Seasonal evaluation of the quality of surface waters of the Amazon River on the waterfront of Macapá City, Amapá, Brazil

Abstract

Water is essential to life on Earth and crucial for humanity, but multiple and complex human activities alter this resource. This study evaluated the physical-chemical and bacteriological water conditions of the Amazon River at the Macapa city waterfront in the State of Amapa. The study was conducted at three points in the section between the mouth of the Igarapé das Pedrinhas and the mouth of the Canal do Jandiá, considering the spatial and temporal variations in seasonal periods. Samples were collected for analysis of the following variables: turbidity, dissolved oxygen, pH, temperature, total phosphorus, nitrate, total solids, biochemical oxygen demand, fecal coliform, and total nitrogen. Descriptive statistical analysis was performed on the data, to include the nonparametric statistical method of Kruskal-Wallis and the coefficient of variation. The results were evaluated individually and compared with the limits established by Resolution 357/2005 of the National Council for the Environment (CONAMA) using "class 2 for fresh water” as a reference. The Biochemical oxygen demand (BOD) values and total phosphorus were not within the resolution threshold. The results of the Water Quality Index (WQI) indicated that during the less rainy and rainy period the water at the Macapa city waterfront was classified as "good" and "excellent", respectively, where the turbidity and BOD were predominant for the decrease in WQI during the less rainy season. It is concluded that in periods of low water flow the contribution of wastewater discharged near the water uptake station for public supply may deteriorate water quality and compromise the health of the population.