Underground River Research Articles

Application of Very Low Frequency (VLF) Method for Underground River Estimation in Donorojo Sub-District, Pacitan

<p class="Keywords"><span lang="EN-US">Pacitan is included in the Gunung Sewu karst area in the Southern Mountain Zone, and carbonate rocks dominate the constituent rocks. Karst has a unique drainage system because it is dominated by subsurface flow. This research was conducted in Cemeng and Klepu villages, Donorojo sub-district, Pacitan, with 4 track data. Data were collected using the very low frequency electromagnetic (VLF-EM) method with a track length ranging from 200-450 m, a measurement spacing of 5 m, and a transmitter frequency of 19.8 kHz. Data processing uses filtering and inversion, resulting in a cross-section of resistivity values. Based on the subsurface resistivity cross-section profile, the cavity in the carbonate rock layer with a resistivity value of 0-500 Ωm is identified as an underground river. The underground river is found on tracks 1, 2, 3, and 4 near the surface, with a depth of about 30 m below the surface.</span></p>

Implementasi Geointerpretasi berbasis Kearifan Lokal di Destinasi Wisata Minat Khusus Gua Cerme, Bantul, Yogyakarta

One of the Gunung Sewu Geopark's three main pillars, geointerpretation of landscape duality, is implemented by special interest tour guides who possess the knowledge and abilities necessary for the job site and who must be proficient in cave exploration methods and cave science. With the primary tourist attraction being a cave with a tunnel length of 1200 meters and an underground river, this study was conducted at the Cerme Cave Tourist Destination, specifically in Srunggo Village, Imogiri District, Bantul Regency, to observe how the Pokdarwis Cerme tour guide implements interpretation in tourism spaces. The research was conducted utilizing a logical approach and qualitative approaches. Data gathering methods included cave and surface area mapping, cave photography, participant observation, and semi-structured interviews. The research findings show that there are two tourism spatial zonings that are related to the content of geointerpretation, and the second finding is interpretation activities of geological objects that are mixed with local wisdom through the story of the spread of Islam by the Wali Songo in Cerme, which is believed to have occurred in the past by the local community. This tale has been passed down through generations and is part of the material given to guests by Cerme Cave tour guides. These beliefs impact the destination's toponymy, ornaments and places within the cave, as well as geointerpretation activities carried out in the Cerme Cave Tourist Destination's dual landscape.

Palawan Peacock Pheasant (Polyplectron Napoleonis) Species Distribution Modeling: A Review of the Impact of Typhoon Rai/Odette on the Diversity and Distribution of an Endemic Bird Species

This study quantified the habitat requirements and, consequently, described the remaining suitable habitats through species distribution modeling of Polyplectron napoleonis within Cleopatra’s Needle Forest Reserve and Puerto Princesa Subterranean River National Park after the onslaught of Typhoon Odette in the Palawan region. This was accomplished using MaxEnt software, a statistical machine-learning algorithm that creates niche models with presence-only (PO) data and surrounding environmental variables (Dudik et al., 2007; Merow et al., 2013). Previous studies have identified precipitation, elevation, and land cover as the top environmental variables influencing tandikan habitat suitability, as revealed by their percent contributions. There were earlier claims of the noticeable movement of habitat-suitable areas to the fringes and beyond Cleopatra's Needle Forest Reserve. The migration seems to be going towards highland forests. Two factors could be behind this migration: the tandikan are responding to climate change or avoiding human disturbance. As this species is known to have a high tolerance for temperature change, the latter could be the more plausible factor. For 2022, post-Odette, MaxEnt analysis revealed a shift of percent contributions with elevation and land cover classification outranking aspect and slope. Environmental layers were limited to four, as these were the only currently available data. This shift in percent contributions could be linked to the direct damage to forests brought by the Typhoon in December of 2021. The land cover map generated for this year has shown large areas of forests that were converted into non-forests. Conservation efforts, therefore, for the tandikan, a forest species, should be recalibrated in response to this current development. Further, measures to mitigate the impact of solid typhoons on forests should be reviewed and evaluated.

Epikarst Controls of Runoff Composition in Subterranean Stream After Rainstorm Events

ABSTRACTEpikarst plays a critical role in karst water circulation, however, its studies have often been limited to small springs or basins, ignoring its importance in larger, highly karstified subterranean streams. This study focused on the Longlingong (LLG) subterranean stream system, where the discharge and electrical conductivity (EC) of the subterranean stream outlet for 2.5 years, and found that 85% of all rainstorm events monitored during this period showed a pattern of increasing and then decreasing EC. High‐resolution hydrochemistry monitoring was conducted at the outlet during a rainstorm event when this response pattern occurred. Simultaneously, epikarst water (EW), saturated zone fissure karst water (FW), and surface water (PW) from this system were collected as three recharge sources for hydrochemical analyses based on the results of the field investigations, and end‐member mixing analyses were performed using the EMMA‐MIX model. These combined methods can accurately characterise the response of the subterranean stream system to rainstorm events, assess the contribution and response of individual recharge sources throughout the rainstorm, and reveal the mechanisms involved. The results indicate that the increase in EC is primarily driven by changes in HCO3− concentration resulting from the rapid discharge of EW through sinkholes and shafts. EW contributes 28.7% of the rain‐induced subterranean stream runoff, exceeding FW. The epikarst exhibits a rapid response to rainstorms, as evidenced by a remarkable 681% increase in EW discharge following a rainstorm event. Flood peaks in the subterranean stream are mainly composed of PW (44%) and EW (43.6%). This study highlights the key role of the epikarst as a karst groundwater reservoir. The sensitivity of the epikarst to rainstorms, particularly its role in facilitating rapid piston‐like migration of EW during initial runoff, highlights its significant influence on discharge and hydrochemistry. This research contributes to a deeper understanding of the function of epikarst within highly karstified subterranean streams.

Turning Sour into Sweet, Darkness into Light

Abstract 9½ Mystics: The Kabbala Today by Rabbi Herbert Weiner introduced the idea of mystical search to a generation of American Jews who were turned off by traditional synagogue Judaism and unsure of how to relate to the emerging counterculture. He met with a number of mystics to find out if their life-secrets can have meaning even for those who do not share the full intensity of their experience. Weiner's search relied in large part on Gershom Scholem's idea that there was a dramatic contrast between rabbinic Judaism and Kabbalistic Judaism. Kabbalah was like an underground stream moving through the heart of Judaism, bringing with it transformative mythic ideas, providing inspiration and spiritual excitement. Weiner's book successfully popularised Scholem's theories of what Kabbalah was, as well as the mystical thought of previously unknown mystics such as Rav Kook. 9½ Mystics transformed the American Jewish religious landscape, especially in the Reform movement.

Distribution of Carbon-Sequestering Microbes in Different Habitats and the Interaction with Habitat Factors in a Natural Karst Cave

The distributional characteristics of microorganisms in karst cave ecosystems have been widely studied. However, in such a dark, humid, and oligotrophic habitat, studies on the differences in carbon-sequestering bacteria in multiple habitats are limited. Therefore, to learn the distribution characteristics of carbon-sequestering colonies in cave habitats and their correlation with habitat factors (e.g., pH, Ca2+, Mg2+, etc.), samples from five cave habitats (weathered rock walls, underground river water, drips, sediments, and air) were collected from the twilight and dark zones of Shiziyan Cave (CO2 concentration 5385 ppm). The results of high-throughput sequencing and statistical analyses showed that there were significant differences in the distribution of communities in different habitats, with higher abundance in sediments habitat and underground river water habitat, and the dominant phyla of Pseudomonadota (30.53%) and Cyanobacteria (75.11%) in these two habitats. The microbial diversity of the carbon-sequestering microbial community was higher in sediments than in underground river water. The pH, and Ca2+, SO42−, and NO3− concentrations can alter the diversity of carbon-sequestering microbes, thereby affecting carbon cycling in caves. Carbon metabolism analyses suggest that microbes in the habitat can cooperate and coexist by participating in different carbon metabolic pathways. These results expanded our understanding of carbon-sequestering microbial communities in cave systems and their responses to the environment.

A phylogeographic approach to Sulawesi’s Maros karst shrimp fauna (Decapoda, Atyidae) reveals several cave invasions and challenges current taxonomic hypotheses

Abstract The unique endemic cave fauna of the Maros karst cave system (Sulawesi, Indonesia) includes atyid freshwater shrimps only known from their species descriptions. An extensive survey revealed a total of ten species in epigean and subterranean rivers: Two non-endemic, four species endemic to Sulawesi (genus Caridina) and four stygobiont species (genus Caridina, Marosina, and Parisia) only endemic to the Maros karst. A molecular phylogeny revealed (1) two independent colonizations of Sulawesi’s Maros karst caves by species of Caridina (Clade 1) derived from endemic ancestors, and (2) an exclusively stygobiont group (Clade 2, Marosina, Parisia) possibly derived from an amphidromous, anchialine cave-dweller. Our approach revealed another cryptic cave species of Caridina and challenges the taxonomic status of four Sulawesi endemics. In conclusion, the freshwater shrimps of the Maros karst are a challenging but rewarding group that can contribute to our understanding of the evolution of cave-dwelling species and atyid phylogenetics.

Assessing the Effectiveness of CCME-WQI, NSF-WQI, OWQI, and Smith Index Water Quality Indices in Karst Areas

Water quality assessment employs various methods, including water quality indices (WQI). This study compares several WQI methods to evaluate Sumurup River and Seropan Underground River in Gunungkidul Regency. The study aims to analyze the effectiveness of CCME-WQI, NSF-WQI, OWQI, and Smith Index methods. Parameter selection was conducted using Principal Component Analysis, and the NSF-WQI method was found to best represent water quality in the study area. OWQI produced consistently poor results due to an overly idealized formula, while CCME-WQI's sensitivity to parameter number reduced its effectiveness. The Smith Index, based on New Zealand standards, yielded the lowest quality results, regardless of parameter modifications. Thus, NSF-WQI is recommended for assessing water quality in karst areas like Sumurup and Seropan Underground Rivers. This research underscores the importance of selecting appropriate WQI methods tailored to specific environmental conditions to support effective water resource management and conservation efforts.

Optimization of the Weir as a Micro Hydro Power Plant in Bayang Nyalo Padang, West Sumatra

The objective of this research is to guarantee that the building of PLTMH Bayang Nyalo achieves maximum energy output and utilizes possible renewable energy sources in a sustainable and efficient manner. This research is a study that aims to describe and analyze data using a quantitative technique. The quantitative research technique is used when study data is in numerical form. Quantitative descriptive research is a method used to examine obtained data by providing a detailed and accurate description of the data. This study aims to determine the optimal value for designing small-scale hydropower plants (PLTMH). In order to do research for this thesis, the author investigates the number of studies performed in the Bead Dam Nyalo Kec. Nagari Bayang North, South Coast Regency West Sumatra. The PLTMH project aims to harness the water flow from the subterranean river, which has a discharge rate of 14.67 liters per second. The power plant is designed to have a power capacity of 623.32 kW, using a high discharge waterfall with an effective height of 5 m. Based on the examination of technological elements, we have reached conclusions: The civil component of this PLTMH includes a gravity concrete dam that is prepared for operation, while the electrical components consist of a Cross flow Turbine. The development of mechanical transmission is ongoing.

ОЦЕНКА ВЗАИМОСВЯЗИ ПОВЕРХНОСТНЫХ И ПОДЗЕМНЫХ ВОД РЕКИ СЫРДАРИЯ (В ПРЕДЕЛАХ КАЗАХСТАНА)

This study analyzes and evaluates the relationship of surface and groundwater of the Syrdarya River within Kazakhstan. The share of groundwater recharge of the river was calculated by two methods: by genetically partitioning the total runoff hydrograph and by calculating low f low. The difference of groundwater flow into the river between the selected hydrostations is also calculated. A comparison of the obtained results for the quasi-natural and disturbed periods is made. In natural conditions, the infiltration of river runoff into underground horizons prevailed along the length of the Syrdarya River, however, under the influence of anthropogenic activity, the picture changed to the opposite: the discharge of groundwater prevails along the length of the Syrdarya River, including the emergence of filtration waters below the dam of the Shardara HPP, collector-drainage and discharge waters from irrigation f ields of the adjacent territory. Also, apparently, the truncation of spring flood peaks leads to an increase in the groundwater level and an increase in the share of underground river supply. Recommendations for the application of the methods used in the work are given.

Exploring the microbial community and biotechnological potential of the sponge Xestospongia sp. from an anchialine cave in the Yucatán Peninsula

Sponge-associated microorganisms are key influencers of nutrient biogeochemistry and important sources of bioactive natural products. This study provides the first insights into the taxonomic diversity of the microbial community associated with the sponge Xestospongia sp. from an anchialine cave in the coastal area of the underground river of the Yucatán Peninsula in Xcalak, Quintana Roo, Mexico, and the potential antimicrobial activity of its cultivable bacteria. High abundances of Sulfurospirillum and Desulfovibrio were detected with 16S rRNA amplicons, suggesting that the microbial community of Xestospongia sp. plays an important role in the geochemical sulfur cycle. Analysis with crude extracts of Nocardiopsis dasonvillei NCA-454 revealed antimicrobial activity against methicillin-sensitive Staphylococcus aureus ATCC 25913 (MSSA) and methicillin-​resistant ​S. aureus ATCC 43300 (MRSA). Studies of the microbiomes of sponges from the anchialine cave system in the Yucatán Peninsula can help elucidate the biogeochemical cycles of these poorly studied environments. Moreover, the microorganisms of these microbial communities represent an untapped source of secondary metabolites with biotechnological potential.

Hydrogeological analysis and remediation strategies for water inrush hazards in highway karst tunnels

Geological hazards, particularly water inrush, pose frequent challenges in tunnel constructions within karst regions. Drawing from the engineering experiences in addressing multiple large-scale water inrush hazards in the Dejiang tunnel, a combined method of field investigation and theoretical analysis was employed for qualitative and quantitative analyses of water inrush mechanisms. The regional geological investigation highlighted the formation of strong and weak aquifers due to alternating weak limestone and mudstone in the synclinal strata, creating favorable conditions for large-scale karst conduit. Atmospheric precipitation water connects karst cavities through groundwater-eroded karst conduit, establishing a recharge system for water inrush hazards. Three empirical formulas are adopted to investigate the influence of rainfall on the tunnel’s actual water inflow. Importantly, it was found that considering only the influence of rainfall or surface water cannot reasonably predict the inflow in this area. The disaster’s primary causes are attributed to the heavy rainfall, karst conduit, underground river, and weak strata, which have contributed to the persistent nature of water inrush events. The principle of “drainage and blockage” was used to address the issue of water inrush. Proposed remediation strategies during construction, including the innovative membrane bag high-pressure grouting, have proved to be effective in addressing the connected karst conduits. The drainage and blockage effects were achieved by installing drainage pipes during the grouting reinforcement process. Finally, the water pressure-resistant structure was employed to enhance the stiffness of the lining. As validated by monitoring data, the measures serve as crucial methods to guarantee the safety of tunnel structures, effectively prevent water inrush and amplify the ecological benefits of water-rich areas.

Heavy Metal Risk Assessment from Agriculture in Shallow Tropical Karst Lake, Gunungsewu Karst Area, Java Island, Indonesia

This research investigates the heavy metal pollution in karst lakes, crucial for fisheries, agriculture, and domestic activities. Target metals include Pb, Cd, Cr, Fe, Zn, and Cu. Objectives comprise assessing pollution levels via the Heavy Metal Pollution Index (HPI) and conducting an ecological risk assessment, incorporating the Enrichment Factor, Geoaccumulation Index, and Ecological Risk Index. The Pearson’s correlation and cluster analysis were performed to analyze the connection between samples. Results reveal strong correlations between metals in soil and sediment, such as Pb in soil correlating with Cu in sediment (r = 0.88), Zn in soil with Cu in sediment (r = 0.75), and Zn in soil with Pb in sediment (r = 0.81). Kedokan Lake emerges as the most representative observation (distance 13.1), while Kepleng Lake is the least representative (distance 535). Cluster analysis identifies two distinct clusters: Cluster 1 encompasses Ngrejek Lake, Kedokan Lake, Sodong Lake, Kanigoro Lake, and Ngampelombo Lake. HPI calculations reveal varying contamination levels in lake water and underground river samples within the Bribin Underground River Catchment Area. Notably, one location in Kedokan Lake is categorized as contaminated (HPI value of 188.05). Mean Enrichment Factor values range from no enrichment factor (<1) to low enrichment factor (1–3). Geoaccumulation Index (Igeo) indicates an overall unpolluted classification (Igeo<0) across all sampling sites. These findings underscore the nuanced pollution status in the studied area, emphasizing the importance of continued monitoring and intervention to ensure the sustainability of karst lakes in the face of heavy metal contamination.

Characteristics of an Inorganic Carbon Sink Influenced by Agricultural Activities in the Karst Peak Cluster Depression of Southern China (Guancun)

Land use in karst areas affects soil properties, impacting carbon sinks. Accurate estimation of carbon sink flux in karst areas through zoning and classification is crucial for understanding global carbon cycling and climate change. The peak cluster depression is the largest continuous karst landform region in southern China, with the depressions primarily covered by farmland and influenced by agricultural activities. This study focused on the Guancun Underground River Basin, a typical peak cluster depression basin, where sampling and analysis were conducted during the agricultural period of 2021–2022. Using hydrochemical analysis and isotopic methods, the results indicated that: (1) The primary hydrochemical type in the Guancun Underground River Basin is HCO3-Ca, with hydrochemical composition mainly controlled by carbonate rock weathering. (2) The primary sources of Cl−, SO42−, and NO3− are agricultural activities, with agriculture contributing 0.68 mmol/L to dissolved inorganic carbon (DIC), accounting for about 13.86%, as confirmed by ion concentration analysis and isotope verification. (3) The size of the depression area is proportional to the contribution of agricultural activities to DIC, while also being influenced by dilution effects. A comparison was made regarding the contribution of other land use types to DIC. The impact of land use on DIC in karst processes should not be overlooked, and zoning and classification assessments of carbon sink flux under different influencing factors contribute to carbon peaking and carbon neutrality goals.

Hydrological and Climatological Aspect Evaluation for Salt Farm Development in the Coastal Area of Gunungkidul Regency, Yogyakarta, Indonesia

Salt has major importance as a basic necessity in households, feedstock for various kinds of industry, and a means of fortification to prevent diseases attributed to iodine deficiency. However, the amount of salt produced in Indonesia has yet to meet the national demand, hence warranting the necessity of salt yield improvement. This research set out to evaluate the hydrological and climatological states of the coastal area of Gunungkidul Regency for potential salt farms. The hydrological analysis identified underground rivers, springs, and surface rivers emptying into the study area, whereas the hydrochemical analysis observed major elements of seawater and salinity and determined the effects of hydrological characteristics on seawater. The climatological evaluation involved analyzing rain, temperature, humidity, and daily wind data from 1979–2013. All of these details were matched against the suitability parameters for salt farms. The results showed that the hydrological and geological conditions were closely related and that the underground rivers, springs, and surface rivers decreased salinity and sodium and chloride contents of seawater. Based on salinity levels, several beaches were highly suitable (S1) for salt farms, but climatologically, the study area was slightly suitable (S3) and suitable (S2) for this purpose.

LITHOLOGICAL-STRATIGRAPHIC CRITERIA OF KARST ZONING OF THE MIOCENE SULFATE LAYER OF WESTERN UKRAINE

The proposed karst regionalization (zoning) is a novel approach to identifying the unique characteristics of karst processes in specific areas. The sulphate karst of western Ukraine, linked to the Miocene evaporite basin at the junction of the East European Platform and the Pre-Carpathian Foredeep, is a prime example. The previous karst zoning schemes of the East European Plain classified the entire area of sulphate rocks distribution in the west of Ukraine as the Podilsko-Bukovinsky karst Area, with the West Podilsky and Pokutsko-Bukovinsky karst Regions within it. However, with the emergence of numerous detailed stratigraphy works on the evaporite formation of this territory, a new approach to karst zoning in evaporites is necessary. This paper presents a systematic approach to upgrading the mentioned regions to the rank of sub-areas and distinguishing the regions within them based on lithologic-stratigraphic differences. The authors studied six localities as examples. In the first one, the gypsum layer is characterized by the stromatolite, grass-like and sabre-like facies. The last two contain thin carbonate-clay layers, leading to the collapse of large rock blocks inside the Kadubivska Cave. On the second site, the gypsum is composed of stromatolite, coarse-crystalline, and sabre-shaped facies. Only one small Tovtry Cave, which has a hypogene morphology, is known here. The third site has grass-like gypsum facies, and intensive modern karst occurs, with numerous sinkholes, underground rivers, and sinkholes. The influence of facies variability on the development of the mesomorphology of underground galleries is traced here in Pionerka Cave. The fourth area is built of nodular gypsum facies. There are no insoluble layers here, but the facies have many thin mineral films between the grains. Therefore, the entrance parts of the caves are unstable for physical weathering. The fifth section is highlighted as a section of the spread of metasomatic limestone, which replaces sulphate deposits here. They contain a significant cave labyrinth, but whether karstification occurred before or after metasomatization remains unclear. The sixth section is completely composed of stromatolite gypsum facies. It is characterized by stability to collapse due to the monolithic structure of gypsum, which is noticeable in the example of the Cave of Popeliushka (Zolushka) on the border of Ukraine and Moldova. The selected areas are proposed to be considered as examples of karst zoning based on lithologic and stratigraphic features. Key words: karst regionalization; gypsum, limestone; caves, breakdown; relief, landscape.

Estimating tourism losses due to COVID-19 Pandemic: The case of Puerto Princesa underground river, Philippines

This study estimated the economic losses of Puerto Princesa Underground River (PPUR) caused by the COVID-19 pandemic. The PPUR in Puerto Princesa City, Palawan, Philippines is part of the Puerto Princesa Subterranean River National Park (PPSRNP) and is recognized as a UNESCO World Heritage Site. The lost tourist arrivals caused declining PPUR revenues, affected the local economy, and posed a potential threat to PPSRNP’s environment. The Seasonal Autoregressive Integrated Moving Average (SARIMA) was used to estimate the revenue and tourist arrivals while the Simple Exponential Smoothing (SES) was used to estimate PPUR expenses. The results revealed that the PPUR lost Php 172,997,905.00 which was attributed to the foregone 281,441 international tourists and 335,687 domestic tourists from 2020-2021. The PPUR management could expect Php 2,230.56 as revenue per potential tourists, an increase in revenue of roughly Php 96.7 million, an increase in international tourist arrivals, and a decrease in domestic tourist arrivals from 2022-2024 had there been no pandemic. Thus, PPUR management should forge active collaboration with different stakeholders for sustainable operation in times of economic disaster.

Subterranean river captures in siliciclastic rocks in a semiarid climate: the case of the Poti River Canyon, Brazilian Northeast

This research investigates a possible subterranean river capture responsible for the morphogenesis of the Poti RiverCanyon, which crosses the uplifted edge of the Parnaíba Basin, in the northern Northeast of Brazil. Morphological andlithostructural evidence of river captures was analysed using remote sensing products (e.g., drainage network, topography,paleotopography, structural framework) and field expeditions. The results indicated a sudden inflexion of the upper courseof the Poti River, low and anomalous divides in the local geomorphological context, canyon with valley segments exhibitingasynchronous morphologies, and block collapse controlled by dissolution along fracture networks. Given this set of data, wepropose an evolutionary model of subterranean river capture for the formation of the Poti River canyon, which, throughpaleotopographic modelling, was linked to the Pleistocene epoch. This drainage rearrangement would have been influencedby a Neogene-Quaternary morphogenetic framework of structural reactivations, regional uplift, and climatic oscillations. Onthis basis, it was concluded that epigenetic processes were significant for a drainage rearrangement of approximately 10,540km² of areas in a semiarid region with sandstone substrate.

Estimation of Groundwater River Availability in Leang Lonrong Cave Using ARIMA Model and Econophysics Valuation Approach

This quantitative descriptive study uses the ARIMA model approach to predict groundwater river water availability. It assesses its valuation with an econophysics orientation in the Leang Lonrong Cave area of TN Bantimurung Bulusaraung. Secondary data from 2010-2023, including Water Discharge and Water Level data from the River Basin Center of Pompengan Jeneberang (BBWS) and primary data on the Valuation of Willingness to Pay, were utilized. The analysis reveals that water discharge predictions (2024-2030) in the Gua Leang Lonrong area indicate consistent annual water availability, with the highest discharge projected in December 2030 (5.08 m3/s) and the lowest in September 2024 (1.12 m3/s). Valuation of utilizing Leang Lonrong River water through willingness to pay showed residents willing to pay Rp 42,142.85/month for clean water management. At the same time, visitors are willing to contribute Rp 21,596.77/visit to enhance water quality management. Elasticity analysis modeling water discharge with willingness to pay suggests a relatively elastic relationship, with a minor impact, indicating unresponsiveness to changes in water discharge percentages. Statistical and economic methods were employed to analyze daily water discharge patterns and evaluate residents' willingness to pay for underground river water utilization. The ARIMA model (0,1,1) forecasted future water discharge patterns with a mean absolute percentage error (MAPE) of 33.7%. The study surveyed 62 respondents, finding an average willingness to pay approximately IDR 21,596.77 per visit to maintain Leang Lonrong River water quality management.

Hydrochemical fingerprints of karst underground river systems impacted by urbanization in Guiyang, Southwest China

Karst groundwater plays an irreplaceable role in the formation and development of urban areas, and land-use and land-cover change (LUCC) and the input of pollutants during the urbanization process would pose potential environmental risks to underground rivers. We analysed the relationship between urbanization processes and underground river hydrochemistry over nearly 35 years in Guiyang city, southwest of China, it was found that concentrations of various cations and anions, as well as total dissolved solids (TDS), gradually increased with the urbanization process, with significant fluctuations during the rapid urbanization periods. The Hydrochemical Facies Evolution Diagram (HFED) clearly showed the influence of urbanization on the hydrochemistry of the underground rivers. The ion ratios of γMg2+/γCa2+—γHCO3−, γNa+/γCl−, Ca2+/Mg2+—Ca2+ or Mg2+/Σ cations, HCO3−/SO42−—HCO3− or SO42−/Σ anions revealed two distinct phases in the hydrochemical evolution of the underground river system, highly consistent with the urbanization process. Before the rapid urbanization, acid deposition and agricultural activities affected the hydrochemistry, with HCO3-Ca·Mg and HCO3·SO4-Ca·Mg as the dominant types controlled by limestone and dolomite dissolution in water-rock interactions. As acid deposition diminished, the input of SO42− from urban sewage compensated for the reduced impact, but the increased impermeable surfaces reduced the infiltration of atmospheric precipitation, leading to a reduced dissolution of dolomite minerals in water-rock interactions, resulting in a decrease in Mg2+ and a change in the hydrochemical type. The hydrochemical type evolved from a single HCO3·SO4-Ca·Mg type and HCO3-Ca·Mg type to multiple types, such as HCO3·Cl-Ca, HCO3·SO4-Ca, HCO3-Ca, and HCO3·SO4-Ca·Mg, and was highly unstable. With changes in land use, the proportions of various cations and anions in the hydrochemistry changed, especially NH4+, NO3−, SO42−, Na+, and Cl−, which were more sensitive to human activities. This study indicated the impact of urbanization on the hydrochemistry of the underground river system, with the input of SO42− from human activities and the increase in paved surfaces due to urbanization collectively altering the hydrochemical types of the underground river system. The rapid response of karst underground river system hydrochemistry indicates a potential impact on groundwater system by urbanization that should not be ignored.