Modelling nutrient losses by wind and water erosion in northern Burkina Faso

In the semi-arid environment of northern Burkina Faso the processes of wind and water erosion occur almost simultaneously and may cause severe soil degradation. Especially in the early rainy season when soils are bare and unprotected, violent winds preceding intense rainfall events result in intense sediment transport by both wind and water. This Ph.D. project aimed at quantifying and modelling wind and water erosion processes, their interaction and related nutrient flows in a Sahelian environment. The source codes of EUROSEM and the stand-alone erosion sub-model of WEPS are translated to the dynamic modelling language PCRaster, further adapted to be applicable to the Sahelian situation and extended with nutrient components. From field measurement and modelling results it is concluded that for water erosion rain splash is the most important detaching agent at the scale of the field and that despite the large volumes of overland flow, erosion is transport capacity limited due to the general low slopes. The material detached by water is available for wind-blown transport. Due to the absence of non-eroding boundaries, intense mass transport under influence of violent winds does not always result in erosion. Depending on wind direction, cover and crust type, net deposition may occur. Further, due to the large spatial variation in wind erosion controlling parameters, areas with erosion and deposition can be identified within a field. Based on model results it is concluded that wind erosion is responsible that wind erosion is responsible for the loss of deposition of large amounts of fine sediment and the nutrients attached to these sediments. Though compared to wind erosion, the nutrient losses under influence of water erosion are small, these losses should not be underestimated; these nutrients flow to the nearest stream and are forever lost for the catchment. Due to the interaction between wind and water, nutrient and soil erosion at field scale may be large, but are limited at village scale. Provided a good management of natural resources as tree and shrub cover and a good insight in the distribution of cultivated and fallow fields around the village, long-term productivity is not at risk in the southern Sahelian zone.