腾格里沙漠西南缘土壤包气带NO3-分布特征

Distribution characteristics of nitrate in the vadose zone of southwestern edge of the Tengger Desert

基于腾格里沙漠西南缘,研究不同植被覆盖类型的包气带中ρ(NO3-)、ρ(Cl-)以及c(NO3-/c(Cl-),探究土壤包气带中硝酸盐的来源以及分布特征.结果表明:两个沙漠包气带剖面中NO3的主要来源为大气沉降,而农作物耕种剖面硝酸盐主要来源于无机氮肥施加以及大气沉降.其中,裸沙剖面中不同土壤深度ρ(NO3-)、ρ(Cl-)基本呈现一致趋势,强降水浸润事件可以将剖面中Cl、NO3-向深层包气带迁移;红柳覆盖沙地剖面中受到植被对养分的选择性吸收影响,硝酸盐质量浓度大幅减少,向深层包气带的迁移量也较裸沙剖面低,表明天然植被对沙漠包气带NO3-富集和变化具有一定的减缓作用;农作物耕种剖面中由于受到额外氮肥施加和作物根系吸收的影响,改变了ρ(Cl-)、ρ(NO3-)在包气带中相对一致的运移关系.沙漠包气带作为活性氮储存的重要位置,需要对其硝酸盐的来源和迁移富集规律进行研究,以便有效管理干旱区地下水资源.

The NO3-and Cl-concentrations and c(NO3-)/c(Cl-)values of the unsaturated zone with different vegetation covers were studied in southwestern Tengger Desert,in order to explore the sources and the distribution of soil nitrate.The results showed that atmospheric deposition was the main source of NO3 in sand profiles,the major sources of NO3-in farmland profiles were the nitrogen fertilizer and atmospheric deposition.A consistent trend of NO3-and Cl-concentrations in different depths of bare sand profiles was presented,and the migration of NO3-and Cl-to the deep vadose zone was accelerated by heavy precipitation infiltration events.The NO3-concentration of vegetated sand profile was sharply reduced due to the influence of the vegetation’s selective absorption of nutrients,and the migration of nitrate to the deep vadose zone was also reduced,demonstrating that the enrichment and changes of nitrate in the desert vadose zone were slowed down by the effect of vegetation.Concerning farmland profiles,the relationship of Cl-and NO3-concentrations was changed by the function of the additional nitrogen fertilizer and the crop absorption.The vadose zone was an important location of nitrate storage.It is necessary to study the NO3-sources,migration and enrichment in desert vadose zone,in order to effectively manage the groundwater resources in arid areas.