Riparian control of carbon dynamics in streams of Rondônia
Alex
Krusche, CENA-USP, alex@cena.usp.br
(Presenting)
Maria
Victoria
Ballester, CENA-USP, vicky@cena.usp.br
Reynaldo
Luiz
Victória, CENA-USP, reyna@cena.usp.br
Linda
Deegan, MBL, ldeegan@mbl.edu
Christopher
Neill, MBL, cneill@mbl.edu
We sampled two paired watersheds in the Western Amazon (Fazenda Nova Vida, Ariquemes, RO) for carbon fractions (coarse and fine particulate and dissolved) at various stages of the hydrograph between years 1998 and 2000. At each watershed, one of the streams drained forest, and the other pastures established 20 years ago. Also, in one of these watersheds, we followed the distribution of C fractions along its course from first to fourth order reaches. We found a significant increase in both dissolved and particulate C at the pasture streams, which was related to the invasion of its waters by naturally growing Paspallum grass. This increase in C availability resulted in important shifts in aquatic metabolism, from oxic conditions in the forests to quasi-anoxic in the pastures. The isotopic composition of riverine C fractions provided evidence of the presence of this grass-derived organic matter in transport. However, along its course from first to fourth order reaches, at one of these paired watersheds, this “signal” of forests to pasture conversion in C dynamics was not evident. Although at the higher reaches streams drained mostly pastures, riverine C resembled that of the forest reaches. Our findings show that, for these streams of the Amazon, in-channel processes and riparian structure are more important than those predominating at the watershed, thus challenging, at least partially, the concept that rivers integrate the processes occuring at their basins.
Submetido por Alex Krusche em 18-MAR-2004
Tema Científico do LBA: SH (Hidrologia e Química das Águas)