Search

The freshwater discharge from melting ice sheets in the deglaciation or glaciation is prone to anomalies in ocean-atmosphere transport between different latitudes, which can lead to a series of abrupt millennial-scale climate events, either obvious or not, such as the Younger Dryas (YD) events and YD-like events. Marine Isotope Stage 11c (MIS 11c) serves as one of the best references for the current Holocene, and the studies of possible YD-like events and their triggering mechanisms during Holocene are conducive to the understanding of the occurrence pattern of extreme climate events. In this paper, the results of the study on the J33 δ18O sequence records of stalagmites in Jinfo Cave, Chongqing, are shown: (1) Stalagmites in the Asian monsoon climate zone reveal a millennial-scale weak monsoon event that occurred around 410 ka BP prior to the Glacial Maximum of MIS 11 interglacial period. (2) Both the 410 ka weak monsoon event and the YD event occurred during the gradual strengthening of the monsoon and ascending branch of summer insolation in the Northern Hemisphere prior to the Glacial Maximum of interglacial period. This was also a time when Atlantic Meridional Overturning Circulation (AMOC) disturbance occurred. The duration, internal structure, and pattern of the events were similar, with differences in the change magnitude and ice volume conditions. (3) The weak monsoon event that occurred in 410 ka BP was primarily influenced by the combined effects of insolation and AMOC. This event was characterized by a sustained warming process that accelerated the melting of the Greenland ice sheet, leading to the destabilization of this ice sheet. The continuous flowing of freshwater into the North Atlantic resulted in a short-lived AMOC oscillation. The weakening of the AMOC resulted in a cold anomaly over the North Atlantic. As a result of atmospheric telecorrelation, the weaker AMOC led to a weaker Asian Summer Monsoon (ASM). [ABSTRACT FROM AUTHOR]

• A physically-based distributed Karst-Liuxihe model (KL) was improved and simplified effectively. • The rainfall-runoff generation and confluence algorithms were improved. • Better flood simulation results showed that the simplified and improved model is successful. • The simplified KL model requires less hydrogeological data when modeling in karst basins. The karst trough valley basin in Zhongliang of Chongqing is one of the most developed karst areas in Southwest China, with unique topographic features such as karst troughs and valleys that are prone to flash floods. Accurate simulation of flood processes in these areas using hydrological models can provide references for predicting future local runoff evolution trends. The main challenge for hydrological modelling in karst areas lies in building a model with limited hydrogeological data. In this study, the Karst-Liuxihe (KL) model was simplified and improved to simulate karst flood processes in the Zhongliang karst trough valley. The KL model consists of multiple, complex structures; a large amount of data is needed to model karst areas. To overcome the modelling data requirements, we modified the model structure and its parameters to propose a simplified KL (SKL) model. Additionally, we improved the runoff generation and confluence algorithms. Compared with the simulation results for 22 flood processes obtained by using the KL model, the results for this SKL model were better with less modelling data. For example, the mean value of the Akaike information criterion (AIC) index decreasing rate was 35%, and the process relative error and the peak flow relative error decreased by 10%, indicating that the technique of simplifying and improving the KL model is effective and that the simplified SKL model can quantitatively depict karst floods in karst trough valley areas. [ABSTRACT FROM AUTHOR]

Karst subterranean streams are important water resources and life-support systems in karst areas and hydrogeochemistry research is an indispensable tool for karst aquifer protection. There are approximately 380 known subterranean streams in the Chongqing area, which are a fundamental groundwater resource. Hydrogeochemical analysis of 84 karst subterranean streams in Chongqing indicated that the solutes mainly came from the dissolution of carbonate rock (using the Gibbs diagram) and most subterranean streams are influenced by the anthropogenic processes. Also, the hydrochemical characteristics showed clear regional effects in natural background chemistry and human impacts. The calcite content decreases and the dolomite content increase from Triassic to Cambrian carbonate rock (except in the Permian carbonate rock), so that subterranean streams that developed in the Cambrian carbonate rock have the highest Mg concentration. Karst subterranean streams that developed in the Permian strata displayed the lowest Mg concentration due to the lowest dolomite concentration in Permian strata. Under the same geological settings, major hydrochemical parameters of karst subterranean streams showed significant diversity across regions as a result of the varying intensity of human activities. Utilizing the Gibbs diagram, it is concluded the karst subterranean streams are deteriorating under the impact of industry activities, agriculture activities and city sewage. [ABSTRACT FROM AUTHOR]

The application of combined isotopic and hydrochemical compositions may be useful for evaluating water quality problems in karst aquifers in which it is difficult to distinguish the sources of solutes from the natural background of those due to human activities. Multiple isotopes (δC-DIC, δS-SO) and chemical parameters were measured in rainwater, groundwater and sewage in order to elucidate the solute sources and impacts from human activities and natural background in the Laolongdong karst catchment in Chongqing Municipality, SW China. Overall, the dissolution of carbonate rock controls Ca, Mg and HCO content in rainwater and karst groundwater. SO originated mainly from gypsum dissolution in karst groundwater. Carbonate rocks in the studied site could be dissolved jointly by HCO from the natural CO-HO reaction and other acids (organic acids and HNO) from sewage and soils. Sewage discharge from urban areas and agriculture activities lead to the increase of NO, PO and Cl in karst groundwater. To protect and sustainably utilize the karst aquifer, sewage originating from urban areas must be controlled and treated and the use of fertilizer should be limited. [ABSTRACT FROM AUTHOR]

Physical and chemical dynamics at Jiangjia Spring (JJS), the outlet of the Qingmuguan karst groundwater system in Chongqing, were monitored in situ during rainfall events to acquire a series of high-resolution data. Principal component analysis (PCA) was employed to identify the sources of chemical compositions in the karst groundwater. The coefficients of variations (CVs) of the physical and chemical data of JJS were utilized to interpret the migration path of the chemical compositions. The results showed that water-rock interactions, agricultural activities, and soil erosion were the main sources of the groundwater chemical compositions. Ions of potassium, sodium, nitrate, chloride and phosphate from agricultural activities together with ions of calcium, magnesium, strontium and bicarbonate derived from carbonate dissolution appear to be stored and regulated by the karst unsaturated zone in features such as fissures, pores and solution cracks. The concentrations of the ions remained relatively stable and they showed low CVs owing to their migration by diffuse flow to recharge the underground river. In contrast, concentrations of ions such as total iron, total manganese and aluminum from soil erosion were unstable and showed high CVs owing to their migration by overland flow to recharge the underground river directly via sinkholes. During heavy rainfall events, the nutrients from agricultural activities and sediment from soil erosion could quickly impair the aquatic ecosystem and pose serious threats to water quality. Therefore, it is necessary to reinforce management of the ecological system for better control of the influx of mass nutrients into the karst aquifer system. [ABSTRACT FROM AUTHOR]

Groundwater from karst subterranean streams is among the world's most important sources of drinking water supplies, and the hydrochemical characteristics of karst water are affected by both natural environment and people. Therefore, the study of karst groundwater hydrochemistry and its solutes' sources is very important to ensure the normal function of life support systems. This paper focused on the major ion chemistry and sulfate isotope of karst groundwater in Chongqing for tracing the sulfate sources and related hydrochemical processes. Hydrochemical types of karst groundwater in Chongqing were mainly of the Ca-HCO type or Ca(Mg)-HCO type. However, some hydrochemical types were the K + Na + Ca-SO type (G25 site) or Ca-HCO + SO type (G26 and G14 sites), indicating that the hydrochemistry of these sites may be strongly influenced by anthropogenic activities or unique geological characteristics. The δS-SO of collected karst groundwater sample fell into a range of −6.8 to 21.5 ‰, with a mean value of 5.6 ‰. In dolomite aquifer, the δS-SO value ranges from −4.3 to 11.0 ‰, and in limestone aquifer, it ranged from −6.8 to 21.5 ‰. The groundwater samples from different land use types showed distinctive δS-SO value. The δS-SO value of groundwater samples had range of −6.8 to 16.7 ‰ (mean 4.0 ‰, n = 11) in cultivated land areas, 1.5-21.5 ‰ (mean 7.2 ‰, n = 20) in forested land areas, and −4.3 to 0.8 ‰ (mean −1.7 ‰, n = 2) in coalmine areas. The δS-SO values of groundwater samples collected from factory area and town area were 2.2 and 9.9 ‰, respectively. According to the δS information of potential sulfate sources, this paper discussed the possible sulfate sources of collected karst groundwater samples in Chongqing. The variations of both δS and 1/SO values of the groundwater samples indicated that the atmospheric acid deposition (AAD), dissolution of gypsum (GD), oxidation of sulfide mineral (OS) or anthropogenic inputs (SF: sewage or fertilizer) contributed to sulfate in karst groundwater. The influence of oxidation of sulfide mineral, atmospheric acid deposit and anthropogenic inputs to groundwater in Chongqing karst areas was much widespread. For protecting, sustaining, and utilizing the groundwater resources, the sewage possibly originating from urban, mine or industrial area must be controlled and treated, and the use of fertilizer should be limited. [ABSTRACT FROM AUTHOR]

Groundwater quality in karst regions is largely controlled by natural processes and anthropogenic activities. Over the past 10 years, dissolved Sr and its radiogenic isotope, Sr/Sr, were widely used to trace the sources of solutes in groundwater. However, there is little research about hydrogeochemistry and Sr isotopic compositions of the karst groundwater in Chongqing karst area. In this paper, thirty-five representative karst groundwater samples were collected from different aquifers (limestone and dolomite) and various land use types. Hydrochemical types of karst groundwater in Chongqing were mainly of the Ca-HCO type or Ca(Mg)-HCO type. The dissolved Sr concentrations of the studied groundwater ranged from 0.57 to 15.06 μmmol/L, and the Sr/Sr varied from 0.70751 to 0.71627. The groundwater samples from different aquifers and land use types showed distinctive dissolved Sr concentrations and Sr/Sr. The very positive relationship between Ca/Sr and Mg/Sr in dolomite and limestone aquifers suggests that Ca, Mg and Sr element come mainly from the release of carbonate rock under the groundwater-rock-CO gas interaction. According to the Sr/Sr ratio, the Sr element in karst groundwater in Chongqing was controlled by the weathering of limestone, dolomite and silicate rock (allogenic water in a non-karst area). The relationship Sr/Sr versus Sr/[K + Na] shows that the anthropogenic inputs also obviously contribute to the Sr contents. The research results show that the karst groundwater in Chongqing is facing serious crisis of water quality, and needs to be protected further. [ABSTRACT FROM AUTHOR]

Globally, it is possible that up to 25% of the world's population depends on karst water supplies. In karst areas, a high degree of groundwater and surface water linkage often results in the direct recharge of groundwater with polluted run-off following rainfall. In order to reveal the hydrochemical variations after rainfall, especially real-time variation of pollutants, high-resolution auto-monitoring techniques were used at the outlet of Qingmuguan subterranean stream (QSS), which is influenced by agricultural activities. In addition to rainfall, high-resolution measurements of pH, water level, electrical conductivity (Ec) and NO concentration were recorded in the monsoon season and fertilizer application period using a data logger with time intervals of 15 min. In the six observed rainfall events, the pH value was mainly controlled by acidic rainfall inputs. The pH showed sharp decline after the rainfall event, and then increased. The Ec was impacted by the rainfall chemistry, dilution effect of rainfall and agricultural wastewater. NO derived from agricultural activities was less impacted by rain chemistry; and its variations were mainly affected by the dilution effect of rainfall and agricultural wastewater. Under the influences of the R1 rainfall, the rapid changes of Ec and NO were opposite in direction. As the rain continued, both the Ec and NO rapidly changed in synchronization within the shortest period of 5 h and the longest of 27 h because of the impact of the agricultural wastewater. The groundwater quality changed due to the influx of agricultural wastewater over the entire monitoring period. According to the National Groundwater Quality Standard, People's Republic of China (GB/T14848-9), the groundwater quality of the QSS moved through the following grades during the monitoring period: Grade III → Grade IV → Grade V → Grade IV → Grade V → Grade IV → Grade V → Grade IV → Grade III. Traditional sampling methods did not reveal accurate hydrochemistry changes of the QSS, and even generated misleading results. Consequently, the high-resolution auto-monitoring technique is necessary for the future protection and sustainable use of karst aquifer in Southwest China. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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 HCO 3 − . 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 (δ 18 O/δ 2 H; δ 34 S–SO 4 ; δ 18 O–SO 4 ) 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-SO 4 ; (2) the δ 2 H and δ 18 O 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 δ 34 S-SO 4 2- and δ 18 O-SO 4 2- 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 SO 4 2− 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. [ABSTRACT FROM AUTHOR]

The concentrations of 16 priority polycyclic aromatic hydrocarbons (PAHs) were investigated in the water, sediment and topsoil of the Laolongdong underground river system (LURS) of Chongqing, Southwest China. The total concentrations of PAHs ranged from 81.5 to 8089 ng/L in water, from 58.2 to 1070 ng/g in sediment, and from 277 to 3301 ng/g in topsoil. These levels of PAHs are relatively low compared to other karst areas. Low molecular weight (LMW) PAHs were dominant in water, sediment, topsoil samples, and high molecular weight (HMW) PAHs were more common in topsoil and sediment. The high levels of LMW PAHs in groundwater and sediment suggested relatively recent local sources of PAHs that were transported into the aquifer via wastewater discharge and surface water leakage. The similar composition of PAHs in topsoil and sediment samples suggested that the sediment originated from topsoil and that PAHs in sediment and topsoil had similar origins. The source of PAHs contamination was diagnosed by using PAH isomer ratios and a principal component analysis (PCA) method. The results indicated that PAHs mainly originated from vehicles, coal combustion and petrogenic sources. Significant correlations of PAHs with total organic carbon (TOC) in topsoil and sediment indicated that TOC was an important factor affecting PAHs content. [ABSTRACT FROM AUTHOR]

Abstract: To explore the potential health hazards of organochlorine pesticides (OCPs) in karst areas, HCHs (including α-HCH, β-HCH, γ-HCH and δ-HCH) and DDTs (including p,p''-DDE, p,p''-DDD, o,p''-DDT and p,p''-DDT) in underground rivers of Chongqing were analyzed, and health risks from OCPs through drinking water were assessed for adults and children. The results showed that the concentrations of OCPs in surface water from underground rivers were in the range of 2.25–29.37ngl−1 for HCHs (sum of α-HCH, β-HCH, γ-HCH, δ-HCH), and 0.19–35.25ngl−1 for DDTs (sum of p,p''-DDE, p,p''-DDD, o,p''-DDT and p,p''-DDT). δ-HCH and p,p''-DDT were the dominant HCHs and DDTs, respectively. In comparison with similar results reported around the world, the level of OCPs in this research was in the mid-range. Ratios of certain metabolites to their parent compounds suggested that HCHs in water from underground rivers mainly came from recent input of lindane, while the residues of DDTs were from earlier application of technical DDT and new input of dicofol. The analysis of health risk assessment indicated that risks from OCPs in most rivers would not be risky to human health according to the acceptable risk level, while carcinogenic effects caused by α-HCH might occur if drinking water from Lao Longdong (LL). α-HCH and β-HCH were the dominating factors for carcinogenic and non-carcinogenic risks, respectively. Risks of OCPs for children were much higher than those caused by OCPs for adults. [Copyright &y& Elsevier]