Hydrogen-Oxygen Isotope Geochemistry And Environmental Indication Of River Water In The Dabieshan Area, The Upper Watershed Of Huaihe River,China

The geochemical composition of the basin,an important part of the study of the earth's surface environment,can demonstrate the characteristics of rocks,soil,climate,vegetation,pollution,etc.,and can also indicate the hydrological cycle of the basin.We systematically collected water samples from rivers,reservoirs,groundwater and ponds in Dabie Mountains area,the upper watershed of Huaihe River during dry season in 2017 and the wet season in 2018,and studied their water chemical composition and the spatial and temporal distribution and variation characteristics of the hydrogen and oxygen isotopic composition of the area.In addition,we discussed the controlling factors of water chemistry and hydrological cycle of the basin.The main conclusions are as follows.?1?The average pH value of the water in the study area is 8.0 in the wet season and 7.8 in the dry season,showing weak alkaline;the average value of EC is 128?S/cm in the wet season and 120?S/cm in the dry season,which are lower than the average level of EC of the world river;the average value of TDS is 72 mg/L in the wet season and 67 mg/L in the dry season,close to other silicate rocks areas of the world rivers.The riverine TDS,consistent to EC,is significantly larger than reservoirs,groundwater and agricultural water.?2?The normality of the cation in water is Ca²⁺>Mg²⁺>Na⁺>K⁺,and the normality of the anion is HCO₃^->SO₄^2->NO₃^->Cl^-.According to the Alekin Classification,the waters in the study area are mainly carbonate-calcium-type I and carbonate-calcium-type II.The study on the controlling factors of water chemistry in the area shows that the chemical composition of the river is mainly controlled by rock weathering?mainly by evaporite,silicate rock and carbonate rock weathering?.The contribution of atmospheric precipitation to Cl^-and Na⁺are 47.2%and 16.9%,while its contribution ratio to other ions is slight.?3?In different water bodies,?¹⁸O and?D showed consistent changes in both the wet season and the dry season:agricultural water>groundwater>river>reservoir.The large amount of groundwater recharging the reservoir caused the?¹⁸O and?D values of the reservoir to be negative.The agricultural water environment is relatively closed,and the water body renewal speed is slow,as the result,the evaporation has a great influence on the isotope composition.?4?The riverine isotope composition is affected by elevation effect,tributary remittance,cascade reservoir evaporation and groundwater recharge.The elevation effect has a significant impact on the hydrogen and oxygen isotope composition of the water.For every 100m elevation,the delta?¹⁸O change is-0.13‰in the dry season and-0.15‰in the wet season.The relation of the water's?D and?¹⁸O is?D=5.26?¹⁸O+10.78 in the dry season and?D=6.82?¹⁸O+2.00 in the wet season.The slope of the equation is lower than the global atmospheric precipitation line and the modern atmospheric precipitation line in China,reflecting the effect of evaporation on the water body in the area.The intercept of the wet season equation is much lower than that of the global atmospheric precipitation line,indicating that there is a strong effect of secondary evaporation under the cloud during the precipitation process.The average d-excess of the water is 11.19‰,and the d-excess during the wet season is slightly lower than the dry season,indicating that there is a strong process of secondary evaporation cycle during the wet season.