Influence of topography and human activity on apparent in situ Be-10-derived erosion rates in Yunnan, SW China

Abstract

In order to understand better if and where erosion rates calculated using in situ Be-10 are affected by contemporary changes in land use and attendant deep regolith erosion, we calculated erosion rates using measurements of in situ Be-10 in quartz from 52 samples of river sediment collected from three tributaries of the Mekong River (median basin area = 46.5 km(2)). Erosion rates range from 12 to 209 mm kyr(-1) with an area-weighted mean of 117 +/- 49 mm kyr(-1) (1 standard deviation) and median of 74 mm kyr(-1). We observed a decrease in the relative influence of human activity from our steepest and least altered watershed in the north to the most heavily altered landscapes in the south. In the areas of the landscape least disturbed by humans, erosion rates correlate best with measures of topographic steepness. In the most heavily altered landscapes, measures of modern land use correlate with Be-10-estimated erosion rates but topographic steepness parameters cease to correlate with erosion rates. We conclude that, in some small watersheds with high rates and intensity of agricultural land use that we sampled, tillage and resultant erosion has excavated deeply enough into the regolith to deliver subsurface sediment to streams and thus raise apparent in situ Be-10-derived erosion rates by as much as 2.5 times over background rates had the watersheds not been disturbed.

Publisher

Copernicus Publications

Publication Date

11-4-2016

Publication Title

Earth Surface Dynamics

Department

Geology

Document Type

Article

DOI

https://dx.doi.org/10.5194/esurf-4-819-2016

Keywords

Denudation rates, Cosmogenic nuclides, Threshold hillslopes, Alluvial sediment

Language

English

Format

text

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