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Membrane Water Treatment   Volume 10, Number 5, September 2019, pages 339-352
Evaluation of long-term water quality management policy effect using nonparametric statistical methods
Kang Young Jung, Jung Min Ahn, Sohyun Cho, Yeong Jae Lee, Kun Yeun Han, Dongseok Shin and Kyunghyun Kim

Abstract     [Buy Article]
    Long term water quality change was analyzed to evaluate the effect of the Total Maximum Daily Load (TMDL) policy. A trend analysis was performed for biochemical oxygen demand (BOD) and total phosphorus (TP) concentrations data monitored at the outlets of the total 41 TMDL unit watersheds of the Nakdong River in the Republic of Korea. Because water quality data do not usually follow a normal distribution, a nonparametric statistical trend analysis method was used. The monthly mean values of BOD and TP for the period between 2004 and 2015 were analyzed by the seasonal Mann-Kendall test and the locally weighted scatterplot smoother (LOWESS). The TMDL policy effect on the water quality change of each unit watershed was analyzed together with the results of the trend analysis. From the seasonal Mann-Kendall test results, it was found that for BOD, 7.8 % of the 41 points showed downward trends, 26.8 % and the rest 65.9% showed upward and no trends. For TP, 51.2% showed no trends and the rest 48.8% showed downward trends. From the LOWESS analysis results, TP began to decrease in most of the unit watersheds from mid-2010s when intensive chemical treatment processes were introduced to existing wastewater treatment plants. Overall, for BOD, relatively more points were improved in the main stream compared to the points of the tributaries although overall trends were mostly no trend or upward. For TP, about half of the points were improved and the rest showed no trends.
Key Words
    TMDLs; LOWESS; Seasonal Mann-Kendall test; Nonparametric statistical methods
Kang Young Jung, Yeong Jae Lee, Kyunghyun Kim: National Institute of Environmental Research Yeongsan River Environment Research Center, 5, Cheomdangwagi-ro 208beon-gil,
Buk-gu, Gwangju 61011, Republic of Korea
Jung Min Ahn: National Institute of Environmental Research Water Quality Assessment Research Division, 42 Hwangyong-ro, Seo-gu, Incheon 22689, Republic of Korea
Kun Yeun Han: Department of Civil Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, Republic of Korea
Dongseok Shin: National Institute of Environmental Research Watershed Pollution Load Management Research Division, 42 Hwangyong-ro, Seo-gu, Incheon 22689, Republic of Korea

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