毛乌素沙地西北部植被覆盖对沙丘移动的影响

Effect of vegetation cover on dune migration in northwest Mu Us Sandy Land

毛乌素沙地生态环境脆弱,近年来沙漠化虽整体呈逆转状态,但西北部仍存在沙丘活化现象,风沙活动强烈,对下风向植被恢复和农牧生产造成了一定影响。利用Google Earth卫星影像对2002—2015年毛乌素沙地西北部裸露沙丘和植被覆盖沙丘进行监测,分析了植被覆盖与沙丘移动之间的内在联系。结果表明:(1)毛乌素沙地西北部存在较严重的风沙活动,沙丘移动速度为0.38~6.05 m·a^-1,其中植被覆盖沙丘平均移动速度为2.29 m·a^-1,裸露沙丘平均移动速度为4.59 m·a^-1,沙丘平均移动方向为122.5°,与当地合成输沙方向基本一致。(2)沙丘移动速度与高度呈负相关,但相关系数比前人报告的低,这与沙丘表面覆盖植被的时空变化密切相关。(3)植被覆盖对沙丘形态变化具有明显的影响,盖度增加使沙丘形态趋于饼状,从而逐渐被固定。(4)风况、地表盐渍化和公路两旁的固沙措施等也影响了沙丘的移动速度。

The ecological environment is fragile in the Mu Us Sandy Land. Although as a whole the desertification has been reversed in recent years,there is still sand dune activation in the northwest of the sandy land and the sandstorm activity is strong,which has impact on the downwind vegetation restoration and agricultural and pastoral production. Google Earth satellite images were used to monitor the migration characteristics of bare dunes and dunes with vegetation in the northwest of the Mu Us Sandy Land from 2002 to 2015,and the internal relationship between vegetation cover and dune migration was analyzed. The results showed that:(1)The sand transport activity in the northwest of Mu Us Sandy Land is more serious than any other regions. The dune migration rate is 0. 38-6. 05 m·a^-1,and dune migration direction is 122. 5° which is similar to the local resultant drift direction. The average migration rate of dunes with vegetation is 2. 29 m·a^-1,while that of bare sand dunes is 4. 59 m·a^-1.(2)The dune migration rate is negatively correlated with dune height,but the correlation coefficient is lower than previous studies,which is closely related to spatio-temporal changes of vegetation cover.(3)Dune morphology is complex. Vegetation coverage has a significant impact on the dune morphology,which leads to the dune fixation and pie shaped dune morphology.(4)The dune migration rate is also affected by wind regime,surface salinization and sand-fixing measures on both sides of roads.