This study investigated the annual variation in nutrients, chemical oxygen demand (COD), and dissolved oxygen (DO) at three stations in Masan Bay from 1995 to 2005. The dissolved inorganic nitrogen (DIN) concentration decreased significantly at all stations after 2001, whereas the dissolved inorganic phosphorus (DIP) concentration showed no distinct annual variation. The DIN/DIP molar ratio also decreased tremendously at all stations after 2001. The COD decreased at all stations after 2001, whereas the DO concentration increased slightly. The decreases in DIN and COD and the increase in DO may have been associated with the almost doubling of the treatment capacity of the Masan wastewater treatment plant, which considerably improved the water quality in the bay.
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