Optimization of Shanghai Marine Environmental Monitoring Sites in the Identification of Boundaries of Different Water Quality Grades
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Water quality is critical to ensure that marine resources and the environment are utilized in a sustainable manner. The objective of this study is therefore to investigate the optimum placement of marine environmental monitoring sites to monitor water quality in Shanghai, China. To improve the mapping or estimation accuracy of the areas with different water quality grades, the monitoring sites were fixed in transition bands between areas of different grades rather than in other positions. Following bidirectional optimization method, first, 18 candidate sites were selected by filtering out specific site categories. Second, three of these were, in turn, eliminated because of the rule defined by the changes in the areas of water quality grades and by the standard deviation of the interpolation errors of dissolved inorganic nitrogen (DIN) and phosphate (PO4-P). Furthermore, indicator kriging was employed to depict the transition bands between different water quality grades whenever new sampling sites were added. The four optimization projects of the newly added sites reveal that, all optimized sites were distributed in the transition bands of different water grades, and at the same time in the areas where the historical sites were sparsely distributed. New sites were also found in the overlap region of different transition bands. Additional sites were especially required in these regions to discriminate the boundaries of different water quality grades. Using the bidirectional optimization method of the monitoring sites, the boundaries of different water quality grades could be determined with a higher precision. As a result, the interpolation errors of DIN and PO4-P could theoretically decrease.
Key wordsbidirectional optimization method boundaries of water quality grades Changjiang River Estuary and its adjacent areas transition bands indicator kriging
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This study is supported by the National Natural Science Foundation of China (Nos. 41376190, 41531179, 41421001 and 41601425), the Scientific Research Project of Shanghai Marine Bureau (No. HuHaiKe2016-05), and the Ocean Public Welfare Scientific Research Project, State Oceanic Administration of the People’s Republic of China (Nos. 201505008 and 201305027). The authors would like to specifically thank the East China Sea Environmental Monitoring Center of China for their marine environment monitoring data.
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