Sources of Organic Carbon in the Rio Purus and Amazon River Suspended Matter and Sediments: 3C Tracing

Abstract

Rivers represent the chief transport medium of carbon from the continents to the oceans. With respect to the total flux of dissolved and particulate carbon carried by rivers ( 1015 gC/yr), the contribution of organic carbon is estimated to represent -40%, with 16% being exported from the tropical rain forest environment as a whole and -3.5 % by the Amazon River (Richey et al., 1990), which is the largest river in the world, both in terms of discharge and drainage basin area. Approximately one half of the total organic carbon in the Amazon River is transported as particulate organic carbon (POC). Organic carbon from different sources contribute to the POC in the Amazon River. They can be characterized by their stable carbon isotopic composition: terrestrial organic matter produced by vascular C3 plants, either from upland or lowland sources, organic matter produced by vascular C4 plants and aquatic algae. Here we consider the POC sources and evolution in the Rio Purus system, which is typical of the white waters, POC variations with depth in sections of the Amazon River and of major tributaries (Rios Negro, Madeira, Trombetas, Tapajos), and POC storage and remobilization in the river beds and banks.