How the Amazonian floodplain vegetation can affect the geochemical status of some trace elements in the Amazon River mainstream (Brazil)?
Viers
Jérome, LMTG IRD, viers@lmtg.ups-tlse.fr
Pinelli
Marcello, Universidade de Brasilia, mpinelli@unb.br
Barroux
Gwénael, LMTG Universite Paul Sabatier, Toulouse França, barroux@lmtg.ups-tlse.fr
Boaventura
R
Geraldo, Universidade de Brasilia, grbunb@unb.br
Seyler
T
Patrick, LMTG IRD, pseyler@lmtg.ups-tlse.fr
(Presenting)
The purpose of the present paper is an attempt to forecast the role of floodplains in the transfer of trace elements by the Amazon River mainstream. The Central Amazon wetland areas constituted by a complex network of lakes, named várzeas, extend over more than 300,000 km2 (Junk, 1985) and represent one of the most productive ecosystems in the world due to the regular enrichment in nutrients by the river waters. The concentration of some trace elements (i.e., Al, Mn, Fe, Co, Cu, Mo, Rb, Sr, Ba, and U) have been measured in the Amazon River water (Manacapuru Station, Amazonas state, Brazil) and in some lake waters and plants (leaves) of a várzea (Ihla de Marchantaria, Manaus, Brazil) at different periods of the hydrological cycle. Four representative plant species (two perennial species: Pseudobombax munguba and Salix humboldtiana, and two annual herbaceous plants: Echinochloa polystachya and Eichhornia crassipes) were selected according to the ecological functioning of the site.
Time series obtained for some elements (e.g., Mn, Cu) in the dissolved phase (i.e., <0.20 µm) of the Amazon River water could not be only explained by tributaries (rivers) contribution or instream processes. The contribution of the waters transiting each year through the floodplains should be considered. The results enlighten the fact that chemistry of the waters draining these floodplains is controlled by reactions occurring at the interfaces between the sediments and waters (large variation of redox conditions) and between plants and waters. Trace elements concentrations in the plants (leaves) vary strongly according to the hydrological season. Based on these concentrations data and the biological productivity of these environments a first order calculation was done in order to estimate the amount of elements that can be stored (permanently or temporarily) in the vegetation of these floodplains. These elemental fluxes are not negligible when they are compared with those exported by the dissolved phase of the Amazon River water.
Submetido por Patrick Thierry Seyler em 18-MAR-2004
Tema Científico do LBA: SH (Hidrologia e Química das Águas)