Adequação do índice de qualidade de água da National Sanitation Foundation para a bacia hidrográfica do rio Guandu, no Estado do Rio de Janeiro

Abstract

Water is fundamental to the maintenance of life and, therefore, its quantity and quality must be adequate for its respective uses. However, there is an increasing deterioration in the physical, chemical and biological characteristics of water resources, due to anthropogenic activities, making water monitoring essential as a form of control and support for better management of water environments. Given this, river basins are considered appropriate territorial units for assessing the implications arising from human actions. The Guandu River Basin represents great importance in the development and supply of the Metropolitan Region of the State of Rio de Janeiro, where the waters are evaluated by the State Institute of the Environment (INEA), using the National Water Quality Index model. SanitationFoundation (IQANSF), the most widespread in Brazil. However, there is a need to adapt the aforementioned index to the environmental characteristics of the Guandu River Basin, in order to express results that are more reliable to its specificities. Thus, the objective of the study was to adapt the Water Quality Index model from the State Environmental Institute (IQAINEA) to the Guandu River Basin, in order to diagnose its real water situation. To this end, the Factor Analysis technique via Principal Components and the Varimax Rotation method were used, in order to calibrate the weights of the variables indicated as relevant in the water status assessment process. In effect, IQAGUANDU-T and the recommended IQAGUANDU were developed, which were applied to samples selected from the years 2018 and 2019 from the raw data bulletins available from INEA. In this way, a comparison was made between the established indices and the index used by INEA (IQAINEA), using non parametric tests. The results demonstrated, for the most part, compliance in the categorization of water conditions in relation to IQAINEA. However, when checking only samples classified as “bad” and “very bad”, the results showed a reduction in samples identified as “bad” and a significant increase in the “very bad” categorization regarding the results presented in IQAINEA. Therefore, the developed indices pointed to a trend towards lower values, and, thus, greater sensitivity in the assessment of more degraded environments in the Guandu River Basin.