Physical and Anthropogenic Controls of the Biogeochemistry of the Ji-Paraná River Basin (Western Amazônia)
Victoria
R.
Ballester, CENA-USP, vicky@cena.usp.br
(Presenting)
Alex
V.
Krusche, CENA-USP, alex@cena.usp.br
Nei
Leite
Kavaguishi, CENA-USP, nkleite@esalq.usp.br
Beatriz
Machado
Gomes, UNIR, gomes@unir.br
Daniel
de Castro
Victoria, CENA-USP, dvictori@cena.usp.br
Alexandra
Ayres
Montebelo, CENA-USP, nandaymo@bol.com.br
Christopher
Neill, Marine Biological Laboratory, cneill@mbl.edu
Linda
Deegan, Marine Biological Laboratory, ldeegan@mbl.edu
Jeffrey
E.
Richey, University of Washington, jrichey@u.washington.edu
Reynaldo
Luiz
Victória, CENA-USP, reyna@cena.usp.br
Several LBA studies have shown that forest clearing in the Amazon can alter the transport of sediments, organic matter and associated nutrients to the rivers. In this study, we present the results of an integrated analysis of physical and anthropogenic controls of river biogeochemistry at the Ji-Paraná basin (RO). Previous results obtained by our group demostrated that both soil properties and pasture cover are the main drivers of river characteristics and metabolism. To quantify the effects of these two drivers, we performed a multiple linear regression analysis, relating basin characteristics (derived from a GIS analysis) and river biogeochemistry at 38 sites along the Ji-Paraná river basin, during wet and dry seasons. Each site represents a different mixture of cover type and soil properties. Effective cation exchange capacity (ECEC) and percentage of pastures were treated as independent variables. River water electrical conductivity (EC) and Na+, Ca2+, Mg2+, K+, Cl- , DOC, TSS, DIC and PO43- concentrations were the dependent variables. Spatially, higher values of all ions were associated with areas dominated by pasture, with the highest concentrations found in the central part of the basin, where pasture areas and soil fertility are at a maximum. As the river enters the lower reaches, forests dominate the landscape, and the concentrations drop. The percentage of the basin area covered by pasture was consistently the best predictor for all parameters during the wet season. Higher DOC concentrations were related to higher values of TSS which, in turn, were originated in pasture areas. During the dry season this pattern was not observed. Our preliminary analysis, relating river biogeochemistry with potential soil erotion in the basin shows that areas covered by pasture are associated with higher concentrations of both DOC and TSS, a pattern also found for other parameters.
Submetido por Maria Victoria Ramos Ballester em 18-MAR-2004
Tema Científico do LBA: SH (Hidrologia e Química das Águas)