Effects of phytogenic mound on overland flow pathway, hydraulic characteristics and soil water redistribution at a patch scale in the Loess Plateau of China

Phytogenic mounds are usually formed under plants that intercept wind and runoff-borne sediment in semiarid environments. These mounds may affect the water source-sink relationship between vegetation patches and interspace patches. However, the impact of phytogenic mound on this relationship and the associated hydrological processes between patches are not well understood. This study aims to assess the effects of phytogenic mound on overland flow pathways, flow hydraulics and soil water redistribution at the patch scale. Upslope inflow experiments were conducted on three different patchy slopes (Caragana korshinskii (CK), Hippophae rhamnoides (HR), and Artemisia gmelinil (AG)) in the Loess Plateau. Results indicated that, compared to soil physicochemical properties, the shape and size of the mounds played a more crucial role in the hydrological processes within the patches. Redundancy analysis and hierarchical partitioning analysis revealed that the most significant factors are mound height (11.16 %) and downslope angle of mound (13.77 %). Most mound parameters exhibited a significant negative correlation with water flowpath width. The effects of mound parameters on runoff hydraulics were highly complex and largely dependent on the flow pathways. The relationships between mound parameters and soil water variables were negative at the upper, middle and lower parts of the mound, but positive at the left part. Differences in soil water between before and after runoff experiments and soil water storage (SWS) at the upper and left parts of the mound were greater than at the middle and lower parts. Average SWS of AG (16.24 ± 3.48 mm) with smaller mound size was found to be greater than that of HR (14.27 ± 3.99 mm) and CK (13.25 ± 2.24 mm). With increasing mound size, the spatial differences in SWS among the four parts increased. Consequently, the water source-sink relationship between the interspace patch surrounding the mound and the vegetation patch on the mound weakened as the mound size increased.