Emissões de óxido nitroso em águas fluviais não poluídas e poluídas da Bacia do Rio Paquequer (Teresópolis, Rio de Janeiro) / Nitrous oxide emissions from unpolluted and polluted rivers of the Paquequer Basin (Teresópolis, Rio de Janeiro)

As concentrações de N2O dissolvido e os fluxos de N2O na interface água-ar (utilizando câmaras estáticas) foram determinados ao longo do Rio Paquequer e em alguns de seus tributários. As concentrações de N2O variaram de 0,32 a 4,7 μgN.L-1, e os fluxos de N2O, de <0,56 a 141 μgN.m- 2 .h-1 . As menores concentrações e fluxos de N2O ocorreram nas cabeceiras do Rio Paquequer e do Córrego Príncipe, e a maiores, nos trechos urbanos e no Córrego Fischer. As concentrações de N2O dissolvido e os fluxos de N2O na interface água-ar foram positivamente correlacionados com a alta variabilidade nas concentrações de NH4+. Espera-se que a taxa de emissão de N2O, em massa de N, no trecho poluído do Rio Paquequer seja maior do que o valor estimado de 0,62 kgN.dia-1, uma vez que a transferência pela purga em razão da turbulência provocada por cascatas, cachoeiras e corredeiras não foi determinada.

Dissolved N2O concentrations and water-air fluxes (using floating chambers) were measured along the Paquequer River and in some tributaries. Concentrations ranged from 0.32 to 4.7 μgN.L-1 and fluxes from <0.56 to 141 μgN.m-2.h-1. The lowest N2O concentrations and fluxes were found in the headwaters of Paquequer river and in Príncipe brook, and the highest within the urban boundaries and in Fischer brook. Dissolved N2O concentrations and water-air fluxes were positively correlated with highly variable NH4+ concentrations. Mass emission rate of N2O in the polluted stretch of Paquequer River is likely to be higher than the estimate 0.62 kgN.day-1 since transfer by turbulent degassing in falls, cascades and rapids were not determined.

Trace gas emissions from ecosystems of the Amazon basin

Tropical forests of Amazonia play a major role in controlling the composition of the earth's atmosphere. Natural ecosystems of Amazonia contribute significant portions to the global budgets of the greenhouse gases methane and nitrous oxide. Amazon forest vegetation contributes to regional atmospheric chemistry as an important source of reduced gases such as volatile organics and carbon monoxide. The forest soils produce nitric oxide. Recent trends in land use change have led to increases in the sources of nitrous oxide and methane. The ozone precursor nitric oxide is internally recycled under forest conditions while deforestation leads to larger net emissions. We have limited knowledge of biosphere-atmosphere exchange of trace gases in Amazonia. However, recent advances in instrumentation approaches and the evolution in the design of interdisciplinary field campaigns enhance the prospects for successful study of this area in earth system science.