| More and more attention has been paid to the exploitation and utilization of the ocean,which provides many necessary resources for human survival.Among them,the coastal shoal resources are particularly important.The construction of reclamation projects in shoal and offshore areas has been the main way to ease the land shortage and expand the development space in coastal areas.At the same time of exploitation and utilization of marine resources,human beings will inevitably have a negative impact on the marine environment.Reclamation often straightens the original coastline and shortens the coastline.This has changed part of the coastal topography,changed the characteristics of regional tidal current movement,and caused the change of pollutant transport law.The reclamation project occupies a large area of water,reduces the tidal capacity,and reduces the capacity of purification of pollutants.High intensity development activities such as reclamation,aquaculture,port construction,transportation and so on have brought environmental pressure to coastal waters.At the same time,the coastal area is the area that receives the most pollutants from land.A large number of industrial wastewater and domestic sewage are discharged into the offshore water body,which makes the water environment quality in the offshore area become worse.The ocean has a strong self purification capacity and can accommodate a large number of pollutants.On the premise of not causing unacceptable impact on the marine environment,the amount of pollutants that the ocean can contain is the marine environmental capacity.The capacity of the marine environment is limited.When the total amount of pollutants discharged exceeds the upper limit of the capacity of the marine environment,the marine environment and marine functions will be damaged or even difficult to recover.Scientific and reasonable determination of marine environmental capacity has become a hot spot of marine environmental research.Combined with the characteristics of open bay,based on the reality,this paper collected and measured topographic and hydrological data,pollution survey,water quality data and mariculture data.Combined with the numerical simulation of Delft 3D software,this paper studies and analyzes the current dynamic characteristics of Haizhou Bay,the current situation and distribution characteristics of the water environment in the sea area,the current situation of the water environment in the estuary and the discharge conditions of pollutants.The hydrodynamic model of tidal current and water quality diffusion model were established,and the model was verified according to the measured hydrological data,and the response coefficient and sharing rate were determined.By using the box model method and the sharing rate method,the marine environmental capacity of sea area of Haizhou Bay and the marine environmental capacity of the coastal estuary of Haizhou Bay are calculated respectively,and the mechanism and characteristics of change are analyzed.The research conclusion shows that:(1)The average water depth of Haizhou bay increased by 4.6 cm in 2016 compared with 2006.The area of the study area decreased by 34.93km2 in 2016 compared with 2006.The volume of seawater in the study area was 0.31725 km2 lower in 2016 than in 2006.The volume of water exchange in Haizhou bay decreased from 5.9182.5 billion m3/day in 2006 to 5.557.5 billion m3/day in 2016,which decreased by 367.5 million m3/day.The COD concentration in Haizhou bay was 1.39 mg/1 in 2006 and increased to 1.63 mg/l in 2016.The COD concentration outside the bay was 1.205 mg/1 in 2006 and 1.4 mg/l in 2016.(2)In 2016,the environmental capacity of COD in Haizhou Bay was 2765.0 tons less than that in 2006.Among them,the static residual environmental capacity decreased by 2948.44 tons,accounting for 106.63%of the total reduction.The dynamic environmental capacity increased slightly,with an added value of 183.35 tons,accounting for-6.63%of the total reduction.(3)Terrain changes and water environment quality changes caused by reclamation from 2006 to 2016 reduced the total environmental capacity of haizhou bay,with an impact ratio of 0.198 to 0.802.Among them,the impact rate of terrain and water environment on static residual environmental capacity is 0.16:0.84.The impact rate on dynamic environment capacity was-0.408:1.408.The decline of the water quality in the bay has a relatively large effect on the reduction of the environmental capacity,and the impact on the total Marine environmental capacity is 4.05 times that of the reclamation.The impact of water quality deterioration on static residual environmental capacity is 5.25 times that of reclamation.The increase of water quality difference inside and outside the bay will result in the increase of dynamic environmental capacity.However,the decrease of net tidal capacity caused by reclamation results in the decrease of dynamic environmental capacity,and the absolute value of the impact rate is 3.45 times.(4)The actual discharge amount of five estuaries in Haizhou Bay Coastal estuary area in 2006 was 102.353 tons/day,and 76.590 tons/day in 2016.The theoretical environmental capacity was 114.571 tons/day in 2006 and 81.410 tons/day in 2016.The remaining environmental capacity was 12.218 tons/day in 2006,and decreased to 4.82 tons/day in 2016.(5)From 2006 to 2016,the change of topography and the amount of pollutants discharged into the sea in the coastal estuary area of haizhou bay reduced the total environmental capacity of the coastal estuary area,with an impact rate of 0.363:0.637.The effect of the amount of pollutants discharged into the sea on the change of environmental capacity was relatively large,on average 1.75 times that of reclamation.There is no significant positive correlation or negative correlation between reclamation and coastal estuarine area.It mainly affects the structure of tidal dynamic field by superposition of coastal reclamation projects,and then the hydrodynamic diffusion transport capacity is affected and the environmental capacity is changed.The influence of the amount of pollutants discharged into the sea on the environmental capacity of the coastal estuary was positively correlated.(6)The change and corresponding relationship between the actual discharge,theoretical environmental capacity and residual environmental capacity of COD in Haizhou Bay from 2006 to 2016 are very complex.Estuaries with large actual emissions play a decisive role in the theoretical environmental capacity of coastal estuaries.It is the focus of the study on the environmental capacity of the coastal estuarine area,and also the key area of the total amount control of land-based pollutants into the sea.The decrease of the amount of pollutants discharged into the sea will lead to the decrease of theoretical environmental capacity.However,there is no clear positive or negative correlation between the actual emissions and the change of environmental capacity.(7)The average environmental capacity of the coastal estuary area of haizhou bay is 98 tons/day,with an average of 3.88 tons/(day*km2).The average ECD of the sea area is 1,186.56 tons/day,and the average is 1.17 tons/day(day*km2).The environmental capacity per unit area of the estuary area is larger than that of the sea area.The hydrodynamic condition is the basic driving force of the environmental capacity of sea area and coastal estuary area.However,the environmental capacity of the sea area is mainly controlled by the difference between the water quality inside and outside the Bay,while the environmental capacity of coastal estuarine area is affected by the value of the amount of pollutants discharged into the sea,the range of the amount of pollutants discharged into the sea and the influence of reclamation project.The main innovation of this study is to expand the boundary of space and time of marine environmental capacity.(1)In this paper,the calculation method system of marine environmental capacity in different time and space scales of open coastal waters is constructed.Based on this,the environmental capacity and its change of Haizhou Bay in different spatial scales from 2006 to 2016 were studied.The environmental capacity of Haizhou Bay in 2006 and 2016 and the environmental capacity of the estuary area were calculated by using the box model and the share rate method,and the characteristics of environmental capacity change are analyzed.(2)The influencing factors and mechanisms of Marine environmental capacity at different spatial scales in the sea area and the inshore estuary are revealed.And the contribution rates of various factors are calculated.The Marine environmental capacity at different spatial scales in 2006 and 2016 in haizhou bay was compared,the variation characteristics of environmental capacity and its influencing factors were analyzed,and the influencing mechanism and degree of different influencing factors were discussed,as well as the superposition and accumulation of various influencing factors.Finally,the contribution rates of various influencing factors were calculated. |
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