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SOIL FLUXES OF CO2, CO, NO AND N2O FROM AN OLD-PASTURE AND FROM NATIVE SAVANNA IN BRAZIL
Varella, R., M. Bustamante, A. Pinto, K. Kisselle, R. Santos, R A. Burke Jr., R G. Zepp, AND L. Viana. SOIL FLUXES OF CO2, CO, NO AND N2O FROM AN OLD-PASTURE AND FROM NATIVE SAVANNA IN BRAZIL. ECOLOGICAL APPLICATIONS 14(4 Supplement):S221-S231, (2004).
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.
We compared fluxes of CO2, CO, NO and N2O, soil microbial biomass, and N-mineralization rates in a 20-year old Brachiaria pasture and a native cerrado area (savanna in Central Brazil). In order to assess the spatial variability of CO2 fluxes, we tested the relation between electrical resistivity and soil CO2 emissions. Although the N-mineralization rates in the pasture were low, net N-immobilization was only observed in the dry season. The conversion of the cerrado to pasture decreased the N-inorganic availability and NO fluxes were lower in the pasture than in the cerrado. N2O fluxes were below detection limit at both sites. The CO fluxes showed weak seasonal variation with slightly higher positive fluxes in the dry season and lower fluxes, including net consumption, during the wet season. The cerrado CO fluxes were higher and more variable than the fluxes in the pasture. Both sites showed a seasonal pattern with lower CO2 fluxes (approximately 2 umol CO2m-2s-1) during the dry season. Considering all the wet season, there was not significant differences between the CO2 soil emissions from the cerrado and from the pasture but the temporal trend of the flux differed in the two systems with higher fluxes in the pasture in the transition from wet to the dry season. The electrical resistivity map showed a region of high resistivity on the southeast border of the pasture, and a narrow band of low electrical resistivity oriented east to west on the north side. The existence of the anomalous region of low electrical resistivity, was detected by the technique independently of the season. The low electrical resistivity region showed significantly greater average soil CO2 emissions than the high resistivity region during the wet season. The correlation between soil electrical resistivity and CO2 soil emissions provide evidence that mineralogical variations may exert significant control on CO2 emissions. Moreover, soil electrical resistivity can be used as an efficient tool to determine spatial variability in CO2 emissions.