Abstract
Because identifying the factors affecting water quality is challenging, water quality assessment of an individual component based on the arithmetic mean method cannot adequately support management policies. Therefore, in this study, we assessed the water quality target attainment at 24 sites in the Nakdong River Basin by applying multivariate log-linear models to identify factors influencing water quality, including flow and season. The temporal and seasonal water quality trend and flow were also analyzed using the calculated model coefficients. Specifically, weekly data on biological oxygen demand (BOD), total phosphorous (TP), and flow during 2013–2018 were used to investigate the 2018 water quality target attainment level for this river. The significance and suitability of the models were analyzed using the F-test, root mean squared error (RMSE), mean absolute percent error (MAPE), and adjusted R2 values. All 24 models applied in this study showed statistical significance and suitability for the prediction of BOD and TP concentrations. Moreover, flow was identified as the main factor affecting water quality and had a predominant effect on BOD and TP concentrations in tributaries and the main stream, respectively. Furthermore, among the 24 sites, BOD and TP targets were evidently attained at 18 and 17 sites, respectively.
Highlights
To assess the quality of public waters, each year, the Ministry of Environment (MOE) in the Republic of Korea uses the arithmetic means of biological oxygen demand (BOD) and total phosphorous (TP) concentrations based on mean annual data to calculate water quality targets and determine the extent to which these targets are being attained
Among 32 representative sites in the sub-basin of the Nakdong River, multivariate log-linear models were applied to 24 sites where flow data were available to analyze the water quality trend and assess the water quality targets
Based on the multivariate linear models, flow was identified as the main factor that affects water quality with respect to BOD and TP
Summary
To assess the quality of public waters, each year, the Ministry of Environment (MOE) in the Republic of Korea uses the arithmetic means of biological oxygen demand (BOD) and total phosphorous (TP) concentrations based on mean annual data to calculate water quality targets and determine the extent to which these targets are being attained. Water quality assessment based on the arithmetic mean method is widely used and easy to apply. It has limited applicability in assessing water quality due to seasonality, non-normality of data distribution, and ambiguous decision criteria for missing data and outliers.
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