First estimates of regional (Allgäu, Germany) and global CH ₄ fluxes from wet colluvial margins of closed depressions in glacial drift areas

Agriculture is one of the major anthropogenic methane source. However, emission inventories of agricultural soils are rather uncertain. One reason for this is the existence of small areas of very high biogeochemical fluxes ('hot spots'), which are not incorporated into soil maps. Here a procedure for an upscaling of one man-made 'hot spot' is presented. In hummocky ground moraines of temperate-humid climate (Allgäu, Germany) erosion and subsequent sedimentation of topsoil material in wet footslope areas has led to very high emissions from depression margins (median annual flux=39 g CH₄ m ^-2). These areas make up 7% of the region studied according to a digital terrain analysis based on a DEM 50. GIS-based modelling showed their regional and global relevance to be a result of the (i) unit area source strength, (ii) relative acreage of depression margins in catchments of hummocky landscapes, and (iii) global dimension of hummocky landscapes with closed depressions. First conservative estimates yielded methane emissions of 1.1 Gg (regional, Allgäu) and 2.5 Tg (global) from colluvial margins in similar landscapes, respectively.