HR: 09:00h
AN: B31B-05 INVITED     [PDF]
TI: Land Use Change Effects on Nitrous Oxide Emissions in Tropical Regions
AU: * Keller, M
EM: michael.keller@unh.edu
AF: International Institute of Tropical Forestry, Jardin Botanico Sur 1201 Calle Ceiba, San Juan, PR 00926-1119 United States
AB: Soil emissions of nitrous oxide (N$_{2}$O) are the single most important natural source for this gas and also the single largest anthropogenic contribution to the global budget of N$_{2}$O. The availability of oxygen, inorganic nitrogen, and organic carbon are the three principle limitations to soil emissions of N$_{2}$O. These limitations play the same roles in soils globally, so there is nothing intrinsically different about processes in the tropical regions versus the temperate and boreal zones. However, the tropical regions are a far more important natural source of soil derived N$_{2}$O and will increase greatly in importance for anthropogenic emissions in the future. Both the area dedicated to agriculture and the quantity of nitrogenous fertilizer applied are relatively stable in the temperate zone while they are increasing rapidly in the tropical zone. When considering N$_{2}$O emissions, there are two important eco-regions in the tropics, savannas and forests. In both of these regions, natural ecosystems are being converted to pasture lands and to intensive agriculture. N$_{2}$O emissions from natural savannas are minimal. Conversion to pasture and to agriculture has limited effects. In savanna systems the natural limitation of nitrogen and the abundance of oxygen combine to minimize N$_{2}$O emissions from soils. In the forested regions, the situation is different. Tropical forests, particularly in humid areas, are nitrogen rich. Conversion of forests to pastures may lead to a brief pulse (from a few months to a decade) of elevated nitrous oxide emissions. Unless pastures are fertilized, their emissions are generally far below native forest emissions of N$_{2}$O. Where N fertilizer use is heavy, conversion of forests (or pastures) to agriculture may lead to significant increases in N$_{2}$O emissions. But under extensive management or careful intensive management, it is possible for agricultural systems in the humid tropics to have lower N$_{2}$O emissions than native ecosystems.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0315 Biosphere/atmosphere interactions
DE: 0330 Geochemical cycles
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2003 Fall Meeting