Human Impact on Historical Fluvial Sediment Dynamics in Europe

Abstract

Rivers and floodplains are dynamic environments formed through hydrologic and geomorphic processes that are in turn governed by environmental conditions in the river catchment, such as climate, tectonics, lithology and soils, vegetation cover, and topography. At longer timescales, river landscapes are in a state of dynamic equilibrium with these controlling factors. However, over the last few thousand years, humans have become another important factor in controlling fluvial-landscape dynamics that in many regions has now overwhelmed the importance of natural controlling factors. This is in particular true for many river catchments in Europe that have a long history of human impact. Anthropogenic changes in land cover (e.g., deforestation and the rise in agriculture) have resulted in increased rates of hillslope erosion and amounts of sediment delivered to river systems. As a result, many floodplains have witnessed increased rates of aggradation. Furthermore, these changes also led to the development of typical anthropogenic fluvial landscapes. In temperate Europe, rivers often changed from anastomosing channels in wetland environments to single-thread meandering rivers with levees and overbank deposits. In Mediterranean Europe, many river valleys also became silted up, creating more-extensive, relatively flat valleys. With the increasing industrialization and urbanization of Europe since the 19th century, but also through the implementation of erosion control measures, many regions experienced a greening of the landscape and a return to less erosive land cover. Several rivers, often in mountainous environments, saw again a reduction in sediment loads and river incision and a return in fluvial style. Humans also impacted European river systems through direct interventions such as mining of river sands and gravel, damming of rivers, artificial straightening, or the hunting and later reintroduction of river-engineering animals such as the beaver. Changes in floodplain sedimentation and floodplain ecology following human impact also affected the amount of carbon sequestered and buried within European floodplains.