养分循环与生态城市——人居环境视角下的综述与展望

Nutrient Circulation and Eco-City:Review and Prospect from the Human Settlement Perspective

当前,全球养分循环和代谢已经出现了相当严重的问题,但却被人居环境领域长期忽视。基于这一背景,介绍近期国际学术界关联生态城市与养分循环的相关论述,从养分循环对生态城市的作用机制、城市养分循环的关键策略(城市农业)、城市养分循环的技术体系及考虑养分循环的生态城市规划建设探索等四个方面进行了文献梳理和研究综述,最后总结当前研究的不足之处,并对后续研究提出建议。

At present,there are serious problems in the global nutrient circulation and urban metabolism,which are ignored by the researchers of human settlement field.Normally,nutrients refer to the substances that an organism obtains from the surrounding environment to support the growth of the organism and maintain life.In the context of ecological problems,nutrients mainly refer to nutrient elements such as phosphorus,nitrogen,and potassium required for farming.These nutrient elements maintain the operation of the whole ecosystem orderly through the natural metabolic process.Similar to energy circulation and water circulation,nutrient circulation has always been an important component of the urban ecological circulation system.It links the natural ecosystem and the human social system as an organic whole with the help of the agricultural system.In the pre-industrial society,the human and animal waste could be recycled to facilitate nutrient recycling.However,the industrialized society abandoned this good tradition and relied entirely on external resources to maintain agricultural cultivation.The nutrients are imported into cities in the form of food,which is consumed by city residents and converted into human excrement and organic waste.The human excrement is dealt with by sewage treatment plants,while the organic waste is mainly sent to suburban areas for landfill or incineration.Thus,a large number of nutrients cannot be returned to the soil,which directly leads to the following serious consequences:on the one hand,surface water is polluted,rubbish is piled up and human health is threatened;on the other hand,due to the decline of farmland fertility,a large amount of minerals and energy is consumed to produce chemical fertilizer so as to supply the land fertility,resulting in a serious nutrient crisis.With the increase of urban population,the one-way-flow of urban nutrients and linear metabolism has increasingly become the dominant factors of nutrient shortage and environmental degradation.Based on this background,closed urban nutrient circulation becomes an important topic in the field of ecological human settlement environment.As a fundamental principle of soil science,the nutrient circulation was analyzed earlier in the agro-food system.And now,it has become one of the most important evaluation indexes for the sustainable development of human society.The close correlation between the degree of nutrient circulation and kinds of environmental pollution problems are generally acknowledged.From the perspective of human settlement,the paper presents the relevant discussion between eco-city and nutrient circulation in recent international academia,and presents a systematic literature review mainly from the following four aspects:the mechanism of nutrient circulation for eco-city,the crucial strategies of urban nutrient circulation(urban agriculture),the technical framework of urban nutrient circulation,as well as the eco-city planning and construction integrated with nutrient circulation.From the perspective of this paper,in recent years,the international academic community has paid more attention to the ecological significance of nutrient circulation and related technical issues.Especially in the decentralized nutrient recovery in low-density and low-income communities,in-situ reuses technology,as well as the urban and rural nutrient recycling.Many technologies related to the nutrient circulation have been successfully applied to ecological communities and building practices,along with the advantages and disadvantages,technological feasibility,benefits and risks of nutrient circulation have also been summarized.As the connector and regulator of urban nutrient metabolism circulation,urban agriculture has also been fully discussed by the researchers and many theoretical researches are presented.China has rich experiences in the use of large-scale sewage treatment plants,treat of urban organic waste by compost yard,as well as reuse urban fertilizers in the rural areas.These research results and practical experiences have laid a foundation for the further development of related theoretical problems in this field.However,there are still insufficient researches in this emerging field,and the following shows four aspects that need to be further strengthened in the near future.1)In the future,it is necessary to further define the constituent system and hierarchical structure of urban nutrient systems in order to further standardize the research content and define environmental intervention strategies;2)The urban nutrient cycle should be regarded as a compound system,which includes the space,technology and society.The study of multi-dimensional interaction mechanism should be further strengthened;3)How to build an appropriate technical system to give the nutrient metabolism process an environmental quality that matches the needs of urban communities and"elegantly"close the nutrient cycle is a new element that needs to be included and a new subject that needs to be solved in the current ecological city construction;4)It is necessary to focus on how to return to traditional ecological wisdom and transform the traditional system of nutrient cycling into a new system with more adaptability,so as to provide a theoretical support for exploring the localization of China’s ecological city construction.