漓江流域δD和δ^18O对蒸发的指示作用

The composition characteristics of hydrogen and oxygenstable isotopes as an indicator of evaporation in the River Lijiang,China

以漓江流域为例查明不同水体之间氢氧稳定同位素组成特征,并探讨氢氧稳定同位素对漓江流域的蒸发过程指示作用.结果表明:流域内不同水体之间,氢氧稳定同位素表现出不同的组成特征,地表水和地下水,在丰水期δD值和δ^18O值要比枯水期更容易富集,地下水的δD值和δ18O值分布范围较地表水小;随着水温的升高,δ18O的变化趋势比d-excess明显.从漓江上游到下游高程逐渐下降,河水线的斜率和截距也在逐渐减小,其中漓江下游河水线的斜率和截距要低于当地大气降水线,表明下游受到蒸发作用较强烈;地下河水线、地表河水线在一定程度上偏离当地大气降水线,但偏离程度较小,表明三者之间有很好的水力联系.受温度和湿度的共同影响,漓江干流丰水期河水的蒸发量占最初水体总量的0.7%~9.1%,枯水期河水的蒸发量占最初水体总量的2.6%~9.7%,丰水期的蒸发比例低于枯水期,从上游到下游蒸发比例在逐渐上升.研究区蒸发量估算值为959.40mm,与多年实测值少43.11mm,相对误差4.70%.氢氧稳定同位素对研究区降水、地表水、地下水之间的转换规律具有重要的实际意义,在今后的漓江流域水文研究中有着更加广阔的空间.

The stable isotope compositon of water(δD andδ18O)were collected in November 2018 and March 2019 along the Lijiang River to estimate their indication of the evaporation.The results showed that:theδD andδ18O values had different composition characteristics among different sampling sietes in the the Lijiang River,theδD andδ18O values of groundwater was smaller than those of surface water,theδD andδ18O values in the wet season were easier to enrich than in the dry season;The variation trend ofδ18O value was more obvious than d-excess under the increasing of water temperature.The elevation gradually decreased from the upstream to the downstream,and the slope and intercept of Lijaing River water line also gradually decreased;Underground river water line and Lijiang River water line were closely to local meteoric water line(LMWL),indicating that there was a close hydraulic connection between underground river,Lijiang River and precipitation in the study area.Due to the influence of temperature and humidity,the evaporation proportion of Lijiang River in wet season and dry season were 0.7%~9.1%,2.6%~9.7%,respectively;The evaporation proportion from upstream to downstream gradually increased in the study area,regardless of in wet season or dry season.The evaluated evaporation value based on isotope mass balance model in the study area was 959.40mm,which was less 43.11mm than the multi-year monitoring data,with the relative error of 4.70%;Using stable isotopes(δD andδ18O)is an essential method to study the hydrological cycle in a river basin,thus stable isotope still has a wide application space in hydrological cycle in Lijiang River Basin.