Origin and evolution of closed depressions in central Belgium,European loess belt |
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| Authors: | T Vanwalleghem J Poesen I Vitse H R Bork M Dotterweich G Schmidtchen J Deckers A Lang B Mauz |
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| Institution: | 1. K. U. Leuven Research Fund, Belgium;2. Physical and Regional Geography Research Group, K. U. Leuven, Belgium;3. Ecology‐Centre, Christian Albrechts University Kiel, Germany;4. Institute for Land and Water Management, K. U . Leuven, Belgium;5. Department of Geography, University of Liverpool, UK |
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| Abstract: | Closed depressions (CDs) are lower lying areas where the sediment eroded from the surrounding soil surfaces draining towards the CD is trapped in the system. CDs have been reported in several regions of the European loess belt and are attributed either to natural processes (e.g. dissolution of subsurface horizons) or to human intervention (e.g. quarrying). Previous studies focussed mainly on cropland areas where, however, only few and largely filled in CDs remain. The objectives of this study were to i) assess the spatial distribution of CDs under forest and cropland, ii) to determine and compare the morphology of CDs under forest and under cropland, and iii) to determine the origin and age of these CDs under forest. In a study area located partly in ancient forest (13 km2) and partly in cropland (29 km2), a systematic survey revealed the presence of 71 CDs under forest (5·3 CD.km?2) and 30 CDs under cropland (1 CD.km?2). Comparison of their morphology showed that CDs under forest were significantly deeper, with steeper sidewalls and a smaller surface area because of the erosion and deposition processes acting on the CDs under cropland. By comparing CDs that had been under cropland for different time intervals, the rate of this morphological evolution could be reconstructed. Analysis of the soil stratigraphy of two representative CDs in the ancient forest area confirmed their origin as quarries. Most probably, calcareous loess was excavated since this soil horizon, about two to five meters thick, was completely absent within the CDs. Dating of the infilling of one CD by optically stimulated luminescence (OSL) shows that the CD filled in between the first century BC and the fourth century AD. This dating corresponds to the dating of sediment deposits in nearby, human‐induced gullies that were attributed to an agricultural land use phase between the 18th century BC and the third century AD. |
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| Keywords: | closed depression quarries ancient forest loess land use |
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