The Amazon River Basin
The vast Amazon basin covers more than two and a half million square miles, more than any other rainforest. The Amazon River basin contains one-fifth of the world’s fresh water. Its flow is 12 times that of the Mississippi, with 12 billion liters flowing down the river every minute –enough to supply New York City for 60 years! Daily it pours enough fresh water out into the Atlantic Ocean to supply the entire water needs of the United Kingdom for nearly two years. Its discharge of approximately 210,000 m_ per second exceeds the combined discharge of the world’s nine next largest rivers.
The Amazon needs no introduction yet remains a relatively uncharted and untouched region of the planet where new discoveries are being made on an almost daily basis.
The tropical rain forest that we know as the Amazon covers nearly half of the Brazilian territory and is responsible for supplying over half the planet’s oxygen. The 4,200-mile (6,760 km) river is home to over 2,000 different types of fish, while the surrounding rain forest supports an estimated 1,800 species of birds, 250 different mammals and a similar diversity of animal and insect life. It is responsible for a tenth of the world’s 10 million living species and 30 per cent of all known plant and animal species. The Amazon River, is the world’s longest, widest, and deepest river. Most of the Basin is covered by tropical rainforest, accounting for more than 56% of all broad leaf forests in the world.
The Amazon River Basin is also an important source of natural resources for human economic development. It contains some of the world’s largest known reserves of bauxite (nearly 15% of the world total), and industries within the Basin are some of the largest suppliers of iron and steel to world markets. Wood and wood byproducts, gold, and tin are other products from the Basin that are increasingly in demand for export.
The population of the Amazon River Basin is estimated at approximately 10 million, mostly concentrated in urban areas along the river and its main tributaries. A high percentage of the total population consists of indigenous communities settled mainly along the banks of the river and belonging, inter alia, to ethno–linguistic groups. In recent decades, there has been an accelerated process of immigration into, and settlement within, the Amazon River Basin. Population growth rates range from 5.2% to 7.2%, well above the national averages for the Amazon countries. These factors, combined with the high levels of poverty, place constant pressure on the region’s natural resources, and in particular on residual native forests.
The Andean slopes are subject to severe erosion, with more than 1,000 tons/km2/year of sediment flowing toward the Atlantic Ocean. Measurements in the upper Madeira River subbasin indicate that, of the 3,200 tons/km2/year of sediment produced, up to 60% reaches no farther than the Andean foothills, at which point, the sharply reduced longitudinal gradients lower the stream’s carrying capacity resulting in internal sediment deposition within the Basin. Overall, the Amazon River transports an average of 600 to 800 million tons of sediment annually, with the majority of the sediment coming from the Solimoes (62%) and Madeira (35%) river sub basins and originating in the Andes.