Podzolization as a deferralitization process: dynamics and chemistry of ground and surface waters in an Acrisol – Podzol sequence of the upper Amazon Basin |
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| Authors: | N R Do Nascimento E Fritsch G T Bueno M Bardy C Grimaldi A J Melfi |
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| Institution: | aDEPLAN/IGCE/UNESP, Instituto de Geociências e Ciências Exatas, Rua 10, n2527, 13500‐230 Rio Claro, SP, Brazil, bNúcleo de Pesquisa em Geoquímica da Litosfera da Universidade de S?o Paulo (NUPEGEL‐USP), Alameda do Aviário 44, 13418‐900, Piracicaba, SP, Brazil, cInstitut de Recherche pour le Développement (IRD), DMEUMR 161 CEREGE, Europ?le Méditerranéen de l’Arbois BP 80, 13545 Aix en Provence cedex, France, dInstitut de Minéralogie et de Physique des Milieux Condensés (IMPMC), UMR 7590, CNRS, Universités Paris 6 et 7, et IPGP, Case 115, 4 place Jussieu, 75252 Paris cedex 05, France, eUnidade Contagem, Pontifícia Universidade Católica de Minas Gerais, Rua Rio Comprido 4580, CINCO, 32.010‐025, Contagem, MG, Brazil, and fInstitut National de Recherche Agronomique (INRA), UMR 1069 Sol Agro et Hydrosystèmes, 65 rue Street Brieuc, CS 84215, F‐35042 Rennes, France |
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| Abstract: | Hydrochemical processes involved in the development of hydromorphic Podzols are a major concern for the upper Amazon Basin because of the extent of the areas affected by such processes and the large amounts of organic carbon and associated metals exported to the rivers. The dynamics and chemical composition of ground and surface waters were studied along an Acrisol‐Podzol sequence lying in an open depression of a plateau. Water levels were monitored along the sequence over a period of 2 years by means of piezometers. Water was sampled in zero‐tension lysimeters for groundwater and for surface water in the drainage network of the depression. The pH and concentrations of organic carbon and major elements (Si, Fe and Al) were determined. The contrasted changes reported for concentrations of Si, organic carbon and metals (Fe, Al) mainly reflect the dynamics of the groundwater and the weathering conditions that prevail in the soils. Iron is released by the reductive dissolution of Fe oxides, mostly in the Bg horizons of the upslope Acrisols. It moves laterally under the control of hydraulic gradients and migrates through the iron‐depleted Podzols where it is exported to the river network. Aluminium is released from the dissolution of Al‐bearing minerals (gibbsite and kaolinite) at the margin of the podzolic area but is immobilized as organo‐Al complexes in spodic horizons. In downslope positions, the quick recharge of the groundwater and large release of organic compounds lead to acidification and a loss of metals (mainly Al), previously stored in the Podzols. |
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