The Amazon, like smaller rivers, is the daughter of its drainage basin. Local climate and interactions over time with the template of topography, geology, and vegetation determine the size and flow of rivers. Likewise, the compositions of the particulate and dissolved materials carried by rivers result from initially similar rainwaters that have been uniquely imprinted by contact with almost every plant, animal, and mineral in the catchment. Rivers thus provide a continuously flowing signal, recorded by isotopes, ions and molecules, of the cumulative effects of drainage basin processes such as weathering, oxidation/reduction, gas exchange, photosynthesis, biodegradation, and partitioning. This recording is complementary to more classical methods of remote sensing based on electromagnetic radiation, but is composited over a wider range of time and space scales and includes effects of subcanopy and subsurface processes. The Amazon River is similar to other rivers in this regard, but is unusual in the size and extent of different environments its waters touch. The Amazon River is the world’s largest river and drains the world’s largest single catchment (∼6,000,000 km2). It discharges an average of about 200,000 m3 of water per second to the Atlantic Ocean. This volume is about 5 times more than the Congo, the second largest river. The Amazon has 1100 major tributaries, three of which are nearly as large as the Congo. From its origins at about 5200 m in the Andes about 200 km from the Pacific Ocean, the Amazon goes through at least 10 name changes as it snakes its way 6500 km eastward to the Atlantic Ocean (Schreider and Schreider 1970). The flooded areas along the lower mainstem are important sources of greenhouse gases such as methane (Bartlett and Harriss 1993, Devol et al. 1994) and the latent heat release from convective precipitation in the basin is sufficient to influence global climate. The Amazon drainage basin contains 40% of the world’s tropical rain forest (dos Santos, 1987) and is home to countless species of plants and animals. The river itself contains some 2000 described species of fish.
The changing course of the Amazon River in the Neogene: center stage for Neotropical diversification