Application Of Sulfur And Oxygen Isotopes In The Study Of Anthropogenic Sulfate Fluxes In The Shaying River Basin

Rivers are important channels for material circulation and energy exchange between land and ocean.The global terrestrial surface environment weathering products and dissolved substances manually input are transported to the ocean through rivers,which is an important basis for marine material circulation.With the rapid development of social economy,anthropogenic inputs have greatly changed the flux of dissolved substances in river systems,but it is still difficult to accurately identify the sources and fluxes of it.This paper selects Shaying river basin as the research object,mainly based on the fact that it is greatly affected by human activities,including agricultural input,domestic sewage,coal mining and other industrial waste water,and human activities have significant differences in the flow space,which is conducive to deducing the contribution of different human activities according to the spatial-temporal changes.Based on water chemical composition,hydrogen and oxygen isotopes(δD andδ¹⁸O_H2O)and sulfur and oxygen isotopes(δ³⁴S_SO4 andδ¹⁸O_SO4)collected from river water and groundwater during normal,dry and wet seasons,the source of SO₄^2-in river water and the influence process of human input on it were identified.The contribution proportion of SO₄^2-from human sources to river water was calculated by combining Bayesian stable isotope mixing model,the influence of human input on SO₄^2-flux was quantified,and providing scientific theoretical basis for water pollution control in Shaying River basin.The main stream of Shaying river is composed of tributaries Jialu river,Sha river,Beiru river and Ying river.Through sampling and analysis of the water of these main streams and tributaries tributaries,and groundwater on both banks,the research results are mainly as follows:（1）The mean values of pH in the normal,dry and wet periods of the main stream of Shaying river are 8.3±0.3,7.7±0.1 and 8.0±0.2 respectively,and the mean values of TDS are 465±19 mg·L^-1,383±53 mg·L^-1and 548±109 mg·L^-1 respectively.The average values of pH value and TDS of Yinghe river,a primary tributary,are 8.3±0.4 and 394±158 mg·L^-1,8.6±0.2 and 447±211 mg·L^-1,8.1±0.4 and 362±183 mg·L^-1,respectively;The mean values of pH and TDS of Jialu river are 8.3±0.1 and 450±16 mg·L^-1,8.2±0.3 and 332±57 mg·L^-1,8.6±0.3 and 483±95 mg·L^-1 respectively;The mean values of pH and TDS in Shahe river are 8.3±0.2 and 479±220 mg·L^-1,8.3±0.6 and 415±122 mg·L^-1,7.8±0.4and 341±112 mg·L^-1,respectively;The mean values of pH and TDS mass concentration of Beiru river,a secondary tributary,are 8.2±0.1 and 411±194 mg·L^-1,8.6±0.1 and 315±139 mg·L^-1,8.2±0.3 and 277±141 mg·L^-1 respectively.The mean values of pH and TDS of groundwater are 7.4±0.2 and 607±263 mg·L^-1,7.0±0.2 and 628±418 mg·L^-1,7.3±0.4and 731±394 mg·L^-1 respectively.（2）The dissolved components of river water in the study area are jointly controlled by carbonate rock weathering,silicate rock weathering and human input.Ca²⁺and Na⁺are the main cations in the river water of the study area.The Ca²⁺/Na⁺equivalent ratio in the main stream of Jialu River and Shaying river is obviously low,and the river anions are mainly HCO₃^-and Cl^-,indicating that they accept a large amount of Na⁺and Cl^-;HCO₃^-and SO₄^2-are the main anions in Sha river,Beiru river and yinghe river above Xuchang river and the SO₄^2-/Cl^-equivalent ratio is significantly higher than that of Jialu river and Shaying river.The results show that the involvement of sulfate in chemical weathering of carbonate rocks is mainly related to the inflow of coal mine wastewater.The proportion of cationic equivalent concentration in groundwater of the three periods is Ca²⁺>Na⁺>Mg²⁺>K⁺,and the order of anion equivalent concentration was mostly HCO₃^->Cl^->SO₄^2->NO₃^-,but a few samples are Na⁺>Ca²⁺.The dissolved components of groundwater are not only controlled by human input（domestic sewage,industrial wastewater and agricultural pollution）,but also related to the influence of cation exchange.（3）The mean values ofδ¹⁸O_H2O andδD of Shaying river mainstream are-6.8‰and-48‰,-6.2‰and-44‰and-8.3‰and-60‰respectively,showing the characteristics of river evaporation in dry season and rainwater recharge in wet season.The mean values ofδ¹⁸O_H2O andδD of Jialu river,a primary tributary were-8.0‰and-56‰,-6.4‰and-48‰and-9.0‰and-63‰respectively;The average values ofδ¹⁸O_H2O andδD in Ying river in three periods were-6.6‰and-47‰,-6.0‰and-42‰and-8.3‰and-59‰,respectively;The average values ofδ¹⁸O_H2O andδD in the three periods of Sha river are-4.9‰and-36‰,-4.7‰and-34‰and-7.7‰and-56‰,respectively.The average values ofδ¹⁸O_H2O andδD of the secondary tributary Beiru river in three periods are-6.1‰and-42‰,-5.2‰and-38‰and-7.0‰and-52‰,respectively.The average values ofδ¹⁸O_H2O andδD of groundwater in the three periods are-8.1‰and-57‰,-8.0‰and-56‰and-8.7‰and-61‰,respectively.It can be seen that the Shahe river is greatly affected by evaporation,and the groundwater is less affected by evaporation.The averageδ¹⁸O_H2O andδD values of the third phase of Jialu river are lower than those of other surface waters,indicating the existence of groundwater recharge,which is closely related to the acceptance of municipal domestic wastewater in the upper reaches of Jialu river.At the same time,the inflow of Jialu river and groundwater is an important reason for the negative average values ofδ¹⁸O_H2O andδD in the main stream of Shaying river.（4）The mean values ofδ³⁴S_SO4 andδ¹⁸O_SO4 in the main stream of Shaying river in normal,dry and wet seasons are 11.6±3.0‰and 5.6±1.0‰,9.5±0.6‰and 12.2±2.1‰,8.8±1.0‰and 3.7±2.0‰,respectively.The mean values ofδ³⁴S_SO4 andδ¹⁸O_SO4 in the first tributary of Jialu river in three periods were 9.0±0.6‰and 5.2±0.6‰,10.3±2.1‰and 9.9±2.8‰,11.3±2.1‰and 7.4±1.8‰,respectively.The mean values ofδ³⁴S_SO4 andδ¹⁸O_SO4in the three periods of Ying river are 10.9±2.7‰and 6.1±1.4‰,9.6±1.4‰and 10.4±1.9‰,9.5±2.5‰and 4.7±0.6‰,respectively.The mean values ofδ³⁴S_SO4 andδ¹⁸O_SO4 in the three periods of Sha river are 12.1±1.4‰and 7.3±1.5‰,11.5±2.1‰and 10.0±2.3‰,11.1±2.3‰and 4.3±2.3‰,respectively.The mean values ofδ³⁴S_SO4 andδ¹⁸O_SO4 in the third phase of Beiru river,the second tributary,are 12.7±2.1‰and 6.3±1.1‰,12.6±2.4‰and 10.0±1.0‰,10.5±3.0‰and 0.7±2.5‰,respectively.The mean values ofδ³⁴S_SO4 andδ¹⁸O_SO4 in the third stage groundwater are 8.9±2.3‰and 7.7±2.1‰,10.4±3.3‰and 9.9±2.8‰,11.3±2.1‰and 7.4±1.8‰,respectively.In different periods,theδ³⁴S_SO4 mean value of Sha river,Beiru river and Ying river andδ¹⁸O_SO4 mean value in normal period are higher than that in the mainstream of Shaying river,but theδ¹⁸O_SO4 mean value in different sections in dry season is obviously higher than that in other periods,among which theδ¹⁸O_SO4 mean value of Jialu river is the highest,which is 13.4±1.3‰.The values ofδ³⁴S_SO4andδ¹⁸O_SO4 of domestic sewage in the study area are 8.7±2.4‰（n=22）and 10.8±2.3‰（n=20）,respectively.Gypsum dissolved sulfate generally has higher values ofδ³⁴S_SO4（>10‰）andδ¹⁸O_SO4（10‰～15‰）.Therefore,in the dry season,the sulfate in the river water of Jialu river and other tributaries in different periods mainly comes from gypsum dissolution,while the values ofδ³⁴S_SO4 andδ¹⁸O_SO4 in the dry Jialu river and Shaying river are close to those of domestic sewage,and the sulfate in the river water is greatly contributed by domestic sewage.Theδ³⁴S_SO4 andδ¹⁸O_SO4 values produced by sulfide oxidation are negative,and the lowerδ¹⁸O_SO4 values in the wet season indicate that the river water in the study area contributes more from sulfide mineral oxidized sulfate.With the help of Bayesian stable isotope mixing model,it is calculated that the contribution ratio of SO₄^2-from gypsum dissolution in Shaying river basin in different periods ranges from 45%to 50%;The contribution of oxidized sulfate from sulfide minerals in normal water period and wet water period is 31.3%and 42.7%respectively,but only 4.1%in dry water period;The contribution of atmospheric precipitation,domestic sewage and chemical fertilizer to river SO₄^2-in dry season is 13.3%,18.5%and 12.3%respectively,which is significantly higher than that in normal season and wet season.Except that the contribution of domestic sewage in normal season is 6.1%,the other proportion is less than 5%;The contribution of soil sulfate to river SO₄^2-is small,accounting for 3%～7%.（5）In Shaying river basin,the SO₄^2-flux of river water output in a hydrological year is about 2.45*10^-3Tmol,and the annual flux of SO₄^2-flux from man-made rivers is0.246*10^-3Tmol,accounting for about 10.04%of the total annual SO₄^2-flux.The influence of human input on sulfate in river water is significantly different in different periods.In dry season,human source SO₄^2-accounts for 30.8%of the contribution of river water SO₄^2-,and human input SO₄^2-accounts for 58.1%of the total output of human source SO₄^2-in the whole year,which exceeds the sum of human input SO₄^2-in normal season and wet season.In normal and wet periods,the input of artificial SO₄^2-only accounts for 4.9%and 37.0%of the total output of artificial source SO₄^2-in the whole year.