Analysis and diagnosis of water quality and trophic status of Lake Paranoá Brasília ? DF

Código

I-EBHE0201

Autores

Davi Camargo dos Santos, Tarcila Neves Generoso, KARINA BASSAN RODRIGUES, LIGIA SILVA VIVEIROS GURGEL, Eloneide Menêses França Arruda

Tema

WG 2.6: Water systems analysis for integrated planning & management

Resumo

Reservoirs are artificial lakes built by man, with the aim of meeting certain purposes. Population increase and its distribution act as factors that can affect the quality of water resources in reservoirs and as a result, monitoring parameters associated with quality are important for carrying out efficient reservoir management. In Brazil, Conama Resolution 357 of 2005 establishes guidelines for the classification of water resources and defines limits for certain parameters according to the intended use. Lake Paranoá is a reservoir framed as class 2, multiple use, built in 1959, it has an area of around 37 thousand m² and a volume of 460 thousand m³. Its basin is entirely within the Federal District, and is surrounded by important urban centers such as Plano Piloto, Guará, Lago Sul and Lago Norte. The lake, between the 70s and 80s, was already considered unfit for use to such an extent that the quality of its waters was severely deteriorated. Nowadays, after the depollution of the lake, in addition to being used by the population for bathing, it serves as landscaping, for releasing treated effluents, generating energy and since 2017 it has been used as a water supply source. The Environmental Sanitation Company of the Federal District ? Caesb, responsible for supplying and treating effluents, monitors the lake weekly through the Bathing program and monthly through the Limnological program. This work aims to present the results of water quality analyzes carried out between 2019 and 2024, at 5 monitoring points (in the 4 arms and 1 in the central part), at a depth of 1 meter. Analyzes were carried out for the parameters E. coli, total phosphorus, dissolved oxygen, nitrite, nitrate, ammonia nitrogen, pH, chlorophyll, turbidity and temperature. Furthermore, the Trophic State Index (TSI) was also calculated for the years considered. The results obtained show that the majority of monitored parameters express a result consistent with the limits of the framing class. For E. coli there were some occurrences of values exceeding the class, on an occasional basis. For total phosphorus, occurrences showed a higher frequency, at different times, for all monitoring points, mainly in 2019 and 2022. Despite this, the lake has been presenting good quality conditions especially in recent years. Furthermore, in the 5 monitored points the value of the Trophic State Index ? TSI, indicates that the trophic state of the lake was classified as oligotrophic throughout the entire period with the exception of 2020 when it was classified as ultra-oligotrophic.