Role of CO2 outgas from small rivers in local and regional net carbon emission in the southwestern Amazon River Basin
Rasera, Centro de Energia Nuclear na Agricultura, USP, email@example.com
Ballester, Centro de Energia Nuclear na Agricultura, USP, firstname.lastname@example.org
Krusche, Centro de Energia Nuclear na Agricultura, USP, email@example.com
Salimon, Universidade do Acre, Departamento de Ciências Naturais, firstname.lastname@example.org
Alin, 3School of Oceanography, University of Washington, Seattle, Washington, email@example.com
A recent estimate of CO2 outgassing from Amazonian wetlands suggests that an order of magnitude more CO2 leaves rivers through gas exchange than is exported to the ocean as organic or inorganic carbon. However, the contribution of smaller rivers, is still poorly understood, mainly due to limitations in mapping their exact extent. Considering that the largest portion of the Amazon River network is composed of small rivers, our objective was to elucidate their role in air-water CO2 exchange, combining estimated CO2 outgas (using the boundary layer equation) and a GIS-based methodology to calculate the surface area covered by rivers with channels less than 100 meters wide in the Ji-Paraná River Basin, Western Amazon. The estimated CO2 outgas was the main carbon export pathway for this river basin, totalizing 316 Gg C yr-1, about 2.8 times the amount of carbon exported as dissolved inorganic carbon (113 Gg C yr-1) and 1.8 times dissolved organic carbon (176 Gg C yr-1). The relationships established here between drainage area and channel width provide a new model for determining surface area of these rivers, thus making it possible to perform regional extrapolations of air-water gas exchange. Extrapolated CO2 outgas from Ji-Paraná rivers lower than 100 meters wide from small rivers to the entire Amazon basin, totalizes124.8 ± 42 Tg C yr-1, about 71 Tg yr-1 higher than previous results. These ecosystems are playing an important role in the regional carbon balance, contributing with 17% (low water) to 38% (high water) of the total Amazon basin CO2 outgassing.