Guajará bay water quality assessment in Belém/PA

Abstract

Water is a vital resource that plays an important role for society and the environment. However, its quality has been suffering due to the disordered population growth, accompanied by urbanization. Water pollution can come from chemical, physical and biological origin, where the release into the water body of any of these pollutants can change water and sediment characteristics and consequently impact the aquatic biota. Thus, this work aimed to evaluate the water quality of Guajará Bay by measuring the physicochemical and microbiological parameters, according to the seasonal rain period. The collections took place in 2015, in March, June, September and December, corresponding to the rainy and less rainy period of the Amazon region. In the studied periods, the precipitated volume was above the average of the climatological normals in the rainy period, and in the less rainy period it was below the average. In the chemical and microbiological analyzes, nitrate, nitrite, chloride and pH concentrations are within the limits allowed by CONAMA Resolution No. 357/05, Class II for freshwater. However, the OD parameter showed at points PT01 CH (3.6 mg/L), PT02 CH (4.4 mg/L) and PT03 CH (4.1 mg/L), below what this resolution allowed. At all points BOD (minimum = 5.2 mg/L; maximum = 14.3 mg/L) found values above the reference limit of CONAMA No. 357/05, as well as high COD concentrations (minimum = 12.5 mg/L; maximum = 27.3mg/L) and high EC (minimum = 86.4 uS/cm²; maximum = 573.4 uS/cm²). The COD and OD pointed to a strong negative correlation, where the increase in COD is causing the decrease in OD in Guajará Bay. In the analysis of thermotolerant coliforms, except for the PT04 of the rainy and less rainy period, all points presented values above those allowed by CONAMA nº357/05. The behavior of these parameters corresponds to the increase in organic matter presented in the region. Due to the frequent port practices in the analyzed area, and the urban concentration that discharges effluent, mainly of domestic origin, without pretreatment in Guajará Bay, which is aggravated by the rainy season. This can cause irreversible damage to the aquatic ecosystem, also harming the population that uses this water body for fishing and/or recreation.