Evaluation of the land use change influence on the hydrosedimentological connectivity in a small catchment of southern Brazilian plateau

Abstract

Sediment connectivity is a concept widely used in the analysis of sediment dynamics that describes the efficiency of material transfer between landscape components. Connectivity can be defined according to the transfer vector (e.g. water), by the material transferred (e.g. sediment) or by the interaction of the vector and the material transferred. Therefore, the assessment of connectivity is a key step in understanding the behavior of the system and thus predicting its response to events and changes that may occur within the catchment. One method of assessing the connectivity of a catchment is by applying connectivity indexes. The hydrosedimentological connectivity index (IHC), proposed by Zanandrea et al. (2021), was developed based on the connectivity index (IC) elaborated by Boselli et al. (2008). Its main objective is to evaluate the spatial-temporal variation of water and sediment connectivity in the catchment, taking into account the runoff generation and the characteristics of the antecedent precipitation that condition the sediment availability generated by previous events. These characteristics allow an assessment of functional connectivity and make it possible to analyze the behavior of the catchment in relation to land use changes. Changes in land use have a significant impact on water and sediment dynamics and, therefore, on connectivity. In this study, analyses of the land use change influence on hydrosedimentological connectivity in a small catchment of the southern Brazilian plateau were carried out by applying the index of hydrosedimentological connectivity (IHC). To carry out the analysis, four different scenarios were considered in which the current land use classes of the region were maintained, but had their coverage modified according to the years evaluated. The IHC was applied to five events with different hydrological characteristics (rainfall magnitude, available sediments, and previous soil moisture). The analysis between the scenarios showed the influence of land use in the dynamic catchment, which varied the pattern of hydrosedimentological connectivity according to the scenario. The highest IHC values were found in the classes of exposed soil (agricultural preparation) and agricultural activities. The lowest connectivity was found in the regions of native forests and planted forests. These regions present a high potential for sediment retention, both by the presence of forest and landscape cover elements (plant litter). In the analysis between events, antecedent precipitation and the antecedent soil moisture condition were shown to be determinants in estimating the hydrosedimentological connectivity of the region.