Geoquímica das águas do médio e baixo rio Madeira e seus principais tributários - Amazonas - Brasil

Abstract

RESUMOEste trabalho teve como objetivo estudar as águas do rio Madeira e seus principais tributários entre a cidade de Humaitá e sua foz no rio Amazonas. Foram analisados pH, condutividade, turbidez, íons maiores, elementos traço e isótopos de Sr nos períodos de seca, cheia e transição para a seca entre 2009 e 2010. As águas do Madeira, classificadas com brancas, são bicarbonatadas-cálcicas, têm pH entre 5 e 6 e são mais concentradas que as dos tributários. Estes têm águas de cor preta, mais ácidas e quimicamente heterogêneas, os da margem esquerda são quimicamente mais semelhantes as do Madeira, enquanto os da margem direita têm alta concentração em SiO 2 . Os cátions, Cl -e NO 3 -são mais concentrados na cheia o que sugere influência do solo, da vegetação e da composição da água da chuva (Cl , Al, Br e P, com maiores concentrações na seca, devem estar relacionados com a química das rochas. A SiO 2 e os elementos terras raras (ETR) com concentrações elevadas na seca e na cheia, estão associados tanto a vegetação e ao solo como as rochas. A interação desses fatores é a causa da heterogeneidade química das águas. Contudo, a semelhança entre as águas dos tributários da margem esquerda e as do Madeira são consequência das rochas dos Andes serem a fonte dos sedimentos cenozóicos percolados por elas, enquanto a química das águas dos tributários da margem direita retrata a estabilidade tectônica, o intenso intemperismo e a baixa taxa de erosão das rochas do cráton Amazônico. PALAVRAS-CHAVE: sazonalidade, íons maiores, elementos traços e isótopos de Sr. Chemistry of waters of the middle and lower Madeira River and its main tributaries-Amazonas -Brazil ABSTRACTThe aim of this paper was study the water of the Madeira River and its tributaries, between the city of Humaitá and its confluence in the Amazon River. There were analyzed: pH, conductivity, turbidity, major ions, trace elements and strontium isotopes during the dry and wet seasons and also, in the transition from the wet to the dry season, throughout 2009 and 2010. The white waters from the Madeira River are bicarbonated, calcic, with pH between 5 and 6 and the ions concentrations are higher than those of the tributaries. The waters of the tributaries are black, are more acidic and are chemically heterogeneous; those from the left margin are chemically similar to the waters of Madeira River, while those from the right margin are enriched in dissolved SiO 2 . The concentrations of cations, Cl -and NO 3 -are higher during the wet season due to the contribution of soils, vegetation and the rainwater composition (Cl , Al, Br e P are concentrated in the dry season, and their higher contents may be related to the bedrock. The higher concentrations of SiO 2 and rare earth elements in both dry and wet season are related to vegetation, soil and rocks. The interaction of these factors causes the chemical heterogeneity of the water. However, the chemical similarities between the water tributaries of the left margin and the water of the Madeira River, are probably, consequen...

A Matter of Scale: Historical and Environmental Factors Structure Anuran Assemblages from the Upper Madeira River, Amazonia

“…Average annual rainfall is 1733 mm (maximum = 245 mm in March, minimum = 26 mm in July), with most rainfall occurring between October and April and a drier season from June–September (1982–2009 data of the National Water Agency, ANA), The relative average humidity is 77 percent in the dry season and 88 percent in the rainy season (Horbe et al . ).…”

“…The climate is consistently warm and humid, with average annual temperatures ranging between 24 and 26°C. Average annual rainfall is 1733 mm (maximum = 245 mm in March, minimum = 26 mm in July), with most rainfall occurring between October and April and a drier season from June- September (1982September ( -2009 data of the National Water Agency, ANA), The relative average humidity is 77 percent in the dry season and 88 percent in the rainy season (Horbe et al 2013). SAMPLING DESIGN.-We collected data in seven sampling locations (grids), each comprising two parallel 5-km long trails that were approximately perpendicular to the river course.…”

The Costs of Evaluating Species Densities and Composition of Snakes to Assess Development Impacts in Amazonia

“…The climate is consistently warm with average monthly temperatures between 20 o and 30°C, and minima and maxima between 18 o and 33°C in July. The dry season extends from June to September, with rainfall less than 30 mm per month in June and July, and a rainy season from October to May, with up to 330 mm of rain per month in December and January [25] . Tributaries of varying sizes are present in the study area, and the smallest of these often dry completely in the dry season.…”

Checklist of chelonians from the upper Madeira River and the lower Madeira-Purus interfluvium (Brazilian Amazon), including a range expansion for Podocnemis sextuberculata Cornalia, 1849

“…The dry season extends from June to September, the rainy season from October to May. Monthly rainfall is less than 30 mm in June to July and up to 330 mm in December to January (Horbe et al 2013). Small streams and pools are present in the forest, and many of these may dry out completely in the dry season.…”