► A conceptual model for karst catchments is proposed. ► The proposed model incorporates a non-linear, hysteretic discharge function. ► It allows the variations in karst and vadoze zone connectivity ...to be modelled. ► Secondary springs are also modelled. ► A modified Nash criterion is proposed to account for measurement imprecision.
A two reservoir conceptual model with a hysteretic transfer function is proposed for hydrological modelling of karst catchments. The main features of the model are (i) a simple model for evapotranspiration based on potential rates, (ii) a non-linear, hysteretic discharge law accounting for the variations of connectivity in the soil/epikarst zone, (iii) a threshold-based discharge law accounting for the time variability of the active catchment area via losses to secondary springs. The structure of the model and the governing equations are proposed on the basis of physical considerations, with the underlying assumption that the model compartments, state variables and parameters should bear a physical reality. The model is applied to the karst system catchment of the Durzon spring (France). Model robustness is assessed by using only 1
year for calibration and 4
years for validation. A modified Nash–Sutcliffe criterion decreases from 91% to 87% between the calibration and validation phase, thus demonstrating the robustness of the model. The proposed model is compared to a model of similar complexity available from the literature, previously applied to similar catchments. The comparison indicates the superiority of the hysteresis-based model in terms of robustness and overall performance.
This paper presents a quantitative study of the relationship between the cave system and the tectonic and karst evolution of the Dong Van Karst Plateau based on analysis and statistics of geometric ...parameters and orientation of cave passages. The region is located in northern Vietnam and belongs to the extended part of the South China karst belt (Yunnan karst plateau), which is composed mainly of carbonate rocks. Cave classification based on cave conduits geometric parameters shows that caves developed mainly in the vadose zone (27 vadose branchwork caves, 10 mixed caves developed under the control of fault systems, and 12 water-table caves). The degree of correlation between cave levels and planation surfaces suggests that the development of horizontal cave passages is related to two levels of planation surfaces, including one at 1250–1450 masl (equivalent to cave level at 1350–1450 masl), and at 1000–1250 masl (corresponding to cave level at 1200–1250 masl). Additionally, cave passage orientation shows that the cave system formed and developed under the influence of tectonic activities in the Cenozoic. The dominant orientation trend is roughly in the East–West direction and occurred in the early phase (Eocene–Miocene). Next is a trend roughly North–South that occurred in the late phase (Pliocene–Quaternary). The last orientation trend follows the NW–SE direction due to the reactivation of paleo-fault systems in the same direction. Although there are limitations due to accessibility and the level of cave exploration, this research suggests that analysis and statistics of the geometric parameters and orientation of cave passages based on cave survey data can be one of the effective approaches used to identify the development and structure of karstification in the karst region.
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•Implications of future changes in climate on tropical karst groundwater resources were examined.•Climate projections were downscaled using SDSM.•Future conditions for two scenarios ...were simulated by MODFLOW model.•The results indicated variations of sustainability in groundwater recharge and spring discharge.•Tailored management strategies to ensure the sustainability of groundwater resource are presented.
Developing tailored management strategies to ensure the sustainability of groundwater resource under climatic and demographic changes is critical for tropical karst catchment, where relatively small watershed and highly porous soil make this natural resource highly susceptible and thus very sensitive to those changes. In this study, long term impacts of climate variability on groundwater recharge and discharge at Oemau spring, Rote Island, Indonesia were selected and investigated. Following calibration and validation of groundwater model using MODFLOW code, groundwater flow was simulated for the period of 2020–2090 under HadCM3 global climate model (GCM) scenarios, using input data of weather variables downscaled by Statistical Downscaling Model (SDSM). The reported analysis suggests that the sustainability of groundwater resources, which was evaluated by assessing the ability of the spring to supply water demand from irrigation requirement and domestic consumption, generally varies over the period and will be adversely affected by climate change during dry periods when the area is projected to variably experience supply shortage of around 29–67 L/s as a result of 5.24–23.63% decrease of rainfall, 2.48–24.57% reduction of recharge, and 2.53–22.80% decrease of spring discharge, under HadCM3 GCM scenarios. A subsequent comprehensive set of management strategies as palliative and adaptive efforts was proposed to be implemented by relevant stakeholders to assist the community dealing with water deficit during the dry periods. Three main adaptive strategies, namely socio-cultural, technical, and ecological measures, were proposed by incorporating physical and socio-economic characteristics of the area. This study presents a blueprint for assessing groundwater sustainability under climate change scenarios and developing tailored management strategies to cope with adverse impacts of climate change, which may become fundamental guidelines across other karst islands in the future.
•The contents of (heavy) metals in ML soils were higher than those in YB and DX soils.•ML soils contained more chlorite in clay minerals/soils than YB and DX soils.•The hydroxyl groups with hydrogen ...bonds were mainly existed in ML soils.•Molecular soil chemistry could affect the accumulation of heavy metals in karst area.
Heavy metals with high average background values in soils from karst regions of China have been reported previously. However, the accumulation mechanism of heavy metals in karst soils derived from different parent materials related to the molecular soil chemistry is still unclear. In this study, six soil cores (0–100 cm) from three locations were collected from Hengxian County, a typical karst basin of Guangxi, among which soils of Maling (ML1 and ML2) were derived from the weathering and leaching residues of carbonate rocks, and soils of Yunbiao (YB1 and YB2) and Dengxu (DX1 and DX2) were mainly developed from deposits of Quaternary formations. Soil heavy metal quantification, X-ray diffraction (XRD) analysis, synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectroscopy, and two-dimensional correlation spectroscopy (2DCOS) analysis were combined to study the contents of heavy metals, mineral compositions, and functional assignments in the karst soils. The results showed that the total concentrations of As, Cr, Cd, Cu, Ni, Pb, and Zn in the soils from ML exceeded the risk screening values from the agricultural soil quality standard in China (GB15618-2018), while the contents in the soils from YB and DX were below the risk screening values. The mineral components were significantly different in soils and their clay minerals. ML soils contained more Fe and Mn oxides than YB and DX soils. Furthermore, it was interesting to find extensive existence of chlorite in ML soils (36.73%-39.07%) and their clay minerals (90.49%-90.97%). While illite was the dominant mineral in YB and DX clay fractions (75.08%-100%) and its percentages decreased to 6.06%-35.23% in the soil samples. In addition, ML soils contained the hydroxyl groups with hydrogen bonds (vO-H: 3523, 3450, and 3378 cm−1) and the hydroxyl groups without hydrogen bonds (vO-H: 3698, 3623 cm−1), while YB and DX soils only had the hydroxyl groups without hydrogen bonds (vO-H: 3695, 3622 cm−1). Our study indicated that the accumulation of heavy metals in karst soils from different parent materials was significantly attributed to their molecular soil chemistry. For instance, the higher contents of Fe-Mn oxides and more reactive vO-H (3523, 3450, and 3378 cm−1) and vSi-O (1000 cm−1) assignments could contribute to the higher contents of heavy metals in ML soils compared to the soils from YB and DX.
Due to the coupled or interconnected relationships among frequent climate extremes, unique geological conditions, discontinuous soil distribution, rugged geomorphology, and highly heterogeneous ...landscapes in different karst watersheds, few studies were conducted to decouple the relative magnitudes of the climate, lithology, soil, topography, and landscape on soil erosion in karst regions. The objective of this study was to quantify the relative importance of these influencing factors on runoff and sediment yield (SY) in 40 typical karst watersheds in southwest China. To address this issue, the Pearson correlation and random forest were first to select the dominant factors influencing runoff and SY. Subsequently, the partial least squares‐structural equation model (PLS‐SEM) was used to decouple the complex relationships among runoff, SY and their potential influencing factors. Results showed that climate, lithology, soil, topography and landscape could explain 79% of the runoff variation, and only climate factors have significant impact on runoff for heterogeneous karst watersheds (P < 0.01, path coefficient (β) = 0.589). The explanation of five factors to SY variability is 59%, and the landscape has the greatest impact on SY (P < 0.01, β = −0.458). Different from runoff, climatic factors have no significant influence on SY. By elucidating a complex coupled relationship framework, this study can provide a scientific basis for the formulation of soil and water loss program, and the optimization of land resources and ecological environment sustainable development in karst watersheds.
Plain Language Summary
The variations of runoff and sediment yield (SY) among heterogeneous watersheds are expected to be influenced by climate, lithology, soil, topography and landscape, which are generally interconnected and coupled. Therefore, it is important to decouple the complex relationship between runoff, SY and their potential influencing factors, especially in karst areas where ecologically fragile regions experience severe soil erosion. The results show that only climate factors play a significant influence on runoff. Unlike runoff, all factors have significant effects on SY except climate factors. Interestingly, landscape factors have the greatest influence on SY. Our findings are conducive to better understanding the hydrological and sediment transport characteristics of karst watersheds, and provide scientific basis for soil erosion control and sustainable development of ecological environment.
Key Points
We decoupled the effects of climate, lithology, soil, topography and landscape on runoff and sediment yield (SY)
Climate and landscape exerted the largest influence on runoff and SY, respectively
Lithology, soil, topography, and landscape significantly affected SY rather than runoff variability
Rational use of karst water resources depends considerably on the existence of a successful approach to estimating karst groundwater potential for exploitation. The term groundwater potential for ...exploitation involves the application of regulatory measures affecting natural outflow regime. Generally, the concept of controlling the artificial discharge regime is based on two principles. The first one, the “borrowing” of water from deeper (storage) part of storage, is based mainly on the construction of groundwater wells. The second one, considers increasing dynamic reserves by providing additional artificial water storage thereby controlling the groundwater discharge regime, is based on the construction of underground dams. This paper examines how these two concepts can be used to increase potential groundwater usage from two karst springs in Serbia—St. Petka and Perućac. The ability to potentially increase the amount of karst ground water available for future exploitation may facilitate and give important directions to the future research.
The importance of the groundwater management of karst aquifers relatively to their complexity requires the knowledge of the subsurface flow and storage behavior. In this study, a methodological ...approach based on the exploitation of daily spring’s discharge data was developed and tested. The methodology makes use of the hydrograph recession curves, the correlograms output, and the logarithmically structured duration curves. This methodological approach was applied to the complex karst system of Louros basin. The Louros karst system consists of individual karst units discharged by respective springs which are distributed on three levels and form three easily distinguishable groups. The application results revealed a well organized karst system with conduits of slow and fast flow. It also revealed the uniformity and the complexity of the different units, as well as the properties, such as the storativity and the evolutionary process. This approach demonstrates the benefits of interpreting different methods in a hydrologically meaningful way for the recharge data evaluation.
Hydrogeological and thermogeological properties of the shallow subsurface in the Dinaric karst area of Croatia were investigated in the context of its utilization for ground- and water-source heat ...pumps (GSHPs and WSHPs). The research encompassed four 100 m deep boreholes with GSHP installations in both coastal and inland Dinaric karst (different limestones and evaporitic rocks at one location), and a set of six exploratory boreholes, abstraction and reinjection wells for WSHP heating and cooling using seawater on the coast (fractured and karstified limestones). It was determined that rock thermal conductivities are favourable for GSHP utilization, but dependent on the wider rock mass characteristics which are hard to predict (size of karst voids and their saturation status). In addition, wells with high enough yield and stabile seawater or groundwater temperatures for WSHP utilization can be designed in appropriate structural settings (tensional fractures and fracture set intersections). Advantages and disadvantages of the utilized methodology have been pointed out, as well as methods which should prove useful in the future, especially if larger systems are planned. Hydrogeological, geotechnical, and thermal risks expected during the drilling, installation, and operational phases have also been identified. Presented case studies have given the insight into heat pump installation options and conditions in Croatian part of the Dinarides, but can be useful to other researchers and engineers both in the Dinarides and in similar karst regions.
The Garrotxa-Banyoles artesian aquifer system in NE Spain includes zones with epigene and hypogene evaporite karst and sinkhole development. The sinkhole fields related to hypogene evaporite ...dissolution are associated with the discharge zones of the aquifer, where groundwater from a confined limestone rises traversing an overlying gypsum formation capped by thick marls. This work analyses the sinkhole field developed in the Sant Miquel de Campmajor Valley (SMCV), a discharge area of the aquifer, where a cartographic inventory including 94 sinkholes has been produced. Sinkholes in this hypogene gypsum karst are mainly large caprock-collapse sinkholes rooted in deep-seated cavities generated by interstratal hypogene karstification, as corroborated by an electrical resistivity imaging (ERI) survey. They show a non-clustered distribution within the sinkhole field and the variations in size and density across the area are mainly controlled by the thickness of the marl caprock. The magnitude and frequency relationships of the sinkholes can be modelled with a high goodness of fit with a log-normal function, like in other regions of the world. However, in this deep-seated hypogene system the depressions show much larger dimensions. Potential differences between the sinkholes developed in hypogene and epigene karst environments are discussed, including their distribution with respect to the groundwater flow system, their spatial patterns and dimensions.
•Sinkholes related to hypogene gypsum dissolution•Caprock-collapse megasinkholes related to deep-seated interstratal dissolution•Frequency-size relationships of sinkholes in different contexts•Differences between sinkholes in epigene and hypogene settings
In recent years there has been increased interest in cave speleothems as archives of palaeoclimate. Monitoring of rainfall and soil and karst water chemistries was performed at Crag Cave, ...Castleisland, Co. Kerry, southwest Ireland, in August 1997 and January 1998 in order to understand temporal and spatial variations in karst water hydrology and chemistry and their implications for interpreting the potential palaeohydrological signal preserved by speleothems at this site. Temporal variations in karst water drip rates and geochemistry allow drips to be classified by hydrological response to rainfall and the associated processes of dilution, piston flow, source change and prior calcite precipitation during aquifer throughflow. Evolution from soil matrix and preferential flow solutions has also been determined to exert an important control on karst water chemistries. As a result of these findings we present hydrogeochemical models and plumbing diagrams that delineate the controls on karst water evolution at a number of sampling locations within the cave at this site. We propose that a palaeohydrological signal may be recorded by Crag Cave speleothems that may be interpreted via the study of Mg/Ca ratios in speleothems linked to monitoring of modern drip water chemistry.
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