Impact of a phytoplanktonic bloom on the trace concentrations of amazonian floodplain lakes (Lago de Curuaï, Para, Brazil)
Barroux
Gwénael, Université Paul Sabatier, TOULOUSE Franca, barroux@lmtg.ups-tlse.fr
Viers
Jérome, Université Paul Sabatier TOULOUSE Franca, viers@lmtg.ups-tlse.fr
Seyler
T
Patrick, IRD, Franca, pseyler@lmtg.ups-tlse.fr
(Presenting)
Maria de Socorro
Rodrigues
Ibanez, Universidade de Brasilia, mrodrigues@unb.br
The Amazon river is one of the most important source of fresh water to the Ocean (~15% of the word fresh water discharge) and contribute significantly to the chemical fluxes to the global ocean. The most part of the Amazon basin is characterised by an extremely low declivity (1 cm/km), and an extended floodplain, which is controlling the liquid and solid transfers to the Ocean trough the storage of large volume of waters during the floods and strong sedimentation processes. These wetland areas constituted by a complex networks of thousands of lakes, named várzeas, extend over more than 300 000 km² [1 ; 3] and represent one of the most productive ecosystems of the world due to the regular enrichment in nutrients by the river waters. These roles set the “várzeas” as key areas to understand the whole transfer process through the Amason basin.. In order to understand which biochemical processes control the concentration and fate of chemical elements inside this ecosystem, an extended scientific survey was conducted in the Curuaï floodplain area (56°1’W, 55°W ; 1°9’S, 2°3’S, Para State, Brazil). With an extention about 1900 km² at the high water level, the Curuai floodplain lakes system is representative of the Amazon basin.
As the Amazon water is stored in this floodplain, the particular conditions induced by the river regime associated with the high vegetation productivity, generates in turn various transformation and degradation processes of the elements present in the river water [2]. One of these process is due to the occurrence of phytoplanktonic blooms. Using a multielement analysis approach in a first step, we present the main biochemical features affecting both major and trace elements during a bloom period. Speciation calculations using MINTEQ code were then used to model the observed results.
A first approach on our results show depletion in dissolved phase for Mn, Y, REE and Th and excess in dissolved phase for Cr, As, Cs and Pb. Thess results might be confirmed by further research.
References
[1] Junk W.J.(Ed.) (1997) The Central Amazon Floodplain Springer Verlag, Ecological studies 126.
[2] Seyler P. and Boaventura G. R. (1998) In The biogeochemistry of the Amazon Basin and its Role in a Changing World. McClain M., Victoria R.L. & Richey J.E.(eds.) Oxford Univ. Press.
[3] Sippel S.J., Hamilton S.K., Melack J.M., and Choudhury B.J. (1994) REMOTE SENS ENVIRON 48, 70-76.
Submetido por Patrick Thierry Seyler em 17-MAR-2004
Tema Científico do LBA: SH (Hidrologia e Química das Águas)