Exploring the role of microtopography in the spatial pattern of soil water at the hillslope scale based on high-resolution observation

Abstract

Terraces have consistently been regarded as crucial measures for water conservation and vegetation restoration, particularly in mountainous environments. However, the hydrological effects of terraces in artificial forests have been rarely studied. In this study, detailed topography, soil properties and high-resolution (30 sites) soil water data (0–70 cm) observed from March 2015 to March 2016 were collected at hillslope scale (0.2 ha). The effects of static (soil properties and topography) and dynamic factors (precipitation) on the dynamics and variability of soil water content (SWC) were studied based on statistical methods, temporal stability and variance decomposition methods. The results showed that slope, topographic wetness index (TWI) and microtopography were the main control factors of different soil layers (shallow, middle and deep layer), which explained 37.2 %, 48.6 % and 47.3 % of the total variance of corresponding soil layers, respectively. Microtopography primarily affects deep layer soil water (40–70 cm). Level terraces show significantly higher soil water content (SWC) (30.89 ± 5.28 %) compared to gentle slopes (25.40 ± 5.33 %), steep slopes (27.05 ± 5.74 %), and scarps (19.71 ± 4.43 %) (P<0.05). Temporal stability of soil water varied across different depths, with shallow layer soil water exhibiting significantly weaker stability compared to other depths, the most representative point of different soil layers was located on relatively flat terraces. Decomposition of spatial variance revealed that the time-invariant component was the primary contributor to the total spatial variance, with a mean value over 70 %. These results highlight that microtopography could weaken the influence of soil-terrain factors on soil water, and the implementation of level terraces can enhance hillslope hydrological conditions in the Rocky Mountain area.