Environmental Capacity And Total Quantity Control Of Nitrogen And Phosphorus In The Northern Part Of Liaodong Bay

In recent years,a large number of pollutants have entered into the sea because of the rapid development of social economy in coastal areas and disorderly exploitation of marine resources,which caused the deterioration of coastal water quality,ecological degradation,productivity decline,and even affect the further development of the social economy in coastal areas.Therefore,protect the marine environment and maintain its ecological health is an important prerequisite for the rational development and utilization of marine resources and sustainable development of society and economy.Liaodong Bay is a typical semi-closed and shallow bay with limited water exchange capacity,which located in the northeast of Bohai Sea.As the major waste material processing place of terrestrial pollution,the northern part of Liaodong Bay became the most polluted area in the whole bay.This study not only assesses the eutrophication level based on the pollution situation of nitrogen and phosphorus of the northern part of Liaodong Bay,but also calculates the environmental capacity of those two pollutants of the study area according to the standards of water quality in each functional zone,and put forward some suggestions on total mass control of pollutants.The main research contents and conclusions of this paper are as follows:(1)The data of conventional water quality and nutrients was gained by the field investigation which were carried out in the summer of 2014—2016,and its spatial distribution characteristics were analyzed.The inorganic nitrogen,active phosphate and COD all showed the features of high concentration in the summer of 2014 and 2016,but relatively lower concentration in 2015,and the high concentration area mostly concentrated in estuaries and coastal waters.(2)Based on the data from field investigation,inorganic nitrogen,active phosphate,COD and chlorophyll were selected as the index to evaluate the eutrophication of Liaodong Bay.Results showed that the eutrophication level was higher in 2014 and 2016,but decreased in 2015 which was almost oligotrophic and mesotrophic waters in study area,and it was higher in coastal and estuary area but lower in outside sea in all three years.(3)Based on the short-term observation data of spring and neap tide in the summer of 2015,we analyzed the characteristics of ellipse elements of tidal currents,type of tidal current and residual current in the northern part of Liaodong Bay through the way of calculating harmonic constants without introducing difference,and gained the mean tidal range and maximum possible tidal difference.The results showed that the tidal currents in northern part of Liaodong Bay are regular semidiurnal ones,and M2 tidal current constituent is dominated,which has the motion type of rectilinear,with the direction of NE—WS.Residual currents in this sea area are barely different between bottom and surface layer,with velocities between 10.15~14.5 cm/s.The study area has a high amplitude,where the amplitude of M2 tide reached 1.31 m,and the mean tide range and maximum possible tide is 2.71 m and 5.23 m respectively.(4)Based on the latest coastline and water depth data in study area,the research space was divided into grids,and then we calculated the environmental capacity of nitrogen and phosphorus in each functional area by determining the number of grid in the study area and water quality requirements of each functional area.The calculation results showed that the inorganic nitrogen and active phosphate were the main pollutants which exceed the standard in almost all functional areas in 2014 and 2016.Due to the decrease of pollutant concentration in 2015,only inorganic nitrogen exceeded the standard in some estuarine functional areas.(5)The main source of pollutants in the northern part of Liaodong Bay including sewage pollution,agricultural non-point source pollution and industrial pollution.This study aimed to the different types of pollution and the process of pollution,suggested that we should adjust industrial structure and make the planting and farming more scientific which would control the pollutants from the source.But in the transport process,the sewage pipeline should be completed to realize sewage concentrated treatment,in the mean while the discharge of sewage should on the basis of the hydrodynamic characteristic of Liaodong Bay to reduce the pollutant accumulation in near-shore.The main mean of pollutants control after the discharge is biological repair which mainly for plantation of phragmites australis and suaeda salsa.According to the current situation of pollutants in the northern part of Liaodong Bay,this study proposed a feasible plan accord with the management requirements of pollutants amount control,which would provide scientific base for the total mass control of Liaodong Bay and have an important sense to controlling ecological environment destruction and improve the quality of water environment.