The improper waste disposal and pollution caused by the human production and consumption activities severely affect both human and natural capital. As such, the focus is placed on the primary metabolism related to the input side of the environmental impact; the urban system is analyzed from the perspective of an organism's metabolism. The studies on various nations focused on the urban material metabolism; most of these studies, however, use different financial procedures for evaluating the natural and human capital values and losses. The production and consumption processes must be taken into consideration by the quantitative analysis of the urban metabolism. As such, there is a burning urge to include a quantitative methodology that can determine the conflicting environmental responses of both the production and use activities, addressing specific damages to the human health and ecosystems. The urban set-up focuses on the energy flows from the immediate environment in a bid to reinforce the intense and diverse activities happening within them. They are the AJAR systems that continuously demand the replenishment of the energy and matter in order to keep these activities alive. They accumulate resources via a dynamic network of channels delivering everything ranging from food to removing the wastewater, waste heat, solid waste, and the completed goods and services for the export. The energy is the primary catalyst in the ecological and social systems; therefore, it is imperative to comprehend its flows. In the ecological systems, one tends to discover the plenty of primary producing organisms that help in capturing and importing the external energy resources into the system.
In order to support the acute and distinct activities within the surrounding areas, the urban systems concentrate the energy flows from these surrounding areas. They are the open systems that regularly require revitalization of energy and matter in order to sustain their activities. Additionally, they obtain the resources through a complex network of channels delivering everything ranging from air and food to materials and fuels, etc. Moreover, it is also true for removing the wastewater, solid waste, and waste heat, as well as finished goods and services for the export.
The energy is the primary driver for the ecological and social systems; thus, it is important to understand the energy flows within both systems. A plenitude of the primary producing organisms can be found; its role is to capture and import the external resources into the system. These solar energy resources are stored, transformed, and transported to the basic and subordinate heterotrophic consumers. As such, the purpose of this paper is to analyze the urban metabolism of Beijing.
Beijing is a city situated in the northern part of the Northern China Plain; it is a political, cultural, and economic center of China. It covers an area of 16410.54km2 and consists of the two counties: Yanging and Miyun (Jiang, 2011). According to the study conducted in 2010, it is the second highly-populated city after Shanghai with nearly 86% of the population living in the urban areas. The city has experienced the rapid economic growth for the past few decades; the tertiary industry accounted for 75% of its GDP in 2010 (Feng, Huang, Wang, & Zha, 2015).
Despite an awesome growth of the tertiary industrial sectors of Beijing, the investments in the urban infrastructure are needed for improving the environment (Hu, 2014). The fog and haze conditions are widespread in Beijing due to rampant urban growth; hence, they point to a metabolically unsustainable development of the city (Marchettini, Brebbia, Pulselli, & Bastianoni, 2014).In addition, Beijing belongs to a group of cities that lack resources. It has small reserves of coal, iron, and building materials and lacks the external inputs that are the basic requirements for the production and life in a city.
Undoubtedly, there is a necessity to comprehend the urban metabolism of Beijing because of its vulnerability to the interruptions in the resource flows (Zhang Yang, Liu, & Yu, 2011).
Table 1 Energy Items of the Urban Metabolism and Transformity
Source: Ferrão, & Fernandez, 2013.
Figure1. Conceptual model of the urban energy metabolic processes.
The Processes Involved
The relationships between the living organisms and societal events are different. Nonetheless, it is presumed that the urban set-ups sectors of the energy discovery, energy changes, and domestic and foreign consumers are a symbol of a significant compatibility with the ecological functions. Primarily, the energy discovery division outlines the main producers; the energy transition division considers the primary consumers, community, and manufacturing part of the economy that are the next consumers while the remaining sector is mostly represented by the bacteria and fungi.
The emergy usually means the quantity of energy of a single category with the greatest part being received from the sun that is immediately required for the provision of the stated movement or keeping the energy and any physical object. It is measured in joules. The energy from the sun is needed for producing a flow unit or keeping the energy present; it is called the solar transformity and depicted as the solar emergy joules per joule of the output flow (seJ/J).
The emergy required directly and indirectly for making one joule of energy of the sun energy is presumed to be equal to 1.0 seJ/J) (Jørgensen, 2007). If the aspect of transformity is applied, the emergy analysis provides one measurement unit that represents the unity of all resources, energy, and cash movements from the town centers to the entire surrounding. In the recent years, the emergy analysis has been applied for studying the socioeconomic and environmental metabolism of many cities, for example, Hong Kong, China, Sydney, Australia, and Toronto, Canada, etc. These studies provide a valuable reference for integrating the metabolic health assessment of the urban systems into the emergy analysis. These studies, however, have put emphasis on the linear accumulation values of the material flows in the city systems, and lack further research on the urban metabolism efficiency based on the input/output perspective, especially in terms of the amounts of the waste emergy.
In order to measure the urban metabolic capabilities, a typical framework of the emergy items describing the urban metabolic system is defined (Rauscher & Momtaz, 2014). The framework covers a comprehensive portfolio of not only the renewable and non-renewable resources emergy inputs in manufacturing the import and export products and services but also the waste outputs.
The total amount of emergy consumed by the city within a year (U) is an essential pointer in the quantifying emergy movement in the urban metabolic system. It points out that the total emergy without the exports and wastes consists of four parts: renewable emergy (R), indigenous renewable emergy (IR), non-renewable emergy (N), and imported emergy (IM) (Pimentel, 2008). The total emergy with exports and wastes (Us) is another indicator that expresses the emergy sum of the import and export, input and output (Dobson, 2009).Similarly, the EU is a proportion of imported (IM) and exported emergy values (EX) accounting for the total emergy with the exports and wastes (Us) that elaborates the system's dependency on the external resources and energy.The higher the EU, the more vulnerable the urban metabolisms are. To explore the trend of the sustainability dynamics of Beijing during its recent economic growth, a set of emergy performance indices was computed (Karatas & Ve Tunca, 2010). The dependence of a process on the local resources can be depicted by the emergy yield ratio (EYR).A well-elaborated rate of the free local resources and imported resources ensures the sustained development of a city.
After the enactment of the Reform and Opening-up Policy, which revealed that the growth of Beijing was followed by an enormous environmental pressure on the local resources, the environmental loading ratio (ELR) has rapidly increased (Chen, 2009).The small drop in 2006 may be the causal factor of the instability of the growth progression and cannot be interpreted as the new data for the following years are available. The loading ratio further increased the environmental loading ratio after considering the additional emergy demand for the emissions impacts since the indirect input flows were mainly of the non-renewable emergy. A study conducted concluded that Beijing suffers higher environment loading and more adverse sustainability condition as compared to Taipei and Macao, which experience a lower environmental loading ratio due to the population peculiarities and respective environs.
Results and Discussion
The Direct and Indirect Inflow Analysis in Different Urban Metabolic Process
A number of studies have focused on the free environmental services and benefits of depending on the existing cycles and processes in the biosphere in a bid to avoid the demand for the extra investment in the damage fixing. Such a technique requires the waste products to be released in quantities that are easy to absorb and also recycle with the little or no extra resource investment. It means that the emissions above the required threshold cannot be sustained. The results indicate that the urban consumption processes release more waterborne emissions than the urban production activities over the investigated period. On the other hand, the airborne emissions typologies of activities are quite close, and emergy values are way behind for the waterborne pollutants. Therefore, Beijing needs to focus on the waterborne emission control in its consumption activities.
The largest emergies of the environmental services required for diluting the airborne contaminant have been decreasing over time. Meanwhile, out of all the waterborne pollutants, the ecological services were mostly utilized in diluting NH3-N (Gupta, & Ali, 2012). Despite a sharp decline in the consumption of the environmental services, the emergy values are still higher than in the production process. It is also essential to know that only a rough accounting is done for ascertaining the environmental ability to absorb, dilute, and process the undesired waste products or by-products. There is a hypothesis that the ecological services of the entire urban area may support the actual pollution rates and gain a dilution to the legal acceptable concentration. Despite the fact that the environmental background value is not considered, dilution is presumed to be insufficient due to the barriers to the water cycle in Beijing placed by the existing small reservoirs and public water facilities. It means that the demand for the clean water to dilute may surpass or exceed the locally available resources.
The Indirect Emergy Input Associated with the Emissions and Ecological Services
The effects of the airborne emissions on the human health include the respiratory complications, climate change, and many other issues. SO2, dust, N20, and other waterborne pollutants such as mercury and arsenic affect the residents of Beijing while the other pollutants are not considered, at all, owing to the inadequate information/data. Nevertheless, the concentrations of nitrogen and dust have increased and surpassed SO2. Evidence point out that nitrogen (IV) oxide has surpassed sulfur (IV) oxide in terms of the environmental pollution treatment. The growth in the destruction rate is caused by the emissions from the urban consumption processes; moreover, it is quickly climbing up. According to the reports, the nitrogen dioxide and sulfur dioxide have significantly contributed to the natural capital loss in Beijing whereas the green gasses and dust have played an immense role in the human capital loss.
Conclusions and Suggestions
The metabolic emergy stores of Beijing have been increasing significantly over the years; the imported emergy have also accounted for the significant increase. According to various studies, it is true to point out that Beijing has had the highest metabolic efficiencies over the years. Surprisingly, since the 2008 Olympics, the efficiencies have been getting even better. Apparently, the population density and GDP per capita of Beijing's tend to have the immensely positive correlations with the urban metabolic capabilities. Therefore, the economic and population agglomeration in Beijing tends to influence the overall metabolism of the city.
The environmental management and industrial outlook positively impact the growth of the metabolic efficiencies. Additionally, the expansion of the lands for construction adds to the inefficiency of the urban metabolic performance. The inclusion of improving the entire efficiency of production and consumption of the non-renewable resources is among the recommended strategies. The overdependence on the renewable resources other than the non-renewable and imported resources needs to be explicitly factored into the urban programs for metabolic improvement of Beijing. There is a need for the improved management of the imported services, products, and fuels. The alternative energy import policies are pivotal for the acquisition of the metropolitan sustainable development by Beijing. Furthermore, it is imperative to provide the decision makers with the detailed analysis of the urban metabolic performances in order to create technologies and policies diversifying the metropolitan renewable resource and energy supplies. The analysis also enhances the metabolic efficiency advancements while mitigating the undesired outcomes from the urban metabolic development. The further research needs to be done in a bid to depict the urban metabolic systems in details. It is evident that such metropolises as Beijing, for example, are prone to the urban desertification and over-reliance on the external resources.
Therefore, it is imperative to capture the urban emergy footprints of the metabolic systems in the years to come. Moreover, it is an essential spatial aspect of the urban metabolisms. It is recommended to begin the studies aimed at improving the setbacks of various metabolic models. Synthesizing the current information is one of the crucial steps. In addition, the cross-cutting field research and multidisciplinary simulations are also considered a necessity. Finally, the planning and management of the urban sustainable metabolisms is mostly incomplete and performed in an integrated way. As a result, an in-depth policy framework is yet to be accounted in the decision-making process while the researchers should focus on the policy-oriented metabolic research and studies.
Looking at the metabolic system of Beijing over the years, it is true to point out that the total amounts of the emergy consumed annually have been growing rapidly. Apparently, the emergy imported has been the primary driver of the growing emergy consumption. The domestic non-renewable emergy is immense; it has been growing steadily for the last decade. Meanwhile, the renewable emergy is tiny or simply has small bases; hence, it is negligible. If taking into account the whole contribution of the imported emergy at the moment, it can be said that the emergy footprint of Beijing is growing immensely. The increased emergy external intensity shows the high level of dependency on the external regions. The high values indicate that more external resources, energy, and services are imported, consumed, and exported in order to satisfy the demands of the urban growth and development. The increase in the emergy consumption indicates that Beijing is predisposed or more vulnerable to its overdependence on the external resources and energy.
The Urban Metabolic Structure
In relation to a number of results reported in various studies, Beijing has the highest energy supply capability. It means that the inputs for the energy transformation sector in the city are relatively large. Beijing, on the other hand, is said to possess a high self-regulation ability and great weight for the industrial consumption. An efficient structure, especially for the urban energy metabolism, should reflect clarity whereby the producers of the sufficient energy are to be at the bottom of the environmental structure.