Sediment uptake rates under extreme rainfall in controlled conditions

FAO and OECD data point at erosion as a main soil degradation factor in the global scale. Although the processes of erosion are considerably well recognized, their quantitative valuation remaining strongly variable between local conditions, still needs continuing and widening of research in various spatial and temporal scales. The goal of the research, presented in this article, was to recognize qualitative and quantitative soil loss mechanisms in result of a dispersed wash-out accompanying extreme rainfall events being the most potent occurrences of soil erosion, generating the most visible losses and costs. The research was performed in controlled conditions of soil humidity and rainfall for a set of ten soil kinds, representative for the geographical area of Poland. Soil samples were placed in uniform model micro-plots (2 m x 1m in size) located with 10% slope inclination and kept in constant black fallow surface conditions, representing the most unfavourable conditions occurring in the real world, where extreme rainfall occurs on a fresh ploughed land causing extreme soil loss events. The approach simplified the estimation of soil susceptibility to erosion by neglecting the plant cover factor. The rainfall was simulated with a sprinkler designed in the Institute of Soil Science and Plant Cultivation, performed in Institute of Agrophysics of Polish Academy of Sciences in Lublin. The results were split into two groups representing different physical phenomena: hydrology and superficial soil erosion. The correlation matrices for the variables addressing hydrology within the whole data population indicate the amount of outflow is very well explained by variables of initial humidity (R = 0.297) and rainfall depth (R = 0.550) and is strongly dependent upon the content of silt fraction (R = 0.406). The results related to soil erosion, sediment uptake and unit sediment uptake, describing the processes of superficial wash out, point at a strong connection between the volume of sediment uptake and the precipitation amount (R = 0.473), the precipitation intensity (R = 0.671) and the volume of outflow (R = 0.700).