Study On The Fluxes And Temporal And Spatial Evolution Characteristics Of Major Chemical Pollutants In Laizhou Bay Based On Sea-land Collaborative Survey

Laizhou Bay is one of the three bays in Bohai Sea,and its offshore industry is an important part of shandong province’s Marine economy.In laizhou Bay and its adjacent sea areas,there are 10 rivers that enter the sea,such as Xiaoqing River,Yellow River and Weifang River,which are the main sources of land-based chemical pollutants pollution in Laizhou Bay.Since the reform and opening up,with the rapid economic development of Dongying,Weifang and Yantai along the coast of Laizhou Bay,the ecological environment of Laizhou Bay has gradually deteriorated,mainly reflected in the serious imbalance of nitrogen and phosphorus nutrient ratio,serious eutrophication,some sea areas are prone to red tide,and the ecological function is gradually weakened.Therefore,it is of great significance to estimate the flux of nitrogen,phosphorus and COD,and to study the temporal and spatial evolution of nitrogen and phosphorus nutrients and eutrophication status in Laizhou Bay.This study took Laizhou Bay and its adjacent waters as the research object.Four sea-land collaborative surveys were conducted in The spring（May）,summer（August）,autumn（October）and winter（January）of 2020 in Laizhou Bay,to estimate the flux of major chemical pollutants into the sea and analyze their temporal and spatial evolution characteristics in different seasons.The eutrophication status and organic pollution degree of Laizhou Bay were evaluated by n/P ratio method and organic pollution index method.The main conclusions are as follows:1、Estimation of chemical pollutant discharge flux in Laizhou Bay in 2020The land sources such as rivers,sewage outlets and farmland in villages and towns are systematically calculated.Mariculture and other Marine sources;The main discharge fluxes of chemical pollutants into laizhou Bay through three ways,such as atmospheric dry and wet deposition.Based on this method,the total amount of nitrogen,phosphorus and COD discharged into laizhou Bay by different pollution sources in 2020 is calculated.The total COD discharge is the highest,176249.5t/a;DIN followed,68446.7t/a;PO₄^3--P was the least,1949.1 t/a.The results show that the main chemical pollutants in Laizhou Bay and its adjacent sea area come from land-based pollution.The total amount of land-based pollutants discharged into the sea was 198651.6 t/a,accounting for more than 80%,followed by air pollution,and sea pollution was the lowest.In land-based pollution,the discharge flux of rivers into the sea reached 148069.6 t/a,which was the main source of land-based pollution.The runoff of Xiaoqing River and Yellow River was higher,and contributed the most to the pollutant discharge flux of rivers.DIN and PO₄^3--P produced by mariculture were absorbed by the shellfish themselves,and COD was the main pollutant produced.In air source pollution,wet deposition is the main source,and the total flux is 46807.3 t/a.2、Spatial and temporal evolution characteristics and eutrophication evaluation of inorganic nitrogen and phosphate in Laizhou BayThe concentrations of DIN and PO₄^3--P in surface and bottom layer of Laizhou Bay and its adjacent sea area are basically the same,but show obvious seasonal changes.DIN concentration is higher in spring and winter than in summer and autumn,and PO₄^3--P is the opposite.Among them,NO₃^--N accounted for more than 50%in the four seasons,and was the main form of DIN.Compared with the Marine Water Quality Standard（GB3097-1997）,the proportion of DIN over classⅡstandard value was the lowest in summer and the highest in autumn.Except in autumn and winter,PO₄^3--P concentration is higher in some sea areas,but lower than classⅠstandard value in other sea areas.From the point of view of plane distribution,the surface and bottom DIN distribution in Laizhou Bay and its adjacent sea area is roughly the same,but the distribution of PO₄^3--P is obviously different.DIN distribution is higher in the west than in the east,and high values are mainly distributed in the Yellow River estuary and Xiaoqing River estuary.Terrigenous input has a great influence on DIN distribution.The distribution of PO₄^3--P is greatly affected by the season and has no obvious distribution regularity.The upward transport of PO₄^3--P in the seafloor sediments is the main reason affecting its distribution.According to the evaluation results,the western and southern waters of Laizhou Bay are polluted by organic pollutants,while the eastern waters have better water quality.There were significant seasonal differences in the polluted sea areas,among which the sea area near xiaoqing River estuary was seriously polluted in spring.Except the eastern part of Laizhou Bay,most of the other sea areas were at the level of phosphorus limited potential nutrient and phosphorus limited potential eutrophication,which were alleviated in summer and autumn.The contents of DIN and PO₄^3--P in Laizhou Bay increased first and then decreased in recent 60 years.Nitrogen restrictions from the 1970s to the early 1990s gradually evolved into phosphorus restrictions today.The rapid economic development,human activities and the promulgation and implementation of relevant policies have a great impact on it.