毛乌素沙地南缘不同活性沙丘土壤水分时空变化

以毛乌素沙地南缘风沙活动区典型的不同活性沙丘(流动沙丘、半流动沙丘、固定沙丘)为研究对象,于2011、2012年4-10月,每月2次,利用烘干法对3种沙丘迎风坡、丘顶、背风坡底部的0~100 cm深度土壤水分进行定位监测,分析了3种沙丘土壤水分时空变化特征。结果表明:土壤水分含量总体表现为固定沙丘>半流动沙丘>流动沙丘。3种沙丘平均土壤水分含量大体上都表现为秋季 >春季 >夏季。3种沙丘背风坡底部土壤水分含量最高,其次是迎风坡,丘顶最低,且迎风坡和丘顶两年平均土壤水分含量差距不大。表层0~10 cm土壤水分含量季节之间差异最大,随深度增加,土壤水分季节变异系数减小。沙丘各部位土壤水分含量垂直变异系数总体变化趋势为从春季到夏季增加,从夏季到秋季减小。土壤水分含量在0~100 cm的垂直变异系数与土壤水分含量为负相关关系,水分含量越高,土壤水分在0~100 cm之间的变化幅度越小。研究区3种沙丘土壤含水量变化水分可分为4个时期:4-5月为春季缓慢积累期,6-8月为夏季消耗期,9-11月为秋季积累期,12月到次年3月为冬季稳定期。总体上,天然植被对水分的涵养效果大于其消耗,本区降水可以维持不同活性沙丘的天然植被生长。

Temporal and Spatial Variation of Soil Moisture in Dunes with Different Vegetation Coverage in Southern Margin of the Mu Us Sandy Land

This research is focused on three types of sand dunes(shifting dune, semi-shifting dune and fixed dune) that are typical to the southern borderline of the Mu Us Sandy Land. Soil moisture was measured for samples from a variety of depths ranging from 0 to 100 cm and from representative locations such as the windward slope, the dune top and the leeward slope. The sampling was conducted from April through October, twice a month, in both 2011 and 2012. The characteristics of the spatial-temporal variation of the soil moisture were established:the overall soil moisture of the three types of sand dunes demonstrates a pattern of fixed dune >semi-shifting dune >shifting dune. Seasonally, average soil moisture of each type of the sand dunes shows the same pattern of autumn >spring >summer. For all the three types of sand dunes, the soil moisture at different locations maintain the following pattern:the leeward slope near dune bottom >the windward slope >the dune top, while the average moisture levels at the windward slope and the dune top are quantitatively close during the two years under study. In terms of temporal variation, soil moisture at 0-10 cm depth exhibits the largest seasonal fluctuation, and shows a diminishing variation with greater depths. Vertical variation of the soil moisture in the sand dune increases from spring to summer, and then decreases from summer to autumn. Along the 0-100 cm depth, vertical variation of the soil moisture is in a negative correlation with the soil moisture level:higher overall soil moisture, lower the vertical variation. Four distinct periodical phases of soil moisture can be identified for the three types of sand dunes in the region:April and May is the spring slow accumulation phase, June to August is the summer depleting phase, September to November is the autumn accumulation phase, and December to March is the winter stable phase. Overall, natural vegetation conserves more than consumes the moisture, and precipitation in the region is able to sustain the natural vegetation on the different types of sand dunes.