Abstract:
We constructed a whole carbon budget for a catchment in the Western Amazon Basin, combining
drainage water analyses with eddy covariance (EC) measured terrestrial CO2 fluxes. As fluvial C export can
represent permanent C export it must be included in assessments of whole site C balance, but it is rarely done. The
footprint area of the flux tower is drained by two small streams (~5–7 km2
) from which we measured the dissolved
inorganic carbon (DIC), dissolved organic carbon (DOC), particulate organic carbon (POC) export, and CO2 efflux.
The EC measurements showed the site C balance to be +0.7 9.7 Mg C ha 1 yr 1 (a source to the
atmosphere) and fluvial export was 0.3 0.04 Mg C ha 1 yr 1
. Of the total fluvial loss 34% was DIC, 37% DOC,
and 29% POC. The wet season was most important for fluvial C export. There was a large uncertainty
associated with the EC results and with previous biomass plot studies ( 0.5 4.1 Mg C ha 1 yr 1
); hence, it
cannot be concluded with certainty whether the site is C sink or source. The fluvial export corresponds to
only 3–7% of the uncertainty related to the site C balance; thus, other factors need to be considered to reduce
the uncertainty and refine the estimated C balance. However, stream C export is significant, especially for
almost neutral sites where fluvial loss may determine the direction of the site C balance. The fate of C
downstream then dictates the overall climate impact of fluvial export.