The Characteristics Of The Hydrogen And Oxygen Isotopes In Different Water Bodies In Jinfo Moutain And Its Environmental Significance

Karst groundwater is an important water resource in karst areas,and karst hydrological system is an important storage and migration medium for groundwater.Because of its high degree of openness and vulnerability,it is easily affected by the external environment.The karst water system has poor regulation capacity and rapid conversion.The highly developed karst pipelines and the underground dual structure of the surface make it easy to enter the surface karst system and spread along with cracks and pipes,thus contaminating groundwater.Therefore,it is great significance to protect the water resources of the karst area,such as atmospheric precipitation and the conversion of stable hydrogen and oxygen isotopes in the groundwater.In this study,Chongqing Jinfo Mountain was used as a fixed observation point,combined with local meteorological data,to sample atmospheric precipitation,surface water?lake water?,groundwater?spring water?,and soil water in the study area from October 2015 to October 2016.Analysis of the characteristics and mechanisms of the stable isotopes of hydrogen and oxygen in different water bodies.In order to obtain the form of recharge of groundwater and surface water in the basin,the law of the hydrological cycle in the karst area can be traced to provide basic scientific evidence for the development and protection of local groundwater resources.Research indicates:?1?Stable isotope characteristics of atmospheric precipitationThe stable isotopic compositions of atmospheric precipitation exhibit great diversities in different seasons,?D,?¹⁸O and d-excess having higher values in winters and lower one in summer.The local meteoric waterline was?D=9.49?¹⁸O+28.7?r=0.98,n=16,P<0.01?,due to the influences of altitude and evaporation conditions,the slope and cut-off of the local meteoric waterline in Jinfo Mountain were high;The statistics of the relationship between the atmospheric precipitation and the?¹⁸O of the atmospheric precipitation indicate that the study area Stable isotopes of atmospheric precipitation exhibited anti-temperature effect and precipitation effect;Seasonal differences in stable isotopes of atmospheric precipitation in the region may be due to differences in the source of water vapor in different seasons.The selection of spring,summer,autumn,and winter precipitation events to simulate the backward air mass trajectories.The result confirmed that,in the summer the precipitation of study area was mainly controlled by the southwest monsoon and the southeast monsoon from the ocean.In the winter controlled by the continental air mass,mainly due to the westerly wind transport and local water vapor re-evaporation.?2?Stable isotope characteristics of surface waterThe surface water?D,?¹⁸O,and d-excess of Yaochiba lake are stable than atmospheric precipitation,and the seasonal fluctuations are relatively small.?D,?¹⁸O and d-excess of surface water have a certain delay effect on the seasonal changes of precipitation.The waterline of surface water:?D=8.13?¹⁸O+9.27?r=0.89,n=19,P<0.01?.The slope and cut-off of the surface waterline are less than the local meteoric waterline,indicating that the surface water in the study area is recharged by precipitation and affected by a certain evaporation.Precipitation flows into the lake through surface runoff,and the lake water needs to be replaced by long-term retention,resulting in the dispersion of?D and?¹⁸O in the lake water.However,the lake is small,and the contact area between the water and surrounding rocks is small,thus the water-rock exchange is not strong.Therefore,the slope and cut-off of the surface waterline deviate from the initial value of the local atmospheric precipitation,but the degree of deviation is not too much.?3?Stable isotope characteristics of groundwaterAffected by the recharge path and the complex aqueous medium,?D,?¹⁸O,and d-excess in groundwater are relatively stable with precipitation,and seasonal fluctuation range,and coefficient of variation in groundwater are the smallest among the four water bodies.There is a positive correlation between daily groundwater?¹⁸O and precipitation,air temperature and relative humidity.The control effect of air temperature and precipitation on relative humidity,affects the enrichment of groundwater stable isotopes.The difference of waterlines in winter and summer is due to the strong evaporation of groundwater in winter,which is accompanied by deep groundwater recharge and a small amount of snowfall meltwater recharge,resulting in a lower waterline slope in winter.In summer,the proportion of groundwater recharged by precipitation increases,and the waterline in the summer is closer to the local meteoric waterline.?4?Stable isotope characteristics of soil waterThe soil water?D,?¹⁸O,d-excess were significantly high at the dry season?from February to June?,while the autumn and winter seasons were low.Soil water stable isotopes gradually enriched with the increase of soil depth.The thickness of the soil layer affects the response of soil water to atmospheric precipitation,in the upper layer is affected directly by in atmospheric precipitation,whereas in the underground water there is not much affected by atmospheric precipitation.The stable isotope of soil water basically falls near the local atmospheric precipitation,indicating that the soil water is recharged by atmospheric precipitation.The?D,?¹⁸O,d-excess of soil water are very close to groundwater,indicating that both the soil water and the groundwater were recharged by stored in the karst pipelines and other aquifers.?5?Jinfo mountain water cyclePrecipitation is the common recharge source of surface water,groundwater and soil water in the study area.However,the composition of surface water and groundwater?D and?¹⁸O are quite different,and there have no obvious response of dynamic changes between two water bodies.There is no direct supply of surface water and groundwater.Through calculations,it was found that the isotope-weighted average of precipitation for the effective recharge of groundwater and surface water was approximately?-9.11‰,-53.2‰?,?-14.3‰,-125.6‰?.Using?¹⁸O as a tracer,calculated the recharge ratio of precipitation and deep groundwater to Shuifang spring in different seasons.The main source of recharge of groundwater was deep groundwater,and it was only in summer that Shuifang spring was recharged by atmospheric precipitation more directly.The atmospheric precipitation is the main source of recharge for the basin,part of the precipitation directly enters the water body,and part of it is supplied to the soil water through runoff,and eventually converted into groundwater or re-evaporated into the atmosphere,and then becomes part of the source of atmospheric precipitation vapor.