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Karstic aquifers are very sensitive and fragile to environmental changes. With more tunnels excavated in karst areas, groundwater levels are increasingly lowered and resulted in changed natural hydrogeological flow system and groundwater-dependent vegetation, soil and hydrology of surface water systems. Water, especially groundwater, is a limited and key factor and significant driving force for karst ecosystem processes. However, the effects of tunnels excavation on the ecosystems in karst areas remain largely unknown. This study aimed at investigating whether there were variations in soil water contents and shifts of plants water uptake patterns between rainy and dry seasons in a karst trough valley affected by tunnels excavation, and comparing their differences with those in a tunnel-free karst trough valley in southwest China. Monthly soil water contents at two soil layers of the upper 20 cm and lower 20–40 cm were measured, and soil water at two soil layers, subcutaneous water and plant (arbor and shrub) xylem water were sampled in February (mid dry season) and September (late rainy season) 2017, respectively, and the δ2H and δ18O of those waters were analyzed. The IsoSource model based on dual stable isotopes of δ2H and δ18O was used to estimate the contributions of different sources to the plant xylem water. Although the soil water contents at both valleys showed similar vertical and temporal variations resulted primarily from the evaporation and precipitation, the soil water contents of two soil layers in the tunneling affected valley were significantly lower than that of the tunnel-free valley at both seasons. Plants uptake water pattern changed from a dominant soil water source during the rainy season to a dominant subcutaneous water source during the dry season at both valleys. However, plants extracted more water from the subcutaneous zone in the tunneling affected karst trough valley than that of the tunnel-free karst trough valley at both seasons, of which the proportion of plants water uptake from the subcutaneous zone was 33% in rainy season and 76% in dry season, respectively, in the tunneling affected karst trough valley, while the proportion of plants water uptake from the subcutaneous zone was 24% in rainy season and 59% in dry season, respectively, in the tunnel-free karst trough valley. The above results indicated that tunnels excavation decreased the soil water contents and then changed plants water uptake patterns in karst areas.

Soil water plays a crucial role in biogeochemical processes within karst ecosystems. However, geochemical variations of soil waters under different land covers and the related karst critical zone processes are still unclear. In this study, five land covers, including grassland, dry land, shrub land, reforestation land, and bamboo land in the Qingmuguan karst area of Chongqing Municipality, Southwest (SW) China were investigated in order to better understand the spatio-temporal variations of soil water geochemistry and its controlling mechanisms. The hydrochemistry of soil water and stable carbon isotopic compositions of dissolved inorganic carbon (δ13CDIC) in soil water were analyzed by a semi-monthly sampling strategy. The results show that there is remarkable spatio-temporal variation in the hydrochemistry and δ13CDIC of soil waters under different land covers in the studied area. Soil waters collected from shrub, dry, and afforestation lands have higher total dissolved solids (TDS), Ca2+, and HCO3− concentrations and heavier δ13CDIC, which is probably associated with the stronger carbonate dissolution caused by higher soil CO2 and carbonate content in soils under these land covers. However, lower TDS, Ca2+, and HCO3− concentrations as well as δ13CDIC values but higher SO42− concentrations are found in soil waters collected from bamboo land and grassland. The reason is that higher gypsum dissolution or oxidation of sulfide minerals and less soil CO2 input occurs in soils under these two land covers. Under the shrub, dry, and afforestation lands, higher concentrations of Ca2+ and HCO3− in soil waters occur in rainy seasons than in dry seasons, which are probably linked to higher CO2 input due to stronger microbial activities and root respiration in the wet summer seasons. In addition, seasonal variations of NO3− concentrations in soil waters from the dry land are observed, and much higher NO3− concentration occurs in the rainy seasons than that in the dry seasons, which suggest that the agricultural fertilization may lead to high NO3− in soil water. On the vertical soil profile, except for the bamboo land, soil waters under different land covers commonly show an increasing trend of main ion concentrations with the increase of depth. This vertical variation of hydrochemistry and δ13CDIC values in soil waters is primarily controlled by the intensity of carbonate dissolution related to carbonate content in soils and soil CO2 production. The soil waters under different land covers have great variations in δ13CDIC values which ranged from −20.68‰ to −6.90‰. Also, the [HCO3−]/([Ca2+] + [Mg2+]), [NO3−]/[HCO3−], and [SO42−]/([Ca2+] + [Mg2+]) molar ratios in soil waters show a large amplitude of variation. This suggested that carbonic acids could not be a unique dissolving agent and sulfuric/nitric acids may play a role in the weathering of carbonate in the Qingmuguan karst area.

Chongqing, located in the southwestern China, was named as “A spa city of the world”. It's most geothermal reservoirs are developed in carbonate rock aquifers, and those thermal waters are characterized by high concentrations of sulfate and low HCO3−. However, little was known about the origin and genesis of those thermal waters, which is necessary for their protection and determination of regime of exploitation. Therefore, thermal and surface waters were sampled seasonally and analyzed for hydrogeochemical and isotopic compositions (δ18O/δ2H; δ34S–SO4; δ18O–SO4) to decipher the origin of the thermal waters in the Triassic carbonate aquifers in Chongqing area. Key questions include the relative significance of hydrothermal processes and solute supply. The results showed that: (1) the major chemical composition of analyzed the thermal waters from Chongqing area was characterized by Ca-SO4; (2) the δ2H and δ18O values of the thermal waters ranged from −48.6‰ to −63.1‰ with an average value of −54.2‰, and from −6.5‰ to −9.2‰ with an average value of −8.0‰, respectively, indicating that the thermal waters originated from the local rain water with an elevation of 415 m to 1453 m above mean sea level; (3) the estimated geothermal temperatures varied from 63.8 °C to 78.3 °C (Quartz), indicating that the depth of the geothermal reservoir varied from 411 m to 1728 m, which is located in the Lower Triassic Jialingjiang formation; (4) the δ34S-SO42- and δ18O-SO42- in the geothermal waters ranged from 29.7‰ to 34.1‰ with a mean value of 32.1‰, and from 12.5‰ to 16.5‰ with a mean value of 15.2‰, respectively, suggesting that the high SO42− concentrations resulted mainly from the dissolution of gypsum in the second part of the Lower Triassic Jialingjiang Formation; (5) three processes of water-rock interactions (gypsum dissolution, carbonate dissolution by carbonic acid and carbonate dissolution by sulfuric acid) in the thermal system were unveiled by the hydrogeochemical and isotopic models. Among these three processes, gypsum dissolution seems to be primarily responsible for solute composition of the thermal water. This study also indicates the integration of hydrogeochemical and isotopic data is very useful tool to decipher the origin and genesis of the carbonate thermal waters.

Cave CO2 is an important part of the carbon cycle in a karst system. From 2008 to 2009 the partial pressure of CO2 (PCO2) of the cave air and cave water (cave stream and dripwater) in Xueyu Cave was studied. The PCO2 for cave air and cave water over two years showed that CO2 concentrations vary seasonally in all field sites, with higher CO2 concentrations in the wet season and lower concentrations in the dry season. These seasonal CO2 variations of cave air and cave water are attributed to seasonally variable soil CO2 production that is controlled by outside temperature fluctuations. Cave ventilation controls synchronous sharp variations of PCO2 from wet season to dry season or dry season to wet season in cave water and cave air. In the wet season, there were no obvious spatial differences of mean PCO2 in cave stream and cave air from upstream to downstream cave. Conversely, there were significant spatial differences of mean PCO2 in cave stream and cave air from upstream to downstream cave in the dry season because of cave ventilation. Mean dripwater PCO2 in D1 site where near cave entrance is much higher than that of the D2 and D3 sites where located in inner cave because D1 has a shorter flowpath from cave ceiling to soda-straw tip and lesser CO2 degassing along the flowpath. Further work in Xueyu Cave needs to clarify the quantitative relationship of CO2 cycle between cave air CO2 and cave water and focus on the influence of CO2 cycle on speleothem form.

In recent years, Generative adversial network(GAN) becomes prevalent in the research and was applied in various fields. Though GAN attracting great attention undoubtedly, it was still blamed for the difficulty of training. Training a GAN is very likely to get into undesirable results such as gradient vanishing, gradient explosion, model collapse. In order to train GAN more efficiently, this study proposes the Swap Ensemble Generative Adversial Network(SE-GAN), a framework for training an ensemble GAN. Based on the concept of information sharing, SE-GAN allows serveral GANs to be trained in parallel: one of them is the leader, while the others are the workers. The leader pair swaps with each worker periodically to collect the information of all workers. At the same time, each worker acquires the information the leader learned. Under such implementation, the leader and workers would help each other.In this paper, a toy dataset was used to describe the concept and better show the effect of swap ensemble framework. And three real-world datasets were used to validate the effect. Results of the experiments shows this framework improves the performance and efficiency in training GAN.

Mapamyum geothermal field (MGF) in western Tibet is one of largest geothermal areas characterized by the occurrence of hydrothermal explosions on the Tibetan Plateau. The geochemical properties of hydrothermal water in the MGF system were investigated to trace the origin of the solutes and to determine the equilibrium temperatures of the feeding reservoir. The study results show that the geochemistry of hydrothermal waters in the MGF system is mainly of the Na–HCO 3 type. The chemical components of hydrothermal waters are mainly derived from the minerals in the host rocks (e.g., K-feldspar, albite, Ca-montmorillonite, and Mg-montmorillonite). The hydrothermal waters are slightly supersaturated or undersaturated with respect to aragonite, calcite, dolomite, chalcedony and quartz (saturation indices close to 0), but are highly undersaturated with respect to gypsum and anhydrite (saturation indices δ D and δ 18 O data confirm that the meteoric water acts as the water source of the geothermal waters. An ~ 220 °C equilibrated reservoir temperature of hydrothermal spring waters was calculated via both the Na–K–Mg ternary diagrams and the cationic chemical geothermometers. The log p CO 2 of hydrothermal waters in the MGF system ranges from − 2.59 to − 0.57 and δ 13 C of the total dissolved inorganic carbon ranges from − 5.53‰ to − 0.94‰, suggesting that the carrier CO 2 in hydrothermal water are mainly of a magmatic or metamorphic CO 2 origin.

A prerequisite for using cave speleothems to reconstruct palaeoenvironmental conditions is an accurate understanding of specific factors controlling calcite growth, in particular the isotopic partitioning of oxygen (δ 18 O) and carbon (δ 13 C) which are the most commonly used proxies. An in situ monitoring study from April 2008 to September 2009 at Xueyu Cave, Chongqing, SW China, provides insight into the controls on calcite growth rates, drip water composition, cave air parameters and δ 18 O and δ 13 C isotopic values of modern calcite precipitation. Both cave air P CO 2 and drip water hydrochemical characteristics show obvious seasonality driven by seasonal changes in the external environment. Calcite growth rates also display clear intra-annual variation, with the lowest values occurring during wet season and peak values during the dry season. Seasonal variations of calcite growth rate are primarily controlled by variations of cave air P CO 2 and drip water rate. Seasonal δ 18 O -VPDB and δ 13 C -VPDB in modern calcite precipitates vary, with more negative values in the wet season than in the dry season. Strong positive correlation of δ 18 O -VPDB vs. δ 13 C -VPDB is due to simultaneous enrichment of both isotopes in the calcite. This correlation indicates that kinetic fractionation occurs between parent drip water and depositing calcite, likely caused by the variations of cave air P CO 2 and drip rate influenced by seasonal cave ventilation. Kinetic fractionation amplifies the equilibrium fractionation value of calcite δ 18 O (by ∼1.5‰) and δ 13 C (by ∼1.7‰), which quantitatively reflects surface conditions during the cave ventilation season. These results indicate that the cave monitoring of growth rate and δ 18 O and δ 13 C of modern calcite precipitation are necessary in order to use a speleothem to reconstruct palaeoenvironment.

Pyrogenic carbon (PyC) is a polyaromatic residue of the incomplete combustion of\ud biomass or fossil fuels. There is a growing recognition that PyC forms an important\ud part of carbon budgets, due to production rates of 116–385 Tg C yr, and the size and\ud ubiquity of PyC stocks in global carbon reservoirs. At least a proportion of PyC exists in a\ud highly recalcitrant chemical form, raising the prospect of long-term carbon sequestration\ud through soil amendment with “biochar,” which is generally produced with the aim of\ud making a particularly recalcitrant form of PyC. However, there is growing evidence\ud that some PyC, including biochar, can be both physically and chemically altered and\ud degraded upon exposure to the environment over annual timescales, yet there is a lack\ud of information concerning the mechanisms and determining factors of degradation. Here,\ud we investigate three main factors; production temperature, feedstock composition, and\ud the characteristics of the environment to which the material is exposed (e.g., pH, organic\ud matter composition, oxygen availability) by analysis of biochar samples in a litterbag\ud experiment before and after a year-long field study in the tropical rainforests of northeast\ud Australia. We find that non-lignocellulosic feedstock has lower aromaticity, plus lower O/C\ud and H/C ratios for a given temperature, and consequently lower carbon sequestration\ud potential. The rate at which samples are altered is production temperature-dependant;\ud however even in the highest temperature samples loss of the semi-labile aromatic\ud carbon component is observed over 1 year. The results of 13C-MAS-NMR measurements\ud suggest that direct oxygenation of aromatic structures may be even more important than\ud carboxylation in environmental alteration of biochar (as a subset of PyC). There is a clear\ud effect of depositional environment on biochar alteration even after the relatively short\ud timescale of this study, as changes are most extensive in the most oxygenated material\ud that was exposed on the soil surface. This is most likely the result of mineral ingress\ud and colonization by soil microbiota. Consequently, oxygen availability and physical or\ud chemical protection from sunlight and/or rainwater is vital in determining the alteration\ud trajectory of this material.

Concentration of dissolved nitrate (NO3 −) and stable nitrogen isotopic composition of nitrate in water samples from 19 epikarst springs in the Jinfo Mountain area were analysed in order to understand the temporal–spatial distribution of nitrate in karst spring waters and trace nitrogen sources for the springs that have suffered from nitrate contamination. The results show that hydrochemistry of epikarst spring water is Ca·Mg–HCO3 facies, reflecting the control of water–carbonate rock interaction. NO3 − concentrations in water of springs within the national nature reserve (NNR) in the Jinfo Mountain area range from 0 to 8.16 mg/L, suggesting that these springs within the NNR have good water quality. However, most springs outside the NNR have high NO3 concentrations (c: 10.5–46.18 mg/L) that have exceeded the value of Chinese national drinking water quality standard (NO3–N ≤10 mg/L), revealing that these springs have suffered from nitrate contamination to a significant degree. δ 15N–NO3 values of these contaminated springs outside the NNR range from −1.2 ‰ to 11.27 ‰, higher than those of unpolluted springs within NNR (−5.2 ‰ –8.6 ‰). Two main sources of nitrate in these contaminated springs have been identified, including animal manure/sewage and chemical nitrogen fertilisers that are from anthropogenic activities. Our study also shows that the nitrate fate and origin are associated with the land use in the recharge catchment of individual epikarst springs, and the establishment of national nature reserve can protect the water quality of epikarst spring.