Characterization of dissolved organic matter in an urbanized estuary located in Northeastern Brazil

Abstract

The Sal River estuary, which is located in the state of Sergipe, Northeastern Brazil, stands out as an urban estuary, anthropogenically impacted by untreated and treated wastewater discharge. Synchronous fluorescence spectroscopy and measurement of dissolved organic carbon (DOC) were used for characterization of dissolved organic matter (DOM) in the estuarine water. Dissolved organic carbon concentrations ranged from 7.5 to 19.0 mg L and, in general, the highest values were recorded during dry season. For both seasons (dry and rainy), DOC presented an inverse linear relationship with salinity, which indicates a conservative dilution of organic matter coming into the estuary. During rainy season, anthropogenic organic constituents and humic substances from land-based sources predominated in DOM composition, carried by river flow. Whereas during the dry season, it has been observed a significant increase of products generated by microbial degradation of anthropogenic organic matter. The relationships between fluorescence intensity and salinity suggest a conservative behavior during rainy season and a non-conservative behavior during dry season, with addition of fluorescent organic matter into the intermediate zone of the estuary. Photodegradation by action of sunlight caused a decrease in fluorescence intensity of humic and tryptophan-like constituents and the release of photoproducts, resulting in an increase in fluorescence intensity of protein-like constituents.

Spatiotemporal variations of DOM in a typical multi-source watershed in northern China: A fluorescent evidence

“…The incluencing factors on the this spatiotemporal variation was studied. On the one hand, a large amount of polluted water entering the river through different pathways (non-point source pollution and urban sewage discharge) has not been reduced in the winter while the total volume of the river has declined, which has led to the increasing concentration and uorescent intensity of DOM (Arguelho et al, 2017;Li et al, 2020b). On the other hand, low temperatures in winter also enhanced uorescence intensity.…”

“…Besides, photodegradation was also suggested as a speci c factor to remove DOM from aquatic environments (Kamjunke et al, 2017). DOM in surface water received more UV light in seasons except for winter, which might promote various photochemical reactions as well as change the composition and concentration of DOM (Arguelho et al, 2017;Houben et al, 2016). However, it is worth noting that the uorescence intensity of the C3 component shown a gradually increasing trend in all seasons.…”

“…In recent years, many researchers have used a variety of technical methods to conduct extensive research on the source and nature of DOM, such as uorescence spectroscopy (Arguelho et al, 2017), ultraviolet-visible spectroscopy (Li et al, 2020b), isotope analysis (Guo et al, 2020), etc. The uorescent spectrum is an effective and attractive approach to monitor water quality (Henderson et al, 2009).…”

Análise jurídica e técnica dos procedimentos de outorga do uso da água na bacia hidrográfica do rio Japaratuba/SE

“…O pico II que variou de 300 -365 nm esteve presente nos P3C e no P4S, P6S e P7S, revela a presença de compostos que podem apresentar em sua estrutura dois a quatro anéis aromáticos, tipo o triptofano, que pode ser encontrado em águas residuais incluindo os efluentes de esgotos e os resíduos agrícolas, dessa forma, o pico II é indicativo de aporte antropogênico (JAFFÉ et al, 2004; HUDSON et al 2007; ARGUELHO et al, 2017). O P3C se comportou de forma isolada, sendo encontrado em seu espectro apenas o pico II, indicando que no período chuvoso, recebeu um aporte extra de conteúdo orgânico de fonte difusa já no período seco apresentou apenas o pico I.Figura 5 -Espectro de fluorescência molecular sincronizado para água da superfície dos rios São Francisco e Jacaré, coletada no período chuvoso (julho de 2018).Figura 6 -Espectro de fluorescência molecular sincronizado para água da superfície dos rios São Francisco e Jacaré, coletada no período seco (dezembro de 2018).Dessa forma, fica evidente que o avanço da urbanização e consequentemente o mau uso e ocupação do solo nas proximidades desses rios já começam a impactar de maneira negativa a qualidade da MOD presente nesses rios.O pico III (370-420nm) observado nos espectros, com valores elevados de IF, representa a classe de fluoróforos, que pode caracterizar o ácido fúlvico, uma das frações que compõem a substâncias húmicas (derivados de plantas e resíduos de árvores que contém uma maior concentração de compostos fenólicos e ligno-derivados) (JAFFÉ et al,GUSSO, 2008;ARGUELHO et al, 2017).…”

“…O pico IV onde o máximo de intensidade está centrado em torno de 450 -460 e reflete a influência dos ácidos húmicos, outra fração da SHA, foi verificada nos espectros, porém com uma baixa contribuição, pois, apresentou baixas intensidades de fluorescência para todos os rios estudados(JAFFÉ et al, 2004;GUSSO, 2008;ARGUELHO et al, 2017). Os picos IV e V representam a origem alóctone natural da MOD.…”