Temporal and spatial trends of surface water quality of Velhas River sub-basin, Minas Gerais state

This article presents a temporal and spatial trend analysis of the surface waters quality of Velhas River, inserted in the Sao Francisco basin, in Minas Gerais. It was analyzed 16,625 data collected between 2002 and 2011 by the water quality monitoring program carried out by the Instituto Mineiro de Gestao das Aguas (Institute of Water Management of Minas Gerais - IGAM). Statistical tests, multivariate and non-parametric tests were used to assess 11 physical, chemical and microbiological variables of 29 monitoring stations. The results of Mann-Kendall/Sazonal MannKendall trend tests indicated that most of the watercourses in the region showed stable values of the parameters over the study period, with changes associated with thermotolerant coliforms, biochemical oxygen demand (BOD), nitrate and water quality index (IQA) mainly near large urban centers. The Cluster analysis identified three major groups of monitoring stations, grouped according to the quality of its waters, corresponding to high levels of pollution, moderate pollution and low pollution. However, throughout all the sub-basin, it was observed the degradation of the water quality, mainly related to the release of wastewater. An important finding was the worsening of water quality in the low stretch of Velhas River, appointed by the downward trend in the IQA at stations located in this region, which deserves attention of government agencies for management actions.