Origin, concentration, availability and fate of dissolved organic carbon in coastal lagoons of the Rio de Janeiro State

Abstract

Abstract:The coastal lagoons in the northern Rio de Janeiro State (Brazil) present a wide gradient of dissolved organic carbon (DOC) and water color, with the highest DOC concentrations reported in the literature for aquatic ecosystems. Thus, they represent a peculiar set of ecosystems for the study of the origin, processing and fate of DOC in inland waters. We reviewed data from 2 decades of studies on the carbon cycle in these coastal lagoons and discussed the fluctuations in the concentration and quality of DOC, factors affecting DOC microbial and photochemical degradation, CO 2 emission, as well as the role of humic and non-humic carbon to the energy flow through the trophic chains. We show that DOC quality, not its quantity, determines the rates of photochemical and microbial degradation both seasonally (within system) and spatially (among systems), with the exception of DOC photo-oxidation among lagoons, which is partially explained by DOC concentration at regional scale. In humic lagoons, there is a fairly predictable pattern of seasonal variation in DOC concentration associated to rainfall-induced inputs of allochthonous C. However, little is known about the exact timing of these allochthonous inputs and how they relate to the seasonal variation of DOC chemical properties (i.e. its quality). Depth-integrated photo-oxidation rates were less representative in highly humic lagoons, due to strong light attenuation in the water column. Nevertheless, the potential contribution of photo-oxidation and bacterial respiration to total CO 2 efflux (~11%) did not differ significantly when all lagoons were pooled together. Contrary to prevailing paradigms for humic waters, microalgae seem to be the main C source in humic lagoons, sustaining pelagic food webs through zooplankton, in spite of some contribution of allochthonous C. Thus, the predominant role of the microbial loop in the DOC recovery to food webs in such systems is to be questioned.Keywords: coastal lagoons, dissolved organic matter, dissolved organic carbon, DOC, humic substances. Resumo:As lagoas costeiras do norte do Estado do Rio de Janeiro apresentam um amplo gradiente de carbono orgânico dissolvido (COD) e coloração da água, com as maiores concentrações registradas na literatura. Portanto, representam um conjunto peculiar de ecossistemas para estudos sobre a origem, processamento e destino do COD em águas continentais. Neste trabalho, revisamos 2 décadas de estudos sobre o ciclo do carbono nas lagoas costeiras desta região e discutimos as flutuações na concentração e qualidade do COD, fatores afetando sua degradação microbiana e fotoquímica, a emissão de CO 2 , assim como a contribuição do COD húmico e não húmico para o fluxo de energia através das cadeias tróficas. Nós mostramos que a qualidade, e não a quantidade do COD, determina as taxas de degradação fotoquímica e microbiana tanto sazonalmente (dentro dos sistemas) como espacialmente (entre sistemas), com exceção da foto-oxidação entre lagoas, a qual foi parcialmente explicada pela concentração ...

Floating Aquatic Macrophytes Decrease the Methane Concentration in the Water Column of a Tropical Coastal Lagoon: Implications for Methane Oxidation and Emission

“…In the lagoon, the plants are juxtaposed forming a mat that hampers light penetration. Another factor probably responsible for light attenuation in Cabiúnas Lagoon is the black-colored water 36 originated from humic substances produced mainly by the decomposition of terrestrial plants from the surrounding sandy soils 49 . The inhibitory effect of light on the activity of methanotrophs has been reported before with increasing light intensities, ranging from a slightly inhibitory effect with low intensities (4.1 to 21 µmol photons m -2 s -1 ) to a complete inhibition with higher intensities (57 to 760 µmol photons m -2 s -1 ) 50,51 .…”

Hatching Under Brownification: DOC-Mediated Changes in Physical, but Not Chemical Properties of Water Affect Hatching Patterns of Cladocera Resting Eggs

“…Atoleiro is a natural intermittent small pond formed by the semi-permanent rising of the water table in the sandy soil in the Restinga de Jurubatiba National Park (22° 13' S and 41° 29' W, Rio de Janeiro State, Brazil). The water of this pond usually contains large amounts of DOC, with more than 90% of its concentration composed by allochthonous humic substances, mostly derived from organic matter present in the impermeable soil layer (Suhett et al 2013). Water from this environment was previously used to evaluate the effects of different DOC concentrations on the life history of the cladoceran Moina macrocopa (Suhett et al 2011).…”

Physicochemical Parameters and Bacterial Composition in Sungai Pusu Gombak

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