Evaluation of Primary Production in the Lower Amazon River Based on a Dissolved Oxygen Stable Isotopic Mass Balance

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Gagne-Maynard, William C. ^[1] ; Ward, Nicholas D. ^{[1, 2, 3]} ; Keil, Richard G. ^[1] ; Sawakuchi, Henrique O. ^{[1, 4]} ; Da Cunha, Alan C. ^[5] ; Neu, Vania ^[6] ; Brito, Daimio C. ^[5] ; Less, Diani F. Da Silva ^[5] ; Diniz, Joel E. M. ^[5] ; Valerio, Aline De Matos ^[7] ; Kamper, Milton ^[7] ; Krusche, Alex V. ^[4] ; Richey, Jeffrey E. ^[1]

Afiliação do(s) autor(es)

^[1] Univ Washington, Sch Oceanog, Seattle, WA 98195 - USA

^[2] Pacific Northwest Natl Lab, Marine Sci Lab, Sequim, WA 98382 - USA

^[3] Univ Florida, Whitney Lab Marine Biosci, St Augustine, FL 32086 - USA

^[4] Univ Sao Paulo, Ctr Energia Nucl Agr, Piracicaba - Brazil

^[5] Univ Fed Amapa, Dept Meio Ambiente & Desenvolvimento, Macapa - Brazil

^[6] Univ Fed Rural Amazonia, Inst Socio Ambiental & Recursos Hidr, Belem, Para - Brazil

^[7] Inst Nacl Pesquisas Espaciais, Dept Sensoriamento Remoto, Sao Jose Dos Campos - Brazil

• Tipo de documento: Artigo Científico
• Fonte: FRONTIERS IN MARINE SCIENCE; v. 4, 2017.
• Citações Web of Science: 5

Resumo

The Amazon River outgasses nearly an equivalent amount of CO2 as the rainforest sequesters on an annual basis due to microbial decomposition of terrigenous and aquatic organic matter. Most research performed in the Amazon has been focused on unraveling the mechanisms driving CO2 production since the recognition of a persistent state of CO2 supersaturation. However, although the river system is clearly net heterotrophic, the interplay between primary production and respiration is an essential aspect to understanding the overall metabolism of the ecosystem and potential transfer of energy up trophic levels. For example, an efficient ecosystem is capable of both decomposing high amounts of organic matter at lower trophic levels, driving CO2 emissions, and accumulating energy/biomass in higher trophic levels, stimulating fisheries production. Early studies found minimal evidence for primary production in the Amazon River mainstem and it has since been assumed that photosynthesis is strongly limited by low light penetration attributed to the high sediment load. Here, we test this assumption by measuring the stable isotopic composition of O-2 (delta O-18-O-2) and O-2 saturation levels in the lower Amazon River from Obidos to the river mouth and its major tributaries, the Xingu and Tapajos rivers, during high and low water periods. An oxygen mass balance model was developed to estimate the input of photosynthetic oxygen in the discrete reach from Obidos to Almeirim, midway to the river mouth. Based on the oxygen mass balance we estimate that primary production occurred at a rate of 0.39 +/- 0.24 g O m(3) d(-1) at high water and 1.02 +/- 0.55 g O m(3) d(-1) at low water. This translates to 41 +/- 24% of the rate of O-2 drawdown via respiration during high water and 67 +/- 33% during low water. These primary production rates are 2-7 times higher than past estimates for the Amazon River mainstem. It is possible that at high water much of this productivity signal is the result of legacy advection from floodplains, whereas limited floodplain connectivity during low water implies that most of this signal is the result of in situ primary production in the Amazon River mainstem. (AU)

• Processo FAPESP: 08/58089-9 - The role of rivers on the regional carbon cycle
• Beneficiário: Maria Victoria Ramos Ballester
• Modalidade de apoio: Auxílio à Pesquisa - Programa de Pesquisa sobre Mudanças Climáticas Globais - Temático