毛乌素沙地沙障固沙机制与效益评估

Sand fixation mechanism and effect evaluation of sand barriers in Mu Us sandy land,China

沙障是沙区广泛应用的一种固沙工程措施,准确理解沙障的固沙机制并优化其配置模式有助于防风固沙技术的完善.本文以毛乌素沙地腹地发育的4个新月形沙丘作为研究载体,通过对9类(3种材料×3种规格)沙障措施下的沙丘开展地形测量、风沙观测、沉积物采样、植被调查和室内分析等研究,揭示了沙障环境下沙丘的表面过程,评估了各类型沙障防风固沙效果及生态恢复效应.结果表明,沙障具有降低沙丘高度、重塑微地貌形态、降低近地表风速、拦阻沙物质输移以及促进植被恢复的作用,其作用强度大小受控于沙障材料、规格配置及铺设坡位;沙柳沙障是该区防风固沙和促进植被恢复的最佳选择,草绳沙障其次,聚乳酸(polylactic acid,PLA)纤维沙袋沙障最差;沙柳和草绳沙障在1 m×1 m规格下的固沙效益最佳,而PLA沙障在2 m×2 m规格下的固沙效益最佳.此外,本文认为,沙障的防风固沙效益受多个要素的共同影响,单以近地表风速大小或微地貌形态作为衡量标准是不充分的;沙障工程应依据区域固沙需求和实地环境,立足重点目标或需求,因地制宜选择出最适宜的沙障配置模式.

Sand barriers are an engineering measure for sand fixation,and play an important role in promoting dune fixation and vegetation restoration.As the most widely used means of sand control,sand barriers have a variety of materials and configurations.In recent years,some new sand fixation materials have appeared,but their benefits of sand fixation have not been compared and evaluated.Moreover,there is an insufficient amount of research on the sand fixation mechanism of sand barriers.Therefore,an accurate understanding of the sand fixation mechanism of sand barriers and the optimization of its configuration mode is conducive to improving the techniques of wind prevention and sand fixation.In this paper,four barchan dunes developed in the Mu Us sandy land were selected as the research carrier.One of the dunes is a reference dune without sand barriers,and the remaining three dunes are covered with sand barriers of different materials and specifications.There are 9 types of sand barriers,which can be divided into 3 materials(Salix,straw rope and PLA)and 3 specifications(1 m×1 m,2 m×2 m and 3 m×3 m).This study revealed the surface processes of dunes under each type of sand barrier and evaluated the benefits of each type of sand barrier on sand fixation and ecological restoration through topography measurements,sand drift observations,sediment sampling,vegetation investigations and laboratory analyses.The results show that the sand barriers have the functions of reducing the height of dunes,reshaping the surface micromorphology,decreasing near-surface wind speed,blocking the sand transport and promoting vegetation restoration,and the strength of the functions is controlled by the material of the sand barrier,the configuration mode of the sand barrier and the relative positions on the dune.Detailed analysis of the benefits in sand fixation and vegetation restoration of each type of sand barrier suggests that the Salix barrier is the best choice in this area,the straw rope barrier is the second best choice,and the PLA barrier is the worst.The best configuration mode of the Salix barrier and straw rope barrier is 1 m×1 m,while that of the PLA barrier is 2 m×2 m.Moreover,this study considered that the effect of sand barriers on wind prevention and sand fixation are decided by multiple factors,and it is not sufficient to take the near-surface wind speed or micromorphology as the measurement standards of these effects.The selection of sand barrier materials and configurations needs to comprehensively consider many issues,such as the efficiency of sand fixation,the ability to promote vegetation restoration,sustainable time,economic cost and secondary pollution.Thus,sand barrier projects should take the regional sand fixation demand and field environment into account and select the most suitable configuration forms according to the main objectives or demand.