This study used multivariate techniques for data analysis in order to determine the natural and anthropogenic factors that contribute to the spatial and temporal variations of water quality in urban watersheds of Caxias do Sul, Brazil. Principal Component Analysis (PCA) was used to analyze data collected at 30 points between September 2012 and January 2014. Monitoring was conducted bimonthly in six urban basins, where a total of 21 physical, chemical and biological parameters were analyzed. We found that PCA can explain 71.3% of the total variance in water quality, and that domestic and industrial pollution are the main Qualidade da água superficial por meio de análise … Rev. Ambient. Água vol. 10 n. 4 Taubaté-Oct. / Dec. 2015 contributors to the water quality variation in the region, especially from the galvanic manufacturing sector. Furthermore, we observed a trend of self-attenuation of pollutants in water downstream from urban areas and great anthropogenic influence as the pressure from urbanized areas decreases.
The natural factors and anthropogenic activities that contribute to spatial and temporal variation in superficial waters in Caxias do Sul’s urban hydrographic basins were determined applying multivariate analysis of data. The techniques used in this study were Principal Component Analysis and Cluster Analysis. The monitoring was executed in 12 sampling stations, during January, 2009 to January, 2010 with monthly periodicity in total of 13 campaigns. Between chemical, biological and physical, 20 parameters were analyzed. The results state that with the use of ACP, a data variance of 70.94% was observed. Therefore, it testifies that major pollutants that contribute to a water quality variation in the county are classified as domestic and industrial pollutants, mainly from galvanic industry. Moreover, two clusters were found which differentiated regarding their location and distance from areas with a high human density, corroborating on identifying of impact due to human activities in urban rivers.
One of the main challenges of water management in developing countries is to control the impact of the urban environment on the natural environment. Identifying sources of pollution in an urban watershed is a critical first step towards providing more integrated environmental planning, proper wastewater disposal and public water supplying. Thus, in this study we assessed 5-year water quality data from six urban river basins in Southern Brazil. In addition to the principal component analysis (PCA), three indexes were evaluated individually: Water Quality Index (WQI), Toxicity Index (TI) and CCME WQI framework (CCME WQI). In order to evaluate the effect of land use, the monitoring sites were assessed according to the urbanization criteria. The application of PCA revealed the existence of six components, explaining 73.78% of data variation. The component that explains most of the variation in water quality (30.80%) is associated with domestic wastewater. The second component showed a strong dependence (29.44%) on industrial activities such as electroplating and metalworking in determining the water quality, while the other components are related to certain industrial and agricultural activities. Likewise, the application of WQIs demonstrated similar results to the PCA. WQI and TI showed scenarios of concern regarding public supply. CCME WQI presented a significant disparity between the assessed watersheds and the Brazilian legal framework goals. Studies in this field significantly contribute to the establishment of environmental licensing criteria, by demonstrating patterns and environmental features. In addition to it, one can identify which watersheds demand greater attention with respect to control and recovery of proper environmental conditions. Furthermore, it can provide support for revisions in urban and watershed planning, especially in qualitative aspects eluding conflicts over water use in future scenarios.
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