Research On Lake Ecological Security Evaluation Based On Improved Variable Weight TOPSIS Model

Lake is one of the most important freshwater resources.It can be useful for flood diversion and storage,ecological habitats and environment purification.With the intensification of human social and economic activities and the development of water resources,lakes ecological safety has become more and more serious.Therefore,it is important to carry out lake ecological safety assessment research.The lake ecological safety evaluation can examine the state of the lake ecosystem as a basis for lake management.Based on the DPSIR(Driver-Pressure-State-Impact-Response)conceptual model,this paper establishes an ecological safety evaluation index system.The entropy weight method and the expert scoring method are used as the calculation method of the basic weight.A variable weight function is used to solve the problem that some bad data may be ignored beacause of good data.The TOPSIS(Technique for Order Preference by Similarity to an Ideal Solution)model is combined with this indicator model to establish a new lake ecological safety evaluation method.Solving the problem that the fixed-weight evaluation will cover the influence of the disadvantage index,and the calculation result of the ordinary TOPSIS evaluation method is not suitable for dividing the ecological safety level.And Dalian Yingnahe Reservoir,Zhuanjiaolou Reservoir,Zhuwei Reservoir and Songshu Reservoir are seemed as research areas,respectively,are evaluated in the currently commonly used ecological safety index method and the improved variable weight TOPSIS evaluation method.Corresponding measures and suggestions are also put forward to solve the environment problems.The main research results are as follows.(1)Based on the DPSIR conceptual model,through index screening,a lake ecological safety evaluation index system was established.(2)The penalty variable weight function is introduced to improve the calculation method of the index weight.(3)The algorithm of the positive and negative ideal solutions in the TOPIS evaluation method has been improved to make the evaluation results more suitable for ecological safety classification evaluation.(4)Apply the comprehensive ecological safety index method and the improved variable weight TOPSIS evaluation method to the four major reservoirs in Dalian.The evaluation results of the comprehensive ecological safety index method show that the ecological safety index values of the four reservoirs are all between80-90,which is in a safe state.The order of ecological safety is Zhuwei Reservoir> YingnaheReservoir> Zhuanjiaolou Reservoir> Songshu Reservoir.The variable weight TOPSIS evaluation results show that,except for the ecological safety status of the Yingnahe Reservoir,which is safer,the remaining reservoirs are all less safe.The ecological safety order of this method is Yingnahe Reservoir> Zhuanjiaolou Reservoir> Songshu Reservoir> Zhuwei Reservoir.By comparing and analyzing the two results,it is found that the improved variable weight TOPSIS evaluation method is more strict,which will highlight the ecological safety problems of the lake and avoid the disadvantages being covered by the advantages.This method is more affected by the worst value in the index system.Combining the two evaluation results,there are eutrophication phenomena in the four major reservoirs in Dalian.The main source of pollution was analyzed by the principal component analysis method for Zhuwei Reservoir with the worst evaluation results.The results showed that the main pollution source may be pollution caused by the use of fertilizers for planting along the two tributaries in the north of Zhuwei Reservoir,and the southern part of Zhuwei Reservoir There may be sewage outfalls at the inlet of the reservoir,causing the total nitrogen in the reservoir to exceed the standard.In the future,it is necessary to strengthen the supervision on the discharge of domestic sewage in the countryside around the reservoir,and properly and effectively regulate the use of agricultural fertilizers along the rivers that flow into the reservoir.