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

• Published in: Acta limnológica brasiliensia 2018, Vol.30, p.1-11
• Main Authors: Mendonça Júnior, Jurandir Rodrigues de, Amado, André Megali, Vidal, Luciana de Oliveira, Mattos, Arthur, Becker, Vanessa
• Format: Article
• Language: English
• Subjects: Aquatic ecosystems; Arid regions; Arid zones; Carbon cycle; Carbon dioxide; carbon dioxide partial pressure (pCO2); carbon sink; carbon source; Chemistry; Chlorophyll; Chlorophyll a; Climate change; Correlation analysis; Decomposition; Drought; Dynamics; Ecosystem biology; Eutrophic environments; Eutrophic waters; Eutrophication; LIMNOLOGY; Metabolism; Nutrients; Oceanography; Partial pressure; Phosphorus; Production increases; Reduction; Regression analysis; Regulators; Reservoirs; Saturation; Semiarid lands; Trophic state; Tropical climate; Volume transport; Water levels; Water shortages
• ISSN: 0102-6712; 2179-975X; 2179-975X
• DOI: 10.1590/s2179-975x1517

Abstract Aim: This study aimed to evaluate the carbon dioxide (CO2) dynamics in tropical semi-arid reservoirs during a prolonged drought period as well as to 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 northeast of Brazil. All samplings were performed between 9 and 12 am using a Van Dorn Bottle. Samples for partial pressure of carbon dioxide (pCO2 ) measurements were taken in the sub-surface as well as samples for total phosphorus and chlorophyll-a. Correlation analysis and linear regression were used to detect relations among the calculated pCO2, water volume and chlorophyll-a. Results The water level reduction due to atypical droughts caused chlorophyll-a concentrations to increase, which in turn, led to CO2 reduction in the water. However, CO2 concentrations were very variable and an alternation between CO2 sub-saturation and super-saturation conditions was observed. This paper showed that water volume and chlorophyll-a were important regulators of CO2 in the water, as well as important carbon balance predictors in the tropical semiarid reservoirs. Conclusions The results of this paper indicate that the eutrophication allied to drastic water level reductions lead to a tendency of autotrophic metabolism of these systems. Resumo Objetivo: Avaliar a dinâmica do dióxido de carbono (CO 2) em reservatórios tropicais semiáridos durante um período prolongado de seca e testar se o estado trófico afeta a saturação de CO2. Métodos Este estudo foi realizado em quatro reservatórios localizados no semiárido tropical do Nordeste do Brasil. Todas as amostragens foram realizadas entre as 9 e as 12 horas com a garrafa Van Dorn. Amostras para pressão parcial de dióxido de carbono (pCO2) foram tomadas na sub-superfície, assim como para fósforo total e clorofila-a. As análises de correlação e regressão linear foram usadas para buscar relações entre a pCO2 calculada, o volume de água e a clorofila- a. Resultados A redução do nível de água devido aos eventos de seca fez com que as concentrações de clorofila-a aumentassem, o que, por sua vez, provocou a redução do CO2 na água. No entanto, as concentrações de CO2 foram muito variáveis e observou-se uma alternância entre as condições de subsaturação de CO2 e supersaturação. Neste trabalho mostramos que o volume de água e a clorofila-a foram importantes reguladores do CO 2 na água e, portanto, são importantes preditores d