Trophic quality of waters in the Patos Lagoon estuary: a comparison between its margins and the port channel located in Rio Grande, RS, Brazil

Abstract

Qualidade trófica das águas no estuário da Lagoa dos Patos (RS, Brasil): comparação entre suas margens e o canal do porto localizado em Rio Grande, RS, Brasil Abstract: Aim:This study aimed to evaluate the Trophic State Index (TSI) at the margin and in the channel of the Patos Lagoon estuary, considering different hydrological conditions. Methods: Surface and bottom water samples were collected in three sites in the channel (margin and center) and in two sites at the Saco da Mangueira in different hydrological conditions in 2011. Results: Waters at the Saco da Mangueira are very contaminated by phosphate and nitrogenous compounds. The TSI classifies these waters as being hypereutrophic, the consequence of both the release of effluents which were poorly treated and the low water flow in the inlet. Contamination was mild at the margins of the channel, where waters were classified as being eutrophic and mesotrophic. Trophic balance (mesotrophic waters -oligotrophic surface -bottom) was found in the center of the channel as a consequence of strong water flow and dilution of contaminants coming from the margins. Conclusions: Spatial variation in the TSI value enabled clear distinction to be observed between the areas at the margins and in the channel, because it reflected the punctual presence of anthropogenic input in the marginal waters, mainly in the Saco da Mangueira. Effluent treatment must be required in order to control severe trophic imbalance in the waters at the margins of the city. Variations of the proposed index are a useful tool to identify sources of phosphate compounds in other aquatic environments.Keywords: effluents; organic contamination; phytonutrients; Trophic State Index.Resumo: Objetivo: O objetivo deste estudo foi avaliar o Índice de Estado Trófico (IET) das margens e do canal da Lagoa dos Patos, considerando diferentes condições hidrológicas. Métodos: amostras de águas da superfície e do fundo foram coletadas em 2011 em três locais no canal (margem e centro) e em dois locais do Saco da Mangueira em diferentes condições hidrológicas. Resultados: As águas do Saco da Mangueira são muito contaminadas por fosfato e compostos nitrogenados. O TSI classifica estas águas como sendo hipertróficas, como consequência de ambos, a liberação de efluentes que são pouco tratados e baixo fluxo de água na enseada. No eixo deste canal houve equilíbrio trófico (águas mesotróficas -superfície e oligotróficas -fundo), consequência da intensa circulação da água e diluição dos contaminantes oriundos das margens. Conclusões: A variação espacial nos valores do TSI indicou uma distinção clara entre as áreas nas margens e no canal, visto que refletem a presença pontual de aportes antropogênicos nas águas de margem, principalmente do Saco da Mangueira. for lagoons has also been modified with the use of nitrite-nitrogen, chlorophyll-a, and Secchi disk depth for the estimation of the status of eutrophication (Gupta, 2014). Other approaches used the trophic index TRIX, based on Chl-a, oxygen saturation, total nitrogen, and ...

Estudo de Cenários de Vazamento de Óleo no Porto de Rio Grande - RS e seus Impactos Ambientais (Study of oil leakage scenarios in the Porto of Rio Grande - RS and its environmental impacts)

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Assessment of the trophic status in a tropical estuarine system

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