Hydrochemical characteristics and genetic mechanism of porous sandstone geothermal water in northern Jinan, Shandong, China.

Porous sandstone geothermal water is an important geothermal resource, which is a low-carbon and clean resource, but lacks systematic research on a regional scale. The northern part of Jinan City is rich in geothermal resources, specifically porous sandstone thermal reservoirs. However, there is still incomplete research on the mechanism of geothermal genesis and the hydrochemical characteristics of geothermal water in porous sandstone. This study aims to address this gap by collecting 21 groundwater samples from northern Jinan and comparing their conventional ion and isotope characteristics to investigate the hydrochemical characteristics during the formation of geothermal water and uncover the genesis mechanism of porous sandstone geothermal water. The results indicate that the geothermal water is classified as Na-Cl type and Na-SO4-Cl type. The hydrochemical characteristics of geothermal water are primarily influenced by water-rock interaction and groundwater mixing. The water source primarily comes from the atmospheric precipitation in the Taiyi mountains, with an altitude of 910.75-1542.2 m.s.a.l.. The estimated temperature of the thermal reservoir ranges from 51 to 78 °C, and the depth of geothermal water circulation is estimated to be between 1316 and 2216 m. Based on the characteristics of the geothermal field, including the "cap rock, water source, heat source, reservoir, and channel," a conceptual model of the porous sandstone geothermal water flow system is proposed. This model offers novel insights into the genesis mechanism of geothermal water under similar geological conditions.

Modeling and assessing the impacts of climate change on groundwater recharge in endorheic basins of Northwest China.

Climate change imposing additional stressors on groundwater resources globally, thereby predicting groundwater recharge (GR) changes is crucial to sustainably managing water resources, especially in the arid endorheic basins. Groundwater in the Endorheic Basins of Northwest China (NWEB) is potentially impacting regional socio-economic output and ecosystem stability due to the imbalance between supply and extraction exacerbated by climate change. Hence, recognizing the impacts of climate change on past and future GR is imperative for groundwater supply and sustainable groundwater management in the NWEB. Here, the impact of historical (1971-2020) and projected (2021-2100) climate changes on GR across the entire NWEB and three distinctive landscape regions (i.e., mountainous, oasis, and desert) were assessed. A coupled distributed hydrologic model (CWatM-HBV model), which integrates the Community Water Model (CWatM) and the HBV model, was run with three shared socioeconomic pathways (SSP1-2.6, SSP2-4.5, and SSP3-7.0) forcing from 10 general circulation models (GCMs) to simulate and analyze the interannual and seasonal variations of GR, along with their driving factors. Over the past 50 years, both precipitation and runoff have undergone significant increases, and leading to a dramatic rise in GR (0.09 mm yr-1). The future annual growth rate of GR is projected to range from 0.01 to 0.09 mm yr-1 from SSP1-2.6 to SSP3-7.0 across the entire NWEB, with the majority of the increase expected during the spring and summer seasons, driven by enhanced precipitation. GR from the mountainous region is the primary source (accounting for approximately 56-59 %) throughout the NWEB with the greatest increase anticipated. Precipitation and runoff have significant influences on GR in mountainous areas, and the impact of precipitation on GR is expected to increase over time. Changes in GR in oasis and desert areas are mainly limited by precipitation variation and increase in the SSP2-4.5 and SSP3-7.0 scenario. Additionally, the processes of glacial retreat and permafrost degradation will complicate the GR dynamics although the process is largely interfered with by anthropogenic environmental changes, especially in oasis-desert systems. The average annual recharge in the NWEB was 8.9 mm in the historical period and 13.6 ± 4.1 mm in the future. Despite an increase in GR due to climate change, groundwater storage is likely to continue to decline due to complex water demands in the NWEB. This study highlights the significance of future precipitation changes for GR and contributes to the understanding of the influence of climate change on groundwater systems and advances the sustainable management of water resources.

Study on inverse geochemical modeling of hydrochemical characteristics and genesis of groundwater system in coal mine area - a case study of Longwanggou Coal Mine in Ordos Basin.

The exploitation of coal resources has disturbed the equilibrium of the original groundwater system, resulting in a perturbation of the deep groundwater dynamic conditions and hydrochemical properties. Exploring the formation of mine water chemistry under the conditions of deep coal seam mining in the Ordos Basin provides a theoretical basis for the identification of sources of mine water intrusion and the development and utilization of water resources. This paper takes Longwanggou Coal Mine as the research area, collects a total of 106 groups of water samples from the main water-filled aquifers, comprehensively uses Piper trilinear diagram, Gibbs diagram, ion correlation, ion ratio coefficient and mineral saturation index analysis, and carries out inverse geochemical modeling with PHREEQC software, so as to analyze the hydrochemical characteristics and causes of the main water-filled aquifers in deep-buried coal seams in the research area. The results show that the main hydrochemical processes in the study area are leaching and cation exchange, and the groundwater is affected by carbonate (calcite, dolomite), silicate (gypsum) and evaporite. Calculations of mineral saturation indices and PHREEQC simulations have led to the conclusion that the dissolution of rock salt and gypsum in groundwater accounts for most of the ionic action. Na+, Cl- and SO42- are mainly derived from the dissolution of rock salt and gypsum minerals, while Ca2+ and Mg2+ are mostly derived from the dissolution of dolomite and calcite. The results of the inverse geochemical modeling are consistent with the theoretical analysis.

Spatiotemporal variability and controlling factors of groundwater depletion in endorheic basins of Northwest China.

Recent global groundwater overpumping is threatening ecosystem stability and food security, particularly in arid basins. A solid investigation regarding the drivers of groundwater depletion is vital for groundwater restoration, hitherto, yet it remains largely unquantified. Here, a framework to quantify the contribution of natural forcing (NF) and anthropogenic perturbations (AP) to groundwater storage anomalies (GWSA) variability by separating the GWSA estimated by the Gravity Recovery and Climate Experiment (GRACE) satellite into natural- and human-induced GWSA was proposed in the northwest endorheic basin (NWEB) of China. Further, a multiple linear regression model was established for GWSA change prediction. Our results showed that, during the period 2003-2020, the GWSA depleted at a rate of 0.25 cm yr-1 in the entire NWEB. In addition, GWSA was found to decrease significantly (exceeding 1 cm yr-1) in the west of NWEB where there are heavily irrigated areas, and has become one of the regions with the most serious groundwater depletion in China. Whereas a significantly increasing trend (greater than 0.5 cm yr-1) was observed in the Qaidam basin and south part of the Tarim River basin, becoming a groundwater enrichment reservoir in NWEB. The negative contribution of AP to groundwater depletion has increased from 3% to 95% in the last decade, as determined by separating the effects of NF and AP on GWSA. The rapid expansion of the cropland area and the increase in water use due to population growth are investigated to be the main reasons for GWSA depletion, particularly in the North Tianshan Rivers, Turpan-Hami, and Tarim River basins. Therefore, we conclude that AP are dominating and accelerating groundwater depletion in the NWEB. The increase of GWSA in the Qaidam basin has been attributed to the increase in solid water melt and regional precipitation. The western route project of China's south-north water diversion and water-saving irrigation are important ways to solve the problem of groundwater depletion in NWEB. Our results emphasize that a more feasible framework capable of reliably identifying the driving factors of groundwater storage change is a necessary tool for promoting the sustainable management of groundwater resources under both NF and AP in arid endorheic basins.

Research on the Genetic Mechanism of High-Temperature Groundwater in the Geothermal Anomalous Area of Gold Deposit-Application to the Copper Mine Area of Yinan Gold Mine.

Geothermal energy is new, environmentally friendly, and clean energy, which is of great significance to realize energy saving and emission reduction. The study of the genesis mechanism of geothermal water is the key to its rational development and utilization. In this study, based on 14 sets of water samples from the eastern section of the copper well mining area of Yinan Gold Mine, mineral saturation index, isotope analysis (δ18O, δD), Si-enthalpy mixing equation, and geochemical geothermal temperature scale were used to analyze the thermal storage temperature, recharge characteristics, mixing ratio, circulation depth, and fluid passage to reveal the geothermal water fugitive transmission pattern and genesis mechanism in the study area and to propose a geothermal water genesis model. The study shows that the water supply elevation in the area is between 687.22 and 1164.15 m and a large amount of cold water recharged it. It is inferred that the recharge area is the precipitation in the Northwest Mountain range and surrounding atmosphere. Groundwater flows along the fracture zone in a south-easterly direction. It receives heating from the surrounding rocks, where the water level rises at the fracture zone intersection and is stored in the lower and middle Cambrian thermal reservoirs and continues to receive heating from deeper heat sources. Based on this study and previous regional research data, the fault structure in this area is within the influence range of the energy field of the Yishu fault zone. Yishu fault zone becomes the heating source under the background of cold water. It is inferred that the east-east Yishu fault zone in the study area may also be the recharge area.

Improved Combination Weighted Prediction Model of Aquifer Water Abundance Based on a Cloud Model.

The sandstone aquifer is an important underground water storage space, and the study of its water abundance is of great significance to ensure the safety of underground engineering and to explore the occurrence mechanism of groundwater sources. Based on the correlation between geological characteristics and aquifer water abundance, this paper proposed an aquifer water abundance prediction model based on a cloud model that improved combination weighting. The model took the roof sandstone aquifer of the Qingshuiying Coalfield as an example and selected five basic geological indicators that are closely related to the water-rich influence degree of the aquifer as evaluation indicators. The model was based on the idea of game theory, combined the analytic hierarchy process (AHP) and the entropy weight method, and introduced the cloud model evaluation method. The establishment of the model was based on the idea of game theory, combining the AHP and the entropy weight method and introducing the cloud model evaluation method. The results show that most of the study areas are located in weak or relatively weak water abundance areas; relatively strong water abundance areas are mainly distributed in the central, western, and southeastern parts of the study; strong water abundance areas are scattered in parts of the northeast, southwest, and southeast. The unit water inflow data of the actual pumping test is consistent with the water-rich prediction partition, which proves the accuracy and scientificity of the method. The model provides a new idea for the study of groundwater geology and a new method for predicting the water abundance of the roof aquifer in coal mines.