为探明南水北调东线工程山东段输水期硫酸盐污染的来源，对南四湖及其周边河流的水化学基本性质进行测定，并结合硫、氧同位素技术，分析南四湖和其入湖河流的水化学以及硫酸盐质量浓度分布特征，计算南四湖各直接来源的贡献率并示踪南四湖流域硫酸盐的根本来源。研究结果表明：南四湖及其周边入湖河流水化学类型与地下水化学类型不同,南四湖SO42-质量浓度自南向北逐渐增高，甚至南阳湖(NE)达到631.50 mg/L；蒸发岩溶解硫酸盐对南四湖贡献率最大，达52.18%,南阳湖硫酸盐直接来源主要是入湖河流携带，来自江苏的调水对南四湖硫酸盐贡献率仅5.34%；南四湖周边入湖河道硫酸盐来源各有不同，主要是污水和蒸发岩溶解。

China is facing with water shortages,and the per capita water resources of China are below the global average.Therefore,to solve the problem of water shortages in the northern region,the Chinese government launched the SouthtoNorth Water Diversion Project (SNDP) in 2002.The Eastern Route Project (SNWD-ERP) is an integral part of the SouthtoNorth Water Diversion Project.The SNWD-ERP diverts water from the lower reaches of the Yangtze River to Shandong and Hebei Provinces,and Tianjin municipality with a complex hydraulic system of interconnected lakes,rivers,and canals,which provides important guarantees for the socioeconomic development of the northern region.Nansi Lake (NSL)which is located in Shandong Province,China,is an important storage hub for the SNWD-ERP.Since the SNWD-ERP has officially been in operation,it was found that the concentrations of sulfate rapidly increased after water transfer from Jiangsu Province to Shandong Province,especially in NSL,where the sulfate concentrations reached 400 mg/L.This was a huge impact on the water quality of the SNWDERP.After sulfate was dissolved in the water,it was stable and easy to accumulate in the water body.Excessive sulfate concentration not only limited the use of water transfer but also had adverse effects on the human body.Therefore,accurately identifying the source of sulfate in lakes and channels and related biogeochemical processes are important conditions for protecting and managing water resources.To ascertain the source of sulfate pollution during the water diversion period in the SNWDERP in Shandong province,monitoring points in NSL and its surrounding rivers and groundwater distribution were sampled to analyze the characteristics of hydrochemical and sulfate concentration distribution in NSL.The δ(34SSO4) value was used to calculate the contribution rate of each direct source in the diversion water period,and combining with the δ(18OSO4) value to explore the sources of sulfate in NSL and the major sources of sulfate in inflowing rivers in the diversion water period.The variety rules of sulfate sources in NSL are analyzed to search for the potential sources of sulfate pollution and appropriate treatment techniques were investigaled to reduce sulfate concentration and ensure the safety of water supply,and provide data support in the SNWD-ERP. The main result were as follows:(1) in the diversion water period,the pH of NSL and its inflowing rivers was alkalescence,and groundwater was neutral.The sulfate concentration in NSL gradually increased from south-to-north,even as high as 631。50 mg/L in the Nanyang sub lake (NE).The main water types of NSL were Na+SO42-Cl- and Na+SO42-HCO3,which was mainly affected by carbonate weathering.But the water types in groundwater were Ca2+SO42-Cl-,which was mainly affected by the dissolution of evaporite salt and the weathering of silicate.(2) Evaporite dissolution has the largest sulfate contribution rate in NSL,reaching 52.18 %.But the direct source of sulfate in Nanyang sub lake was mainly carried by rivers,especially Zhuzhaoxin River,Old Canal,and Wanfu River.The contribution rate to Nanyang Lake sulfate was much higher than that of evaporite dissolution,and contribution rate of water transfer in NSL from Jiangsu was only 5.34 %.(3) For the inflowing river,sewage inflow was the main source of sulfate in the Baima River,Chengguo River,Panlong River,and Dongyu River,and the main sulfate source in Zhuzhaoxin River,Wanfu River,Old Wanfu River,Guangfu River,and Old Canal were evaporite dissolution,while the Zhushui River sulfate was affected by both sewage and evaporite dissolution.(4) Based on the analysis of the source of sulfate in the Nansi Lake basin during the water transfer period,a reasonable sulfate prevention and control system was constructed.For rivers with a high contribution rate,the "river chief system" should be adopted to assign responsibility to people,and reasonable treatment measures should be taken before the water is transferred and used.