南伊沟水体水化学及氢氧同位素特征分析

南伊沟是林芝地区重要水源涵养区,研究南伊沟水体水化学和氢氧同位素特征,揭示“三水转化”规律,对提高林芝地区水体水文地球化学研究程度,支撑当地林水关系研究,服务高原地区水生态保护具有重要意义。运用水化学和氢氧同位素分析方法,分析了地区水化学特征、水岩作用情况和水循环特征。结果表明: 南伊沟水体为极低矿化度淡水,地表水水化学类型为HCO₃-Ca·Mg型和SO₄·HCO₃-Ca·Mg型,地下水水化学类型为HCO₃-Ca·Na型; 地表水和地下水的水化学离子成分主要受岩石风化控制,离子来源主要受碳酸盐岩溶解和硅酸盐岩风化影响,地表水中Na⁺、K⁺、Cl^-主要来源于盐岩溶解,同时还受降雨影响,地表水和地下水中Ca²⁺、Mg²⁺主要来源于碳酸盐岩矿物溶解; 地下水和地表水水岩作用较弱,对比上游雅鲁藏布江和拉萨河地表水,大部分δ¹⁸O、δD值具有明显的高度效应和大陆效应; 南伊沟枯水年内强烈的不平衡蒸发作用是导致地区大气降雨线斜率和截距偏小的主要原因之一。

Analysis of hydrochemistry and hydrogen and oxygen isotope characteristics of Nanyi Gully water body

Nanyi Gully is an important water source conservation area in Linzhi. The study of hydrochemistry and hydrogen and oxygen isotope characteristics of Nanyi Gully water body reveals the law of “three water transformation”, which is of great significance for improving the hydrochemistry research degree, supporting the research on the relationship between local forests and water, and serving the protection of water ecology in the plateau area. The characteristics of regional water chemistry, water-rock interaction and water cycle were analyzed by water chemistry and hydrogen and oxygen isotope analysis methods. The results show that water body of Nanyi Gully is very low salinity fresh water. The chemical types of surface water are HCO₃-Ca·Mg type and SO₄·HCO₃-Ca·Mg type, and the chemical types of the underground water are HCO₃-Ca·Na type. The hydrochemical characteristics of surface water and groundwater are mainly affected by the weathering of rocks, and the ions source is mainly affected by the carbonate dissolution and silicate rocks weathering. Na⁺, K⁺, Cl^- ions mainly come from the dissolution of evaporative salt rocks, which is also affected by the rainfall. The Ca²⁺ and Mg²⁺ mainly come from the dissolution of carbonate rock minerals. The water-rock interaction of the underground and surface water in the study area is weak, and most of the δ¹⁸O and δD values have obvious height effect and continental effect compared with the surface water in Yarlung Zangbo River and Lhasa River. The strong unbalanced evaporation during dry years is one of the main reasons for the small slope and intercept of the regional atmospheric rainfall line.