Nutrient Input and CO₂ Flux of a Tropical Coastal Fluvial System with High Population Density in the Northeast Region of Brazil

Moacyr Araujo, Carlos Noriega, Dóris Veleda, Nathalie Lefèvre

Departamento de Oceanografia, Centro de Estudos e Ensaios em Riscos e Modelagem Ambiental, Universidade Federal de Pernambuco, Recife, Brazil.
Laboratoire d’Océanographie et du Climat: Expérimentation et Approches Numériques, Université Pierre et Marie Curie. 4, Paris, France.

DOI: 10.4236/jwarp.2013.53A037                

Abstract

The carbon dioxide flux through the air-water interface of coastal freshwater ecosystems must be quantified to understand the regional balances of carbon and its transport through coastal and estuarine regions. The variations in air-sea CO₂ fluxes in nearshore ecosystems can be caused by the variable influence of rivers. In the present study, the amount of carbon emitted from a tropical coastal river was estimated using climatological and biogeochemical measurements (2002-2010) obtained from the basin of the Capibaribe River, which is located in the most populous and industrialized area of the northeast region of Brazil. The results showed a mean CO₂ flux of +225 mmol·m^-2·d^-1, mainly from organic material from the untreated domestic and industrial wastewaters that are released into the river. This organic material increased the dissolved CO₂ concentration in the river waters, leading to a partial pressure of CO₂ inthe aquatic environment that reached 31,000 μatm. The months of April, February and December (the dry period) showed the largest monthly means for the variables associated with the carbonate system (, DIC, CO_2(aq), CO₃^2-, TA, temperature and pH). This status reflects the state of permanent pollution in the basin of the Capibaribe River, due, in particular, to the discharge of untreated domestic wastewater, which results in the continuous mineralization of organic material. This mineralization significantly increases the dissolved CO₂ content in the estuarine and coastal waters, which is later released to the atmosphere.

Keywords

Tropical River; Nutrient Load; CO2 Flux; Anthropogenic Pollution; Freshwater Ecosystem Impact

Conflicts of Interest

The authors declare no conflicts of interest.

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