The organic layer reduces water repellency of surface mineral soil under a humid-temperate forest

Abstract

Surface soil under forests often shows soil water repellency (SWR). The organic (O) layer (e.g., litter layer) and SWR are both well known to affect water movements on hillslopes, yet little is known about their interaction. In this research, we established five O-layer removal (no O layer; NO) plots and seven O-layer remaining (with O layer; WO) plots on the same slope, which had developed thick O layers, and repeatedly measured in situ SWR and moisture content of surface mineral soil at multiple points in each plot. We calculated the percentage of water repellent points (SWRarea) in each plot and found lower SWRarea and higher soil moisture content in WO plots. SWR in WO plots was more spatially heterogeneous; some measurement points frequently showed SWR, and other points were frequently wettable. The frequently water repellent points were drier than those frequently wettable. NO plots, on the other hand, showed large SWRarea more often than did WO plots. These findings imply that O layers could reduce surface runoff via decreasing in situ SWR and cause preferential water flow by maintaining both SWR and wettable regions.