The pollution of karst aquifers by acid mine drainage (AMD) waters is increasing. Major and minor ions (Ca2+, Mg2+, HCO3−, SO42−, F−, and Fe), stable sulfur and oxygen isotopes of dissolved sulfates ...(δ34SSO4 and δ18OSO4) and oxygen isotope of water (δ18OH2O), were analyzed in rainwater, surface water, groundwater, and AMD water sampled from the Babu subterranean stream watershed, in Southwest China. The principal aim of this study was to explore the impact of AMD waters on the evolution of karst aquifers. Based on hydrogeochemistry and stable isotopes (δ18OH2O, δ18OSO4 and δ34SSO4): (1) the chemistry of AMD waters was primarily controlled by pyrite oxidation, karst conduit water by AMD waters and mixing with calcite and dolomite dissolution, and spring water by atmospheric precipitation and carbonate dissolution; (2) contamination of the karst conduit water was mainly attributed to the input of AMD waters, resulting in a shift of δ34SSO4 towards more negative values (from 3.4‰ to −13.2‰); (3) the quality of karst conduit water changed from suitable to unsuitable for irrigation and drinking, particularly due to the increase in total Fe, SO42−, and F− concentrations, reflecting the cumulative effect of AMD waters derived from tailings dumps; this influence was enhanced during rainstorm/drought and anthropogenic activities; and (4) the flow of contaminated groundwater through the conduit promoted the dissolution of carbonates, especially during the dry season due to the greater proportion of AMD in the groundwater. This released more CO2 to the atmosphere. We believe that analysis of stable isotopes (δ18OH2O, δ18OSO4, and δ34SSO4), combined with hydrogeochemistry, is effective for exploring the impact of AMD on karst aquifers. Therefore, reasonable treatment methods should be taken to reduce the negative impacts of tailings dumps on karst aquifers.
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•Hydrogeochemistry and stable isotopes were employed to assess the impact of AMD on karst aquifers.•Total Fe, SO42− and F− were identified as the predominant pollutants in groundwater.•Groundwater contamination occurred because of the Houlongshan AMD waters.•The contaminated groundwater promoted the dissolution of carbonates, especially during the dry season.
The Karst aquifers are usually characterized by high spatial heterogeneity in the humid tropics and subtropics, evidenced by specific landforms features (e.g., heavily fractured outcrops, sinkholes, ...etc.) and complex subterranean conduit networks. The marked high heterogeneity leads to the temporal–spatial variability of hydrological and hydro-chemical processes, making its environments extremely vulnerable to natural and anthropogenic hazards. The complicated temporal–spatial variability of hydrochemistry in karst systems depends on several underlying factors which influence the hydro-chemical processes. Investigating the factors of the karst water hydrochemistry variability is necessary to understand the hydro-chemical processes and mitigate natural and anthropogenic hazards for ensuring the sustainability of karst water resources. In this paper, an attempt is made to couple geostatistical and geochemical analysis to extract the underlying controlling factors and effective information about the geochemical evolution behave of karst water in Houzhai karst area, southwestern China. Factor analysis was performed to obtain significant statistical relationship of the hydrochemistry variation in the Houzhai karst basin. The ordinary kriging method was applied to the factor scores to investigate the contributions of factors on different regions. The results of the factor analysis indicated four principal factors which explained > 81.678% of the total sample variance: (1) the dilution effect by rainfall; (2) the dissolution effect dominated by calcite; (3) the human agricultural activities effect; (4) the migration of dissolved components under the control of alkaline environments in karst water. It revealed that the dilution effect was more significant (36.579%) than the dissolution effect (22.036%) and human agricultural activities effect (14.596%). These factors made more significant difference of contributions on the karst area in the dry periods than in the rainy periods. The dilution process by rainfall and the dissolution process of carbonate rock had a great influence on the upstream area whereas the human agricultural activities played important roles in the middle-stream area, especially in the dry periods. This integrated approach which combine factor analysis with kriging method is effective in the identification and interpretation of factors related to the variability of hydrochemistry, as well as the contributions of these factors on space and time.
Karst tiankengs in China are globally significant locations for studying ecological environments and plant diversity. However, there are few reports on how the unique geographical environment of ...tiankengs affects plant genetic diversity and genetic structure. This study used Hyper-seq gene sequencing technology to develop large-scale genomic SNPs of Manglietia aromatica, both within and outside the tiankengs. Its aim was to investigate the impact of tiankengs on the genetic diversity and genetic structure of the M. aromatica population. The analysis results indicate that the genetic diversity of the populations within the tiankeng (π = 0.2044) is higher than that of the populations outside of it (π = 0.1671), indicating that the tiankengs have a positive impact on species diversity. The genetic differentiation coefficient (Fsub.ST ) between the populations inside and outside the tiankeng was 0.0534 and the Fsub.ST values of populations within the tiankeng were 0.077, 0.082, and 0.141, meaning that the genetic variation in the tiankengs is very high. The genetic similarity outside the tiankengs is also very high, indicating that the tiankengs are effectively preserving the genetic diversity of M. aromatica. Furthermore, the gene introgression analysis results gave no proof of gene flow between the three tiankeng populations. This suggests that the tiankengs not only protect species diversity, but also hinder gene flow between populations to some extent. However, this hindrance may gradually subside with the evolution of the tiankengs. The genetic structure analysis revealed that the M. aromatica population in Guangxi, China, can be classified into three subpopulations. The first is the tiankeng subpopulation, including all the populations in tiankengs. The second subpopulation consists of populations surrounding the tiankengs. These two subpopulations are distributed in Leye County in northwestern Guangxi, China, and are very close to each other. The third is the Huanjiang subpopulation, which is located far away from the tiankengs. Considering the direction of gene flow and genetic structure, it is speculated that the populations in the tiankengs evolved from the populations near the pit mouth. This study confirms that the tiankengs are shelters and provide a suitable habitat for the endangered plant M. aromatica, because its genetic diversity is well conserved and the species is well adapted to the habitat within the tiankengs.
•Infiltration-based stormwater management reduce peaks and volumes of urban runoff.•Stormwater infiltration is promoted to restore groundwater recharge.•The fate of infiltrated stormwater and its ...impact on baseflow is poorly known.•Impacts of LIDs could be altered by the ‘urban karst’ (pipes, trenching).
The covering of native soils with impervious surfaces (e.g. roofs, roads, and pavement) prevents infiltration of rainfall into the ground, resulting in increased surface runoff and decreased groundwater recharge. When this excess water is managed using stormwater drainage systems, flow and water quality regimes of urban streams are severely altered, leading to the degradation of their ecosystems. Urban streams restoration requires alternative approaches towards stormwater management, which aim to restore the flow regime towards pre-development conditions. The practice of stormwater infiltration—achieved using a range of stormwater source-control measures (SCMs)—is central to restoring baseflow. Despite this, little is known about what happens to the infiltrated water. Current knowledge about the impact of stormwater infiltration on flow regimes was reviewed. Infiltration systems were found to be efficient at attenuating high-flow hydrology (reducing peak magnitudes and frequencies) at a range of scales (parcel, streetscape, catchment). Several modelling studies predict a positive impact of stormwater infiltration on baseflow, and empirical evidence is emerging, but the fate of infiltrated stormwater remains unclear. It is not known how infiltrated water travels along the subsurface pathways that characterise the urban environment, in particular the ‘urban karst’, which results from networks of human-made subsurface pathways, e.g. stormwater and sanitary sewer pipes and associated high permeability trenches. Seepage of groundwater into and around such pipes is possible, meaning some infiltrated stormwater could travel along artificial pathways. The catchment-scale ability of infiltration systems to restore groundwater recharge and baseflow is thus ambiguous. Further understanding of the fate of infiltrated stormwater is required to ensure infiltration systems deliver optimal outcomes for waterway flow regimes.
The Mucille karst depression is one of the few examples of polje on the Italian side of the Classical Karst Region, a shared area between Italy and Slovenia. The polje is subject to frequent ...flooding, becoming more problematic since 2000, as swallow holes more frequently have affected housing and recreational areas, leading the population to believe that their ability in draining the area had stopped functioning. Climate changes play an important role as there has been an intensification in extreme events (30-day cumulative precipitation of more than 350 mm) within the considered time-period 1919–2020. The necessity to provide answers to the inhabitants required in-depth studies such as hydrogeological investigations, discharge measurements and Electrical Resistivity Tomography (ERT) acquisitions. Over the 3 years of monitoring (2017–2020), two flood events reached the Selz settlement. In total, four events have been analysed to build a hydrogeological model of the area in order to properly estimate its recharge and regression curve, and to define the functionalities of the swallow holes. The defined model allowed a better knowledge and a greater awareness in proposing the proper mitigation measures able to increase the drainage capacity of the area avoiding always more frequent future floodings.
•Multiple climate change and groundwater abstraction scenario testing procedure for future development of karst spring discharge.•Climate change has a major effect on the future evolution of spring ...discharge.•Groundwater abstraction constitutes a secondary factor in the spring dry-up.•The aquifer is not overexploited yet but still highly sensible to groundwater extraction.
The Mediterranean region is a climate change hotspot where the rate of climate change exceeds the global mean. The rapidly changing climate in combination with an increase in anthropogenic pressures cause water resources in the Mediterranean basin to become increasingly scarce. Modelling future water resource availability considering both climate and anthropogenic changes on karst catchments remains a major challenge in the field of hydrology. The purpose of this study is to assess the relative effects of climate change and anthropogenic forcing on the spring discharge of a Mediterranean karst system by coupling 12 climate model simulations under two emission scenarios (RCP 4.5 and RCP 8.5) with three hydrological models and four scenarios of future groundwater extraction for drinking water supply (no abstraction, present-day abstraction, +50% abstraction and + 100% abstraction at horizon 2100). The study area is the Oeillal spring’s karst catchment which is located at the Fonfroide-Monredon massif located in Southern France. The periods of spring drying-up can increase up to 30% according the RCP 4.5 and up to 70% according the RCP 8.5. This may be aggravated by groundwater abstraction in the area which, combined with climate change, could contribute to double the length of spring drying-up period in the worst scenario. The main results of the study suggest that climate change has a major effect on the future evolution of the Oeillal spring’s discharge and that groundwater abstraction constitutes a secondary but non-negligible factor which increases the occurrence of drying-up of this Mediterranean spring.
To investigate the hydrogeological characteristics of the karst trough zone in China, two groundwater systems (Yuquandong YQD and Migongquan MGQ) in Sixi Valley, western Hubei, were discussed. Seven ...groups of tracer experiments were conducted, with consideration of regional topography, geology and hydrogeology. By means of high-resolution continuous monitors, tracer breakthrough curves (BTC) of two systems were obtained and it was found that karst conduits of YQD system were more developed. From their hydrological and hydrochemical performance, two different systems were verified with relatively independent flow paths. Additionally, boundaries of the two systems were confirmed, sub-regions of recharge were delineated, and five conceptual models of groundwater recharge were determined, which are typical of the karst trough zone of China.
Background and aims
Karst rocky desertification (KRD) influences soil properties and plant species. Soil microbes are important factors in maintaining ecosystem stability. However, little is known ...about the role of fungi in adaptation of plants to KRD.
Methods
Fungi colonized in bulk soil, rhizosphere, and roots of
Themeda japonica
at strong and slight KRD were analyzed by ITS2 amplicon sequencing. The relationship between soil nutrients and fungal diversity was estimated by redundancy analysis (RDA) and Spearman analysis.
Results
AN, NN, SOC, TN, TP content and pH in strong KRD soil were higher than those with slight KRD. Rhizosphere with slight KRD had higher fungal richness and diversity than it with strong KRD, but there was no difference in root endophyte between KRD grades. The bulk soil with slight KRD had higher fungal richness compare to strong KRD. The fungal communities in bulk soil, rhizosphere, and root between plants at different KRD grades were significantly different. In addition, the fungal communities of rhizosphere were sensitive to the change of KRD environment. Ascomycota and Basidiomycota were the predominant phyla in bulk soil, rhizosphere and root endophyte at strong and slight KRD. SOC, AN and pH influenced the composition of fungal communities at strong KRD. In contrast, TN and AN had a negative impact on richness.
Conclusion
Our results suggest that fungal communities of rhizosphere may play a role in adaptation of
T. japonica
to KRD and may contribute to promote plant growth and ecological performance in karst areas.
The diversity of small, medium, and large solution features of zonal karsts and high mountain karsts is described here. It was taken into consideration how diversity changes according to the ...distance from the Equator in case of small, medium and large features of various zonal karsts and how it varies based on the distance from altitude in case of the karren features (small features) of high mountain karsts. It can be established that the diversity of karst features decreases according to the distance from the Equator (independent of the size of the features), while in high mountains the diversity of karren features first increases with altitude and then it decreases. The decrease of the diversity of medium and large features moving away from the Equator can be explained by the decrease of dissolution intensity. The diversity change of karren features shows a relation with the diversity of the inclination of the bearing slope. Since on tropical karsts and in the medium elevated areas of high mountains (1600-2100 m) where bare slopes with large expansion and various slope inclination occur, the diversity of karren is great. On tropical karsts, slopes with diverse inclination were created by karstification and in high mountains by glacial erosion.
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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.
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