•Advanced application of time series analysis in complex karst systems.•Wide spatial distribution of monitoring points and high temporal data resolution.•Cross-correlation analysis not sufficient to ...study the effects of allogenic recharge.•An innovative approach using partial cross-correlation analysis (PCCF) is presented.•PCCF enables separation of the effects of allogenic and autogenic recharge.
Karst aquifers have very heterogeneous structure and complex hydrodynamics through conduits, fractures and matrix, therefore characteristics of groundwater flow and solute transport differ from those in intergranular and fissured aquifers. Appropriately adapted techniques of hydrogeological research are required for understanding of their functioning. This paper presents an advanced application of time series analysis in a binary karst aquifer known for its complex hydrodynamics and mixing of water from various sources of recharge. A classical approach with high temporal data resolution was extended to a spatial domain with simultaneous monitoring of precipitation, sinking streams, water flow in cave systems, and springs. The main objectives of this study were to define and compare the flow characteristics and storage capacity of selected springs and their catchments, and to determine the influence of different types of recharge (autogenic versus allogenic). The time series of recharge were analysed as input functions in the correlation and spectral analysis. The results undoubtedly show differences in water transfer through the system, storage capacity, and recharge characteristics. However, they also highlight the limitations of using cross-correlation functions to distinguish the influence of autogenic and allogenic recharge. Due to their interference, the interpretation of the results in complex karst systems can be ambiguous, therefore a method of partial cross-correlation analysis was additionally used. Although it has been used before in karst aquifers to spatially characterise groundwater circulation and autogenic recharge, in this study it was used for the first time to investigate the mutual influences of allogenic and autogenic recharge. The results confirmed that this approach provides additional insight into the functioning of binary karst aquifers.
•Solute transport in a karst vadose zone studied by 3 long-term tracer tests.•Tracer breakthrough curves monitored over 11 successive hydrological years.•Defined various processes with significant ...effects on solute transport in karst.•Demonstrated long-lasting storage in the vadose zone of karst aquifers.
The processes influencing the solute transport in the karst vadose zone were studied by long-term tracer tests with artificial tracers. The results of three successive tracer tests with different modes of injection were compared. Tracer breakthrough curves were monitored at three drips of different hydrological types inside one of the cave galleries of the system of Postojnska Jama over several years. Comparison of the results indicates the highly significant influence of preceding hydrological conditions (dry vs wet), injection mode (artificial flushing vs natural infiltration by subsequent rainfall, and on a bare rock vs on an overlying layer) and geologic heterogeneities within the vadose zone on solute transport in the karst vadose zone. Injection with artificial flushing resulted in rapid infiltration and the tracer traversed almost one hundred meters of bedrock in hours. However, the majority of tracer can be stored within less permeable parts of the vadose zone and then gradually flushed out after additional abundant and intensive precipitation in the period of several years. Long-continued sampling in each of the tests proved to be important for reliable characterization of the long-term solute transport dynamics.
Large-scale forest disturbances (LSFD) are an essential component of forest ecosystem dynamics. The effects of rapid loss of forest cover and other changes in forest ecosystems are inextricably ...linked to hydrologic processes such as evapotranspiration, soil and recharge processes. Among all hydrogeological systems, karst aquifers are important because of their exceptionally rich and unique biodiversity, biomass, and groundwater resources. At the same time, they are characterized by specific hydrological processes that make them highly vulnerable to environmental changes. Therefore, this study paid special attention to the effects of LSFD on karst hydrology. Using the PRISMA checklist, a thorough literature review of studies published between 2001 and 2020 was compiled into a comprehensive matrix dataset. In addition, an initial assessment of the global and regional distribution of forests on carbonate rocks was made based on publicly available geodatabases of forests and karst aquifers. The compiled information provides the first global overview of hydrological processes affected by LSFD, and identifies important knowledge gaps and future research challenges. The matrix dataset contained 117 full-text articles with a total of 160 case studies. Most publications were from 2011 to 2017, with more than half of the studies at the plot level and more than one-third at the catchment level. Studies on the effects of fires and pest and diseases infestations predominated. However, no articles were found on the effects of ice storms on hydrology in general or on the effects of pest and disease infestations on hydrology in karst areas. Of the 45.6 M km2 of forested land worldwide, 6.3 M km2 or 13.9% of all forests are underlain by carbonate rocks. Carbonate rocks cover about 15% of the land surface, which means that 31.3% of the world's karst aquifers are covered by forest. 29% of all case studies were conducted in karst areas, which is a high proportion compared to the proportion of forests in karst areas. However, these studies are unevenly distributed geographically. Most studies were conducted at the plot level, and only 21% of studies focused on natural LSFD, so forest management and land use change studies predominated. Although studies on the effects of LSFD on evapotranspiration processes between vegetation, air and soil are fairly well represented, infiltration and recharge processes in karst areas remain poorly understood and knowledge is lacking, particularly on groundwater flow and related hydrological processes. Regional studies and impacts on groundwater resources are also insufficient. The results indicate an urgent need for an integrated holistic interdisciplinary approach and a comprehensive understanding of the individual influencing factors, which would allow more accurate modelling of hydrological processes in forested karst aquifers.
The effects of large-scale forest disturbances on hydrology and evaluation of the basic hydrological processes through the karst aquifer. In general, after large-scale forest disturbance interception and stemflow are expected to decrease because of the damaged forest. Consequently, infiltration and percolation of water through the aquifer are expected to increase, which means higher groundwater recharge and greater susceptibility to pollution. Changes in hydrological processes are indicated by the signs “greater than”, “less than”. Display omitted
•First global and regional overview of forests in karst aquifers.•Literature search yielded 160 case studies, 29% of which were in karst areas.•Lack of hydrological studies related to natural large-scale forest disturbances at the regional scale.•Most studies in karst areas examine the effects of forestry and land use change.•Holistic interdisciplinary research on infiltration and recharge processes in karst is needed.
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•Streamwater isotope values homogenise along the preferential conduits.•Stable isotopes indicate local recharge of karst springs during low-flow conditions.•Small differences in the ...MTTs indicate water mixing along underground flowpaths.•Young water fractions at karst springs/sinks are high.
Karst systems can be generally characterised by their high hydrological heterogeneities related mainly to highly variable permeabilities, which can significantly change over small spatial scales. This makes tracing and quantification of water flow pathways an extremely demanding task. In this study we present an analysis of hydrological characteristics of a complex karst system, the Ljubljanica river catchment in central Slovenia. Spatially distributed data on stable isotope composition (δ18O, δ2H) of precipitation as inputs, and of several karst springs/sinks as outputs, were obtained. These data were used to identify spatial and seasonal patterns and hydrological behaviour of the karst system in contrasting hydrological conditions. The intensive mixing of continental and Mediterranean air masses over the Ljubljanica river catchment makes the precipitation source identification difficult. However, the results of the precipitation isotopic composition analysis indicate a spatial pattern that could be recognised also in the δ18O and δ2H values of the karst springs and sinks. Along the prevailing karst conduits, the spatial differences in the δ18O and δ2H values decreased. The mean transit time (MTT) estimates using δ18O or δ2H as tracers were similar, with those for the main karst conduits and tributaries ranging between 0.34 and 0.74 years. Such a relatively short MTT could be expected for karst catchments without extensive deep groundwater storage. The fraction of young water (Fyw) for the whole catchment was 0.28, meaning that more than one-quarter of the total discharge was younger than approximately 2.3 months (assuming that the catchment transit time is described by exponential distribution). Small differences in the MTT over different parts of the karst catchment area might indicate intensive mixing and homogenisation of water along the underground conduits. However, the catchment’s homogenisation strongly depends on the preceding hydrological conditions; the differences in the isotope composition can be identified during low-flow conditions, which might indicate the dominant influence of the local recharge of the karst springs.
AMP-activated protein kinase (AMPK) is a cellular energy gauge and a major regulator of cellular energy homeostasis. Once activated, AMPK stimulates nutrient uptake and the ATP-producing catabolic ...pathways, while it suppresses the ATP-consuming anabolic pathways, thus helping to maintain the cellular energy balance under energy-deprived conditions. As much as ~ 20–25% of the whole-body ATP consumption occurs due to a reaction catalysed by Na
+
,K
+
-ATPase (NKA). Being the single most important sink of energy, NKA might seem to be an essential target of the AMPK-mediated energy saving measures, yet NKA is vital for maintenance of transmembrane Na
+
and K
+
gradients, water homeostasis, cellular excitability, and the Na
+
-coupled transport of nutrients and ions. Consistent with the model that AMPK regulates ATP consumption by NKA, activation of AMPK in the lung alveolar cells stimulates endocytosis of NKA, thus suppressing the transepithelial ion transport and the absorption of the alveolar fluid. In skeletal muscles, contractions activate NKA, which opposes a rundown of transmembrane ion gradients, as well as AMPK, which plays an important role in adaptations to exercise. Inhibition of NKA in contracting skeletal muscle accentuates perturbations in ion concentrations and accelerates development of fatigue. However, different models suggest that AMPK does not inhibit or even stimulates NKA in skeletal muscle, which appears to contradict the idea that AMPK maintains the cellular energy balance by always suppressing ATP-consuming processes. In this short review, we examine the role of AMPK in regulation of NKA in skeletal muscle and discuss the apparent paradox of AMPK-stimulated ATP consumption.
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•A critical analysis of legislation on karst water sources protection was prepared.•A disagreement in current protection approaches for karst water sources was proved.•For adequate ...protection detailed exploration and in-depth knowledge is crucial.•The application of a multi-methodological approach instead is justified.•Legal adoption of novel strategies for improved protection in karst is required.
Karst water sources already meet about a quarter of the world's drinking water needs, and their importance is growing. Due to the complexity of water flow in carbonate aquifers, karst water sources require particularly appropriate protection. The scientific literature lacks analytical evidence of the effects of the current legislative frameworks and improved methodological approaches for ecological indications to design alternative strategies. This gap is addressed in the present study, which draws on a combination of investigation methods considering specifics of water flow in karst and on a comprehensive database of general knowledge to gain relevant understanding of the hydrological system functioning. An advanced, multi-methodological approach, which was developed in this study and includes geological and hydrogeological mapping, spring monitoring, tracer tests, water balance and groundwater vulnerability assessment, enabled achievement of optimized indicators for the adequate karst water source protection measures. It demonstrates, that protection zoning based solely on fundamental hydrogeological knowledge, general prediction of groundwater residence times or distance criteria may lead to a high degree of imprecision. Currently valid protection measures may therefore generally be associated with great uncertainties and the high vulnerability of karst areas may be underestimated. In addition to the existing legal requirements for karst water source protection zoning, environmental indicators such as natural and artificial tracers should be considered, which most reliably confirm the directions and characteristics of groundwater flow in karst. Similarly, mapping of groundwater vulnerability to contamination can be of particular importance for the implementation of freshwater protection and spatial planning at least in karst-rich countries. The approach enables scientists to gain relevant insights into the functioning of the hydrological system and environmental managers to protect karst water sources.
Water suppliers should provide safe drinking water following preventive measures. This is especially important for karst water sources, as they are among the most vulnerable. Recently, there has been ...a strong focus on the early warning system, which mainly involves monitoring proxy parameters, but does not consider drainage area conditions and other monitoring recommendations. Here, we present an innovative strategy for assessing contamination risk of karst water sources that covers spatio-temporal dimensions and can be integrated into management practices. It is based on event-based monitoring and risk mapping and has been tested in a well-known study area. The holistic early warning system provides accurate spatial hazard and risk assessment and operational monitoring guidelines, including locations, indicator parameters, and temporal resolution and duration. In the study area, the high contamination risk, representing 0.5 % of the area, was spatially delineated. The highest probability of source contamination occurs during recharge events when proxy parameters such as bacteria, ATP, Cl, and Ca/Mg ratio should be monitored in addition to continuous monitoring of turbidity, EC, and T. Monitoring of sinking streams should serve as a preventive measure, since water transfer from ponors to springs has been shown to take about one day, and poor quality water is present for at least another day. Therefore, intensive monitoring should be conducted at intervals of a few hours for at least a week. Although hydrologic systems vary, the proposed strategy is particularly useful in systems where water flows rapidly and where remediation is not feasible.
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•A comprehensive early warning system for water source contamination risk is presented.•It includes spatiotemporal dimension that can be integrated into management practices.•The EWS consists of event-based monitoring and contamination risk mapping.•It provides guidance for contamination risk assessment and operational monitoring.•Monitoring locations, parameters, temporal resolution, and duration are proposed.
The karst environment presents a special challenge when it comes to identifying groundwater/surface-water interactions. Existing definitions of areas of regular flooding in karst regions are too ...general and lack a measurable approach for the determination of flood-liable land. This paper proposes a means of specific definition and quantitative determination of intermittently flooded karst areas, which takes into account the extent, duration and frequency of flooding, and includes the identification of data sources and processing methods. The procedure, involving spatial layers, was developed using a pilot area and tested in three additional areas in Slovenia. The derived definition determines that flood-liable land within karst poljes and intermittent lakes comprise areas where stagnant water or stream overflow is present for at least 10 days/year over a period of 30 years, and these waters have direct contact with groundwater. The results show that the proposed procedure is applicable to areas with different geomorphological settings and to areas where the quantity and quality of available data vary. The study is an example of the practical application of knowledge on karst, as the findings can be used for short-term purposes (mapping flood areas, determination of habitats) and long-term purposes (study of impacts of environmental changes). Attention should be drawn to the lack of available data and the fact that the national networks of hydrological observatories are often too sparse for this purpose. This study raises awareness of these shortcomings and improves the planning or expansion of such a network in collaboration with experts.
•We list parameters assumed to control flooding in poljes.•We test them with simple models.•We combine the findings to model a real field case.•Two modelling approaches are used.•The method can be ...applied to other poljes.
Poljes are large flat closed depressions that can be found in most karst areas around the world. They are prone to regular flooding, which occurs after abundant rainfall or snowmelt events. The floods can form several meters deep intermittent lakes that can persist for months. Human settlements around poljes have been traditionally positioned above the level of the most severe floods. However, many neighbouring villages expanded during the last decades to areas that might be endangered by large flood events. In addition, a recent study has shown that several poljes encountered floods of more severe amplitude in mid-Holocene due to a prevailing humid climate. As current knowledge of polje’s hydrology appears to be still insufficient, further research is needed. This work aims to identify the factors controlling polje flooding and evaluates their impact on the flood amplitude and duration. To do so, a list of parameters potentially controlling flooding is established. The relevance of each parameter is tested by using two idealized numerical models. The first one considers exclusively the polje from the springs to the ponors, whereas the second integrates the aquifer adjacent to the polje outflow side. First results show the usefulness of simple numerical models to identify the effect of each parameter on the flood amplitude and duration. The findings are combined to simulate a flood of medium intensity and long duration that occurred on a typical polje. A comparison of the results with real data demonstrates that the aquifer draining the polje needs to be considered to understand properly the flooding dynamics. The approach presented within this work has the potential to be used in other poljes encountering similar hydrological situations, but also lays foundation for flooding modelling in other karst areas.
Karst aquifers hold important water resources such as regional water budgets and freshwater supply. Due to highly dynamic hydrological processes in comparison to other less permeable systems, they ...are particularly susceptible to environmental changes. However, little research directly characterizes the impacts of climate and vegetation cover changes on karst water sources. In this study, we aimed to evaluate individual long-term impacts and impacts of sudden large-scale forest disturbances on changes in groundwater recharge and in spring discharge. The work is based on temporal analysis of forest cover and a comparison of trend analysis of hydro-meteorological parameters. To investigate and evaluate vegetation cover change impacts on groundwater recharge, we used a soil water balance model and compared estimated actual daily values of effective precipitation to its fictional estimation disregarding the vegetation cover change. The applied methodology enabled quantification of the impacts of climate and vegetation cover change on selected karst water sources. The study suggests that the vegetation cover can have a significant impact on the spring recharge. Large-scale disturbances that occurred in a short-term mitigated the effects expected from the trend analysis of hydro-meteorological parameters. In the long-term, in addition to climate changes, the multi-decadal natural vegetation overgrowth significantly contributed to the reduction in the spring’s discharge values, especially in the warm season when water demand is higher. Therefore, the results are of key importance for developing proper water management and environmental policies.
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