The organic matter (OM) contained in a natural aquatic environment, located in a tropical region in Notheastern Brazil, was characterized using synchronous fluorescence spectroscopy and UV-Vis absorbance. The synchronous fluorescence spectra did not show qualitative differences for samples collected during dry and rainy seasons. They also revealed two peaks, one at 390 nm and other at 460 nm, associated with humic substances. The lack of peaks with significant fluorescence intensity at 270 - 300 nm and at 320 - 370 nm confirms it is an environment with natural OM. The A254/A436 ratios obtained during the dry and rainy seasons (13.55 to 14.97) indicate the presence of allochthonous OM of terrestrial origin, with high level of aromatic carbon associated with humic substances. The OM photodegradation by natural sunlight was more pronounced in the first five days, with a decrease of FImax from 23.6 to 55.4%. Also, titration with Cu(II) ions was used to determine the complexation ability of the two fluorescent sites, obtaining log K values of 4.26 and 4.27.

RESUMO Nesse estudo foi avaliada a eficiência da rede de monitoramento da qualidade da água da bacia hidrográfica do rio Sergipe, usando a análise multivariada de dados, através da análise de componentes principais (ACP) e análise de agrupamento hierárquico (AAH). A ACP foi aplicada a uma matriz de dados composta por 12 estações de amostragem e concentrações médias de 23 parâmetros da qualidade da água, obtidos em quatro campanhas de amostragem no período de junho/2013 a novembro/2015. Todas as 12 estações de amostragem foram consideradas como principais (peso>0,7) e, portanto, devem ser mantidas no programa de monitoramento. A ACP apontou que dos 23 parâmetros medidos, são essenciais para avaliação da qualidade da água, apenas 16 no período seco e de 17 no período chuvoso. A AAH separou as estações da rede de monitoramento em 4 grupos em função das características da qualidade da água, considerando os impactos naturais e antropogênicos. Os principais impactos foram originários de fontes naturais (constituintes minerais) e de aportes antropogênicos associados a despejos urbanos, sanitários, indústrias e escoamento superficial de áreas agrícolas.

ABSTRACT This study evaluated the efficiency of the water quality monitoring network of the Sergipe river basin, using multivariate data analysis, such as principal component analysis (PCA) and hierarchical cluster analysis (HCA). The PCA was applied to a data matrix consisting of 12 sampling stations and mean concentrations of 23 water quality parameters, obtained in four sampling campaigns from June/2013 to November/2015. All 12 sampling stations were considered as main (weight>0.7) and therefore should remain in the monitoring program. The PCA pointed out that of the 23 measured parameters, only 16 are essential for water quality assessment, in the dry period and 17 in the rainy season. The HCA separated the stations of the monitoring network in 4 groups according to the water quality characteristics, considering the natural and anthropogenic impacts. The main impacts were originated from natural sources (mineral constituents) and the anthropogenic contributions were associated with urban input, sewage, industrial dumps and surface runoff from agricultural areas.