Ecological Security Evaluation Of Laizhou Bay Based On DPSIR-GM(1,1) Model

Laizhou Bay is the largest bay in Shandong Province,surrounded by more than ten rivers,and many rivers bring a lot of nutrients to Laizhou Bay,making it an important fishing ground in the north.With the development of the society,large amount of land-based pollutants are discharged into the ocean,which not only destroys the ecological environment of Laizhou Bay,but even affects the dynamic balance of the ecosystem.Therefore,it is crucial to understand the changing trend of ecological security in Laizhou Bay and provide scientific basis for the sustainable development of Laizhou Bay.In this paper,four voyages were surveyed in Laizhou Bay in May,August,October and December in 2021,and the organic pollution index method and eutrophication index method were used to evaluate the water quality of the bay.Based on the basic characteristics of Laizhou Bay,referring to previous research,36 typical indicators were selected,and the analytic hierarchy method,entropy method and DPSIR model were used to comprehensively analyze the ecosystem security status of Laizhou Bay under the influence of human activities from 2015 to 2020,and on this basis,the gray GM（1,1）prediction model was used to predict the ecosystem security of Laizhou Bay in 2021 and 2022.The main conclusions are as follows:1.Spatial-temporal distribution characteristics of nutrients in Laizhou Bay（1）The nutrient content of the surface and bottom layers of Laizhou Bay varies similarly in the four seasons.DIN content was low in spring,high DIN content were in autum,and NO₃^–-N was the main contributor to DIN.The DIP content in winter was higher than in spring,and the DIP content in the surface and bottom layers were lower than theⅠclass Sea water quality standard.（2）The plane distribution of DIN and DIP on the surface of Laizhou Bay showed a trend of nearshore high and far-shore low.The concentration of surface DIN was higher in spring,the highest concentration of bottom DIN was in winter,and the high value area was mainly concentrated in the estuary of rivers,and the horizontal distribution of surface and bottom DIN were consistent.Except for summer,the concentration of DIP in the surface and bottom layers changed consistently,and there was no obvious seasonal change,and the transport of DIP in the bottom sediment was the main reason affecting its distribution.（3）The seasonal distributions of organic pollution were similar to those of surface DIN,in which the southwest sea area and the Yellow River estuary sea area were seriously affected by organic pollution,and the water quality in the eastern sea area was better than that in the western sea.The sea area showed smallest area of organic pollution in winter,and autumn season showed largest area under organic pollution.（4）In the past 40 years,the surface eutrophication index and DIN/DIP of Laizhou Bay had shown an"inverted U-shaped"trend,and the transport of land-based pollutant was the main source of DIN in Laizhou Bay.The nutritional structure of Laizhou Bay has changed from the N restriction in the 1980s to the current P restriction.2.Ecological security evaluation of Laizhou Bay based on DPSIR modelThe representative indicators of Laizhou Bay were selected,and the subjective weight and objective weight of each index in the ecological security system of Laizhou Bay were obtained by Analytic Hierarchy Process and Entropy value method,and then the comprehensive weight of the index was obtained.Referring to the previous research,the ecological security evaluation level suitable for Laizhou Bay was divided,and the scores of each index layer,criterion layer and target layer from 2015 to 2020 and the ecological security level in each year were obtained by using the comprehensive weight.Finally,according to the evaluation results,the key indicators affecting the ecological security of Laizhou Bay were screened out,mainly including:natural population growth rate,per capita gross regional product,ammonia nitrogen discharge flux of major rivers,COD discharge flux of major rivers,water eutrophication index,etc.People are the main body of promoting economic development,but also the root cause of pollutants discharged into the ocean,economic development and the improvement of living standards,resulting in an increase in sewage and waste from industry and life.The Yellow River is the main river around Laizhou Bay,which not only brings rich nutrients to the bay,but also an important source of pollutants,impacting security of the bay,and natural climate changes will also affect the marine system.While developing and utilizing the ocean,people also actively take measures to protect the marine environment and improve the ecological security level of Laizhou Bay.From 2015 to2020,the overall ecosystem security status of Laizhou Bay showed a fluctuating and rising trend,except for the poor ecosystem security status in 2016,all other years were at the general level or above,indicating that the ecosystem security of Laizhou Bay gradually improved and the ecological environment developed better after treatment and other measures.3.Gray forecast of ecological security in Laizhou BayFive target layers were obtained by constructing the ecological security evaluation system of Laizhou Bay through 36 indicators,and the gray GM（1,1）prediction model was established after each target layer passed the hierarchical ratio test,and the ecological security status of Laizhou Bay in 2021 and 2022 was predicted after each prediction model passed the posterior difference ratio test and the small error probability test.The results showed that the ecological security level of Laizhou Bay gradually increased,and the marine ecological security level in 2021 and 2022 was very good and excellent,respectively,indicating that the marine ecosystem in Laizhou Bay showed a trend of sustainable and healthy development.