青藏高原纳木错湖水主要化学离子的时空变化特征

为揭示青藏高原纳木错湖水化学离子的时空变化特征、来源以及主要控制因子,于2006～2010年连续定点(30°47.27’N,90°58.53’E,4 718 m a.s.l.)采集近岸表层湖水样品;于2009年8月采集湖心区剖面样品;于2010年10月采集湖心区剖面样品及表层湖水样品;对其主要化学离子进行分析.结果表明,纳木错湖水中主要阳离子为Na+,主要阴离子为HCO3-.绝大多数离子浓度在季风期较高(6～9月),而非季风期尤其是封冻期(1～4月)偏低;Ca2+浓度的变化则相反,即封冻期较高,而非封冻期较低且变化较小.对垂直剖面湖水分析表明,在湖水垂直结构稳定的非季风期(如10月),除Ca2+浓度随深度无显著变化外,其他离子浓度随深度增加而增大.纳木错湖水主要离子来源于入湖河水的贡献;影响离子时空变化的因素包括蒸发、降水、pH值等,其中蒸发是最主要的影响因素,它造成湖水Na+浓度不断升高而Ca2+浓度降低.

Temporal and Spatial Variations of Major Ions in Nam Co Lake Water, Tibetan Plateau

In order to investigate the temporal and spatial variations, sources, and major controlling factors of the major ions in Nam Co Lake water, inshore surface water samples were collected at a fixed site (30°47.27'N, 90°58.53'E, 4718 m a.s.l.) from 2006 to 2010, at the vertical profiles in the center of the lake in August 2009, and at both the vertical profiles in the center of the lake and at the surface layers of different sites in the Nam Co Lake in October 2010. The results indicated that Na⁺ was the dominant cation and HCO₃^- was the dominant anion in the lake water. The concentrations of most ions were higher in monsoon seasons (June -September) and lower in non-monsoon seasons, especially when the lake was frozen (January -April). However, the Ca²⁺ concentration showed a reverse trend of seasonal variations, namely, higher values in the frozen period and lower in monsoon seasons. Analysis of water samples collected from the vertical profiles indicated that the concentrations of all ions except Ca²⁺ increased with the depth in non-monsoon seasons (e.g. October). The major ions in Nam Co Lake were mainly contributed by river input. There were a variety of factors that influenced the temporal and spatial variations of the major ions in the Nam Co Lake, such as evaporation, precipitation, pH values, etc., among which, evaporation was the most important controlling factor, causing the increasing Na⁺ concentration and decreasing Ca²⁺ concentration in the lake water.