Extreme droughts drive tropical semi-arid eutrophic reservoirs towards CO2 sub-saturation

Jurandir Rodrigues Mendonça Junior, Luciana Oliveira Vidal, André Megali Amado, Arthur Mattos, Vanessa Becker


Aim: This study aimed to evaluate the carbon dioxide (CO2) dynamics in tropical semi-arid reservoirs during a prolonged drought period and test if the trophic state affects the CO2 saturation. Methods: This study was performed in four reservoirs located in the tropical semi-arid region in the northeastern of Brazil. All samplings were performed between 9 and 12 am using Van Dorn Bottle. Samples for partial pressure of carbon dioxide (ρCO2) measurements were taken in the sub-surface as well for total phosphorus and chlorophyll-a. Correlation analysis and linear regression was used to seek relationships between the calculated ρCO2 and water volume, and chlorophyll-a. Results: The water level reduction due to atypical droughts caused chlorophyll-a concentrations increase, which in turn, cause reduction of the CO2 in the water. However, CO2 concentrations were very variable and it was observed an alternation between CO2 sub-saturation and super-saturation conditions. This paper showed that water volume and chlorophyll a were important regulators of CO2 in the water and thus, is important predictors to carbon balance in the tropical semiarid reservoirs. Conclusion: Our results indicate that the eutrophication allied to drastic water level reductions lead to a tendency of autotrophic metabolism of these systems.


carbon sink, carbon source, carbon dioxide partial pressure (ρCO2), reservoirs, eutrophication

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