区域水生态承载力多目标优化方法与例证

水生态承载力是指维系水生态系统健康状态下的人类活动阈值,揭示的是某一区域人类活动与水生态系统之间的耦合规律,可为水生态环境保护与经济社会的协调发展提供依据. 基于水生态承载力的概念,构建了区域水生态承载力指标体系,建立了区域水生态承载力多目标优化模型,采用模糊方法进行求解,并采用遗传投影寻踪方法对方案进行优选. 以浙江省湖州市为例进行实证分析,以污染物环境容量利用率作为情景方案设定的依据,分别设定了双指标(COD_Cr、NH₃-N)、三指标(COD_Cr、NH₃-N、TN)、四指标(COD_Cr、NH₃-N、TN、TP)3种控制方案. 结果表明,3种控制方案的优化结果均具有一定的可行性和合理性,并推荐四指标控制方案为优选方案. 四指标控制方案优化结果表明:2020年状态指标水环境容量利用率、生态用水比例分别为99.3%、59.1%；调控指标GDP增长速度、人口增长速度、城镇化率分别控制在7.4%、0.5%、70.3%以下,污水治理资金占GDP的比例为0.9%,第三产业比例为52.1%,化肥施用强度为251.0 kg/hm2；在此基础上,湖州市2020年可承载目标人口总量为350.0×104人,GDP为2 965.4×108元. 

Multi-Objective Optimization for Regional Water Ecological Carrying Capacity and Case Study

The regional water ecological carrying capacity reveals an interactive coupling law between human activities and the water ecological system. The relationship between population and economic scale suitable for water ecological carrying capacity can be defined according to the results of this study, which could provide a scientific basis for coordinating water ecosystem protection and economic development. Based on the concept of water ecological carrying capacity, indicators of water ecological carrying capacity were set up, and a multi-objective optimization model combined with a scenario analysis was established for predicting and optimizing water ecological carrying capacity. The multi-objective optimization model was solved using a fuzzy mathematics method, and an optimal scheme was selected by using a genetic projection pursuit model. Huzhou City was selected as the study case. The environmental capacity utilization rate was used to set up three analyses with respect to the following pollutants meeting environmental capacity requirements:1) COD_Cr and NH₃-N; 2) COD_Cr, NH₃-N and TN; 3) COD_Cr, NH₃-N, TN and TP. The results showed that all of the above three schemes were practical and feasible. The final scheme, using the analysis of four pollutants, met the environmental capacity requirements and was indicated to be superior to the genetic projection pursuit model. Using the recommended analysis, in 2020 the utilization rate of water environmental capacity was 99.3%, the ecological water proportion was 59.1% of the total water resources, while the GDP growth rate, population growth rate and urbanization rate would be kept within 7.4%, 0.5% and 70.3%, respectively. The sewage treatment funds should be at least 0.9% of the total GDP, the proportion of tertiary industry would be 52.1% and the fertilizer use intensity would be 251.0 kg/hm2. Accordingly, the maximum carrying capacity of the water ecosystem in Huzhou City was a population of 3.5 million, and a GDP of 296.54 billion RMB in 2020.