羊卓雍流域雪坑中化学离子记录研究

Ionic Chemistry in Snowpits from Yamzhog Yumco Basion

2006年8-9月在西藏南部羊卓雍流域采集了3个不同地点的50个雪坑样品,分析了所有样品的阳离子（Na^＋、NH4^＋、K^＋、Ca^2＋和Mg^2＋）、阴离子（Cl^-、SO4^2-和NO3^-）和氧稳定同位素.分析表明,3个雪坑的化学特征一致,阴离子中NO3^-的浓度最高,为93.7μg·L^-116.1-187.2μg·L^-1;阳离子中Ca^2＋浓度最高,为81.0μg·L^-119.0-236.7μg·L^-1,分析结果同青藏高原南部其它地区的雪坑离子浓度相当（两者比值为0.5-2.0）,而仅为高原北部离子浓度的2/5-1/25.该区域雪坑中离子浓度在季风季节和非季风季节差异显著,在季风季节NO3^-、NH4^＋浓度升高30%-40%,是因为受植被、牲畜、人为活动以及雷暴的影响;Ca^2＋、Mg^2＋陆源离子浓度在季风季节降低了80%,是由于季风季节来自北方的沙尘、大风减少和印度季风带来丰富的降水对岩屑气溶胶的＂淋洗＂使Ca^2＋、Mg^2＋浓度显著降低.阴、阳离子浓度的变化受到海拔高度的差异和沉积后作用的影响,表现为Ca^2＋、Mg^2＋浓度随海拔降低而升高,SO4^2-、NO3^-随海拔降低和沉积后作用的影响而降低.

During August and September,2006,a total of 50 samples had been collected from three different snowpits at the Yamzhog Yumco Basion in the south of the Tibetan Plateau.All samples were analyzed for major cations（Na^＋,NH^＋4,K^＋, Ca^2＋and Mg^2＋）,anions（Cl^-,SO4^2- and NO3^-） and stable oxygen isotope ratio.The results of analyses show that the three snowpits represent accordant chemical characteristics,with NO3^-（16.1-187.2μg·L^-1,averaging at 93.7 μg·L^-1） and Ca^2＋（19.0-236.7 μg·L^-1,averaging at 81.0 μg·L^-1） being the highest concentration of anions and cations respectively.Compared with data from other representative sites,major ion concentrations in the Yamzhog Yumco Basion accord with those in the south of the plateau,but they differ much from those in the north of the plateau.Remarkable variabilities of major ion concentrations from monsoon period to non-monsoon period are demonstrated.Ion concentrations of NO3^-,NH^＋4increase 30%-40% in monsoon period due to the influences of vegetation,live-stock,anthropogenic activity and thunderstorm,whilst the concentrations of crustal source ions,such as Ca^2＋,Mg^2＋reduce 80% due to decrease of dust and strong wind from the north of the plateau and crustal aerosols being washed out of the atmosphere by heavy precipitation during the monsoon period.Variation of ion concentrations are also impacted by elevation and post-deposition process,with Ca^2-,Mg^2＋ increasing with a decrease in elevation and SO4^2-, NO3^-decrease with an increase in elevation and the influence of post-deposition.