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Dissolved black carbon in rivers and oceans can have old origins

Carlos Eduardo de Rezende (2) - 1000 x 750Carlos Rezende: "More studies are needed"The two residues of organic matter combustion are charcoal and Black Carbon (BC), and these materials are derived from natural combustion and anthropogenic activities. A study published on the Nature Geoscience website suggests that BC remains in the soil from decades to centuries as it gradually leaches from the soil into the river water and is then transported to the ocean. Carlos Eduardo de Rezende and Alvaro Ramon Coelho Ovalle – UENF's researchers – are among the authors of the article and are responsible for a long term approach in basin drainage of Paraíba do Sul river. This study is also a part of National Institute for Science and Technology.

During almost 20 years of research in Paraíba do Sul River, Carlos Rezende and his group have collected water samples every 2 weeks and recently, through the CNPq Bilateral Cooperation with Thorsten Dittmar – researcher from the Max Planck Institute in Germany – were able to determine the BC in river, estuarine and marine water. However, this paper is considering only the temporal variability of BC during the 10 years of measurements in the river water and the other studies have been prepared for future publications.

This study showed that 190 to 740 tons of BC is produced every year in the Paraíba do Sul Basin, which includes areas from São Paulo, Minas Gerais and Rio de Janeiro States. One important result showed that the amount of BC was 3 to 16 times higher than today´s production rate and therefore the historical BC production rates were several orders of magnitude higher than today. It really explains why the actual numbers don´t fit well and show us that the deforestation process, which started in 1850 and intensified in the 20th Century, was responsible for a high BC production.

According to Rezende, the decision to study this subject stemmed from the Atlantic Forest's role as a deplorable example of land use management. The Atlantic Forest Biome currently has less than 10% of its original area. In light of this situation, Rezende believes the use of BC as an important proxy for land use can be applied to other Brazilian rivers.

Finally, Carlos Rezende explains that the dissolved BC carbon indicates anthropic influence on the natural cycle of this element and that high levels of this chemical form of carbon in river and ocean waters may interfere or disrupt organism metabolisms and the functioning of aquatic ecosystems. More studies, however, are needed in order to evaluate this hypothesis.

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