洱海流域地下水稳定同位素、水化学特征与补给转化规律研究

Research on Stable Isotopes, Hydrochemical Characteristics, and Recharge and Transformation Laws of Groundwater in the Erhai Lake Basin

摘要: 洱海流域处于澜沧江、金沙江和元江三江分水岭地带，地下水补给转化规律复杂。探究洱海流域地下水稳定同位素、水化学特征与补给转化规律对区域地下水资源开发和合理利用具有重要意义。本研究于2023年8月在洱海流域选取海西盆地、邓川盆地、洱源盆地、江尾–喜洲盆地、凤羽盆地和牛街–三营街盆地这六个典型的地下水系统进行采样，共采集58组地下水样品的稳定同位素和水化学数据，以及57组地表水和33组降水数据，综合运用描述性统计、空间分析、Piper三线图、Gibbs图及离子比值端元图方法研究区域地下水的补给转化规律。结果表明：① 洱海流域主要离子TDS和EC的统计特征呈现：井水 > 泉水，各地下水系统地下水TDS呈现：牛街–三营街盆地 > 邓川盆地 > 江尾–喜洲盆地 > 洱源盆地 > 海西盆地 > 凤羽盆地，阴离子${\text{HCO}}_3^{-}$ 和阳离子中${\text{Ca}}^{+}$ 占主要优势，表明流域地下水总体流向为周边汇入洱海且流经路径上方解石和白云石等碳酸盐岩矿物普遍存在。② 研究区地下水水化学类型以${\text{HCO}}_3^{-}\text{Ca}$ 型为主，而泉水中${\text{Na}}^{+}$ 的平均浓度较井水相对较高，水中${\text{HCO}}_3^{-}\text{Ca}\cdot \text{Na}$ 型占比显著增加，表明泉水受碳酸岩石风化作用更强。此外，除凤羽盆地地下水以${\text{HCO}}_3^{-}\text{Ca}\cdot \text{Na}$ 型为主，其余五个地下水系统均以${\text{HCO}}_3^{-}\text{Ca}\cdot \text{Mg}$ 型为主，占比大都在65%以上。③ 研究区地下水化学特征主要受水岩相互作用和蒸发浓缩作用控制，其中井水受蒸发浓缩作用更显著；各地下水系统中，海西盆地地下水系统中水样TDS总体较低，地下水总体位于碳酸盐类、硅酸盐类及蒸发盐类中心。泉水受硅酸盐岩矿物及碳酸盐类矿物的风化溶解影响显著，井水受蒸发盐类矿物的风化溶解影响显著。④ 研究区地下水样品大部分${\text{Na}}^{+}$ 与${\text{SO}}_4^{2-}$ 的比值高于1，说明大部分地下水${\text{Na}}^{+}$ 与${\text{SO}}_4^{2-}$ 主要来源为芒硝的风化作用；研究区地下水样品均落在$\text{N}\left({\text{Cl}}^{-}+{\text{SO}}_4^{2-}\right)/\text{N}\left({\text{HCO}}_3^{-}\right)=1$ 关系线的上方，说明碳酸盐岩的溶解作用控制了洱海流域地下水离子化学组分来源。⑤ 研究区井水所受蒸发作用更强，各地下水系统中地下水蒸发强度呈现：海西盆地 > 凤羽盆地 > 江尾–喜洲盆地 > 洱源盆地 > 牛街–三营街盆地 > 邓川盆地。

Abstract: The Erhai Lake Basin is located in the watershed of the Lancang River, Jinsha River, and Yuanjiang River, where the groundwater recharge and transformation laws are complex. Exploring the stable isotopes, water chemistry characteristics, and recharge and transformation laws of groundwater in the Erhai Lake Basin is of great significance for the development and rational utilization of regional groundwater resources. This study sampled six typical groundwater systems in the Erhai Lake Basin, namely the Haixi Basin, Dengchuan Basin, Eryuan Basin, Jiangwei-Xizhou Basin, Fengyu Basin, and Niujie-Sanyingjie Basin, in August 2023, collecting a total of 58 sets of stable isotope and water chemistry data of groundwater, 57 sets of surface water and 33 sets of precipitation data. Descriptive statistics, spatial analysis, Piper trilinear diagram, Gibbs diagram, and ion ratio end-member diagram methods were comprehensively used to study the recharge and transformation laws of regional groundwater. The results show that: ① The statistical characteristics of the main ions TDS and EC of groundwater in the Erhai Lake Basin are: well water > spring water. The TDS of groundwater in each groundwater system is: Niujie-Sanyingjie Basin > Dengchuan Basin > Jiangwei-Xizhou Basin > Eryuan Basin > Haixi Basin > Fengyu Basin. Anions ${\text{HCO}}_3^{-}$ and cations ${\text{Ca}}^{+}$ are dominant, indicating that the overall flow direction of groundwater in the basin is from the periphery to Erhai Lake and that calcite dolomite and other carbonate rock minerals are widely distributed along the flow path. ② The water chemistry type of groundwater in the study area is mainly ${\text{HCO}}_3^{-}\text{Ca}$ type, while the average concentration of ${\text{Na}}^{+}$ in spring water is relatively higher than that in well water, and the proportion of ${\text{HCO}}_3^{-}\text{Ca}\cdot \text{Na}$ type in water significantly increases, indicating that spring water is more affected by the weathering of carbonate rocks. In addition, except for the Fengyu Basin, where the groundwater is mainly ${\text{HCO}}_3^{-}\text{Ca}\cdot \text{Na}$ type, the other five groundwater systems are mainly ${\text{HCO}}_3^{-}\text{Ca}\cdot \text{Mg}$ type, with a proportion of more than 65% in most cases. ③ The chemical characteristics of groundwater in the study area are mainly controlled by water-rock interaction and evaporation concentration. Among them, well water is more significantly affected by evaporation concentration. In each groundwater system, the TDS of groundwater in the Haixi Basin is generally lower. Groundwater is generally located at the center of carbonate, silicate, and evaporite classes. Spring water is significantly affected by the weathering and dissolution of silicate rock minerals and carbonate minerals, while well water is significantly affected by the weathering and dissolution of evaporite minerals. ④ Most of the ${\text{Na}}^{+}$ /${\text{SO}}_4^{2-}$ ratios of groundwater samples in the study area are higher than 1, indicating that the main source of ${\text{Na}}^{+}$ and ${\text{SO}}_4^{2-}$ in most groundwater are the weathering of mirabilite. All groundwater samples in the study area are located above the $\text{N}\left({\text{Cl}}^{-}+{\text{SO}}_4^{2-}\right)/\text{N}\left({\text{HCO}}_3^{-}\right)=1$ relationship line, indicating that the dissolution of carbonate rocks controls the source of ionic chemical components of groundwater in the Erhai Lake Basin. ⑤ Well water in the study area is more affected by evaporation. The evaporation intensity of groundwater in each groundwater system is: Haixi Basin > Fengyu Basin > Jiangwei-Xizhou Basin > Eryuan Basin > Niujie-Sanyingjie Basin > Dengchuan Basin.