Search Results (17)

This study examines speleothems, sediments, rock, and water to assess geochemical and mineralogical processes in deep karst systems. Focusing on Slovačka jama cave (−1320 m deep) and the Velebita cave system (−1026 m deep), we identify elemental and mineralogical anomalies that provide valuable records of element transport, mineral formation, and paleoenvironmental changes. Heavy metal anomalies (Al, B, Co, Mn, Na, Tl, Ba, Be, Cr, Cu, Fe, K, Pb, Rb, Ti, U, Zn) at 300–400 m of depth in Slovačka jama indicate a complex interplay of geological conditions, geomorphological processes, atmospheric deposition, and potential anthropogenic influences. Factor analysis reveals two elemental associations: (1) Fe, Pb, Cu, and Zn, linked to terrigenous aluminosilicates, and (2) Cd, Cr, Mo, and Ni, suggesting airborne or geological sources. Mineralogical analysis confirms the dominance of calcite, with quartz, clay minerals, feldspars, magnetite, and goethite also detected. High magnetic susceptibility values in sediment-rich samples suggest Fe-rich mineral inputs from weathering, biogenic activity, or industrial sources. Ba anomalies in feldspar-rich samples and Sr accumulation at depth indicate distinct geochemical processes. These findings enhance our understanding of deep karst geochemistry, crucial for paleoenvironmental reconstructions and groundwater protection. Full article

The surface and subsurface karst features of the Eocene limestone plateaus along the Middle Nile Valley in Egypt were formerly believed to be epigene in origin and to have developed during post-Eocene pluvial periods. However, the morphology of the caves and their restriction to particular stratigraphic intervals suggests that they are hypogene. The geochemistry and mineralogy of the soft, thick-bedded, brown/black cave infills shows that these sediments originated from hydrothermal processes, as evidenced by their Fe, Mn, Co, Ni, and Cu concentrations. Thus, the karst features are hypogene and probably formed during the opening of the Red Sea Rift at the end of the Oligocene and early Miocene. At this time, there was abundant volcanic activity, as shown by basalt lavas ~70 km northwest of Assiut; this triggered the release of large amounts of CO₂ that made the hydrothermal waters acidic and dissolved the caves. Full article

The Cetina River Basin (CRB) belongs to a Dinaric karst area (Croatia). According to the obtained results on water and sediment quality, the Cetina River reaches the sixth goal of Sustainable Development (source of drinking water). Together with the CRB water quality assessment, it was confirmed that sediments undoubtedly contribute to the purification of watercourses from trace metals as well as organic matter. In 5 years, water samples were collected at 20 sampling sites and sediment samples were collected at 18 sampling sites. The fresh water of the Cetina River belongs to the hydrocarbonate type due to its lithology. The concentrations of the measured elements in the sediments, normalized to Al, are an indicator of possible pressures affecting the ecosystem of the river. According to the Principal Component Analysis (PCA) for elements in sediments, Principal Component 1 (PC1) describes the geogenic origin of the elements, while Principal Component 2 (PC2) describes positive values reflecting anthropogenic pressures (Total Nitrogen, TN; and Total Phosphorus, TP). Depending on element composition, the factor scores related to PC1 and PC2 resulted in four different groups of sites. The first three groups of sediments showed geological impact, while the fourth group was partially anthropogenic in origin. The hierarchical cluster analysis showed four clusters in relation to the content of the elements. Cluster analysis of all elements and the Total Organic Carbon (TOC) in the sediments showed grouping in only two clusters, the first cluster consisting of Ca, and the second of TOC with other elements. Full article

The Yellow River has played an indispensable role in supporting Chinese civilization because it provides water resources and rich soil for agriculture. This study analyzes the major ions and the isotopic ratios of the hydrogen (δD), oxygen (δ¹⁸O), and carbon (¹⁴C) of groundwater samples to identify the sources of recharge and the impact of the Yellow River on the Changqing-Xiaolipu karst aquifer. The major ion/Cl⁻ ratios generally follow the mixing line between the Yellow River and the karst groundwater recharge in the southern mountain areas, indicating the importance of mixing under natural influences in the Yellow River Basin. The dominant hydrochemical type of karst groundwater is Ca·Mg-HCO₃·SO₄, whereas that of Yellow River water is Ca·Na·Mg-SO₄·Cl. Most karst groundwater consists of 10–30% Yellow River water, indicating that the water resources of the Yellow River Basin are generally supplemented by the Yellow River. Therefore, the Yellow River must be considered during the characterization of the chemistry and budget of water resources in the Yellow River Basin. Full article

Knowledge about subsurface geological characteristics and a geothermic genetic model plays an essential role in geothermal exploration and resource assessment. To solve the problem in the Shunping area along eastern Taihang Mountain, geothermal geological conditions were analyzed by geophysical, geochemical, and geological methods, such as magnetotelluric, gas geochemistry, and structural analysis. The geothermic genetic model was developed by analyzing the characteristics of the heat source, water source, migration channel, reservoir, and cap rock of the geothermal geological conditions. Favorable deep thermal conduction conditions and sufficient atmospheric precipitation in the study area provide an original heat source and water supply for geothermal formation. The faults and unconformities of different scales have become effective channels for the migration of underground hot water. The thermal reservoir formed by marine carbonate rocks with karst fissure development provides suitable space for the storage of underground hot water. Although the Cenozoic strata have good thermal insulation and water insulation function, the thermal insulation and water insulation effect is not ideal because of the shallow coverage in the Shunping area and the damage by tectonic action, which affected thermal insulation and water insulation to some extent, restricting the practical preservation of underground heat energy in the Shunping area. The bedrock geothermal resource in the Shunping area is original from the combined action of multiple indexes of source, transport, reservoir, and cap. The geothermal geologic conditions of source and reservoir in the Shunping area are very similar to those in the Xiongan new area, and have obvious advantages in hydrodynamic conditions. Although limited by the cap’s effectiveness, the geothermal resources in the Shunping area can provide some clean energy support for local production and life, thereby satisfying economic development conditions and encouraging further geological exploration. Full article

During the sedimentary period of the Ordovician Yingshan Formation, the carbonate platform of the Gucheng area in the Tarim basin was characterized by a distally steepened ramp. Relative sea-level changes exerted a strong influence on the shoal facie dolomite reservoirs of the 3rd Member of the Ordovician Yingshan Formation (the Ying 3 member), sedimented in the context of a shallow water environment on the carbonate ramp. However, previous studies that lacked high-frequency sea-level changes in the Gucheng area prevent further dolomite reservoir characterization. The current work carries out systematic sampling based on the continuous core from the upper and middle parts of the Ying 3 member in two newly drilled exploration wells (GC17 and GC601) and a series of geochemistry analyses, such as C-O isotope, Sr isotope, and rare earth elements (REE), which helps to investigate the features of the shoal facies dolomite reservoir development against high-frequency sea-level changes. With the help of Fischer plots of these two wells, high-density δ13C data (sample interval is about 0.272 m) were merged to construct a comprehensive curve, contributing to characterizing the high-frequency sea-level changes of the upper and middle parts of the Ying 3 member in the Gucheng area and validating the relationship between the pore-vug vertical distribution and high-frequency sea-level changes. Results revealed that the porosity of dolomite reservoirs increased when the high-frequency sea-level fell and decreased when it rose. Furthermore, the karst surface can be found at the top of the upward-shallowing cycle during the high-frequency sea-level falling; the pore-vug reservoirs are concentrated below the karst exposure surface, and porous spaces are more developed closer to the top of the cycle. The high frequency sea-level curve built in this study can be used as a standard for further research of regional sea-levels in the Gucheng area, and this understanding is highly practical in the prediction of shoal facies carbonate reservoir in carbonate ramp. Full article

The results of a series of continuous characterizations of physical parameters (flow, temperature, water conductivity) and chemical analyses in water springs fed by karst aquifers located in the Piedmont region (northwestern Italy) are presented in this work. Rock masses in carbonate rocks, characterized by very different hydrogeological situations, linked to a different degree of karstification, fracturing, and development of the saturated zone, were examined. A series of data-loggers were installed, operating for several years, and different water sampling missions and subsequent chemical analyses (main ions, metals, and rare earth elements) under different hydrodynamic conditions were carried out. The results show very different trends of chemical–physical water parameters, particularly following significant infiltrative events. Aquifers characterized by a high karstification and reduced saturated zone highlight water mineralization decreases, even within a few hours, as a result of significant flow rate increases (prevalent substitution). Aquifers with a well-developed saturated zone, during an entire flood event, highlight an increase in mineralization linked to the remobilization of water present in the less permeable sectors of the aquifer (piston flow phenomenon). Lastly, aquifers fed by very fractured rocky masses and reduced karstification have a water flow rate with mild annual variations and constant chemical–physical parameters over time (homogenization phenomenon). Full article

The analysis of geochemical markers is a known valid tool to explore the water sources and understand the main factors affecting natural water quality, which are known issues of interest in environmental science. This study reports the application of geochemical markers to characterize and understand the recharge areas of the multi-layer urban aquifer of Como city (northern Italy). This area presents a perfect case study to test geochemical markers: The hydrogeological setting is affected by a layered karst and fractured aquifer in bedrock, a phreatic aquifer hosted in Holocene sediments and connected with a large freshwater body (Lake Como); the aquifers recharge areas and the water geochemistry are unknown; the possible effect of the tectonic setting on water flow was overlooked. In total, 37 water samples were collected including water from two stacked aquifers and surface water to characterize hydrochemical features. Moreover, six sediment samples in the recent palustrine deposits of the Como subsurface were collected from cores and analyzed to understand the main geochemistry and mineralogy of the hosting material. The chemical analyses of water allow to observe a remarkable difference between the shallow and deep aquifers of the study area, highlighting different recharge areas, as well as a different permanence time in the aquifers. The sediment geochemistry, moreover, confirms the differences in trace elements derived from sediment-water interaction in the aquifers. Finally, an anomalous concentration of As in the Como deep aquifer was observed, suggesting the need of more detailed analyses to understand the origin of this element in water. This study confirms the potentials of geochemical markers to characterize main factors affecting natural water quality, as well as a tool for the reconstruction of recharge areas. Full article

Speleothems have proven to be one of the most reliable terrestrial archives for palaeoclimate research. However, due to the complexity of karst systems, long-term monitoring and high-resolution analyses of the cave atmosphere and water geochemistry have become essential to better constrain the factors that control calcite growth and how geochemical palaeoclimate proxies are encoded into speleothems. While calcite precipitation incorporates the palaeoclimate signals into the speleothem fabric, certain conditions in caves can favour dissolution, which may form hiatuses or even destroy these signals. In extreme cases, in-cave dissolution by dripwater can form cup-shaped features (i.e., corrosion cups), which were the main focus of this study. The study site in Postojna Cave, Slovenia was investigated through cave climate monitoring and drip and cup water sampling, which took place during 2017–2021. We found that the cups are fed by low-calcium drips as the consequence of the thin rock overburden above the cave. Due to the specific configuration of the airflow pathways, the study site accumulates high levels of CO₂ (>10,000 ppm), which shifts low-calcium dripwater into undersaturation. This causes dissolution on the rock surfaces and speleothems on the cave floor. The results of this study have broader significance in addressing the suitability of cave environments and speleothems used in paleoclimate research. Full article

The background value of cadmium (Cd) in soil and water sediments in the karst area is 0.31 mg kg⁻¹, with a typical high background of cadmium geochemistry. It is well-known that Cd is classified as a highly toxic metal. Therefore, at the Yelang reservoir in Guizhou province, eco-toxicological tests were carried out using Daphnia pulex. The Geo-Accumulation Index and Potential Ecological Risk Index were used to assess the environmental risk of Cd in sediments. The Cd contents in the sediments of Yelang reservoir ranged from 2.51 to 5.23 mg kg⁻¹, while the LC₅₀ values of the acute toxicity test of Daphnia pulex and Cd at 24, 48, 72, and 96 h were 1.17, 0.50, 0.24, and 0.12 mg L⁻¹, respectively, giving a Safe Concentration threshold of Cd of 1.20 × 10⁻³ mg L⁻¹ in the water body. Based on curve fitting the solid–liquid two-phase distribution model of cadmium in Yelang reservoir was Y = 7.59 × 10⁻⁹ × X^2.58 (R² = 0.9995). The safety threshold sediment Cd concentration was 103 mg kg⁻¹, and was much higher than the Cd content in the sediment of the Yelang reservoir. The Geo-Accumulation Index (I_geo 2.432–3.491) results show that the sediments had reached medium-strong or strong risk levels. The Potential Ecological Risk Index ($E_r^i$ 242.8–505.9) reached a very high or extremely high-risk level. However, due to high concentrations of Ca²⁺ and Mg²⁺, and the pH being in the neutral–alkaline range of water body in karst areas, the Daphnia ecotoxicology evaluation method showed slight ecological risk, quite different from other assessment results, thus this method could be considered to use in such areas. Full article

Hypogene karst is a special manifestation of karst development in spatial scale. Intensive study of its development mechanism has significant meaning for engineering construction, shale gas and geothermal exploitation. To reveal the developing pattern of hypogene karst in Huanjiang syncline, karst groundwater at different depths in wells HD1-2 and HD1-4 and karst springs was selected as the research object. Through the analysis of geochemistry and stable isotopes of karst groundwater, it was revealed that the circulation pattern of deep karst water came from the common recharge of meteoric water and fossil water hosted in karst caves, runoff of deep faulting belts and discharge of large karst springs, over Huanjiang syncline, which provides good hydrodynamic conditions for hypogene karst development. Meanwhile, the widely developed faulting belts and structural fissures provide primitive dissolution space. Through the above analysis, the paper constructs a hypogene karst development pattern controlled by the deep cycle of groundwater in Huanjiang syncline. Full article

Land use conversion could directly or indirectly influence heavy metal geochemistry by changing soil properties. The aim of this study was to explore the effect of land use conversion on surface soil heavy metal contamination in the karst plateau lakeshore wetlands of Southwest China. Based on this, a total of 120 soil samples were collected from 30 sites from different types of land uses (farmlands, grasslands and woodlands) around a lake in Suohuangcang National Wetland Park in August 2017. Contents of As, Cd, Cu, Cr, Hg, Pb and Zn were analyzed, and soil heavy metal contamination was assessed in all three land use types. Results showed that land use transformation from farmland to grassland or woodland was not conducive to the release of soil heavy metal. Surface soil of all three land use types have been moderately polluted by As, Cr, Pb, and Zn, and grassland and woodland also had moderate Cd contamination. The pollution load index (PLI) results revealed low heavy metal contamination in grassland and woodland but no contamination in farmland. Although the integrated contamination in the studied region did not pose a serious potential ecological risk (RI < 150), it might affect human health through the water supply and food chain. Therefore, it is necessary to monitor and control As, Cd, Cr, Pb, and Zn concentrations of surface soil through controlling pollutants, improving waste treatment, as well as strengthening supervision and management in the vicinity of the Suohuangcang National Wetland Park. Full article

The present paper deals with a field experiments on evaporite rock samples and groundwater investigations in the Quinis test site, a hamlet of the Enemonzo municipality in NE Italy, were sinkholes occurred in the past and are still occurring causing severe damage to the existing infrastructures. The area is characterised by a Carnian evaporitic bedrock made of gypsum and anhydrite mantled by alluvial and colluvial deposits. In order to evaluate the loss of weight and volume of the subcropping evaporites as responsible for sinkholes, a field-experiment was carried out. Inside seven piezometers, at different depths, evaporitic rock samples were exposed to the naturally occurring variable climatic conditions such as degree of humidity, different air flow and hydrodynamic. The rock samples were installed at the beginning of April 2017 in the dry sections of piezometric tubes, in the vadose zone and in the phreatic zone. Data related to water level fluctuations were recorded by using data-logger devices and highlight significant changes in the water table. After 13 months of data recording (May 2018), rock samples were removed, reweighted and the volume loss measured. In addition, water from piezometer-experiment, representative of the groundwater circulation, were collected at different depths. The obtained results indicate that rock sample reduction is dependent on the hydrological regime and water chemistry and not on the number of days during which the samples remained submersed. In particular, the water geochemistry highlights the possible role in gypsum/anhydrite dissolution due to NaCl water admixing in a complex scenario. In additional, the geochemical data highlight the occurrence of some potentially toxic elements (As, Fe, Mn) at concentrations of concern in some water. This approach represents a novel contribution in the study of karst hazard in evaporites adding a tile to the knowledge of the fast evolutionary processes which cause sinkhole formation. Full article

The origin of the mineralization at the world-class Las Cuevas (the largest single fluorite deposit in the world) has been historically disputed, essentially between skarn-related and Mississippi Valley Type (MVT) models. A systematic study of fluid inclusions in these deposits revealed that they were formed by low temperature (49 to 177 °C) and low salinity (0 to 1.9 wt % NaCl equiv) fluids. The obtained δ¹³C (between −2.39 and 0.20‰ VPDB) and δ¹⁸O (between −14.03 and −7.37‰ VPDB) data from local host limestones agreed with regionally representative values in the literature. The obtained δ¹³C (between −15.60 and −12.99‰ VPDB) and δ¹⁸O (between −5.56 and −1.84‰ VPDB) data from hydrothermal calcite associated with fluorite mineralization indicated that the isotopic composition of hydrothermal fluids initially reflected buffering by the host rocks, and then recorded the interaction between meteoric water and basinal brines. It is likely that such processes occurred with concurrent maturation of organic matter, and that the obtained compositions may also have recorded a thermal effect on the local limestones. Halogen geochemical studies in inclusion fluids showed a distribution that suggests that solutes in mineralizing fluids were due to scavenging of Na⁺ and Cl⁻ through water–rock interaction or halite dissolution, and that secondary sources would have been the evaporation or infiltration of seawater. The basinal brines with which the formation of these deposits was associated were massively diluted by deeply evolved meteoric water, thus making a significant fluorine input by basinal brines unlikely. Fluorine would have been provided by local groundwater through its interaction with Oligocene topaz rhyolites and other F-rich volcanic and hypabyssal rocks. Such a possibility is supported by present-day groundwater, which presents a regional endemic case of fluorosis. The precipitation of fluorite is possible at low temperatures (at which the solubility of this mineral is very low) by means of chemical reactions and physical interactions among very diluted F-poor basinal brines, F-rich groundwater, and host carbonate rocks. The latter systematically experienced hydrothermal karstification, which would have provided Ca²⁺ for reaction with F⁻ and resulted in the precipitation of fluorite. This scenario stands for a depositional model that recalls those proposed for MVT and associated industrial mineral deposits, but is distinct from common models with regard to the primal source for fluorine and the extremely low salinities of inclusion fluids. Full article

The geochemical equilibrium in seawater must be observed taking into account the chemical and geological, as well as biological, processes. The concept of equilibrium takes into account the composition of the system and the kinetics of the reactions taking place therein. In coastal waters, nutrients and trace elements can be delivered not only through rivers but also through atmospheric input and submarine groundwater discharges. In addition to natural sources, levels of different elements can also be influenced by growing and diverse human activities along coasts. Consequently, the pathways and fate of different environmental chemicals in coastal areas are governed by various factors. The multiparameter approach, combined with different statistical tools, is a well-established way of interpreting their inputs and behaviour in marine systems. Nevertheless, the data for the karst regions, as found in the Mediterranean, are particularly scarce. This Special Issue—Geochemical Equilibrium and Processes in Seawater—of Geosciences gathers five articles on different topics related to water and sediment geochemistry of the coastal karst areas of the Mediterranean, including Slovenia, Croatia and Egypt. The topics included in this Issue refer to (1) geochemistry of sediments in the area of intensive anthropogenic activity; (2) the geochemistry of sediment and biota in a protected area under increasing pressure due to tourist activity; (3) the influence of a thermal power plant on the geochemistry of the surrounding area; (4) the influence of underground water discharges on water quality; and (5) the possibility of monitoring natural and anthropogenic processes in karst systems by using a specific group of elements. Full article