Assessment of key transport parameters in a karst system under different dynamic conditions based on tracer experiments: the Jeita karst system,Lebanon

Artificial tracer experiments were conducted in the mature karst system of Jeita (Lebanon) under various flow conditions using surface and subsurface tracer injection points, to determine the variation of transport parameters (attenuation of peak concentration, velocity, transit times, dispersivity, and proportion of immobile and mobile regions) along fast and slow flow pathways. Tracer breakthrough curves (TBCs) observed at the karst spring were interpreted using a two-region nonequilibrium approach (2RNEM) to account for the skewness in the TBCs’ long tailings. The conduit test results revealed a discharge threshold in the system dynamics, beyond which the transport parameters vary significantly. The polynomial relationship between transport velocity and discharge can be related to the variation of the conduit’s cross-sectional area. Longitudinal dispersivity in the conduit system is not a constant value (α?=?7–10 m) and decreases linearly with increasing flow rate because of dilution effects. Additionally, the proportion of immobile regions (arising from conduit irregularities) increases with decreasing water level in the conduit system. From tracer tests with injection at the surface, longitudinal dispersivity values are found to be large (8–27 m). The tailing observed in some TBCs is generated in the unsaturated zone before the tracer actually arrives at the major subsurface conduit draining the system. This work allows the estimation and prediction of the key transport parameters in karst aquifers. It shows that these parameters vary with time and flow dynamics, and they reflect the geometry of the flow pathway and the origin of infiltrating (potentially contaminated) recharge.     

Application of a solute transport model under variable velocity conditions in a conduit flow aquifer: Olalde karst system, Basque Country, Spain

A model based on numerical solutions, which allows for solving the dispersion equation under variable recharge and velocity conditions, is developed to simulate solute transport in conduit flow aquifers during flow recession periods. As an example, the evolution of a tracer in the little known karst conduit that links the sinking stream of Oma valley to the Olalde spring is investigated in the karstic region of Santa Eufemia-Ereñozar (Basque Country, Spain). The model, with different hypothetical structures, allows for obtaining series of tracer breakthrough curves, which are fitted to experimental data using an optimization algorithm. These results, although they can be used to simulate the tracer evolution between the two points considered, do not allow for determining the internal structure and spatial disposition of contributions in the aquifer.     

Hydrogeological controls of variable microbial water quality in a complex subtropical karst system in Northern Vietnam

Karst aquifers are particularly vulnerable to bacterial contamination. Especially in developing countries, poor microbial water quality poses a threat to human health. In order to develop effective groundwater protection strategies, a profound understanding of the hydrogeological setting is crucial. The goal of this study was to elucidate the relationships between high spatio-temporal variability in microbial contamination and the hydrogeological conditions. Based on extensive field studies, including mapping, tracer tests and hydrochemical analyses, a conceptual hydrogeological model was developed for a remote and geologically complex karst area in Northern Vietnam called Dong Van. Four different physicochemical water types were identified; the most important ones correspond to the karstified Bac Son and the fractured Na Quan aquifer. Alongside comprehensive investigation of the local hydrogeology, water quality was evaluated by analysis for three types of fecal indicator bacteria (FIB): Escherichia coli, enterococci and thermotolerant coliforms. The major findings are: (1) Springs from the Bac Son formation displayed the highest microbial contamination, while (2) springs that are involved in a polje series with connections to sinking streams were distinctly more contaminated than springs with a catchment area characterized by a more diffuse infiltration. (3) FIB concentrations are dependent on the season, with higher values under wet season conditions. Furthermore, (4) the type of spring capture also affects the water quality. Nevertheless, all studied springs were faecally impacted, along with several shallow wells within the confined karst aquifer. Based on these findings, effective protection strategies can be developed to improve groundwater quality.     

The stochastic simulation of karst conduit network structure using anisotropic fast marching,and its application to a geologically complex alpine karst system

Hydrogeology Journal - Anisotropic fast-marching algorithms are computationally efficient tools for generating realistic maps of karst conduit networks, constrained by both the spatial extent and...     

Comparison of a karst groundwater model with and without discrete conduit flow

Karst aquifers exhibit a dual flow system characterized by interacting conduit and matrix domains. This study evaluated the coupled continuum pipe-flow framework for modeling karst groundwater flow in the Madison aquifer of western South Dakota (USA). Coupled conduit and matrix flow was simulated within a regional finite-difference model over a 10-year transient period. An existing equivalent porous medium (EPM) model was modified to include major conduit networks whose locations were constrained by dye-tracing data and environmental tracer analysis. Model calibration data included measured hydraulic heads at observation wells and estimates of discharge at four karst springs. Relative to the EPM model, the match to observation well hydraulic heads was substantially improved with the addition of conduits. The inclusion of conduit flow allowed for a simpler hydraulic conductivity distribution in the matrix continuum. Two of the high-conductivity zones in the EPM model, which were required to indirectly simulate the effects of conduits, were eliminated from the new model. This work demonstrates the utility of the coupled continuum pipe-flow method and illustrates how karst aquifer model parameterization is dependent on the physical processes that are simulated.     

Spatial operations in a GIS-based karst feature database

This paper presents the spatial implementation of the karst feature database (KFD) of Minnesota in a GIS environment. ESRI’s ArcInfo and ArcView GIS packages were used to analyze and manipulate the spatial operations of the KFD of Minnesota. Spatial operations were classified into three data manipulation categories: single layer operation, multiple layer operation, and other spatial transformation in the KFD. Most of the spatial operations discussed in this paper can be conducted using ArcInfo, ArcView, and ArcGIS. A set of strategies and rules were proposed and used to build the spatial operational module in the KFD to make the spatial operations more efficient and topographically correct.     

Chemistry and source identification of wet precipitation in a rural watershed of subtropical China

South China is one of the regions severely suffering from acid rain in the world.However,few systematic studies of rural precipitation chemistry have been performed in comparison with the extensive studies on their urban counterparts of this region.In order to characterize the current acid rain status and identify its possible sources in the rural area of South China,we analyzed precipitation collected event by event from a rural forested watershed in southern Anhui Province between March 2007 and February 2010.The results showed that the concentrations of major ions within precipitation in the studied rural area were significantly lower than those reported for the urban areas of the same latitude in China.Nevertheless,the precipitation acidity(with an average pH value of 4.49) and the frequency of acid rain(95%) were considerably high.The relatively high ratio of(SO42+ NO 3)/(Ca2+ +NH4+) was the main cause of acid rain in this rural area,as SO 2 and NO x were the main precursors of acid rain,while Ca2+ and NH4+acted as the dominant neutralizers to the acidity.Source identification indicated that Ca2+ and Mg2+ mainly were derived from alkaline dust,SO42,NO 3 and NH4+originated mainly from anthropogenic sources such as industrial and agricultural activities,most Na +,Cl,K + and some of Mg2+ were derived from the sea.The results suggested that the major ions within precipitation in the rural area of South China were related to the meso-scale and long-range transport of particles and aerosols in the air.     

Chemical parameters as natural tracers in hydrogeology: a case study of Louros karst system,Greece

The Louros Basin hosts one of the most important karst systems of Epirus Prefecture (Greece) and plays a key role in supplying three counties with drinking water. Aiming to investigate the origin of groundwater and its flow patterns, a multi-tracer approach was used to describe and evaluate the hydrogeology of the system. Therefore, 271 surface water and groundwater samples were collected and analyzed for physicochemical parameters, major ions, and trace and rare earth elements, as well as stable isotopes (δ¹⁸O and δ²H). These data provided meaningful tracing of the water origin, water–rock interaction processes, and relationships among the aquifers. In particular, the elaboration of the major ions supported by the distribution of rare earth elements indicated that there are three aquifers located at different levels hosted in the Senonian and Pantokrator limestone formations. These aquifers are hydraulically interconnected by a cascade and constitute the Louros karst system which is drained by the homonymous river. Hydrochemical and isotopic data revealed that the Louros karst system is isolated from the adjacent northern Ioannina Basin and it is being recharged by precipitation. Higher groundwater salinity, where present, is mainly associated with increased water–rock interaction due to longer and deeper hydrologic flow, favoring the dissolution of evaporitic, carbonate and phosphate minerals.     

Spring and conduit sediments as storage reservoirs for heavy metals in karst aquifers

Sediment samples were collected from six springs draining the karst aquifer at Fort Campbell, Kentucky/Tennessee. These were analyzed by ICP-MS following an extraction procedure that separates the metals into exchangeable, carbonate, oxide, organic and residual fractions. Aluminum and iron are primarily present in the residual fraction while manganese may be dominantly in either the oxide or carbonate fraction. The redox-sensitive metals (Fe and Mn) have the greatest fractional distribution in the spring with the thickest sediments. Trace metals detected include Cr, Cd, Ni, Pb, and Zn in the range of a few to 200 mg/kg. In Beaver Spring, nickel is distributed between the exchangeable, carbonate and organic fractions, while in Gordon Spring, nickel is largely residual. Chromium is almost entirely associated with the organic fraction in Beaver Spring while it is largely residual in Gordon Spring.     

On the occurrences of dry and wet sequences in the Brahmaputra valley

Occurrence of dry and wet days in the Brahmaputra Valley has been studied using a first-order Markov Chain model. The model is fitted to the daily rainfall series recorded at ten stations widely distributed in the valley. The adequacy of the model is tested and found suitable. At all the stations, dry and wet spells having different durations follow geometric distribution. For pre-monsoon and monsoon seasons, the expected dry and wet days, the expected length of a weather cycle and the return period of dry spells having different, durations are calculated, and the results for different stations are compared.     

武汉市大气干湿沉降中溶解态黑碳的季节分布特征

本研究采集了武汉市城区2018年3月至2019年2月的大气总沉降及湿沉降样品,使用苯多羧酸法测定溶解态黑碳含量,并结合气象条件分析溶解态黑碳沉降通量季节变化特征及其影响因素。结果表明,总沉降中溶解态黑碳月浓度范围为0.12～0.83 mg/L,均值为0.40 mg/L,湿沉降溶解态黑碳浓度范围为0.04～0.18 mg/L,均值为0.10 mg/L;溶解态黑碳总沉降和湿沉降年通量分别为269 mg·m^-2·a^-1和65 mg·m^-2·a^-1。溶解态黑碳总沉降通量季节变化为春季>冬季>夏季>秋季,湿沉降通量季节变化为冬季>春季>夏季>秋季。溶解态黑碳湿沉降通量主要受降雨量影响,而总沉降通量除受降雨量影响外还受风速、风向和空气质量等因素的共同影响。     

Spatial variability of flow parameters in a stratified sand

The spatial variability in porosity, hydraulic conductivity, compressibility, and various grain size fractions is analyzed for several sets of samples from the Quadra Sand. This unit is a well-sorted, medium grained, horizontally stratified sand with relatively few silt or gravel interbeds. Both random and uniformly spaced sample plans are used. The heterogeneity of the flow parameters is characterized by frequency histograms and their estimated moments, by their sample autocorrelation functions, and the estimated power spectra. Emphasis is placed on the nature of the spatial dependence between neighboring values of the flow parameters. A nearest neighbor stochastic process model is fit to the data to consider its adequacy in describing the spatial dependence within the porosity and hydraulic conductivity sequences. Even though the Quadra Sand is relatively uniform, a fairly complex spatial structure is observed. A simple monotonically decaying autocorrelation function may not adequately represent the spatial continuity. Statistical anisotropy is observed in both the extent of the spatial autocorrelation and in its functional form. Results show the importance of scale in constructing a probability model to describe the spatial variability.     

广西北山岩溶管道—裂隙—孔隙地下水流数值模拟初探

本文从水动力学角度分析各种岩溶含水介质中的水流特征,将其归纳为储水介质、导水介质和控水介质,并根据折算渗透系数ＫＬ的概念和建立耦合达西流和百达西流于一体的岩溶管道－裂隙－孔隙三重介质地下水模型,对广西环江北山矿区岩溶含水系统进行了初步探讨。北山实例的模拟结果表明,三重介质模型较全面地刻画了岩溶水动态的特征,反映了相对均匀裂隙流与控制性管道流并存、线性流与非线性流相互转变的运动特点,不仅理论上比较合     

Role of karstification and rainfall in the behavior of a heterogeneous karst system

 The complex functioning of karst systems depends on several factors (e.g., geology, karstification status, climate) which influence flow conditions. Understanding a system requires monitoring that includes a sampling interval well adapted to the system's size, and the use of hydrodynamic and geochemical approaches. From our own observations, the general physical and geochemical characteristics of the aquifers are perennial and representative of karst evolution at a given moment. The Notre-Dame-des-Anges karst system, which is situated in France on the rim of the Vaucluse karst region, was studied during 2 water years. This study demonstrates that several parameters are not definitive, and that they do not provide information about the actual status of the karst evolution of the system. We were able to observe that hydrological parameters in particular are dependent on the configuration of the outlets, which can dramatically change. For example, a heavy storm (300 mm of rain in 4 h), which occurred in the intake area on 22 September 1992, produced a piston effect in the aquifer, which was expressed by extensive unclogging of the whole aquifer. The appearance of a new gryphon at the outlet induced a change in the flow rate and added to the unclogging. The other major result of this study is the demonstration of intensive, even preponderant, participation of water originating in the infiltration zone in the behavior of the system. This contribution, often minimized in previous studies, is closely dependent upon flow conditions and especially upon the recharge status of the infiltration zone. Physical and chemical parameters allowed us to trace this water, and to demonstrate the existence of an actual hanging reserve which plays not a negligible part in flow, during both high and low water levels. This paper demonstrates the necessity of coupling a hydrodynamic study with a hydrochemical approach, and of questioning the representativeness of parameters during a given period, for a better understanding of the functioning of the karst system. This is especially true if the infiltration zone of the karst system is heavily developed, and if external factors (e.g., river, landslip, clogging) influence the outlet Received: 10 June 1996 / Accepted: 11 November 1996     

Kinetics of fine wet grinding of zeolite in a steel ball mill in comparison to dry grinding

Batch wet grinding of zeolite was studied with emphasis on a kinetic study in a laboratory size steel ball mill of 200 mm diameter. The breakage parameters were determined by using the single sized feed fractions of − 850 + 600 µm, − 600 + 425 µm and − 425 + 300 µm for the zeolite samples. The S_i (specific rate of breakage) and B_i,j (primary breakage distribution) values were obtained for those feed size fractions in order to predict the product size distributions by simulation for comparison to the experimental data. The specific rates of breakage values for wet grinding in the first-order breakage region were higher than the dry values reported previously by a factor 1.7 at the same experimental conditions, but the primary breakage distribution (B_i,j) values were approximately the same. The simulations of the product size distributions of zeolite were in good agreement with the experimental data using a standard ball mill simulation program. The wet grinding of zeolite was subjected to slowing-down effect in the mill at 2 min of grinding, corresponding to an 80% passing size of about 400 µm. On the other hand, the slowing down effect in the dry grinding of zeolite was also seen at 4 min of grinding. In addition, effects of some operational parameters on dry and wet grinding of zeolite were determined by simulation using the breakage parameters obtained experimentally.     

Flow and solute transport monitoring in the karst aquifer in SW Slovenia

The role of the unsaturated zone in the karst aquifer hydraulic behaviour was brought into focus in these studies of the catchment of the Hubelj spring (SW Slovenia). The variations of natural tracers in precipitation and in groundwater during a summer storm event made it possible to trace local flow and solute transport in the observed aquifer. The results produced data on the aquifer recharge, storage and discharge processes, as well as on mechanisms that affected them, which reflects a karst groundwater dynamics also at a regional scale. They point out the significance of effects of the fast preferential flow—epiflow that is the main factor controlling solute/contaminant transport towards the aquifer saturated zone. Numerous arguments indicate that the karst aquifer flow and solute transport mechanisms depend on the hydraulic behaviour of the epikarst zone.     

瞬变电磁在干旱地区探测岩溶水的应用

岩溶含水带及断层破碎带的电阻率,与其完整的围岩有明显的物性差异.在多测道V/I剖面图上显示为双峰异常,在视电阻率和纵向电导断面图上,分别显示低阻和高电导异常.为干旱地区找水、圈定富水地段、确定井位提供了依据.     

Chernobyl radiocaesium in a karst system,Marble Cave,Crimea

 Surface contamination with radioactive caesium introduced into the environment after the accident at the Chernobyl nuclear plant was high enough in the Crimean Mountains to allow using radiocaesium as an indicator of penetration of radioactive contamination into a karst system. Caesium concentrations have been studied in soils above Marble Cave, Tchatyrdag Plateau, in percolation waters and in sediments transported by percolation waters within the cave. Contamination of the daylight surface with ¹³⁷Cs is about 30 kqB m^–2 which is approximately 13 times higher than the density of global fallouts. Besides ¹³⁷Cs, almost all samples showed presence of ¹³⁴Cs with the ¹³⁷Cs/¹³⁴Cs ratio close to that of Chernobyl contaminations. Concentrations of ¹³⁷Cs range from 9 to 15 mBq l^–1 in the present percolation waters in the cave. In sediments related to percolation waters ¹³⁴Cs is detected in some samples besides ¹³⁷Cs, although the effect of ²²⁸Ac is not ruled out. Surprisingly, the highest concentrations of radiocaesium were measured in "old" sediments in the cave's lower series. These sediments are not associated with modern percolation and are represented by a clay/moonmilk alternating sequence deposited in an old dried cave lake. Moonmilk layers have higher caesium content than clay. It is assumed that Chernobyl caesium was transported into the cave with aerosols which were then deposited mainly in areas where condensation occurs. The sampling site is located just in the boundary between two microclimatic zones with a temperature gradient of 0.5  °C. Active condensation processes occur in this area. Caesium was not detected in another similar sampling site (old lake deposits) located within homogeneous microclimatic conditions. If the above interpretation is correct, these results show the geochemical significance of the aerosol-condensation mechanism of mass transport and localisation. Received: 1 June 1995 · Accepted: 4 December 1995