Effective visualization for the spatiotemporal trend analysis of the water quality in the Nakdong River of Korea

Spatial and temporal trend analyses were performed to obtain more meaningful water quality information in table and three-dimensional graph forms. Using the statistical approaches of the Seasonal Mann-Kendall (SMK) and LOcally WEighted Scatter plot Smoother (LOWESS) methods, the trends of three water quality parameters, including Biochemical Oxygen Demand (BOD), Total Nitrogen (TN), and Total Phosphorus (TP) measured along the Nakdong River of Korea between 1992 and 2002 were analyzed. The trends of the slopes were calculated using the SMK method for two consecutive stations and years. These values are provided in the trend tables which indicate the extreme upward and downward trends. Also, three-dimensional graphs of the water quality in the Nakdong River were generated with respect to the distance from upstream of the river and time of month. From this study, it was concluded that these tables and three-dimensional maps could be used as a useful tool to provide the spatiotemporal trend information such as the hot spots/moments of improvement and deterioration in the water quality of the Nakdong River, with the present web-based information system.