Continental Sources, Sinks and the Human Factor in Large Tropical Rivers: the Case of South America

Abstract:

Knowledge of river basins sediment yield at a continental scale and accumulation in sedimentary basins (sinks) provides useful information for quantitative models of landscape evolution, geochemical and sediment mass balance studies for estimating continental and regional net erosion intensities, to assess the volume of solids and to provide understanding to a variety of environmental and engineering applications. Although several estimations exist on the flow of sediments by large rivers from the continent to the Ocean, the role of continental sedimentary basins and fluvial environments (large rivers, megafans) acting as major sedimentary sinks is still partially understood. This assessment is additionally complicated by the human activities that contributed to modify the original rates of production, trapping and transference of sediments at continental scales. South America is an ideal place to discuss these aspects because it contains a) the longest mountain chain of the planet, the Andes; b) the longest and more extensive foreland systems, c) huge lowlands/plains, d) the largest rivers, e) the largest megafans, f) major intracratonic, continental platform and aulacogen sedimentary basins. The analysis of some of the most active sedimentary basins of the continent can help to improve our perspective on what can be preserved and how much sediment is being stored by fluvial systems.

In this presentation I assess the biggest source areas and the larges trapping systems at continental scale with focus on megarivers and megafans, as well us I discuss some study cases of sediment budgets in large rivers that were intensively modified by human disturbances in recent times (dams, deforestation, etc).