2.2. Sampling
Around NSL and the surrounding rivers, two samplings campaigns were conducted during nondiversion and diversion water periods (Jul. 2018, and Jan. 2019). According to the previous monitoring data for sulfates in NSL (obtained from the Shandong South-to-North Water Diversion Project Construction Administration), 17 samples were collected during the diversion water period, including samples from 11 rivers entering NSL, one from groundwater, one from a transfer channel and four from the center of the lake; the samples were named Sample 1-17 (S1-S17). Moreover, 11 samples were collected during the nondiversion water period (Fig. 2 ). The water samples were filtered through a 0.45-μm Millipore membrane of cellulose acetate and were hermetically stored in high-density polyethylene (HDPE) bottles for chemical and isotope analysis. In addition, a gypsum sample was collected from a large gypsum mine near NSL.