The temporal scale effect is an important issue for groundwater system evolution research. The selection of an appropriate time scale will enhance the understanding of the characteristics and mechanisms of groundwater flow field evolution. In this study, a methodology was provided to analyze the groundwater system evolution, focusing on the choice of the suitable time step for identifying the distinct stages of evolution, characterized by different behavior linked to the management of the groundwater system. The evolution trend of the groundwater level in the center of the cone of depression at different time scales, combined with the F test and the groundwater system balance index (R_e) categories, were used for the choice of the time step and the division of the evolution stages. Based on the transformed groundwater level time series using the selected best time step, the main factors controlling the groundwater evolution were assessed for the different stages. Our results show that the methodology can exactly identify the different important stages of the evolution, and they can be used to individually study these stages, which can help to reveal the mechanisms of the groundwater evolution more easily. Therefore, it is useful to obtain an increased knowledge of the regional groundwater dynamics.

Climate change and human activities have intensified the imbalance between water supply and demand in the Shule River Basin. Prominent issues such as groundwater over-exploitation and insufficient ecological base flow have significantly constrained the high-quality development of the region. An evaluation system was developed comprising 20 indicators across four subsystems: water resources, society, economy, and ecosystems. The entropy weighting method was employed to determine the weights of each indicator. The coupling coordination degree of the water resource–society–economy–ecosystem system from 2003 to 2022 was assessed using a coupling coordination degree model. Network analysis was applied to evaluate the correlation and connectivity among indicators. A barrier diagnostic model based on indicator deviation was further constructed to identify key constraints within the system. The results showed that the overall coordination degree of the coupled system increased from 0.217 in 2003 to 0.409 in 2022, shifting from a moderately uncoordinated state to a weakly coordinated one. However, the coordination level remained low due to fluctuations in the water resource subsystem. The ecological and economic subsystems functioned as critical coupling hubs, while strong negative interactions within the water resource subsystem emerged as major constraints to coordinated development. Long-term dominant barriers included the proportion of water used for ecological and agricultural purposes, as well as per capita food production. After 2019, water resource-related indicators, such as per capita water availability and water production modulus, showed a marked increase in obstruction levels, highlighting the persistent challenges posed by water scarcity and inefficient utilization.

Background and aims Fluorine (F) is an essential trace element for humans, but excessive F poses risks to human health. Consequently, the sources and safety risks of high-F soils have garnered significant attention. The Nanyang Basin is a major agricultural region in China, known for its wheat and other staple crops. This study investigated the spatial geochemical characteristics of fluoride in surface soils (0–20 cm) and the vertical change characteristics, analyzed the relationship of fluorine content between crop and soil, and identified its potential safety risks. Methods We collected soil samples regionally and crop samples and rhizosphere soil in typical areas, analyzed the geochemical distribution of soil F and its relationship with crop uptake integrating geostatistical analysis with GIS techniques, were. Results The background F content in surface soils of the Nanyang Basin is higher than the background levels of topsoil in Henan Province and China. The primary source of F in surface soils is external input (pollution-related), with geological background having a secondary influence. Conclusions The high-F surface soils in agricultural areas of the basin have a relatively low impact on the safety of wheat and peanut grains. The F content in crop grains is generally below the maximum allowable limits for food, indicating an overall "safe" status, except that a few areas exceeding the maximum allowable limits for food contamination in alkaline soil regions with high F levels,and identifying these areas as potential safety risk zones requiring enhanced monitoring and management.