Evaluating the effect of natural-artificial linear landscape elements on flow and sediment connectivity in a typical agricultural terraced catchment, China

Abstract

Linear landscape elements, such as man-made ditches and road networks, play a pivotal role in the transport of water and eroded sediments. Yet very few studies have focused on the variations in drainage flow paths disturbed by artificial linear landscapes and their contribution to flow and sediment connectivity (FSC). This study utilized the index of connectivity (IC) to examine and distinguish the impact of natural and artificial linear landscape elements (i.e., natural streams, man-made ditches, and road networks) on the spatial distribution of FSC. The method was employed in a typical agricultural terraced catchment of the Honghe Hani Rice Terraces World Heritage Site of China, based on two weight factors - roughness index (RI) and Rndvic factor. The results indicate that the incorporation of the linear landscape elements for the IC calculation remarkably affected the spatial distribution of FSC. Specifically, FSC values notably increased by closing the distance to linear landscape elements within a specific threshold. Moreover, in the confluence between natural and artificial linear landscape elements, the mean value of FSC was higher compared to scenarios without any or only one linear landscape element. In comparison, the presence of road networks only improved lateral connectivity by modifying the surface flow along east-west directions, while man-made ditches significantly influenced both longitudinal and lateral connectivity to a larger degree, especially in the terraced area. This finding underscores the effectiveness of ditch constructions as management practices for the regulation of water resources and facilitating the downstream transfer of sediment. Field observations and validation confirmed that Rndvic, which incorporates vegetation variable as a weight factor in the calculation of IC, yields more accurate and reliable maps of FSC than that of RI. This study holds far-reaching significance for water resources management and landscape sustainability within terrace-protected areas, providing invaluable insights for decision-makers.