Sulfur Isotope and Stoichiometry–Based Source Identification of Major Ions and Risk Assessment in Chishui River Basin, Southwest China

Abstract

Hydrochemistry and sulfur isotope (δ34S–SO42−) of Chishui River watershed in Southwest China were measured to identify the sources of riverine solutes, the potential impact of human activities, water quality, and health risk. The main findings indicated that the HCO3− (2.22 mmol/L) and Ca2+ (1.54 mmol/L) were the major ions, with the cation order of Ca2+ (71 ± 6%) > Mg2+ (21 ± 6%) > Na+ + K+ (8 ± 3%) and the anion sequence of HCO3− (55 ± 9%) > SO42− (41 ± 9%) > Cl− (4 ± 3%). The riverine δ34S–SO42− values fluctuated from −7.79‰ to +22.13‰ (average +4.68‰). Overall, the water samples from Chishui River presented a hydrochemical type of Calcium–Bicarbonate. The stoichiometry and PCA analysis extracted three PCs that explained 79.67% of the total variances. PC 1 with significantly positive loadings of K+, Mg2+, F−, HCO3− and relatively strong loading of Ca2+ revealed the natural sources of rock weathering inputs (mainly carbonate). PC 2 (Na+ and Cl−) was primarily explained as atmospheric contribution, while the human inputs were assuaged by landscape setting and river water mixing processes. The strongest loadings of SO42− and NO3− were found in PC 3, which could be defined as the anthropogenic inputs. The H2SO4–involved weathering processes significantly impacted (facilitated weathering) the concentrations of riverine total ions. Sulfur isotope compositions further indicated that riverine SO42− were mainly controlled by anthropogenic inputs SO42− compared to the sulfide oxidation derived SO42−, and the atmospheric contribution was very limited. The results of risk and water quality assessment demonstrated that Chishui River water was desirable for irrigation and drinking purposes due to low hazard quotient values (<1, ignorable risk), but long–term monitoring is still worthy under the circumstances of global environmental change.

Major ion compositions, sources and risk assessment of karst stream under the influence of anthropogenic activities, Guizhou Province, Southwest China

“…Due to the relatively strong influence of agricultural activities, the NO 3 – /Na + , NO 3 – /K + , and NO 3 – /Cl – ratios at point Z2 are 1.44, 3.50, and 1.89, respectively. The characteristics of the ratios are similar to the water sample of rivers studied by Liu et al (2006) that are subject to the obvious influence of agricultural activities (NO 3 – /Cl – >1) ( Liu et al, 2006 ), which is also similar to the the Han River and Chishui River that is affected by agricultural activities ( Ge et al, 2021 ; Li et al, 2009 ) ( Fig. 9 ).…”

“…For the underground water in the area underlain by carbonate rocks, the Cl – content is very low, and Cl – in natural conditions mainly comes from atmospheric precipitation and anthropogenic activity ( Ge et al, 2021 ; Lang et al, 2005 ). Urban domestic sewage is rich in Na + and Cl – , and K + usually comes from the application of agricultural potassium fertilizer (KCl) ( Ge et al, 2021 ; Grosbois et al, 2000 ; Liu et al, 2006 ; Sheikh et al, 2014 ; Widory et al, 2005 ). The Cl – concentration in the Youyu stream is relatively low (0.11 mmol·L −1 ), which only accounts for 1.69% of total anions in the watershed.…”

“… Data sources are Qin et al (2018) for Jialing River, Han & Xu (2022) for Nanming River (NMR), Ge et al (2021) for Chishui River (CSR) and Li et al (2009) for Han River (HR). …”

Riverine Hydrochemical Characteristics of a Typical Karst Urban Watershed: Major Ion Compositions, Sources, Assessment, and Historical Evolution

“…In contrast, the values of children in the tributaries of the Nanming River were in the order of HQ F (mean: 0.39) > HQ N (mean: 0.29), and those of adult were the following: HQ F (mean: 0.50) > HQ N (mean: 0.37). The results of HQ N (mean value of children: 0.28 and mean value of adult: 0.11) and HQ F (mean value of children: 0.13 and mean value of adult: 0.05) in the Nanming River were greater than those of the Chishui River catchment, which is also located in the karst area with relatively slight disturbance by anthropogenic activities . The urbanization may indeed have polluted the Nanming River.…”

“…The results of HQ N (mean value of children: 0.28 and mean value of adult: 0.11) and HQ F (mean value of children: 0.13 and mean value of adult: 0.05) in the Nanming River were greater than those of the Chishui River catchment, which is also located in the karst area with relatively slight disturbance by anthropogenic activities. 78 The urbanization may indeed have polluted the Nanming River. The HQ values of adults were always higher than children in the Nanming catchment, and the total HQ value (HQ T ) of adults was higher than 1 in almost all sites of main stream and 5 sites in tributaries.…”