Evaluation of the effect of seasonality on the quality of surface water in the lower Guamá sub-basin, Belém, PA

Abstract

Water, as a universal solvent, has fundamental functions such as diluting and transporting materials. In this sense, the issue of urbanization has changed the conditions of surface water quality. The city of Belém is among the worst in the country in terms of basic sanitation, aggravating the problems in its waterways. Thus, the objective of this study was to evaluate the influence of rainfall seasonality on the quality of the Guamá River, which is important for the city's public supply system. The study was carried out in the sub-basin of the lower Guamá, Belém section, where interference from urbanization and tourism is perceived. Water samples were collected from the river at eight different points in the months of October, the wettest month, and December, the wettest. According to the descriptive statistics, the parameters pH, total phosphorus (TP) and turbidity were non-compliant with the legislation in most of the points. In the multivariate statistics it was observed the grouping of two distinct groups in both seasonal periods, group "A" had the characteristic of a polluted aquatic environment due to the proximity to the urban area and in group "B" the anthropic interference is still not expressive. Precipitation had an influence on the parameters total solids (TS), chlorophyll a (CLa), PT, and dissolved oxygen (DO). For EIT we obtained mesotrophic, eutrophic and supereutrophic levels for the period of lower precipitation and the ultraoligotrophic level for the period of higher precipitation. The parameters pH and turbidity are characteristics intrinsic to the type of white water in the Guamá River and their nonconformity with the national legislation does not necessarily show a bad quality. On the other hand, the behavior of PT indicates a possible contamination by point sources in the less rainy period by domestic sewage. The Mann-Whitney test was important to compare the two periods resulting in a significant difference for LA, PT, ST, and DO. Therefore, sampling points closer to the urban area are with a greater compromise of water quality, given the numerous anthropic interferences in the environment. Another point, considered touristy, with the presence of restaurants, hotels and local residences, the compromising of the water quality is observed, since the area also demands good sanitary conditions. Finally, the points farthest from urbanization were characterized by water preservation.