Karst aquifers are one of the main potable water sources worldwide. Although the exact global karst water utilisation figures cannot be provided, this study represents an attempt to make an upgraded ...assessment of earlier and often circulated data. The main objective of the undertaken analysis is not only to provide an assessment of the utilisation of current karst aquifers, but also to estimate possible trends under various impact factors such as population growth or climate changes. In > 140 countries, different types of karstified rocks crop out over some 19.3 × 10
6
km
2
, covering > 14% of ice-free land. The main ‘karst countries’, those with > 1 × 10
6
km
2
of karst surface are Russia, USA, China and Canada, while among those with > 80% of the territories covered by karst are Jamaica, Cuba, Montenegro and several others. In contrast, in a quarter of the total number of countries, karstic rocks are either totally absent or have a minor extension, meaning that no karst water sources can be developed. Although the precise number of total karst water consumers cannot be defined, it was assessed in 2016 at approximately 678 million or 9.2% of the world’s population, which is twice less than what was previously estimated in some of the reports. With a total estimated withdrawal of 127 km
3
/year, karst aquifers are contributing to the total global groundwater withdrawal by about 13%. However, only around 4% of the estimated average global annually renewable karstic groundwater is currently utilised, of which < 1% is for drinking purposes. Although often problematic because of unstable discharge regimes and high vulnerability to pollution, karst groundwater represents the main source of potable water supply in many countries and regions. Nevertheless, engineering solutions are often required to ensure a sustainable water supply and prevent negative consequences of groundwater over-extraction.
Rise From Want explores the ways in which a family of poor peasants from the Karst plateau above Trieste, Italy, lived through the great changes brought about by industrialization and modernization.
Electrical conductivity (EC) of karst spring discharge has always been a fundamental variable to characterize karst systems. However, to incorporate EC into the lumped hydrologic modeling is ...challenging but has a huge potential since EC observations are widely collected. In this study, we present a new framework to integrate EC into lumped karst hydrological models for model structure identification and parameter uncertainty reduction. Our framework is tested in a small, well‐instrumented karst catchment near Guilin city (China) where EC dynamics are mostly controlled by the dissolution of carbonate rock and dilution by event water. Four karst models with different structures were equipped to consider the linear growth of EC with the carbonate rock dissolution and its mixing within the karst system. Applying a parameter estimation framework that accounts for uncertainty in discharge and EC simulations, we find that all hydrologic models obtain similar performances concerning spring discharge. However, their performances in simulating spring EC strongly differ permitting us to identify the most realistic model out of the four model structures. Our analysis further shows that including EC into parameter estimation reduces parameter uncertainty concerning concentrated flow in the conduits and helps to estimate immobile water storage in the system. Consequently, our new framework to include EC in karst models provides new directions for the more realistic simulation that can easily be transferred to other karst systems where EC dynamics are controlled by rock dissolution and dilution by event water.
Key Points
A new framework to integrate electrical conductivity (EC) observations into lumped karst hydrologic models is presented
Spring EC shows a high potential for more realistic modeling
Incorporation of spring EC in models can reduce parameter uncertainty concerning concentrated flow in the conduits
Large areas of Europe, especially in the Alps, are covered by carbonate rocks and in many alpine regions, karst springs are important sources for drinking water supply. Because of their high ...variability and heterogeneity, the understanding of the hydrogeological functioning of karst aquifers is of particular importance for their protection and utilisation. Climate change and heavy rainfall events are major challenges in managing alpine karst aquifers which possess an enormous potential for future drinking water supply. In this study, we present research from a high‐alpine karst system in the UNESCO Biosphere Reserve Großes Walsertal in Austria, which has a clearly defined catchment and is drained by only one spring system. Results show that (a) the investigated system is a highly dynamic karst aquifer with distinct reactions to rainfall events in discharge and electrical conductivity; (b) the estimated transient atmospheric CO2 sink is about 270 t/a; (c) the calculated carbonate rock denudation rate is between 23 and 47 mm/1000a and (d) the rainfall‐discharge behaviour and the internal flow dynamics can be successfully simulated using the modelling package KarstMod. The modelling results indicate the relevance of matrix storage in determining the discharge behaviour of the spring, particularly during low‐flow periods. This research and the consequent results can contribute and initiate a better understanding and management of alpine karst aquifers considering climate change with more heavy rainfall events and also longer dry periods.
The investigated karst system contributes to the transient atmospheric CO2 sink with about 270 t/a.
Carbonate denudation rates vary between 23 and 47 mm/1000a.
Rainfall‐discharge modelling results indicate the importance of matrix storage particularly during low‐flow periods.
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.
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