4.3. Contributions from different sulfate sources
After sulfate dissolves in water, it is difficult to change its isotopic
composition
(microbial reduction has little effect on sulfate in natural water);
therefore, the source information is retained ( Li et al., 2011;
Zhou et al., 2016) used the characteristics of the isotopic composition
in natural water and successfully determined that the sulfate in the
Jialing River in the rainy season is mainly derived from sulfide
oxidation with a 56% contribution ratio, and in the dry season, the
sulfate is mainly derived from domestic and industrial wastewater with a
49% contribution ratio. Therefore, in this paper, stable isotopes were
also used to calculate the contribution ratios from each source of
sulfate in NSL.
To accurately calculate the contribution rates, according to the
geographic position
of each main SO42- source, NSL was
divided into different areas. In the nondiversion water period, the
SO42- contents in the Nanyang sublake
and its inflowing rivers were high, and the concentrations in other
sublakes and their inflowing rivers were low, except in the Chengguo
River. Additionally, low SO42-contents have little effect on the environmental and water quality in
natural waters. Therefore, the Nanyang sublake, as the key research area
of NSL, was divided into different areas to calculate the contribution
rates of each main SO42- source.
Unlike in the nondiversion water period, NSL was divided into different
areas in the diversion water period, because of the environmental
influence of high SO42- contents in
each sublake and the inflowing rivers during the diversion water period
could not be ignored.