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Upstream, downstream.

MOST TRIPS to the Amazon begin by flying to Manaus, the belle epoque jungle capital built some one thousand miles inland from the Atlantic Ocean. A more historically appropriate starting point however is near the river's mouth at Belem, a once resplendent but now sleepy city of baroque cathedrals, azulejo-tiled mansions, and aging dockworks. Formally known as Santa Maria de Belem do Grao Para, the city's name and riverfront both are witness to the fallen hopes and glory of New World exploration, Portuguese empire building and British transatlantic trade.

Indeed, to approach Belem by water is to follow in the wake of Spanish conquistadors, dauntless seekers of El Dorado, and linen-suited rubber merchants. To enter the Amazon from the Atlantic is also to see up close the topographical ambiguities that occur when equatorial tides encounter the world's largest river and its flatest, most extensive tropical floodplain. It is no accident that Brazilians have as many words for jungle--mondongo, varzea, baixo, teso, resinga, igapo, campo, campina, campinarana, to name but a few--as the Inuit have for ice and the Bedouin have for sand.

But with a Brazilian's precision in describing the Amazon's fine distinctions of jungle terrain, the river's mouth is surprisingly reluctant to let itself anywhere simply be called terra firma. The farther one penetrates up the channels and subchannels of the delta, the less likely one is to find a dry place to come ashore.

The irony of being at sea for weeks before finally sighting the New World and then entering its mightiest river, but without ever having glimpsed the continent itself, never once seeing the actual soil that anchors its flora and houses its fauna, was not lost on H.M. Tomlinson in his classic 19th century travel narrative The Sea and the Jungle. With characteristic understatement he glanced at his watch and wrote, "It was two in the afternoon. There was America. I discovered it with some difficulty. What showed as land was of too unsubstantial a quality, too thin and broken a rind on that vast area of water to be of any use as a foothold."

So confusing does the delta make even a question of simple geography that many scientists wonder if Belem should be called an Amazonian port of call in the first place, or rther if it belongs exclusively to the Para River, once considered to have a completely separte basin. Studies have since shown that a significant amount of the Amazon drains to the Para through the lacelike waterways known as furos, some almost 400 feet deep and one-half mile in width. The more stable channels in the Para and the furos make upstream navigation much easier than through the Amazon's northern mouth, subject to shifting mud bars and strong currents.

But what really happens at the Amazon's mouth when 7,067 cubic feet of fresh water discharge every day into the Atlantic Ocean? As one might expect, such a massive volume of fresh water, sufficient to cover the state of Texas in 47 days or to refill the Mediterranean Sea in a year, has extraordinary but still imperfectly understood consequences on coastal Brazil's environment, marine life, tides, and weather.

The Amazon River system, containing more than twenty percent of all the world's river water, consists of some 1,100 major tributaries, their combined length stretching more than 4 million miles. Seventeen of its feeders are longer than 1,000 miles if measured from their sources to the Atlantic, and the Madeira and Rio Negro affluents would then count as the second and third longest rivers in the world. The drainage basin contains more than 4 million square miles, running from the source in a 17,000 foot high Andean lake, within 100 miles of the Pacific Ocean, for more than 4,000 miles to its mouth on the Atlantic. While the discharge of the Congo, the world's second largest river, has been repeatedly adjusted downwards, the recorded flow of the Amazon has more than doubled since the first hydromorphic study one hundred years ago.

Squarely in the river's mouth is Marajo, the world's largest fluvial island, measuring 31,000 square miles during the dry season, or roughly 20 percent greater than Switzerland, but becoming half submerged by seasonal rains. It is Marajo and her sisster islands Mexiana and Caviana that give the Amazon's mouth its dual personality of both delta and estuary, witht he deltaic features facing the continent and estuarine features facing the ocean.

A delta on the seaward side of Marajo has not formed because the North Brazil Current sweeps nearly one and a third million tons of river sediment a day swiftly along the continent's northern coast. The eastern side of Marajo itself is constantly being eroded by this current. A wide band of accumulated alluvium, mostly composed of eroded soisl from the Andes, forms the coastline of the Territory of Amapa.

Shifting mud banks make navigation along this shore particularly dangerous, as the French scientist Charles Marie de la Condamine noted in 1745 when he sailed from Para to Cayenne in French Guyana. The estuary's 400 foot depths, the strong outflowing current, the relatively light sedimentary load, and the prevailing northwesterly tradewinds all discourage the development of a classic fan-shaped delta with slower moving currents. This is the only estuary of a world class river with no salt water mixing at any depth.

Whereas on its seaward and northern sides Marajo exhibits purely estuarine features, with thick mangrove vegetation and minimal sedimentation, the island's westerly side reveals a delta of sorts, formed from many alluvial finger islands. The Ilhas de Gurupe, dos Porcos, do Para, and Mututi, to name but a few, are laced by the furos that divert some of the Amazon's flow into the Para system to the south.

Because of the para River's weaker outflow, consisting of only one major tributary, the Tocantins, there is some salt water intrusion up the lower Para's mouth at the Bahia do Marajo. The flow of the furos sometimes, in fact, reverses during high tides, which facilitates the upstream navigation of passenger ferries from Belem into the Amazon system.

The hydrology of the Amazon's mouth has a notable impact on Marajo's very pronounced and highly localized wet and dry seasons. Rainfall ranges from 26 inches in March to one-half inch in October. In nearby Belem on the mainland, the range for the same months is much narrower, 16 inches to 4 inches. Marajo's downpours cause the low lying eastern half of the island, covered with baixas, or marsh swamp, to disappear for four months each year under several feet of standing water. Marajo's western half, covered with closed high forest and better drained, remains dry year round.

In the center of the island lies the mondongo, a great year-round swamp where a half million water buffalos graze. This herd, by far the largest in Brazil, was started more than a hundred years ago when a boat carrying the animals from India to an upriver plantation sank offshore, but close enough so that several made it to land. Although Jesuits had brought cattle to Marajo in 1750, cows could not fatten on the perennial swampland. Already adapted to a wet environment, the buffalos quickly began to thrive. Most conservationists still believe that Marajo is the only place in the Amazon suitable for such kinds of ranching.

While a mysterious Marajoan culture had previously flourished on the island from 400 to 1350 AD, little is known of its origin. It seems, in fact, to have sprung up fully developed, noted for its complexly designed ceremonial vases. The current theory is that the Marajoans were Mayan colonists from Middle America by way of the Guyanas, and that the civilization died out because of increasing population density. Perhaps the culture's greatest gift to posterity is a small triangular-shaped ceramic piece thought to have been the world's first tanga.

Most food fishing on Marajo today is still done with nets and fish corrals, made from reeds bent into half moon, heart, or barrel shapes. The island is also famous for its large schools of Serrasalmus Nattereri, better known as piranhas, which inhabit the permanently flooded tree swamps, igapos, and streams, igarapes. Piranhas are one of the few fish species exhibiting the rare trait of group predation. Overcrowding, lack of food, or low water can set off an attack on any sized meal, man and buffalo included, intruding into their area. Whenever Marajo experiences a prolonged drought, numerous accounts appear in Belem newspapers of attacks on humans, although fatalities are rarely reported.

Far offshore Marajo, Amazon river water stubbornly refuses to mix completely with the surrounding salt water. Called by oceanographers a fresh water lens, but in fact quite brackish in taste, this "lake in the sea" can migrate as far north as Barbados and as far as 200 miles offshore. An occasional break in the coastal current somehow permits the river's discharge to pass through and avoid absolute dilution. Some scientists also think the phenomenon is related to the Amazon "Canyon," a 900 foot deep underwater trench running east-west for several miles that cuts sharply through the ancient alluvial cone that sits atop the continental shelf.

Another of the area's oceanographic oddities is the pororoca, or tidal bore. The name stems from poroc-poroc the Tupi-guarani word for "big roar," one of its most unique features. It occurs primarily during syzygial tides around the spring equinox when the river is at the flood stage. The incoming tide and the outgoing river flow meet some miles offshore, with the sea level at that spot bulging until equilibrium is broken by the stronger tide which causes an inward rush of water. Non-conformities in the estuary's bed then can form 15 foot waves that travel up to 25 knots and cause considerable damage upon reaching shore.

Pororocas occur more often in the Amazon's northern mouth, due to its stronger current. In 1850 one is said to have cut a wide channel through Caviana Island, which to this day has two distinct halves. The earliest scientific explanations attributed the pororoca to seismic forces, chemical reactions of mixing salt and fresh water, and tides entering a suddenly narrowed channel. Local fishermen believe that the letter "r" causes the pororoca, since it occurs most frequently in February -- in Portuguese, as in English, February is the only month with two "r"s.

The first written account of the pororoca was made by the Portuguese explorer Pedro de Texeira in 1637, who noted in his log, "As the ships lay at anchor, a fearful noise was made by the strong imp of the fresh water against the water of the sea coming to meet it, and the ships were raised four fathoms, and from this proceeded great danger."

In the 19th century, Marajo served as a handy laboratory for such famous naturalists as Henry Walter Bates, who discovered mimicry in the insect world and thereby advanced his Amazonian colleague Alfred Russel Wallace's theory of evolution. Close on Bates' heels came the indefatigable botanist Richard Spruce, who spent 17 years in the Amazon collecting over 7,000 new plant species and the following 27 years in a rented room in England pouring over his notes, among which were 600 pages about moss.

Spruce was particularly fascinated by the floating isles of mud and grass, the terras caidas, that pass through the mouth of the Amazon on their way to sea. These tangled masses of aquatic vegetation, sometimes several acres in size and 20 feet deep, break off from the river bank when the flood recedes. Spruce describes climbing aboard one such slowly disolving island as it drifted downstream in order to measure the roots of its grass.

Perhaps most prominent among Amazonian naturalists in the 20th century is Harald Sioli. For the past fifty years Sioli has been a pioneer in the study of river water, a field known scientifically as riverine limnology. It comes as no surprise that scientists should decide to focus on what the river can tell them about the rain forest, for as one young limnologist has noted, "It's so difficult to reach some places on foot, why not let the river do the walking for you? Let it bring things like leaf debris and soil sediments downstream to where you are."

Sioli first visited Brazil in 1934 with the intention of studying the dry season hibernation of land toads in the northeast. Ironically, prolonged rains forced him to cancel this project and travel instead to Belem, where he fell forever in love with the lush wetness of the Amazon. His pathbreaking studies of Amazonian limnology, in the course of which he has explored nearly every furo, igarape, and parana of the lower river, earned him Brazil's Cruzeiro do Sul medal, the country's most prestigious award for foreign citizens.

Professor Sioli advocates a fully integrated ecological analysis of the Amazon's waters, and it is his example that perhaps has most united the narrow scientific disciplines that on their own make so little sense of such a blurred bio-realm. This approach is now bearing fruit as multidisciplinary teams begin the basic research that might one day show what, if any, are the downstream consequences of clearcutting trees, damming tributaries, refining gold with mercury, and dumping pulp mill waste upriver.

In the last two years, a research program known as AMASSEDS (A Multidisciplinary Amazon Shelf Sediment Study) has brought together Brazilian and U.S. scientists to study the Amazon's outer mouth. While findings are still preliminary, U.S. coordinator Chuck Nittrouer thinks it unlikely they will find any traces of man's impact farther upstream. "The volumes of water and sediment at the Amazon's mouth are so gigantic, the natural processes down here far outweigh anything man can do upriver. But that's not to say that nothing ever changes. Tremendous erosions and acretions of sediment can occur in just a matter of years."

But while the AMASSEDS team works in the river's outer mouth and a sister project called CAMAREX focuses its attention above the Obidos gorge, the Amazon's final five hundred miles remain unexamined in any systematic way except by Sioli's preliminary research. This stretch of the river, which includes the confluences of the Tapajos and Xingu tributaries, the furos system between the Amazon and the kera, and the entire fluvial island complex, poses perhaps the greatest scientific and physical challenges of all.

As Alberto Figueiredo, a marine geologist at the Universidade Federal Fluminense and the Brazilian coordinator of AMASSEDS, remarks when asked why that part of the river is not better known, "Too much goes on there to be able to exercise any kind of research control. In order to answer one question, you'd have to account for just too many unknowns." And besides, it can be a very dangerous place to work. The small motor launches required to navigate the sometimes shallow depths are no match for the fierce water boils, crosscurrents, eddies, and tides that can capsize much larger ships.

Considered almost as a kind of "no man's water," this zone has too much salt water for the limnologist and too much fresh water for the oceanographers to feel completely at home. And without stable channels and banks, the river's mouth provides few fixed points from which to be measured over time. The lower Amazon's physical frame of reference is simply too complex to record, much less to comprehend. its awesome size remains just as daunting to modern scientists as it was to the 16th century explorers and 19th century naturalists who were intrigued by one of the world's greatest mysteries.

Louis Werner is a freelance writer and independent producer/director of documentary films.
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Title Annotation:includes related article; Perspectives on the Amazon
Author:Werner, Louis
Publication:Americas (English Edition)
Date:Nov 1, 1990
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