盐度对水体蒸发氢氧稳定同位素分馏的影响

Effect of salinity on the hydrogen and oxygen stable isotope fractionation in water

干旱区强烈的蒸发作用导致地表水体和土壤水、浅层地下水中盐度不断升高,而盐分亦会导致蒸发强度降低,水体蒸发导致的氢氧稳定同位素分馏特征是确定蒸发量的有效手段,但目前水体蒸发过程中氢氧同位素分馏特征的研究主要集中于淡水和低矿化度盐水,为探求不同盐度对水体蒸发过程中的氢氧稳定同位素分馏的影响,开展浓度分别为0、10、20、50、100和200 g/L盐溶液的室内蒸发实验,比较纯水与不同浓度盐水蒸发过程中氢氧稳定同位素的差异,探究其分馏过程,定量评价盐度对水分蒸发分馏过程的影响。实验结果表明:蒸发量随着水体盐度的升高而呈指数形式降低;蒸发过程中,重同位素在水体中不断富集,0~200 g/L盐水中^(2)H、^(18)O和^(17)O的瑞利分馏系数分别在1.089~1.155、1.019~1.033和1.009~1.018之间,并呈现随着盐水浓度的增大瑞利分馏系数逐渐增加的趋势;纯水和盐水中的δ^(2)H-δ^(18)O、δ^(2)H-δ^(17)O和δ^(17)O-δ^(18)O之间均呈良好的线性关系,部分纯水与盐水的蒸发线之间存在比较显著的差异;不同浓度盐水中氘盈余随着剩余水体积比的减小而迅速降低,两者之间呈显著的线性关系,但直线斜率随着盐水浓度的增大而呈现先降低后增大的规律。

The intense evaporation in arid areas leads to the increasing salinity of surface water,soil water and shallow groundwater,and the salinity leads to the reduction of evaporation intensity,the characteristics of hydrogen and oxygen stable isotope fractionation caused by evaporation is an effective means to determine the evaporation.However,at present,the research on the characteristics of hydrogen and oxygen isotope fractionation in evaporation mainly focuses on fresh water and low mineralized brine.In order to explore the impact of different salinity on hydrogen and oxygen stable isotope fractionation during water evaporation,indoor evaporation experiments were conducted on salt solutions with concentrations of O,10,20,50,100,and 200 g/L,to compare and explore the differences in stable hydrogen and oxygen isotopes during the evaporation process of pure water and different concentrations of saline water.The fractionation process was explored,and the effect of salinity on the water evaporation fractionation process was quantitatively evaluated.The results show that the amount of evaporation decreases exponentially with the increase of the salinity of the water.During the evaporation process,heavy isotopes are continuously enriched in the left water,and the NaCl concentration has an inhibitory effect on the isotope fractionation.The fractionation coefficients of ^(2)H,^(18)O and ^(17)O in the saline water with the salinity from 0 to 200 g/L are between 1.089~1.155,1.019~1.033 and 1.009~1.018,respectively,and show a gradual increasing trend with increasing salinity.There is a good linear relationship between δ^(2)H and δ^(18)O,δ^(2)H and δ^(17)O,δ^(17)O and δ^(18)O of pure water and saline water.There is a significant difference between the evaporation lines of pure water and some saline water.The deuterium excess decreases rapidly with the left water volume ratio decreasing as a significant linear relationship,but the line slope of the d-excess vs.f line decreases at start stage and then increases as the salinity increases.