季风期前后西藏纳木错湖水及入湖河流水化学特征变化

Water Chemistry Variations of Lake and Inflowing Rivers Between Preand Post-monsoon Season in Nam Co,Tibet

2011年季风期前和季风期后,分别对纳木错湖中两个站点的湖水和周边16条入湖河流进行水样采集,水化学分析结果表明:湖水中各离子含量在季风期后都比季风期前有明显的增加,其中Mg2+在两个站点分别增加46.84%和46.95%,Ca2+分别增加67.02%和75.11%,HCO3-分别增加27.61%和25.02%。河水中大部分离子含量也都表现为季风期后的增加,而F-、Cl-和NO3-则表现为降低趋势。离子含量的动态变化主要受流域内风化作用影响,即风化产物是造成大部分离子含量升高的主要来源,而蒸发作用对湖水离子含量的升高也起一定作用。

In mid-May（pre-monsoon season） and late October（post-monsoon season）,water samples were taken from 2 sites in Nam Co Lake and 16 rivers around the lake for dynamic changes study of water chemical composition in different seasons.Water chemistry analysis and comparative studies have been conducted to illustrate the dynamic changes of ions concentrations between the two seasons.The results indicated that all ions showed higher concentrations in post-monsoon than that in pre-monsoon season for lake water.Among them, Mg2＋ increased by 46.84% and 46.95% on average in two sites,while Ca2＋ increased by 67.02% and 75.11% on average,respectively.Na ＋ and K ＋ showed relatively less increase in concentration.As for anions,HCO3showed the largest increase of 27.61% and 25.02% in two sites,respectively.Meanwhile,most ions in river water also showed the similar trends,Mg2 ＋ and Ca2 ＋ increased by 40.55% and 33.20% on average in all rivers. HCO3-and SO4 2-increased 36.81% and 28.48%.However,F-,Cl-and NO3-showed opposite patterns,i.e.,the concentrations were lower in post-monsoon season.Cl-was the most remarkable decreasing ion,averagely decreased 28.43% in all rivers.It is indicated that the ion concentrations dynamic changes of Nam Co Lake and river water were mainly influenced by weathering in the drainage area.Weathering production such as Mg2 ＋, Ca2＋ and HCO3-were the main source of increased ions,resulting from the weathering of carbonate in the catchment. On the other hand,lake evaporation has also slightly contributed to ion concentrations increase of lake water.The river Cl-decrease in post-monsoon season was mainly influenced by individual river flux,more changes in river flux between two seasons led more decrease of Cl-concentration and the ultimate controlling factors should be water supply from precipitation and glacier melting water within the catchment.