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Université des géosciences de Chine (2018)

An Investigation on Groundwater Origination in Deserts Indicated by Hydrogen and Oxygen Isotopes

吴秀杰;

Titre : An Investigation on Groundwater Origination in Deserts Indicated by Hydrogen and Oxygen Isotopes

Auteur : 吴秀杰;

Grade : Doctoral Dissertation 2018

Université : Université des géosciences de Chine

Résumé
The origin of water in the Badain Jaran Desert is a long running controversy,it is strongly related to the local environmental and ecological protection,and how to make the plan of water resources management and utilization.This paper provides a perspective to understand the water sources problem by focusing on evaporation effect on the isotopes of water in the desert.A series of evaporation experiments were also conducted in the desert to examine how the isotopic signature of water may change during evaporation and infiltration under local environmental conditions.Both local groundwater and lake water were monitored in the evaporation experiments,in the meantime,the infiltration water was collected under three pits which were designed to be in different depth under a flat ground surface.On the other hand,hydrogen and oxygen isotope ratios,and d-excess values were measured,the water samples for these measurements were collected from local unconfined aquifers,lakes and one spring.The results of experiments show the water isotope contents became progressively enriched along an evaporation line in the experiments and the d-excess values decreased with the increasingδ18O in a linear way,d-excess=-3.4δ18O-30.3(R2=0.974).The trend line of the stable isotopes of natural water samples from the desert is similar to the evaporation line of the experiments,which indicates a signature of strong evaporation under the modern or similar-modern arid environment in the desert.It is ruled out the hypothesis that water was recharged by the precipitation that fell in the past during the early Holocene when the climate was much wetter than today.Furthermore,all of the water samples from the Qilian Mountains are plotted above the evaporation line of the Badain Jaran Desert,so the Qilian Mountain should not be the origin area of the water in the desert.However,the evaporation line of the Yabulai Mountain extends through some of the lakes in theδD-δ18O figure.It suggests that the Yabulai Mountain could be a recharge area of the desert.In all,the local precipitation is the main water source and the possible recharge area including the sand dune area and the sounding mountains.Even though,the results of radiocarbon DIC-14(dissolved inorganic carbon)tests reveal the age of the groundwater is 28 kyr BP,which is different from the above consequence.This can be explained by the dissolution of radiocarbon-free or low radiocarbon contained carbonates from the local aquifer.Moreover,the previous published studies and data of d-excess andδ18O values in groundwater from some typical arid areas together with the Badain Jaran Desert are analyzed and summarized.The result reveals a similarity between the conclusion above and previous researches in desert regions,such as the Arabia deserts,Chile and central Australia.Despite the short of precipitation and the strong evaporation in the areas,the local precipitation is a water source of groundwater.This work demonstrated that the characteristic of isotopic water patterns could provide a clue to the ambiguous origin of water in the arid areas

Mots clés : Arid area; Environmental isotopes; Groundwater; d-excess; Badain Jaran Desert;

Présentation (CNKI)

Page publiée le 4 avril 2019