Evaluation of organic pollution and eutrophication status of Kaohsiung Harbor, Taiwan

• Organic pollution index and eutrophication index were used to assess the water quality of Kaohsiung Harbor, Taiwan.
• Spatial distribution of dissolved inorganic N and dissolved inorganic P was estuaries > channels > harbor entrance.
• Seasonal distribution was observed for EI in Kaohsiung Harbor.

The pollution level and eutrophication conditions of bottom water in Kaohsiung Harbor (Taiwan) were evaluated using organic pollution index (OPI) and eutrophication index (EI). Water samples were seasonally collected (February, May, August, and October) from 20 sites of the harbor in 2012. Distribution of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), chemical oxygen demand (COD), and dissolved oxygen (DO) in the water samples were investigated. Results showed that the average concentrations with standard deviations of DIN, DIP, COD, and DO for all water samples (n = 80) were 0.16 ± 0.11, 0.18 ± 0.07, 3.06 ± 1.09, and 5.49 ± 0.84 mg L−1, respectively. The distribution of DIN, DIP, and COD concentrations presents a trend that estuary > channel > harbor entrance. These observations clearly indicate that upstream industrial and municipal wastewater discharges along the river bank are major sources of contamination in the harbor water. Based on the analyses using the OPI and EI, results show that pollution was much heavily in the wet season (OPI = 25.9 and EI = 38) than dry season (OPI = 13.4 and EI = 18.0). Moreover, it is worth to notice that all of water collected from Kaohsiung Harbor were classified as the heavily polluted and eutrophication situation.