| With the rapid development of economy and society in China,the contradiction between economic benefit and lake environment is becoming more and more serious.The government has invested a lot of resources in the governance of lake water environment,but the governance effect and efficiency have not reached the expectation.Therefore,it is urgent to find a set of practical and effective decision for lake water environment governance.The main body of water consumption in the lake basin is interrelated and restricted,which requires that the economic and social development in the basin must be realized with the overall benefit of the basin as the goal.The inputs of lake pollution come from industrial,agricultural and urban development activities.Nutritional inputs are the by-products of these activities,and the benefits of these activities are related to the inputs.Therefore,decision makers need to balance the benefits of polluting activities against the ecological values that are forgoing due to the consequences of pollution.In this context,taking the Taihu Lake Basin as an example,the thesis constructes a multi-objective optimization model based on the complex system of the Taihu Lake Basin under the mutual constraints of economy and environment,in order to seek the optimal management strategy under the premise of avoiding the irreversible nutrient state of the lake.First of all,the thesis sorts out related theoretical studies on water environment governance and multi-objective optimization,and clarifies the technical route and algorithm model of the research.The main pollution problem in Taihu Lake Basin is eutrophication,and as a complex system,there is deep uncertainty in the basin.Based on the actual situation of Taihu Lake,a multi-objective and multi-scenario optimization method is used to achieve the effectiveness and robustness of the water environment governance strategy in the Taihu Lake Basin.Then,using the model of the classical lake problem for reference,the thesis builds a multi-objective optimization model of water environment governance in Taihu Lake Basin,including the economic and environmental models and the objective function that mutually restrict each other and form a closed loop.The economic model mainly considers the utility caused by phosphorus input and the loss caused by phosphorus concentration,and combines the utility and loss to form the economic benefit of the Taihu Lake Basin.The environment model improvs the natural inflow of phosphorus on the basis of the classical lake model and builts the dynamic iteration model of phosphorus concentration.Then from the perspective of economy and environment,four objectives are selected,including expected economic benefit,phosphorus concentration,maximum pollution reduction control and water quality reliability,to balance the objectives of multiple dimensions.The model involves two types of parameters: certainty and uncertainty.The method of fitting historical data is used to estimate the certainty parameters.With reference to existing studies,the uncertain parameters are assumed to follow lognormal distribution.The constraint condition of the model consists of two parts.In addition to setting the reliability of water quality in the environmental model itself,the thesis also summarizes five governance strategies,namely non-control strategy,economic strategy,pollution control strategy,strong emission reduction strategy and weak emission reduction strategy,from the perspective of the water environment governance planning policy of Taihu Lake Basin,and adds them into the multi-objective optimization model in the form of constraint conditions.Finally,the thesis adopts two optimal distribution methods of single scenario and multi-scenario respectively for decision analysis,and visually displays the target performance of the strategy through multi-dimensional visualization method.According to Monte Carlo simulation,10000 scenarios are constructed,and 100 of them are randomly selected as future scenarios for the Taihu Lake Basin from 2015 to2040 for research.In the single scenario optimization,through the comparison and analysis of the performance of each strategy,the trade-off relationship between the research objectives and the performance characteristics of each strategy are summarized.Decision makers need to make a trade-off between economic development and water environment protection in the watershed.To obtain better economic benefits,it is necessary to pay the price of increasing phosphorus concentration and decreasing water quality reliability.At the same time,in order to ensure that the water quality of the Taihu Lake basin does not receive excessive pollution,the annual range and intensity of pollution reduction should also be increased.When making multi-scenario decision analysis,the thesis conducts calculation experiments on all 100 scenarios through NSGA-II algorithm.The concept of relative efficiency is introduced,and the solution set is optimized by using the method of data envelopment analysis.Based on this,the strategies under multiple scenarios are compared and analyzed.Taking economic and environmental factors into consideration,the weak emission reduction strategy has a more efficient,stable and balanced performance under uncertain future scenarios,and it has a good performance in terms of economic benefit,phosphorus concentration and water quality reliability.Because the performance distribution of each strategy has its own characteristics,decision makers can choose the most appropriate strategy according to the actual situation when they have target preference. |
