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Determination of predevelopment denudation rates of an agricultural watershed (Cayaguás River, Puerto Rico) using in-situ-produced Be in river-borne quartz |
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| Authors: | Erik Thorson Brown Robert F Stallard Matthew C Larsen Didier L Bourls Grant M Raisbeck Franoise Yiou |
| Institution: | a Large Lakes Observatory, University of Minnesota, Duluth, MN 55812, USA b United States Geological Survey, 3215 Marine St., Boulder, CO 80303, USA c United States Geological Survey, GSA Center, 651 Federal Dr. Guaynabo, PR 00965, USA d Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, CNRS-IN2P3, Bât. 108, F-91405 Campus Orsay, France |
| Abstract: | Accurate estimates of watershed denudation absent anthropogenic effects are required to develop strategies for mitigating accelerated physical erosion resulting from human activities, to model global geochemical cycles, and to examine interactions among climate, weathering, and uplift. We present a simple approach to estimate predevelopment denudation rates using in-situ-produced cosmogenic 10Be in fluvial sediments. Denudation processes in an agricultural watershed (Cayaguás River Basin, Puerto Rico) and a matched undisturbed watershed (Icacos River Basin) were compared using 10Be concentrations in quartz for various size fractions of bed material. The coarse fractions in both watersheds bear the imprint of long subsurface residence times. Fine material from old shallow soils contributes little, however, to the present-day sediment output of the Cayaguás. This confirms the recent and presumably anthropogenic origin of the modern high denudation rate in the Cayaguás Basin and suggests that pre-agricultural erosional conditions were comparable to those of the present-day Icacos. |
| Keywords: | denudation erosion rates Puerto Rico Be-10 |
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