Florações de cianobactérias no reservatório Carnaubal no trópico cearense, Brasil

Abstract

The state of Ceará, specifically the region of Inhamuns, is marked by periods of drought and low rainfall, making water a scarce resource. One of the concerns around this theme is also the quality of the water. The expressive blooms of cyanobacteria and their by-products directly interfere with water quality, and may introduce negative effects, both aesthetically and public health, due to the production of potentially toxic compounds. Thus, the objective of this work is to identify the factors that contribute to accelerate the process of eutrophication of the waters of the Carnaubal dam, a water source used for human supply in the municipality of Crateús. To this end, statistical treatments were applied to a database obtained through the monitoring of water resources carried out by the Company of Water Resources of the state of Ceará, comprising the period from 2018 to 2021. Twenty-eight parameters were selected, in which fifteen were chemical, six physical, two biological and five hydroclimatic parameters. Multivariate data analysis was applied to detect possible patterns between the variables analyzed using the PALeontological STatistics software – PAST version 4.11 and Excel. Among the set of analyzed variables, it was verified that five parameters, precipitation, total nitrogen, total dissolved solids, potassium and sodium, presented significant correlations with the cyanobacteria count. Being sodium and total dissolved solids, strong and positive correlations. Potassium had a moderate and positive correlation. Total nitrogen and precipitation had strong and negative correlations with cyanobacteria. Multivariate analysis of the principal component (PCA) data showed that correlations between total dissolved solids, sodium and potassium increase as the cyanobacterial count increases. It was found that the concentrations of cyanobacteria decrease, while total nitrogen and precipitation increase. In addition, the Lamparelli Trophic State Index, applied to classify water quality and trophic status, for most of the studied period, showed that the classification of the reservoir was supereutrophic and this indicates anthropic interference for this acceleration in the eutrophication of the reservoir . This study is important, as it can contribute to combating this scenario, because through the study of the main components by multivariate analysis, it was possible to assess which parameters are most correlated with the acceleration of eutrophication in the Carnaubal dam.