A reduced relevance of vegetation change for alluvial aggradation in arid zones

Posted By News On November 15, 2012 - 1:06am

This study by Jose Luis Antinao and Eric McDonald assesses the hypothesis that a climatically induced decrease in vegetation density on arid region hillslopes is a major factor behind erosion, sediment transport, and aggradation (sedimentation) downstream.

This linkage is often used to explain sedimentation in alluvial fans during the Late Pleistocene Holocene period (8 to 14-thousand years ago) in the U.S. Southwest deserts. Antinao and McDonald compiled paleo-botanical and alluvial fan sedimentation histories during this period in the Mojave and northern Sonoran deserts.

Timing of actual downstream aggradation was compared to timing of vegetation change in altitudinal zones susceptible to generate sediment, assuming that compositional changes in vegetation indicate changes in plant density or canopy cover.

Their results reveal that onset of extensive alluvial fan deposition developed well before a decrease in catchment vegetative cover in all regions. Fan sedimentation could be linked, unexpectedly, to increased cover in one region. These ambiguous linkages indicate that vegetation change probably has a reduced role in aggradation.

Antinao and McDonald conclude that the analysis of hillslope response to climate change should therefore incorporate other factors like local storm intensity or sediment redistribution in hillslopes, given the importance of coupled hillslope/alluvial system evolution in arid region ecosystem functions

Jose Luis Antinao, Division of Earth and Ecosystem Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno, Nevada 89512, USA; and Eric McDonald. Posted online 19 October 2012; doi: 10.1130/G33623.1

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