南水北调工程（SNWDP）极大地改善了华北平原的缺水状况。然而，SNWDP 对地下水化学特别是氟化物和盐度演化的影响仍然未知。沧州是SNWDP的受援城市之一，地面沉降严重，被选中采集SNWDP前后的深层承压地下水样品。结果表明，SNWDP后地下水氟化物浓度下降，2017年和2021年的中值分别为4.39 mg/L和3.00 mg/L。这种趋势在地面沉降区更为明显，这可能与深部地下水停止抽水导致地面沉降减少有关。粘土沉积物中的孔隙水含氟量高达 7.02 mg/L，由于SNWDP之前的沉积物压实，可以释放到地下水中。过去几十年的广泛开采改变了地下水的补给模式，导致超过 60% 的深层地下水被粘土沉积物释放的孔隙水补给。小基线子集干涉合成孔径雷达（SBAS-InSAR）的结果表明，SNWDP之后地面沉降有所减缓，特别是在地面沉降的中心区域，从而限制了富氟孔隙水的释放。但SNWDP后地下水盐度增加，超过饮用标准（TDS <1000 mg/L）的样本增加了26.4%。地下水位上升有利于水-岩石相互作用，促进可溶性矿物质的溶解，例如石盐，这反映在使用 PHREEQC 的逆向和正向建模的结果中。SNWDP后的地下水盐碱化可能会导致萤石溶解并导致地下水氟化物浓度升高。然而，计算结果表明，与地下水盐渍化相关的 F 高程显着低于粘土沉积压实中富含氟化物的孔隙水的贡献。本研究结果全面评估了 SNWDP 对地下水质量的影响，并为地下水资源管理提供了一些新见解。计算结果表明，与地下水盐渍化相关的 F 高程显着低于粘土沉积压实中富氟孔隙水的贡献。本研究结果全面评估了 SNWDP 对地下水质量的影响，并为地下水资源管理提供了一些新见解。计算结果表明，与地下水盐渍化相关的 F 高程显着低于粘土沉积压实中富氟孔隙水的贡献。本研究结果全面评估了 SNWDP 对地下水质量的影响，并为地下水资源管理提供了一些新见解。
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Evolution of groundwater salinity and fluoride in the deep confined aquifers of Cangzhou in the North China plain after the South-to-North Water Diversion Project
The South-to-North Water Diversion Project (SNWDP) has greatly improved the water shortage in the North China Plain. However, the impact of the SNWDP on the evolution of groundwater chemistry, especially fluoride and salinity, was still unknown. Cangzhou, one of the recipient cities of SNWDP and suffered from severe land subsidence, was selected to collect the deep confined groundwater samples before and after the SNWDP. The results showed that groundwater fluoride concentration decreased after the SNWDP, with a median value of 4.39 mg/L in 2017 and 3.00 mg/L in 2021, respectively. This trend was more clearly observed in the land subsidence area, which could be related to the reduction of land subsidence, due to the stopping pumping of deep groundwater. The pore water in clayey sediments contains fluoride up to 7.02 mg/L, which can be released into groundwater due to the sediment compaction before the SNWDP. The extensive exploitation during last decades changed the groundwater recharge patterns, resulting in over 60% deep groundwater being recharged by the pore water released from clayey sediment. The results of the Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-InSAR) suggested that land subsidence has slowed down after the SNWDP, especially in the central area of land subsidence, thereby restricting the release of fluoride-rich pore water. However, groundwater salinity increased after the SNWDP, and the number of samples exceeding the drinking standard (TDS <1000 mg/L) increased by 26.4%. The rising groundwater level favors the water-rock interaction, promoting the dissolution of soluble minerals, for instance, halite, which was reflected by the results of inverse and forward modeling using the PHREEQC. Groundwater salinization after the SNWDP potentially induces the fluorite dissolution and causes the elevation of groundwater fluoride concentration. However, the calculated results indicate that the amount of F elevation related to groundwater salinization is significantly lower than the contribution of fluoride-rich pore water from clay sediment compaction. The findings of this study provide a comprehensive assessment of the influence of the SNWDP on the groundwater quality and some new insights for the management of groundwater resources.
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