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 (Cayaguas 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 Cayaguas. This confirms the recent and presumably anthropogenic origin of the modern high denudation rate in the Cayaguas Basin and suggests that pre-agricultural erosional conditions were comparable to those of the present-day Icacos.
Bibliographical noteFunding Information:
We thank J. Lestringuez and D. Deboffle for their expert assistance with AMS measurements. The assistance in sample collection and processing of A. Torres, and I. Concepción is gratefully acknowledged. Comments of two anonymous reviewers have improved the manuscript. This study has been partially supported by the program `Dynamique et Bilan de la Terre' of INSU and is part of the `Global Change Hydrology — Water, Energy and Biogeochemical Budgets Program' of the USGS Water Resources Division. Tandétron operation is supported by the CNRS, CEA and IN2P3. [MK]
- Benyllium 10
- Erosion rates
- Puerto Rico