和流中土壤胶体释放及迁移特征。结果表明,消落带原状土柱饱和淋洗液中胶体颗粒浓度先总体快速降低（184.58～28.04 mg/L）再缓慢增加（21.18～97.58 mg/L）,存在较大的时间变化（变异系数为0.46）。胶体颗粒累计释放量为714.43 mg,比非消落带土柱高34.4%,而淋洗液的峰值粒径（13.25～19.90 μm）和中值粒径（14.98～22.90 μm）均远远小于非消落带土柱的相应值,表明反复淹水-排干作用导致消落带土壤中胶体及细颗粒的释放和迁移潜力增大。溶解性有机碳（DOC,Dissolved Organic Carbon）是影响消落带饱和土壤中胶体释放的关键因子,对胶体浓度动态变化的解释率高达42.3%,而水化学因素（EC、Ca2+及Mg2+）对非消落带土壤中胶体颗粒的释放影响相对更大。在消落带管理中,应注意减控DOC的流失,以减少消落带土壤胶体颗粒的释放,同时建议加强消落带土壤DOC来源及其与胶体偶合并促进污染物如农化物质迁移进入库区水体的研究。     

Field parameterization of an empirical sheetwash transport equation

Specially designed instruments were used to sample surface water and sediment discharge on a set of small hillslopes. The data set produced is unique as it includes simultaneous observations of surface water and sediment discharge, local surface declivity and drainage area at several points over the slope surface, and the precipitation intensity taken a number of times through natural storm events. The data are used to parameterize an empirical sediment transport law, expressing sediment transport as a power function of the local declivity and surface water discharge. A good fit to the observed data is achieved, suggesting that these field techniques may be used to parameterize the equation for different soils. A dynamic catena effect involving surface grain size, local declivity and the form of the sediment transport equation is recognized that may have significant implications for the form of sediment transport and long-term hillslope development.     

Field parameterization of an empirical sheetwash transport equation

Specially designed instruments were used to sample surface water and sediment discharge on a set of small hillslopes. The data set produced is unique as it includes simultaneous observations of surface water and sediment discharge, local surface declivity and drainage area at several points over the slope surface, and the precipitation intensity taken a number of times through natural storm events. The data are used to parameterize an empirical sediment transport law, expressing sediment transport as a power function of the local declivity and surface water discharge. A good fit to the observed data is achieved, suggesting that these field techniques may be used to parameterize the equation for different soils. A dynamic catena effect involving surface grain size, local declivity and the form of the sediment transport equation is recognized that may have significant implications for the form of sediment transport and long-term hillslope development.     

An experimental and numerical study on flow and transport in a field soil using zero-tension lysimeters and suction plates

Zero-tension lysimeters are widely applied to study the fate of chemicals in the subsurface environment. However, conditions in lysimeters differ from the field situation, because local saturation is required at the lower boundary to collect leachate. The objective was to characterize the influence of the lower boundary on the flow and transport behaviour of bromide observed in six 1.2-m-long lysimeters and in the field by 30 suction plates installed at 1.2-m depth, which were operated with a time-variable suction equal to the ambient soil water potential. A bromide pulse was applied at the bare surface of a silty soil in autumn 1997 and monitored for 2.5 years. The mean leachate flux was 0.98 mm day⁻¹ for the lysimeters versus 0.66 mm day⁻¹ for the suction plates. The lysimeters had a slightly slower effective mean pore-water velocity, expressed as transport distance per unit of leaching depth, and exhibited more solute spreading than the suction plates. Numerical simulations revealed that the amount of water collected with the suction plates was sensitive to the hydraulic conductivity of the plates. The spatial variability in hydraulic properties in the model explained the observed variability in cumulative leachate, at least qualitatively. The arrival time and spreading of the breakthrough curves (BTCs) were well described by the simulations in the lysimeters, but were underestimated in the suction plates. Preferential flow through macropores, which is not an effective carrier for bromide, might be the reason for this discrepancy. Molecular diffusion contributed significantly to solute spreading and enhanced lateral mixing. Both the experiments and the simulations revealed that the dispersivity derived from BTCs is significantly influenced by the observation method and experimental conditions.     

Influence of water-dispersible colloids from organic manure on the mechanism of metal transport in historically contaminated soils: coupling colloid fractionation with high-energy synchrotron analysis

Purpose

Colloid-facilitated transport of metals is widely observed while manure is used for the improvement of contaminated soil. Details on the mechanism of colloid-associated metal transport are still lacking. This work investigated the nature of water-dispersible colloids (WDC) from different organic manures, differentiated the significance of clay and organic colloids in the metal transport, and finally provided direct and quantitative evidence for the importance of WDC in the colloid-facilitated transport of metals.

Materials and methods

Column experiments were conducted to assess the overall significance of WDC from effective microbial inoculated manure (EM) and leaf mulch (LM) for metal transport in alkali-contaminated soil. The properties of organic colloids such as hydrophilicity, aromaticity, and functional characteristics were analyzed by DAX-8 resin column, specific UV absorbance, and Fourier-transform infrared spectroscopy, respectively. Colloid identification and metal species determination were conducted using a combination of X-ray absorption near-edge structure, X-ray fluorescence spectroscopy, and transmission electron microscopy coupled with energy-dispersive X-ray analysis.

Results and discussion

Approximately 100 % of Pb, 69 % of Zn, and 38 % of Cu in the colloidal particles came from soil clay in the presence of EM colloids, while more than 80 % of Pb, Zn, and Cu in the LM colloids. Combined with the quantities of colloidal metals, it revealed that clay release was inhibited in the former and enhanced in the latter. The quantities of Cu and Zn associated with the EM colloids were much higher than that with the LM colloids. The contrary result was observed for Pb. LM colloids increased the quantities of organically associated Pb significantly.

Conclusions

Clay-associated metal transfer was influenced by the nature of WDC. Microbial manure colloids inhibited the clay-associated transfer of metals in the soils probably due to the presence of polysaccharide and microbially derived extracellular proteins. Leaf mulch colloids, with more hydrophobicity and aromaticity, enhanced the clay-facilitated transfer of metals in the soils.

     

Comparative study on different sediment transport capacity based on dimensionless flow intensity index

Journal of Soils and Sediments - Sediment transport plays a vital role in the development of soil erosion process models. The primary purpose of this study is to establish new sediment transport...     

闽南农业小流域土壤反硝化作用研究

土壤反硝化是流域土壤氮损失的重要途径之一。利用乙炔抑制培养法对五川流域内表层土壤的反硝化进行测定,研究发现,闽南农业小流域土壤具有较强的反硝化作用强度,在种植季节土壤平均反硝化作用强度为N 0.1 kg/(hm2.d),最高达到N 0.6 kg/(hm2.d),其中蔬菜地反硝化作用强于其他土地利用类型。反硝化作用同土壤的含水量、温度以及NO3-含量都存在有正相关关系,温度是流域土壤反硝化作用的最主要影响因子。五川流域土壤经由反硝化作用氮损失量占流域施肥量的16%,稍高于国内其他地区。     

Phytolith transport in soil: a laboratory study on intact soil cores

Column experiments on phytolith transport were conducted to assess the partial contributions of water percolation and earthworm activity to phytolith transport in loamy and sandy soils. Six intact cores of a loamy sandy Haplic Cambisol and nine cores of a silty loamy Stagnic Luvisol were excavated. With the Luvisol, three treatments were perfomed: a percolation treatment with periodic irrigation, but without earthworms, a percolation and earthworm treatment with periodic irrigation and earthworms (Aporrectodea caliginosa) and a control. The Cambisol cores did not contain earthworms and hence only percolation and control treatments were tested. The phytoliths of common reed (Phragmites australis) were labelled with the fluorescent dye fluorescein isothiocyanate and applied to the soil surface of each core. Except for the control treatment, 3600 mm of water was applied over 6 months. In the Cambisol, the weighted mean transport distance of phytoliths was significantly greater with percolation (2.2 ± 0.1 cm) than in the control (0.9 ± 0.3 cm), indicating that water percolation is a driving mechanism of phytolith transport. In the Luvisol, the difference in mean transport depth between control and percolation treatments (1.0 ± 0.2 and 1.5 ± 0.3 cm) was not significant. The earthworms did not affect the mean transport distance of phytoliths in the Luvisol, but the phytolith concentrations in the leachates were significantly greater and their size distribution did not change with soil depth as observed in the percolation treatment without earthworms. Further studies are required to quantify the effect of earthworms on phytolith transport.     

基于GRNN的坡面径流输沙能力模型的试验研究

坡面径流输沙能力是建立土壤侵蚀过程模型的重要水力学参数,研究定量计算坡面径流输沙能力的实用模型具有重要的理论和实践意义.通过室内模拟径流冲刷试验,计算不同坡度和流量条件下的裸地坡面径流输沙能力,利用平均影响值(MIV)方法对影响坡面径流输沙能力的因子进行分析,建立以干密度、能坡、进口流量、出口流量、水力半径、流速为输入,以坡面径流输沙能力为输出的广义回归神经网络(GRNN)模型,并应用Adaboost算法对模型进行优化.验证结果表明,所建模型能够用于对坡面径流输沙能力的模拟预测.与BP神经网络模型进行对比分析的结果表明:在试验训练样本条件下,广义回归神经网络(GRNN)模型的模拟预测结果优于BP神经网络模型;Adaboost算法能够有效减小广义回归神经网络(GRNN)模型的模拟预测误差.     

表面电荷性质对离子在土壤胶体界面扩散的影响

采用动力学方法测定了中性紫色土胶体和砖红壤胶体的电荷性质,研究了不同pH、电解质体系、浓度条件下离子在带电土壤胶体中的扩散过程,分析了两种土壤胶体在不同条件下离子扩散通量和扩散系数的特点。结果表明:1)中性紫色土胶体和砖红壤胶体中离子平衡扩散量为2.6～3.1 mg g-1和0.26～0.51 mg g-1,前者的扩散平衡量是后者的6倍～10倍;2)中性紫色土胶体不同温度条件下,离子扩散系数为1.17×10-9～1.91×10-9cm2s-1,砖红壤胶体中在与其对应温度条件下,离子扩散系数为0.23×10-9～0.45×10-9cm2s-1,前者是后者的4倍～5倍。表面电荷性质对离子在带电土壤胶体界面扩散的影响起决定性作用。     

Cytomolecular characterization of rDNA distribution in various Citrullus species using fluorescent in situ hybridization

The 18S–28S and 5S rDNA sites are useful chromosome landmarks and provide valuable evidence about genome organization and evolution. This investigation was the first attempt to study the dynamics, distribution and directionality of rDNA gains and losses, as well as to understand the contribution of site number variation in the speciation of the genus Citrullus. In this study, we employed fluorescent in situ hybridization (FISH), using the18S–28S and 5S rDNA gene loci, to evaluate the differences between the (1) cultivated type watermelon C. lanatus var. lanatus (sweet watermelon), (2) the “bitter” desert watermelon C. colocynthis (colocynth) that is indigenous to the deserts of northern Africa, the Middle East and Asia, (3) the C. lanatus var. citroides (citron) “Tsamma” or “cow watermelon” that is known as and is indigenous to southern Africa, (4) and C. rehmii that thrive in the Namibian Desert. The FISH analyses showed that the sweet watermelon and colocynth have similar rDNA configuration. The sweet watermelon and colocynth genomes contain two 18S–28S rDNA gene loci, each located on a different chromosome, and one 5S rDNA locus which is co-localized with one of the 18S–28S rDNA gene loci. On the other hand, the C. rehmii has one 18S–28S rDNA locus and one 5S rDNA locus positioned on different chromosomes, while the citron has one18S–28S rDNA and two 5S rDNA loci, each located on a different chromosome. A FISH analysis of F₁ (citron × sweet watermelon) chromosome spreads revealed uniparental homeologous rDNA gene copies pertaining to the sweet watermelon versus the citron chromosomes, with the sweet watermelon chromosome containing the 18S–28S and 5S rDNA locus versus the citron homologue chromosome that has the 5S rDNA locus, but not the 18S–28S rDNA locus. Genomic in situ hybridization (GISH) analysis, using the entire citron genome as a probe to be differentially hybridized on sweet watermelon chromosome spreads, revealed that the citron genomic probes mainly hybridize to subtelomeric and pericentromeric regions of the sweet watermelon chromosomes, suggesting extensive divergence between the citron and sweet watermelon genomes. The FISH and GISH cytogenetic analysis here indicate major differences in genome organization between the cultivated watermelon type sweet watermelon and its counterpart citron that thrive in southern Africa and considered a useful germplasm source for enhancing disease and pest resistance in watermelon cultivars.     

Exploring the effects of the vegetation on passive tracer transport by using the multifractal analysis

Multifractal turbulence formalism has been used to describe the time series in simulated passive tracer transport in a vegetated open-channel, phenomenon characterized by a high temporal non-linear variability. A study of the empirical statistical moments scaling function for several scale ratios reveals the presence of a multifractal phase transition associated with one critical moment. The parameters of the universal multifractal model have been estimated using the double trace moment method. The theoretical statistical moments scaling was simulated by using the universal multifractal model showing an acceptable agreement with the corresponding empirical function. The universal multifractal parameters estimated here have different values to those reported for obstacle-free phenomena such as the atmospheric turbulence and passive scalar transport in turbulent oceanic flows.     

Evaluation of linear and nonlinear sediment transport equations using hillslope morphology

Although some simple erosive processes like soil creep or tillage redistribution may be satisfactorily described by linear diffusive equations, the complexity of erosion phenomena requires the use of more complete nonlinear equations. Roering et al. [Roering, J.J., Kichner, J.W., Dietrich, W.E., 1999. Evidence for nonlinear, diffusive transport on hillslopes and implications for landscape morphology. Water Resour. Res., 35 853–870.] have proposed a single test, based on the relationship between the curvature and gradient of a hillslope, rather then using a linear diffusion equation. Nevertheless this test, based on steady state conditions, is not complete as it is shown in this work with a counter-example. The hillslope profile used by Roering et al. [Roering, J.J., Kichner, J.W., Dietrich, W.E., 1999. Evidence for nonlinear, diffusive transport on hillslopes and implications for landscape morphology. Water Resour. Res., 35 853–870.], (Fig. 2) can be generated either by a linear diffusion equation under transient conditions or a nonlinear diffusion equation under steady state conditions. Additional information on the soil profile changes would give a more complete interpretation of the hillslope evolution.     

Evaluation of linear and nonlinear sediment transport equations using hillslope morphology

Although some simple erosive processes like soil creep or tillage redistribution may be satisfactorily described by linear diffusive equations, the complexity of erosion phenomena requires the use of more complete nonlinear equations. Roering et al. [Roering, J.J., Kichner, J.W., Dietrich, W.E., 1999. Evidence for nonlinear, diffusive transport on hillslopes and implications for landscape morphology. Water Resour. Res., 35 853–870.] have proposed a single test, based on the relationship between the curvature and gradient of a hillslope, rather then using a linear diffusion equation. Nevertheless this test, based on steady state conditions, is not complete as it is shown in this work with a counter-example. The hillslope profile used by Roering et al. [Roering, J.J., Kichner, J.W., Dietrich, W.E., 1999. Evidence for nonlinear, diffusive transport on hillslopes and implications for landscape morphology. Water Resour. Res., 35 853–870.], (Fig. 2) can be generated either by a linear diffusion equation under transient conditions or a nonlinear diffusion equation under steady state conditions. Additional information on the soil profile changes would give a more complete interpretation of the hillslope evolution.