|Lupker, M., C. France-Lanord, J. Lavé, J. Bouchez, V. Galy, F. Métivier, J. Gaillardet, B. Lartiges, J.-L. Mugnier, A Rouse-based method to integrate the chemical composition of river sediments: application to the Ganga basin, JGR - Earth Surface, 2011|
The Ganga river is one of the two main conveyors of the sediments produced during the Himalayan erosion. These sediments are carried during summer monsoon to the Bay of Bengal through the Gangetic plain. Determining the flux of elements transported through the system is essential to understand the dynamics of the basin. Using Acoustic Doppler Current Profiler (ADCP) acquisitions with sediment depth profiles sampling of the Ganga in Bangladesh performed between 2002 and 2010, we build a simple model upon classical sediment transport theory to derive the annual flux and grain size distributions of the sediments exported. The model output of 390 (± 30) Mt/yr as suspended sediments and ~ 4 Mt/yr as bed-load sediments is in accord with previous studies. Modeled average sediment grain size parameters D50, D84 are 27 (± 4) and 123 (± 9) µm respectively. These grain size parameters were used to infer average chemical compositions of the sediments owing to a strong grain size-chemical composition relation. Himalayan erosion principally delivers particulate Si, Al and Fe to the oceans with fluxes of 4.4·1012, 9.6·1011 and 2.4·1011 mol/yr respectively for the Ganga basin. The comparison with an average Himalayan crust and flood plain composition shows that c.a. 10 % of the initial Himalayan sediment flux is stored in the Gangetic flood plain. The associated, globally averaged sedimentation rates in the flood plain are found to be ~ 0.06 mm/yr and yielded average Himalayan erosion rate of ~ 1mm/yr. This study stresses the need to carefully address the average composition of river sediments before solving large-scale budgets.