Land use and soil erosion during the period of prehistoric agriculture in Southeastern USA
Zusammenfassung der Projektergebnisse
This research project aimed to explore erosion forms, colluvial sediments and buried soils in four selected 0-order and 1st-order watersheds in south-eastern USA in order to gain, solidify, and evaluate general data on soil erosion during the Native American land use period and its respective long-term effects on the environment. This has been achieved by 1) recording the stratigraphy of colluvial and alluvial sediments and buried soils, 2) mapping the extent of erosional and colluvial forms, 3) analysing chemical and physical soil and sediment properties, 4) establishing chronological control using various dating techniques including radiocarbon and OSL dating, and 5) quantifying soil erosion using hillslope sediments. The data gathered has been used to i) compare the spatial extent of prehistoric and historic erosion and the short-term and long-term pedological and geomorphological effects of subtle soil erosion against extreme events, ii) assess the feedbackmechanisms of soil erosion on soil fertility and measurable land use changes in prehistoric and historic times, and (iii) estimate the long term effects of soil erosion and sediment deposition on archaeological features. The results yield new insights into the relative influence of human activities (both prehistoric and historic) versus natural geomorphodynamic processes controlled by climate when it comes to soil erosion processes. All investigated sites show predominantly a geomorphodynamic stability with soil development under natural vegetation. Only at the Dogwood Gully system in Western Tennessee, a short period of soil denudation occurred in the mid-Holocene. It is likely, that at this site climatic changes modified or reduced the protecting vegetation cover, triggering fires, enhanced runoff, and soil erosion. All other sites were under stable geomorphic conditions until the second half of the first millennia CE. From then until about the 14th/15th century CE, woodland was cleared, soil erosion occurred and sediments accumulated along the valley bottoms and gully fans at all four investigated sites. From the 16th century onwards until the arrival of European farmers, the surface was again in a stable condition. With European settlers arriving, woodland was once again cleared and a similar quantity of soil was quickly eroded within a period of about one century. In the 1930s, all investigated sites were transformed into forests or grassland. Since then, soil erosion has been reduced but surface runoff and gullying are still active on bare surfaces. Prehistoric soil erosion raises questions regarding the general impact of prehistoric land use patterns on the geomorphic system at a local scale. Further geomorphic studies should integrate archaeological data and carefully survey small catchments to detect legacies of prehistoric sediments and soil formations which may persist underneath historic sediments on foot slopes, gully fans, and small depressions. On a regional scale, a re-evaluation of the interactions between Native American land use practices, soil erosion, and floodplain sedimentation is crucial. Consequently, the impact of prehistoric land use patterns on the geomorphic system could be generally much more important than previous studies have suggested.
Projektbezogene Publikationen (Auswahl)
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(2013): The history of human induced soil erosion: geomorphic legacies, early descriptions and researches, and the development of soil conservation – a global synopsis. Geomorphology 201: 1-34
Dotterweich, M.
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(c 2015) Natural and human induced prehistoric and historical soil erosion and landscape development in southwestern Tennessee, USA. Anthropocene Volume 8, December 2014, Pages 6-24
Dotterweich, M., Ivester, A.H., Hanson, P.R., Larsen, D., Dye, D.H.
