A temporarily changing Holocene sediment budget for a loess-covered catchment (central Belgium)

Abstract

This study presents a Holocene sediment budget for the Nethen catchment, a typical river catchment (55 km 2) in the Belgian loess belt. Soil erosion and hillslope sediment storage are quantified by extrapolating detailed data obtained from soil profile truncation studies in three representative zero-order sub catchments. Floodplain sediment storage is estimated by augerings along several transects across the main river and some of its tributaries. The sediment budget shows that ca. 38% of the soil eroded during the Holocene is redeposited as colluvium on hillslopes and in dry valley bottoms. Another 23% of the eroded sediment is now stored as alluvium in the floodplain. The remaining 39% or 21 × 10 6 Mg is exported from the catchment. Dating of both colluvial and alluvial sediment deposits reveals that sediment dynamics between the hillslopes, the dry valley bottoms and the floodplain behave highly non-linearly. Before ~ 500 BC, sediment delivery from the hillslopes to the river channels was near maximum. However, since the onset of significant agriculture in the Late Bronze Age–Early Iron Age, increased rates of soil erosion are only reflected in the colluvium, but not in the floodplain, resulting in very low hillslope sediment delivery ratios. From the Medieval period onwards, soil erosion increased even further, mainly as a result of a further increase in agricultural land use, but now also accelerated floodplain sedimentation took place due to an improved slope-channel coupling and the management of floodplains.