Avaliação e proposta de adequação da rede de monitoramento da qualidade das águas superficiais das sub-bacias do Rio das Velhas e do Rio Paraopeba, utilizando técnicas estatísticas multivariadas

Surface water quality monitoring is essential for a sustainable management of water resources and an efficient pollution control. However, the monitoring of several parameters of water quality in several monitoring stations demand a high cost. Therefore, it is essential to design a well-structured sampling network, in order to present the most cost-effective and practical logistics, without losing useful and relevant information of the monitored water quality. Thus, this study aimed to evaluate and propose an adjustment for water quality monitoring network for surface freshwaters in Velhas river and Paraopeba river basins, using a multivariate statistical method. The Cluster Analysis, Principal Components Analysis and Factor Analysis were associated with non-parametric tests and an analysis of violations of the limits prescribed by law, to identify the parameters and the most relevant monitoring stations in each sub-basin, which must be kept on the network, and to evaluate the sampling frequency performed. Considering the two sub-basins, the parameters fecal coliforms, total manganese and phosphorus were considered the most relevant for the characterization of water quality. On the other hand, total chromium, total cadmium, selenium, total dissolved copper, total boron and oils and greases were considered less relevant. The discharge of domestic sewage and industrial wastewater, mining activities and the diffuse pollution from agriculture and pasture areas are the main sources of pollution responsible for surface water quality deterioration in these sub-basins. Several monitoring stations showed high contamination by biodegradable organic matter and solids input, but the AV320 (Córrego da Mina - Raposos) and BP073 (Riacho das Pedras Betim) are the stations whose water quality are the most degraded in the Velhas river basin and Paropeba river basin, respectively. The analysis of sampling frequency, which could only be held in the Velhas river basin, showed that the water quality is influenced by hydrological conditions (dry and rainy seasons). However, the water quality presents some variations along the year. Thus, monthly frequency is the most suitable for assessing the water quality in regions affected by various sources of pollution. Therefore, multivariate analyzes were efficient to guide the adequacy of the water quality monitoring network of Velhas river and Paraopeba river basins, and it can be used for other monitoring data from another watersheds.