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羊卓雍错水体pH偏高的成因
保宏运1, 郭建阳1, 杨海全1, 张红梅2, 马丽2
1.中国科学院地球化学研究所;2.西藏自治区山南市生态环境局
摘要:
羊卓雍错(羊湖)是我国生态环境保护的重点区域,虽然大部分水质指标优良,但pH常常处于超标状态,令当地管理部门倍感压力。为了解羊湖水体pH偏高的成因,笔者以羊湖水体和流域水源作为研究重点,从水化学和流域风化的角度,利用地球化学方法寻找相关的线索。结果表明:目前羊湖水体pH主要在8.5~9.3之间波动,具有明显的季节性变化特征,全年水体pH值超标概率为49%。羊湖水体pH超标与水源无关,而是流域风化和其自身长期自然演化的结果。羊湖流域不但存在常见的碳酸盐岩和硅酸盐岩的风化,还有促进碳酸盐岩风化的硫化物矿物风化。流域强烈的碳酸盐岩风化为羊湖水体提供了大量的HCO3-离子,这是羊湖水体pH在特定条件下自然演化的物质基础。羊湖封闭型水动力学特征使HCO3-离子滞留并累积在水体中,这为羊湖pH的自然演化提供了一个必要条件。在长期蒸发浓缩过程中,水体中的HCO3-一部分转化为CO32-,导致水体的pH逐渐上升,这是羊湖水体pH偏高的充分条件。简言之,羊湖pH偏高是流域风化、封闭型的水动力学和水体长期蒸发浓缩共同作用的结果。鉴于羊湖水体pH偏高是长期自然演化的结果,建议将pH从羊湖水质管理的考核指标中排除,以免造成不必要的管理成本和压力。
关键词:  羊卓雍错,pH,水化学,流域风化
DOI:
分类号:
基金项目:国家自然科学基金项目(91647205, 41877406)
Mechanism on high pH value in Yamzhog Yumco, South Tibet
保宏运, Guo Jianyang1, Yang Haiquan1, Zhang Hongmei2, Ma Li2
1.State Key Laboratory of Environmental Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences;2.Ecological environment bureau of Shannan city,Shannan
Abstract:
Yamzhog Yumco is the key area of ecological environment protection in China. Although most water quality indexes are sound, pH value is often in excess, which makes the local government under great pressure. In order to understand the cause of high pH value in Yamzhog Yumco, geochemical methods were used to find the clues on the formation mechanism of high pH value based on the hydrochemistry in Yamzhog Yumco and the watershed weathering. The results shown that pH value of Yamzhog Yumco are mainly between 8.5 and 9.3 presently, with obvious seasonal characteristic and the exceeding probability of 49% in the whole year. High pH of Yamzhog Yumco is the result of the watershed weathering and the long-term natural evolution of water body, and is nothing to do with the water source. Watershed weathering of Yamzhog Yumco is characterized by not only the weathering of carbonate and silicate rocks, but also the weathering of sulfide minerals, which can strength the weathering of carbonate. The strong weathering of carbonates in the watershed provides a lot of HCO3- for Yamzhog Yumco, becoming the basis for the evolution of pH under specific conditions. The closed hydrodynamics of Yamzhog Yumco make HCO3- stayed and accumulated in the water body, being a necessary condition for the evolution of pH in Yamzhog Yumco. As the sufficient condition for the high pH value in Yamzhog Yumco, long-term evaporation and concentration process caused part of HCO3- converted to CO32-, resulting in the increase in pH value. In short, high pH of Yamzhog Yumco is a joint result of the watershed weathering, the closed hydrodynamics and the long-term evaporation and concentration of the water body. Due to the high pH value is a result of natural long-term evolution, it is suggested that pH should be excluded from the water quality management of Yamzhog Yumco, so as to avoid unnecessary management cost and pressure.
Key words:  Yamzhog  Yumco, pH, Hydrochemistry, Watershed weathering