Abstract
Abstract. Nitrous oxide (N2O) is the third most important anthropogenic greenhouse gas. Globally, the main sources of N2O are nitrification and denitrification in soils. About two thirds of the soil emissions occur in the tropics and approximately 20% originate in wet rainforest ecosystems, like the Amazon forest. The work presented here involves aircraft vertical profiles of N2O from the surface to 4 km over two sites in the Eastern and Central Amazon: Tapajós National Forest (SAN) and Cuieiras Biologic Reserve (MAN), and the estimation of N2O fluxes for regions upwind of these sites. To our knowledge, these regional scale N2O measurements in Amazonia are unique and represent a new approach to looking regional scale emissions. The fluxes upwind of MAN exhibited little seasonality, and the annual mean was 2.1±1.0 mg N2O m−2 day−1, higher than that for fluxes upwind of SAN, which averaged 1.5±1.6 mg N2O m−2 day−1. The higher rainfall around the MAN site could explain the higher N2O emissions, as a result of increased soil moisture accelerating microbial nitrification and denitrification processes. For fluxes from the coast to SAN seasonality is present for all years, with high fluxes in the months of March through May, and in November through December. The first peak of N2O flux is strongly associated with the wet season. The second peak of high N2O flux recorded at SAN occurs during the dry season and can not be easily explained. However, about half of the dry season profiles exhibit significant correlations with CO, indicating a larger than expected source of N2O from biomass burning. The average CO:N2O ratio for all profiles sampled during the dry season is 94±77 mol CO:mol N2O and suggests a larger biomass burning contribution to the global N2O budget than previously reported.
Highlights
Nitrous oxide (N2O) is the third most important anthropogenic greenhouse gas with a global warming potential about 310 times higher than CO2 over a 100-year timehorizon
The main reason is the increase in anthropogenic sources, like land use (Nfertilization) and industry, and current estimates are that about 40% of total N2O emissions are anthropogenic (IPCC, 2007)
Air entering the Amazon basin is dominated by trade-wind easterlies coming from the tropical Atlantic Ocean, with relative influence of Northern and Southern Hemisphere air which depends upon the seasonally varying latitude of the Inter-Tropical Convergence Zone (ITCZ)
Summary
Nitrous oxide (N2O) is the third most important anthropogenic greenhouse gas with a global warming potential about 310 times higher than CO2 over a 100-year timehorizon. Its atmospheric lifetime is estimated to be 120 years (Schindlbacher, et al, 2004; IPCC, 2007). The average annual growth rate from 1999 to 2000 was 0.85±1.1 ppb yr−1 (IPCC, 2007) and 0.73±0.06 ppb yr−1 from 1988–2005 (Hirsch, et al, 2006). The main reason is the increase in anthropogenic sources, like land use (Nfertilization) and industry, and current estimates are that about 40% of total N2O emissions are anthropogenic (IPCC, 2007). The IPCC Fourth Assessment report (AR4) estimates 60% of total N2O anthropogenic contribution (6.7 Tg N yr−1) is from agricultural soils (1.7 to 4.8 Tg N yr−1). Others authors have published that direct N2O emissions from agricultural soils contribute about 77% of total anthropogenic contribution, with 6.2 Tg N yr−1
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