Tracing the Iron-Carbon interactions in the Amazonian black River headwaters – TICAR

The response of tropical wetlands to climate change in terms of carbon storage remains highly uncertain, in particular because the mineralization of organic matter as a function of bacterial activity and the reduction of iron over time is still debated. The objective of this project is therefore to better understand the coupled dynamics of organic matter, iron oxyhydroxides and water in these wetlands and the black water rivers they feed. Based on existing experimental and theoretical studies, our objective is to quantify, through a several years monitoring, the relative share of the different processes proposed for the transformations and transfers by (sub)surface waters of carbon and iron from these wetlands. We will notably combine for the first time long term observations on hydrochemistry, the stable isotopes Fe-C-O-H for the tracing of sources and dominant reactions, the study of organo-metallic speciations and the search for functional genes in the field. We thus expect to show, among the possible mechanisms identified during laboratory experiments, those which really play an important role for the balances of these elements. This knowledge, acquired in the context of the Rio Negro basin in Brazil (SO HyBam) which remains relatively untouched by human activity, will help reduce the uncertainties of climate change modeling mentioned in the 2019 IPCC report on Climate Change and Land. It will also provide a baseline to better highlight the effect of other major anthropogenic disturbances in Amazonia, such as deforestation.