Biogeochemistry of the Amazonian Floodplains: Insights from Six End-Member Mixing Models

Author(s)

Bustillo, Vincent ^{[1, 2]} ; Victoria, Reynaldo Luiz ^{[3, 1]} ; Sousa de Moura, Jose Mauro ^[1] ; Victoria, Daniel de Castro ^[4] ; Andrade Toledo, Andre Marcondes ^[5] ; Collicchio, Erich ^{[1, 6]}

Affiliation

^[1] Ctr Energia Nucl Agr, Lab Geoproc & Tratamento Imagens, Piracicaba - Brazil

^[2] Univ Tours, UFR Sci & Tech, Univ Orleans, CNRS, INSU, Inst Sci Terre Orleans, UMR 6113, F-37200 Tours - France

^[3] USP ESALQ, NUPEGEL, Piracicaba - Brazil

^[4] Embrapa Monitoramento Satelite, Campinas, SP - Brazil

^[5] Univ Fed Mato Grosso, Rondonopolis - Brazil

^[6] Univ Fed Tocantins, AgroUnit, Palmas - Brazil

• Document type: Journal article
• Source: Earth Interactions; v. 14, SEP 2010.
• Web of Science Citations: 3

Abstract

The influence of Amazonian floodplains on the hydrological, sedimentary, and biogeochemical river budget was investigated along the Vargem Grande-Obidos reach, by applying six mixing models based on variable regional and/or variable hydrological sources. By comparing the output of many different models designed for different purposes, the nature and the magnitude of processes linking water and biogeochemical budgets of the Amazonian floodplains were clarified. This study reveals that most of the chemical baseline of the Amazon River basin is acquired before the studied 2000-km Amazonian reach. However, the tight connection between the hydrograph stage of the river and the chemical signals provides insightful information on the dynamics of its floodplains. The chemical expression of biotic and abiotic processes occurring in the Amazonian floodplains can be particularly perceived during falling waters. It appears delayed in time compared to the maximum extension of submerged area, because the alternating water circulation polarity (filling versus emptying) between the main channel and the adjacent floodplains determines delayed emptying of floodplains during falling waters. It results also in a longer time of residence in the hydrograph network, which strengthens the rate of transformation of transiting materials and solutes. Biotic and biologically mediated processes tend to accentuate changes in river water chemistry initiated upstream, in each sub-basin, along river corridors, indicating that processes operating downstream prolong those from upstream(e.g., floodplains of the large tributaries). Conversely, the flood wave propagation tends to lessen the seasonal variability as a result of the water storage in the floodplains, which admixes waters of distinct origins (in time and space). The morphology of floodplains, determining the deposition and the diagenesis of the sediments as well as the variable extension of submerged areas or the chronology of floodplains storage/emptying, appears to be the main factor controlling the floodplains biogeodynamics. By coupling classical end-member mixing models (providing insight on hydrological source) with a variable regional contribution scheme, relevant information on the biogeochemical budget of the Amazonian floodplains can be achieved. (AU)

• FAPESP's process: 05/58884-5 - A large-scale synthetic model applied to the hydroclimatology and eco-geodynamics of the Amazon River basin
• Grantee: Vincent Bustillo
• Support Opportunities: Scholarships in Brazil - Post-Doctoral