Avaliação da qualidade da água e do sedimento no reservatório de abastecimento público do ribeirão João Leite-GO

Abstract

The reservoir João Leite is located upstream of the city of Goiânia (Goiás-Brazil), and has as its sole objective the public water supply to the city of Goiânia and conurbated areas. In view of the constant deterioration of the water resources along the drainage basin, it is necessary to include the sediment quality assessment in order to complement the environmental monitoring protocols. The objective of this research was to evaluate the water and sediment quality of the João Leite reservoir in the rainy season and in the dry season, with the purpose of assisting in the process of water purification that will be distributed to the population, together with other processes operation and maintenance of a water treatment plant. Water and sediment samples were collected at five sampling points during rainy and dry periods during the year 2016. In the sediments were determined grain size, pH, CTC, organic matter, oxygen consumed, total nitrogen, macronutrients, micronutrients and pesticides. The pH, electrical conductivity, water temperature, turbidity and dissolved oxygen were determined on the surface, medium and bottom, and the concentrations of ammonia, nitrate, nitrite, total phosphorus, TOC and pesticides. Also, acute toxicity tests were performed with lettuce seeds (Lactuca sativa L.) for the sediment samples. Concentrations of atrazine, ranging from 0.166 to 0.304 μg.L-1 and from trifluralin (0.200 μg.L-1) were identified in the water samples collected during the dry season. All values found remained within the maximum values allowed by Conama Resolution 357/2005 for Class 2 fresh waters. High concentrations of total iron (190.7 and 196.5 mg.kg-1 in drought and of manganese (159.7 and 177.2 mg.kg-1 in drought and from 163 to 179.5 mg.kg-1 in the rainy season), which may alter the characteristics of water during events of destratification. The acute toxicity tests indicated that, with the bottom sediments of the João Leite reservoir sampled in the regions closest to the bus (P2 and P3), the seeds presented reduced growth, both the root and the hypocotyl. However, the presence of toxic substances has not been identified in the analysis of pesticides capable of causing harmful effects.