In addition to the tracks of destruction in the forest, the fires in the Amazon leave traces in the Amazon River and its tributaries. Incomplete burning of tree wood results in the production of a type of carbon - known as black carbon - that reaches Amazonian waters in the forms of charcoal and soot and is transported to the Atlantic Ocean as dissolved organic carbon.
An international group of researchers quantified and characterized, for the first time, the black carbon that flows through the Amazon River. The results of the study, published in Nature Communications magazine, showed that most of the material transferred to the ocean is "young," suggesting that it was produced by recent forest fires.
"We found through radiometric dating analysis [a method that uses the radioisotope of natural carbon-14 occurrence to determine the age of carbonaceous materials up to about 60,000 years] and molecular composition that the largest proportion of the black carbon we found in the Amazon was produced in recent years by burning trees," said Jeffrey Edward Richey, professor at the University of Washington, United States, and one of the authors of the study.
A visiting researcher at the Center for Nuclear Energy in Agriculture at the University of São Paulo (Cena-USP), Richey has conducted in the past five years a project supported by FAPESP in the São Paulo Excellence Chair (SPEC) modality, with the aim of clarifying the role of the Amazon basin in the global carbon cycle.
During the project, the researchers collected samples of dissolved black carbon in the main channel of the Amazon River and in four tributaries - the rivers Negro, Madeira, Trombetas and Tapajós - in November 2015, during one of the driest seasons in the region.
This period was chosen for the study because the water flow was low and the connectivity of the Amazon River to its floodplain was limited. "This allowed us to obtain samples of only permanent water and more accurately identify the sources of black carbon in the watershed," said Richey.
The concentration and content of carbon-14 in the samples were measured by molecular markers, such as polycarboxylic acids, released by oxidation of polycyclic aromatic hydrocarbons from black carbon.
Quantitative marker measurements were combined with molecular characterization of the samples using ultra-high resolution mass spectrometry techniques.
The results of the analyses revealed that the black carbon dissolved in the Amazon River and its tributaries and transported to the ocean is usually "young", but undergoes an aging process as it moves towards the sea.
The samples collected farthest from the Atlantic Ocean, as in Óbidos, Pará, are younger. The material found closer to the ocean is older.
"This suggests that black carbon aging can occur along the path between land, river and ocean, and that more reactive components can be removed during transport of this material," said Richey.
"The newer material could enter a process of mineralization until it reaches the ocean, which would cause a change in its molecular profile, leaving it with a sign that it is older. But there are still several aspects of storing and transporting this material from land to river and then to the ocean that we need to understand better," he said.
Through a new project, also supported by FAPESP, the researchers intend to make a greater number of measurements to compare with those made in 2015. In this way, it will be possible to identify whether the production of "young" black carbon and, consequently, the forest fires have increased in recent years.
"There is great concern about the recent forest fires in the Amazon in relation to the fate of this carbon generated. Part of it goes to the atmosphere, in the form of carbon dioxide, but much of it is trapped on land or in water in the form of black carbon," Richey said.
An international group of researchers quantified and characterized, for the first time, the black carbon that flows through the Amazon River. The results of the study, published in Nature Communications magazine, showed that most of the material transferred to the ocean is "young," suggesting that it was produced by recent forest fires.
"We found through radiometric dating analysis [a method that uses the radioisotope of natural carbon-14 occurrence to determine the age of carbonaceous materials up to about 60,000 years] and molecular composition that the largest proportion of the black carbon we found in the Amazon was produced in recent years by burning trees," said Jeffrey Edward Richey, professor at the University of Washington, United States, and one of the authors of the study.
A visiting researcher at the Center for Nuclear Energy in Agriculture at the University of São Paulo (Cena-USP), Richey has conducted in the past five years a project supported by FAPESP in the São Paulo Excellence Chair (SPEC) modality, with the aim of clarifying the role of the Amazon basin in the global carbon cycle.
During the project, the researchers collected samples of dissolved black carbon in the main channel of the Amazon River and in four tributaries - the rivers Negro, Madeira, Trombetas and Tapajós - in November 2015, during one of the driest seasons in the region.
This period was chosen for the study because the water flow was low and the connectivity of the Amazon River to its floodplain was limited. "This allowed us to obtain samples of only permanent water and more accurately identify the sources of black carbon in the watershed," said Richey.
The concentration and content of carbon-14 in the samples were measured by molecular markers, such as polycarboxylic acids, released by oxidation of polycyclic aromatic hydrocarbons from black carbon.
Quantitative marker measurements were combined with molecular characterization of the samples using ultra-high resolution mass spectrometry techniques.
The results of the analyses revealed that the black carbon dissolved in the Amazon River and its tributaries and transported to the ocean is usually "young", but undergoes an aging process as it moves towards the sea.
The samples collected farthest from the Atlantic Ocean, as in Óbidos, Pará, are younger. The material found closer to the ocean is older.
"This suggests that black carbon aging can occur along the path between land, river and ocean, and that more reactive components can be removed during transport of this material," said Richey.
"The newer material could enter a process of mineralization until it reaches the ocean, which would cause a change in its molecular profile, leaving it with a sign that it is older. But there are still several aspects of storing and transporting this material from land to river and then to the ocean that we need to understand better," he said.
Through a new project, also supported by FAPESP, the researchers intend to make a greater number of measurements to compare with those made in 2015. In this way, it will be possible to identify whether the production of "young" black carbon and, consequently, the forest fires have increased in recent years.
"There is great concern about the recent forest fires in the Amazon in relation to the fate of this carbon generated. Part of it goes to the atmosphere, in the form of carbon dioxide, but much of it is trapped on land or in water in the form of black carbon," Richey said.
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