CO2 effluxes from streams and rivers have been hypothesized to be a critical pathway of
carbon flow from the biosphere back to the atmosphere. This study was conducted in three
small Amazonian catchments to evaluate carbon evasion and dynamics, where land-use change
has occurred on small family-farms. Monthly field campaigns were conducted from June 2006
to May 2007 in the Cumaru (CM), Pachibá (PB) and São João (SJ) streams. Electrical
conductivity, pH, temperature, and dissolved oxygen measurements were done in situ, while
water samples were collected to determine dissolved organic carbon (DOC) and dissolved
inorganic carbon (DIC) concentrations, as well as carbon dioxide partial pressures (pCO2) and
CO2 evasion fluxes. Instantaneous discharge measured by a current meter was used to calculate
DOC fluxes. Considering all the sites, DOC, DIC, pCO2, and CO2 flux measurements ranged
as follows, respectively: 0.27 - 12.13 mg L-1; 3.5 - 38.9 mg L-1; 2,265 - 26,974 ppm; and
3.39 - 75.35 μmol m-2 s-1. DOC annual flux estimates for CM, SJ and PB were, respectively,
281, 245, and 169 kg C ha-1. CO2 evasion fluxes had an average of 22.70 ± 1.67 μmol m-2 s-1.
These CO2 evasion fluxes per unit area were similar to those measured for major Amazonian
rivers, thus confirming our hypothesis that small streams can evade substantial quantities of
CO2. As secondary vegetation is abundant as a result of family farming management in the
region, we conclude that this vegetation can be a major driver of an abundant carbon cycle.
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