Past human-landscape interactions in the Netherlands: Reconstructions from sand belt to coastal-delta plain for the first millennium AD

The first millennium AD represents a transition period in the Netherlands from a mainly natural prehistorical lowland landscape to a landscape that was increasingly influenced by humans. This thesis focuses on human-landscape interactions in the coastal plain, the delta, and the Pleistocene sand area during this time interval. Geomorphological changes were identified using new reconstruction maps, and their causes and effects were assessed and compared to archaeological records following an integrative approach.
Already in the first millennium AD, human activities caused major unintended geomorphological changes in all studied landscapes. In the coastal plain, intensified agricultural use of artificially-drained peatlands since the Late Iron Age (250–12 BC) led to soil subsidence, on a large scale turning peatland into tidal areas that for many centuries would remain unsuitable for habitation. Ingressive tidal systems reached furthest inland where the peaty back-barrier was widest, whereas sea-ingression formation was hampered in areas with abundant beach-barriers and supratidal levees protecting the coast from drowning. Human-induced peatland subsidence also led to a major reorganization of the river network in the lower delta: it caused the formation of the new Hollandse IJssel and Lek river branches, which now invaded the extensive peatlands. In the Rhine-Meuse delta, natural levees were important elements in the landscape. Especially new generations of natural levees, which developed during the first millennium AD, were positioned 0.5 to 1.0 m higher than preceding levee generations. This is attributed to an increase in suspended sediment supply caused by deforestation of the hinterland, as well as by increased flooding intensity during their formation. The increased flooding frequency in the first millennium AD also caused settlements on the natural levees to shift towards higher locations within the river area. In areas where new large river branches developed (around the Waal) this effect was strongest. Despite the dynamic of the landscape, no large-scale settlement abandonment occurred and route networks between settlements remained largely intact. In the Pleistocene sand area, sand drifting occurred on a relatively small scale. This phenomenon, most frequently occurring close to human movement corridors, increased after ca. AD 900, coeval with rising population density and large-scale deforestation. This implies that sand drifting was strongly related to human pressure on the landscape.
Reclamation and overexploitation led to unintended loss of land, because it became more prone to storms and floods. This study provides more insights in the circumstances under which impact of human action on the landscape was largest. This impact forced humans to adapt or to abandon the area in case the new situation could not be coped with. Better understanding of human impact on the natural landscape in the past is especially relevant to better cope with threats from floods or sea-level rise, especially in densely populated and subsiding deltas.