Avaliação de indicadores de qualidade da água em diferentes níveis de influência antrópica entre as cidades de Novo Airão e Manaus - AM

Abstract

The Rio Negro is a river with a vast extension, bathing six municipalities of the State of Amazonas, among them Novo Airão and Manaus, distant 127 km by river. The Brazilian Institute of Geography and Statistics (IBGE) estimated in 2019 for Novo Airão a population of 19,454 inhabitants, where 15.4% have adequate sanitary sewage. In Manaus the estimate was 2,182,763 inhabitants and 62.4% have access to sewage collection. Therefore, these scenarios can characterize different levels of anthropic influence on the water quality of the water bodies present in the surroundings of these municipalities. The present study aims to evaluate water quality indicators under different levels of anthropic influence among the mentioned cities. It was conducted in November 2019, studying the low water period scenario, covering a total of 32 water and suspended solids sampling points. As a control area, 12 points were sampled in Anavilhanas National Park (PNA), considered with low anthropic influence due to its character as a Conservation Unit (UC), 12 points on the coast of Novo Airão (NA) and 8 points on the coast of Manaus (MAO). The parameters used in this study were: temperature, hydrogen potential (pH), electrical conductivity (EC), oxirreduction potential (ORP), dissolved oxygen (DO), Total Suspended Solids (STS), Turbidity (NTU), and the determination of potentially toxic metals such as Chromium (Cr), Copper (Cu), Iron (Fe), Manganese (Mn), Nickel (Ni), Lead (Pb), Vanadium (V) and Zinc (Zn) dissolved in surface water and associated in the suspended solids (SS), whose analyses were performed by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). These water quality indicators were evaluated according to the Maximum Allowable Values (MPV) established in the CONAMA resolution 357, of 2005 and NOAA (National Oceanic and Atmospheric Administration) legislation for sediments and compared with studies focused on the Negro River region during the drought, specifically. The evaluation of the means and respective standard deviations obtained in each parameter showed that pH, ORP, EC were indicators that suggested variability between the areas. PNA showed expected measurements of the physicochemical parameters, considering its local characteristics as an environment without significant anthropic influence and considered natural. In NA, the measurements of physical and chemical parameters were similar to the control region, unlike MAO, which had high values for some parameters and points, with great emphasis on the mouth of the Forty stream, which showed high pH and EC (6.69 and 409.57 µS/cm, respectively), indicating high content of dissolved ionic species. As for the dissolved metals, they presented values below the VMP, but indicated evident behavior differences between the regions studied. In the water, Zn showed an increasing trend: PNA < NA < MAO. In SS, Cu and Ni showed an increasing trend between regions: PNA < NA < MAO. Pb in SS exhibited high concentrations in NA, which is of concern. Shapiro-Wilk, Kruskal-Wallis and Dunn's post hoc tests and Principal Component Analysis (PCA) showed that the data were non-normally distributed, exhibiting significant differences, demonstrating the levels of anthropogenic influence among the investigated regions during the 2019 drought period. Amazonian environments under different scenarios of anthropic influence need to be studied, serving as a subsidy for future environmental diagnostics.