Effect of stand origin and slope position on infiltration pattern and preferential flow on a Loess hillslope
<p>Preferential flow is expected to provide an important pathway to replenish soil water&#160;at deep soil layers in arid or semiarid areas; however, few studies have addressed this&#160;topic, especially in semiarid Loess hillslopes. This study aimed to quantify the effect of&#160;stand origin and slope position on the contribution of preferential flow to total&#160;infiltration and spatial variations in water flow. A blue dye tracer experiment was&#160;conducted to visualize water flow in <em>Robinia pseudoacacia</em> plantation (PL), natural&#160;forestland (NF), and natural grassland (NG) at the upslope, midslope, and downslope,&#160;and semivariance analysis was used to determine spatial variability at the centimeter&#160;scale. The results showed that role of macropore flow was dominant in upslope and&#160;midslope, and larger in NF than that in PL and NG, due to presence of abundant root&#160;systems in the upper soil of NF. Moreover, contribution of preferential flow at the&#160;upper slope in NF was larger than that in PL. At the downslope, the role of rock&#160;fragments coverage at the downslope was emphasized, leading lateral flow dominant&#160;at the downslope in PL and NG. In addition, contribution of preferential flow and vertical&#160;variability of infiltration at the downslope in PL was higher than that in NF. The&#160;findings demonstrate that compared with PL, NF has a more positive impact on&#160;increasing infiltration and preferential flow that can replenish deep soil water, and&#160;reducing surface runoff and soil erosion. The presence of rock fragments coverage&#160;can make lateral flow dominant at the downslope on the Loess hillslope, related to&#160;water movement along the slope toward streams and catchment outlets.</p>