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\begin{document}

\title{Significance of isotopic and geochemical methods to determine the
evolution of inland brackish and bitter water: an example from the Zuli
river in the upper reaches of the Yellow River, China.}



\author[1]{zihao liu}%
\author[1]{Hongbing Tan}%
\author[2]{Mark Brusseau}%
\affil[1]{Hohai University}%
\affil[2]{The University of Arizona}%


\vspace{-1em}



  
  \date{May 23, 2024}


\begingroup
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\maketitle
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\selectlanguage{english}
\begin{abstract}
With the increasing demand for water resources, the utilization of
marginal water resources of poor-quality has become a focus of
attention. The brackish water developed in the Loess Plateau is not only
salty but also famous for its ``bitterness''. In the present work,
multi-isotope analysis (Sr, B) was combined with geochemical analysis to
gain insight into the hydrogeochemical evolution and formation
mechanisms of brackish water. These results demonstrate that groundwater
in the headwater is influenced by carbonate weathering. After the
confluence of several tributaries in the headwater, the total dissolved
solids (TDS) of water is significantly increased. The dissolution of
evaporates is shown to be the main source of salinity in brackish water,
which also greatly affects the Sr isotopic composition of water. This
includes the dissolution of Mg-rich minerals, which is the main cause of
the bitterness. Furthermore, the release of calcium from the dissolution
of gypsum may induce calcite precipitation and incongruent dissolution
of dolomite, which also contributes to the enrichment of magnesium. The
highly fractionated boron isotopic values observed in the upstream
groundwater were explained by boron interacting with clays, illustrating
the important role played by the cationic exchange reaction. The inflow
of brackish groundwater is the source of the observed quality of the
river water. River water with relatively enriched 11B contents reflects
the occurrence of evaporation along the flow path of the river. This
process further aggravates the salinization of river water, with water
quality evolving to saline conditions in the lower reach. When the river
reaches the valley plain, the 87Sr/86Sr ratios decreases significantly,
which is primarily related to erosion of the riverbanks during runoff.
These results indicate that water resource sustainability could be
enhanced by directing focus to mitigating salinization in the source
area of the catchment.%
\end{abstract}%



\sloppy


\textbf{Significance of isotopic and geochemical methods to determine
the evolution of inland brackish and bitter water: an example from the
Zuli river in the upper reaches of the Yellow River, China}

\textbf{Abstract}

With the increasing demand for water resources, the utilization of
marginal water resources of poor-quality has become a focus of
attention. The brackish water developed in the Loess Plateau is not only
salty but also famous for its ''bitterness''. In the present work,
multi-isotope analysis (Sr, B) was combined with geochemical analysis to
gain insight into the hydrogeochemical evolution and formation
mechanisms of brackish water. These results demonstrate that groundwater
in the headwater is influenced by carbonate weathering. After the
confluence of several tributaries in the headwater, the total dissolved
solids (TDS) of water is significantly increased. The dissolution of
evaporates is shown to be the main source of salinity in brackish water,
which also greatly affects the Sr isotopic composition of water. This
includes the dissolution of Mg-rich minerals, which is the main cause of
the bitterness. Furthermore, the release of calcium from the dissolution
of gypsum may induce calcite precipitation and incongruent dissolution
of dolomite, which also contributes to the enrichment of magnesium. The
highly fractionated boron isotopic values observed in the upstream
groundwater were explained by boron interacting with clays, illustrating
the important role played by the cationic exchange reaction. The inflow
of brackish groundwater is the source of the observed quality of the
river water. River water with relatively enriched \textsuperscript{11}B
contents reflects the occurrence of evaporation along the flow path of
the river. This process further aggravates the salinization of river
water, with water quality evolving to saline conditions in the lower
reach. When the river reaches the valley plain,
the\textsuperscript{87}Sr/\textsuperscript{86}Sr ratios decreases
significantly, which is primarily related to erosion of the riverbanks
during runoff. These results indicate that water resource sustainability
could be enhanced by directing focus to mitigating salinization in the
source area of the catchment.

\textbf{Key words} : Water salinization; Strontium isotope; Boron
isotope; Geochemical tracers; Inland river catchment.

\textbf{1. Introduction}

The region of the Loess Plateau in China comprises an inland area with
limited freshwater resources and a considerable amount of brackish water
resources. The brackish water resource is valuable to the irrigated
agricultural in this region. However, the formation mechanism of this
water resource remains unclear, which is constraining the rational
utilization of brackish water. (Luo, Chen, \& Han, 2010). Numerous
studies have been conducted over the past several decades to assess the
origin of brackish groundwater on a regional scale (Barth, 1998; Brenot,
N\selectlanguage{ngerman}égrel, Petelet-Giraud, Millot, \& Malcuit, 2015; Cartwright, 2004; Cary
et al., 2015; Jørgensen, Andersen, \& Engesgaard, 2008; Werner et al.,
2013; Sahib, Marandi, \& Schüth, 2016). Most of these previous studies
were focused on the coastal areas, where the formation of saline
groundwater was usually related to seawater intrusion. With the
increasing water demand, there is increasing study and focus on the
formation of brackish water in inland areas, where the geological
contexts and hydrological conditions are more complex than coastal areas
(Farid, Zouari, Rigane, \& Beji, 2015; Gamboa, Godfrey, Herrera,
Custodio, \& Soler, 2019; Gil-Márquez, Barberá, Andreo, \& Mudarra,
2017).The sustainable management of inland brackish water resources is a
global issue and requires a thorough assessment of the formation
mechanism of brackish water (Alcalá \& Custodio, 2008; Cartwright, 2004;
Cary et al., 2015; Ghassemi, Jakeman, \& Nix, 1995; Gil-Márquez et al.,
2017; Monjerezi, Vogt, Aagaard, Gebru, \& Saka, 2011).

The Zuli River is a first-order tributary of the Yellow River, which is
located in the western Loess Plateau. Except in the headwater, the
groundwater and surface water in this catchment are both brackish, with
a characteristic of ``bitterness''. Bitterness is an important factor
affecting the quality and usability of water resources, particularly in
inland areas (Gil-Márquez et al., 2017). However, few studies have been
conducted to investigate the formation mechanism of bitterness in water.

Our previous study showed that groundwater recharge in the Zuli River
catchment is produced by the infiltration of precipitation in the
headwaters (Liu, Tan, Shi, Xu, \& I.Elenga, 2019). During this
recharging process, the upstream groundwater undergoes rapid
salinization. Several hypotheses have been advanced in previous studies
as to the source of salinity in brackish water. Current knowledge
typically attributes the salinization of groundwater in most inland
areas to the mixing of old groundwater in deep strata (Herrera et al.,
2018), which usually means the salinity of groundwater originated from
long periods of water-rock interactions (Petrides, Cartwright, \&
R.Weaver, 2006; Skrzypek, Dogramaci, \& F.Grierson, 2013). However, our
recent study showed that even under the rapid renewal of groundwater,
the fresh groundwater from the headwaters still evolves into brackish
water with rapid salinization (Liu et al., 2019). Several hypotheses
have been advanced in previous studies as to the source of salinity in
brackish water. The large amounts of soluble salts in loess were
identified as a potential source of salinity (Luo et al., 2010). The
contribution of other hydrogeochemical processes still needs to be
considered comprehensively, especially the origin of the bitterness.

The shortage of freshwater resources in many areas has led to the use of
brackish water resources for agriculture in the Zuli River catchment.
The long-term utilization of this poor-quality water resources has
severely restricted local economic development. In recent years, the
government launched several agricultural water conservancy projects,
such as ''The Taohe River Diversion Project '' and '' The Yellow River
Diversion Project '' that divert freshwater flow into the Zuli River for
the dilution of saline river water, but they had minimal impact. How to
optimize water resources in a cost-effective and sustainable manner is a
critical question for this area.

The present contribution uses an integrated approach of geochemical and
isotopic analysis to identifying the origins of salinity and evaluating
salinization processes. The general water chemical methods are difficult
to discriminate the source of solutes in groundwater precisely. Research
increasingly suggests that a multi-isotope approach is necessary to
resolve the outstanding source of solutes in water (Cary et al., 2015;
Gamboa et al., 2019; Jørgensen et al., 2008). Such an approach has been
shown to be more effective in characterizing hydrogeochemical processes
(Bullen, Krabbenhoft, \& Kendall, 1996; Cartwright, Weaver, Cendón, \&
Swane, 2010; Cary et al., 2015; Harrington \& Herczeg, 2003). The study
uses strontium isotopes and boron isotopes to investigate the possible
processes responsible for the formation of brackish water. As a
relatively stable element, strontium isotopes are minimally fractionated
in chemical and biochemical processes. Groundwater in equilibrium with
Sr-bearing minerals attains\textsuperscript{87}Sr/\textsuperscript{86}Sr
values that reflect the isotopic ratio of the minerals, leading to
variation of the strontium isotopic ratio in different settings
(Harrington \& Herczeg, 2003; Monjerezi et al.,2011; Sahib et al.,
2016). Therefore, the\textsuperscript{87}Sr/\textsuperscript{86}Sr ratio
is classically used to provide information on the water-rock interaction
under different geological contexts (Bullen et al., 1996; Brenot et al.,
2015; Cartwright, 2004; Cartwright et al., 2010; Monjerezi et al., 2011;
Palmer \& Edmond, 1992; Pingitore \& Eastman, 1986). On the contrary,
boron is a relatively reactive element and mainly enriched in various
types of rocks and water. Due to the isotopic distinctions, boron
isotopes are prone to fractionate in many geochemical processes because
of the larger relative difference in mass between its primary isotopes
(Palmer, Spivack, \& Edmond, 1987; Vengosh, Heumann, Juraske, \& Kasher,
1994). Boron isotopes have been gradually applied to distinguish the
original solute sources in groundwater, such as marine sources with
enriched \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B values and continental sources with
significantly depleted \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B values (Barth, 1998;
Palmer \& Swihart, 1996; Vengosh, 2005). Therefore, boron isotope is
also an effective tracer for understanding the geochemical evolution
processes on a regional scale (Barth, 1993; Cary et al., 2015; Morell et
al., 2008; Palmer et al., 1987; Vengosh et al., 1994). Thus, the
combination of boron and strontium isotopes can be used more precisely
to understand the hydro-geochemical evolution processes in the
groundwater system on a regional scale. To our knowledge, this study is
the first to report on the strontium isotopes of brackish water as well
as the boron isotopes of local precipitation, river water, and
groundwater from the study area. It is anticipated that the results
obtained herein will fill in that gap in the isotope study of the Loess
Plateau.

\textbf{2. Study area}

The Zuli River is a first-order tributary of the Yellow River. The total
length of this river is 224 kilometers, and the annual runoff is nearly
about 1.19\selectlanguage{ngerman}×10\textsuperscript{8}m\textsuperscript{3}. The Zuli River
Catchment occupies l0, 653 km\textsuperscript{2} of the western Loess
Plateau. The Zuli river originates from the Huajialing Mountain area and
is composed of the Zu and Li Rivers (Fig. 1). The main tributary of the
Zuli River is the Guanchuan River (Fig. 1).

The Zuli River Catchment can be classified as an arid-semi arid climate
zone. Temperatures in the whole catchment (Huining weather station in
the midstream area; Fig.1) shows highly seasonal variations (Fig.2a).
The climate is characterized by cold winters with a mean temperature of
-6.3 \selectlanguage{english} and warm summers with a mean temperature of 18.9 \selectlanguage{english}. The mean
multi-annual precipitation recorded from 2005 to 2019 in the Huining
weather station is about 387.1 mm (Fig.2b). Affected by the continental
monsoon, the annual precipitation in the Zuli River catchment is mainly
dominated by summer rainfall from May to August (Fig.2a). With respect
to precipitation, the mean annual potential evaporation is about 1800mm
and is nearly five times greater than the mean annual precipitation in
the Zuli River catchment (Luo et al., 2010).

The Huajialing Mountain area is the source region of the Zuli River
Catchment, which is also the watershed between the Zuli River and the
Weihe River. Thick layers Silurian carbonate rocks are deposited in this
area (Fig.3a), affected by large-scale tectonic activity, joints and
fissures were developed in the strata of headwater. Additionally,
karstic features have developed, and fissure water and bedrock fissure
water are present in the fracture zone (Liu et al., 2019).

The Zuli River Catchment is a typical hilly area on the Loess Plateau.
This river is located in the canyon area, with an altitude ranging from
1396 to 2377m (Fig. 3). The geological strata of the Zuli River
Catchment can be divided into three main units. Simplified geology with
major structural characteristics of the Zuli River catchment is
displayed in Fig. 3. The basement is constituted by Silurian carbonate
rocks, Cretaceous clastic rocks and Permian monzonitic granite (Fig.
3a). A Tertiary red clay layer and the Quaternary loess layer are
deposited successively in the basement (Fig. 3b). A large amount of
soluble minerals exists in the loess, such as halite, gypsum, etc
(Tsunekawa, Liu, Yamanaka, \& Du, 2014; Fan et al., 2016; Xiao, Zhang,
\& Jin, 2016).

\textbf{3. Materials and methods}

A total of 63 samples were collected from the Zuli River Catchment and
these samples were divided into five types: precipitation (n=5),
groundwater (n=20), river water (n=25), soil, and river suspended
particulates (n=13)(Fig. 1). Local precipitation of headwaters was
sampled monthly from May to September for one season (Fig. 1). TDS and
pH measurements were performed in the field with a calibrated portable
Multi-Parameter Analyzer (HACH HQ40D; typical EMC deviation: +-0.1 pH,
+-1\% of TDS). Water samples were filtered in the field at 0.45 \selectlanguage{greek}μ\selectlanguage{english}m for
hydrochemistry analyses and acidified for cations
and\textsuperscript{87}Sr/\textsuperscript{86}Sr analysis to pH
\textless{} 2 with ultrapure HNO\textsubscript{3}. For the
hydrochemistry analysis, the water samples with TDS \textgreater{}1000
mg/l were diluted to TDS less than 500 mg/l. Samples for Boron isotopic
analysis were collected in a separate bottle.

All chemical compositions of the samples (n=50) were analyzed at the
State Key Laboratory of Hydrology-Water Resources and Hydraulic
Engineering, Hohai University, China. Major cations were analyzed by
inductively coupled plasma-atomic emission spectrograph (ICP-AES)
(Instrumental Error \textless{}5.0\%), and major anions were analyzed by
ion chromatography (ICS-2000) (Instrumental Error \textless{}2.0\%).

For strontium isotopes, the isotopic compositions of Sr (n=18; Table 1)
were determined by TIMS (Thermal Ionization Mass Spectrometry, Triton,
VG354) with nine Faraday collectors at the Institute of Geochemistry,
Nanjing Nantai. The \textsuperscript{87}Sr/\textsuperscript{86}Sr value
for the standard NIST987 was 0.710236 \selectlanguage{ngerman}± 0.000007 (2r, n=62) during the
measurement period of our samples. The total blank for Sr was less than
0.5 ng, negligible with respect to the total strontium in the analyzed
precipitation samples.

Boron isotopes (n=28; Table 1) were analyzed using a Neptune Plus
MC-ICP-MS (Nanjing) with an ESI PFA 50 \selectlanguage{greek}μ\selectlanguage{english}L/min nebulizer in a quartz
cyclonic spray chamber. The isotopic standard
(\textsuperscript{11}B/\textsuperscript{10}B) \textsubscript{standard
NIST 951} =4.04362. To reduce the memory effect, continuous washing with
3\% HNO\textsubscript{3} and 1\% HNO\textsubscript{3} and Millipore
water in sequence for \textasciitilde{}25 min was conducted. The final
isotopic compositions are reported as \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B= 1000
(R\textsubscript{sample}/R\textsubscript{standard}-1). The average
internal analytical precision (n=100) and the external reproducibility
of the measured \textsuperscript{11}B/\textsuperscript{10}B ratios of
200 ng/mL NIST 951 are \selectlanguage{ngerman}±0.02 \selectlanguage{english}%0 (2 SE) and 0.11 \selectlanguage{english}%0 (2\selectlanguage{greek}σ\selectlanguage{english}), respectively.

\textbf{4. Results}

The chemical parameters,\textsuperscript{87}Sr/\textsuperscript{86}Sr
ratios and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B values of the analyzed samples are
given in Table 1. The pH in water samples shows a narrow range
(7.32-8.85), with a mean value of 8.08 \selectlanguage{ngerman}± 0.36 (Table 1). The TDS of all
water samples varied considerably from 356.7 to 11296 mg/l (Table 1),
with a general increase from the source region to downstream. The source
groundwater with low TDS is dominated by Mg-Ca-Na-HCO\textsubscript{3}
type, while the upstream groundwater and river water were saline water
with a Na-Mg-Cl-SO\textsubscript{4} -type facies. Cl/Br ratios of source
groundwater samples ranged from 409.0 to 519.3. The upstream groundwater
and river water samples had a relatively steady trend of Cl/Br ratios,
ranging from 1242 to 2405. Ca and Mg concentrations of these water
samples are well correlated to SO\textsubscript{4}, with
(Ca+Mg)/SO\textsubscript{4} ratio of most saline water samples close to
1. The Mg/Ca ratio of saline water samples generally exceeds 1, which
indicates the enrichment of Mg with water salinization.

Strontium concentrations
and\textsuperscript{87}Sr/\textsuperscript{86}Sr ratios in groundwater
ranged from 0.5 to 9.9 mg/l, and from 0.710903 to 0.711784,
respectively. The upstream groundwater samples had a higher strontium
concentration and higher \textsuperscript{87}Sr/\textsuperscript{86}Sr
ratios than source groundwater. The strontium concentration of river
water samples varied between 4.2 and 11.1 mg/l,
with\textsuperscript{87}Sr/\textsuperscript{86}Sr ratios between
0.710916 and 0.711427. The river water presents higher Sr contents and
lower\textsuperscript{87}Sr/\textsuperscript{86}Sr values compared to
that of upstream groundwater (Table 1). The Strontium concentrations are
in a relatively narrow range (0.23-0.53) in the soil samples
(water-soluble) collected from riverbanks, while
the\textsuperscript{87}Sr/\textsuperscript{86}Sr ratio varied between
0.710912 and 0.713937 with an increasing trend from mountaintop to the
foothills. Strontium correlated well with Calcium and Chlorine in
brackish water samples. The Sr/Cl ratio of source groundwater samples
ranged from 0.034 to 0.036 and is significantly higher than that of the
upstream groundwater (0.002-0.007). The Sr/Ca ratio of water samples
also presents a systematic increase with water salinization.

Values of \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B in water are highly variable and ranged
from -5.79%0 to +3.47%0, from -8.35%0 to -5.77%0, from +11.48%0 to +23.17%0
and from +17.45%0 to +37.32%0 for precipitation, the source groundwater,
the upstream groundwater and the river water, respectively. The Boron
isotope ratios of the river water samples displayed a broader range
(17.45%0 to 37.32%0) relative to upstream groundwater (11.48%0 to 23.17%0)
(Table 1), but still lower than the \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B values of
seawater (39.5\selectlanguage{ngerman}±1\selectlanguage{english}%0) (Vengosh et al., 1994). The river suspended
particulates samples had \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B values of 3.50%0 to
5.42%0. The \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B values of soil samples collected from
profiles under water and acid treatment were from -2.13%0 to +5.66%0 and
from 0.60%0 to 7.42%0, respectively (Table 1).

\textbf{5. Discussion}

\textbf{5.1 Formation of saline water}

\textbf{5.1.1 Formation of freshwater in headwater}

The strata of the mountain area in the headwater of the Zuli River are
mainly composed of a set of marine carbonate rocks (Zhan et al., 2010).
In our previous study, groundwater was considered as recharged by
precipitation in the headwaters based on the analysis of stable isotopes
data (\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{2}H, \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O) (Liu et al., 2019).
The groundwater in the headwater region is characterized by higher
strontium concentration and\textsuperscript{87}Sr/\textsuperscript{86}Sr
ratios relative to those determined for precipitation (strontium
concentrations:
(0.002-0.3mg/l),\textsuperscript{87}Sr/\textsuperscript{86}Sr
ratio:0.7078-0.7092 (Bullen et al., 1996))(Table 1). This suggests that
there is dissolution of Sr-containing minerals in the source
groundwater, with this process increasing the strontium concentration
and affecting the strontium isotopic composition of water. The higher
Sr/Cl ratio in source groundwater probably reflects rock weathering as
an important control of the chemical composition of groundwater with low
TDS (Monjerezi et al., 2011) (Fig. 5b). The Sr/Cl ratio and
the\textsuperscript{87}Sr/\textsuperscript{86}Sr ratio show an inverse
correlation in the source groundwater (Fig.5b). The inverse correlation
between the Sr/Cl ratio and\textsuperscript{87}Sr/\textsuperscript{86}Sr
ratio is generally related to the significant dissolution of carbonate
minerals (Harrington \& Herczeg, 2003). This process is also supported
by the\textsuperscript{87}Sr/\textsuperscript{86}Sr ratio of source
groundwater (0.710903-0.711041, NO.2,4) compatible with the signature of
limestone (\textsuperscript{87}Sr/\textsuperscript{86}Sr: 0.709-0.713)
(Cartwright et al., 2010) (Table 1).

Studies focusing on boron isotopic composition in precipitation in the
Loess Plateau are sparse. In this work, the source groundwater (Sample
NO. 1-2) shows lighter boron isotopic composition than precipitation
(Sample NO. 46-50) (Table 1), which may indicate that there is an input
of boron with low \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B value in source groundwater. In
the mountain area of headwater, there are many exposed carbonatite rocks
(Zhan et al., 2010). The narrow range of \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B
variation in the source groundwater (-8.35%0\textasciitilde{}-5.77%0,
NO.1-2) can be attributed to carbonate rock weathering in which
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B values usually range from -15%0 to -5%0 (Palmer \&
Swihart, 1996; Romer, Meixner, \& F\selectlanguage{ngerman}örster, 2014). Due to the
conservative property of chloride and bromide, the Cl/Br ratio (weight)
was used as an indicator to judge the source of salinity in groundwater,
especially in distinguishing between marine and non-marine (Cartwright,
2004; Edmunds, Ma, Aeschbach-Hertig, Kipfer, \& Darbyshire, 2006). In
this study, the Cl/Br ratio of groundwater in headwater is similar or
slightly higher than that of seawater (Alcalá \& Custodio, 2008) (Fig.
4a), suggesting these ions are of marine origin (Skrzypek et al., 2013).
These above characteristics indicate that the dissolution of carbonate
minerals is the main process that influences the geochemical and
isotopic composition of groundwater in headwater.

\textbf{5.1.2 Formation of brackish groundwater in the upstream}

The upstream groundwater shows an obvious salinization than groundwater
in headwater. The TDS in upstream groundwater varies from 1177 to 8216
mg/l (Table 1), which is classified as brackish water (Freeze \& Cherry,
1979). According to the previous work, the upstream groundwater is
recharged by groundwater in headwater and precipitation. And the tritium
data shows a rapid circulation of groundwater (less than 40 years) in
the upstream area (Liu et al., 2019). Groundwater still evolves to
brackish water from headwater to the upstream area under such a rapid
replenishing, which is rare in most similar inland areas around the
world.

The \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B values of upstream groundwater are
significantly lower than those of seawater (Barth, 1993), which
indicates the geochemical composition in upstream groundwater is of
non-marine origins (Fig. 7). The variation range of
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B value in these water load samples (3.39%0-5.42%0;
NO.61-63) and soil samples (acid-extracted) (0.6%0-7.42%0; NO.58-60) are
in the range of \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B value for the non-marine
evaporates (Vengosh et al., 1994) (Table 1) (Fig. 7). The boron isotopic
characteristic indicates that the dissolution of non-marine evaporates
is the possible source of solutes in brackish groundwater.

In the quaternary loess layers of the study area, there are reserves a
large amount of soluble evaporates minerals (Tsunekawa et al., 2014;
Xiao et al., 2016), such as halite, gypsum, etc. The increase of
strontium concentration and\textsuperscript{87}Sr/\textsuperscript{86}Sr
ratio observed in upstream groundwater relative to the source
groundwater (Fig. 5a) implies that there exists a strontium input with
higher\textsuperscript{87}Sr/\textsuperscript{86}Sr ratio during the
evolution of groundwater. However, there is no correlation between Sr/Cl
ratio and Sr isotopic composition in upstream groundwater (Fig. 5b), as
would be suggested weathering of carbonates rocks is no longer the major
geochemical process in water. Strontium and calcium belong to one family
and strontium usually reserve in Ca-containing minerals (Yokoo, Nakanob,
Nishikawac, \& Quan, 2004). Strontium shows a significant correlation
with calcium (R\textsuperscript{2} = 0.9037; Fig. 5c) in upstream
groundwater, which means strontium origin from the dissolution of
Ca-containing mineral in the evolution of groundwater.
The\textsuperscript{87}Sr/\textsuperscript{86}Sr ratios of upstream
groundwater are close to those reported for aquifers where evaporates
dissolution occurs (0.711; Palmer \& Edmond, 1992). Therefore, the
dissolution of gypsum mineral is the main source of strontium, which
also is an important source of solutes in upstream water.

When there is a dissolution of non-marine evaporates mineral, the Cl/ Br
ratio will significantly increase with the increase of chloride
concentration in water (Brenot et al., 2015). The Cl/Br vs. Cl diagram
displays a well-defined relationship between these two conservative
indicators in the upstream groundwater and Cl/Br ratio of upstream
groundwater shows obvious high relative to that of source groundwater
(Fig. 4a), indicating progressive reaction derived from the dissolution
of non-marine evaporates with high Cl/Br ratio during the evolution of
groundwater. With the increase of Cl/Br ratio, the Na/Cl ratio of
groundwater samples gradually approaches 1 (Fig. 4b), which clearly
argues for the dissolution of halite mineral as an important source of
salinity in groundwater.

Nevertheless, the \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B values of upstream groundwater
samples (11.48%0-22.58%0; NO.5-7,11,16-17) are significantly higher than
those of water affecting by non-marine evaporates dissolution (-32%0-8%0)
(Vengosh et al., 1994) (Fig. 7), meaning that the boron isotopic
signature is altered by additional B inputs from other sources beyond
the dissolution of non-marine evaporates. Indeed, the loess layer is
rich in clay minerals which have a high cation exchange capacity
(Cartwright, Weaver, \& Petrides, 2007; Tsunekawa et al., 2014), such as
kaolinite and illite. This characteristic usually promotes cationic
exchange reaction to be active in groundwater (Ghassemi et al, 1995).
The preferential\textsuperscript{10}B adsorption occurs on exchange
phases (clay minerals), while the \textsuperscript{11}B will remain in
the liquid phase (groundwater), which will lead to the relative
enrichment of\textsuperscript{11}B in water (Palmer et al., 1987). Since
chloride behaves as a conservative element, the low B/Cl ratio usually
reflects a loss of boron related to the preferential adsorption
of\textsuperscript{10}B in cation exchange (Cary et al., 2015). The B/Cl
ratio gradually decreased with the increase of TDS in upstream
groundwater also reflect the existence of the cation exchange reaction
(Fig. 6b).

As suggested above, the dissolution of non-marine evaporates is the main
source of solutes in the upstream groundwater. These soluble minerals
can dissolute into water rapidly during the flow path of groundwater and
lead to the salinization of water. In addition, the cation exchange
reaction occurs in the upstream groundwater significantly modify the
boron isotopic signature of water, which also influence the geochemical
composition of water.

\textbf{5.1.3 Further salinization of river water}

After being recharged by brackish groundwater, the river water shows
further salinization, with a higher strontium concentration,
lower\textsuperscript{87}Sr/\textsuperscript{86}Sr ratios (Fig. 5a) and
a much heavier boron isotopic composition relative to groundwater. Few
river samples (NO.44-45) even evolve to saline water (TDS>10000 mg/l).

Because of chloride and bromide are conservative elements with similar
geochemical behavior, evaporation would not change the Cl/Br ratio of
water (Brenot et al., 2015). The river water shows a higher TDS compared
to groundwater (Table 1), but the variation of the Cl/Br ratio of river
water still keeps steadily (Fig. 4a), which implies that evaporation
imparts a significant influence on the salinization of the river water.
Under the condition of airflow, evaporation will cause the
light\textsuperscript{10}B in the water to enter the vapor phase
preferentially, while \textsuperscript{11}B will remain in the liquid
phase (Barth,1993), thus resulting in an enrichment
of\textsuperscript{11}B in water (Fig. 6a). Therefore, the heavier boron
isotopic composition of river water can also attribute to evaporation.

According to the above discussion, the further increase of strontium
concentration in river water compared to groundwater can be attributed
to the concentrating by evaporation. However,
the\textsuperscript{87}Sr/\textsuperscript{86}Sr ratio in river water
shows a decreasing trend, which indicates there is additional strontium
input in river water (Fig. 5a). These soil samples collected from the
hillside is contained strontium with a
lower\textsuperscript{87}Sr/\textsuperscript{86}Sr ratio
(0.710912-0.711110, Table 1; Fig. 5a). And these soil profile samples
(water-extracted) collected from one site where adjoin to the riverbanks
also exhibit a depleted boron isotope (-2.13 %0 to -1.72 %0) in the upper
soil (NO.55-56) relative to the deeper soil (NO.57) (Table 1). These
characteristics suggest the occurrence of soil erosion events in the
runoff of the river, which includes the leaching process along the
riverbanks, and the infiltration process occurring on the hillside in
precipitation events. These processes provide additional salts and
strontium with a lower\textsuperscript{87}Sr/\textsuperscript{86}Sr
ratio for the river, which also leached a large amount of
\textsuperscript{11}B in the upper soil layer into the river water.

\textbf{5.2 Formation of bitter water}

Magnesium sulfate mineral is nicknamed ``bitter salt'' in mineralogy
(Maik, Redel, Blank, \& Meyerhof, 2019). This is because water solution
with high magnesium concentration usually exhibits a taste of bitterness
(Maik et al., 2019). The brackish water in the study area is most of the
Na-Mg-Cl-SO\textsubscript{4} type, which indicates the magnesium is the
one of major cations in water. Bitterness is another typical feature of
the brackish water in the Zuli River Catchment.

According to the above discussion, the dissolution of carbonate minerals
exists in groundwater of headwater. The Mg vs. Ca diagram (Fig. 8b)
shows groundwater samples in headwater were close to the 1:1 line, which
indicates that the occurrence of dolomite dissolution in source
groundwater. Then with the evolution of water, there is a considerable
enrichment in magnesium compared to calcium in upstream groundwater and
river water (Fig. 8b), implying that there must be an additional
source(s) of magnesium besides carbonates dissolution in the brackish
water.

In the (Ca+Mg) vs. SO\textsubscript{4} diagram, the distribution of
groundwater samples maintains a good linear relationship (Fig. 8a),
reflecting the theoretical dissolution of sulfated minerals containing
calcium and magnesium. Although sulfate minerals bearing magnesium, such
as epsomite (MgSO\textsubscript{4}*7H\textsubscript{2}O) or hexahydrate
(MgSO\textsubscript{4}*6H\textsubscript{2}O), are not the main
composition of minerals in the Zuli River Catchment (Tsunekawa et al.,
2014; Fan et al., 2016). But their existence at depth, even in small
quantities, could explain the good linear relationship between (Ca+Mg)
and SO\textsubscript{4} in the brackish water. Those minerals are
characterized by high solubility, which can permit a faster dissolution
process and a great impact on the magnesium concentration of water
(M\selectlanguage{ngerman}árquez et al., 2017). The dissolution of these magnesium sulfate
minerals is the initial and most important source of magnesium in
brackish water and result in the brackish water to be bitterness.

According to the above discussion, the dissolution of gypsum is an
important source of salinity in brackish water, and the rise of
gypsum-derived solutes (Ca\textsuperscript{2+} and
SO\textsubscript{4}\textsuperscript{2-}) along with the salinization of
water. Due to these carbonate minerals has reached saturation in
brackish water, which was reported in the previous study (Liu et al.,
2019). Then with Ca\textsuperscript{2+} continuously entering the water,
incongruent dolomite dissolution and calcite precipitation are driven by
gypsum dissolution due to the common ion effect (Appelo \& Postma, 1993;
Edmunds, Bath, \& Miles, 1982). These processes also lead to the further
enrichment of magnesium in water, serving as another important source of
magnesium. This process is occurring in groundwater according to this
reaction:

CaMg\selectlanguage{english}(CO\textsubscript{3}\selectlanguage{english})\textsubscript{2}(S)+H\textsubscript{2}CO\textsubscript{3}\selectlanguage{english}-Ca(CO\textsubscript{3})(S)+
Mg\textsuperscript{2+}+2HCO\textsubscript{3}\textsuperscript{-}\begin{CJK}{UTF8}{gbsn}。

\end{CJK}\selectlanguage{english}The increase of the Sr/Ca ratio and the characteristics of Sr isotope in
groundwater also confirms the existence of this process. It is
interfered with Sr isotopes that strontium mainly originates from the
dissolution of gypsum, and this process usually reduces the Sr/Ca ratio
(Cartwright et al., 2007). But with the salinization of groundwater, the
Sr/Ca ratio of upstream groundwater is also increasing (Fig. 8c). This
is because when strontium, like calcium, precipitates from solution into
calcite, the strontium is more inclined to retain in solution compared
to calcium (Pingitore \& Eastman, 1986). Therefore, precipitation of
carbonate minerals tends to increase the Sr/Ca ratio in the residual
water due to the rejection of strontium in preference for calcium in
carbonates (Monjerezi et al., 2011).

\textbf{6. Conclusion}

This study has presented a comprehensive understanding of the primary
geochemical processes that occur in an inland catchment of the Loess
Plateau, based on an integration of information derived from the
chemical and isotopic signatures of water and soil. Therefore, we
conclude that: 1) Affected by the carbonate formation, the
Mg-Ca-Na-HCO\textsubscript{3} type groundwater is formed in the
headwater. Groundwater in the headwater is also characterized by a
lower\textsuperscript{87}Sr/\textsuperscript{86}Sr and depleted
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B value. The dissolution of non-marine evaporites,
such as halite and gypsum, is the main source of salinity in brackish
groundwater of upstream, and these processes also contribute the
strontium ions with high \textsuperscript{87}Sr/\textsuperscript{86}Sr
ratios and the boron ions with high \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B value into
water. Additionally, the cation exchange reaction occurs in upstream
groundwater has a significant influence on the geochemical composition
of water and resulting in a much heavier boron isotopic composition of
water. After recharged by brackish groundwater, the river water was
affected by evaporation and various soil erosion events during runoff.
Then the river water showed further salinization, decease
of\textsuperscript{87}Sr/\textsuperscript{86}Sr ratios, and enrichment
in heavy boron isotopes.

2) The magnesium sulfate minerals in loess provide an initial source for
magnesium enrichment in upstream groundwater. In addition, the
incongruent dissolution of dolomite coupled with gypsum dissolution and
calcite precipitation also contributed to the enrichment of magnesium in
groundwater. In addition to the impact of brackish groundwater, the
river water is further affected by evaporation, which enhance the level
of ''bitterness''.

These results indicate that water salinization in the Zuli River
catchment primarily originates from the dissolution of soluble minerals
in the upstream area, large-scale treatment for the brackish water
resources in the downstream area should be avoided, instead of
strengthening the water treatment in front of the mountain pass or
exploration of the high-quality groundwater in the headwater should be
encouraged.

\textbf{Acknowledgments}

This study was supported by the National Natural Science Foundation of
China (41271041) and the Fundamental Research Funds for the Central
Universities (2019B60514). The authors gratefully acknowledge financial
support from China Scholarship Council.

\textbf{Data Availability Statement}

The data that support the findings of this study are available from the
corresponding author upon reasonable request.

\textbf{References}

Alcal\selectlanguage{ngerman}á, F., \& Custodio, E. (2008). Using the Cl/Br ratio as a tracer to
identify the origin of salinity in aquifers in Spain and Portugal. J.
Hydrol., 359(1-2), 189-207.

Appelo, C.A.J., \& Postma, D. (1993). Geochemistry, Groundwater and
Pollution. A.A. Balkema, Rotterdam, 536p.

Barth, S. (1993). Boron isotope variations in nature: A synthesis. Geol.
Rundsch., 82, 640-65.

Barth, S. (1998). \textsuperscript{11}B/\textsuperscript{10}B Variations
of Dissolved Boron in a Freshwater/Seawater Mixing Plume (Elbe Estuary,
North Sea). Marine Chem., 62, 1-14.

Bullen, T.D., Krabbenhoft, D.P., \& Kendall, C. (1996). Kinetic and
mineralogic controls on the evolution of groundwater chemistry
and\textsuperscript{87}Sr/\textsuperscript{86}Sr in a sandy silicate
aquifer, northern Wisconsin, USA. Geochim. Cosmochim. Acta, 60(10),
1807-1821.

Brenot, A., Négrel, P., Petelet-Giraud, E., Millot, R., \& Malcuit, E.
(2015). Insights from the salinity origins and interconnections of
aquifers in a regional scale sedimentary aquifer system (Adour-Garonne
district, SW France): Contributions of \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{34}S and
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O from dissolved sulfates and
the\textsuperscript{87}Sr/\textsuperscript{86}Sr ratio. Appl. Geochem.,
53, 27-41.

Cartwright, I. (2004). Hydrogeochemical and isotopic constraints on the
origins of dryland salinity, Murray Basin, Victoria, Australia. Appl.
Geochem., 19(8), 1233-1254.

Cartwright, I., Weaver, T., \& Petrides, B. (2007). Controls
on\textsuperscript{87}Sr/\textsuperscript{86}Sr ratios of groundwater in
silicate-dominated aquifers: SE Murray Basin, Australia. Chem. Geol.,
246(1-2), 0-123.

Cartwright, I., Weaver, T., Cend\selectlanguage{ngerman}ón, D., \& Swane, I. (2010).
Environmental isotopes as indicators of inter-aquifer mixing, Wimmera
region, Murray Basin, Southeast Australia. Chem. Geol., 277(3-4), 0-226.

Cary, L., Petelet-Giraud, E., Bertrand, G., Kloppmann, W., Aquilina, L.,
Martins, V., Hirata, R., Montenegro, S., Pauwels, H., Chatton, E.,
Franzen, \& M., Aurouet, A. (2015). Origins and processes of groundwater
salinization in the urban coastal aquifers of Recife (Pernambuco,
Brazil): A multi-isotope approach. Sci. Total Environ., 530-531,
411-429.

Edmunds, W.M., Bath, A.H., \& Miles, D.L. (1982). Hydrochemical
evolution of the East Midlands Triassic sandstone aquifer, England.
Geochim. Cosmochim. Acta, 46(11), 2069-2081.

Edmunds, W.M., Ma, J.Z., Aeschbach-Hertig, W., Kipfer, R., \&
Darbyshire, D.P.F. (2006). Groundwater recharge history and
hydrogeochemical evolution in the Minqin Basin, North West China. Appl.
Geochem., 21(12), 0-2170.

Farid, I., Zouari, K., Rigane, A., \& Beji, R. (2015). Origin of the
groundwater salinity and geochemical processes in detrital and carbonate
aquifers: Case of Chougafiya basin (Central Tunisia). J. Hydrol., 530,
508-532.

Fan, B.L., Zhao, Z.Q., Tao, F.X., Li, X.D., Tao, Z.H., Gao, S., \& He,
M.Y. (2016). The geochemical behavior of Mg isotopes in the Huanghe
basin, China. Chemical Geology, 426, 19-27.

Freeze, R.A., \& Cherry, J.A. (1979). Groundwater Prentice-Hall,
Englewood Chffs, New Jersey.

Gamboa, C., Godfrey, L., Herrera C., Custodio E., \& Soler, A. (2019).
The origin of solutes in groundwater in a hyper-arid environment: A
chemical and multi-isotope approach in the Atacama Desert, Chile. Sci.
Total Environ., 690, 329-351.

Ghassemi, F., Jakeman, A.J., \& Nix, H.A. (1995). Salinisation of land
and water resources: Human causes, extent, management, and case studies.
CAB International, Wallingford.

Gibbs, R. J. (1970). Mechanisms controlling world water chemistry.
Science, 172(3985), 870--872.

Gil-Márquez, J.M, Barberá, J.A, Andreo, B., \& Mudarra, M. (2017).
Hydrological and geochemical processes constraining groundwater salinity
in wetland areas related to evaporitic (karst) systems. A case study
from Southern Spain. J. Hydrol., 2017, 538-554.

Harrington, G.A., \& Herczeg, A.L., 2003. The importance of silicate
weathering of a sedimentary aquifer in arid Central Australia indicated
by very high\textsuperscript{87}Sr/ \textsuperscript{86}Sr ratios. Chem.
Geol., 199(3), 281-292.

Herrera, C., Gamboa, C., Custodio, E., Jordan, T., Godfrey, L., Jódar,
J., Luque, J.A., Vargas, J., \& Sáez, A. (2018). Groundwater origin and
recharge in the hyperarid Cordillera de la Costa, Atacama Desert,
northern Chile. Sci. Total Environ., 624, 114-132.

Jørgensen, N. O., Andersen, M. S., \& Engesgaard. P. (2008).
Investigation of a Dynamic Seawater Intrusion Event using Strontium
Isotopes (\textsuperscript{87}Sr/\textsuperscript{86}Sr). J. Hydrol.,
348, 257-269.

Liu, Z.H., Tan, H.B., Shi, D.P., Xu, P., \& I.Elenga, H. (2019). Origin
and formation mechanism of salty water in Zuli River catchment of the
Yellow River. Water Environ. Res., 1, 1-17.

Luo, C.S., Chen, W.W., \& Han, W.F. (2010). Experimental study on
factors affecting the quality of ice crystal during the freezing
concentration for the brackish water. Desalination, 260(1-3), 231-238.

Maik, B., Redel, U., Blank, K., \& Meyerhof, W. (2019). The human bitter
taste receptor TAS2R7 facilitates the detection of bitter salts.
Biochem. Biophys. Res. Commun., 512, 877-881.

Monjerezi, M., D.Vogt, R., Aagaard, P., Gebru, A.G., \& Saka, J.D.K.
(2011). Using\textsuperscript{87}Sr/\textsuperscript{86}Sr,
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{2}H isotopes along with
major chemical composition to assess groundwater salinization in lower
Shire valley, Malawi. Appl. Geochem., 26(12), 0-2214.

Morell, I., Pulido-Bosch, A., S\selectlanguage{ngerman}ánchez-Martos, F., Vallejos, A., Daniele,
L., Molina, L., Calaforra, J.M., Roig, A.F., \& Renau, A. (2008).
Characterization of the Salinisation Processes in Aquifers Using Boron
Isotopes; Application to South-Eastern Spain. Water, Air, Soil Pollut.,
187(1-4), 65-80.

Palmer, M.R., Spivack, A.J., \& Edmond, J.M. (1987). Temperature and pH
controls over isotopic fractionation during adsorption of boron on
marine clay. Geochim. Cosmochim. Acta, 51(9), 2319-2323.

Palmer, M.R., \& Edmond, J.M. (1992). Controls over the strontium
isotope composition of river water. Geochim. Cosmochim. Acta, 56(5),
2099-2111.

Palmer, M.R., \& Swihart, G.H. (1996). Boron isotopes geochemistry: An
overview. Boron: Mineralogy, Petrology and Geochemistry. Rev. Mineral.
Geochem., 33, 709-744.

Petrides, B., Cartwright, I., \& R.Weaver, T. (2006). The evolution of
groundwater in the Tyrrell catchment, south-central Murray Basin,
Victoria, Australia. Hydrogeol. J., 14, 1522-1543.

Pingitore, N.E., \& Eastman, M.P. (1986). The coprecipitation of
Sr\textsuperscript{2+} with calcite at 25°C and 1 atm. Geochim.
Cosmochim. Acta, 50(10), 2195-2203.

Romer, R.L., Meixner, A., \& Förster, H. (2014). Lithium and boron in
late-orogenic granites -- Isotopic fingerprints for the source of
crustal melts. Geochimica et Cosmochimica Acta, 131, 98-114.

Skrzypek, G., Dogramaci, S., \& F.Grierson, P. (2013). Geochemical and
hydrological processes controlling groundwater salinity of a large
inland wetland of northwest Australia. Chem. Geol., 357, 164-177.

Spivack, A.J., \& Edmond, J.M. (1987). Boron isotope exchange between
seawater and the oceanic crust. Geochim. Cosmochim. Acta, 51, 1033-1043.

Tsunekawa, A., Liu, G., Yamanaka, N., \& Du, S. (2014). Restoration and
Development of the Degraded Loess Plateau, China. Springer, Tokyo.

Vengosh, A., Heumann, K.G., Juraske, S., \& Kasher, R. (1994). Boron
Isotope Application for Tracing Sources of Contamination in Groundwater.
Environ. Sci. Technol., 28(11), 1968-1974.

Vengosh A. (2005). Salinization and saline environments
{[}M{]}//Elsevier Science Technology: Treatise on geochemistry volume 9:
Environmental Geochemistry, 168 -333.

Werner, A.D., Bakker, M., Post, V.E.A., Vandenbohede, A., Lu, C., \&
Ataie-Ashtiani, B. (2013). Seawater intrusion processes, investigation
and management: recent advances and future challenges. Adv. Water
Resour. 51, 3-26.

Sahib, L., Marandi, A., \& Schüth, C. (2016). Strontium isotopes as an
indicator for groundwater salinity sources in the Kirkuk region, Iraq.
Sci. Total Environ., 562, 935-945.

Xiao, J., Zhang, F., \& Jin, Z.D. (2016). Spatial characteristics and
controlling factors of chemical weathering of loess in the dry season in
the middle Loess Plateau, China. Hydrol. Process., 30, 4855-4869.

Yokoo, Y., Nakanob, T., Nishikawac, M., \& Quan, H. (2004).
Mineralogical variation of Sr--Nd isotopic and elemental compositions in
loess and desert sand from the central Loess Plateau in China as a
provenance tracer of wet and dry deposition in the northwestern Pacific.
Chem. Geol., 204, 45-62.

Zhan, T., Guo, Z.T., Wu, H.B., Ge, J.Y., Zhou, X., Wu, C.L., \& Zeng,
F.M. (2011). Thick Miocene eolian deposits on the Huajialing Mountains:
The geomorphic evolution of the western Loess Plateau. Sci. China: Earth
Sci., 54, 241-248.

\textbf{Figure Legends}

\textbf{Fig. 1} Location of sampling sites within the Zuli River
Catchment.

\textbf{Fig. 2} (a) Annual of total precipitation and mean temperature
and (b) monthly variation of total precipitation in the center of the
Zuli River catchment (data from Huining weather station) (The blue
dashed line refers to annual mean total precipitation in the past 15
years from 2005 to 2019).

\textbf{Fig. 3} (a) Schematic geological map of the Zuli river catchment
and (b) simplified hydrogeological cross-section along with the
mainstream of Zuli river (topographical profile A-A' corresponding to
the line in the map (a). The main strata, groundwater flow paths,
recharge, and discharge processes in the catchment were also
schematically marked in the map.

\textbf{Fig. 4} Cl/Br vs. Cl (a), Cl/Br vs. Na/Cl (b) relationships of
the analyzed water samples. The blue horizontal line marks the Sr/Cl
ratio for seawater. The yellow dashed line in Fig. 4b represents the
halite dissolution line.

\textbf{Fig. 5} Relationship
between\textsuperscript{87}Sr/\textsuperscript{86}Sr vs
Sr\textsuperscript{2+}(a); \textsuperscript{87}Sr/\textsuperscript{86}Sr
Vs Sr/Cl (b); Sr\textsuperscript{2+} Vs Ca\textsuperscript{2+} (c) from
the analyzed samples.

\textbf{Fig. 6} Relationship between \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{11}B Vs B (a);
B/Cl Vs TDS (b) from the analyzed samples.

\textbf{Fig. 7} The boron isotopic composition in the analyzed samples.
Data from seawater samples (Barth, 1993) and from non-marine evaporates
(Vengosh et al., 1994) are also indicated.

\textbf{Fig. 8} Relationship between (Ca+Mg) Vs SO\textsubscript{4} (a);
Ca Vs Mg (b) and Sr/Ca Vs. TDS from the analyzed water samples. The dark
dashed line in Fig. 8b represents the dolomite dissolution line.\selectlanguage{english}
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