[Hydrochemical Characteristics and Control Factors of Shallow Groundwater in Anqing Section of the Yangtze River Basin]

Shallow groundwater is the main source of water for living and industrial and agricultural production in Anqing City, which is an important basic guarantee to maintain the sustainable development of the social economy and regional ecological environment. In order to further study the water chemical characteristics and controlling factors of shallow groundwater in Anqing City, 196 groups of shallow groundwater samples were collected. A Piper diagram graph, Gibbs chart, ion ratio, and mathematical statistics were comprehensively used to study the water chemical characteristics and controlling factors of groundwater in Anqing City, and the contribution of different sources to the water chemical components of groundwater was quantitatively evaluated. The results showed that the shallow groundwater in Anqing City was weakly alkaline, with pH values ranging from 5.84 to 8.38, with an average value of 7.21. The TDS ranged from 47 to 1 620 mg·L-1, with an average of 324.21 mg·L-1. HCO3- and Ca2+ were the main anions, and the water chemical type was HCO3-Ca type. The chemical components of groundwater were affected by rock weathering leaching, cation alternating adsorption, mineral dissolution and precipitation, and human activities. Ca2+, Mg2+, and HCO3- were mainly derived from the weathering dissolution of carbonate and silicate; Na+, Cl-, and SO42- were affected by industrial activities and domestic sewage discharge; and K+ and NO3- were affected by agricultural activities. The APCS-MLR receptor model analysis further revealed that the chemical components of groundwater were mainly geological factors, industrial factors, agricultural factors, and unknown sources, and their contribution rates were 45.35%, 14.19%, 25.38%, and 15.08%, respectively. Geological factors were important sources of hydrochemical components of shallow groundwater, and human activities aggravated the evolution of groundwater hydrochemistry.

[Hydrochemical Characteristics and Control Factors of Surface Water and Groundwater in Huainan Coal Mine Area]

To clarify the hydrochemical characteristics and control factors of surface and underground water in Huainan mining area, 115 groups of groundwater and 30 groups of surface water samples were collected, and the hydrogeochemical characteristics of surface water and groundwater in Huainan mining area were analyzed. Additionally, the hydrochemistry evolution law was discussed by comprehensively using mathematical statistics, the Piper triangular diagram, Gibbs diagram, mineral stability field diagram, and ion ratio relationship, etc. The results showed that the groundwater and surface water in the study area were weakly alkaline, the dominant anion was HCO3-, and the dominant cations were Ca+ and Na+. The hydrochemical types of groundwater and surface water were dominated by HCO3-Ca type and HCO3-Ca·Na·Mg type, respectively. The hydrochemical composition of groundwater and surface water was mainly controlled by rock weathering, as well as by alternating adsorption of cations and evaporation concentration. Silicate and carbonate minerals were mainly dissolved in the water-rock interaction. The main ions such as Ca2+, Mg2+, and HCO3- came from the dissolution of carbonate rocks. The Cl-, SO42-, NO3-, and Ca2+ were affected by exogenous inputs caused by human activities. The chemical components of groundwater and surface water in Huainan coal mining area were affected by water-rock interactions and human activities, and groundwater was greatly affected by human activities.

Experimental investigation on chemical clogging mechanism of loose porous media in recharge process of groundwater heat pump

Groundwater heat pumps (GWHP) are an efficient utilisation of shallow geothermal energy technology and of great significance in terms of promoting energy conservation and reducing emissions. However, recharge clogging has been a key problem restricting the continuous operation of GWHP. In this study, a simulation test device for sand column was designed with the aim of addressing chemical clogging induced by heat pump reinjection in a porous saline aquifer in the Huaibei Plain, China. The trend in the variation of the permeability coefficient was studied based on the detection of the sand sample composition, recharge water quality, and sand layer temperature, and the cause of formation was analysed using the saturation index (SI) and ion ratio method. The results indicated that the permeability coefficient in the sand column decreased exponentially, with a maximum and minimum decrease of 8.14% and 71.65% of the original coefficient, respectively, found in sections P2-P3 and P8-P9. Therefore, the clogging effect of the aquifer at approximately 200-400 mm from the recharge well was significant. Water-rock interactions predominantly involved the dissolution of halite, albite, chlorite, anhydrite, and dolomite and the precipitation of calcite, as well as the exchange adsorption of Ca²⁺ and Mg²⁺ to Na⁺, which were the key sources of ions during the water chemical evolution process. Finally, quartz was formed by the weathering and dissolution of aluminosilicate minerals such as albite, and particle migration and precipitation during the hydrodynamic disturbance were the primary causes of the front-end blockage of the column.

Groundwater geochemical signatures and implication for sustainable development in a typical endorheic watershed on Tibetan plateau

Groundwater resource is significantly important for sustainable development of the world, especially for arid endorheic watersheds. A total of 28 groundwaters were collected for hydrogeochemical analysis from the arid Chaka watershed on Tibetan plateau to illustrate the hydrochemical evolution, formation mechanisms and feasibility of groundwater in small arid endorheic watersheds where groundwater is much scarcer. The results showed groundwater has a slightly alkaline nature, and varies from soft fresh HCO₃-Ca type to hard brackish/saline Cl-Na type along the groundwater flow path in the watershed with the total hardness in the range of 270-2,127 mg/L and the total dissolved solids in the range of 282-41,770 mg/L. Nitrogen and fluoride in phreatic water are found sporadically exceeding the permissible limits with the maximum value of 118 mg/L for nitrate, 1.2 mg/L for ammonia and 1.2 mg/L for fluoride. Hydrochemistry of phreatic and confined groundwater is naturally governed by water-rock interactions including minerals (halite, gypsum and anhydrite) dissolution, silicate weathering and cation-exchange reaction. The salinity of phreatic water is also dominantly controlled by the strong evaporation. Human activity is one of the important mechanisms influencing the hydrochemical signature of groundwater regardless of the depth. Groundwater has a great hydrogeochemical discrepancy spatially across the watershed and varies from excellent to extremely poor quality in phreatic aquifers. A better water quality that under the good to medium categories was observed in the confined aquifers with 80% of samples having the EWQI value less than 100 and others in the range of 100-150. Phreatic groundwater away from the river and in the downstream area has a relatively poor quality for domestic and agricultural purposes, and should be avoided to direct utilization. This research can improve the understanding of groundwater hydrogeochemical feature, genesis, and its constraints on the availability and feasibility of groundwater resources in small arid watersheds worldwide.

Deterioration and Oxidation Characteristics of Black Shale under Immersion and Its Impact on the Strength of Concrete

Black shale, which usually contains pyrite, is easily oxidized and generates acid discharge. This acidic environment is not favorable for concrete in engineering applications and is likely to affect the durability of engineering structures. This study investigated the effect of acid discharge from the weathering of black shale on the strength of concrete under partially immersed conditions. Black shale concrete immersion tests were conducted at different immersion depths to evaluate the oxidation conduction of black shale. Water chemistry and oxidation products were monitored during and after the immersion tests. The quality and strength of the black shale and concrete specimens were obtained before and after the immersion by testing the ultrasonic wave velocity and uniaxial compressive strength. The results indicated that a lower immersion depth of black shale reveals a higher degree of oxidation, and the capillary zone in black shale is critical for black shale oxidation in terms of mass transfer. The ultrasonic velocity of the concrete showed different change patterns in the immersed and non-immersed zones. Precipitation and additional hydration enhanced the quality and entirety of the concrete (increased ultrasonic velocity) at the non-immersed or partially-immersed zones, while the dissolution of concrete was dominant in the immersed zone (decreased ultrasonic velocity) and induced a reduction of concrete quality. The compressive strength of the concrete was enhanced after immersion. The concrete strength slightly increased by 5-15%. This phenomenon is attributed to the filling of the voids by the precipitations of minerals, such as goethite and anhydrite.

Hydrogeochemical Characteristics and Conceptual Model of the Geothermal Waters in the Xianshuihe Fault Zone, Southwestern China

Abundant geothermal waters have been reported in the Yalabamei, Zhonggu, Erdaoqiao, and Yulingong geothermal areas of the Xianshuihe Fault Zone of western Sichuan, southwestern China. This study focused on the hydrogeochemical evolution, reservoir temperature, and recharge origin of geothermal waters using hydrochemical and deuterium-oxygen (D-O) isotopic studies. Shallow geothermal waters represented by geothermal springs and shallow drilled water wells are divided into two hydrochemical groups: (1) the Ca–Na–HCO₃ type in the Erdaoqiao area, and (2) Na–HCO₃ in other areas. Deep geothermal waters represented by deep drilled wells are characterized by the Na–Cl–HCO₃ type. The major ionic compositions of geothermal water are primarily determined by the water–rock interaction with silicate and carbonate minerals. The reservoir temperatures estimated by multi-geothermometries have a range of 63–150 °C for shallow geothermal water and of 190–210 °C for deep geothermal water, respectively. The δ¹⁸O and δD compositions indicated geothermal waters are recharged by meteoric water from the elevation of 2923–5162 m. Based on the aforementioned analyses above, a conceptual model was constructed for the geothermal system in the Xianshuihe fault zone.

[Indicators of Groundwater Evolution Processes Based on Hydrochemistry and Environmental Isotopes: A Case Study of the Dongyuan Drinking Water Source Area in Ji'nan City]

The Dongyuan groundwater source area, which is the main drinking water source of Ji'nan City, is karst fissure water. To identify groundwater recharge sources, the influence of surface water, hydrochemical evolution, hydrochemical and isotopic components (²H and ¹⁸O) of groundwater and surface water samples collected from the Dongyuan groundwater source were investigated.The results showed that the hydrochemical characteristics of groundwater were similar, and the main ions were Ca²⁺, HCO₃^-, and SO₄^2-. The groundwater, which suffered evaporation to varying degrees, was recharged mainly by precipitation. The hydrochemical composition of regional groundwater is mainly controlled by water-rock interactions, including dissolution/precipitation of carbonate minerals in the limestone aquifers and hydrolysis of silicates minerals in the quaternary aquifers, above the limestone aquifers. In some areas, groundwater was polluted by infiltration of river water. The main indicators of groundwater pollution that exceeded groundwater quality standards were total hardness, NO₃^-, NH₄⁺, SO₄^2-, Fe, and Mn.

[Impact of Human Activities on Water-Rock Interactions in Surface Water of Lijiang River]

The influence of human activities on karst surface water quality has received increasing attention. To explore the impact of human activities on water-rock interactions in karst surface water, water samples were collected from July to November in 2016 in the Lijiang River, which is dominated by human activities. The samples were analyzed for the hydrochemistryand the characteristics of δ¹³C_DIC. The results show that:①The Lijiang River is mainly characterized by HCO₃-Ca chemical composition.. The SO₄^2- and NO₃^- concentrations are inferior to HCO₃^- concentrations in the anion composition; besides, the concentrations of SO₄^2- and NO₃^- in the river between Guilin and Yangshuo are higher than in the other sampling sites, caused by tourism and urban development. ②Equivalent ratios of[Ca²⁺+Mg²⁺]/[HCO₃^-] are between 1.01 and 1.51 and the equivalent ratios of[Ca²⁺+Mg²⁺]/[SO₄^2-+NO₃^-+HCO₃^-] are between 0.85 and 1.12, indicating that the sulfuric acid and nitric acid have participated in the water-rock interaction. ③The proportions of carbonic acid dissolving carbonate rocks range from 32.10%-98.01% with an average of 75.89%. The proportions of sulfuric acid and nitric acid dissolving carbonate rocks vary from 1.99%-67.90% with an average of 24.11%. The proportions of sulfuric acid and nitric acid dissolving carbonate rocks in the rainy period with an average of 24.31% is higher than in the brief rain period with an average of 23.88%. In addition, the proportions of sulfuric acid and nitric acid dissolving carbonate rocks present a fluctuated increasing trend from upstream to downstream and the maximum strength and the minimum strength of the sulfuric and nitric acid dissolving carbonate rocks occur in Lingchuan and Huajiang, respectively. ④ HCO₃^- mainly originated from the carbonate rocks dissolved by carbonic acid, with an average of 83.58%, followed by the carbonate rocks dissolved by sulfuric acid and nitric acid, with an average of 14.24%. The contribution of carbonic acid weathering silicate rocks is the smallest with an average of 2.18%. ⑤ δ¹³C_DIC of the Lijiang River ranges from -11.95‰--7.61‰; the calculated δ¹³C_DIC-rock using the mixture endmember model ranges from -14.24‰--7.23‰. δ¹³C_DIC is close to δ¹³C_DIC-rock in the rainy period and δ¹³C_DIC is significantly higher than δ¹³C_DIC-rock in the brief rain period. The difference between δ¹³C_DIC and δ¹³C_DIC-rock is caused by the influence of aquatic photosynthetic organisms.

Nitrate pollution of groundwater; all right…, but nothing else?

Contamination from agricultural sources and, in particular, nitrate pollution, is one of the main concerns in groundwater management. However, this type of pollution entails the entrance of other substances into the aquifer, as well as it may promote other processes. In this study, we deal with hydrochemical and isotopic analysis of groundwater samples from four distinct zones in Catalonia (NE Spain), which include 5 different aquifer types, to investigate the influence of fertilization on the overall hydrochemical composition of groundwater. Results indicate that intense fertilizer application, causing high nitrate pollution in aquifers, also homogenize the contents of the major dissolved ions (i.e.; Cl(-), SO4(2-), Ca(2+), Na(+), K(+), and Mg(2+)). Thus, when groundwater in igneous and sedimentary aquifers is compared, significant differences are observed under natural conditions for Cl(-), Na(+) and Ca(2+) (with p-values ranging from <0.001 to 0.038), and when high nitrate concentrations occur, these differences are reduced (most p-values ranged between 0.054 and 0.978). Moreover, positive linear relationships between nitrate and some ions are found indicating the magnitude of the fertilization impact on groundwater hydrochemistry (with R(2) values of 0.490, 0.609 and 0.470, for SO4(2-), Ca(2+) and Cl(-), respectively). Nevertheless, the increasing concentration of specific ions is not only attributed to agricultural pollution, but to their enhancing effect upon the biogeochemical processes that control water-rock interactions. Such results raise awareness that these processes should be evaluated in advance in order to assess an adequate groundwater resources management.