HR: 11:50h
AN: U32A-06 INVITED     [Abstracts]
TI: Constraining Soil Erosion Mitigation using Cosmogenic Nuclides in Sediment
AU: * von Blanckenburg, F
EM: fvb@mineralogie.uni-hannover.de
AF: Institute of Mineralogy, University of Hannover, Callinstrasse 3, Hannover, 30167 Germany
AU: Vanacker, V
EM: v.vanacker@mineralogie.uni-hannover.de
AF: Institute of Mineralogy, University of Hannover, Callinstrasse 3, Hannover, 30167 Germany
AU: Hewawasam, T
EM: tilak@sab.ac.lk
AF: Faculty of Applied Sciences, Sabaragamuwa University, Sri Lanka, Buttala, 1 Sri Lanka
AU: Kubik, P W
EM: kubik@particle.phys.ethz.ch
AF: PSI and ETH Zurich, ETH Hoenggerberg, Zurich, 8093 Switzerland
AB: Humans are the strongest agents of geomorphic change. The amount of soil moved per year by humans exceeds the annual sediment discharge by a factor of five. Mountain regions are particularly susceptible to soil erosion, given their steep topography, high rainfall, and rapid land use change. The combination of in situ-produced cosmogenic nuclides, measured in river sediment, and sediment gauging can estimate the human acceleration of erosion processes. The long integration time of the cosmogenic nuclide method (1ky - 100ky) makes it insensitive to short-term perturbations. In contrast, river load gauging and reservoir sedimentation (time scale 10-50 years) can be used to quantify present erosion rates. It has been shown that deforestation of tropical highlands has accelerated soil erosion up to 100 times (1). However, a means to determine whether erosion mitigation strategies can reverse soil erosion to pre-anthropogenic levels has not been in place, and the efficiency of erosion mitigation is generally not assessable. In the Southern Ecuadorian Andes the present-day erosion in 37 catchments was measured based on sediment accumulation in small reservoirs. Erosion rates are ca. 10mm/y for highly degraded lands, and 0.05 mm/y for forested catchments. These short-term erosion rates correlate inversely with vegetation cover. Present-day erosion rates of the catchments with the highest vegetation cover equal long-term pre-anthropogenic rates (which are unexpectedly low at 0.02-0.15mm/y from cosmogenic 10Be). Importantly, the low present erosion rates are a feature of both native vegetation and introduced land cover. A high degree of land cover (regardless of the actual type) moves present-day erosion into the pre-anthropogenic range as defined by cosmogenic nuclides. This comparison shows for the first time that erosion mitigation by appropriate land cover can potentially reduce human-accelerated erosion rates back to their natural baseline. Cosmogenic nuclides might therefore provide land use planners with a premier tool for designing adequate erosion mitigation strategies. 1 T. Hewawasam, F. von Blanckenburg, M. Schaller and W. Kubik, Increase of human over natural erosion rates in tropical highlands constrained by cosmogenic nuclides, Geology 31, 795-600, 2003.
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1815 Erosion
DE: 4918 Cosmogenic isotopes (1150)
DE: 8175 Tectonics and landscape evolution
SC: Union [U]
MN: Fall Meeting 2005