Emerging organic contaminants (EOCs) are a vast group of often (very)persistent, (very)mobile and toxic (PMT/vPvM) substances that are continuously released worldwide, posing environmental and human ...health risks. Research on occurrence and behavior of EOCs in karst is in its infancy, thus policy measures and legislative control of these compounds in groundwater are still lacking. The Dinaric karst aquifers are an essential source of drinking water for almost half of Croatia's territory. Intense karstification, complex heterogeneous characteristics, and high fracture-cavernous porosity result in rapid, far-reaching groundwater flow and large karst springs, but also high intrinsic vulnerability due to low contaminant attenuation. To prioritize future monitoring and establish appropriate thresholds for EOCs detected in Croatian karst drinking water resources, in silico tools based on quantitative structure-activity relationships were used in PBT (persistence, bioaccumulation, and toxicity) and PMT/vPvM analyzes, while toxicological assessment helped identify potential threats to human health. In 33 samples collected during two sampling campaigns in 2019 at 16 karst springs and one lake used for water supply, we detected 65 compounds (EOCs and some legacy chemicals), of which 7 were classified as potentially PBT or vPvB compounds (PFOS, PFHxS, PFHpA, PFOA, PFNA, boscalid, and azoxystrobin), while only 2 compounds were assessed as not PMT/vPvM. This finding underlines that most of detected EOCs potentially endanger karst (ground)water ecosystems and important drinking water sources in Croatia. Comparison of maximum concentrations with existing or derived drinking water guideline values revealed how 2 of 65 detected compounds represent a potential risk to human health at lifelong exposure (sulfadiazine and hydrochlorothiazide), while 5 chemicals warrant additional human health impacts studies and groundwater monitoring. Although most compounds do not individually pose a significant risk to human health at current environmental levels, their potential synergistic and long-term effects remain unknown.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Karst aquifers contribute substantially to freshwater supplies in many regions of the world, but are vulnerable to contamination and difficult to manage because of their unique hydrogeological ...characteristics. Many karst systems are hydraulically connected over wide areas and require transboundary exploration, protection and management. In order to obtain a better global overview of karst aquifers, to create a basis for sustainable international water-resources management, and to increase the awareness in the public and among decision makers, the World Karst Aquifer Mapping (WOKAM) project was established. The goal is to create a world map and database of karst aquifers, as a further development of earlier maps. This paper presents the basic concepts and the detailed mapping procedure, using France as an example to illustrate the step-by-step workflow, which includes generalization, differentiation of continuous and discontinuous carbonate and evaporite rock areas, and the identification of non-exposed karst aquifers. The map also shows selected caves and karst springs, which are collected in an associated global database. The draft karst aquifer map of Europe shows that 21.6% of the European land surface is characterized by the presence of (continuous or discontinuous) carbonate rocks; about 13.8% of the land surface is carbonate rock outcrop.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Karst aquifers typically have desirable physicochemical properties and can provide an important source of groundwater for drinking. Kiyan karst springs, located in the geological region of the Zagros ...(western Iran), consist of two springs (Keder and Zolal) situated 3 m apart. The water of Zolal spring is always clear, with no turbidity during rainfall or earthquake phenomena, but Keder spring, which also provides drinking water to a city of 10,000 inhabitants (Kiyan city), has very high turbidity in these conditions. This situation disrupts the drinking water supply for about 1 month per year in the study area. The interpretation of discharge time series diagrams, precipitation, and turbidity in different rainfall and earthquake conditions, composite diagrams, and stable isotope concentrations show this study area to be a well-developed karst environment with a highly eroded tectonic zone and large karst conduits along with turbulent water flow. In general, the difference in the behavior of the two springs is related to different paths of water movement through the drainage area. The two springs share the same source of recharge from rainfall and the same initial underground drainage path from the largest sinkhole in the region; although the path of water movement is divided into two branches, with Zolal spring water entering a narrower fault channel. In the Zolal spring pathway, a siphon-shaped reservoir is formed where muddy rainwater settles, so that the water from this spring is clear but has higher concentrations of some ions analyzed here than Keder spring water.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•A theoretical model was proposed to simulate discharge periodic variation.•The model was verified by physical experiments and applied extensively.•The model reveals the relationship between water ...level and discharge periods.•The model can estimate the permeability coefficient according to periodic changes.
Intermittent karst springs (IKS) are common phenomena in karst areas where spring flow rates rise and fall in variable periods, which is generally attributed to the siphon structure in karst aquifers. However, the previous model assumed that the siphon cavity received a fixed recharge rate, thus the IKS showed a fixed periodic characteristic. In this study, an improved theoretical model (IKS model) was proposed to simulate the hydrological process of IKS with changing periods by considering the varying recharge rate from aquifers to the siphon cavity. The model uses two tandem tanks to represent the karst aquifer and siphon cavity separately. The numerical solution was obtained by the iterative method to predict the periodic variations of flow rate and eruption time of IKS. The IKS model was verified by physical experiments under four representative recharge conditions, showing good consistency between theoretical and experimental results. It reveals the hydrologic processes mechanism of the IKS by quantitatively describing the relationship between the cycle period of the IKS discharge variations and the flow exchanges in the siphon cavity-aquifer system. Furthermore, this model performs well in simulating the hydrological process of Chaoshuidong Spring in central China and approximately estimated the hydraulic coefficient of the aquifer in the basin based on observed periodic changes in spring discharge. These findings might be essential for the development, management, and protection of groundwater resources in IKS.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Modification of drought index allows easy comparison of future droughts.•Scenario means predict 14.2% to 25.1% decrease in flow depending on the spring.•After 2059, multi-year droughts are forecast ...for all springs under all scenarios.•Drought duration & monthly water deficit increase (36.8%–533% and 27.3%–83.6%)•Drought duration and intensity increase as spring water retention time increases.
Karst springs are the exclusive source of water during dry months for many Mediterranean regions. The impact of climate change on the hydrology of Mediterranean karst springs has not received proper attention in the scientific literature. Specifically, the effect of climate change on the drought characteristics of karst springs has not been studied. Here, the response to climate change of three Mediterranean karst springs with different retention times is examined, focusing on the frequency, duration and intensity of their drought events. The Karst-SWAT model is used to quantify the karst springs flow. A set of representative climate change scenarios are used to assess the climate change impact on the springs and surface flow for the period 2019–2098. A non-parametric drought index is modified to estimate the future meteorological and hydrological drought characteristics in comparison to the reference period. The most adverse effects of climate change on the three karst springs are expected to prevail after 2059. Depending on the spring, the mean annual karst flow decreases from 14.2% to 25.1%, the mean number of drought events ranges from a decrease of 8.1% to an increase of 77.5%, the duration of drought events increases from 36.8% to 533%, and the mean monthly water deficit increases from 27.3% to 83.6%, when comparing the period 2059–2098 to the reference period (1979–2018). As the water retention time of the spring increases, the duration and intensity of the droughts are likely to increase more significantly. After 2059, multi-year droughts are forecast for all springs under all scenarios. Both low and high flows will increase, with the former occupying even wet months. The results of this study can be used as a guide for local and regional authorities and water management organizations, to adapt their practices for the mitigation of the impact of climate change on the water resources of Mediterranean karst springs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Road deicing has caused widespread environmental Na+ and Cl− release for decades, yet the transport and retention of these contaminants in karst aquifers and soils are poorly understood. We examined ...the transport dynamics of Na+ and Cl− from road salt in shallow groundwater during flooding and over seasonal timescales by intensively monitoring an urban and a rural karst spring over approximately 2 years. Furthermore, we used a 20-year dataset for the rural spring to determine how salt retention affected long-term geochemical trends in the shallow groundwater. Salt transport was governed by hydrologic pathways through karst aquifers: during winter and early spring floods, flow through preferential pathways rapidly transported salty meltwater or stormwater over hours to days, while the remaining salt-contaminated water moved diffusely through the rock matrix on timescales of months to years. Flood hydrograph separations revealed that event water constituted 61.2% of stormflow on average at the urban spring, leading to more extreme variability in salt concentrations during flooding and throughout the year. This variability indicates that baseflow contributions to urban streams overlying karst aquifers with preferential flowpaths are likely less effective at buffering salt concentrations. In contrast, salt concentrations were less variable in the baseflow-dominated rural spring (28.7% event water). Furthermore, salt was episodically released from soils to shallow groundwater throughout the year during first flush events. A Cl− mass balance indicates that Cl− applied during previous winters persists within the springs' recharge basins for more than a year, raising baseline concentrations as road salt is introduced faster than it can be flushed from the basin. Inter-annual salt retention by soils or slow groundwater movement likely caused significant Cl− and specific conductivity (SpC) increases at the rural spring from 1996 to 2016. Accumulation of salt in shallow groundwater can elevate baseflow concentrations in surface waters, where it threatens aquatic organisms.
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•Continuous karst spring data elucidated salt transport over multiple timescales.•Conduit flow rapidly transported some salt while the rest moved via diffuse flow.•An urban spring had more conduit flow while a rural spring had more diffuse flow.•Salt stored in soil was released year-round by first flush events during flooding.•Cl− increased at a rural spring over 20years due to inter-annual salt retention.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Despite many existing approaches, modeling karst water resources remains challenging as conventional approaches usually heavily rely on distinct system knowledge. Artificial neural networks (ANNs), ...however, require only little prior knowledge to automatically establish an input–output relationship. For ANN modeling in karst, the temporal and spatial data availability is often an important constraint, as usually no or few climate stations are located within or near karst spring catchments. Hence, spatial coverage is often not satisfactory and can result in substantial uncertainties about the true conditions in the catchment, leading to lower model performance. To overcome these problems, we apply convolutional neural networks (CNNs) to simulate karst spring discharge and to directly learn from spatially distributed climate input data (combined 2D–1D CNNs). We investigate three karst spring catchments in the Alpine and Mediterranean region with different meteorological–hydrological characteristics and hydrodynamic system properties. We compare the proposed approach both to existing modeling studies in these regions and to our own 1D CNN models that are conventionally trained with climate station input data. Our results show that all the models are excellently suited to modeling karst spring discharge (NSE: 0.73–0.87, KGE: 0.63–0.86) and can compete with the simulation results of existing approaches in the respective areas. The 2D models show a better fit than the 1D models in two of three cases and automatically learn to focus on the relevant areas of the input domain. By performing a spatial input sensitivity analysis, we can further show their usefulness in localizing the position of karst catchments.
Stable isotopes oxygen-18 (δ
18
O) and deuterium (δD) and the hydrochemistry of the main springs of well-developed karst aquifers in Lar watershed in the Haraz basin, northern Iran, were ...investigated. Water samples were collected in the recession period for analysis of major ions and the stable isotopes. Predominant hydrochemical types of main karst springs samples were Ca
2+
– Mg
2+
–
HCO
3
−
type. The hydrochemical composition of the karst springs is dominated by Ca
2+
, Mg
2+
,
HCO
3
−
and
SO
4
2
−
ions. The hydrochemical results indicate that dissolution of carbonate rocks (limestone and dolomite) governs the major ion concentrations, with minor effects of silicate weathering, ion exchange and precipitation effects on concentrations of Na
+
, Cl
−
, K
+
, and
SO
4
2
−
. In the northern parts of the study area, hydrothermal fluid affects the chemistry of the draining springs. The isotopic content ranges from −43.8 to −52.9‰ and from −7.09 to −8.97‰ for δD and δ
18
O, respectively. The karst spring samples lie above the local meteoric water line, similar to the δ
18
O and δD signature of the snowpack samples, and have small spatial and temporal variability. The similarity of the isotopic composition of the springs to the snowpack suggests that the dominant recharge is by snowmelt water.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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