Preliminary measurements of N2O partial pressures in the Negro and Solimões Rivers, Amazon Basin, Brazil
Oliveira, USP/CENA/ESALQ, firstname.lastname@example.org
Rasera, USP/CENA, email@example.com
Cunha, CPCR - Instituto Nacional de Pesquisas da Amazônia, firstname.lastname@example.org
Souza, CPCR - Instituto Nacional de Pesquisas da Amazônia, email@example.com
Krusche, USP/CENA, firstname.lastname@example.org
The concentrations of nitrous oxide (N2O), an important component of the greenhouse effect and with long residence time in the atmosphere, have significantly increased in this century. The reasons for this atmospheric increase in N2O are still partially unexplainable. This uncertainty is worse in relation to aquatic environments. In this article we report on preliminary measurements of N2O partial pressures in the rivers of the Amazon basin. The studied area is located in the Brazilian Amazon, in the state of Amazonas. The rivers Solimões and Negro were sampled from September 2005 to April 2006. River water was collected with immersion pumps, lowered in the middle of the channel to 60% of total depth. To avoid contact with air, water was pumped into a 1 L graduated cylinder and a headspace methodology was used to equilibrate the dissolved N2O with N2. The resulting gas sample was stored in evacuated and sealed 25 mL vials. Atmospheric samples were taken from one meter above the water column and stored the same way. N2O partial pressures were determined on a Shimadzu GC-14 "Green House Analyzer". Partial pressures of N2O in Solimões and Negro river water showed little variations around an average of 0.48 ± 0.08 µatm (n=67) and 0.38 ± 0.04 µatm (n=64), respectively. The atmospheric averages were approximately 0.32 ± 0.03 µatm (n=134) in both rivers. These preliminary results indicate that partial pressures of N2O in the Amazon rivers, although probably not a major source of this gas to the atmosphere, may constitute an important part of the Nitrogen cycling in these systems.