Search Results (18)

This study isolated five acid-producing strains (XQ₁ and YZ₁–YZ₄) from naturally fermented pomace of Rosa roxburghii Tratt (RRT) in Guizhou’s karst region. Genetic and phenotypic analyses identified XQ₁, YZ₂, and YZ₄ as Lactobacillus plantarum (L. plantarum), YZ₃ as Weissella cibaria, and YZ₁ as Bacillus licheniformis. A comparative evaluation with commercial strain AC revealed that XQ₁, YZ₂, and YZ₄ exhibited superior acidification (reaching the stationary phase at 40 h) and tolerance to acidic conditions (pH 3.0), ethanol (6% v/v), bile salts (0.3%), and osmotic stress (6.5% NaCl), along with broad-spectrum antimicrobial activity against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Shigella dysenteriae, and Pseudomonas aeruginosa. Their cell-free supernatants (CFSs) showed comparable superoxide dismutase activity and total antioxidant capacity (2.54–2.66 FeSO₄·7H₂O eq mmol/L) to AC (2.68), with DPPH radical scavenging exceeding 50%. YZ₃ displayed weaker acid production, tolerance, and limited antimicrobial effects. Safety assessments confirmed non-hemolytic activity and antibiotic susceptibility. In conclusion, the L. plantarum strains XQ₁, YZ₂, and YZ₄ demonstrated strong ensiling potential and remarkable probiotic properties, establishing them as promising indigenous microbial resources for the preservation of RRT pomace and other food products. Full article

Corrosion of traditional cement mortar is a critical issue in karst areas. Composite salt, i.e., sulfate–chloride salt, represents a typical corrosion agent due to the abundance of Cl⁻ and SO₄²⁻ ions in such geological environments. In this study, we used nano-metakaolin to enhance the physical and mechanical properties of cement mortar in the early aging stages, simulating groundwater corrosion by a compound salt solution in the karst region. The appearance and the change in the flexural/compressive strength of cement mortar upon the nano-metakaolin addition in the early aging stages under dry and wet cycling conditions were analyzed and combined with the results of scanning electron microscopy, thermogravimetric analysis, and other methods, revealing the underpinning mechanism behind the function changes of nano-metakaolin-modified cement mortar. The results show that nano-metakaolin effectively promotes cement hydration in the early aging stages. The flexural/compressive strength after 7 days of aging with 1% of added nano-metakaolin increased by 10.38% and 4.41%, respectively, compared to ordinary cement mortar. Furthermore, adding 1–5% of nano-metakaolin under dry and wet cycling and the coupling effect of chloride and sulfate erosion effectively reduce the damage of harmful ions on the cement mortar, leading to evident corrosion inhibition. The generation of hydration products increased after adding the Ghanaian metakaolin, filling the microcracks and micropores, and increasing the overall microstructural compactness. Full article

Nitrogen injection technology has become an important production technology after water injection development in the karst fracture-vuggy reservoir in Tahe Oilfield. However, due to the influence of reservoir heterogeneity and the high mobility of gas fluid, nitrogen easily forms a dominant channel and gas channeling occurs, and the recovery effect time is short. Based on this, a visual surface karst model is designed and created to study nitrogen foam-assisted gas drive. The results show that after gas channeling occurs in the dominant channel of nitrogen flooding, foam injection-assisted gas flooding can improve oil recovery. In the longitudinal direction, foam-assisted gas drive mainly displaces the remaining oil because of gravity differentiation and the reduction of oil–water interfacial tension. In the horizontal direction, foam-assisted gas drive is mainly used to block the large pore cracks and dominant channels, promote the gas to turn into large tortuous and small cracks, and expand the swept efficiency of the gas. After forming the dominant channel, injecting 0.3 pv salt-sensitive foam with a gas–liquid ratio of 2:1 in the middle of the gas channel can improve the recovery rate of the model from 4% to about 25%, and the recovery rate can be increased by about 20%, which improves the effect of gas flushing and improves the development efficiency of the oil field at the same time. Full article

The Sangu Spring Basin is located in an important economic area, and groundwater is the main source of water for local life and industry. Understanding the sources of chemical components in groundwater is important for the development and utilization of groundwater. In this paper, we analyzed the origin of the chemical components of groundwater and their evolution in the Sangu Spring Basin using statistical analysis, Piper diagrams, Gibbs diagrams, ion ratios, and combined hydrochemistry–isotope analyses. The results show that the groundwater in the Sangu Spring Basin is mainly derived from atmospheric precipitation, that the groundwater in stagnant and confined environment zones was formed under colder climatic conditions, and that the surface water (SW) has a close hydraulic relation with the groundwater. Water–rock interaction is the main factor controlling the composition of groundwater. The compositions of groundwater are mainly derived from carbonate weathering, silicate weathering, and dissolution of gypsum. Na⁺ and K⁺ in groundwater mainly come from the dissolution of albite and potassium feldspar, rather than rock salt. Ion exchange occurs in karst groundwater (KGW) and fissure groundwater (FGW), and ion exchange is dominated by the exchange of Mg²⁺ and Ca²⁺ in the groundwater with Na⁺ and K⁺ in the rock or soil. Sulfate in groundwater is derived from dissolution of gypsum, infiltration of atmospheric precipitation, and leakage of SW. Groundwaters with the highest sulfate content are located in the vicinity of SW, as a result of receiving recharge from SW seepage. Groundwaters with higher sulfate contents are located in the stagnant and deeply buried zones, where sulfate is mainly derived from the dissolution of gypsum. SW seepage recharges groundwater, resulting in increased levels of Cl⁻, NO₃⁻ and SO₄²⁻ in groundwater. These insights can provide assistance in the protection and effective management of groundwater. Full article

We study the interrelations between salt karst and landscape evolution at the Ze’elim and Hever alluvial fans, Dead Sea (DS), Israel, in an attempt to characterize the ongoing surface and subsurface processes and identify future trends. Using light detection and ranging, interferometric synthetic aperture radar, drone photography, time-lapse cameras, and direct measurements of floodwater levels, we document floodwater recharge through riverbed sinkholes, subsurface salt dissolution, groundwater flow, and brine discharge at shoreline sinkholes during the years 2011–2023. At the Ze’elim fan, most of the surface floodwater drains into streambed sinkholes and discharges at shoreline sinkholes, whereas at the Hever fan, only a small fraction of the floodwater drains into sinkholes, while the majority flows downstream to the DS. This difference is attributed to the low-gradient stream profiles in Ze’elim, which enable water accumulation and recharge in sinkholes and their surrounding depressions, in contrast with the higher-gradient Hever profiles, which yield high-energy floods capable of carrying coarse gravel that eventually fill the sinkholes. The rapid drainage of floodwater into sinkholes also involves slope failure due to pore-pressure drop and cohesion loss within hours after each drainage event. Surface subsidence lineaments detected by InSAR indicate the presence of subsurface dissolution channels between recharge and discharge sites in the two fans and in the nearby Lynch straits. Subsidence and streambed sinkholes occur in most other fans and streams that flow to the DS; however, with the exception of Ze’elim, all other streams show only minor or no recharge along their course. This is due to either the high-gradient profiles, the gravelly sediments, the limited floods, or the lack of conditions for sinkhole development in the other streambeds. Thus, understanding the factors that govern the flood-related karst formation is of great importance for predicting landscape evolution in the DS region and elsewhere and for sinkhole hazard assessment. Full article

The hydrogeological conditions of Huainan Coalfield are complex. The Taiyuan formation limestone water (Taihui water) in this area is a direct threat to the water source of the 1# coal mining floor. In order to prevent and control water disasters, Gubei Coal Mine adopted ground high-pressure grouting with fly ash cement to block the hydraulic connection between the Taiyuan formation limestone aquifer and the Ordovician limestone aquifer. However, the injected slurry will destroy the original hydrochemical balance of Taihui water and change its hydrochemical characteristics. Taking the influence area of the 2# karst collapse column in the Beiyi 1# coal mining area of Gubei Coal Mine as an example, a total of 25 Taihui water samples were collected. The hydrochemical characteristics and evolution law of Taihui water before and after grouting are studied via the multivariate statistical method. The research methods include constant index statistics, Piper diagram, correlation analysis, ion combination ratio, and saturation index analysis. The results show that after grouting, the concentrations of Na⁺ + K⁺, Ca²⁺, Mg²⁺, and Cl⁻ in Taihui water decrease, while the concentrations of SO₄²⁻ and HCO₃⁻ increase. The average values of PH and TDS become larger. The hydrochemical types of Taihui water are more concentrated, mainly HCO₃-Na and Cl-Na. The correlations between conventional indicators decrease. According to the analysis of ion combination ratio, dissolution, cation exchange, and pyrite oxidation mainly occur in Taihui water, and these effects are enhanced after grouting. The saturation index results show that after grouting, the saturation index of dolomite, calcite, and gypsum is significantly reduced, and the saturation index of rock salt is slightly increased. The conclusion of this study is that the hydrochemical characteristics of Taihui water are greatly affected by fly ash cement. Moreover, because fly ash cement contains a lower calcium oxide content than ordinary Portland cement, the effect of fly ash cement on the ion concentration of Taihui water and the resulting hydrogeochemical effect are significantly different. Therefore, in the treatment of mine water disasters, the hydrogeochemical evolution law affected by fly ash cement grouting should be identified. Full article

To elucidate the hydrochemical characteristics, controlling factors, sources and mechanisms of strontium ion enrichment in groundwater in the northwest plain of Shandong Province, China, 88 groundwater samples were collected, including 51 shallow pore groundwater samples, 29 deep pore groundwater samples and 8 karst groundwater samples. The hydrochemical characteristics of the different types of groundwater were quite different. The karst groundwater samples were all fresh water with a single hydrochemical type, either HCO₃-Ca or HCO₃-Ca·Mg. The deep pore groundwater samples were mainly brackish water, and the shallow pore groundwater samples were brackish water–salt water, which has complex hydrochemical types. The hydrochemical characteristics of all the types of groundwater were controlled by mineral dissolution and active positive cation exchange. In shallow pore groundwater, deep pore groundwater and karst groundwater, the dissolution of silicate, evaporite and carbonate minerals dominated the hydrogeochemical process. The strontium in groundwater was derived from the dissolution of minerals with strontium isomorphism. The average contents of strontium in shallow, deep and karst groundwater were 1.59 mg/L, 0.58 mg/L and 0.50 mg/L, respectively. The strontium in shallow pore groundwater was mainly derived from the enrichment of groundwater runoff, and its sources are abundant, with silicic rock being the main source. The deep pore groundwater mainly derived from the evaporative minerals containing strontium, and the karst water mainly derived from carbonate rock dissolution with similar characteristics. Full article

The authors discuss a case that is full of examples of the problems faced by civil engineers whose task is to develop areas in the face of natural, technological, or post-mining hazards. The study area is in the central part of Inowrocław, a town located on a massive salt dome of Zechstein salts. A strong deformation zone expanded in its upper part; this was caused by a natural process (related to so-called salt karst) and by mining activities that occurred in the past, creating a problem with regard to any potential spatial development in the town. The authors show a combination of data obtained using gravimetric and geodetic methods, which helps us to assess the geohazard risk. These include remote sensing data, which can be used to evaluate displacements of the ground surface. The authors used an approach that they term the Elevation Difference Method. This consists of determining displacements between ground surfaces: estimated on the basis of remote sensing data and on the basis of the historical data, when mounted measurement points (and remote sensing data) did not exist. The authors discuss the results in the light of the geological background. Within the area of the study, the displacements of the positive values dominate. The displacement occurs at 6 mm/yr on average and indicates diapiric uplift movement. The results are important for the town authorities for planning and development and for infrastructure management. Full article

Subsurface salt layer dissolution along the western shores of the Dead Sea is considered to be the primary cause for extensive large sinkhole formation in the past 40 years. Many of these sinkholes are arranged in clusters and are filled with water from nearby springs. The Mineral Beach resort was built in an area with a thermal spring with water emerging at around 40 °C at the Shalem sinkhole cluster. Unfortunately, the same spring was responsible for the destruction of the resort as it supplied water undersaturated with respect to halite, which promoted dissolution and sinkhole formation. The sinkholes in the Shalem cluster drain out in sudden catastrophic events and then slowly fill again. The drainage mechanisms of this phenomenon are studied in the Shalem-2 sinkhole cluster using leveling data collectors and ground-based LiDAR surveys over a period of 5 years, including thirty-five drainage events. Drainage volume and fluxes calculated using water level and topographic data obtained by LiDAR scans suggest that the formation of additional sinkholes beneath the pond’s bottom triggers drainage events. The subsequent flux shows that the evolution of the newly formed sinkholes either improves the hydraulic connection or temporarily seals the connection between the surface pond and deeper caverns/aquifers. The drainage event ends when either the hydraulic connection is sealed or when the level of water in the pond drops to the level of the newly formed sinkhole. The large volumes of drained water and drainage fluxes imply the existence of a well-developed active underground draining system. Full article

From the 1970s, the Dead Sea experienced severe halo-karstification and anthropogenic modifications. Progressively, but at an accelerating rate, subsidence, landslides, and sinkholes have increased in number and magnitude. The hazards’ triggering factors are the terminal lake level lowering at more than one meter per year and the dynamic equilibrium of the hydrogeological system. Over the Lisan peninsula, archived satellite images revealed the extent of the damaged areas. On 22 March 2000, the destruction of dike 19 represented a loss of 38 M USD. This is the most important event recorded since the beginning of the Dead Sea recession some 50 years ago. In 2018, a rehabilitation project of that dike started. This research analyses the viability of the reinstatement works. The advanced space borne radar interferometry technique is applied to map ground deformations before and during the project. This article reveals that the ongoing rehabilitation and reinstatement works of dike 19 are threatened by ongoing halo-karstification processes. Field observations and subsidence/uplift dynamics support this statement. The past experiences are taken into consideration to adapt industrial expansion strategies. However, the permeability of the salt pan floor could trigger a fast development of a karst system able to destroy the rehabilitated dike 19. Full article

Numerous coastal karst springs of the Mediterranean region have problems with salinization. Salinization usually occurs during summer dry periods as a result of long droughts and excessive pumping for water supply. The Boljkovac water supply pumping station has slightly increased parameters that indicate the possibility of salinization during the dry summer periods, but the main salinization occurs post heavy rains which appear after long dry periods in the fall, winter, and spring. Due to the occasional occurrence of salinization, continuous monitoring of the aquifer by depth was set up at the piezometric well drilled near the water supply pumping station. The results of the monitoring were analyzed in relation to external factors that can negatively affect the disruption of the labile dynamic balance of salt and fresh water. The analyzed external factors are the pumping rate for the water supply, the amount of precipitation, surface flow and the interaction of surface water and groundwater, as well as the sea level changes. In Croatia, and the wider Mediterranean area, there are a large number of springs and water wells that have the same or similar problems, so the results of this analysis can be used in designing monitoring and setting up management systems for these coastal aquifers. Full article

In this study, the simulation of artificial conditions, containing various chemical additives similar to a bog environment, was hypothesised as a relatively short way to develop a more sustainable wood product with better properties. This study aimed to determine how hydrothermal treatment with different iron additives with and without tannic acid, performed at 100 °C for 75 h, changed the mass and density of wood of different tree species (Pinus sylvestris L., Picea abies (L.) H. Karst., Pseudotsuga menziesii (Mirb.) Franco, Juglans regia L., and Acer platanoides L.); total phenolic compounds in biobased solvents after the hydrothermal processing andiron concentration in different wood layers. We also aimed to determine the wood chemical composition using Fourier-transform infrared technique. The study results showed that the softwood samples were more susceptible to hydrothermal modification than the hardwood samples, indicated by minorly different intensities on infrared spectra. The FTIR results showed bands of hardwood and softwood samples which along with the spectral characterisation of the wood constituents, which can further be utilized for creating a larger FTIR spectral database of wood samples for their identification. The factors with the most significant effect on the hydrothermal modification were tannic acid and inorganic Fe₃O₂ salt, used as an additive. The results indicated the suitability of inorganic Fe₃O₂ salt and tannic acid combination applied in this type of modification, because a higher concentration of iron was distributed on the inner and intermediate sublayers of wood samples. The hydrothermal modification approach to anchor tannic acid–Fe macromolecules in wood shown in this study has promising capabilities and may attract interest in the field of wood protection against weathering. Full article

InSAR (Interferometric Synthetic Aperture Radar) cloud computing and the subtraction of LiDAR (Light Detection and Ranging) DEMs (Digital Elevation Models) are innovative approaches to detect subsidence in karst areas. InSAR cloud computing allows for analyzing C-band Envisat and Sentinel S1 SAR images through web platforms to produce displacement maps of the Earth’s surface in an easy manner. The subtraction of serial LiDAR DEMs results in the same product but with a different level of accuracy and precision than InSAR maps. Here, we analyze the capability of these products to detect active sinkholes in the mantled evaporite karst of the Ebro Valley (NE Spain). We found that the capability of the displacement maps produced with open access, high-resolution airborne LiDAR DEMs was up to four times higher than InSAR displacement maps generated by the Geohazard Exploitation Platform (GEP). Differential LiDAR maps provide accurate information about the location, active sectors, maximum subsidence rate and growing trend of the most rapid and damaging sinkholes. Unfortunately, artifacts and the subsidence detection limit established at −4 cm/yr entailed important limitations in the precise mapping of the sinkhole edges and the detection of slow-moving sinkholes and small collapses. Although InSAR maps provided by GEP show a worse performance when identifying active sinkholes, in some cases they can serve as a complementary technique to overcome LiDAR limitations in urban areas. Full article

Temporal rainwater chemistry was used to reveal air pollution in the Maolan National Karst Forest Park (MNKFP), which is representative of the typical karst forest region of southwest China (SW China). The rainwater ions’ sources, variations, trends, and potential environmental effects were investigated from 2007 to 2010 and from 2013 to 2014. Based on the analysis of the temporal ionic concentrations of rainwater in the MNKFP, significant variations of ions were observed, including in NH₄⁺ (9.7~266.6 μeq L⁻¹) and SO₄²⁻ (14.5~1396.4 μeq L⁻¹), which were mainly controlled by variations in the source and rainfall amount; a decreased trend of rainwater pH was also observed. Accordingly, NH₄⁺, Ca²⁺, SO₄²⁻, and Cl⁻ were regarded as the most dominant ions. Typical ionic ratios and positive matrix factorization (PMF) model-based source apportionment suggested that anthropogenic inputs (coal combustion, industrial, traffic, and agricultural emissions) contributed 51% of F⁻, 93% of NO₃⁻, 62% of SO₄²⁻, and 87% of NH₄⁺, while the natural sources (crustal dust and sea salt) were the main sources of Cl⁻ (74%), Na⁺ (82%), K⁺ (79%), Mg²⁺ (94%), and Ca²⁺ (93%). In combination with the reducing neutralization trend of temporal rainwater observed in the MNKFP and the potential effect of rainwater ion deposition on karst forests, more detailed monitoring of the rainfall-related deposition process is required for a better understanding of its potential environmental effects on the Earth’s surface. Full article

We investigate the long-distance salinity in a dual permeability coastal karst aquifer with a double conduit network using a three-dimensional variable-density groundwater flow and multispecies transport SEAWAT model. Sensitivity analyses were used to evaluate the impact of the parameters and boundary conditions on the modeling saltwater wedge in a karstic aquifer situated in the Cuban land territory, including hydraulic conductivity, vertical anisotropy and salinity concentration; both in the conduits network and the fractured medium. These analyses indicated that hydraulic conductivity of the fractured medium and salt concentration were the ones that have a stronger effect on saltwater intrusion in a karstic aquifer. We also show results of the three-dimensional numerical simulations on groundwater salinity for different scenarios with the variabilities of the important parameters and compare results with electric conductivity profiles measured in a well. Full article