Linking soil erosion dynamics with identification of source areas and stratigraphic-geochemical sediment core analysis for deciphering the impact of land-use change in the watershed of a drinking water reservoir in Central Kenya

在东非等热带地区，土地使用的变化和农业集约化常常导致土壤侵蚀和沉积物增加。这种土壤流失导致农业肥力退化，以及水库蓄水量减少，而水库蓄水量对供水和/或水力发电至关重要。尽管侵蚀造成了严重的环境问题，但迄今为止，关于东非河流中侵蚀和悬浮沉积物运输的规模和动态的知识有限。该项目采用了一种新的“从源到汇”的方法，将小区实验、河流监测和对过时沉积物岩心的详细地层地球化学分析与基于地图和卫星图像分析的历史土地利用变化重建相结合。调查将在肯尼亚中部高地的Ruiru河流域进行。自1949年建成以来，该水库一直为首都内罗毕的饮用水供应而运作。该项目的重点是详细分析预计将造成大部分侵蚀和河流沉积物负荷的短期暴雨事件。通过磷组分和选定的生物标志物从源到汇追踪侵蚀颗粒。这就可以确定沉积物来源地区，并通过这种方式连接从地块到集水区的不同空间尺度。详细的过程研究和历史重建相结合，将提高土地利用变化对土壤侵蚀的影响和相关的物质运输在过去的七十年和短期暴雨事件在东非高地的典型农村景观的理解。

Land-use change and agricultural intensification frequently lead to increased soil erosion and sediment loads in tropical regions such as East Africa. This soil loss results in degraded agricultural fertility, as well as reduced storage volume in reservoirs, which is critical for water supply and/or hydropower generation. Despite the severe environmental problems caused by erosion, to date only limited knowledge regarding the magnitude and dynamics of erosion and transport of suspended sediments in rivers of East Africa exists. This project follows a novel ‘source-to-sink’ approach combining plot experiments, river monitoring, and detailed stratigraphic-geochemical analyses of dated sediment cores with the reconstruction of historical land-use change based on the analysis of maps and satellite images. The investigations will be carried out in the catchment of River Ruiru in the central Kenyan highlands. The river drains into the reservoir that since its construction in 1949 has continuously been operated for the drinking water supply of the capital city Nairobi. The project focuses on a detailed analysis of short heavy rainfall events that are expected to cause most of the erosion and river sediment load. Eroded particles are traced from source to sink by means of phosphorus fractions and selected biomarkers. This allows for the identification of sediment source areas, and by this to connect the different spatial scales ranging from plot to catchment. The combination of detailed process studies and historic reconstruction will improve the understanding of the impact of land-use change on soil erosion and associated matter transport during the last seven decades and short heavy rainfall events in a typical rural landscape of the East African highlands.