Seasonal and diel modulation of DOM in a mangrove-dominated estuary

• Published in: The Science of the total environment Vol. 857; p. 159045
• Main Authors: Vidal, L.O., Lambert, T., Cotovicz Jr, L.C., Bernardes, M.C., Sobrinho, R., Thompson, F., Garcia, G.D., Knoppers, B.A., Gatts, P.V., Régis, C.R., Abril, G., Rezende, C.E.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20.01.2023; Elsevier
• Subjects: CDOM; Dissolved organic matter; Environmental Sciences; FDOM; PARAFAC; River-ocean gradient; Tropical estuary; CDOM; River-ocean gradient; Dissolved organic matter; Tropical estuary; FDOM; PARAFAC
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.159045

Rivers and estuaries are the main links between continents and oceans. The Paraíba do Sul River is among the most important rivers of the southeastern Brazilian region, carrying an average of 0.08 Tg of dissolved organic matter (DOM) to the ocean but has been facing significant changes in river discharge. In this study, we aimed to provide insights into the sources and transformations of chromophoric dissolved organic matter (CDOM) and fluorescent dissolved organic matter (FDOM) sources across a salinity gradient under changing river discharge scenarios. Three spatial surveys were performed covering the entire salinity gradient of the main estuarine channel and surrounding mangrove waters under contrasting river discharge (178 to 1240 m3 s−1), and diel sampling was conducted in the mangrove tidal creek. The characterization of DOM through the parallel factor analysis (PARAFAC) model identified six components across the river-ocean gradient and mangrove creek: terrestrial origin (C1 - fulvic acid and C2 and C3 - humic-like), protein-like (C4), tryptophan-like (C5), and tyrosine-like (C6). Our results showed a shift in DOM composition and contribution along the salinity gradient, from terrestrial (C3) to autochthonous (C5 and C6) signatures. The October–17 dry campaign was characterized by a higher proportion of microbial protein-like component C4 and a lower contribution of humic-like components compared to February-17 and March-18 across the salinity gradient with an increase in the mixing zone. The DOM compositions of the February 17 dry and March 18 wet campaigns were similar. Additionally, the March–18 wet campaign, marked by the highest river discharge, showed higher inputs of terrestrial DOM (C1-C3 components) compared to February-17 in the estuary, which allowed DOM to be transported rather than transformed. The mangrove diel study showed that tidal fluctuations are also an important driver of carbon input to the mangrove creek with a possible impact on DOM composition in estuarine waters. [Display omitted] •CDOM and FDOM across an estuarine salinity gradient under three river discharge conditions were studied;•Six DOM components across the river-ocean gradient and mangrove creek were identified;•DOM allochthonous-authochonous components showed similar contribution during high and low discharges;•The combination of lower river discharge and tide influenced DOM components contribution across the river-ocean gradient;•High river discharge showed the highest terrestrial DOM transport to the ocean;•Mangrove terrestrial carbon showed to be tidal modulated and contributed to estuarine DOM.