Holocene sediment budgets in the Northern upper Rhine area
Final Report Abstract
Current changes of terrestrial and coastal environments are attributed to a changing climate and intensified land use. River catchments play a key role within the environmental system of terrestrial mass fluxes. Water, sediment and biogeochemical compounds are collected, stored, transported and yielded by catchment processes. However, basic quantitative properties of erosion, transfer, storage and delivery of particulate matter considerably vary in space and time. The Rhine catchment is one of the world's large river catchment that is tremendously affected by human interferences for several millennia of land use. However, studies on catchment-scale fluxes of particulate matter from hillslopes to streams and further downstream to the Rhine delta are still rare. Thus we present a study that unravels the quantitative magnitude of man-induced sediment flux in agricultural catchments since the start of agriculture. The results include unprecedented information about rates of man-induced sediment production, temporal storage and sediment transfers within and export from subcatchments of the Upper Rhine area. Man-induced soil erosion and within-catchment transfers are summing up to an impressive magnitude over the period of agriculture and for large-scale catchments. For example, more than one billion tons of particulate matter has been detached from the soils of the Nidda catchment (1942km2). The investigation also demonstrated that the larger portion of sediments produced is still residing in the catchment. The numbers calculated for the investigated Rockenberg catchment (10 km2) can be regarded as representative for loesscovered agricultural catchments of low relief. For the past seven millennia nearly 10,000 tons per hectare have been removed by man-induced soil erosion. More than 60 % of sediments that were produced are resting on hillslopes. In this particular catchment, high sediment production rates but low net erosion rates caused the generation of a thick sedimentary cover on hillslopes. From a farmer's point of view, this colluvial cover shows improved soil productivity for crop production when compared to pristine soils. It can be concluded that for this type of low-relief catchment man-induced soil erosion is less significant in terms of loss and export of material. By contrast, in steeper sloping upland catchments soil erosion endangers the preservation of fertile soil surfaces. The effect of topography can be illustrated by comparing the mean residence time of sediments in catchments. Whereas the mean residence time for hillslope sediments in the low-relief catchment is 18,000 years, the average interval of sediment storage is only 320 years in the studied badland-like upland catchment. The calculations are based on a systems approach defining catchment-scale sediment budgets for the period of agriculture in question. Datamodeling techniques for deriving large-scale sediment budgets at spatial scales of 10hoch2 to 10hoch3 km2 were developed. We focused on advanced GIS and database applications for data processing of spatially distributed soil data. An empirical sediment budget that relies on independently retrieved field-based data served as validation data. In combination with age determination of sediments this study provides more detailed information on variations of sediment flux in space and time in an exemplary manner.
Publications
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2005. Soils, sediments and slope processes and their effects on sediments fluxes into the river Rhine. Erdkunde, 25: 184-198.
Thiemeyer, H., Blümel, W.-D., Dambeck, R., Dieckmann, B., Eberle, J., Glade, T., Hecht, S., Houben, P., Moldenhauer, K.-M., Schrott, L., Schulte, A., Vogt., R., Wunderlich, J.
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2006. Land use and climatic impacts on the Rhine system during the period of agriculture. Catena, 66: 42-52.
Houben, P., Hoffmann, T., Zimmermann, A., Dikau, R.
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2007. Der Sedimenthaushalt geomorphologischer Systeme seit Beginn des menschlichen Einflusses. Zeitschrift für Geomorphologie, Suppl. 148: 32-40.
Dikau, R., Houben, P., Hoffmann, T., Schrott, L.
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2007. Holocene floodplain sediment storage and hillslope erosion within the Rhine catchment. Holocene 17, 105-118.
Hoffmann, T., Erkens, G., Cohen, K. M., Houben, P., Seidel, J., Dikau, R.
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2007. Reconstructions of Holocene land-use change and sediment budgets in the Rhine system: Focus 4 PHAROS programme 'Past Climate-Human-Environment Interactions'. PAGES Newsletter, 15(1): 17-18.
Houben, P., Burggraaff, P., Hoffmann, T., Kleefeld, K., Zimmermann, A., Dikau, R.
