Spatio-Temporal Variation of Water Quality in the Guandu River Basin: an Approach to Water Resources Management

Abstract Efficient water resources management relies on spatiotemporal water quality analysis, particularly in the Guandu River basin, the main water supply source for the Rio de Janeiro Metropolitan Region. This study aims to perform a spatiotemporal analysis of water quality parameters and indices in the Guandu River basin, highlighting seasonal variability and anthropogenic influences. Data from 28 water quality monitoring stations distributed across the basin, covering the period from 2014 to 2022, were analyzed. The analysis was based on nine parameters of the National Sanitation Foundation Water Quality Index (NSF-WQI), a standardized and weighted method for water quality assessment. Comparisons of individual parameters and the NSF-WQI between dry (April–September) and rainy (October–March) periods, as well as among monitoring stations, were conducted using nonparametric statistical tests, in conjunction with Brazilian water quality standards and NSF-WQI classification criteria. Seasonal differences were identified, with lower concentrations of total phosphorus, turbidity, and dissolved oxygen during the dry season, and higher concentrations of nitrogen compounds during the rainy season. The results indicate a clear relationship between water quality degradation and land use patterns, as stations located in areas under greater urban pressure exhibited poorer water quality. Overall, the Guandu River basin presents a concerning water quality condition. These findings highlight the need to expand and intensify monitoring efforts and to implement evidence-based public policies targeting the specific sources and seasonal dynamics of pollution identified through this spatiotemporal analysis.