Using
sulfur and oxygen isotopes to analyze the source of sulfate associated
with the Eastern Route of the South-to-North Water Diversion Project in
China
Running Head : Sulfate sources in the South-to-North Water
Diversion Project in China.
Abstract:Since
the Eastern Route of the South-to-North Water Diversion Project
(SNWD-ERP) officially began operation, it was found that the
concentrations of sulfate rapidly increased after water transfer from
Jiangsu Province to Shandong Province, especially in Nansi Lake (NSL).
The direct and original sources of sulfate in NSL and its surrounding
inflowing rivers were investigated by analyzing the hydrochemical
properties of the water bodies and sulfur and oxygen isotope
compositions of dissolved sulfate during nondiversion and diversion
water periods. During the diversion water period, the largest direct
source of high SO42- concentrations in
NSL was evaporite dissolution, accounting for 52.18% of the total
contribution. In contrast, during the nondiversion water period, the
maximum contribution of SO42- came
from inflowing river inputs. To ensure the safety of the water supply of
the SNWD-ERP, some measures must be taken to decrease the sulfate inputs
from inflowing rivers, such as formulating strict discharge standards to
reduce the direct discharge of sewage into the inflowing rivers around
NSL.
Keywords:Nansi
Lake; Sulfate; δ34SSO4;
δ18OSO4;
Diversion
water period
Introduction
China is a country with water shortages, and the per capita water
resources of China are below the global average (Du, Fan, Liu,
Park, Tang, 2019;Liu & Yang, 2012; State Council, 2012) . The most
obvious feature is the disequilibrium in water resources between the
north and the south, which is largely due to the uneven spatial
distribution of precipitation, and the northern region is generally less
water-rich than the South China region (Bian, Yan & Xu, 2014;
Peng, Zhang, Yin & Wang, 2018; Wei, Yang, Abbaspur, Monsavi & Gnauck,
2010; Xinchun et al., 2017; Yang & Zehnder, 2016; Zhao, Zuo &
Zillante, 2017) . The socioeconomic development of the northern region
is greatly limited by the lack of water resources (Li, Xiong,
Zhang, Wang & Wang, 2016; Zhao et al., 2017; Zhang & Anadon, 2014) .
Therefore, in 2002, the Chinese government launched the South-to-North
Water Diversion Project (SNDP) to solve the problem of water shortages
in the northern region (He, Hipel & Kilgour, 2014) . The SNDP
is divided into three routes, including the Western Route Project, the
Middle Route Project and the Eastern Route Project.
The Eastern Route Project (SNDP-ERP) is an integral part of the
South-to-North Water Diversion Project in China. The project spans the
Yangtze River basin, Yellow River basin, Huai River basin and Hai River
basin, and the total channel distance of water diversion is
approximately 1,466.24 kilometers (Zhuang et al., 2019 ). The
SNWD- ERP diverts water from the lower reaches of the Yangtze River to
Jiangsu, Shandong and Hebei Provinces, and to Tianjin
municipality
with a
complex hydraulic
system of interconnected lakes, rivers and canals (Fig. 1 ).
Interconnected lakes, such as Nansi Lake, are thus used as storage
reservoirs and water channels. The SNWD-ERP has officially been
operational for six years, starting in May 2012; it runs during the dry
season and stops during the wet season, which greatly reduces the
water-shortage pressure along the water transfer line. However, it is
difficult to ensure long-term water quality due to the complex
hydraulic
system (Gu, Shao & Jiang, 2012; Li, Li & Zhang, 2011; Zhuang
et al., 2019) . Long-term monitoring indicated that the sulfate
concentrations increased rapidly after water transfer from Jiangsu
Province to Shandong Province and reached 400 mg/L in Nansi Lake.
Sulfur is not only quite common in the Earth’s crust but is also a
common and important biological element (Schlesinger, 2005;
Valiente et al., 2017 ). Sulfur acts as an electron acceptor and
electron donor in many redox reactions; therefore, the sulfur cycle
plays an important role in biogeochemical processes (Clark &
Fritz, 1997; Hoefs, 2015; Feng; Li et al., 2011; Ono, Sim & Bosak,
2014; Rock & Mayer, 2009; Spence & Telmer, 2005).Although sulfate is nontoxic, if
sulfate concentrations are too high, water quality declines, and high
concentrations may even cause diarrhea in humans (Killingsworth
& Bao, 2015; Nakano et al., 2005 ). Sulfate is a ubiquitous component
in surface waters. The origins of sulfate in surface water are divided
into two groups: a) natural sources, that is, form evaporite
dissolution, atmospheric deposition, and sulfide oxidation, and b)
anthropogenic emissions, that is, form chemical fertilizer use, urban
sewage and industrial mine wastewater discharge ( Brenot,
Carignan, France-Lanord & Benoit, 2007; Calmels, Gaillardet, Brenot &
France-Lanord, 2007; Cao, Wu, Zhou, Sun & Han, 2018; Killingsworth &
Bao, 2015; Krouse & Mayer, 2000; Otero, Soler & Cannals, 2008; Sun,
Kobayashi, Strosnider & Wu, 2017;Yang, Telmer & Veizer, 1996; Yoon et
al., 2008 ).
The sulfur isotope compositions of sulfate are different if the sulfate
sources are different (Brenot et al., 2007; Ingri, Torssander,
Andersson, Morth & Kusakabem, 1997; Krouse & Mayer, 2000; Morth,
Torssander, Kusakabe & Hultberg, 1999; Schiff, Spoelstra, Semkin &
Jeffries, 2005; Tuttle, Breit & Cozzarelli, 2009; Yoon et al., 2008;
Yuan & Mayer, 2012 ). Therefore, stable sulfur isotopes have been used
in the past several decades to track the sources of dissolved sulfates
(Hosono, Delinom, Nakano, Kagabu & Shimada, 2011; Killingsworth
& Bao, 2015; Kim, Yun, Yoon & Mayer, 2019; Rivas, Pozo & Paz, 2014;
Valiente et al., 2017; Yoon et al., 2008; Zhou et al., 2016; ). However,
it is difficult to study the original sources of dissolved sulfates in
lakes; e.g., the dissolved sulfates from atmospheric precipitation and
sulfide have the same isotope signature (Mayer, Shanley, Bailey
& Mitchell, 2010; Yang et al., 2010 ; Tuttle et al., 2009). As
a result, the δ34S value range may overlap (the
δ34S values from both of the above sulfate sources are
low). The sulfur isotope composition is affected by biological reduction
and negatively correlated with the sulfate concentrations (low
concentrations and high isotope values), which may coincide with the
sulfur isotope values of the sulfates formed by evaporite dissolution(Krouse & Mayer, 2000; Stam, Mason, Pallue & Cappellen, 2010;
Young, Cadieux, Peng, White & Pratt, 2018 ). The abovementioned
phenomena make analyses of the sources of dissolved sulfates
complicated.
The oxygen isotope composition of newly formed sulfates depends on many
different factors in natural water bodies, and it is possible to
characterize sulfate sources by coupling the isotopes of sulfur and
oxygen (Balci, Shanks, Mayer & Mandernack, 2007; Karim &
Vezier, 2000 ). Therefore, studies have begun to confirm the sulfate
sources of in rivers, glaciers, groundwater, wetlands and the atmosphere
by using a dual isotope approach (Cao et al., 2018; Guo et al.,
2019; Killingsworth & Bao, 2015; Li, Gan, Zhou & Liu, 2015; Young et
al., 2018; Zhou et al., 2016 ). However, there are few studies of the
sulfate sources associated with artificial water transfer.
The aims of this study is to trace the sources of dissolved sulfate
after water enters Shandong Province using a dual isotope approach.
Nansi Lake was chosen as the targeted study area because it has the
highest sulfate concentrations in Shandong Province.
The geological characteristics, hydrochemical types and sulfur and
oxygen isotope compositions of sulfate in Nansi Lake, the surrounding
rivers, and underground water during the nondiversion and diversion
water periods (Jul. 2018, and Jan. 2019) were investigated and analyzed.