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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.)

The distribution of groundwater temperature and flow can be used to describe the hydrogeological process in a geothermal system, which is of great significance to the exploitation of geothermal resources. The traditional gravity-driven groundwater system theory takes less consideration of thermal convection, resulting in a deviation in the investigation of geothermal systems. The rise of water table and the acceleration of the flow of geothermal water in the discharge section suggest the existence of geothermal buoyancy. The changes in temperature, salinity and viscosity comprise the physical basis for the formation of geothermal buoyancy. Geothermal buoyancy due to free heat convection in a fault-controlled discharge section is discussed in the Xinzhou geothermal field, South China. The geothermal buoyancy is the additional pressure head created by the increase in temperature, increase in salinity and decrease in viscosity. At the convection point, geothermal buoyancy appears and forms a maximum of + 417.6 m. Geothermal buoyancy gradually decreases in the discharge section due to temperature domination. The salinity effect and viscosity effect on geothermal buoyancy are minor and negligible, respectively. Comparing the vertical velocity of geothermal water in the discharge section (32.47 × 10−3 m/d) and the average vertical circulation velocity (3.15 × 10−3 m/d), the geothermal buoyancy has an obvious acceleration effect on groundwater flow in the discharge section. The geothermal buoyancy at typical points provides the framework and control points for geothermal water flow in the discharge section of a geothermal system. [ABSTRACT FROM AUTHOR]

Shallow geothermal energy (SGE) is a renewable energy source that has the advantage of being low-cost, clean, and locally sourced compared to fossil fuels, and is thus significant for China to achieve its future goals of carbon peaking and carbon neutrality. However, determining how to improve the operational efficiency of SGE systems is a key factor in the sustainable development and utilization of geothermal energy. This study examined the long-term operational efficiency of SGE systems and applied numerical simulation methods of hydro-thermal coupling to a SGE utilization project in Shandong Province, China. The effect of the distribution of pumping and injection wells on the operation efficiency of the SGE system was analyzed, and the parameter of operation efficiency, defined by the ratio of the practical minable shallow geothermal energy to the theoretical shallow geothermal energy, was applied to quantify the operation efficiency of the SGE system. The simulated results show that the phenomenon of heat transfixion is significant in the current operation scheme, where one of three pumping wells is located downstream of the study area, which indicates that the local groundwater flow field mainly controls the operation efficiency of the SGE system. In the optimized operation scheme, the distribution of pumping and injection wells can be adjusted according to the feature of groundwater flow and temperature fields. The degree of heat transfixion significantly declines and the operation efficiency increases by 71.5%. In addition, further improvements in the operational efficiency of the SGE system can be considered through the running time. The findings of this paper will be useful for the construction and management of SGE systems. [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.)

Copyright of Environmental Science & Technology (10036504) is the property of Editorial Board of Environmental Science & Technology 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.)

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.)

Reservoir construction greatly affects the regional ecological environment, particularly surface water–groundwater interactions around the reservoir. Xiluodu Reservoir, a representative large‐scale reservoir in China, has had substantial impacts on surface water–groundwater interactions at the dam site since impoundment. This study analysed the dynamic characteristics of surface water–groundwater level, temperature, and hydrochemistry to determine the evolution of surface water–groundwater interaction before and after the impoundment. The levels of groundwater and some surface water rose by more than 100 m after impoundment and the water level of saturated limestone gradually stabilized, whereas basalt saturation in the affected area continued to expand. The groundwater temperature did not decrease significantly, whereas the hydrochemical types and ion contents of both surface water and groundwater experienced significant changes. Calculation of the saturation index indicated spatiotemporal changes in the saturation state of minerals. The replenishment source of each type of water and their mutual relationships were determined using cluster analysis and isotope characteristics. The results confirmed continuous, significant, and variable surface water–groundwater interactions at the dam site, which were partially reversed after impoundment. Changes in surface water–groundwater interactions were due to impoundment, the impact of which decreases with distance from the dam, as well as the unique geological conditions and artificial construction. [ABSTRACT FROM AUTHOR]

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office 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.)

Subterranean soil erosion is a common form of soil failure that is caused by groundwater seepage. In this paper, we present a subterranean soil erosion model ideally supposed as pipe flow with four conditions. By using the theories of pipe flow, its critical expressions are derived, including the critical flow quantity (Qcr), the critical velocity (Vcr), and the hydraulic gradient (Icr). A simulating experiment is designed to test Qcr to calculate the other critical values. In a case study, 14 clay samples from Guiyang, Guizhou, China, are tested via a simulation experiment. As a result, the critical shear stress of samples is found to be 32.01 Pa. Furthermore, three critical values of suffusion, including Qcr, Vcr and Icr, are calculated with different diameters of soil pores by using the critical expressions. Analyzing the relationship among the values shows that the pore diameter and groundwater temperature influence the critical hydraulic condition of subterranean soil erosion. [ABSTRACT FROM AUTHOR]

The Jizhong Depression is located in the western Bohai Bay Basin, eastern China. The deep strata are mainly composed of carbonate buried hill, and the shallow strata are a mainly siliciclastic deposition. In the present work, the Na-K-Mg triangle diagram and geothermometers were used to investigate the geochemical characteristics of shallow groundwater and reservoir temperature features of three geothermal reservoirs in the depression, including the Ordovician, the Cambrian, and the Precambrian Wumishan Formation. The results showed that the geothermal water in the depression could be divided into three groups: group I, Cl· HCO 3 -Na type; group II, Cl-Na type; and group III, Cl-Na·Ca type. By using the Na-K-Mg triangle diagram, group II and group III geothermal water samples were identified as the partially equilibrated water, whose temperature of the geothermal reservoir can be calculated based on the cation geothermometers. The ranges of the calculated temperature of the shallow strata and the deep strata are 91~146°C and 147~176°C, respectively. It has the good results obtained with some cation geothermometers in a geothermal system hosted in carbonate rocks like the studied area. The analysis workflow and calculation data obtained in this work contribute to the evaluation of the temperature field and the exploration and development of the geothermal resources in the Bohai Bay Basin. [ABSTRACT FROM AUTHOR]

A new significant aspect in the utilization of hydrothermal energy in China is the large-scale exploitation using multiwells from a single geothermal site. This requires detailed hydrogeochemical investigations to gain insight about deep groundwater circulation. At the Xiongxian karst geothermal site in North China, where the demonstration project of large-scale utilization was conducted, 40 boreholes with depths from 1000 to 1800 m were drilled in a region of 50 km2. A total of 25 water samples were collected, and temperature loggings were conducted in 16 of these wells. At the site scale, the hydraulic head was observed to decline from SW to NE, i.e., orthogonal to that at the regional scale. Moreover, the geothermal groundwater temperature, borehole temperature gradient, and heat flow in the caprock all exhibited the same spatial trend with the groundwater head. Based on the hydrogeochemical and temperature logging data, this was explained by mixing of lateral recharging groundwater with ascending thermal fluids through the Xiongxian Fault, after excluding the causes of pumping activities and geologic structure. In addition, geothermal groundwater 81Kr age was estimated to be approximately 760 k yr, which is much older than the 14C age of 20 to 30 k yr. The older 81Kr age implies a low renewability of deep groundwater circulation, which should be considered in terms of sustainable management in relation to the large-scale utilization of geothermal resources. [ABSTRACT FROM AUTHOR]

Over a hundred sizable lakes, some even larger than ~1 km2, are distributed across the lowlands between megadunes in the southeastern Badain Jaran Desert (BJD), northwest China. With rather limited precipitation and hardly any surface runoff, these lakes are fed mainly by groundwater. However, the source of the groundwater and the groundwater discharge rates to these lakes are poorly understood. Water level and temperature of four representative lakes in the southeastern BJD were monitored continuously between 2013 and 2017. Water surface evaporation and rainfall in this area were also measured. Combining these acquired data, groundwater discharge rates were estimated using water balance models. The results show that the four lakes have similar recharge and discharge patterns, but at different average net groundwater discharge rates ranging from 1.79 to 3.09 mm d−1. The lake level variation mainly depends on groundwater discharge and lake surface evaporation. We found that diurnal lake level variation may be controlled by earth tide and atmospheric pressure change, and is five times greater than the evaporation. The desert precipitation and deep confined groundwater with high temperature were found also recharging the desert lakes. An Empirical Mode Decomposition (EMD) method was used to identify the lake level trend. All lake levels increased over the last four years, except one decreased in 2015 and 2016. The lake levels' increasing trend is synchronously similar with the precipitation in north China. This study analyzes annual and seasonal lake level variations, and also finds the diurnal water cycle between the groundwater and lake water for the first time. [ABSTRACT FROM AUTHOR]

The adsorption–desorption processes of pymetrozine were investigated in three cultivated soils in China through a batch method. Pymetrozine was determined by high-performance liquid chromatography (HPLC). At a relatively low temperature, the adsorption of pymetrozine improved with increasing organic matter content, and the Freundlich model precisely illustrates the adsorption isotherms. The adsorption of pymetrozine was classified as physical, considering that the Gibbs free energy change values of this process in the three soils ranged from –21.195 kJ/mol to –23.956 kJ/mol. The ΔH value was –37.236 kJ/mol for soil A, –13.723 kJ/mol for soil B, and –9.154 kJ/mol for soil C, suggesting that the major interaction in the adsorption involved hydrogen bonds and that the adsorption of pymtrozine in the three soils was exothermic. Soil C was shown to have the highest hysteresis among the samples. The hysteresis was enhanced at high temperatures for soil B and soil C but reduced for soil A. Pymetrozine adsorption increased with decreasing temperature, suggesting that pymetrozine may infiltrate groundwater at high temperatures. [ABSTRACT FROM AUTHOR]

Various physical, geophysical, geochemical, electrical and hydrological parameters are measured on the surface and in shallow/deep boreholes throughout mainland China to obtain early warning signals of impending earthquakes. Numerous wells are equipped with water level and temperature sensors for continuous observations of the water level and groundwater temperature. An analysis of water temperature data from boreholes equipped with water temperature sensors reveals that nearly half of the boreholes show coseismic response associated with the Wenchuan earthquake (Mw 7.9, 12 May, 2008). The coseismic response of the groundwater temperature cannot be differentiated from the groundwater flow or movement when the earthquake occurred, but there is no fixed relationship between the temperature variation and the water flow. At the same time, we observed that the rock temperature in dry wells can record the seismic events and even the pre-seismic abnormal information. The spatial distribution of the coseismic groundwater temperature response is random and irregular, which does not support the dislocation model of seismic faults at the regional or larger scale. Changes in the groundwater temperature are closely related to the borehole temperature gradient, lithology profile and geological environment of the borehole and depths of the aquifers. The mechanism of the coseismic groundwater temperature response can be explained by an enhanced permeability induced by an earthquake. The groundwater temperature increases if the temperature sensor in the borehole is located near the deep-circulating aquifer and decreases if the sensor is near the shallow-circulating aquifer when seismic waves arrive. The groundwater temperature may be slightly affected or even unchanged if the temperature sensor is far from the aquifer during the propagation of seismic waves. However, it was hard to conclude the changes of rock temperature observed in six dry wells. [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.)

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.)

Characterizing the temporal variation of microbial community is essential to better understand the biogeochemical cycles in groundwater systems. So far, the roles of microbial metabolisms in affecting the seasonal variation of shallow groundwater biogeochemistry remains largely unknown. In this study, shallow groundwater was sampled during rainy season (RS) and dry season (DS) at Yuncheng Basin, a semi-arid region in northern China. Based on results of hydrogeochemical, environmental isotopic (δ18O, δ2H and δ13C) and high-throughput sequencing analysis, we found that 1) the seasonal variation of groundwater geochemistry is closely related to the stronger evaporation, mineral dissolution, and anthropogenic activities in DS and enhanced cation exchange and stronger recharge in RS; 2) the seasonal dynamics of microbial community were mostly driven by groundwater temperature (T) and total organic carbon (TOC); 3) potential functional consequences indicated stronger microbial carbon fixation and denitrification in RS; 4) the microbial contribution to SO 4 2− in groundwater may increase when gypsum dissolution was weaker while sulfur oxidation was stronger during RS. Our findings suggest that the seasonal variation of microbial metabolisms play important roles in the dynamic characteristics of groundwater geochemistry. [Display omitted] • Water-rock interaction and microbial activity drive groundwater chemistry variation. • The microbial community shows significant variation between rainy and dry seasons. • Temperature and TOC affect the seasonal dynamics of microorganisms in groundwater. • Carbon fixation, denitrification and sulfur oxidation were stronger in rainy season. [ABSTRACT FROM AUTHOR]

• An analytical solution of heat transfer in karst conduit was proposed. • Conduit structure and flow properties determine thermal equilibrium depth. • Insufficiently heat exchange results in temperature fluctuations in karst springs. • Event thermal response was verified by heat exchange and mixing function. Thermal responses of groundwater are useful signatures to reveal the recharge-discharge process and characterize aquifer structure in karst groundwater. Four karst springs with varying circulation depths ranging from ∼ 60 to 820 m in South China, were used to decipher the mechanism of heat exchange between recharge water and surrounding rock formations. An analytical solution of heat transfer in karst conduit was proposed to simulate the peak or trough temperatures of pulse flow. Hydraulic diameter, flow velocity, input temperature and circulation depth in karst aquifer, mainly depending on the recharge water volume after rainfall events, are important transport factors to control the thermal equilibrium depth and the efficiency of heat exchange that directly controls the behavior of warm peaks or cold troughs in groundwater temperature. In shallow karst aquifers wherein the circulation depth is less than its theoretical thermal equilibrium depth, the recharge water does not sufficiently exchange heat with the surrounding rocks, resulting in clear event-scale warm peaks in summer and cold troughs in winter. Otherwise, the recharge water will firstly reach a thermal equilibrium state and then mix with the warmer base flow at deeper location, which is verified in a karst spring with anomalous event-scale temperature drops after rainfall events all year around. The thermal response simulations obtained from this work provide new ways and insights to characterize geographic structure of karst aquifer and elucidate heat transfer mechanism in karst aquifer systems. [ABSTRACT FROM AUTHOR]

• H. ammodendron reduced optimal photosynthetic temperatures at deep groundwater depth. • H. ammodendron increase photochemical efficiencies at deep groundwater depth. • Photosynthesis rate and stomatal conductance were decouple at high twig temperature. • H. ammodendron changed twig size and biomass distribution at deep groundwater depth. Climate change and anthropogenic exploitation will increase groundwater lowering rates and aggravate groundwater shortage, particularly in desert ecosystems that rely heavily on groundwater. We conducted detailed studies about morphological and ecophysiological traits of two Haloxylon ammodendron communities across different groundwater depths in the Gurbantonggut Desert in China during an extreme drought period. When photosynthetic twig temperatures exceeded 45°C, photosynthesis was suppressed and dropped to zero, while stomatal conductance and transpiration rate increased rapidly. This decoupled behavior may cool photosynthetic tissues to prevent permanent damage. The optimum temperature decreased by ∼3°C in H. ammodendron at deep groundwater sites with less soil-water availability, which contributed to improving water use efficiency (WUE) at lower temperatures. H. ammodendron at the deep groundwater site had lower photosynthetic twig size and plant height while higher proportion of twig and branch biomass, which induced a denser canopy structure, and they had greater leaf dry mass content, photosynthetic pigments, and non-structural carbohydrates, and more negative predawn shoot water potential. Overall, our study indicates that H. ammodendron could alleviate adverse effects of reduced soil water availability and maintain photosynthetic capacity through multiple morphological and physiological adjustments. This establishes the basis for predicting responses of desert shrubs to groundwater drawdown. [ABSTRACT FROM AUTHOR]

• High arsenic in groundwater was generally related to high Na+ and low Ca2+. • The middle-Pliocene aquifer sediments had low contents of water-soluble Ca and SIC. • Endogenic CO 2 was responsible for silicate weathering in middle-Pliocene aquifer. • Silicates weathering in middle-Pliocene aquifer released arsenic into groundwater. • High temperature promoted arsenic desorption and weathering of silicates. High arsenic (As) groundwater in reduced shallow Holocene and Pleistocene aquifers has been intensively investigated, but the occurrence and the genesis mechanisms of high As groundwater in deep Pliocene aquifers affected by geothermal activity still remain unclear. To address these issues, geochemical characteristics of groundwater and aquifer sediments in both middle-Pliocene aquifers and Quaternary aquifers of the Guide basin were investigated to clarify groundwater-sediments interaction and the causes of As enrichment in groundwater from middle-Pliocene aquifer. Higher As and Na+ concentrations were observed in groundwater from middle-Pliocene aquifer (GPA) than those in groundwater from Quaternary aquifer (GQA), while GPA had lower Ca2+ concentrations than GQA. Results showed that middle-Pliocene aquifer sediments had low contents of carbonate minerals, and water-soluble Ca-bearing minerals relative to Quaternary aquifer sediments, which explain higher concentration of Ca2+ in GQA than in GPA. Na+ from weathering of silicates (i.e. (Na+)*), being calculated based on mass balance, accounted for high proportion of dissolved Na+ (up to 68%) in GPA. Weathering of silicates was related to As accumulation in GPA, which was proved by a positive correlation between As and (Na+)* in GPA, and high proportion of As bound to unweathered silicates (up to 65.7%) in middle-Pliocene aquifer sediments. The weathering of silicate minerals directly released As bound to silicates into GPA, and indirectly led to As desorption from solid surfaces by increasing pH, HCO 3 – and CO 3 2–. Both (Na+)* and As in groundwater increased with the increasing groundwater temperature, showing that high temperature was conducive to weathering of silicates and As enrichment. This paper establishes a bridge between high groundwater temperature and high As concentration with weathering of silicates in aquifers. [ABSTRACT FROM AUTHOR]

456 water samples collected from 152 water sources in 2006 were analyzed for 21 volatile organic compounds (VOCs). Concentrations of 21 VOCs ranged from below method detection limits of the laboratory to 7.65 μg/L (toluene), but seldom exceeded the concentration limits set in the National Drinking Water Quality Standards (GB5749-2006) or the National Environmental Quality Standards for Surface Water (GB3838-2002) of China. Of the 21 individual VOCs analyzed, 11 VOCs were detected in at least one sample at or above 1.0 μg/L; 6.6% of the water samples had a detection of at least one VOC at or above 1.0 μg/L, and 2.6% had a detection of at least two VOCs at or above 1.0 μg/L. Based on the statistical data of detection frequencies above the method detection limits, 75% of the samples detected at least one VOC, and 65% of the samples detected at least two VOCs. Chloroform, toluene, and 1,2-dichloroethene were the three most frequently detected VOCs, with detection frequencies of 76.97%, 68.42%, and 44.08%, respectively. Volatile halogenated hydrocarbons and gasoline components were the two most frequently detected VOC groups. [ABSTRACT FROM AUTHOR]

Abstract: The well-known temperature dependence of noble gas solubilities in water enables the determination of absolute paleotemperature records from radiocarbon dated groundwater. An advantage of the noble gas paleothermometer is that noble gas temperatures (NGTs) can directly be related to stable isotope ratios from the same groundwater archive in order to calibrate the stable isotope thermometer over long time scales. Our record from heavily used aquifers of the North China Plain constitutes a unique combined NGT and stable isotope data set from the region affected by the East Asian monsoon. In addition to providing a reliable estimate for the glacial–interglacial temperature change, the data enable the separation of the effects of temperature and precipitation (monsoon strength) on the stable isotopes. Although the record extends from modern waters to near the limit of the radiocarbon dating range at about 40 kyr BP, the last glacial maximum is not represented, probably because arid conditions limited groundwater recharge during that period. The coldest observed period at about 30 kyr BP was 4.6±1.2 °C cooler than the Holocene. Whereas NGTs show no systematic variation during the Holocene, the δ 18O-values increased by about 1‰ between the early and late Holocene. A similar increase of δ 18O has been observed before in speleothems and ascribed to decreasing monsoon strength in response to decreasing insolation during the Holocene. Our results confirm that the Holocene trend in stable isotopes is not related to temperature. In contrast, δ 18O and NGT are correlated within the Pleistocene group of samples, indicating a δ 18O-NGT slope of 0.18±0.05‰ °C−1, similar to the temperature effect in modern precipitation of the region. Thus, of the overall increase of δ 18O by about 2‰ between 30 kyr BP and the late Holocene, about half is due to a temperature increase, whereas the other half is due to a decrease of monsoon strength. [Copyright &y& Elsevier]

Doublet well system composed by extraction and injection wells is widely used for heat production from deep geothermal reservoirs. The large-scale implementation of doublet well systems lead to hydro-thermal interaction with the natural hydro-thermal flow system; this affects heat production efficiency and sustainable management of geothermal energy and groundwater resources. However, the interaction between artificial operations and nature hydro-thermal status was seldom considered in the well placement optimization. In this study, the natural status of hydro-thermal flow was determined by fitting numerical modeling output to the groundwater level and temperature observations, in a realistic site of the Gonghe Basin, China. The well separation and relative position were then optimized against background water flow direction. It was found that a well separation of 1200 m with the injection well located upstream (south) to the extraction well can maximize the volume of injected water entering extraction well, without influence on the outflow temperature. Based on this finding, we further compared the effects of "extensive well placement" where the wells were located sparsely in entire geothermal field, and "intensive well placement" where the wells were located centrally in a local region. The calculation showed that the performance of intensive well placement was superior to extensive well placement with higher outflow temperature and lower interruption in groundwater levels. Further optimization of intensive well placement resulted in the outflow temperature higher than 92 °C under the total outflow rate of 30,000 m3/d for 30 years, and the groundwater level changes can be controlled below 6.0 m. The multiple-step well placement optimization approach and novel intensive heat production mode regarding nature status of hydro-thermal flow in geothermal reservoirs, provides important reference to the other geothermal field for large-scale geothermal exploitation. • An intensive heat production mode was established for sustainable geothermal energy production. • Heat production system was optimized considering background water flow in reservoirs. • Application in Gonghe, China resulted in outflow temperature >90 °C under water level change <6.0 m. [ABSTRACT FROM AUTHOR]

• Polycyclic aromatic and polyphenols and As were co-mobilized in confined aquifer. • Groundwater pH and temperature increased along the flow path in confined aquifer. • High pH and temperature mobilized the polycyclic aromatics and polyphenols. • The mobilized recalcitrant organic compounds were likely conducive to As release. Organic matter (OM) has been accepted as an important trigger fueling Fe(III) oxide reduction and arsenic release in the late Pleistocene-Holocene anoxic aquifers, whereas its fates and roles on arsenic mobility in the Pliocene aquifer are unclear. To fill this gap, groundwaters from a confined Pliocene aquifer (CG) and an unconfined Holocene aquifer (UG) were sampled in the Guide Basin, China, to monitor evolutions of groundwater geochemistry and OM molecular signatures along the groundwater flow path. The outcomes showed that groundwater pH, temperature, and arsenic concentrations in the CG samples generally increased along the groundwater flow path, which were much higher than those in the UG samples. The numbers and intensities of recalcitrant molecules (polycyclic aromatics and polyphenols) in the CG samples remarkably increased along the path, but relatively labile molecules (highly unsaturated and phenolic compounds and aliphatic compounds) showed the opposite trends. The arsenic-poor (<10 μg/L) UG samples contained more labile molecules than the arsenic-rich CG samples. High groundwater pH, temperature, and sediment age in the confined aquifers may be responsible for the selective mobilization of the unique polycyclic aromatics and polyphenols. The mobilized recalcitrant organic molecules may enhance arsenic release via electron shuttling, complexation, and competition. Furthermore, high temperature and pH may also facilitate arsenic desorption. The study provides molecular-scale evidences that the mobilization of recalcitrant organic molecules and arsenic were concurrent in the geothermal confined groundwater. [Display omitted] [ABSTRACT FROM AUTHOR]

Water samples from rainfall, river, springs, and wells in the Xianshui River fault region near Xialatuo, China were collected during two sampling campaigns to investigate the complex groundwater circulation in the region. The major ions, stable isotopes, and four natural radium isotopes of the water samples were analyzed, and the results were utilized to identify different groundwater circulation depths. Most water samples excluding the one at a hot spring and the one at a borehole possess similar hydrochemical compositions and lower total dissolved solids (TDS), implying that their circulation depth is relatively shallow or that residence time is short. The sample at the hot spring has high TDS and high temperature as well as the high F concentration, inferring that it may circulate at a deeper depth. The sample at the borehole contains mixed hydrochemical characteristics of other samples. Three groundwater flow systems may exist in the study area: the shallow groundwater system recharged by precipitations and local groundwater flow, the deep groundwater system recharged by the regional groundwater flow, and the intermediate one between the above two systems. The finding of the three flow systems is supported by the δ2H and δ18O as well as the apparent radium ages of the samples. The δ2H and δ18O values at the intercept of the line formed by the shallow groundwater samples and the local meteoric water line (LMWL) are similar to those of modern precipitations. The δ2H and δ18O values at the intercept of the line formed by the deep groundwater samples and the LMWL show that it is probably recharged by relatively older precipitations. The 2H and 18O values of the borehole samples are between the above two intercept points. The deep-circulated groundwater with high temperature has longer apparent radium age than other water samples. The apparent radium ages of the shallow groundwater are similar but less than that of the deep groundwater. Groundwater at the borehole may circulate at a depth between the above two. The results of this study improve our understanding of the complex groundwater circulation and enable us to better protect and manage the groundwater resources in the region. [ABSTRACT FROM AUTHOR]

Long-term tree growth is significantly affected by climate change, which have become a global concern. Tree-ring width and isotopic information can show how trees respond to climate change on a long-term scale and reveal some phenomena of tree decline or death. In this study, we used isotopic techniques and investigated annual changes in carbon isotope composition and tree-ring width of Populus simonii Carr. in Zhangbei, as well as trends in tree-ring carbon discrimination (Δ13C) and iWUE in normal, mildly declining and severely declining trees, in order to make a retrospective analysis and further understand the process of tree decline. We found that there were significant differences (p < 0.01 **) in δ13C, Δ13C, ci and iWUE at different decline stages, meaning that the δ13C and iWUE could be new indicators of tree health. The iWUE of all groups increased significantly, while the growth rate of declined P. simonii was much higher than that of normal growth P. simonii. According to the analysis, there may be a threshold of iWUE for healthy trees, which once the threshold value is exceeded, it indicates that trees are resistant to adversity and their growth is under stress. Similarly, the changing trend of BAI supports our conclusion with its changes showed that tree growth became slower and slower as degradation progressed. iWUE inferred from tree-ring stable carbon isotope composition is a strong modulator of adaptation capacity in response to environmental stressors under climate change. Elevated annual temperatures and increased groundwater depth are all contributing to the decline of P. simonii in north China. [ABSTRACT FROM AUTHOR]

Groundwater heat pump (GWHP) systems are central heating and cooling systems that utilize groundwater heat. With the rapid development of this technology in China, it has become imperative to study the changes in the ground environment, including the flow features, heat transfer characteristics and clogging caused by long-term recharge, during the operation of GWHP systems. In this paper, a mathematical model considering the effect of particle deposition was proposed to describe a GWHP system based on the typical geological and hydrogeological conditions (i.e., a dual-structure strata) in Wuhan, China. During research on a GWHP engineering project in the Baibuting Garden community, four groundwater flow conditions (including no flow, forward flow, reverse flow and cross flow) and two typical flow modes (continuous and flushing modes) were considered. The groundwater temperature and flow rate were measured through measuring wells, and a comparison between theoretical and actual values shows that this model can provide an easy yet effective way to describe GWHP engineering. The seepage and temperature fields both display periodic trends under the continuous flow mode and can be significantly affected by well flushing. The central area is marginally influenced by groundwater flow when compared with the surrounding areas; for instance, the temperature fluctuation at MW3 can reach 8.2 °C, while the fluctuation reaches 2.9 °C at MW1. Particle deposition can affect the parameters of the ground environment; we find considerable correspondence between the concentration of deposited particles and the porosity. Moreover, both the concentration of deposited particles and the porosity change by a large margin after flushing, especially in regions around pumping wells (the concentration of deposited particles can fluctuate by 108 g/L, and the porosity can change by 0.055). [ABSTRACT FROM AUTHOR]

Pathogenic bacteria are frequently detected in groundwater. However, little is known about the abundance and diversity of potentially pathogenic bacteria and their influencing factors in the groundwater of the Jianghan Plain (JHP), one of the most densely habited areas in central China. Here, we investigated the diversity and abundance of potentially pathogenic bacteria in 156 groundwater samples collected from one 400 km2 area of the JHP by using 16S rRNA-based Illumina sequencing and quantitative PCR. A total of 193 potentially pathogenic bacterial species were identified in the studied groundwater. Phylogenetic results showed that opportunistic pathogenic Acinetobacter baumannii -like and enteric pathogenic Vibrio cholerae -like bacteria were most prevalent, occurring in 99% and 32% of the studied groundwater samples, respectively. Spatial factors contributed more (5.5% vs 2.4%) than the measured environmental factors to shaping of the potentially pathogenic bacterial distribution, although a large proportion (92.0%) of variation was unexplained. The groundwater temperature was the most important measured factor influencing the abundances of the identified potentially pathogenic bacterial species. In addition, certain opportunistic pathogenic bacterial species showed statistically significant co-occurrence in the studied JHP groundwater samples. Collectively, this data of this study provide new insight into the diversity, distribution and influencing factors of potential pathogens in the JHP groundwater. • Potentially pathogenic bacteria were abundant and diverse in the Jianghan Plain groundwater. • Most of the potentially pathogenic bacteria appeared to be opportunistic pathogens. • Spatial and environmental factors affect the potentially pathogenic bacteria distribution. • Some of the potentially pathogenic bacteria showed co-occurring pattern. [ABSTRACT FROM AUTHOR]

Hot springs occurring in two plunging ends of a very long and narrow anticline is unique. This study focuses on the hydrogeochemical characteristics and formation of the anticline-controlled thermal groundwater which may provide a perspective for geothermal resources potential. The low-to-middle temperature thermal groundwater of the Taozidang anticline in the Sichuan Basin, China, was examined to estimate the temperature of the deep reservoir and identify the main hydrogeochemical processes affecting the composition of hot water during circulation and evolution. The occurrences of thermal groundwater of these springs strongly controlled by anticline are in the two plunging ends of the anticline and differ from that of the more common deep-fault circulation controlled by faults or by faults and anticlines. Incongruent dissolution of the gypsum or anhydrite of the Lower Triassic Jialingjiang and Middle Triassic Leikoupo Groups is affected by the anticline structures and results in hot water of SO4–Ca type. Meteoric water infiltrates through the karst channels and fissures at the outcropping area of carbonates to feed the groundwater. Part of the groundwater flows to depth and circulate along the two flanks of the anticline after heated. It issues in the form of hot springs or wells in the plunging ends of the anticline. Another part of the groundwater undergoing a shallow circulation forms the normal temperature spring near the hot springs. This study of the anticline-controlled thermal groundwater is important for exploitation and utilization of geothermal energy (tourism) and provides a perspective for the anticline-controlled geothermal resources potential. [ABSTRACT FROM AUTHOR]

The effect of spring snowmelt infiltration in a seasonal soil frost area on groundwater recharge was evaluated by systematically monitoring meteorological factors, soil temperature and humidity, groundwater table and temperature, electrical conductivity, and the value of δ18O in a small field site over a 2-year period. The variation of soil temperature and humidity, groundwater table during the freezing period, and the snowmelt period respectively, as well as their correspondence to the relevant environmental factors, and the influencing factors of the permeability of frozen layer were analyzed. The results showed that the evaluation of precipitation infiltration in seasonal soil frost areas should be divided into three stages: a non-freezing period, a freezing period, and a snowmelt period. Snow is the main form of precipitation during the freezing period, and groundwater cannot be recharged. During the snowmelt period of spring, the snow cover that accumulated during the freezing period infiltrates together with rainfall and has a significant effect on groundwater recharge. The general precipitation infiltration process occurs after the frozen soil thaws completely. These research results can improve the accuracy of groundwater recharge calculations for snowmelt infiltration in the seasonal soil frost area of Northeast China and provide a scientific basis for the evaluation and management of regional water resources. [ABSTRACT FROM AUTHOR]

The temperature of geothermal reservoirs is the key factor influencing the exploration and development of geothermal resources. It is an effective method for evaluating the feasibility of commercial exploration and development of the geothermal reservoirs to predict the temperature of deep geothermal reservoirs using the analyzed macroelements of shallow groundwater. The Jizhong Depression is located in the western Bohai Bay Basin, eastern China. The deep strata is mainly composed of carbonate buried hill and the shallow strata is mainly siliciclastic deposition. In the present work, we investigated the geochemical characteristics of shallow groundwater and reservoir temperature features of three geothermal reservoirs in the Jizhong Depression, including the Ordovician, the Cambrian, and the Precambrian Wumishan Formation, using the Giaggenbach diagram and geothermometers. The results showed that the underground water in Jizhong Depression can be divided into three types: type I, Cl·HCO3-Na groundwater; type II, Cl-Na groundwater; type III, Cl-Na·Ca groundwater. By using the Giaggenbach diagram, type II and type III groundwater was identified as the partially equilibrated waters, whose geothermal reservoir temperature can be calculated based on the cationic geothermometers. On the basis of the features of ion adjustment in the circulation of groundwater, the geothermal reservoir temperature in the shallow strata was determined by the K-Mg geothermometer, the geothermal reservoir temperature in the deep strata was calculated using the Na-K geothermometer. Moreover, some special water samples with high Ca2+ concentration was estimated by the Na-K-Ca geothermometer in our conducted analyses. The ranges of the calculated temperature of the shallow strata and the deep strata are 119-146 ºC and 151-172 ºC, respectively. In order to verify the accuracy of the predictions, the results of the shallow geothermal reservoir temperature were compared with the temperature from the drilling test. The agreement between the predicted and drilling results was encouraging. The analysis workflow and calculation data obtained in this work are contribute to the evaluation of the temperature field and the exploration and development of the geothermal resources in the Bohai Bay Basin. [ABSTRACT FROM AUTHOR]

The article studies the detection of the leakage passage of leachate in a waste landfill dam. The leachate of waste landfill has its own features, like high conductivity, high chroma and an increasing temperature, also, the horizontal flow velocity of groundwater on the leakage site increases. This article proposes a comprehensive tracing method to identify the leakage site of an impermeable membrane by using these features. This method has been applied to determine two leakage sites of the Yahu municipal solid waste landfill site in Pingshan District, Shenzhen, China, which shows that there are two leachate leakage passages in the waste landfill dam A between NZK-2 and NZK-3, and between NZK-6 and NZK-7., (© The Author(s) 2015.)