Analysis of the spatial variability of soil moisture in degrading alpine meadowin the Qilian Mountains

Traditional statistics and geostatistics methods are used to study the soil moisture variation characteristics in vertical direction,spatial heterogeneity in horizontal direction and spatial distribution in the overgrazed and the nocuous grass invading alpine meadowin the Qilian Mountains. The results showthat in vertical direction,soil moisture decreases with depth,and so does the variation rate. Coefficient of variation of the soil moisture distribution in superficial layer and deep layers are larger than that in middle layers. In horizontal direction,the soil moisture in 0 ~ 40 cm depth range possesses a feature of moderate variability. The 10 ~ 20 cm depth range is mainly affected by root system,with the maximum variability in the random section. For the rest layers,soil moisture due to variability of random section decreases with depth,while that due to the autocorrelation section increases. In macroscopic view,content of soil moisture is closely related to micro-topography,with positive correlation with the distance to rivers and negative correlation with the height above sea level.