Variabilidade espacial e temporal da qualidade das águas em reservatório da região semiárida

Abstract

The low availability of water in the Northeast of Brazil is related to semiaridez condition Where water scarcity is a result of the irregularity of rain in space and time, in addition to the high evapotranspiration rate However, frequent eutrophication of those water sources resulting from nutrient enrichment, favored the excessive proliferation of phytoplankton that compromisse various uses of water. The main goal of this work was to assess the impact of rainfall and the accumulated volume on the quality attributes of water in the brazilian semiarid region reservoir, as well as study the spatial and temporal variation of cyanobacteria. The research was developed in Orós reservoir, where were carried out seasonal water sampling (dry and rainy seasons) from 2008 to 2010. Secchi transparency, turbidity, pH, color Apparent Electrical Conductivity, Total Solids, Total Phosphorus, Orthophosphate Soluble, TKN, Ammonia, Nitrate, Chlorophyll-a and Cyanobacteria were the atributes analyzed. Through historical databases were obtained data of rainfall parameters and volume water of the reservoir. The t test, Pearson correlation, Principal Component Analysis (PCA) and Cluster Analysis (CA) were used to statistical analysis of the data. Results showed that were found that the physical and biological atributes showed significant differences (p < 0.05) between the points of collection and periods, as for chemical attributes only NKT significant difference between the points (P5 and P7). A higher correlation of attributes with rainfall and the volume of water in the dry season compared to the wet season was found. Regarding the cyanobacteria were identified a total of 17 species, that aPTer application of the PCA had been reduced to 10 species with a cumulative variance of 72.47%. Based on the identified species was conducted to CA, in which 4 groups were formed in the rainy season and 3 groups in the dry season, showing the influence of seasonal and spatial variability of the water system in the formation of groups. Cyanobacteria showed higher concentrations in the dry season especially species Aphanocapsa spp, Cylindrospermopsis sp and Geitlerinema sp, which showed a higher affinity to the physical attributes. It was concluded that the strong correlations between water attributes in the dry period in comparasion to rainy period are due to its greater stability. The seasonality has a strong influence on the attributes of water quality, so as to directly reflect the spatial distribution of cyanobacteria.