中文摘要：

根据IKONOS和Quick Bird影像解译和实地调查，对拉萨河下游河谷区风沙源分布特征、沙源粒度特征、植被特征以及人类活动的作用进行了探讨。结果表明，受大中小尺度风场的影响，风沙源地沿河谷两侧呈小面积零星分布在多个地貌部位；河流冲积物是最主要的沙源，沙源粒径90％以上分布在0．25mm以下，以细沙、极细沙和粘粒成分为主，平均含量占60．69％，易于发生风沙活动；风沙活动是影响沙生植被的主导因素，植物种类和盖度能很好反映沙源地的稳定程度；特别在流动沙地和半流动沙地上，植被演替朝着有利于风沙活动发展的方向进行，是风沙活动的主要驱动因素之一，也是风沙活动不断加剧的产物。尽管自然因素是该区域风沙活动的主要成因，人类活动对其发展起到了强化作用。

英文摘要：

Based on IKONOS and Quickbird interpretation and field survey, the effects of human activities and characteristic of sand distribution, grain diameter of sand sources and vegetation in the valley of lower reaches of Lhasa River are discussed. The results indicate that valley sand sources distribute along fiver valley and its two sides, in patch and particle form from slope to bottom of valley, and have close interrelation with large, medium and small scale of wind field in space; There are three categories of accumulation substanceswhich are sand sources in the lower reaches of Lhasa River valley： fiver alluvium, flood depositand weathering substances of mountain rock. Among them, river alluviumis the most important sand source, grain diameter of sand source is mainly made of silver sand, extreme silver sand and sticky sand, and over 90% of whose grain size is less than 0.25 mm, and inclinedto produce wind erosion. Sand activity is the dominant factor affecting sand-nurtured vegetation. Especially the vegetation on semi-fixedand semi-movablesand duneis affected most seriously, species and coverage of vegetation can well reflect the stability of sand sources. Vegetation succession is developing in the tendency in favor of sand activities, which is one of a main driving factors and outcome of worsening sand activities. Though natural factors are the main cause of the sand activities in thisarea, human activitieswill further strengthen sand activities.