西藏江夏湿地水化学变化规律及灌溉效用评价

Change Law of Water Chemical Characteristics of Jiangxia Wetland in Linzhou County of Tibet and the Evaluation of Its Irrigation Effect

以西藏林周县江夏湿地为研究区域,对其水体全年主要离子进行季节监测,分析了该湿地水体水化学特征和主要离子时空变化规律,探讨了主要离子的初步来源,并对湿地不同季节水体灌溉效用进行了评价。结果表明:湿地水体pH值在7.8~8.3之间,为弱碱性水,HCO_3^-在阴离子中占绝对优势,阳离子中春季Na^+占优势,夏秋季节Ca^(2+)、Mg^(2+)占优势,冬季Mg^(2+)占优势。TDS均<1g/L,为淡水水体。依据舒卡列夫分类法,江夏湿地水体化学类型为春季HCO_3—Na型水;夏季、秋季HCO_3—Ca、Mg型水;冬季HCO_3—Mg型水。阴离子中除了SO_4^(2-)之外,其余HCO_3^-、Cl^-、NO_3^-含量均为出水口大于进水口。从同一离子不同空间位置来看,Cl^-空间变异系数最大,其次是Mg^(2+),Na^+最小;而从同一空间位置来看,3个位置离子浓度总体变化程度不大。根据离子间相关性分析和Gibbs分类法表明,江夏湿地水体离子来源主要是受拉萨河流域岩石风化的影响,枯水期(春、冬季)伴随一定程度的蒸发—结晶作用影响,大气降水影响不明显。灌溉效用评价结果显示,江夏湿地春季水体不适用于灌溉,而其他3个季节水体均可用于农业灌溉。

Through systematically monitoring the ion compositions of the water bodies in Jiangxia wetland,which is located in Linzhou county of Tibet,a study was conducted to analyze the water chemical characteristics of the water bodies in Jiangxia wetland and the change laws of the major ions in water,discuss the main sources of these ions,and evaluate the irrigation effect of the water bodies in different seasons in the wetland.The results showed that pH value of water was between 7.8to 8.3,which indicated that the water in Jiangxia wetland was weak alkaline water.HCO_3^-was the absolutely predominant anion,while Na＋was the predominant cation in spring,Ca^（2＋）and Mg^（2＋）were the predominant cations in summer and autumn,and Mg^（2＋）was the predominant cation in winter.TDS of water was always lower than l g/L,which indicated that the water in Jiangxia wetland was fresh water.According to Mischka Lev classification method and the water chemical characteristics of water bodies in Jiangxia wetland,we found that：in spring the water belonged to HCO_3—Na type,while in summer and autumn,the water belonged to HCO3—Ca.Mg type,and in winter,the water belonged to HCO_3—Mg type.The contents of all anions except SO_4^（2-）,such as HCO_3^-,Cl^-,and NO_3-,were higher in outlets than in inlets.About the different spatial locations of the same ion,we found that the spatial variation coefficient of Cl-was the maximum,and then was that of Mg^（2＋）,while the spatial variation coefficient of Na＋was the minimum.In the same spatial location,the variation degrees of concentrations of all the ions were very small.Based on the correlation analysis among the ions,and the Gibbs classification method,we found that the main source of ions in water bodies of Jiangxia wetland was rock weathering along Lhasa Riven basin,which was affected by a certain degree of crystallization and evaporation in dry season（spring and winter）,but the influence of atmospheric precipitation was not obvious.The evaluation resultsof irrigation effect showed that the water in Jiangxia wetland was not suitable for irrigation in spring,while it was suitable for agricultural irrigation in the other 3seasons.