Impacts of pre- vs. postcolonial land use on floodplain sedimentation in temperate North America

This paper evaluates the relative importance of anthropogeomorphic sedimentation on floodplains in the mid latitudes of North America before and after the arrival of EuroAmericans. Geohistorical and geoarchaeological theories have emerged that have conflicts concerning the relative effectiveness of pre- and postcolonial anthropogeomorphic change in North America. Many geoarchaeologists, paleoecologists, historians, and cultural geographers have concluded that intensive precolonial land use resulted in substantially humanized landscapes prior to the arrival of colonists. This presents a geomorphic paradox to fluvial geomorphologists and river restorationists who interpret buried floodplain soils as evidence of landscape stability. Evidence for these theories is reviewed from a geomorphic perspective while making distinctions between ecological and geomorphic change and recognizing spatial and temporal variability. In some locations, mid-millennial land use generated erosion and floodplain sedimentation. Subsequent indigenous population declines and reductions in land-use intensity may have been followed by precolonial geomorphic stability and pedogenesis. An abandoned landscape hypothesis, that floodplain soils developed on precolonial anthropogenic alluvium and were subsequently buried, should be considered where indigenous populations and land-use activities were high. Variability is also noted in postcolonial floodplain sedimentation. Many stratigraphic studies show that rates of sedimentation increased greatly after colonization in response to land clearance for agriculture, timbering, and mining. An inventory of studies that document postcolonial floodplain sediment shows strong spatial patterns. Most studies of postcolonial sedimentation cluster in the eastern USA from the Mid-Atlantic southward and in the Mississippi Valley from Wisconsin to Mississippi, but many occurrences of mining sediment are scattered throughout the west. Few of the studies reviewed in the west document anthropogenic floodplain sediment from agriculture or logging, although more thorough regional inventories could change that. Vast areas of temperate North America do not have historical deposits that are well represented in the scientific literature, so assumptions that legacy sediment on floodplains is ubiquitous are ill-founded. Spatial and temporal variations in pre- and postcolonial floodplain sedimentation are complex and more research is needed to fill in the knowledge gaps. (C) 2018 Elsevier B.V. All rights reserved.