盐溶液法测定非饱和膨润土的水分特征曲线

对于高放废物的最终处置，深地质处置被国内外公认为最合适的方法，而膨润土也被认为是高放废物处置库缓冲回填材料的良好基质。鉴于膨润土各项性质研究的重要性。本文介绍了利用盐溶液法进行非饱和膨润土水分特征曲线的测定工作，发现盐溶液法适合测定吸力极高的非饱和土，是一种值得推广的方法。     

一种用于突发性场地污染模拟的解析模型

为了及时有效地应对各种突发性环境污染事故,有必要开发一种简单实用、适于各类型污染物的场地污染数学模型。通过污染事故发生后污染物在包气带、饱和带迁移转化的概化,建立了污染物运移的自由入渗模型以及降雨入渗模型并给出各自相应的解析解。无降雨时,考虑污染物在重力作用下随包气带向下渗透的作用,建立一维垂直入渗模型。有降雨时,考虑污染场地(包气带)中污染物迁移和转化的对流作用、扩散作用及挥发、生物降解、吸附、根系吸收等作用,建立包气带剖面二维溶质运移模型和饱和带平面二维溶质运移数学模型。建模过程中,假定降雨量的平均分布及土壤质地、水力参数以及有机物成分、种类均相同,同时假定污染物与多孔介质间的作用为线性吸附,植物根系对污染物的吸附遵循一级动力学。基于模型的解析解,实现案例的模拟计算。模拟结果表明:该模型具有适用范围广、模拟高效快捷等优点,能够较准确预测污染发生后污染物在土壤中的动向、到达饱和带的时间以及饱和带中污染物的迁移情况。     

Watershed structural influences on the distributions of stream network water and solute travel times under baseflow conditions

Watershed structure influences the timing, magnitude, and spatial location of water and solute entry to stream networks. In turn, stream reach transport velocities and stream network geometry (travel distances) further influence the timing of export from watersheds. Here, we examine how watershed and stream network organization can affect travel times of water from delivery to the stream network to arrival at the watershed outlet. We analysed watershed structure and network geometry and quantified the relationship between stream discharge and solute velocity across six study watersheds (11.4 to 62.8 km²) located in the Sawtooth Mountains of central Idaho, USA. Based on these analyses, we developed stream network travel time functions for each watershed. We found that watershed structure, stream network geometry, and the variable magnitude of inputs across the network can have a pronounced affect on water travel distances and velocities within a stream network. Accordingly, a sample taken at the watershed outlet is composed of water and solutes sourced from across the watershed that experienced a range of travel times in the stream network. We suggest that understanding and quantifying stream network travel time distributions are valuable for deconvolving signals observed at watershed outlets into their spatial and temporal sources, and separating terrestrial and in‐channel hydrological, biogeochemical, and ecological influences on in‐stream observations. Copyright © 2016 John Wiley & Sons, Ltd.     

APPLICATION OF UNIT HYDROGRAPH TECHNIQUES TO SOLUTE TRANSPORT IN CATCHMENTS

Current models of solute movement in catchments are based on rainfall–runoff models and are consequently biased towards processes which determine the magnitude and timing of water flux. It is shown here that the instantaneous unit hydrograph (IUH), or runoff response function, obtained from a hydrograph is fundamentally different from the residence time distribution which governs the response to solutes/tracers. Using hydrometric and tracer data obtained from a small (25 ha) catchment in the humid tropics a modification of the IUH technique is demonstrated which also allows approximate modelling of the tracer data. New features of the modified conceptual model are identified with known hillslope processes.     

Solute provenance,transport and denudation in a high arctic glacierized catchment

Recent understanding of chemical weathering in glacierized catchments has been focused on mid-latitude, Alpine catchments; comparable studies from the high latitudes are currently lacking. This paper attempts to address this deficiency by examining solute provenance, transport and denudation in a glacierized catchment at 78°N in the Svalbard High Arctic archipelago. Representative samples of snow, glacier ice, winter proglacial icing and glacier meltwater were obtained from the catchment during spring and summer 1993 and analysed for major ion chemistry. Seasonal variations in the composition of glacier meltwater occur and are influenced by proglacial solute acquisition from the icing at the very start of the melt season, and subsequently by a period of discharge of concentrated snowmelt caused by snowpack elution; weathering within the ice-marginal channels that drain the glacier, particularly carbonation reactions, continues to furnish solute to meltwater when suspended sediment concentrations increase later in the melt season. Partitioning the solute flux into its various components (sea-salt, crustal, aerosol and atmospheric sources) shows that c. 25% of the total flux is sea salt derived, consistent with the maritime location of the glacier, and c. 71% is crustally derived. Estimated chemical denudation, 160 meq m⁻² a⁻¹ sea salt-corrected cation equivalent weathering rate, is somewhat low compared with other studied glacierized catchments (estimates in the range 450–1000 meq m⁻² a⁻¹), which is probably attributable to the relatively short melt season and low specific runoff in the High Arctic. A positive relationship was identified between discharge and CO₂ drawdown owing to carbonation reactions in turbid meltwater. © 1997 John Wiley & Sons, Ltd.     

近海地下石油储备库海水入侵风险研究

地下石油储备库于近海处建立,可降低石油运输成本,同时有较强的军事意义。但是临近海岸线,海水易入侵库区,导致库区内金属结构腐蚀,使储备库的使用年限降低。以某近海地下石油储备库工程为背景,构建了综合断层、节理密集带、导水通道等15种地质结构的精细化三维水文地质模型,研究了库区自然状态下和运行期的地下水渗流场及溶质运移场,模拟海水入侵风险。研究表明：（1）自然状态下地下石油储备库无海水入侵。（2）运行期只在洞库顶部以上25 m处设置四周超出洞室50 m、水幕孔间距为10 m、孔径0.11 m的水平水幕时,不能有效防治海水入侵。（3）洞库运行9 a时,3#洞室东南侧Cl−物质的量浓度超过7 mol/m3,海水开始入侵洞室群;运行22~23 a时,海水入侵速率最快;运行41 a 时,3#洞室东南侧Cl−物质的量浓度超过143 mol/m3,海水入侵达到对钢筋的强腐蚀程度;运行50 a时,除1#洞室外其余所有洞室均受到海水入侵,3#、4#洞室有部分区域达到强腐蚀程度,海水入侵最严重。建议增设垂直水幕等设施,以增强对海水入侵的防治。研究成果可为近海地区地下石油储备库抑制海水入侵提供借鉴。     

FLOW SEPARATION IN UNDISTURBED SOILS USING MULTIPLE ANIONIC TRACERS. PART 1. ANALYTICAL METHODS AND UNSTEADY RAINFALL AND RETURN FLOW EXPERIMENTS

Tracers provide one of the few ways of obtaining realistic information on the flows of water and solutes in undisturbed structured soils. Three fluorinated organic acids [pentafluorobenzoic acid, 2,6-diflurobenzoic acid and o-(trifluoromethyl) benzoic acid] and bromide were tested as anionic tracers in situations where the separation of different flow components is of interest. The fluorobenzoates were relatively conservative (approximately 90% for loam soil) although, in some instances, co-elution or complexation may lead to apparently non-conservative behaviour. Tracer mixtures applied to soils, were separated and quantified by high-performance liquid chromatography. The relative mobilities of the tracers were studied during unidirectional steady flow in large undisturbed soil columns brought back to the laboratory. The breakthrough curves showed highly dispersive behaviour, with very early breakthrough of solute and a long tail. Contributions to the column outflow of different simultaneous applications of rainfall and return flow, labelled with different tracers, were separated using multicomponent mixing equations. The results show the importance of preferential flow and relatively immobile storage in the transport process.     

FLOW SEPARATION IN UNDISTURBED SOIL USING MULTIPLE ANIONIC TRACERS. PART 2. STEADY-STATE CORE-SCALE RAINFALL AND RETURN FLOWS AND DETERMINATION OF DISPERSION PARAMETERS

A series of experiments designed to study the separation of flow components from two large undisturbed cores under steady-state rainfall (downward) and return (upward) flows under near-saturated conditions is summarized. The experiments were conducted on soil columns collected from Lancaster University and the Slapton Wood catchment, Devon. The use of the relatively conservative tracers, potassium bromide, o-(trifluoromethyl)benzoic acid and 2,6-difluorobenzoic acid and a combination of application rates made it possible to quantify the different sources of water contributing to the discharge hydrographs. There is significant retention of tracer within the cores, despite the application of several pore volumes of water. The use of steady flow conditions allowed the determination of dispersion coefficients, dispersivity and proportion of ‘mobile’ water content parameters of the advection–dispersion equation. It was found that there were significant differences between the dispersivities at different flow-rates under upward and downward flux conditions and that in the undisturbed cores studied here the apparent proportions of mobile pore water ranged between 0.33 and 1.0, with an apparently complex relationship to flux rate. Prediction of transport in undisturbed soil remains problematic and tracer experiments will continue to be needed to provide a fundamental understanding of the complex flow processes involved.     

Temporal variability of solute transport under vadose zone conditions

The heterogeneity of the solute flux field in the horizontal plane at the field scale has been documented in several field studies. On the other hand, little information is available on the persistence of certain solute transport scenarios over consecutive infiltration cycles. This study was initiated to analyse the recurrence of solute leaching behaviour as estimated in two soil column tests emphasizing the preferential flow phenomenon. Twenty-four small-sized soil samples were subjected to two consecutive unsaturated steady-state flow leaching experiments with bromide as tracer. Observed breakthrough curves (BTCs) were analysed by the method of moments and by the advection–dispersion equation (ADE) to classify solute behaviour. Frequency distributions of the parameters indicating the solute velocity were heavily skewed or bimodal, reflecting the broad variability of the leaching scenarios, including some with pronounced preferential solute breakthrough. Exclusion of the preferential flow columns from our calculations revealed an average amount of 37% of immobile water. The large-scale BTCs derived from assembling the individual concentration courses of each run showed similar features, such as an early bromide breakthrough. However, two distinct apices, viz. one preferential and one matrix, were observed only in the first run, whereas the concentration decrease between the peaks was missing from the second run. A change in soil structure with continuous leaching was presumed to modify the interplay of the various flow domains, thereby altering the spreading of the BTCs. Correlation analysis between parameters of both tests suggests that preferential transport conditions are likely to occur at the same locations in the field over several infiltration cycles, whereas the ‘classical’ or expected matrix flow is time variant and therefore seems to be hardly predictable. © 1998 John Wiley & Sons, Ltd.