3.2. Isotopic data
The dual isotopic data for lake, river and underground water samples are shown in Table 1. In the nondiversion and diversion water periods, the δ34SSO4 values in the lake samples ranged from 9.5‰ (in Zhaoyang sublake) to 13.35‰ (in Nanyang sublake (SW)) and from 11.78‰ (in Zhaoyang sublake) to 14.63‰ (in Dushang sublake) respectively, with average values of 11.78‰ and 13.34‰, respectively. The fluctuation ranges of δ34SSO4 in the nondiversion and diversion water periods showed little variation. The δ34SSO4 values in river samples in the nondiversion and diversion water periods ranged from -0.07‰ (in the Chengguo River) to 22.15‰ (in the Zhuzhaoxin River) and from 4.62‰ (in the Sihe River) to 14.55‰ (in the Zhuzhaoxin River), respectively, with mean values of 10.92‰ and 10.19‰, respectively. Compared with those for the lake samples, the fluctuation ranges of δ34SSO4 values in the river samples were greater, and the δ34SSO4 value range during the nondiversion water period was greater than that during the diversion water period.
The values of δ18OSO4 in lake samples ranged from 8.33‰ (in Zhaoyang sublake) to 11.22‰ (in Nanyang sublake (SW)) and from 8.6‰ (in Zhaoyang sublake) to 9.88‰ (in Dushan sublake) in the nondiversion and diversion water periods, respectively, with average values of 10.14‰ and 9.34‰, respectively. In the river samples, the values of δ18OSO4 varied from 7.59‰ (in the Guangfu River) to 13.45‰ (in the Zhuzhaoxin River) and from 6.27‰ (in the Sihe River) to 11.81‰ (in the Zhuzhaoxin River) in the nondiversion and diversion water periods, respectively, with mean values of 9.90‰ and 9.15‰, respectively. The fluctuation ranges of δ18OSO4 values from lake samples displayed the same pattern as the δ34SSO4 values. However, the fluctuation ranges of δ18OSO4 values from river samples were definitely smaller than those of δ34SSO4 values. The maximum δ18OSO4 and δ34SSO4 values for both the lake and river samples appeared at the same location during the nondiversion and diversion water periods. The change in δ34SSO4 values was not clear in most of the samples for different periods, except samples from the Chengguo River (Table 1 and Fig. 4(i) ), and the δ18OSO4 values in samples all approached a trend of 1:1 (Table 1 and Fig. 4(j) ), except for the Sihe River. It can be assumed that the SO42- source in these two rivers had changed. In addition, the δ34SSO4 and δ18OSO4 values from the gypsum collected around NSL were 15.70‰ and 15.17‰, respectively.