The impact of water temperature on water quality indexes in north of Liaodong Bay

•COD, DO and fecal coliform vary a little with the changes of water temperature at the north of Liaodong Bay.•TBC increases dramatically when the water temperature is over 16°C at the north of Liaodong Bay.•The concentration of TBC in summer is more 30 times than that in winter at the north of Liaodong Bay. The north of Liaodong Bay is one of the most severely polluted areas in Bohai Sea. Because the self-purification capacity from the sea water exchange process is limited, the pollutants from the land and river sources cannot be completed degraded and an obviously contaminated zone was formed in the north of Liaodong Bay. Therefore the self-purification capacity from biological process is essential for maintaining ecosystem balance. Marine heterotrophic bacteria play an important role in degradation of the dissolved organic matters and constitution of the primary production in the coastal areas. The shift of water temperature between winter and summer is about 28°C in the north of Liaodong Bay, which causes changes in the self-purification capacity of the sea area. Certain indexes of water quality in Liaodong Bay were investigated in order to detect how these indexes response to the changing of water temperature. The experimental results show that COD, DO and the concentration of fecal coliform vary a little with the changing of water temperature; TBC increases dramatically when the water temperature is over 16°C; and TBC in summer is 30 times more than that in winter. By this study, the paper provides a reference to assess the environmental purification capacity of the sea area during different seasons.