山东省肥城断块岩溶水系统地下水水化学特征及演化分析

地下水是肥城地区最主要的供水水源，近年来受到工农业生产、煤矿开采、闭坑、矿井排水等人类活动影响，肥城地区地下水动力场及化学场都发生了变化，为查明地下水的环境质量状况，文章在研究水文地质调查和样品采集分析基础上，综合运用数理统计方法、水化学方法（Piper三线图、Gibbs模型、矿物饱和指数、离子比例分析）等，探讨肥城断块地下水水化学特征及演化规律。结果表明：（1）研究区地下水均呈弱碱性，$ {mathrm{C}mathrm{a}}^{2+} $、$ {mathrm{M}mathrm{g}}^{2+} $、$ {{mathrm{H}mathrm{C}mathrm{O}}_{3}}^{-} $和$ {mathrm{S}mathrm{O}}_{4}^{2-} $为主要离子，主要来源于方解石、白云石及石膏溶解；矿物饱和指数表明方解石和白云石绝大多数处于饱和状态，石膏和岩盐矿物呈溶解未饱和状态。（2）区内岩溶水化学类型主要为$ {mathrm{H}mathrm{C}mathrm{O}}_{3}-mathrm{C}mathrm{a}left(mathrm{M}mathrm{g}right) $型，其次为$ {mathrm{H}mathrm{C}mathrm{O}}_{3}·{mathrm{S}mathrm{O}}_{4}-mathrm{C}mathrm{a} $型和$ {mathrm{H}mathrm{C}mathrm{O}}_{3}·mathrm{C}mathrm{l}-mathrm{C}mathrm{a} $型。孔隙水主要为$ {mathrm{S}mathrm{O}}_{4}·{mathrm{H}mathrm{C}mathrm{O}}_{3}-mathrm{C}mathrm{a} $型、局部出现$ {mathrm{S}mathrm{O}}_{4}{·mathrm{N}mathrm{O}}_{3}-mathrm{C}mathrm{a} $型。河流水化学类型相对复杂，包括$ {mathrm{S}mathrm{O}}_{4}·{mathrm{H}mathrm{C}mathrm{O}}_{3}-mathrm{C}mathrm{a}·mathrm{N}mathrm{a} $型、$ mathrm{C}mathrm{l}·{mathrm{S}mathrm{O}}_{4}-mathrm{C}mathrm{a}·mathrm{N}mathrm{a} $型等。（3）区内地下水中$ {mathrm{C}mathrm{l}}^{-} $、$ {mathrm{S}mathrm{O}}_{4}^{2-} $和$ {mathrm{N}mathrm{O}}_{3}^{-} $含量相比1999年、2013年显著升高。裂隙水及岩溶水水质整体较好，局部呈点状变差，孔隙水及河水水质普遍较差，影响区域地下水水质的主要因素有化肥施用、禽畜养殖、生活污水下渗以及煤矿排水等。

Groundwater hydrochemical characteristics and evolution of the karst water system in the Feicheng fault block in Shandong Province

The Feicheng area is one of the important industrial bases in Shandong Province with the early development of coal mine, power generation and chemical industry. Besides, vegetable farming is widely distributed. Karst groundwater is the main source of water supply and the only source of drinking water in this area. In recent years, due to human activities such as industrial and agricultural exploitation of groundwater, and reduction of water emissions from coal mine closures, the groundwater dynamic and chemical fields in this area have undergone changes. The current status of groundwater environmental quality needs to be determined. On the basis of hydro-geological survey, this study collected 59 groundwater samples and 6 river water samples in the dry season of 2022, and comprehensively used mathematical statistical methods, hydrochemical methods (Piper three-line diagram, Gibbs model, mineral saturation index, ion proportion analysis) to explore the hydrochemical characteristics and evolution rules of groundwater in the Feicheng fault block.The results show that, (1) The average pH of groundwater in the study area is 7.34–7.47, all of which are weakly alkaline, and Ca2+, Mg2+, ${rm{HCO}}_3^{-}$ and ${rm{SO}}_4^{2-}$ are the main ions in the water. The hydrochemical composition is mainly controlled by water rock interaction, while the influence of atmospheric precipitation and evaporation concentration is relatively small. The water-rock interaction of calcite and dolomite plays a major role in controlling the chemical composition of karst water and fissure water, and the dissolution of evaporite plays an important role in the chemical composition of pore water. The mineral saturation index shows that most of calcite and dolomite is in a saturated state, while gypsum and halite minerals are in a dissolved but unsaturated state.(2) Karst hydrochemical types in the area are mainly HCO3-Ca (Mg) type, accounting for 47.9%, followed by HCO3·SO4-Ca type and HCO3·Cl-Ca type, 16.7% and 20.8%, respectively. Pore water is mainly of SO4·HCO3-Ca type and HCO3·Cl·SO4-Ca type, with SO4·NO3-Ca type appearing locally in the area of Wangguadian town. The chemical types of river water are relatively complex, including SO4·HCO3-Ca·Na type, Cl·SO4-Ca·Na type, etc.(3) From the perspective of component content, the average TDS content of pore water, karst water, and fissure water is 1,207.13 mg·L−1, 670.96 mg·L−1, 514.5 mg·L−1, respectively. The coefficient of variation of Ca2+ and Mg2+ in groundwater is relatively small, indicating that they are relatively stable ions. The average values of ${rm{SO}}_4^{2-}$, Cl− and ${rm{NO}}_3^{-}$ in pore water are 288.29 mg·L−1, 155.86 mg·L−1, 195.41 mg·L−1, respectively, with high content and small coefficient of variation, indicating that they are mainly influenced by external inputs from human activities. The content of ${rm{SO}}_4^{2-}$, Cl− and ${rm{NO}}_3^{-}$ in karst water is relatively low, but the coefficient of variation is large, with uneven concentration distribution, and occurrence of enrichment in local areas. The average ${rm{SO}}_4^{2-}$ in the Huihe river reaches 345.83 mg·L−1, which is much higher than that of the surrounding groundwater and has a small coefficient of variation, indicating that its source is mainly from external inputs and may be related to the drainage of surrounding coal mines.(4) Some sources of Ca2+ are related to the dissolution of gypsum minerals and the infiltration of pollutants containing Cl− and ${rm{NO}}_3^{-}$, and the nitrate pollutants mixed into aquifers may promote the dissolution of carbonate rocks. The cation exchange is weak in groundwater, but strong in river water.(5) From a time-scale perspective, the groundwater quality in the study area has shown a decreasing trend compared to the quality in 1999 and 2013, with significant increases in the content of Cl−, ${rm{SO}}_4^{2-}$, and ${rm{NO}}_3^{-}$ in groundwater over the years. From the perspective of groundwater types and spatial distribution, the chemical characteristics of groundwater in the Feicheng area are significantly influenced by human activities. Both the concentrations of nitrogen and chlorine are generally low in the fissure water of magmatic rocks, and hence the water quality is relatively the best. The overall quality of karst water is good, and the rise of the water level in the closed pit mine in Feicheng has not caused cross-layer pollution to the surrounding karst water. However, there are local occurrences of "high nitrogen" or "high chlorine" in Wangzhuang, Taoyuan, Shiheng, Dayang, and other places, which may be affected by pollution sources such as agricultural fertilization, livestock breeding, and domestic sewageinfiltration. Both the concentrations of nitrogen and chlorine are high in most of the pore water, and hence the water quality is generally poor, with ${rm{NO}}_3^{-}$, as the main ion exceeding the permitted level, which may be related to the application of chemical fertilizer for large-scale agricultural vegetable farming in the study area, and the infiltration of surface nitrate and other pollutants into the groundwater with rainwater. The nitrogen concentration in both Kangwang river and the Huihe river is generally low, while those of chlorine and sulfur are high, reflecting the significant impact of urban sewage discharge and coal mine drainage on these two rivers.