The influences of total dissolved inorganic carbon (DIC) concentrations and pH on potential outgassing from rivers in Rondônia.
Maria de Fátima
Fernandes Lamy
Rasera, CENA / USP, mrasera@cena.usp.br
(Presenting)
Alex
Vladimir
Krusche, CENA / USP, alex@cena.usp.br
Nei
Kavaguichi
Leite, ESALQ / USP, nkleite@esalq.usp.br
Recent studies point to the importance of CO2 outgassing from rivers of the Amazon, suggesting that a significant part of the carbon fixed by forests return to the atmosphere through this pathway. Gas exchange between the atmosphere and supersaturated waters is a function of gaseous gradients across the air-water interface. Water pCO2 is strongly determined by the concentrations of dissolved inorganic carbon (DIC) and pH, which, in turn, are a function of physical, chemical and biological processes. This study focus on the influence of DIC concentrations and the pH on potential CO2 outgassing to atmosphere, using as study area the basin of Ji-Paraná river, Rondônia. Several rivers of the basin were sampled nine times between May/99 and April/02. DIC concentrations were analyzed with a non-dispersive infra-red detector, in a Shimadzu TOC500A analyzer. Temperature, pH and DIC concentrations were used do calculate pCO2, based on equilibrium equations. A theoretical diffusive flux model was used to estimate CO2 evasion. The results show that rivers draining areas with more fertile soils present larger concentrations of DIC and of potential CO2 evasion, although with significant seasonality. During high waters, even with lower DIC concentrations, the parallel decrease in pH is of a magnitude enough to promote higher potential evasions.
Key-words: Carbon dioxide, dissolved inorganic carbon, pH, Amazonian rivers.