Dinâmica temporal da qualidade da água em um córrego urbano
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Data
2020-08-07
Autores
Bega, João Miguel Merces
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Universidade Estadual Paulista (Unesp)
Resumo
Inúmeros cursos de água impactados por área urbana em nível mundial têm apresentado péssima qualidade de suas águas. Uma forma de monitorar tais ambientes trata-se do uso de Índices de Qualidade das Águas (IQA). No entanto, atualmente, existe a escassez de informações sobre o comportamento desses indicadores ao longo do dia, uma vez que as amostragens são frequentemente realizadas no período da manhã. A presente pesquisa consistiu em avaliar as oscilações nos valores do IQA e dos parâmetros envolvidos no seu cálculo entre os períodos da manhã, tarde e noite (i.e., 8h00, 14h00 e 19h00, respectivamente), para um córrego urbano. Buscou-se, ainda, analisar a variação sazonal dessas variáveis e inferir a eficiência da cafeína como indicador de poluição pelo lançamento de esgotos domésticos. Os parâmetros avaliados foram: temperatura, turbidez, sólidos totais, potencial hidrogeniônico, oxigênio dissolvido (OD), demanda bioquímica de oxigênio (DBO), fósforo total (PT), nitrogênio total (NT) e coliformes termotolerantes (E. coli). Foi verificado a piora na qualidade da água do córrego em comparação aos anos de 2002 e 2011, decorrente da intensificação das atividades antrópicas associadas ao uso e ocupação do solo urbano da bacia (e.g., aumento de despejos de esgotos domésticos e diminuição da vegetação ripária). De maneira geral, foram obtidas baixas concentrações de OD e altos teores de DBO, PT e NT, além de grande quantidade de E. coli na água do córrego. Tais parâmetros, na maioria das amostras, apresentaram desconformidade com a Resolução CONAMA n° 357/05. Em relação aos períodos do dia, houve variação estatística significativa da média do índice apenas entre manhã (15,50±1,97) e tarde (20,83±5,42), na estação de estiagem. Entretanto, foi comum valores distintos ao longo do dia em todos os meses, apresentando, inclusive, diferença igual a 30 entre manhã (49) e noite (19). Por sua vez, a cafeína foi identificada em todas as amostras, com concentrações variando de 0,01-7,80 mg/L. Inferiu-se que o córrego recebe o lançamento de esgotos domésticos, confirmando a existência de ligações indevidas em residências do município. Além disso, as maiores concentrações foram encontradas no período da manhã, assim como os menores valores de IQA, o que indicou a forte influência dessas ligações na qualidade da água do córrego avaliado.
Many watercourses impacted by urban areas at a global level have shown poor water quality. One way of monitoring such environments is the use of Water Quality Indexes (WQI). However, currently, there is a scarcity of information on the behavior of these indicators throughout the day, since sampling is often carried out in the morning. The present research consisted of evaluating the fluctuations in the values of the WQI and the parameters involved in its calculation between the periods of the morning, afternoon and night (i.e., 8:00 am, 2:00 pm and 7:00 pm, respectively), for an urban stream. It was also sought to analyze the seasonal variation of these variables and to infer the efficiency of caffeine as an indicator of pollution by the release of domestic sewage. The parameters evaluated were: temperature, turbidity, total solids, hydrogen potential, dissolved oxygen (DO), biochemical oxygen demand (BOD), total phosphorus (TP), total nitrogen (TN) and thermotolerant coliforms (E. coli). There was a worsening in the quality of the stream water compared to the years 2002 and 2011, due to the intensification of anthropogenic activities associated with the urban soil use and occupation of the basin (e.g., increase in domestic sewage discharge and decrease in riparian vegetation). In general, low DO concentrations and high levels of BOD, TP and TN were obtained, in addition to a large amount of E. coli in the stream water. Such parameters, in most samples, were not in compliance with CONAMA Resolution n° 357/05. In relation to the periods of the day, there was a statistically significant variation in the average of the index only between morning (15,50±1,97) and afternoon (20,83±5,42), in the dry season. However, different values were common throughout the day in all months, with a difference equals to 30 between morning (49) and night (19). In turn, caffeine was identified in all samples, with concentrations ranging from 0,01-7,80 mg. L −1 . It was inferred that the stream receives the release of domestic sewage, confirming the existence of improper connections in households in the municipality. In addition, the highest concentrations were found in the morning, as well as the lowest WQI values, which indicated the strong influence of these connections on the water quality of the assessed stream.
Many watercourses impacted by urban areas at a global level have shown poor water quality. One way of monitoring such environments is the use of Water Quality Indexes (WQI). However, currently, there is a scarcity of information on the behavior of these indicators throughout the day, since sampling is often carried out in the morning. The present research consisted of evaluating the fluctuations in the values of the WQI and the parameters involved in its calculation between the periods of the morning, afternoon and night (i.e., 8:00 am, 2:00 pm and 7:00 pm, respectively), for an urban stream. It was also sought to analyze the seasonal variation of these variables and to infer the efficiency of caffeine as an indicator of pollution by the release of domestic sewage. The parameters evaluated were: temperature, turbidity, total solids, hydrogen potential, dissolved oxygen (DO), biochemical oxygen demand (BOD), total phosphorus (TP), total nitrogen (TN) and thermotolerant coliforms (E. coli). There was a worsening in the quality of the stream water compared to the years 2002 and 2011, due to the intensification of anthropogenic activities associated with the urban soil use and occupation of the basin (e.g., increase in domestic sewage discharge and decrease in riparian vegetation). In general, low DO concentrations and high levels of BOD, TP and TN were obtained, in addition to a large amount of E. coli in the stream water. Such parameters, in most samples, were not in compliance with CONAMA Resolution n° 357/05. In relation to the periods of the day, there was a statistically significant variation in the average of the index only between morning (15,50±1,97) and afternoon (20,83±5,42), in the dry season. However, different values were common throughout the day in all months, with a difference equals to 30 between morning (49) and night (19). In turn, caffeine was identified in all samples, with concentrations ranging from 0,01-7,80 mg. L −1 . It was inferred that the stream receives the release of domestic sewage, confirming the existence of improper connections in households in the municipality. In addition, the highest concentrations were found in the morning, as well as the lowest WQI values, which indicated the strong influence of these connections on the water quality of the assessed stream.
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Palavras-chave
Poluição da água, Degradação ambiental, IQA, HPLC, Cafeína, Water pollution, Environmental degradation, WQI, Caffeine