Understanding sediment connectivity from soil erosion perspective

Sediment connectivity is closely related to geomorphology, topography, ecological hydrology, soil erosion, nutrient and pollutant movement, and water quality conservation. As one of the hot topics in soil erosion research during the past decade, sediment connectivity is required to be fully examined from the perspective of soil erosion. Sediment connectivity describes the interactions of sediment cascades between different topographical and landscape units in a system which is usually quantified with the structural connectivity and functional connectivity in four dimensions, i.e., lateral, longitudinal, vertical and temporal. Its impacting factors include climate, lithology, geomorphology, watershed characteristics, topography, soil properties, vegetation, hydrological processes, soil erosion and human activities as well as their temporal and spatial variations. The specific influencing mechanisms vary among these factors and among different spatial scales, therefore resulting in distinct responses of sediment connectivity. Field survey and mapping, graph theory, index and model simulation are frequently applied to investigate and quantify sediment connectivity. The theories behind these methods are different, so do the required data, specific procedures, and the corresponding results. The index of connectivity (I_C) is the most widely employed in the quantification of sediment connectivity. Nevertheless, I_C well reflects the structural connectivity, rather than the functional connectivity. From the perspective of soil erosion, future studies regarding sediment connectivity should focus on the concept, influencing factors and their dynamic mechanisms, method comparison and index optimization, relationships of sediment connectivity with hydrological connectivity, soil erosion and sediment delivery ratio, as well as the effects of soil conservation measures on sediment connectivity and the corresponding mechanisms.