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SEASONAL SOIL FLUXES OF CARBON MONOXIDE IN BURNED AND UNBURNED BRAZILIAN SAVANNAS
Kisselle, K., R G. Zepp, R A. Burke Jr., S. P. Opsahl, A. Pinto, M. Bustamante, L. Viana, AND R. Varella. SEASONAL SOIL FLUXES OF CARBON MONOXIDE IN BURNED AND UNBURNED BRAZILIAN SAVANNAS. JOURNAL OF GEOPHYSICAL RESEARCH 107(D20):8051-8051, (2002).
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.
Soil-atmosphere fluxes of carbon monoxide (CO) were measured from September 1999 through November 2000 in savanna areas in central Brazil (Cerrado) under different fire regimes using transparent and opaque static chambers. Studies focused on two vegetation types, cerrado stricto sensu (20-50% canopy cover) and campo sujo (open, scrubland), which were either burned every 2 years or protected from fire (for 26 years). CO emissions in transparent chambers varied seasonally with highest fluxes during the late dry season (August-October) and lowest fluxes late in the wet season (February-April). Daytime fluxes in the transparent chambers were always higher than in the opaque chambers. Similarly, a diurnal study showed negative fluxes for all nighttime measurements and positive measurements for all daytime measurements. No significant differences were found between the daytime annual average fluxes from unburned cerrado and unburned campo sujo (160 x 109 molec. cm-2 s-1 and 190 x 109 molec. cm-2 s-1, respectively). Fire increased soil surface CO emissions significantly in the burned cerrado plot. Thirty days after the fire, daytime CO production was over 10 times higher than that of the unburned cerrado (812.8 x 109 molecules cm-2 s-1 vs. 76.8 x 109 molecules cm-2 s-1). The increase in CO production occurred in both transparent and opaque chambers, suggesting the fire created photochemically- and thermally-reactive precursors. Removal of litter and standing dead plant material from plots in unburned campo sujo and a pasture was shown to dramatically decrease CO emissions. CO production in burned plots (using opaque chambers) was similar to previous measurements from Venezuelan and African savannas.