Recent Temporal and Spatial Variation in Active Phosphate Concentration in Seawater of the Central Bohai Sea

Abstract:

The Bohai Sea is a semi-closed gulf with weak hydrodynamic condition and self-purification capacity. Therefore its eco-system is more sensitive and fragile than open seas. A serious oil spill accident occurred in the Penglai 19-3 oil field located in the central Bohai Sea in 2011, which severely affected the marine ecological environment and fishery resources. To determine the aftermath in fishery ecological environment, nine surveys were carried out in the central Bohai Sea in 2012–2014. Based on part of the survey data, we analyzed the temporal and spatial variation in active phosphate and the corresponding factors in the central Bohai Sea. The results showed that the levels of active phosphate met the second class of sea water quality standard in spring and summer from 2012 to 2014, but the pollution caused by active phosphate was observed in part of the survey in autumn and winter; the horizontal and vertical distribution of active phosphate varied in different seasons, and in spring and summer the concentration of active phosphate gradually decreased along with the increase in depth, while in autumn and winter it was almost constant from the surface to the bottom; the seasonal mean concentration of active phosphate followed the order winter>autumn>spring>summer, and it was obviously higher in winter than in summer, plus the mean concentration was lower in 2014 than in 2013; The distribution and variation of active phosphate in the central Bohai Sea was affected by many factors, and key ones included exogenous supplement, endogenous release of nutrients, and biological consumption.