Water quality dynamics in urban river of the semiarid region under anthropogenic pressure: a spatiotemporal analysis in the stretch of the municipality of Mossoró (Brazil).

Over the years, urban rivers have suffered from environmental degradation due to anthropogenic activities, becoming a public concern. Thus, the objective of this study was to evaluate the spatiotemporal evolution of water quality in the Apodi-Mossoró River, in the urban section of Mossoró-RN, during the dry and rainy seasons. To this end, the physical-chemical and microbiological attributes of water samples collected at six points along the urban stretch of the Apodi-Mossoró River were characterized. Using the water quality data, the Water Quality Index was calculated, and multivariate statistical analysis was performed. The Water Quality Index varied considerably. At the Genésio Dam, a more positive assessment was observed, with ratings ranging from excellent to good. However, the other points showed significant variations, especially the Barrocas Dam, which received all ratings. The attributes that most influenced the results were total Kjeldahl nitrogen, turbidity and biochemical oxygen demand. The river water showed a high salt content, resulting in a classification as brackish at all points evaluated for most of the year, except during the rainy season, when it was considered fresh.