Biogeochemistry of Carbon in the Amazonian Floodplains over a 2000-km Reach: Insights from a Process-Based Model

• DOI: 10.1175/2010ei338.1
• Publication Date: 2010-10-19T18:59:02Z
• Authors: Vincent Bustillo; Reynaldo Luiz Vic...; Jose Mauro Sousa ...; Daniel de Castro ...; Andre Marcondes A...; Erich Colicchio
• Keywords: Biogeochemical Cycle; Autotroph; Biogeochemistry; Total inorganic carbon

Abstract The influence of Amazonian floodplains on the hydrological, sedimentary, and biogeochemical river budget was investigated over a 2000-km reach. A process-based model relying closure chemical fluxes isotopic signals implemented. On average for whole studied reach, overall carbon associated with mineralization aquatic photosynthesis were estimated to 35.7 15.3 Tg C yr−1, respectively. Almost 57% sequestrated by comes from aerial sources (flooded forest); remaining 43% resulted (várzea grasses phytoplankton). process rates substantially fluctuate annual cycle, depending particularly extension flooded area river–floodplain connectivity. As level declines, drastic decrease turbidity lower supply substrates promote autotrophy detriment heterotrophy, leading substantial changes pH gaseous equilibria in water. main consequences are (i) side-chain oxidation dissolved organic matter concomitant rises nitrogen atomic ratio nitrate contents (ii) sorption hydrophobic humic acids, which fractionate 13C thus lead 13C-depleted particulate (fine fraction) compared matter. flow rises, heterotrophy prevails this tends attenuate signature imprinted latter. significant contribution autochthonous indicates that sustained net primary production corridors. variable submerged areas defines proportions CO2 exported released atmosphere. rate outgassing reach (18.8 yr−1) represents about 50% incoming inorganic flux. methane emission is as 2.2 yr−1 denitrification 0.87 N representing 1.5 times flux (DIN) Amazon River at station Óbidos (0.64 yr−1).