Organic matter supply, degradation and transport on flooded areas in the lower Amazon River: implications for reconstitution of Quaternary environmental changes and regional carbon balance

• Grant number: 20/09631-7
• Support Opportunities: Scholarships in Brazil - Doctorate
• Start date: December 01, 2021
• End date: April 30, 2024
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: André Oliveira Sawakuchi
• Grantee: Kleiton Rabelo de Araújo
• Host Institution: Instituto de Geociências (IGC). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 18/18491-4 - Biogeochemical blindspots along the lower Amazon River continuum: from land to the atmosphere and ocean, AP.SPEC
• Associated scholarship(s): 22/14193-4 - Tidal influence on methane (CH4) and carbon dioxide (CO2) fluxes in the lower Amazon River, BE.EP.DR

Abstract

The Amazon River is responsible for approximately 20% of the freshwater discharge into ocean and is also recognized as an important source of terrigenous sediments to the Atlantic ocean and carbon to the atmosphere as carbon dioxide (CO2) and methane (CH4). Terrestrial or aquatic organic materials are continuously transported, processed and deposited along the Amazon River continuum, whose degradation generates and emit both CO2 and CH4 to the atmosphere. In this way, a large amount of the organic sediments that reaches the Amazon River is degraded on inland waters. However, the remaining fraction is mainly composed of refractory organic material, which is carried to the ocean. The downstream course of the Amazon River is characterized by a complex network of fluvial and tidal channels surrounded by flooded forests. This drainage network connects continental environments and their sediments to the equatorial Atlantic Ocean. In the lower Amazon River, extensive flooded forest areas are subject to seasonal and daily flooding due to the influence of the South American Monsoon System and tides, respectively. In this way, this area also represents an important source of particulate and dissolved carbon. Amazonian flooded and aquatic environments have high efficiency for organic material degradation, with CH4 generation in flooded soils and sediments exposed to anoxic conditions and/or CO2 generation in the water column. The relationship between hydrological changes and biogeochemical processes in the lower Amazon River region is a critical factor determining the transference of particulate organic matter to the ocean and sources and potential production of CO2 and CH4 source, both action as relevant components to the carbon balance on a regional and global scale. However, the processes involved in organic matter generation and degradation within the lower Amazon River remain poorly characterized so far, especially with regard to the sources of organic matter and influence of hydrological conditions on biodegradation processes. Therefore, the objectives of this study include determining the sources of organic matter in the lower Amazon River and quantifying Dissolved Organic Carbon (DOC), Dissolved Inorganic Carbon (DIC), CO2 and CH4 in waters draining flooded forest areas, small channels and the Amazon River main channel as well as the CO2 and CH4 emissions from waters to atmosphere. This goal will integrate the ""Pontos cegos biogeoquímicos ao longo do continuum do baixo Rio Amazonas: da terra para a atmosfera e oceano"", process 2018/18491-4"" project. In addition, understanding the particulate organic carbon origin and changes before transference to the ocean is essential to calibrate paleoenvironmental conditions indicators applied to organic components of sediments retrieved under the Trans-Amazon Drilling Project (FAPESP 2018/23899-2), which aims with the past Amazon environments during the Quaternary and beyond. (AU)