On the measurement of alpine soil erosion

Abstract

Abstract The knowledge of soil erosion processes and especially soil erosion rates in alpine grassland regions is scarce due to the lack of detailed studies. The non-existence of validated methods which are suitable to quantify alpine soil erosion is one of the key issues for the limited process understanding. The aim of this study is to compare different methods and to conclude on suitability for the determination of alpine soil erosion. Furthermore, the advantages and disadvantages of the single measurement methods with regard to alpine basins are focused. We distinguish between sediment traps and sediment cups to determine erosion rates bi-weekly in 2007 and 2008, and Cesium-137 based measurements to measure long term erosion rates since 1986. The latter method integrates over a time span of 22 years. We investigate three different land cover types: hayfields, pasture with dwarf shrubs and pasture without dwarf shrubs in the Urseren Valley (Central Switzerland) with a mean slope steepness of 37°. Sediment traps are suitable to quantify erosion rates during summer time. However, measurements are not possible during winter time. Sediment cups are an ideal tool for soil movement observation within the plot size but are limited to quantitative measurements. Cesium-137 investigations enable erosion quantification all-throughout-the-year but without identifying related processes. The combination of all three methods turns out to be useful for erosion quantification and process understanding. Mean monthly erosion rates during the vegetation periods 2007 and 2008 based on the sediment traps are between 0.006 t ha−1 mo−1 and 0.045 t ha−1 mo−1. These generally low erosion rates can be explained by a low overland flow of 0.5–1.8% of the measured precipitation. Cesium-137 based measurements yield mean annual erosion rates for the time span 1986–2008 between 8.3 t ha−1 yr−1 and 26 t ha−1 yr−1. We conclude that erosion rates on alpine grassland are dominated by snow driven processes during winter time.