The longest rivers on Earth are not only enduring and silent witnesses to all of the 10,000 years of human civilization, but also survivors of the many millions of years of our planet’s active geologic and climatologic past.
The Nile River
Africa’s Nile River is the longest and most renowned of the world’s rivers. It flows northward through arid regions of the dark continent for 4,145 miles from its mountainous, central African source- a Rwandan tributary of the famed Lake Victoria called the Kagera River, then continues through nine countries before emptying from Egypt into the southeastern Mediterranean Sea. Cartographers have given colorful names to broad sections of the Nile River: The Victoria Nile, between Lake Victoria and Lake Albert; the White Nile, as it is called in the Sudan; and, finally, the Nile River for its last 1,900 miles, after it joins with Ethiopia’s Blue Nile at the city of Khartoum.
The Amazon River
South America’s Amazon River is the second longest river on the planet and flows west-to-east to the Atlantic Ocean for approximately 4,000 miles, most of which flows through Brazilian rainforests. Uncertainty surrounds the exact length of the massive river due to the fact that any of a number of Andean mountain tributaries in the west could be claimed as the ultimate source of the river.
The Amazon River serves as drainage for the northern half of South America, an area which receives 400 inches of rain each and every year. So tremendous is the volume of water carried by the Amazon River that this, the second longest river in the world, actually carries a greater volume of water than any other river. The river has such depth that ocean vessels have travelled two thirds of the way up the river from its mouth in eastern Brazil.
The Yangtze River
China’s Yangtze River is the world’s third longest river. Estimates vary slightly from one cartographic source to another as to an exact number, but a length of 3,916 miles appears to be a commonly agreed upon estimate as it divides the country into north and south. The Yangtze begins in the western part of China, in the Kunlun Mountain Range, and flows its almost four thousand mile winding course to the East China Sea, near the city of Shanghai.
The origin for the name of the Yangtze River comes from a European misspelling and mispronunciation of the Chinese “Yangtzhou”, a word used for the lower section of the river.
Negative effects from civilization
Due to a combination of natural drought and a massive hydroelectric project, the Yangtze has recently experienced its lowest levels in over 140 years- ever since reliable records have been kept. The low levels have been devastating to local river shipping and have left lakes and reservoirs short of water.
These three great rivers equally serve the major terrestrial and aquatic ecosystems upon which humans depend, but the health of these natural resources is in jeopardy due to human impact.
The Amazon River has become polluted with the toxic element mercury from gold mining operations along its many tributaries. The element is converted to methyl mercury by bacteria and absorbed into the flesh of the river’s major food fish stocks. Deforestation has greatly increased the rate of erosion of land surfaces, in turn increasing sedimentation of the Amazon and its tributaries with deleterious effects on aquatic life. Sewage and discharges from manufacturing into the river from the major towns and cities along the river have polluted the water. Coral reefs in the Atlantic Ocean, close to the rivers massive discharge, have all but died off after becoming layered with the toxic sediment.
The Nile River has suffered for decades due the construction of the Aswan Dam in the northern portion of the river. No longer does the river deposit nourishing, natural sediment along its banks and estuary. Instead, the Nile flows through a constant channel, eroding the banks of the river into the sea.
The Yangtze River is suffering from China’s explosive growth and modernization. As with the Amazon and Nile Rivers, manmade discharge into the waters has had massive negative effects on the health of the river. The government recently dammed a portion of the river for hydroelectricity, contributing to the current problem of low volume downstream. Over fishing, habitat loss, and pollution have officially caused the recently announced extinction of the Yangtze River dolphin.
SOURCES:
http://www.zsl.org/zsl-london-zoo/news/yangtze-river-dolphin-declared-extinct,381,NS.html
http://mistupid.com/geography/longestrivers.htm
http://www.vaughns-1-pagers.com/geography/longest-rivers.htm
http://encarta.msn.com/media_461524422/World%e2%80%99s_Longest_Rivers.htm
http://www.swgfl.org.uk/rivers/row.htm
http://www.factmonster.com/ipka/A0001779.html
http://www.east-buc.k12.ia.us/00_01/BW/st/st.htm
http://www.trivia-library.com/b/rivers-of-the-world-the-yangtze-river.htm
http://www.reuters.com/article/latestCrisis/idUSPEK30130
http://www.extremescience.com/AmazonRiver.htm
http://www.trivia-library.com/b/rivers-of-the-world-nile-river.htm
