Variação sazonal e interanual da qualidade das águas de rios do semiárido brasileiro

• Ano de defesa: 2020
• Autor(a) principal: Freire, Letícia Lacerda
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Palavras-chave em Português: Rios intermitentes; Poluição da água; Secas; Sazonalidade; Interanualidade
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/53507

The rivers in the semi-arid are intermittent and temporary, but perennialized by hydraulic works. These water courses arouse great interest from the scientific community because they present differentiated processes from the perennial rivers and have considerable representativeness over the total world's total rivers, which suffer great anthropic pressure and tendency to aridization and intermittence due to climate changes. The present work investigated the main findings in the literature for watersheds inserted in the Brazilian semiarid, as well as presented scientific contributions on the dynamics of interannual and seasonal variation in the physical-chemical and microbiological quality of these sources. The interannual (2013 to 2018) and seasonal differences in water quality were investigated using the Kruskal-Wallis test (confidence interval 95%), also checking the normality of the data using the Shapiro-Wilk test (confidence interval 95%) and outliers using the interquartile range method. Trends in seasonal variation (dry and rainy) were evaluated and quality variables (pH, color, biochemistry oxygen demand, total phosphorus, ammonia, nitrate, dissolved solid nitrite, chlorophyll-a and total thermotolerant coliforms) were compared to standards of national classification for class II in monitored stretches of 11 hydrographic basins in the Brazilian semiarid region, in the state of Ceará. The rivers that flow through urban areas showed the worst water quality standards, mainly due to the discharge of sanitary effluents. A drought hit the watersheds between 2013 and 2017. We found out an increase of pH in the dry season, of colour (true) in the rainy season after the drought, of turbidity in the rainy season of wetter years, of BOD and total phosphorus in the drier years, of inorganic nitrogen in the rainy season, and of chlorophyll-a in the dry season of wetter years after the drought. The interannual variability of the river water quality was much more relevant than the seasonal one for the watersheds, probably due to both the continuous discharge of effluents throughout the seasons that undermined the seasonal hydrological effects and the combination of a prolonged drought and moist years that drove rather different streamflow regimes.