4.3.1 Nondiversion water period
Fig. 3 shows that there were significant differences in the
chemical types of water
in the Old Canal and in the Nanyang sublake and that the
SO42- concentrations in the Old Canal
were lower than those in the Nanyang sublake. Therefore, the Old Canal
was not the main source for the Nanyang sublake, and the impact of the
Old Canal on sulfates in the Nanyang sublake could be ignored during the
nondiversion water period.
In addition, the converging area of the Sihe River and the Nanyang
sublake was the boundary of the distribution of the gypsum salts in the
WSD, and there was more gypsum salts distributed in the area of
southwest of the Sihe River (Qi, 2010 ). Therefore,
SO42- from evaporite dissolution was
not considered as the main source of sulfate in the Nanyang sublake,
except in the converging area of the Sihe River and the Nanyang sublake.
According to the spatial distribution of the adjacent main
SO42- source, the Nanyang sublake was
divided into three parts: NYSL-1, NYSL-2 and NYSL-3 (Fig.
7(a) ). NYSL-1 was the mixing area of the Guangfu River, the Zhushui
River and the Nanyang sublake. NYSL-2 was the convergence area of the
Sihe River and the Nanyang sublake. NYSL-3 was the mixing area of the
Zhuzhaoxin River, the Old Wanfu River and the Nanyang sublake. We
hypothesized that the δ34SSO4 values
in each region reached the value observed in the Nanyang sublake during
the nondiversion water period. The
δ34SSO4 values were measured to the
northeast and southwest of the Nanyang sublake due to the complex
SO42- concentration distributions in
the Nanyang sublake. In the NYSL-1 and NYSL-2 regions, the
δ34SSO4 value was 12.50‰, and the
δ34SSO4 value was 13.35‰ in the NYSL-3
(Table 1 ).
The SO42- contribution rates of each
main source can be calculated by the following formulas (Li et
al., 2011 ):
δ34Slake=δ34Si*A+δ34Sj*B
(1)
A + B= 100% (2)
δ34Slake =
δ34Sgypsum * C +
δ34Sk *D (3)
C + D = 100% (4)
where δ34Slake is the value of
δ34SSO4 in the lake;
δ34Si,
δ34Sj and
δ34Sk are the values of
δ34SSO4 from different inflowing river
inputs; and δ34Sgypsum is the value of
δ34SSO4 in gypsum (15.70‰ here). A, B,
C and D are the contribution rates. Eq. (1) and Eq.(2) were used for NYSL-1 and NYSL-3, and Eq. (3) and
Eq. (4) were used for NYSL-2.
All the calculated contribution rates are summarized in Table
2 , and the maximum contribution of
SO42- in the Nanyang sublake came from
the Old Wanfu River input and was as high as 32.56%, followed by the
contribution of evaporite dissolution (25.60%). Therefore, the
inflowing river inputs were the main sulfate source in the Nanyang
sublake in the nondiversion water period.