Relación de la calidad del agua de la quebrada El Salado con el uso de suelo urbano y periurbano de la parroquia Baños

Abstract

This study investigates the relationship that exists between water quality and the characteristics of land use / land cover for the El Salado stream, which runs through an urban and peri – urban area of the parish of Baños, Cuenca, Ecuador. An influence zone that covers an area of 624.17 ha, and a route of 7.98 km of the stream was delimitated, where four representative sample points distributed in the upper, middle, and lower part of the stream were located. Five water monitoring campaigns were carried out monthly during the rainy and dry season, in a period between October 2019 - February 2020. 15 physical, chemical, and microbiological parameters, and 4 heavy metals were analyzed from the water samples. The results allowed to determine the stream water quality by applying three water quality indices. NSF – WQI scores indicated that, in general, the water quality of the El Salado stream in both dry and rainy seasons, was classified as a medium quality water because the scores obtained were in the range of 51 – 70. The second index of DINIUS – WQI for agricultural use indicated that the water is relatively acceptable, establishing that no purification is necessary, but suggesting at the same time the application of minor purification processes before its use in crops, because most of the scores were obtained in the range of 71 – 90 for both seasons. Furthermore, the general value of the HPI index provided corroborating evidence indicating that the water of the stream is not safe for human consumption, since the results obtained exceeded the critical limit for drinking water for both seasons, classifying it as a water that contains high levels of pollution caused by heavy metals. In addition, it was established through the Analysis of Variance method, that there were no statistically significant differences between the data sets of the water quality indices according to the sampling point and to the monitoring month, indicating that there was no relevant influence of spatio – temporal variables on the water quality (p>0.05). Consequently, the correlation method was applied to find the degree of association between water quality parameters, which allowed to determine that most of the existing correlations found were moderate and weak positive. On the other hand, the land use proportions found in the influence zone were determined using the information of the land cover / land use map provided by the decentralized autonomous government of Cuenca. To find the relationship between water quality and land use / land cover patterns, the Principal Component Analysis method was applied with the purpose of grouping the land use categories, where three principal components were established. The first component was characterized by natural areas, the second one by intervened areas in terms of short – cycle crops and sports and recreational areas, and the third one by the discontinuous urban area. Finally, the correlations were found using the Pearson Coefficient between land use categories, PC1, PC2, PC3, and the water quality parameters, which allowed to explain that natural areas were negatively correlated with physicochemical parameters and positively correlated with heavy metals, while it occurred the opposite in intervened zones such as cultivation and recreational areas, as well as the discontinuous urban area. Therefore, the correlations revealed that the contamination of “El Salado” is not only caused by anthropogenic sources but also by natural sources, specifically in terms of heavy metals concentration, given by the geographical area in which the stream is located.