HR: 10:50h
AN: B42A-03    [Abstracts]
TI: $^{14}$C and $^{13}$C Constraints on CO$_{2}$ Cycling in Pristine and Deforested Lowland Amazonian Rivers
AU: * Mayorga, E
EM: emiliom@u.washington.edu
AF: University of Washington, School of Oceanography Box 355351, Seattle, WA 98195-5351 United States
AU: Aufdenkampe, A K
EM: aufdenkampe@stroudcenter.org
AF: Stroud Water Research Center, 970 Spencer Road, Avondale, PA 19311 United States
AU: Krusche, A V
EM: alex@cena.usp.br
AF: Centro de Energia Nuclear na Agricultura, Caixa Postal 96, Piracicaba, SP 13416-000 Brazil
AU: Masiello, C A
EM: masiello@gps.caltech.edu
AF: Rice University, Department of Earth Science 6100 Main St, Houston, TX 77005 United States
AU: Quay, P D
EM: pdquay@u.washington.edu
AF: University of Washington, School of Oceanography Box 355351, Seattle, WA 98195-5351 United States
AU: Richey, J E
EM: jrichey@u.washington.edu
AF: University of Washington, School of Oceanography Box 355351, Seattle, WA 98195-5351 United States
AB: "Lowland" rivers in the Amazon are those that, unlike the Amazon mainstem, do not drain the Andean cordillera and are not directly influenced by sediments recently eroded from the Andes. The Brazilian Amazon is predominantly drained by lowland watersheds. We examined the sources and fate of CO2 and Dissolved Inorganic Carbon (DIC) in a range of small to large lowland rivers across the region. In particular, we focused on the Ji-Parana basin, which spans the deforestation arc in the state of Rondonia. Carbonate weathering appears to be a strong source of DIC in the western lowland basins (Jurua and Purus); however, carbonate-derived DIC in these systems is completely flushed out downstream through outgassing and mixing with contemporary respiratory CO2 inputs and carbonate-free tributaries. DIC exported from carbonate-free lowland soils appers to be predominantly contemporary, but some regions in the Ji-Parana headwaters export CO2 with a mean age of several decades. In that system, replacement of C3 forests with C4 pastures appears to exert a strong influence on riverine carbon cycling from small to large rivers. Inputs from riparian grasses may play a disproportionately important role. Finally, we found tentative evidence that anoxic conditions in wetlands may result in mineralization of previously protected, aged organic matter, leading to significant aging in riverine DIC.
DE: 9360 South America
DE: 1806 Chemistry of fresh water
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting