Distribution of Inorganic Nutrients and Potential Eutrophication Assessment in Bohai Bay in Spring

Based on the nutrient data of 20 stations from Bohai Bay in May 2011,the distribution of major inorganic nutrients in Bohai Bay and seawater potential eutrophication were analyzed.The results show that NO-3-N concentration in the investigated sea area ranged from 150.5 to 276.3,μg/L,NO-2-N concentration ranged from 4.072 to 29.49,μg/L,and the concentrations of NH+4-N,PO34--P as well as SiO23--Si ranged from 47.55 to 194.8,μg/L,4.73 to 26.35,μg/L and 170.2 to 544.1,μg/L,respectively.In general,nutrient concentrations decreased from near-shore to offshore but exhibited little variations between the surface and bottom within the water column.The concentration of all DIN species gradually increased from the east to the west while the concentration of SiO23--Si displayed an inverse trend.The concentrations of NO-3-N,NH+4-N and SiO23--Si progressively went up from the north to the south,opposing the patterns of NO-2-N and PO34--P.Time-series of data indicated that the nutrient concentration,particularly that of DIN,synchronized the diurnal tidal fluctuations in the studied area,being lower at high tides and higher at low tides.Nutrient concentrations were not significantly correlated to salinity.NO-3-N was the dominant DIN species,accounting for on average 69.56% of the total DIN.The Bohai ecosystem seemed to be evolving from P-limitation to combined P-and Si-limitation,which is in line with our assessment of the potential eutrophication in this area.