Increase of human over natural erosion rates in tropical highlands constrained by cosmogenic nuclides
- 1Isotope Geology, University of Berne, Erlachstrasse 9a, 3012 Berne, Switzerl
- 2Paul Scherrer Institute, Institute of Particle Physics, ETH Hönggerberg, 8093 Zürich, Switzerland
Abstract
We quantify the difference between the human-caused sediment yield and the natural rates of soil production and bedrock erosion in a now largely deforested tropical highland. The present-day rate of soil loss in the Upper Mahaweli catchment, Sri Lanka, is calculated by using suspended river-load fluxes. These data provide spatially averaged sediment yields of 130–2100 t·km−2·yr−1. Local rates of soil loss from agricultural plots on hillslopes are as high as 7000 t·km−2·yr−1. By comparison, natural rates of sediment generation, as determined by measuring cosmogenic 10Be in quartz from sediments and soils, are only 13–30 t·km−2·yr−1. The natural rates presented here provide a benchmark against which recent erosion rates, determined by various sediment gauging techniques, can be referenced. In the Sri Lankan highlands, these results suggest that soil is now being lost 10–100 times faster from agriculturally utilized areas than it is being produced.
Footnotes
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↵*Also at: Hewawasam—Department of Natural Resources, Faculty of Applied Sciences, Sabaragamuwa University, Buttala 91100, Sri Lanka. Current addresses: von Blanckenburg—Institut für Mineralogie, Universität Hannover, Callinstrasse 3, 30167 Hannover, Germany, fvbmineralogie.uni-hannover.de; Schaller—Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
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↵GSA Data Repository item 2003092, Appendix DR1 (analytical and data-processing procedures), Table DR1 (river-load data), and Table DR2 (cosmogenic nuclide data), is available from Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, editinggeosociety.org, or at http://www.geosociety.org/pubs/ft2003.htm.
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- Accepted March 27, 2003.
- Received January 30, 2003.
- Revision received March 26, 2003.
- Geological Society of America
