Multi-tracer methods to assess soil redistribution for soil conservation, sustainable production and environmental protection

Despite increased understanding of erosion processes and advances achieved in soil erosion modeling during the last 2 decades, we are still far from accurately simulating the large temporal and spatial variability in soil redistribution. Only few studies evaluated the spatial predictive capacity of models by means of measured data, which puts the reliability of our model-predicted values on the line. Fallout radionuclides (FRNs) 137Cs, 210Pbex and 7Be can provide the necessary data to validate erosion models. However, protocols for sampling and interpreting of all three FRNs are based on assumptions, which are put to question. The overall objective of this study is to develop scientifically sound FRNs sampling, measuring and interpreting protocols to estimate the spatial and temporal soil redistribution for sustainable soil productivity and environment protection at field and watershed scales. Specific research objectives are to: i) refine protocols for documenting soil redistribution using FRNs, ii) test, calibrate and validate conventional and new soil erosion models using FRNs collected data, and iii) evaluate the effect of specific land use management on soil redistribution, providing data to underpin soil conservation strategy selection. At first, batch experiments to study the adsorption of 7Be on soil particles will be performed. Previous studies at our research group showed measurements of 7Be with a high uncertainty due to a low efficiency of 24% of the previously used High Purity Germanium (HPGe) detector. To decrease the uncertainty a protocol was established to extract and concentrate 7Be in smaller samples. Furthermore, the FRNs radioactivity will be measured in our laboratory by means of a new broad energy HPGe detector with an efficiency of 50%. Once the protocols are refined, a selection of spatially distributed soil erosion models (e.g. STM-3D) will be calibrated and validated at watershed scale using the sediment load delivery and soil redistribution data provided by FRNs for the erosive rainfall events. The study is taking place in the Flemish Ardennes (Upper-Scheldt basin), where soil erosion and flood control measures are of high importance. The actual focus is on the Mariaborrebeek watershed, part of the larger Maarkebeek watershed, which can be considered as a representative watershed for the Flemish Ardennes in terms of topography and land use