Gaomi City, the hinterland of Jiaolai Plain in Shandong Peninsula, was selected as the research object. A total of 8197 surface soil samples were collected to determine the contents of eight soil heavy metals (HMs)including Copper (Cu), Lead (Pb), Zinc (Zn), Nickel (Ni), Chromium (Cr), Cadmium (Cd), Arsenic (As), and Mercury (Hg). Statistical methods were used to find out the geochemical background (GCB) in the area, systematic clustering and factor analysis were used to study the homology between HMs, and single-factor evaluation method was used to evaluate the ecological risks in the study area. The results of the study show that the ecological risk of the surface soil in the study area is relatively low, dominated by a planar distribution, with only a few high-risk points. The uneven distribution of Hg in the surface soil is affected by human activities to a certain extent. The ratio of the GCB of the geological unit area to the GCB of the whole area shows that the Hg content of the Qingshan Group and Dasheng Group geological units is higher, and the Pb content in the subvolcanic rock area is slightly higher. The ecological pollution risk in the study area is generally low, and only exists individual high-risk areas, distributed radially in densely populated areas.

To elucidate the hydrochemical characteristics, controlling factors, sources and mechanisms of strontium ion enrichment in groundwater in the northwest plain of Shandong Province, China, 88 groundwater samples were collected, including 51 shallow pore groundwater samples, 29 deep pore groundwater samples and 8 karst groundwater samples. The hydrochemical characteristics of the different types of groundwater were quite different. The karst groundwater samples were all fresh water with a single hydrochemical type, either HCO₃-Ca or HCO₃-Ca·Mg. The deep pore groundwater samples were mainly brackish water, and the shallow pore groundwater samples were brackish water–salt water, which has complex hydrochemical types. The hydrochemical characteristics of all the types of groundwater were controlled by mineral dissolution and active positive cation exchange. In shallow pore groundwater, deep pore groundwater and karst groundwater, the dissolution of silicate, evaporite and carbonate minerals dominated the hydrogeochemical process. The strontium in groundwater was derived from the dissolution of minerals with strontium isomorphism. The average contents of strontium in shallow, deep and karst groundwater were 1.59 mg/L, 0.58 mg/L and 0.50 mg/L, respectively. The strontium in shallow pore groundwater was mainly derived from the enrichment of groundwater runoff, and its sources are abundant, with silicic rock being the main source. The deep pore groundwater mainly derived from the evaporative minerals containing strontium, and the karst water mainly derived from carbonate rock dissolution with similar characteristics.

Groundwater is crucial for human survival and social development. In this study, ArcGIS 10.8, Origin 2024, and Excel were employed to investigate the hydrochemical properties of groundwater in the Rizhao reservoir (RZR) through statistical analysis, Durov plots, ion ratio analysis, and the entropy weight water quality index (EWQI). The analysis is based on monitoring data from six sites located both upstream and downstream of RZR, focusing on dynamic changes in groundwater quality and major ion concentrations. The findings suggest that the groundwater in RZR exhibits weak alkalinity and is categorized as hard freshwater. The predominant anion and cation are HCO₃⁻ and Ca²⁺, which together determine that the dominant water chemistry type in RZR is HCO₃-Ca type. Groundwater ions predominantly stem from the dissolution of silicate and evaporite rocks. In comparison to the dry season, the fluctuations in groundwater parameters are more pronounced during the wet season. Between 2020 and 2022, the concentrations of most ions exhibited an upward trend. Notably, nitrate (NO₃⁻) experienced significant fluctuations and relatively high concentrations, peaking in the wet season of 2023. The primary source of nitrate in RZR is agricultural activities. Overall, the quality of groundwater in RZR is good and suitable for human consumption. Nevertheless, the EWQI values are increasing at most monitoring sites, with the most significant rise observed at site R02. Moreover, while the upstream monitoring point exhibits better water quality, its EWQI value has increased significantly, and ion concentrations display substantial fluctuations. Local authorities are advised to adopt active measures to manage groundwater quality in RZR to ensure its sustainable use.

Groundwater represents a critical resource for sustaining the livelihoods of both urban and rural populations, facilitating economic and social development, and preserving ecological equilibrium. This study leverages groundwater quality monitoring data from the northern Baiquan spring basin (NBSB) to elucidate groundwater hydrochemical characteristics and decipher the temporal variability in water quality. Findings suggest that groundwater within the NBSB is predominantly weakly alkaline and characterized as hard-fresh, with HCO₃⁻ and Ca²⁺ as the predominant ions, which collectively demarcate the hydrochemical type as predominantly HCO₃-Ca. The principal constituents of NBSB groundwater are influenced predominantly by the weathering of carbonates and silicates alongside the dissolution of gypsum and halite. Moreover, agricultural operations and similar human activities have exerted an impact on the hydrochemical attributes of NBSB’s groundwater. Generally, fluctuations in groundwater anion concentrations over time are more pronounced than those of cations, exemplified by a significant upward trend in the major ion concentrations at the BQ03 monitoring site in the later stages. While the general groundwater quality within the NBSB is deemed satisfactory, most monitoring sites have experienced an escalation in water quality indices over time, notably at BQ03, which warrants serious attention. The findings of this research contribute to the efficient management and sustainable utilization of groundwater resources in the NBSB.