Nutrient Input and CO<sub>2</sub> Flux of a Tropical Coastal Fluvial System with High Population Density in the Northeast Region of Brazil

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 CO 2 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)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(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 CO 2 flux of +225 mmol·m, mainly from organic material from the untreated domestic and industrial wastewaters that are released into the river. This organic material increased the dissolved CO 2 concentration in the river waters, leading to a partial pressure of CO 2 in the 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 ( 3 HCO  , DIC, CO 2(aq) , , 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 CO 2 content in the estuarine and coastal waters, which is later released to the atmosphere.

Caracterización de los flujos de CO2 y los parámetros asociados con el sistema de carbonato en el estuario Río Formoso, Brasil

“…De acuerdo con Neal et al (1998) y Araujo et al (2013), cuando las concentraciones de CO 2 (ac) son altas, resultado de la producción bacteriana, HCO 3 -es producido haciendo disminuir el pH. Sin embargo, si las características del cuerpo de agua son tales que la concentración de CO 2 en el medio acuoso está cerca del equilibrio con el CO 2 atmosférico, fuertes correlaciones entre la AT, pCO 2 y el pH se pueden esperar.…”

“…De acuerdo con Da Silva et al (2004) la biomasa fitoplanctónica varía estacionalmente (2,4 a 70,2 mg m -3 ) mostrando concentraciones mayores en el periodo lluvioso. El CO 2 (ac) mostró bajos valores en este estudio (promedio: 14,5 ± 7,8 mol L -1 ) comparado con otros estudios realizados en estuarios tropicales próximos (Araujo et al 2013, Noriega et al 2015.…”

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INTRODUCCIÓNLos ríos y estuarios juegan un papel importante en el transporte y la transformación de carbono del continente a la zona costera adyacente y por lo general actúan como fuente de CO 2 para la atmósfera (Borges 2005, Araujo et al 2013. Se estima que, aproximadamente 60% de las entradas globales de agua dulce y el 80% del carbono orgánico total se producen en latitudes tropicales y subtropicales (Mackenzie et al 2004), el número de investigaciones en que, se han cuantificado los intercambios agua-atmósfera de CO 2 en los estuarios tropicales y ríos todavía está muy limitada (Borges 2005).

Las estimaciones de la variabilidad de los flujos de CO 2 en escalas de tiempo estacional e interanual en los estuarios tropicales son necesarias para definir la partición neta de CO 2 entre la atmósfera, los océanos y la biosfera terrestre.

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Alkalinity, inorganic carbon and CO2 flux variability during extreme rainfall years (2010-2011) in two polluted tropical estuaries NE Brazil

“…Araujo et al (2013) , increasing over time, and attributed the pattern to an enhanced organic load associated with population growth over the period.…”

Nutrient distribution in a shallow subtropical lagoon, south Brazil, subjected to seasonal hypoxic and anoxic events

“…This event was one of the causes for low light penetration in summer in the CCL, initiating the anoxic/hypoxic events, and confirming the anthropogenic activity effects on turbidity and water quality of this system. Aerobic respiration processes are primarily responsible for DO consumption in the water column, boosting the anoxic and hypoxic events (GUPTA et al, 2008;ARAUJO et al, 2013). The exceeding allochthonous organic matter from domestic sewage and continental runoff increases the rates of aerobic oxidation of OM in the CCL waters, and consequently remineralization, and hypoxia/anoxia in the bottom waters (FONSECA; BRAGA, 2006;ABREU, 2009).…”