ABSTRACT The estimation of loads of pollutants is of crucial interest to identify the level of water quality, understand the processes and identify the sources of pollution. The aim of this study was to calculate time trends of loads and concentrations of eleven physical, chemical and biological parameters, in nine quality monitoring stations of the Verde River Basin from 2008 to 2014. The time series analysis was performed with different tests. First, with the verification of autocorrelation of the time series using the Spearman correlation test. Then, Kruskal-Wallis test was used to check significant differences between the seasons and, afterwards the Mann-Kendall or the Seasonal Mann-Kendall time trend tests were applied accordingly. The analysis results indicated differences between the spatial distribution of loads and concentrations for most of the parameters evaluated in this study. The results showed that the simultaneous analysis of concentration data and flow data is essential for a more comprehensive and reliable evaluation of water quality, since the changes in river flow over time can mislead the interpretation of the concentration data. Moreover, to analyze only the pollutant load data, without looking how the flow and concentration behaves, does not provide conclusive results, since it does not allow to evaluate whether changes in the load values were caused by alterations of the flow or concentration. Thus, the results indicate the need to monitor water quality along with flow measurement, providing more complete and reliable assessments of the evolution of water quality.
Trend analysis of selected water-quality constituents in the Verde River basin, central Arizona