民勤绿洲边缘积沙带的稳定性动态

甘肃河西走廊经过60年的防沙治沙,在绿洲上风向边缘形成了一条流沙堆积带,即积沙带。其中,民勤绿洲上风向边缘的积沙带最高大、最连续。为了揭示积沙带的稳定性动态,在民勤绿洲上风向边缘设置11条观测样线,从2016年11月上旬至2019年4月上旬进行了7次风蚀积沙观测和沙面特征点位移观测。民勤绿洲上风向边缘积沙带按形成方式可分为人工固沙林积沙带、天然灌丛积沙带和乔灌木混交单行林积沙带。结果表明:人工固沙林积沙带风蚀最严重且前移速率最快,天然灌丛积沙带次之;风蚀程度越轻则积沙带前移速率就越慢,草本植物盖度越高沙面风蚀程度就越轻,积沙带前移速率就越慢。草本植物盖度与沙面稳定性二者相辅相成;积沙带迎风坡为风蚀面,而背风坡为积沙面,一蚀一积,维持着积沙带的前移及其动态稳定性。

Dynamic stability of sand-accumulation belt along the upwind edge of Minqin Oasis

Drifting sand accumulation belts are formed after 60 years of desert control along the edge of the upwind direction of the oasis in Hexi Corridor,Gansu Province.Among them,the sand accumulation belts on the edge of the upwind direction of Minqin oasis are the largest and most continuous.To reveal the stability dynamics of sand accumulation belts,11 sampling lines were set on the upwind edge of Minqin oasis,with which we observed wind erosion/sand accumulation and characteristic points of sand surface displacement for seven times from early November2016 to early April 2019.The sand accumulation belts on the edge of upwind direction of Minqin oasis could be divided into three types based on their formations:Sand accumulation belt of artificial sand-fixing forest,of natural shrub,and of tree-shrub mixed single-row forest.Wind erosion is the most serious and the forward moving speed is the fastest in the sand accumulation belt of artificial sand-fixing forest,followed by that of natural shrubbery.The lighter the degree of wind erosion on the sand surface,the slower the sand accumulation belt moves forward.The higher the coverage of herbaceous plants,the lighter the degree of wind erosion on the sand surface,and the more slowly the sand accumulation belt moves forward.The coverage of herbaceous plants and the stability of sand surface complement each other.The windward slope of sand accumulation belt is wind erosion surface,while leeward slope is sand accumulation surface.One side of wind erosion and the other side of accumulation maintain the forward movement and dynamic stability of sand accumulation belt.