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SOIL EMISSIONS OF N2O, NO AND CO2 IN BRAZILIAN SAVANNAS: EFFECTS OF VEGETATION TYPE, SEASONALITY, AND PRESCRIBED FIRES
Citation:
Pinto, A., M. Bustamante, L. Viana, R. Varella, R G. Zepp, R A. Burke Jr., M Molina, AND K. Kisselle. SOIL EMISSIONS OF N2O, NO AND CO2 IN BRAZILIAN SAVANNAS: EFFECTS OF VEGETATION TYPE, SEASONALITY, AND PRESCRIBED FIRES. JOURNAL OF GEOPHYSICAL RESEARCH 107(D20):8089-8089, (2002).
Impact/Purpose:
The overall objective of this task is to develop quantitative relationships for assessing the vulnerability of aquatic resources to global change. The task will contribute experimental and modeling tools for assessments of the interactions of global climate and UV changes with coral reefs and selected watersheds and estuaries in the U.S. These activities are contributing primarily to two APGs in the ecosystems component of the Global Change Research Multiyear Plan: the 2006 APG (APG 3) on building the capacity to assess global change impacts on coastal aquatic ecosystems, including coral reefs and estuaries and the 2004 APG (APG 2) on building capacity to assess and respond to global change impacts on selected watersheds. One major task objective is to assess interactions of global warming and UV exposure that are contributing to the observed coral bleaching and disease. Our lab is working with scientists at the NHEERL Gulf Ecology Lab to characterize UV exposure and effects at several coral reef sites. Other research in this task is examining the interactions between UV-induced breakdown of refractory organic matter in estuaries and coastal areas that enhance UV penetration into the water and concurrently form biologically-labile nitrogen-, phosphorus- and carbon-containing substances that stimulate productivity and microbial activity. This task also involves research in central Brazil that is part of the Large Scale Biosphere Atmosphere Experiment (LBA). The objectives of this project are to assess the impacts of land use and climatic changes on soil nutrient cycles and microbiota, trace gas exchange and water quality in the Brazilian cerrado. This work involves a close collaboration between EPA and a group of scientists from the Department of Ecology, University of Brasilia, Brazil. Other objectives of this task are to assess the interactions of land use and climate changes with the ecological functioning of streams in watersheds of the Piedmont region of the southestern U.S.
Description:
Using closed chamber techniques, soil fluxes of NO, N20 and C02 were measured from September 1999 through October 2000 in savanna areas in central Brazil (Cerrado) subjected to prescribed fires. Our studies focused on two vegetation types, cerrado stricto sensu (20-50% canopy cover) and campo sujo (open, grass-dominated), which were either burned every 2 years or protected from fire. Soil moisture and vegetation type were more important in controlling NO and C02 fluxes than fire regime. N20 flux, however, could not be detected in any of the vegetation-fire treatments. NO emissions increased slightly after burning (1 .0 NO-N CM-2 h-1), but quickly returned to levels equal to or slightly lower than pre-fire fluxes. In comparison, NO emissions increased 100-fold (to 10.5 ng NO-N cm-2 h-1) during a water addition experiment in unburned campo sujo and to 1.0 ng NO-N cm-2 h-1 with the first rains in unburned cerrado and to 1.9 ng NO-N cm-2 h-1 in burned cerrado. Although NO flux did not correlate with N availability, low NO and N20 emissions, low nitrification rates, and the majority of inorganic N in the form of NH4+ all indicate a conservative N cycle in the Cerrado. C02 fluxes increased significantly with the onset of rain and during a water addition experiment. The highest CO2 measured in wet season was 6.3 mol C02 m-2 s-1 in burned campo sujo. During the dry season, there were no differences between burned and unburned treatments (average flux (1.6 - 2.3 mol C02 m-2 S-1. Differences between fire treatments of cerrado and campo sujo fluxes are attributed to differences in relative litter production and root activity.