Isotopic Constraints on Organic and Inorganic Carbon Cycling in the Amazon River System
Emilio
Mayorga, University of Washington, emiliom@u.washington.edu
Anthony
K
Aufdenkampe, Stroud Water Research Center, aufdenkampe@stroudcenter.org
(Presenting)
Alex
V
Krusche, CENA-USP, alex@cena.usp.br
Caroline
A
Masiello, California Institute of Technology, masiello@gps.caltech.edu
Paul
D
Quay, University of Washington, pdquay@u.washington.edu
Jeffrey
E.
Richey, University of Washington, jrichey@u.washington.edu
We analyzed the 14C and 13C isotopic composition of dissolved inorganic carbon (DIC) and organic carbon (OC) size fractions in Amazonian rivers ranging from mountain and lowland streams to the mainstem. Associated measurements include DIC, POC and DOC, organic geochemical tracers, and major ions. Carbonate weathering is a dominant or significant source of DIC in many rivers draining the Andes and headwaters of the Jurua and Purus in the central-western Amazon; because of this confounding influence, assessment of biotic controls on DIC cycling requires consideration of weathering regimes. In the majority of mid to large lowland river systems that are not influenced by carbonate weathering, DIC is very young, and its associated CO2 is 13C-enriched compared to bulk OC or its primary size fractions. Bulk OC is unlikely to be the main source of this DIC; a small, labile OC fraction appears to dominate respiration. Nevertheless, old POC is stored and respired throughout the basin; Andean POC is ultimately replaced by lowland-derived OC. However, respiration of old OC is generally not a dominant source of DIC, except in lowland peat wetlands. In small lowland rivers, lateral transport of aged soil CO2 is a significant source of DIC; this terrestrial DIC is evaded downstream. We will present estimates of the isotopic signature of CO2 evading from central Amazon lowland rivers and discuss implications for regional carbon budgets.
Submetido por Emilio Mayorga em 18-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)