Study On The Total Amount Control Of Pollutants Based On Environmental Capacity

The study of total amount control of pollutants in the bay area plays a significant role in achieving continuous improvement of the marine environment quality,and promoting the coordinated development of the economy and the marine environment.In China,due to the differences between land and sea areas’environmental regulatory systems,there is a lack of connection between land-based pollution discharge and water quality of near-shore sea areas,which resulted in difficulty applying of total control technologies.To resolve this issue,this research took Dalian Bay as an example and calculated the environmental capacity of the bay based on an analysis of the hydrodynamic nature and water exchange characteristics.It also established a total amount control method of"outfall to the sea-marine environmental functional area-environmental residual-graded supervision"by combining the results of discharge load and environmental capacity allocation.The research provided an effective reference for using environmental capacity resources and making land-sea connective regulation policies.The main research contents of the paper are as follows.（1）A hydrodynamic model of Dalian Bay was established based on the MIKE 21 model.The measured tide level and current data were used to verify the hydrodynamic parameters;the validation results show that the simulated value has a small error from the measured value.The established numerical model portrays the hydrodynamic conditions of Dalian Bay waters accurately,which provides the necessary physical condition for subsequent studies.After analyzing the tidal field,it could be seen that Dalian Bay belongs to the informal semi-daily tidal area,and the average tidal velocity was 0.3 m/s.The closer to the top of the bay,the lower velocity was,and the overall flow velocity of the Dalian bay was lower than other bays.（2）Based on the hydrodynamic field,a convective-diffusive water exchange model was established to study the seawater dynamics.The water exchange characteristics of Dalian Bay were measured holistically and regionally using the concentration tracer method.The semi-exchange time of Dalian Bay as an entity is about 5.4 tidal cycles,with each partition ranging from 0.5 d to 31.7 d.The water exchange capacity of different locations varies significantly,to which the closer to the bottom of the bay,the stronger the hydrodynamics of the sea.The clarification of the water exchange capacity of the bay provides a theoretical basis for the regulation and layout of the land source outlets.（3）The environmental capacity solution model of the Dalian Bay sea area is established.Water quality control points are set considering the mixed zone and marine functional area.The environmental capacity allocation resulted from the outfall with the largest total discharge load is calculated by the improved discharge optimization method.The environmental capacities of chemical oxygen demand（CODMn）,dissolved inorganic nitrogen（DIN）,and active phosphate(PO4^3--P)in Dalian Bay are calculated to be 17350.3 t/a,1533.4 t/a,and 148.6 t/a.Multiple outfalls were severely overloaded with inorganic nitrogen.Considering the functional areas of the marine environment,combined with the environmental capacity and pollution discharge,the discharge supervision method and outfall improvement proposal for the graded management of direct discharge into the sea in Dalian Bay was proposed.This management approach improved the precision of pollution management and effectively connects the near-shore sea and land-based pollution sources,promoted the achievement of total control of pollutants entering the sea.