| Abstract: | To obtain a better understanding of the colluvial deposits in two catchments in the Luxembourg Ardennes, structural aggregates from forest and farmland soils were subjected to the impact of falling water drops. The changes that the aggregates underwent and the material eroded from them were studied in thin section. Predictably, forest aggregates were more resistant to water-drop impacts than those from farmland. Farmland aggregates tended to slake upon wetting and to break down into many micro-aggregates having a size-frequency distribution similar to that of the micro-aggregates in the undisturbed soil. The forest aggregates were eroded slowly under water-drop impact, losing material from their surfaces or occasionally shearing into several smaller equally resistant aggregates. The size-frequency distributions of the break-down products differed from the micro-aggregates in the untreated aggregates or original forest soil, probably because of bonding by organic material. The differing composition of the aggregates points to the importance of oriented clay and planes for the lack of stability of the farmland aggregates. It can be concluded that agricultural colluvium is probably largely deposited by processes other than splash and that splash is an important process, but not the only one, in the formation of colluvium under forest. |
