Karst hydrological models are widely used for simulating groundwater dynamics at the aquifer scale. However, modeling streamflow of a topographic catchment that is partially covered by karst is ...rarely reported. This absence is due to difficulties of properly considering the strong differences of karstic and nonkarstic hydrodynamics and the widespread occurrence of unclosed water balances in karstic regions due to intercatchment groundwater flow (IGF). In this study, we present a new approach that uses hydrological signatures to identify important natural processes and appropriate model structures for the simulation of karst‐influenced catchments. We account for karstic IGF and apply our approach to six karst‐influenced catchments in Europe and the Middle East. We estimate the contributions of karstic and nonkarstic parts to the total streamflow sensitivity. With different model structures identified at different sites, our approach reduces water balance errors by 18% and reduces the root mean squared error by 20% for catchments where the IGF is deemed important. We find that IGF modifies the contribution of karstic areas to the total streamflow sensitivity. The total streamflow sensitivity increases under gaining conditions and decreases under losing conditions for catchments with larger karstic discharge elasticity, while it shows the converse change for catchments with smaller karstic discharge elasticity. Modeling streamflow at karst‐influenced catchments requires the consideration of differences between karstic and nonkarstic areas, and the IGF matters for catchments with unclosed water balances.
Key Points
We integrate modeling approaches for karstic and non‐karstic systems to account for intercatchment groundwater flow in mixed catchments
We show that our combined approach reduces on average water balance errors by 18% and RMSEs by 20% at six test catchments
We find that karst controls between 65% and 93% of the total streamflow sensitivity to precipitation in these studied catchments
Karst water are important for water supply and ecological protection. However, climate changes and human activities have caused severe water supply crisis. The Jinci spring, one of the famous karst ...springs in China, is located at the basin‐mountain coupling belt and dried up since 1994. This study integrated hydrogeological conditions, water table logs, hydrogeochemistry, multiple isotopes, and numerical modeling to understand dynamic changes of interaction pattern between karst water‐Quaternary groundwater response to human activity in the basin‐mountain coupling belt over the past 60 years. Our investigation indicated that under natural conditions (1960s), karst water discharges as springs and laterally recharges into Quaternary groundwater at the fault area. In the 1980s, overexploitation caused a significant reduction in spring discharge and a decline in karst water levels, especially in coal mining areas. Further declines in water levels and mixing recharge by karst water‐Quaternary groundwater were observed in the 2000s, which were eased in 2018. Calculations both by oxygen isotope and models indicated that contribution of Quaternary groundwater to Jinci spring ranged from 11.8% to 42.1%, with the highest in the 2000s. Evidenced by multiple isotopes, the recharging of karst water‐Quaternary groundwater varied spatially along the belt in 2018, with delayed water level elevation in coal mining and heavy groundwater exploration areas. This study demonstrated that artificial disturbance fundamentally affected the karst water‐Quaternary groundwater flow and water exchange between them. Precautions should be taken when evaluating global water resources changes, in view of the dynamic interaction between the karst water‐Quaternary groundwater spatially and temporally.
Plain Language Summary
Global changes and human activities have changed groundwater flow and cycle, which is more pronounced in basin‐mountain coupling belt. However, how human activity influences the groundwater dynamics is unknown. The Jinci spring, one of the famous karst springs located at basin‐mountain coupling belt, was selected as a study area to address this knowledge gap. Based on the hydrogeological investigation, multiple isotopes and numerical modeling, we demonstrated the dynamic interaction of the karst water‐Quaternary groundwater and the potential impact of human activity along basin‐mountain coupling belt over the past decades. The interaction between the karst water‐Quaternary groundwater has changed in time and space. Under natural conditions in 1960s, karst water laterally flows into the Quaternary water. However, in 1980s, water level declines, and thus a part of Quaternary groundwater recharge into the karst water, which was even worse in 2000s. In 2018, water level rises, with a delay elevation in coal mining and heavy groundwater exploration areas. Over the past decades, Quaternary groundwater contributes to Jinci spring with varying ratios (11.8%–42.1%, with the highest in 2000s). Our findings emphasize that precautions should be taken when evaluating global water resources changes, considering the dynamic interaction between the karst‐Quaternary groundwater spatially and temporally.
Key Points
Hydrodynamic field and interaction between karst water‐Quaternary water have changed in spatial and temporal scales
Human activity have fundamentally affected the natural groundwater evolution
Precautions are required for the evaluation of global water resources changes
•An Improved Karst-Liuxihe (IKL) model for karst basins was developed successfully.•19 karst flood events under 4 extreme land use scenarios were analyzed in detail.•The annual runoffs of 2030, 2040, ...and 2050 were forecasted effectively.•The critical proportion of urbanization area throughout the watershed area was 45%.
Urbanization, especially land use pattern changes, has a great impact on natural flood events in a karst basin. Quantitative simulations of the effects of urbanization on karst flood events and forecasts of future evolution trends are difficult based on the current hydrological models. These models often require a large amount of data when used in karst areas due to the complex model structure and model parameters. To overcome the limitations of model applications, a physically based and fully distributed karst hydrological model, i.e., the improved Karst-Liuxihe (IKL) model, was proposed in this study to simulate and forecast karst flood events under the influence of urbanization. This IKL model was developed through the overall improvement of the Karst-Liuxihe (KL) model. The main additions were the improved runoff generation algorithm and the underground river confluence module. The karst flood simulation results of the IKL model were much better than those of the KL model: the average values of the Nash–Sutcliffe coefficient, correlation coefficient, and coefficient of the water balance increased by 23%, 23% and 26%, respectively, while the process relative error, flood peak flow relative error, and flood peak flow time error decreased by 21%, 22%, and 3 h, respectively, which confirmed that the improvements to the model were effective and feasible. Therefore, this paper used the IKL model to simulate karst flood events and annual runoff under the influence of urbanization based on 4 extreme land use scenarios. In addition, the model effectively forecasted the future runoff in 2030, 2040, and 2050. The results indicated that the critical proportion of urbanized area throughout the watershed area was 45%. When the urban proportion exceeded 45%, waterlogging could occur in the study area.
The global karst distribution area is nearly 22 million km2, accounting for ca. 15% of land area, and the population living in karst areas is approximately one billion. Strong karstification makes ...the soil environment dry and with high pH and high content of calcium (bicarbonate). The karst environment with a high spatiotemporal heterogeneity seriously affects the growth and development of plants. Faced with these heterogeneous environments, plants have adopted diversified adaptive strategies. This Special Issue is a collection of 15 important research works, which demonstrated some achievements on the physiological and ecological adaption of plants to heterogeneous karst environments, and also explore how to extend the service period of plant resources in karst regions. These works will help to understand the karst-adaptability of plants from multiple perspectives and provide a scientific reference for the selection of karst-adaptable plants and the restoration of vegetation in karst areas. Meanwhile, they will provide theoretical support for organic integration towards economic, social and environmental sustainability of karst areas, and the beautiful vision of "green water and green mountains are golden mountains and silver mountains". In the future, we look forward to more emerging research on adaptive plants in the karst ecosystem, which will serve better in maintaining ecosystems (carbon neutral), ensuring food supply and promoting sustainable social development.
•The nitrogen concentration in karst groundwater has spatial heterogeneity.•The redox characteristics of different karst aquifer media are heterogeneous.•Different karst aquifer media have different ...N transformation processes.
Karst aquifers, a significant source of drinking water worldwide, are vulnerable to anthropogenic pollutants because of their special hydrogeological conditions. However, distinguishing the nitrogen transformation process is difficult owing to the heterogeneity of karst media. Therefore, the process of nitrogen transformation in different karst aquifer media remains poorly understood. In this study, multiple stable isotopic and physicochemical indicators are combined, the sources of water and nitrogen are analysed, and the degree of openness and redox conditions of different media are discussed to elucidate the nitrate sources and N transformation in groundwater with different degrees of openness. Water isotopes indicate local meteoric groundwater origin. However, different karst aquifer media have different degrees of openness, resulting in the highest deuterium–oxygen isotope values in surface water, followed by conduit water, fissure water, and isolated cave water. Based on the evidence from isotope and physicochemical indicators, different karst aquifer media have different redox processes. Isolated cave water environments were under anoxic conditions dominated by sulfate reduction reactions. Fissure water was under temporary anoxic or sub-anoxic conditions dominated by denitrification reactions. Conduit water and karst surface water were between micro-oxygen and oxidising conditions, and nitrification was the key process. This phenomenon was observed because the diversity of karst media produces different conservation conditions and openness. The nitrate isotope and Bayesian mixing model indicate that the main sources of nitrate in karst groundwater in the study area are mostly associated with manure and sewage wastes, and a few are from soil organic nitrogen, atmospheric deposition, and chemical fertilizer. This study helps identify the migration and transformation patterns and processes of nitrogen in different karst aquifer media, providing a scientific basis for the restoration and remediation of contaminated karst groundwater.
•LuKARS – Land use change modeling in KARSt systems.•Construction of a hydrotope-based modeling approach for karst hydrological modeling.•Simulating spring discharge in a dolomite-dominated karst ...system.•Modeling land use change impacts in karst hydrological systems.
Hydrological models represent valuable tools to investigate the impacts of land use changes on water resources. Most commonly, distributed, physically-based models are applied for land use change impact studies in hydrology. However, providing a physically-based and detailed description of subsurface flows in karst systems is challenging. Lumped models, in contrast, are easy to implement and widely used in karst hydrological research, albeit not applicable for land use change impact studies. To overcome these limitations, we developed a new semi-distributed model LuKARS (Land use change modeling in KARSt systems) that lumps the predominant hydrotopes (i.e. distinct landscape units characterized by homogeneous hydrological properties as a result of similar land use and soil types) present in a catchment as independent, non-linear units. Flows from each hydrotope represent a specific response of the vadose zone (soil-epikarst-infiltration zone) in a defined recharge area. The saturated zone consists of a single linear storage unit recharged by each hydrotope independently. The main goal of this approach was to investigate land use change impacts in a dolomite karst system exploited for the water supply of the city of Waidhofen a.d. Ybbs (Austria) by changing the area covered by each hydrotope. Here, land use changes occured in the form of increasing spaces used for dolomite mining and at the expense of existing forest sites. With our parametrized model, we were able to reproduce the measured discharge in the largest spring of the Waidhofen karst system (Kerschbaum spring). Moreover, we succeeded in transferring the parametrized hydrotopes to other recharge areas (Hinterlug and Mitterlug) and validated the transferability of the modeling approach. Finally, we successfully showed the model’s applicability for land use change impact studies by validating the calibrated model in a period in which the space of the dolomite quarries in the Kerschbaum recharge area almost doubled. The results of our study show that an increase of the dolomite quarries negatively affects the water supply of the city of Waidhofen a.d. Ybbs.
Karst reservoirs are distributed widely in China, for which integrated geological, logging, testing, and seismic identification marks can be made and their ages can be determined using unconformity ...surfaces, the lithologic features, and paleobiology of cavern clastic fillings and element geochemistry. The karst reservoirs can be classified as buried hill karst, reef-bank karst, internal karst, bedding deep-underflow karst, vertical deep-infiltration karst, and hydrothermal fluid karst. The first three belong to base-level karsts, controlled by different-order sequence interfaces; the last three belong to nonbase-level karsts, which are controlled by tectonics and fracture. The division of karst facies should take full account of the internal relation of the base-level karsts and the nonbase-level karsts, the existence of deep-turbulent flow zones and the genetic type of karsts. There are many types of corrosion fluid in carbonate rocks in petroleum basins. It is important for the reservoir evaluation and prediction to reconstruct them and to analyze the genetic mechanics of the karst pore-cave-fracture and large-scale cave. As for the controlling factors for the karst development, the study of zonal exogenic forces should be enhanced while the study of azonal endogenic forces is emphasized.
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•Developing an integrated sediment source assessment index based on long series hydrologic signals.•Developing Karst Surface Characteristic Index based on karst desertification ...factors.•Karst Surface Characteristic Index is closely related to hydrological processes.•Clockwise hysteresis is the most frequent and efficient type of sediment transport.
The source and transport processes of suspended sediment are issues that require further study. The complex relationship between the integrated surface characteristics and the mechanisms of sediment sources and transport in heterogeneous karst watersheds remains unclear. This study proposes a comprehensive assessment framework for sediment sources that combines the surface characteristics of karst watersheds, such as exposed rock and shallow topsoil in karst areas. Additionally, the Karst Surface Characteristic Index (KSCI) is developed to evaluate the potential supply capacity of sediment in karst watersheds. The hysteresis index (HImid) is calculated using a long series of hydrological data to study runoff and sediment relationships in eight watersheds in the karst region of southern China. Results indicated that plan curvature, terrain relief, NDVI, and rock exposure contributed most to KSCI, with these four factors contributing 65%. The Q-SSC hysteresis analysis results based on 445 hydrological events showed that a clockwise hysteresis pattern was the most frequent and efficient pattern of sediment transport in the studied watershed (clockwise hysteresis pattern accounted for 72.3% of 445 hydrological events) owing to the limited sediment supply in the karst watersheds. The quantitative analysis results of HImid and KSCI showed that HImid was closely related to KSCI. With an increase in KSCI, a clockwise hysteresis pattern was more likely to appear, indicating that watershed characteristics exerted a significant influence on sediment transport velocity and efficiency. In terms of spatial distribution, near the outlet of the watershed or the river channel, high KSCI values were distributed, and clockwise hysteresis was more likely to occur. In contrast, at the far end of the watershed outlet or the river channel, high values of KSCI were distributed, and anticlockwise hysteresis was more likely to occur. Our findings further enrich the theory of soil erosion and the runoff-sediment relationship at the watershed scale in karst areas, and serve as valuable decision-making references for integrated water and soil sources management.
Carbonate strata are widely distributed in China, which can be found in more than 30 provinces and cities, covering about 1/3 of the country’s territorial area. Affected by different geological and ...climatic conditions, carbonate strata in China geographically present different karst landscapes and groundwater resources. Specifically, northern China is dominated by large karst springs, while southern China is characterized by underground rivers. By determining the distribution range of carbonate strata in China, this paper pointed out the locations of large karst springs in the north and underground rivers in the south, analyzed the distribution characteristics of carbonate rocks in the north and south, the degree of karst development as well as their geological and climate genesis, and discussed the differences between karsts in northern and southern China in terms of occurrence forms of karst water and groundwater systems.
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