Temporal stability of soil moisture on two transects in a desert area of northwestern China

Abstract

Temporal stability of soil moisture has important implications for optimal and effective field monitoring and has been observed for a range of soil and landscape conditions. However, relatively less is known about temporal stability of soil moisture in desert areas. In this study, two 5-km transects (TranA and TranB) with different soil properties in a desert area of northwestern China were chosen to assess the characteristics of the temporal variability and stability of soil moisture, to identify representative sampling locations (RSLs), and to evaluate the effect of sampling frequency on the determination of temporal stability. For each transect, moisture contents of the surface soil were measured using Theta Probes on 35 occasions at 51 locations from April to October 2012. The results showed that soil moisture for the finer-textured TranA was consistently higher and more variable than for the coarser-textured TranB. Both transects exhibited strong temporal stability during the monitoring period. Locations with higher sand contents tended to have more pronounced temporal stabilities. The RSL identified in each transect accurately represented the mean moisture contents of the transects over time, with coefficients of determination (R 2) higher than 0.95 and root mean square errors lower than 1 % vol/vol. Soil moisture has significantly higher degrees of temporal stability during dry periods than during wet periods. The effect of sampling frequency on temporal stability of soil moisture was not as evident, particularly for the coarser-textured soil. This study provides insights for designing strategies for the sampling and monitoring of soil moisture in the hydrological applications in desert areas.