Analysis of eutrophication trend of surface water in Tianjin coastal area

In this study, the concentration of COD, inorganic nitrogen（IN） and active phosphate(PO43-) in surface water of Tianjin coastal area in the spring and autumn of 2008, 2010, 2013 and 2016 were collected. The results showed that the COD concentration had no obvious change while the concentration of IN and PO43- had a significant decline after land reclamation projects. As for seasonal changes, COD concentration is generally higher in autumn than in spring, while the concentration of IN and PO43- is generally higher in spring than in autumn. As for eutrophication index (E), it is generally higher in spring than autumn. In the spring of 2008 and 2010, the eutrophication index (E) bigger than 3 showed moderate eutrophication of surface waters. Since the reclamation began in 2010, the eutrophication index (E) of the coastal waters has decreased sharply, the level of eutrophication is mild during the construction period. With the construction of the port area, large-scale dredging and backfilling, the land-based pollutants have been effectively controlled, and the water quality of Tianjin coastal waters has been improved.