3.1. Hydrochemistry
Table 1 shows the chemical data for each water sample in the
nondiversion (n=11) and diversion water periods (n=17). In the
nondiversion and diversion water periods, the
SO42- concentrations ranged from 158
mg/L to 277.65 mg/L and from 170.49 mg/L to 631.5 mg/L, respectively.
The SO42- concentrations in the
diversion water period were notably higher than those in the
nondiversion water period. The SO42-concentrations in NSL showed a gradual increasing trend from south to
north in both periods, and the maximum value of
SO42- was observed in the Nanyang
sublake (NE). The highest concentrations of some major ions, such as
HCO3-, Cl-,
Na+ and Mg2+, were observed in the
Nanyang sublake (SW) (HCO3- up to
245.51 and 215.28 mg/L, Cl- up to 155.51 and 138.02
mg/L, Na+ up to 226.59 and 170.33 mg/L and
Mg2+ up to 7.77 and 42.85 mg/L in the two periods).
The SO42- concentrations and
concentrations of other major ions, except for Na+ and
K+, in the Nanyang sublake (SW) were similar to those
in the Nanyang sublake (NE). The pH and EC values in the Nanyang sublake
(SW) were greatest in NSL during the nondiversion water period and
reached 8.5 and 1,388 μs/cm, respectively. The concentrations of
SO42- and other ions in the Dushan and
Zhaoyang sublakes were lower than those in the Nanyang sublake, except
for NO3- and Ca2+.
The SO42- concentrations in the main
inflowing rivers around NSL ranged from 149.00 mg/L to 685.49 mg/L
during the nondiversion water period. The maximum
SO42- concentrations appeared in the
Chengguo River, the main river entering the Zhaoyang sublake. The Sihe
River, Old Wanfu River, Guangfu River, Zhushui River, Zhuzhaoxin River
and Old Canal are important inflowing rivers around the Nanyang sublake.
The average SO42- concentration in
these rivers was approximately 319.34 mg/L, with maximum concentrations
being observed in the Zhuzhaoxin River (up to 590.65 mg/L). Similar to
the findings in the nondiversion water period, the
SO42- concentrations in the inflowing
rivers around NSL ranged from 142.06 mg/L to 671.32 mg/L during the
diversion water period, and the maximum value appeared in the Zhuzhaoxin
River, a major inflowing river of the Nanyang sublake (NE). The
Na+ content in the Zhuzhaoxin River was also maximum
value among those for all the inflowing rivers, reaching 357.04 mg/L,
and the Cl- content was slightly lower than that in
the Old Wanfu River. The Old Wanfu River not only displayed the maximum
Cl- value (320.66 mg/L) but also the highest EC (1,967
μs/cm) and HCO3- values (451.18 mg/L)
among all river samples. Additionally, there was little difference in
the SO42- concentrations between the
Zhuzhaoxin River and the Old Wanfu River. The Old Wanfu River is a main
inflowing river of the Nanyang sublake (SW). The
SO42- concentration in the Old Canal
was 559.69 mg/L and was slightly lower than that in the Zhuzhaoxin
River. The proportions of SO42- and
other major ions in the river samples around NSL exhibited trends
similar to those in NSL.
Compared to those in the rivers, the
SO42- concentrations in groundwater
were lower during the nondiversion water period, whereas
HCO3- contents were as high as 506.47
mg/L and the Ca2+ content reached a maximum value of
143.81 mg/L. In contrast to the trends in the nondiversion water period,
the SO42- concentrations in
groundwater clearly increased, and other major ion contents, such as
HCO3-, Cl-,
Na+, Mg2+ and
Ca2+, displayed marked increases during the diversion
water period.
These hydrochemical data can be used to determine the water type. The
main water types of NSL during the nondiversion and diversion water
periods were
Na+-SO42--Cl-and
Na+-SO42--HCO3-,
respectively (Fig. 3 ). Similar to NSL, the water types of the
main inflowing rivers were
Na+-SO42--Cl-and
Na+-SO42--HCO3-,
respectively. The water type in NSL and the surrounding rivers was
similar to Gonghe geothermal water (Liu, Guo, Zhang, Wang &
Wang, 2017) , where the ions mainly came from gypsum dissolution;
therefore, the ions in NSL and the surrounding rivers might have the
same ion sources. However, the water types in groundwater was
Ca2+-SO42--Cl-during both the nondiversion and diversion water periods. This finding
indicates that the impact of groundwater inputs on NSL is low.