Study On Hydrogen And Oxygen Isotope And Hydrochemistry Characteristics Of Hulun Lake Basin

Hulun Lake is the fourth largest freshwater lake in China and the largest lake in the north of China.Compared with other lakes,Hulun Lake is known for its unique geographical location,climatic conditions and characteristics of human activities.At the same time,Hulun Lake,as a lake in the Mengxin plateau area,is not only representative of typical lakes in the cold and arid regions in northern China,but also under the global climate and environmental factors,the lakes in the cold and arid regions of the north have distinctive regional characteristics and their water cycle composition.As an important indicator of historical climate change and the entry point for environmental change research.this paper mainly studies systematically the hydrogen and oxygen isotopes and water chemistry features in different water bodies in the ice-covered and non-icing Hulun Lake basins,and provides scientific guidance and basis for the development of drinking water safety,rational development and utilization of water resources,and water resources protection measures.The main results are as follows:1.During the non-freezing period Hulun Lake,the hydrogen and oxygen isotope values of the Hulun Lake were more enriched than the freezing period,and its fractionation was significant and stable.Based on the collection and analysis of rainfall in the basin,the atmospheric precipitation line?LWML?equation in the Hulun Lake region was established as:?D=6.68?¹⁸O-5.89‰?R²=0.96?.The comparison of the precipitation lines in the three major lake regions on the Inner Mongolia Plateau shows that the precipitation characteristics of typical lakes in the cold and arid regions of the Inner Mongolia Plateau have similar consistency,and their weak differences indicate that the degree of evaporation is different during precipitation.2.Exchanges among the various compounds during the strong evaporative fractionation process in groundwater are responsible for the gradual depletion of?¹⁸O.By regression fitting analysis of non-freezing lake water and river water hydrogen and oxygen isotopes,the equation of evaporation trend line EL₁ in Hulun Lake area is obtained as:?D=4.99?¹⁸O-32.89‰?R²=0.89?.Hulun Lake water is received groundwater recharge during non-icing period,the lakes in the freezing period also drained to the surrounding groundwater through the fault zones on both sides of the lake basin.The relationship between the water cycle under different periods also maintained the tendency of the lake water to avoid salt water.3.The dominant anions in the chemical composition of lake,river and groundwater in the Hulun Lake Basin at different times were HCO₃^-and Cl^-,and the cation composition characteristics were different.Among them,the dominant cations in lake water and groundwater are Na⁺and Mg²⁺;the dominant cations in river water are Na⁺and Ca²⁺;The average order of anion concentration in precipitation in the basin is HCO₃^->SO₄^2->Cl^-?NO₃^-,and cation is Ca²⁺>Na⁺>K⁺>Mg²⁺.The type of water chemistry in the Hulun Lake is dominated by Na⁺-HCO₃^-,and the rivers flowing into lakes are dominated by Ca²⁺-Na⁺-HCO₃^-,while the groundwater around the lake is dominated by Na⁺-Cl^-and HCO₃^-.There are Mg²⁺,Ca²⁺-HCO₃^-,and SO₄^2-type groundwater distributed locally on the east bank and the west bank of the Lake District.The change of ion concentration in the non-freezing period lake water was stable compared with the freezing period,and there was a significant migration process during the period of freezing period from non-freezing period.4.Gibbs diagram and piper diagram display that precipitation in the Hulun Lake Basin is mainly affected by land-sourced materials,and the main source and change characteristics of major ions in groundwater and surface water are not controlled by atmospheric precipitation.The water body of the watershed is mainly controlled by the synergistic effect of carbonate and evaporite.The change of TDS in groundwater is mainly affected by the evaporation:East Bank Groundwater>South Bank Groundwater>West Bank Groundwater.The correlation analysis indicates that NO₃^-is also the main ion component of part of groundwater.The pollution of the nitrate mines is the main factor that causes the NO₃^-content of groundwater to exceed the water quality standard.Herders'unreasonable storage of haystacks and dung heap are also one of the factors causing NO₃^-pollution in groundwater.5.According to the characteristics of F^-variation in the river water in the Hulun Lake Basin under different periods,the F^-concentration changes in the Kherlen River are significantly different from other rivers entering the lake.The ion content of groundwater in the south bank of the lower reaches of the Kherlen River is generally higher than that in the north bank.The indicators show that the water quality on the South Bank is worse than that on the North Bank.The North Shore is more suitable for human production and life.Although the F^-content of groundwater in the lower reaches of the Kherlen River exceeds the national drinking water standard,more of it is based on the natural phenomena based on comprehensive hydrogeological conditions.The variation of deuterium surplus reveals that the evaporation and fractionation degree of the Kherlen river is stronger than that of the groundwater.Besides the influence of geological and geomorphology,the water evaporation of the basin is mainly influenced by the human activities,especially the surrounding groundwater.