Spring Catchment Research Articles

Hydrogeochemical and isotopic characterization of the main karst aquifers of the middle Valseriana (Northern Italy): Nossana and Ponte del Costone springs

Karst springs are one of the most exploited drinking water resources in the world. Isotopic and chemical analyses on these waters reveal essential insights into their hydrodynamics. Valseriana (Northern Italy) is a valley within the Italian Pre-Alps, characterized by high water availability. The main reasons are a bedrock consisting of very permeable carbonate formations and a mean annual precipitation above 1800 mm/y. In this context, the Valseriana spring catchments have become strategically important for the water exploitation and the domestic supply of Bergamo and the neighboring municipalities. This study general aim is to expand the knowledge on the two main karst systems (Nossana and Ponte del Costone), which together include twenty-three major and minor springs, by defining a state-of-the-art that will be useful in future decades to preserve this crucial resource. Specific objectives include i) verifying the applicability of the 3H/3He dating method in karst environments, ii) defining groups of springs according to their chemical and isotopic characteristics for possible safeguard actions, and iii) establishing a conceptual model of the internal dynamics of the two spring systems. A chemical and isotopic sampling campaign was specifically conducted between May 2018 and July 2019. A total of 34 water points were sampled, including natural springs, rivers, wells, karst caves, and nearby mines. Water sampling for 3H/3He isotopic analyses was proved possible through careful selection of the sampling points and the insertion of the pump tubing in the spring fractures. A first classification of springs into uniform hydrochemical groups was obtained by applying the hierarchical cluster analysis technique on major ions contents. These outputs were combined with information from the 3H/3He dating analyses and resulted in three different classes of springs. The three classes showed a clustering for elevations: at high, medium, and valley bottom elevations, respectively. Finally, the elaborations simplified the two karst systems by a hierarchical flow system model, dynamically controlled by different karst network development and infiltration water.

River–Spring Connectivity and Hydrogeochemical Processes in a Karst Water System of Northern China: A Case Study of Jinan Spring Catchment

Frequent surface water–groundwater interactions and prevalent anthropogenic inputs make karst water systems vulnerable to human disturbance. As a typical karst region in North China, the Jinan Spring Catchment has become increasingly threatened due to rapid population growth and urban expansion. In this study, the local river–spring interaction and its interference with the hydrogeochemical evolution of groundwater are evaluated based on water stable isotopes and hydrochemistry. Twenty-two karst groundwater, eleven Quaternary pore water, sixteen spring water, and thirty-two surface water samples were collected during low- and high-flow conditions over the course of a year. The isotopic signatures of four different water types display significant differences, reflecting the recharge–discharge relationship of the karst water system. Mountainous springs feature lighter isotopes, whereas urban springs have significantly heavier isotopes. The result of end-member mixing analysis shows that the surface–groundwater interaction varies spatially and temporally within the spring catchment. Urban springs receive considerable replenishment from the surface water, especially after rainy episodes (up to 50%), while mountainous springs show little hydraulic dependence on surface water leakage (4~6%). Local mineral dissolution (including calcite, dolomite, gypsum, and halite), CO2 dissolution/exsolution, and cation exchange are the main hydrogeochemical processes constraining water chemistry in the spring catchment. The deterioration of water quality can be attributed to anthropogenic influences involving the discharge of domestic effluents, agricultural activities, and irrigation return flow. The findings of this work can improve our understanding of the complex karst water system and serve as a reference for sustainable groundwater management in other karst areas of northern China.

Spring Water Catchment Building and Water Distribution System for Domestic Needs

The population growth implies that the population's need for clean water tend to increase. Clean water availability is not optimal due to geographical factors and discharge reductions during dry season. This research was conducted to design spring water catchment building and water distribution system at Kalikajar Village, Wonosobo. The population data, water demand, and spring discharge were utilized in this research. The population growth was calculated with arithmetic, geometric, exponential, and logistic method. Then water demand was calculated based on SNI 19-6728.1-2002. The population growth which predictably reaches 5328 people in 2050 will result in increasing clean water demand by 9.68% with domestic water demand of 4.63 L/s. The spring discharge measured at the research location showed an average of 10.80 L/s. Therefore, the spring discharge is able to meet the population needs in the projected year. The spring catchment building was designed with Type B, while three reservoir were designed with the capacity of 7 m3 each. The water distribution is designed with gravity system because the elevation difference between the spring and the village is more than 10 m. The PVC pipeline used diameter of 100 – 150 mm, with total length of 11843 m. The design meets the calculated requirement and could be implemented. Keywords: Distribution system, Reservoir, Spring water, Hilly areas, Water consumption

Assessment of occurrence, diversity, and biomass of macroinvertebrates in Swiss groundwater systems using citizen science data

Groundwater is a vast ecosystem harboring a high diversity of specialized taxa. Despite its diversity, groundwater is a still relatively unexplored and threatened ecosystem. Especially the linkage of groundwater with other ecosystems remains largely unknown from the perspective of groundwater fauna. Here, we used citizen science data to get a first baseline knowledge of the occurrence, diversity, and biomass of major macroinvertebrate groups found in shallow groundwater systems of Switzerland. We investigated all organisms collected from the groundwater in 346 spring catchment boxes of municipal drinking water providers. We morphologically identified the organisms on a broad taxonomic level and estimated their biomass and pigmentation using automated image processing. Crustaceans, particularly Niphargus and groundwater isopods, were the most common taxa of obligate groundwater organisms. We also found a surprisingly high number of macroinvertebrates associated with surface and subsurface ecosystems. These taxa might be accidentally entering the groundwater or use it as temporary habitat. In both cases they possibly contribute essential allochthonous energy imports from the surface. We found a positive relationship between the estimated biomass of macroinvertebrates in the samples and the occurrence and abundance of Niphargus. Owing to the widespread occurrences of surface and subsurface macroinvertebrates in our groundwater samples, our study provides evidence for common interactions between groundwater, soil, and surface ecosystems.

Integrating citizen science and environmental DNA metabarcoding to study biodiversity of groundwater amphipods in Switzerland

Groundwater is the physically largest freshwater ecosystem, yet one of the least explored habitats on earth, both because of accessing difficulties and the scarcity of the organisms inhabiting it. Here, we demonstrate how a two-fold approach provides complementary information on the occurrence and diversity of groundwater amphipods. Firstly, we used a citizen science approach in collaboration with municipal water providers who sampled groundwater organisms in their spring catchment boxes over multiple weeks, followed by DNA barcoding. Secondly, we collected four 10 L water samples at each site, in one sampling event, for environmental DNA (eDNA) metabarcoding. We found that citizen science was very effective in describing the distribution and abundance of groundwater amphipods. Although the single time-point of eDNA sampling did not detect as many amphipods, it allowed the assessment of the entire groundwater community, including microorganisms. By combining both methods, we found different amphipod species co-occurring with distinct sequences from the eDNA-metabarcoding dataset, representing mainly micro-eukaryotic species. We also found a distinct correlation between the diversity of amphipods and the overall biodiversity of groundwater organisms detected by eDNA at each site. We thus suggest that these approaches can be used to get a better understanding of subterranean biodiversity.

Hydrochemical Characteristics and Formation Causes of Ground Karst Water Systems in Gudui Spring Catchment

As one of the famous karst springs in Shanxi Province, the Gudui spring is the only medium-low temperature hot spring, with a long history of development and a rich cultural accumulation. The karst groundwater in the Gudui spring catchment was taken as the research object. Through systematic sample collection and isotope analysis, hydrochemistry (Durov map, ion ratio, Gibbs map, and hydrogen and oxygen isotope) methods were comprehensively used to analyze groundwater hydrochemistry and groundwater system runoff characteristics. The87Sr/86Sr value of karst groundwater in the Gudui spring catchment was 0.709 to 0.717, and the Mg/(Mg+Ca) value was 0.27 to 0.74. By analyzing the Sr isotope composition and Mg/(Mg+Ca) and 1/Sr variation characteristics, it was concluded that the karst groundwater in the Gudui spring catchment was a mixture of deep hot water and shallow cold water. The karst water subsystem of Nanliang spring presented the characteristics of carbonate stratum runoff. The karst water subsystem of Fuling Mountain Gaoxian Haitou spring and the deep circulation subsystem of Houma Basin exhibited the runoff characteristics of carbonate rock and igneous rock strata. The karst water subsystem of Taiershan Jiuyuanshan Gudui spring presented the runoff characteristics of carbonate rock and ancient silicoaluminate strata. The δ18O value in karst groundwater of Guodui spring area ranged from -11.46‰ to -7.81‰, and the average value was -10.08‰. The range of the δD value was -83.7‰ to -60.8‰, and the average value was -73.6‰. This showed that karst groundwater in the spring area was the result of mixing of various types of water. Through comparative analysis of hydrogen and oxygen isotopes of 2014 and 2021 sampling points at the same location, it was concluded that the change in water samples at the Guduiquan resulted from the gradual accumulation of water supplied by Sanquan Reservoir. The change in Sanquan Reservoir was due to the influence of Yellow River diversion. The karst groundwater in the spring area were characterized by large calcium ion, magnesium ion, and sodium ion values; a small potassium ion value; a large sulfate value; and a small chloride value. The hydrochemical types of karst groundwater in Gudui spring catchment could be divided into SO4-Na, SO4-Ca, HCO3-Na, HCO3-Mg, HCO3-Ca, and Cl-Na. The hydrochemical types of karst groundwater showed evident hydrochemical composition zoning from HCO3-Ca·Mg→HCO3·SO4-Ca·Mg→SO4·HCO3-Na·Ca→SO4·Cl-Na·Ca. According to the comprehensive analysis of hydrochemical isotope and hydrogeological conditions, the karst water subsystem of Nanliang spring was primarily recharged by rainfall infiltration in the exposed limestone area and river infiltration, and its karst groundwater was recharged by runoff from south to north to the karst water subsystem of Fuling Mountain Gaoxian Haitou spring and the deep circulation subsystem of Houma Basin. The karst water subsystem of Taier Jiuyuan Mountain Gudui spring received rainfall infiltration supplement and upstream runoff supplement from the exposed limestone area. Its karst groundwater flowed from north to south and received the supply of Sanquan Reservoir from Yellow River water in the natural discharge area of Gudui spring.

The migration and transformation processes of dissolved organic matter in rainwater- drip water- phreatic water of a typical karst spring catchment, in South China

The dissolved organic matter (DOM) migration and transformation in karst aquifer are of great significance for geochemical processes but remain poorly understood. In this study, we selected the Guilin Yaji Karst Experimental Site as a natural laboratory and collected rainwater (RW), drip water (DW), and phreatic water (PW) from September 2019 to September 2021 to study the DOM migration and transformation in a typical bare karst spring catchment. Hydrochemical and stable hydrogen and oxygen isotopes were applied to study the water cycle of the aquifer. Absorbance and fluorescence spectroscopy were used to characterize the DOM quality. Three-dimensional fluorescence combined with fluorescence regional integration was used for identifying the DOM compositions. The RW DOM had a weak humification degree and strong terrestrial characteristics. It was affected by the monsoon and showed higher humification in the dry season than in the wet season. The higher rainfall intensity had a dilution effect on the DOM fluorescence components levels when the rain intensity was>10 mm/day (not the threshold value). Continuous rain events led to the continuous dilution effect on RW DOM in the dry season, but such a phenomenon was not obvious in the wet season. The DW DOM inherited weak humification characteristic that was close to RW DOM but was altered by the hydrogeology conditions and plant root and microbial activities intensities of the upper vadose zone. The higher humification degree of PW DOM may be related to the higher degree of microbial processing caused by the longer groundwater residence time. The humic and hydrophobic degree of DOM for fissure PW was weaker than that for conduit PW because fissure media provides a superior condition for DOM to adsorb to the mineral surface. In the wet season, when the preferential channel of the aquifer was activated, the PW DOM showed similar characteristics to RW DOM, indicating a significant hydrologic effect on the PW DOM. Our results provide a valuable reference to advance understanding of DOM behavior in karst aquifer and highlight the importance of hydrogeologic conditions and hydrologic processes on DOM migration and transformation.

Simulation of spring discharge using graph neural networks at Niangziguan Springs, China

Over past decades, extensive groundwater development in karst aquifers has led to significant declines in groundwater levels and spring discharges. While the recent implementation of sustainable karst aquifer development policies appears to have lessened the declining trend of spring discharge, many aspects of karst aquifers remain to be explored. This paper applied two spectral-based graph neural networks (GNN) models of ChebNet and graph convolutional networks (GCN) for karst hydrological processes by considering the correlations among precipitation, spring discharge, and human impacts. This approach captures the spatial dependence of precipitation infiltration, groundwater propagation in heterogeneous karst aquifer and spring discharge from bared karst aquifer. This study proposed three graph structures (complete graph, information flow graph, and association graph of groundwater flow field) to depict relations between precipitation and spring discharge in the GNN models in Niangziguan Springs, China. The results show that the association graph of groundwater flow field is the optimal graph structure of GNN models. Based on the optimal structure, we investigated precipitation-driven-discharge models using ChebNet and GCN to predict the discharge. The results show that the high-order ChebNet is more adaptable to simulate the karst hydrological processes with nonlinear and nonstationary behaviors than that GCN. Moreover, the study confirms that the groundwater sustainable development policy has achieved a prominent contribution 2 m3/s in water conservancy in Niangziguan Springs catchment.

Hydrogeological characterization of karst springs of the white (Proteus anguinus anguinus) and black olm (Proteus anguinus parkelj) habitat in Bela krajina (SE Slovenia)

The springs west of Črnomelj, in SE Slovenia, are the habitat of the black (Proteus anguinus parkelj) and the white olm (Proteus anguinus anguinus). Some of these springs are also the only known habitat in the world of endemic species of black olm. A steady decline in olm populations has been observed in this area over the past decades. Owing to the rapid runoff and groundwater flow high-resolution monitoring is essential in providing better insight into the hydrogeological characterization of the catchment area of springs. Specific factors and critical parameters of water behind said olm degradation have not yet been defined. Because the olm’s environment is largely aquatic, one potential critical parameter could be the higher water temperatures (>12 °C) or higher nitrate concentration (>9.2 mg/l). The six-month observation of the springs (July – December 2021) point to water temperature as a potential critical parameter since the water temperature of the springs exceeded 12 °C in months July and August. Nitrate concentrations could also be a second critical parameter in the degradation of the olm’s habitat. Maximum nitrate concentrations above 9.2 mg/l throughout much of the observation period (except for Dobličica spring). Due to less agricultural activity in December in the spring catchment area and a higher dilution rate due to reduced evapotranspiration and increased effective precipitation during this time of the year, the nitrate concentrations are decreased. The results of the measured parameters of groundwater could show the hydrogeological connection between the Otovski and Pački breg springs and between Šotor, Jamnice and Dobličica. The Obršec spring has an independent catchment area. A detailed estimation of the springs catchment area is possible due to a detailed geologic map. It is necessary to determine the origin of the nitrate (nitrate isotope analysis), to quantify the threshold values of the critical parameters, to define precisely all the causes of the olm deterioration, and to make proposals for appropriate measures to limit or even stop the decline of the olm population.

Traceability and Biogeochemical Process of Nitrate in the Jinan Karst Spring Catchment, North China

Accurate identification of nitrate (NO3−) sources is critical to addressing groundwater pollution, especially in highly vulnerable karst aquifers. The groundwater hydrochemistry and δ15NNO3 and δ18ONO3 isotopes were analyzed in samples taken from the Jinan Spring Catchment, which has been affected by urbanization and agricultural activities. The study highlighted the use of hydrochemistry, environmental isotopes, and a multisource linear mixed model for NO3− source identification and apportionment. The results showed that, controlled by carbonate rocks, the hydrochemical types in both rainy and dry seasons were highly consistent, and HCO3·SO4−Ca was the dominant type, accounting for 60%. Except for Ca2+, Mg2+ and HCO3−, the coefficients of variation of other ions were all greater than 0.5 in rainy and dry seasons. The chemical composition of groundwater was mainly controlled by water–rock interaction. Ca2+ and HCO3− were mainly derived from carbonate rock dissolution; K+, Na+, SO42−, NO3− and Cl− were partially derived from atmospheric precipitation. The IsoSource model quantitatively revealed that the majority of the groundwater and surface water was influenced by manure and sewage (M&S) contributing 39.3% and 52.3% in the rainy season, and 37.1% and 56.9% in the dry season, respectively. The NO3− source fraction rates were in the order M&S > SON > AF > CF > AD. In addition, nitrate pollution control measures and suggestions for different areas are put forward. In rural residential areas, the free discharge of livestock manure and sewage should be strictly controlled. In agricultural planting areas, chemical fertilizers and pesticides should be used rationally to prevent non-point source pollution. In urban areas, the centralized treatment of industrial and residential sewage should be strengthened to prevent point source pollution.

Low antimicrobial resistance in Escherichia coli isolates from two large Austrian alpine karstic spring catchments

The increasing occurrence of antibiotic resistant bacteria poses a threat to global public health. Clinically relevant resistances also spread through the environment. Aquatic ecosystems in particular represent important dispersal pathways. In the past, pristine water resources have not been a study focus, although ingestion of resistant bacteria through water consumption constitutes a potentially important transmission route. This study assessed antibiotic resistances in Escherichia coli populations in two large well-protected and well-managed Austrian karstic spring catchments representing essential groundwater resources for water supply. E. coli were detected seasonally only during the summer period. By screening a representative number of 551 E. coli isolates from 13 sites in two catchments, it could be shown that the prevalence of antibiotic resistance in this study area is low. 3.4 % of the isolates showed resistances to one or two antibiotic classes, 0.5 % were resistant to three antibiotic classes. No resistances to critical and last-line antibiotics were detected. By integrating fecal pollution assessment and microbial source tracking, we could infer that ruminants were the main hosts for antibiotic resistant bacteria in the studied catchment areas. A comparison with other studies on antibiotic resistances in karstic or mountainous springs highlighted the low contamination status of the model catchments studied here, most likely due to the high protection and careful management while other, less pristine catchments showed much higher antibiotic resistances. We demonstrate that studying easily accessible karstic springs allows a holistic view on large catchments concerning the extent and origin of fecal pollution as well as antibiotic resistance. This representative monitoring approach is also in line with the proposed update of the EU Groundwater Directive (GWD).

Community adaptive capacity to drought in Kakap Springs catchment area

Water in karst areas flows deep below the surface due to geological causes, making it difficult to get pure air on the surface. The karst region has passed with drought as a result. In the watershed Kakap Springs, this paper will examine the adaptability of the community to drought. The study area covers seven villages. The evaluation uses a quantitative descriptive method based on human, social, natural, physical, and financial factors. Adaptation capacity in the research area varies with the driving factor is financial. This is because exposure to drought has been going on for a long time and every year, so people have prepared themselves financially. Intensive exposure also causes the distribution of adaptive capacity in each village to be regulated at a moderate level. It is necessary to increase social capacity so that the adaptive capacity of the community becomes higher.

Groundwater environmental DNA metabarcoding reveals hidden diversity and reflects land-use and geology.

Despite being the most important source of liquid freshwater on the planet, groundwater is severely threatened by climate change, agriculture, or industrial mining. It is thus extensively monitored for pollutants and declines in quantity. The organisms living in groundwater, however, are rarely the target of surveillance programmes and little is known about the fauna inhabiting underground habitats. The difficulties accessing groundwater, the lack of expertise, and the apparent scarcity of these organisms challenge sampling and prohibit adequate knowledge on groundwater fauna. Environmental DNA (eDNA) metabarcoding provides an approach to overcome these limitations but is largely unexplored. Here, we sampled water in 20 communal spring catchment boxes used for drinking water provisioning in Switzerland, with a high level of replication at both filtration and amplification steps. We sequenced a portion of the COI mitochondrial gene, which resulted in 4917 ASVs, yet only 3% of the reads could be assigned to a species, genus, or family with more than 90% identity. Careful evaluation of the unassigned reads corroborated that these sequences were true COI sequences belonging mostly to diverse eukaryotic groups, not present in the reference databases. Principal component analyses showed a strong correlation of the community composition with the surface land-use (agriculture vs. forest) and geology (fissured rock vs. unconsolidated sediment). While incomplete reference databases limit the assignment of taxa in groundwater eDNA metabarcoding, we showed that taxonomy-free approaches can reveal large hidden diversity and couple it with major land-use drivers, revealing their imprint on chemical and biological properties of groundwater.

A Combined Stochastic–Analytical Method for the Assessment of Climate Change Impact on Spring Discharge

This study describes a novel methodology for the prediction of spring hydrographs based on regional climate model (RCM) projections, with the goal of evaluating climate-change impact on karstic-spring discharge. A combined stochastic–analytical modeling methodology to predict spring discharge was developed and demonstrated on the Bukovica spring catchment at the Durmitor National Park, Montenegro. As a first step, climate model projections of the EURO-CORDEX ensemble were selected; and then bias correction was applied based on historical climate data. The regression function between rainfall and peak discharge was established by using historical data. Baseflow recession was described by using a double-component exponential model, where hydrograph decomposition and parameter fitting were performed on the Master Recession Curve. Rainfall time series from two selected RCM scenarios were applied to predict future spring-discharge time series. Bias correction of simulated hydrographs was performed, and bias-corrected combined stochastic–analytical models were applied to predict spring hydrographs based on RCM-simulated rainfall data. Both simulated climate scenarios predict increasing peak discharges and decreasing baseflow discharges throughout the 21st century. The model results suggest that climate change is likely to exaggerate the extremities both in terms of climate parameters and spring discharge by the end of the century both for moderate (RCP 45) and pessimistic (RCP 85) CO2 emission scenarios. To investigate the temporal distribution of extremities throughout the simulated time periods, the annual numbers of flood and drought days were calculated. Annual predicted flood days show an increasing trend during the first simulation period (2021–2050) and a slightly decreasing trend during the second simulation period (2071–2100), according to the RCP45 climate scenario. The same parameter shows a stagnant trend for the RCP 85 climate scenario. Annual predicted drought days show a decreasing trend both for the RCP 45 and RCP 85 climate scenarios. However, the annual number of drought days shows a large variation over time. There is a periodicity of extremely dry years with a frequency between 5 and 7 years. The number of drought days seems to increase over time during these extreme years. The study confirmed that the applied methodology can successfully be applied for spring-discharge prediction and that it offers a new prospect for its wider application in studying karst aquifers and their behavior under different climate-change scenarios.

Groundwater recharge mechanisms in a vegetated epikarst spring catchment using water isotopes methods

Groundwater recharge mechanisms in a vegetated epikarst spring catchment using water isotopes methods

Community Capacity Bulding In The Kakap Spring Catchment Area

<p>Faktor geologi menyebabkan aliran air kawasan karst terkonsentrasi di bawah permukaan sehingga masyarakat sulit dalam mengakses air. Seperti pada wilayah Daerah Tangkapan Air (DTA) Kakap yang terletak di Kecamatan Giriwoyo, Kabupaten Wonogiri, Jawa Tengah. Masyarakat pada setiap tahunnya mengalami permasalahan pada ketersediaan air. Sistem hidrologi kawasan karst juga dapat terancam karena kurangnya pengetahuan terhadap keberadaan ponor/luweng. Kondisi Ponor/luweng sendiri menjadi kurang terawat dengan dipenuhi banyak sampah baik sampah organik maupun sampah rumah tangga. Pengabdian ini bertujuan untuk meningkatkan kapasitas dan partisipasi masyarakat dalam konservasi di kawasan karst. Melalui Focus Group Discusion (FGD) secara partisipasi, untuk memberikan pemahaman tentang kerentanan kawasan karst sumber utama air bersih. Kapasitas masyarakat dalam mitigasi bencana kekeringan belum terbentuk dengan sempurna akibat kurangnya kesadaran dan pengetahuan akan upaya mitigasi yang dapat dilakukan secara gotong royong oleh masyarakatAbstrak dalam bahasa Indonesia mengikuti kaidah dalam Pedoman Umum Ejaan Bahasa Indonesia (PUEBI).</p>

Spatial-temporal behavior of precipitation driven karst spring discharge in a mountain terrain

• Obtain the active time length of precipitation driven spring discharge (SD). • Rank the contribution of precipitation at each subarea (ESA) to the SD process. • Classify rainfall-SD in three patterns depending on landform and aquifer behaviors. • Quantify the contribution of precipitation at ESA to the maximum and medium SD. Behaviors of karst springs are manifestations of spatial and temporal dynamics involving multi-hydrogeological processes, including precipitation, surface water runoff, infiltration, groundwater flow, and anthropogenic activities. These dynamic processes are usually nonlinear and nonstationary. In this study, we couple the Shapley Additive exPlanation (SHAP) with a Long Short-Term Memory (LSTM) recurrent neural network to produce an interpretable deep learning model to explore the precipitation driven spring discharge mechanism and to predict spatial–temporal behaviors of karst springs. Applying the model to Niangziguan Springs catchment, China, we show that the precipitation infiltration volume of each catchment subregion is the primary factor driving the spring discharge, and the precipitation over the 12-month period has the most significant effect on the spring discharge. We categorize the precipitation-driven spring discharge at the catchment into three patterns according to each subregion's landform and karst aquifer characteristics based on the SHAP analysis. In the regions with deeply buried karst aquifers, moderate to light precipitation recharges the karst aquifer. On the other hand, heavy precipitation recharges the karst aquifer in the river valley regions more efficiently than others. In the regions where karst aquifers are exposed and groundwater discharges, the groundwater level is the primary factor dictating precipitation and spring discharge processes.

Tracing sources and fate of nitrate in multilayered karstic hydrogeological catchments using natural stable isotopic composition (δ15N-NO3− and δ18O-NO3−). Application to the Toulon karst system (Dordogne, France)

• Nitrate contents and isotopes are measured in a large multilayered karst aquifer. • Primary and secondary sources of nitrate are determined, at the local scale, using nitrate isotopes. • Origins of nitrate, over a karstic hydrogeological catchment, are assessed by nitrate isotopes. • The fate of nitrate in a karst aquifer is specified/ elucidated/ quantified/ combining isotopes and hydrogeological approaches. In groundwater management, the determination of the origins of nitrate (NO 3 – ) endmember sources is the first step in improving the management over a hydrogeological catchment. The generally multiple source contamination by nitrate over the karst systems makes it difficult to identify the exact nitrate origins in surface water and groundwater. This work aims to assess nitrate vulnerability of a karst system fed by several karst aquifers. The Toulon karst system offers the opportunity to study the relationships between two multilayered karst aquifers. It shows an increase in mean NO 3 – concentrations over decades. However, the origins of the NO 3 – remain unclear. Natural stable isotopic composition of NO 3 – (δ 15 N -NO3 – and δ 18 O -NO3 – ) measurements combined with concentrations were used to identify the origins of nitrogen causing this increase. This information was also integrated into the local hydrogeological situation to improve knowledge of the contamination of both confined and unconfined karst aquifers. δ 15 N -NO3 − and δ 18 O -NO3 − in potential nitrate sources over the hydrogeological catchment were analysed in order to identify the range of values that can be measured in both rivers and groundwater. Over the Toulon Springs catchment, rivers are contaminated with nitrate coming from N synthetic fertilizer mineralized in agriculturalsoils. Most of the springs are also contaminated by this nitrate source, but some record an isotope composition of nitrate coming from sewage effluents. Toulon Springs are only contaminated with nitrate from N synthetic fertilizer mineralized in agricultural soils. Finally, from a hydrogeological point of view, the analysis of δ 15 N -NO3 − and δ 18 O -NO3 − values improves knowledge on the functioning of the study area and shows that the upper Jurassic karst confined aquifer has nitrate of the same origins (sources) as the upper Cretaceous unconfined aquifer. The results here highlight that the lower aquifer can be fed by the Upper Cretaceous unconfined aquifer, contrary to previous belief that the lower aquifer was confined. From a more fundamental standpoint, this work provides a set of parameters adapted for karstic hydrogeological catchment. It lays the foundation for the use of isotope biogeochemistry as a powerful tool for understanding the recharge of drinking water catchments and beyond the efficient management of water quality at the scale of karstic hydrogeological catchment.

Karst spring discharge modeling based on deep learning using spatially distributed input data

Abstract. 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.

Temporal and spatial characterization of sediment transport through a karst aquifer by means of time series analysis

The process of sediment transport through a karst aquifer is investigated by means of time series analysis. The correlation and spectral analyses are used for determination of the temporal characteristics of this process, such as timing, synchronization with discharge from spring, and time delay between arrivals of sediment and infiltrated rainwater to spring. The partial correlation analysis is used for the spatial characterization. The study area is the catchment of Jadro Spring in Croatia. The analyzed hourly time series are discharge, water temperature, electrical conductivity, and nephelometric turbidity recorded at the source of this spring, as well as the rainfall collected at three locations in the catchment of spring. They cover the period of four years, from 2017 to 2020. The main aims of this research are (1) presentation of the methods of time series analysis that can be used for the investigation of sediment transport through karst aquifer, (2) analysis of the applicability of partial cross-correlation functions for the spatial characterization of sediment transport process, and (3) extension of the existing knowledge about the sediment in water from karst springs with a special reference to the Jadro Spring. The obtained results show that the partial cross-correlation function can be very useful in the investigation of mass transport through the karst aquifer. They enable identification of the specific contribution of each rain-gauge location to the quantity and quality of spring water. Specifically, the origin of sediment in water from Jadro Spring is determined in this study, as well as the origin of quick-flow and baseflow component in discharge from this spring, including the timing of fresh rainwater arrival, rainwater withdrawal, and emptying of previously accumulated water in vadose and phreatic zone. The sediment transport through the karst aquifer of Jadro Spring is initiated after heavy rainfall in the central and eastern part of the catchment. The origin of sediment in spring water is dominantly the remobilized autochthonous sediment from aquifer, and possible limited contribution of allochthonous sediment from the part of catchment located in hinterland of spring.