Avaliação da evolução do estado de degradação ambiental das bacias hidrográficas urbanas de Caxias do Sul/RS como subsídio ao planejamento urbano

Abstract

Human activities have caused degradation of water bodies over time. Understanding the evolution of water quality in time and space is a tool that makes it possible to highlight the impact of human actions on the environment and support decision-making regarding environmental preservation and conservation, considering human dependence on good quality water. and quantity and its multiple uses. In this context, the general objective of this work was to evaluate the state of environmental degradation of the urban river basins in the municipality of Caxias do Sul as a subsidy for urban planning based mainly on the evolution of water quality and urban land use. Data from bimonthly campaigns in 2022 were analyzed, with a total of 23 parameters covering 6 urban sub-basins of the municipality. The water quality results from the year 2022 were compared to the water quality results from the study carried out in the years 2012 to 2014 in order to understand the evolution over time and the relationship with the urban configuration in the study sub-basins. The results obtained were used to calculate the Water Quality Index (WQI), Trophic State Index (IET), Toxicity Index (TI) and the Framework Compliance Index (ICE). The results were treated statistically using multivariate statistics through Cluster Analysis (AA) and Principal Component Analysis (PCA) and the analysis of descriptive statistics of the results of the variables. The IQA and IET results demonstrate that the sub-basins studied have contamination by domestic effluents in their water bodies. The Tega sub-basin, in addition to domestic contamination, presents contamination from industrial effluents, a result observed by IT. It should be noted that Tega is the sub-basin with the largest number of companies authorized to release effluents and the one with the largest number of inhabitants based on the 2010 Census. ACP's statistical analysis resulted in three main components, and these components ended up helping with water quality indices, where CP1 reflected the IQA, CP2 the IET and CP3 partially reflected the IT, as it did not present ammonia nitrogen. Therefore, it is suggested that future studies related to IT may disregard ammonia nitrogen from the analysis, facilitating the understanding of industrial contamination of water bodies. Ammonia nitrogen is associated with domestic contamination, and other indices such as the AQI help to understand this type of contamination. The ACP ended up demonstrating that redundant indices were not used in the study, with the ICE reflecting the average results of the aforementioned statistical analysis and also helping to understand the AA. Data from the urban analysis demonstrated that in 2010 Caxias do Sul had an urbanization rate of 94% and approximately 40% of the population lived in the Tega sub-basin. These results demonstrate the importance of studies of this nature so that they can assist public authorities in managing water in their territory, understanding the sources of contamination, as well as the priority actions to be defined. [resumo fornecido pelo autor]