Nutrient behavior in a highly-eutrophicated tropical estuarine system

Abstract

Aim: There are few studies dealing with the biogeochemical processes occurring in small estuaries receiving high sewage loading in tropical regions. The aim of this investigation was to characterize the biogeochemical behavior of nutrients in superficial waters collected at the Iguaçu estuarine system, during specific conditions (neap tide), located at the inner sector of a heavily eutrophicated embayment (Guanabara Bay, SE Brazil). Methods Physical and chemical variables were measured in situ (pH, temperature, conductivity, salinity, total dissolved solids, transparency, dissolved oxygen), whereas suspended particulate matter, chlorophyll a, phaepigments and nutrients (carbon, nitrogen and phosphorus forms) were measured in laboratory across the mesohaline estuarine gradient. Results The Iguaçu River mouth is in a high stage of eutrophication, considering nutrient concentrations, chlorophyll a and transparency of water column. Results indicate a transition from heterotrophic conditions to autotrophic conditions, since the nutrients concentrations showed a decreasing pattern along the saline gradient, while the chlorophyll an increased over the transects. The pH values and chlorophyll : phaeopigments ratios are significantly related to the amount and quality of organic matter contents, especially at transects under strong marine influence. More than 95% of the dissolved and total nitrogen concentrations are represented by NH4+ contributions, which are related to the ammonification of organic matter contents in this region, indicating the existence of untreated sewage loads in this area. Conclusion In this study, the Iguaçu River seemed to contribute with high inputs of nutrients that support important phytoplankton production at the inner regions of the bay related to the CO2 sink and autotrophic metabolism, showing the importance of verifying the biogeochemical behaviors of nutrients in estuarine areas, even in small scale.

Increase in the bioavailability of trace metals after sediment resuspension

“…Total nitrogen in water (TN) showed the opposite behavior, higher concentrations in the internal sector (1.1 mg L −1 ) and lower in the external sector (0.9 mg L −1 ) (Kruskal-Wallis, p < 0.05). This behavior was also observed by Rodrigues et al [47] in the same area of the present study and by Brandini et al [6] in the estuarine area of Iguaçu River, in Guanabara Bay-RJ, Brazil. These authors suggested that the decrease in NT concentration along the saline gradient is related to the increase in primary productivity, where part of the TN is assimilated by biota.…”

“…TP, OP and IP values showed a similar trend, with higher concentrations in the internal sector and lower in the central sector (Table 1). Brandini et al [6] observed the same behavior in a saline gradient on Guanabara Bay and suggested that phosphorus could suffer remineralization by the bacterial community activity along the gradient. Dias (2006) pointed out that in this region of Sepetiba Bay, organic phosphorus could be transformed in exchangeable phosphorus and this geochemical phase can be adsorbed on the surface of oxy-hydroxides of iron (forming the geochemical phase of phosphorus linked to iron compounds-ferric phosphorus).…”

Parâmetros de Qualidade de Água em Nascentes no Município de Olho D’Água do Casado, Semiárido Alagoano

“…Desta forma, ocorre maior absorção dos raios solares, maior aquecimento e consequentemente maior irradiação de calor, especificamente na área estudo, que está inserida no Semiárido Alagoano e apresenta tipicamente variações acentuadas de temperatura ao longo do ano, de um mês ao A temperatura da água, que relacionase com a intensidade de calor, pode ser transferida por radiação, condução ou convecção. De acordo com Brandini et al (2016), a temperatura da superfície é influenciada pela estação do ano, circulação do ar, hora do dia, cobertura de nuvens, vegetação ciliar, profundidade do corpo d'água, vazão, latitude e altitude. Correia et al (2015), paralelamente, atribuem o aumento de temperatura na água por causas oriundas de fontes naturais (principalmente energia solar) ou antropogênicas, e seu aumento resulta na redução de oxigênio dissolvido e no consumo de oxigênio, que se torna menos solúvel em água.…”

Sources and sinks of dissolved inorganic carbon in an urban tropical coastal bay revealed by δ13C-DIC signals

“…S3; supplementary file). Studies have shown that, in general, the PO 4 3--P was the dominant limiting nutrient in the bay, presenting sometimes an almost depletion and related to the strong phytoplankton uptake (Costa-Santos, 2015;Brandini et al, 2016). The calculated isotopic signature of the added DIC for the samples located in these polluted regions (excluding the data with Chl a concentrations > 50 μg L −1 ) gives a stable isotopic signature of sewage source of −12.2‰ (Fig.…”