Nanling County, situated on the southern bank of the Yangtze River’s middle and lower reaches in China, and has not yet carried out hydrogeochemical geological surveys. This study is pivotal in ensuring the reliability of the drinking water supply, particularly during emergencies. Utilizing an array of analytical methods—statistical analysis, Shularev classification, Piper trilinear diagram, Gibbs diagram, ion ratio method, and mineral saturation index—this research elucidates the hydrogeochemical characteristics and principal water–salt interactions in Nanling’s shallow groundwater. Our findings, derived from the Shularev classification and Piper trilinear diagram, reveal that, in the southern mountainous and river valley plain regions, the primary hydrogeochemical type of groundwater is HCO₃-Ca. Conversely, in the northern area of Sanli Town and the adjoining plain, groundwater predominantly falls under the HCO₃-Na•Ca category, with some regions showing the characteristics of HCO₃•Cl-Ca, HCO₃•Cl-Na•Ca, and, occasionally, HCO₃•SO₄-Na•Ca. According to the Gibbs diagram analysis, the predominant source of groundwater in this region is attributed to water–rock dissolution processes occurring during groundwater runoff. The increase in Na⁺, Ca²⁺, Cl⁻, HCO₃⁻, and SO₄²⁻ concentrations in the water–rock interaction in the study area is mainly due to the dissolution of rock salt, gypsum, calcite, and dolomite, and the alternating cation adsorption occurs during the reaction. Finally, the mineral saturation index points to the ongoing dissolution of gypsum, calcite, and dolomite, until a state of precipitation–dissolution equilibrium is reached. This comprehensive study provides vital insights into the hydrogeochemical dynamics of Nanling County’s groundwater, contributing significantly to our understanding of regional water quality and its management.

The natural oases in the plain area of the northwest inland basin strongly depend on the groundwater depth. With the overexploitation and utilization of groundwater, natural oases are faced with the problems of serious degradation and rehabilitation. How to evaluate the degree of the degeneration crisis of groundwater ecological function has become one of the key scientific and technological problems to be solved. In this paper, the Shiyang River basin of Gansu Province was selected as a typical research area. The remote sensing interpretation, groundwater–soil ecology comprehensive investigation, and groundwater in situ monitoring were adopted to carry out the research. Based on the correlation analysis method of natural ecology and groundwater, the interactive relationship between the natural ecological environment and groundwater depth in different ecological types of the region were studied: (1) under the arid climate condition in northwest China, the relationships between the ecological situation and the groundwater depth in different ecological types of the region were obviously different, and as a result, the optimal or limit ecological water level of groundwater in different ecological types was also different; (2) in the natural wetland area, the suitable ecological water level of groundwater was between 0.5 m to 1.5 m, and the limit ecological water level was 8.0 m; in the natural vegetation area, the suitable ecological water level was between 3.0 m to 5.0 m, and the limit ecological water level was 10.0 m; and in the farmland area, the suitable ecological water level was between 2.0 m to 5.0 m, and the limit ecological water level was 2.0 m; (3) in order to effectively protect the natural ecology in different ecological types, a five-level early warning and control index system should be established for the ecological function degeneration crisis of groundwater. It may be beneficial to promote restoration and protection of the groundwater ecological function and natural ecology in the inland area of northwest China.

In arid and semi-arid areas, due to drought climate and shortage of water resources, groundwater is crucial for natural ecological protection and economic development. It serves a dual role as a resource function and an ecological function. However, with the continuous improvement of the exploitation and utilization of groundwater by human activities during rapid economic development, the phenomenon of groundwater overexploitation is becoming more and more serious, which has destroyed the natural balance of groundwater recharge and discharge. As a result, natural vegetation has lost the maintenance of the ecological function of groundwater, and a series of ecological and environmental problems have occurred, such as natural vegetation degradation, land desertification, sandstorms, and so on. In recent years, scholars have carried out research on groundwater resource management and optimization of water resource allocation, trying to solve the problem of water balance in arid regions. However, there is still a lack of comprehensive understanding and systematization regarding influencing factors and degeneration mechanisms related to groundwater’s ecological function. By summarizing and analyzing the previous research results, this paper summarizes the influencing factors, evaluation methods, existing problems and future directions of groundwater ecological function research in China to provide a reference for rational exploitation and utilization of groundwater and ecological protection. This paper is divided into four main contents. The first part introduces the definition of groundwater ecological function (GEF); the second part summarizes the research status of influencing factors of GEF, including the groundwater table depth, vegetation root system and lithologic structure of vadose zone, etc.; the third part analyzes the evaluation of groundwater ecological function; the fourth part discusses the existing problems in the study of groundwater ecological functions, and based on the above research the evaluation framework of GEF is proposed with the Shiyang River basin as a case study; and finally, it highlights the future research directions about GEF.

The farmland around wetlands in the lower reaches of an arid area is susceptible to salinization. To explore the effects of the groundwater level control at an irrigation cycle scale on the salt concentration of the topsoil solution, this study carried out groundwater level control and irrigation experiments using the intelligent groundwater control and in-situ field monitoring system (also referred to as the groundwater control system) in the experimental base for groundwater control of the Shiyang River basin. On this basis, this study compared and analyzed the changes in groundwater depth, soil salinity, soil moisture content, and total water potential in zones with and without groundwater control (also referred to as the control and non-control zones, respectively). Results show: (1) When the groundwater depth increased by about 50 cm under the influence of the groundwater control system, the salt accumulation layer of the soil bulk shifted downward by about 20 cm, and the topsoil bulk salt (at a depth of less than 40 cm) decreased to below 5.0 g/kg; (2) In summer, the pore water electrical conductivity (EC_p) of the topsoil in the control and non-control zones exhibited alternating rapid decreases and slow increases. In the concentration stage of the soil solution, the EC_p of the topsoil in the non-control zone had significantly higher increased amplitude than that in the control zone, especially 3–8 days after irrigation. At this stage, the EC_p of the topsoil in the control and non-control zones increased in two (slow and rapid increase) and three (slow, rapid, and fairly rapid increase) periods, respectively; (3) At the concentration stage of the topsoil solution, both the moisture content and solution salt content of the topsoil in the control zone were in a negative equilibrium state, with the absolute values of the equilibrium values gradually increasing. In contrast, the moisture content and solution salt content of the topsoil in the non-control zone were in negative and positive equilibrium, respectively, with the absolute values of their equilibrium values gradually increasing. The groundwater control system can mitigate the concentration rate of the topsoil solution by increasing the groundwater depth and influencing the water and salt equilibrium of the topsoil solution, which can create a suitable topsoil salt environment for crop growth. This study is of great significance for determining an appropriate ecological water level interval and optimizing groundwater control strategies for farmland around wetlands.

The natural vegetation in arid areas of northwest China is strongly dependent on the availability of groundwater. Significantly, capillary water plays an essential role in regulating the ecological groundwater level in the multilayered structure of the vadose zone. The soil-column test and field survey in the lower reaches of the Shiyang River Basin were conducted to investigate the influence of the multi-layered structure of the vadose zone on maintaining the ecological effect of groundwater. Based on the field survey, the results show that the depth of groundwater is 3.0 m, and the rising height of capillary water is 140 cm. In the soil-column test, the height of the wetting front of the column was 125 cm. During the water releasing test, the water held by the vadose zone was 182.54 mm, which would have maintained Haloxylon’s survival in a growing season. Therefore, the multi-layered structure of the vadose zone extends the ecological groundwater depth and consequently enhances the ecological function of groundwater. Importantly, with a lower groundwater level, the clay soil layer within the rising height range of the original capillary water would hold more water and maintain a higher water content for a certain period to supply surface vegetation.

As a critical link connecting groundwater and vegetation, the vadose zone’s lithological structural heterogeneity directly influences soil water distribution and vegetation growth. A comprehensive understanding of the ecological effects of the vadose zone can provide scientific evidence for groundwater ecological protection and natural vegetation conservation in arid regions. This study, taking the Minqin Basin in the lower reaches of China’s Shiyang River as a case, reveals the constraining effects of vadose zone lithological structures on vegetation water supply, root development, and water use strategies through integrated analysis, field investigations, and numerical simulations. The findings highlight the critical ecological role of the vadose zone. This role primarily manifests through two mechanisms: regulating capillary water rise and controlling water-holding capacity. They directly impact soil water supply efficiency, alter the spatiotemporal distribution of water deficit in the root zone, and drive vegetation to develop adaptive root growth patterns and stratified water use strategies, ultimately leading to different growth statuses of natural vegetation. During groundwater level fluctuations, fine-grained lithologies in the vadose zone exhibit stronger capillary water response rates, while multi-layered lithological structures (e.g., “fine-over-coarse” configurations) demonstrate pronounced delayed water release effects. Their effective water-holding capacities continue to exert ecological effects, significantly enhancing vegetation drought resilience.