Interpretation of groundwater level monitoring results in karst aquifers: examples from the Dinaric karst

The paper presents an attempt to determine the characteristics of karst aquifers using information on groundwater level (GWL) in natural holes and boreholes with different data quantity and time resolution of GWL measurements. In this paper the particulars of karst aquifers were analysed for four examples from the Dinaric karst. In all four study areas, aquifers are formed in bare, deep and well‐developed Dinaric karst consisting of Cretaceous limestones. The first example represents a wide area of Imotsko polje in the karst. The aquifer was analysed on the basis of infrequent water level monitoring in natural karst water features (jamas, lakes, wells) and discharges of springs and rivers. The karst aquifer in this example is complex, non‐homogenous and variable in space and time, which is frequent in the Dinaric karst. Regardless of the aforementioned it was possible to determine its elementary characteristics. The second example represents 10 wells used for the water supply for the city of Pula. The GWL and salinity were measured once a week in the period between 1981 and 1996. Even though these measurements were relatively infrequent in space and time, they served as bases for assessment of average and maximum aquifer conditions as well as boundaries of saltwater intrusion. In the third example only a portion of aquifer of the karst spring Blaz, which is in the contact with the Adriatic Seas, has been analyzed. It is a spring with an intrusion of salt water. For purposes of study of saltwater intrusion, 26 piezometers were drilled in its vicinity in which GWL, salinity and temperature were measured once a day during 168 days, a period comprising one complete cycle of seawater intrusion and retreat. These measurements proved the existence of dispersed discharge from the aquifer into the sea and its non‐homogeneity in space. In the fourth example GWL was measured continuously in 10 deep (up to 300 m) piezometers in the hinterland of the Ombla Spring catchment. The measurement period lasted 2 years (January 1988 to December 1989). The analyses are made with hourly data. The results made it possible to determine numerous characteristics of the karst aquifer and a significant non‐homogeneity of groundwater distribution in karst aquifers, depending more on the underground karst phenomena than the surface karst forms. Copyright © 2000 John Wiley & Sons, Ltd.     

Impact of an inter‐basin water transfer and reservoir operation on a karst open streamflow hydrological regime: an example from the Dinaric karst (Croatia)

This paper describes the hydrological changes caused by inter‐basin water transfer and the reservoir development on the hydrological regimes of two rivers. The Sabljaki Reservoir in the Zagorska Mre?nica River and the Bukovik Reservoir in the upper Dobra River began operation in 1959. Both are part of the hydroelectric power plant (HEPP) Gojak, whose installed capacity is 50 m³/s. Their water volumes at the spillway altitudes of 320·10 and 320·15 m a. s. l. are 3·3 × 10⁶ and 0·24 × 10⁶ m³ respectively. Both the Dobra and Mre?nica Rivers are losing, sinking and underground karst rivers. A 9376‐m‐long tunnel provides water from the Sabljaki Reservoir to the HEPP Gojak, which was constructed in the Lower Dobra River. The Sabljaki Reservoir is located in the Pla?ki karst polje, while the Bukovik Reservoir is located in the neighbouring Ogulin karst polje. The consequences of the inter‐basin water transfer are strong and have caused abrupt changes in the hydrological regimes of the downstream sections of both rivers. At the same time, the construction and development of both the reservoirs have also caused hydrological changes to the upstream section of the Upper Dobra River. Copyright © 2010 John Wiley & Sons, Ltd.     

Hydrology of Blue Lake in the Dinaric karst

The aim of this paper is to analyse hydrological measurements obtained from Blue Lake located near the town of Imotski (Croatia), during the period from 6 November 2009 at 10:26 h to 4 September 2010 at 03:26 h (7230 h or 302 days). The water depth, water temperature and electrical conductivity of the water were continuously measured during this period. The measurements were obtained with a CTD DIVER (Schlumberger Water Services). The instrument was fixed at the bottom of Blue Lake, which means that all the measured data refer to a single point of measurement. The data represent the first systematic and continuous monitoring of the hydrological parameters of this fascinating karst phenomenon. The hydrological analysis also involved daily rainfall data and daily mean air temperatures recorded at the nearby Imotski meteorological station. The rate of water level rise and fall and the hourly and daily average inflow and outflow into and from the lake were calculated using the available data. The analysis led to the conclusion that Blue Lake is mainly recharged by water coming from the karst aquifer, the dimensions and the characteristics of which have not yet been adequately studied. Copyright © 2013 John Wiley & Sons, Ltd.     

Monthly and annual effective infiltration coefficients in Dinaric karst: example of the Gradole karst spring catchment

Abstract

The method of “historic event” is used to generate synthetic hyetographs based on statistical analysis of precipitation data. A synthetic triangular model was developed based on rainfall data of Zioud watershed (central Tunisia) with a standard time step of one hour. A database of 2799 observed rainfall events was used to provide statistical parameters for a simple triangular-shaped hyetograph model. The developed model provides a synthetic hyetograph in dimensionless form for different storm durations (2, 3 and 4 hours). For a given season and location, the variation of the first dimensionless moment with duration was relatively small, with an average range of 13% for all the stations. The resulting dimensionless hyetographs were found to be nearly identical when they were non-dimensionalized using the rainfall depth and duration, showing some seasonal effect and insignificant effects of the rainfall duration. A good agreement between simulated and observed hyetographs was achieved based on not only visual impressions, but also statistical numerical and graphical tests.     

The influence of hydroelectrical development on the flow regime of the karstic river Cetina

The Cetina River is a typical karst watercourse in the deep and well‐developed Dinaric karst. The total length of the Cetina River open streamflow from its spring to the mouth is about 105 km. Estimated mean annual rainfall is 1380 mm. The Cetina catchment is built of Triassic, Jurassic, and Cretaceous carbonate strata. The western part of the catchment by the Cetina River is referred to as the ‘direct’ or topographic catchment. It was defined based on surface morphologic forms, by connection between mountain chain peaks. This part of the catchment is almost entirely situated in the Republic of Croatia. The eastern part of the catchment is referred to as the ‘indirect’ catchment, and is mainly situated in Bosnia‐Herzegovina. Water from the ‘indirect’ catchment emerges from the western ‘direct’ catchment in numerous permanent and temporary karst springs. Since 1960, numerous hydrotechnical works have been carried out on the Cetina River and within its catchment. Five hydroelectric power plants (HEPPs), five reservoirs, and three long tunnels and pipelines have been built. Their operation has significantly altered the natural hydrological regime. The Cetina River is divided into two hydrological reaches. In the 65 km upstream, the hydrological regime was redistributed within the year: low flows had increased and high flows had decreased, although the mean annual discharge remained the same. Part of the Cetina watercourse downstream from the Pran?evi?i Reservoir lost the majority of its flow. The mean annual discharges dropped from 100 m³ s^?1 to less than 10 m³ s^?1 because of the Zaku?ac HEPP development. Copyright © 2003 John Wiley & Sons, Ltd.     

Impact of groundwater flow on meandering; example from the Geul River,The Netherlands

The Geul River, located in the south‐eastern part of The Netherlands, is a meandering river with a planform shape characterized by large loops consisting of multiple bends. We evaluate the effect(s) of groundwater flow on the shapes of meanders as a possible explanation for the multi‐bend loops, using a combined meandering–groundwater computer model. In the model seeping groundwater enhances bank erodibility. Based on the simulation results, we present a conceptual, generalized model for groundwater–meandering interaction, based on wavelength selection and fixation effects. Wavelength selection occurs because of the positive feedback between growing meander bends and groundwater flow patterns and velocities. The promoted wavelengths have the same spatial scale as the groundwater flow system in the aquifer underlying the floodplain. In the case of the Geul River these wavelengths are of the order of 100 m. Since groundwater flow velocities are largest close to the recharging hill‐slopes, the seepage‐enhanced bank erodibilities are at a maximum near the floodplain limits. At these locations the difference in erodibility between banks facing the floodplain and those facing the hill slopes is large, so it is difficult for the river to migrate away from the floodplain limits. This causes long stretches of the river to be aligned along the floodplain limits, which we term a fixation effect. This mechanism best explains the multi‐bend loops of the Geul River. The general interaction between groundwater flow and meandering is site specific since it depends on climatic, fluvial and hydrogeological parameters. The Geul is characterized by a wide floodplain and steep hill‐slopes, and it is underlain by coarse‐grained deposits with good aquifer properties, favoring an important groundwater system. Since this kind of river frequently occurs, our results could apply to many other river systems. Copyright © 2008 John Wiley & Sons, Ltd.     

Changes in hydrological regime caused by human intervention in karst: the case of the Rumin Springs

ABSTRACT

Any human intervention or action in karst terrains can unexpectedly, suddenly, strongly and, generally, dangerously change a local and/or a regional hydrological regime. A characteristic example of the Dinaric karst is given in this paper. The operation of two reservoirs in Livanjsko Polje at an altitude of about 702 m above sea level (m a.s.l.) and hydro-electric development of the Cetina River system started in 1973. This year marked a drastic and instantaneous change in the regional hydrological regime. A significant drop in the minimum, mean and maximum annual discharges of two neighbouring karst springs, Rumin Mali and Rumin Veliki, was caused by this anthropogenic construction. The exits of the two analysed karst springs, Rumin Mali and Veliki, are located at altitudes of about 326.8 m a.s.l. and 307.6 m a.s.l. respectively. The areal distance between them is 640 m. Their hydrological regimes have been altered in different ways. The drop in discharges is stronger for the Rumin Veliki than for the Rumin Mali. The analysis shows that the system development influenced the redistribution of the regional karst aquifer and, in this manner, contributed to the reduction of both karst springs’ recharge areas.

Editor D. Koutsoyiannis Associate editor E. Rozos     

Water and air dynamics within a deep vadose zone of a karst massif: Observations from the Lukina jama–Trojama cave system (−1,431 m) in Dinaric karst (Croatia)

Extreme heterogeneity of karst systems makes them very challenging to study. Various processes within the system affect its global response, usually measured at karst springs. Research conducted in caves provides a unique opportunity for in situ analysis of separate processes in karst underground. The aim of the present study was to research the water and air dynamics within a deep karst system. Air and water basic physical parameters across the Lukina jama–Trojama cave system (?1,431 m) were continuously monitored during a 1‐year period. Recorded hydrograph of the siphon lake at the bottom of the cave was used to interpret the characteristics of an unexplored phreatic/epiphreatic conduit network. Water origin in the siphon was determined based on temperature and electrical conductivity. Air temperature and humidity monitoring revealed a strong inflow of air of sub‐zero temperature into the upper portion of the cave during winter. Cave passage morphology was interpreted as the main determinant of air dynamics, which caused ice to accumulate extensively in the upper portions of the cave and caused the temperature on the top of the homothermic zone to be significantly below the mean outside temperature. Air dynamics also lowered the temperature of water flowing through the cave vadose zone and feeding the phreatic zone of the massif. The pronounced temperature difference between the phreatic zone and the top of the homothermic zone probably contributed to the thermal gradient observed in the cave, which is steeper than in ice‐free caves in the area. Our results enabled the development of a conceptual model that describes coupling between air and water dynamics in the cave system and its surroundings.     

旅游酒店排污影响下的岩溶地下水水化学变化

岩溶地下水系统具有高度的开放性和脆弱性,使得地下水极易遭受污染.为探究旅游酒店排污对岩溶地下水水化学变化的影响,以金佛山世界自然遗产地水房泉流域为例,对水房泉地下水的水化学进行自动化监测,对流域内雨水、土壤水、某酒店自来水、污废水进行定期采集,结合流域硝酸盐氮氧同位素分析.结果表明,监测期间水房泉水化学变化随酒店入住游客量总体表现为3个阶段：前期受降雨影响显著,旅游高峰期间水质急剧恶化,后期水质明显好转.酒店生活污废水的排放成为水房泉水化学演变的重要因素,硝酸盐氮氧同位素表明水房泉的NO₃^-主要来自粪便、污废水以及土壤N的混合.H₂SO₄及污水中HCl、有机酸等可能参与了碳酸盐岩的溶蚀,使水房泉Ca²⁺、Mg²⁺、HCO₃^-浓度增加明显.流域岩溶管道发育,地下水流速快,使污染物质扩散迅速,故在研究期间水房泉主要离子的浓度高峰对污废水排放高峰的响应仅滞后约4 d.     

Geochemical modeling of groundwater in karst area and its application at Pingdingshan coalfield

Several approaches including hydrogeochemistry and isotope hydrogeology have been used to investigate the karst groundwater systems at Pingdingshan coalfield in recent years. The results of the modeling and evaluation of groundwater chemistry, as parts of recent research progress at the area, are presented. The characteristics of Cambrian karst groundwater flow was analyzed in terms of tritium distribution of groundwater based on the fact that the Guodishan fault, the largest one within the coalfield, is divided into permeable (southern and northern) and impermeable (middle) sections. The evolution of groundwater chemistry, the suitability of geothermometers and the feature of karst development were deduced and discussed using the speciation modeling and mass balance approach. Project partially supported by China Postdoctoral Science Foundation.     

The role of antecedent groundwater heads in controlling transient aquifer storage and flood peak attenuation in karst watersheds

Transient storage of floodwaters in aquifers is known to attenuate peak flows in rivers and drive subsurface dissolution. Transient aquifer storage could be enhanced in watersheds overlying karst aquifers where caves facilitate surface and groundwater exchange. Few studies, however, have examined controls on, or magnitudes of, transient aquifer storage or flood peak attenuation in karstic watersheds. Here we evaluate flood peak attenuation with multiple linear regression analyses of 10 years of river and groundwater data from the Suwannee River, which flows over the karstic upper Floridan aquifer in north-central Florida and experiences frequent flooding. Regressions show antecedent river stage exerts the dominant control on magnitudes of transient aquifer storage, with recharge and time to peak having secondary controls. Specifically, low antecedent stages result in larger magnitudes of transient aquifer storage and thus greater flood attenuation than conditions of elevated antecedent stage. These findings suggest subsurface weathering, including cave formation and enlargement, caused by transient aquifer storage could occur on a more frequent basis in aquifers where groundwater table elevation is lowered due to anthropogenic or climatic influences. Our work also shows that measures of groundwater table elevation prior to an event could be used to improve predictive flood models. © 2018 John Wiley & Sons, Ltd.     

Hydrogeological investigation of karst system properties by common use of diverse methods: a case study of Lička Jesenica springs in Dinaric karst of Croatia

Li?ka Jesenica is a sinking river situated in the Dinaric karst environment of the Lika region of Croatia. The two main karst springs, Veliko Vrelo and Malo Vrelo, provide the majority of Li?ka Jesenica's water. Because of the quality and abundance of the water they contain, these springs are strategically important to the public water supply. Previous knowledge regarding the springs` karst system has been negligible. Therefore, a bulk hydrogeological research program was conducted with the purposes of establishing protection zones and assessing the springs' water‐supply potential. The research work comprised the following methods: hydrogeological mapping, setting up of monitoring stations for evaluating discharge and water quality, time series analyses (hydrograph–chemograph), hydrochemical analyses, and geophysical surveys. The main results and conclusions of the research include the following: (i) confirmation that both springs drain a common aquifer; (ii) determination of the highly vulnerable nature of the karst systems; (iii) identification of the Veliko Vrelo Spring's more direct connection to the aquifer‐drainage system in comparison to the Malo Vrelo; (iv) estimation of the positions and depths of the springs` main feeding conduits; (v) confirmation of the extent of the geologically presumed catchment area; and (vi) finally, establishment of sanitary protection zones. Copyright © 2012 John Wiley & Sons, Ltd.     

Sources and transport of nitrate constrained by the isotopic technique in a karst catchment: an example from Southwest China

The concentration and isotopic composition of nitrate were analyzed to improve an understanding of nitrate sources and transformation processes in a typical karstic agricultural field in the Houzhai catchment, Guizhou Province, Southwest China. The results revealed that no distinct spatial pattern of content and isotopic composition of nitrate exists in this karst catchment. Nitrate in surface stream (SFS) had slightly lighter isotopic composition and lower concentration compared with nitrate in subterranean stream (STS) during the dry season. Concentrations of SFS nitrate increased to concentrations similar to those of STS during the wet season. The isotopic values indicated that nitrate were mainly impacted by manure sources during the dry season and influenced by a mix of chemical fertilizer and manure during the wet season. The denitrification rates were roughly estimated based on the isotopic compositions of nitrate after considering volatilization and ignoring assimilation. The calculated result showed that approximately one fifth of nitrate load was removed by denitrification in the catchment. Annual nitrate flux from the outlets accounted for 14.2% of applied total fertilizers used in the catchment, approximately 85% of total transported flux from the catchment in the wet season. Furthermore, chemical weathering processes were enhanced by using nitrogen fertilizer because liberated protons and enhanced HCO₃^? flux were produced through by nitrification. Copyright © 2014 John Wiley & Sons, Ltd.     

Assessment of groundwater recharge processes through karst vadose zone by cave percolation monitoring

Recharge processes of karst aquifers are difficult to assess given their strong heterogeneity and the poorly known effect of vadose zone on infiltration. However, recharge assessment is crucial for the evaluation of groundwater resources. Moreover, the vulnerability of karst aquifers depends on vadose zone behaviour because it is the place where most contamination takes place. In this work, an in situ experimental approach was performed to identify and quantify flow and storage processes occurring in karst vadose zone. Cave percolation monitoring and dye tracing were used to investigate unsaturated zone hydrological processes. Two flow components (diffuse and quick) were identified and, respectively, account for 66% and 34% of the recharge. Quickflow was found to be the result of bypass phenomenon in vadose zone related to water saturation. We identify the role of epikarst as a shunting area, most of the storage in the vadose zone occurring via the diffuse flow component in low permeability zones. Relationship between rainfall intensity and transit velocity was demonstrated, with 5 times higher velocities for the quick recharge mode than the diffuse mode. Modelling approach with KarstMod software allowed to simulate the hybrid recharge through vadose zone and shows promising chances to properly assess the recharge processes in karst aquifer based on simple physical models.     

Estimating groundwater recharge for an arid karst system using a combined approach of time‐lapse camera monitoring and water balance modelling

Groundwater is the principal water resource in semi‐arid and arid environments. Therefore, quantitative estimates of its replenishment rate are important for managing groundwater systems. In dry regions, karst outcrops often show enhanced recharge rates compared with other surface and sub‐surface conditions. Areas with exposed karst features like sinkholes or open shafts allow point recharge, even from single rainfall events. Using the example of the As Sulb plateau in Saudi Arabia, this study introduces a cost‐effective and robust method for recharge monitoring and modelling in karst outcrops. The measurement of discharge of a representative small catchment (4.0 · 10⁴ m²) into a sinkhole, and hence the direct recharge into the aquifer, was carried out with a time‐lapse camera. During the monitoring period of two rainy seasons (autumn 2012 to spring 2014), four recharge events were recorded. Afterwards, recharge data as well as proxy data about the drying of the sediment cover are used to set up a conceptual water balance model. The model was run for 17 years (1971 to 1986 and 2012 to 2014). Simulation results show highly variable seasonal recharge–precipitation ratios between 0 and 0.27. In addition to the amount of seasonal precipitation, this ratio is influenced by the interannual distribution of rainfall events. Overall, an average annual groundwater recharge for the doline (sinkhole) catchment on As Sulb plateau of 5.1 mm has estimated for the simulation period. Copyright © 2015 John Wiley & Sons, Ltd.     

Quantifying the role of karstic groundwater in a snowmelt-dominated hydrologic system

River discharge in mountainous regions of the world is often dominated by snowmelt, but base flows are sustained primarily by groundwater storage and discharge. Although numerous recent studies have focused on base-flow discharge in mountain systems, almost no work has explicitly investigated the role of karst groundwater in these systems across a full range of flow conditions. We directly measured groundwater discharge from 48 karst springs in the Kaweah River and its five forks in the Sierra Nevada mountains, California, United States. Relationships between spring and river discharge showed that karst aquifers and springs provide significant storage and delayed discharge to the river. Regression models showed that, of all potential seasonal groundwater storage compartments in the river basin, the area of karst (0.1–4.4%) present provides the best explanation of base-flow recession in each fork of the Kaweah River (directly measured contributions from karst springs ranged from 3.5 to 16% during high-flow to 20 to 65% during base-flow conditions). These results show that, even in settings where karst represents a small portion of basin area, it may play an over-sized role in seasonal storage and water resources in mountain systems. Karst aquifers are the single most important non-snow storage component in the Kaweah River basin, and likely provide similar water storage capacities and higher base flows in other mountain river systems with karst when compared with systems without karst.     

Complementary use of dating and hydrochemical tools to assess mixing processes involving centenarian groundwater in a geologically complex alpine karst aquifer

Environmental dating tracers (³H, ³He, ⁴He, CFC-12, CFC-11, and SF₆) and the natural spring response (hydrochemistry, water temperature, and hydrodynamics) were jointly used to assess mixing processes and to characterize groundwater flow in a relatively small carbonate aquifer with complex geology in southern Spain. Results evidence a marked karst behaviour of some temporary outlets, with sharp and rapid responses to precipitation events, while some perennial springs show buffer and delayed variations with respect to recharge periods. The general geochemical evolution shows a pattern, from higher to lower altitudes, in which mineralization and the Mg/Ca ratio rise, evidencing longer water–rock interaction. The large SF₆ concentrations in groundwater suggest terrigenic production, whereas CFC-11 values are affected by sorption or degradation. The groundwater age in the perennial springs—as deduced from CFC-12 and ³H/³He—points to mean residence times of several decades, although the large amount of radiogenic ⁴He in samples indicate a contribution of old groundwater (free of ³H and CFC-12). Lumped parameter models and shape-free models were created based on ³H, tritiogenic ³He, CFC-12, and radiogenic ⁴He data in order to interpret the age distribution of the samples. Results evidence the existence of two mixing components, with an old fraction ranging between 160 and 220 years in age. The correlation of physicochemical parameters with some dating parameters, derived from the mixing models, serves to explain the hydrogeochemical processes occurring within the system. Altogether, long residence times are shown to be possible in small alpine systems with a clearly karst behaviour if the geological setting features highly tectonized media including units with diverse hydrogeological characteristics. These findings highlight the importance of applying different approaches, including groundwater dating techniques, when studying such groundwater flow regimes.     

基于修正SWAT模型的岩溶地区非点源污染模拟初探——以横港河流域为例

岩溶流域含水系统的主要特征之一是连通地表的落水洞等垂直管道将近水平的地下暗河联系起来,降水及其形成的地表径流可以通过这些管道迅速地灌入地下河系,从而改变了水及其所携带的非点源污染物质在垂直与水平方向的传输速度与数量,使岩溶流域内地表-地下之间的物质交换与传输过程变得比较复杂;应用广泛的SWAT模型在模拟岩溶地区的水文、水质时会存在一些不足与局限.为此,本文针对岩溶水系统特征,引入落水洞、伏流、暗河的水文过程以及主要营养盐的输移过程,修正SWAT模型原有的水文循环过程及相关算法,改变其只适用于松散均匀介质流域非点源污染模拟的单一特征,并研究建立适合于岩溶流域的非点源污染模型和相应的模拟方法.选取横港河流域岩溶地区作为非点源污染的对象,应用修正后的模型通过控制性的模拟方法和敏感性性分析,定量评估落水洞、伏流、暗河等岩溶特征对氮、磷等主要非点源污染物质输移的影响及其带来的时空效应,并进一步探讨落水洞、伏流、暗河等对地表-地下水文与营养盐的交互作用及转换机理.结果表明,岩溶特征对流域的氮、磷负荷有增加作用,其中总磷的增加明显大于总氮的增加,总磷和总氮的增量分别为0.86%和2.12%;植被岩溶指数的增加会导致流域可溶性磷、有机磷的产出量增加,有机氮、地表产流中硝酸氮和沉积磷的产出量则居其次,落水洞改变了降雨的产流方式,增加了落水洞所在流域的有机磷和有机氮的产出,其增量变化在0~0.7和0~0.3 kg/hm²之间.     

Hydrogeological characterization of groundwater storage and drainage in an alpine karst aquifer (the Kanin massif,Julian Alps)

The Kanin massif is an important trans‐boundary aquifer, which stretches between Slovenia and Italy. The groundwater is only partially exploited, mainly for water supply, but the aquifer exhibits great potential for future exploitation. Since no consistent regional overview of the hydrogeological functioning of the Kanin massif was available, the decision was made to perform a study of this area, using a pragmatic approach based on 3D geological and hydrogeological modelling. The so‐called KARSYS approach was applied, with the aim of characterizing the groundwater reserves within this karst massif and of locating the main drainage axes that carry groundwater from the recharge areas to the respective springs. Delineation of the catchment areas of the corresponding springs was carried out, and some new explanations were obtained, especially with regard to the Mo?nica spring, which is located in Slovenia and forms a potential source of drinking water. It was found that this spring's catchment area extends as far as the Italian ski resort of Sella Nevea. The conceptual model also provides a possible explanation about the underground drainage towards the Boka spring and waterfall, which has been a challenge for decades. This new explanation is based on the existence of a perched groundwater body that feeds the Boka spring via a system of conduits. Despite some limitations, the results, which consist of a visualization of the underground drainage and groundwater storage within the Kanin massif, can be used as a basis for planning the sustainable management of karst waters in the studied area. Copyright © 2014 John Wiley & Sons, Ltd.     

Insights into groundwater salinization from hydrogeochemical and isotopic evidence in an arid inland basin

In the Manas River basin (MRB), groundwater salinization has become a major concern, impeding groundwater use considerably. Isotopic and hydrogeochemical characteristics of 73 groundwater and 11 surface water samples from the basin were analysed to determine the salinization process and potential sources of salinity. Groundwater salinity ranged from 0.2 to 11.91 g/L, and high salinities were generally located in the discharge area, arable land irrigated by groundwater, and depression cone area. The quantitative contributions of the evaporation effect were calculated, and the various groundwater contributions of transpiration, mineral dissolution, and agricultural irrigation were identified using hydrogeochemical diagrams and δD and δ¹⁸O compositions of the groundwater and surface water samples. The average evaporation contribution ratios to salinity were 5.87% and 32.7% in groundwater and surface water, respectively. From the piedmont plain to the desert plain, the average groundwater loss by evaporation increased from 7% to 29%. However, the increases in salinity by evaporation were small according to the deuterium excess signals. Mineral dissolution, transpiration, and agricultural irrigation activities were the major causes of groundwater salinization. Isotopic information revealed that river leakage quickly infiltrated into aquifers in the piedmont area with weak evaporation effects. The recharge water interacted with the sediments and dissolved minerals and subsequently increased the salinity along the flow path. In the irrigation land, shallow groundwater salinity and Cl^? concentrations increased but not δ¹⁸O, suggesting that both the leaching of soil salts due to irrigation and transpiration effect dominated in controlling the hydrogeochemistry. Depleted δ¹⁸O and high Cl^? concentrations in the middle and deep groundwater revealed the combined effects of mixing with paleo‐water and mineral dissolution with a long residence time. These results could contribute to the management of groundwater sources and future utilization programs in the MRB and similar areas.