A framework designation for the assessment of urban ecological risks

ABSTRACT

Urban ecological risks stemming from urbanization are increasing and limiting the capability of China to effectuate sustainable urban development. Therefore, addressing urban ecological risks is an urgent need. Numerous factors are involved in urban ecological risks, including air, water, and soil. Additionally, risk sources and risk receptors are complex and diverse. In this study, urban ecological risks are defined as adverse effects and possibility of impacts on urban ecosystem services resulting from urbanization. Urbanization is recognized as the risk source, and the urban ecosystem is considered the risk receptor. Based on this understanding, the components of urban ecological risks are defined, and the relationships between the components of urban ecological risks are illuminated by establishing an indicator system. Based on previous studies on urban ecological risks, an explicit framework for identification, assessment, and management of urban ecological risks is proposed. For purposes of identification, there are three types of risk sources: population growth, industrial development, and the expansion of built land. Stressors include the accumulation of contaminants, consumption of resources, and occupation of space. Assessment endpoints are divided into provisioning, regulating, cultural, and supporting services. In response to urban ecological risks having multiple stressors and multiple assessment endpoints, we assessed risks both with a single stressor/single endpoint and comprehensive ecological risks. In our framework, the physical or material assessment of ecosystem services is adopted as the core method for the analysis of urban ecological risk, because it is believed that the analysis of urban ecological risk should be based on the physical or material assessment of ecosystem services instead of the value assessment of ecosystem services. The results of the single value assessment of urban ecosystem services will cause the deviation from the purpose of urban ecosystem services assessment. The purpose of urban ecosystem services assessment is to maintain and/or improve the capability of urban ecosystems of providing physical or material services, and further to reduce or avoid the occurrence risks of unsustainable cities. Additionally, a multi-level characterization method was adopted for the results of urban ecological risk assessment. In this study, we established a platform to manage urban ecological risks based on landscape ecology and environmental internet of things technologies, and to effectuate online urban ecological risk identification, assessment, and management via this platform.

KEYWORDS:

• Urbanization
• identification
• assessment
• management
• framework

1. Introduction

The urban economy, politics, society, and culture are all enhanced by urbanization; conversely, urban ecology is progressively jeopardized. When the urban ecological environment is disrupted, the economy, politics, society, and culture are also restricted. Additionally, the health and welfare of human beings is in danger. Environmental issues are complex and transnational, and most countries are challenged with ecological risks. For instance, although urbanization has boosted the economy of Southeast Asian countries, carbon emissions have simultaneously increased in this region (Brahmasrene and Lee 2017). Currently, degradation of urban ecosystems is widespread in China. Most of its cities are not only encountering serious ecological issues but also facing ecological risks with potentially serious consequences. This degradation has resulted primarily from limited ecological risk management measures and insufficient awareness of risk prevention methods. To manage urban ecological risks reasonably and effectively, and to promote healthy and sustainable urbanization, a systematic research of approaches to ecological risk assessment and management is needed.

Ecological risk assessment is a process by which one can evaluate the likelihood that adverse ecological effects may occur or are occurring as a result of exposure to one or more stressors (US. Environmental Protection Agency (EPA) 1998a). In the 1970s, risk assessments primarily focused on the possibility of adverse effects stemming from accidents such as those associated with nuclear power plants. In the 1980s, risk assessments tended to focus on human health risks (Hua et al. 2017). In the 1990s, risk assessments began to be applied to ecological risks. Carolyn Hunsaker et al. developed an intellectual foundation that showed how ecological risk assessment could be applied to the landscape at a regional level (Landis 2003). Risk assessments generally follow a procedural framework. The Netherlands, USA, Australia, New Zealand, United Kingdom, Canada, and other countries are committed to developing ecological risk assessment frameworks relevant to their research fields (Power and McCarty 2002). The ecological risk assessment framework (1992) proposed by the US National Environmental Protection Agency was based on a human health risk assessment framework (1983). After several revisions, it was further developed to be ‘The Guideline for Ecological Risk Assessment’, and the risk assessment process was reduced from four to three steps: problem formulation, risk analysis, and risk characterization (Suter 2006). Although this framework can be applied widely, the roles of risk managers and stakeholders are not well defined. Ecological risk assessment started late in China, and relevant documents such as technical guidelines and framework systems have not yet been issued by the authority (Mao and Ni 2005). Although many scholars have assessed ecological risks, most of them have focused on evaluating the ecological risks of watersheds, coastal zones, rainforests, and other natural systems, as well as garbage dumps, mining sites, oil pollution points, and other special ecological areas (Yan and Xu 2010), while paying less attention to urban ecological risks (Hua et al. 2017).

The risk sources and risk receptors of urban ecological risks are complex and various. To address the need for urban ecological risk management in response to increasing urbanization, to elaborate the components, definitions, and boundaries of urban ecological risks, and to construct an urban ecological risk assessment and management framework, terms must be defined first. We begin by considering urbanization as the risk source and urban ecosystems as the risk receptor.

2. Components of urban ecological risks

2.1. Risks, ecological risks, and urban ecological risks

The term ‘risks’ has long been in use, and yet there is still no unified definition for this term. Some data have indicated that risks generate both profits and losses, with a positive risk perceived as an opportunity and a negative risk deemed a threat. Other data have indicated that risks only bring losses. There are different understandings of and emphases in risks. In project management, risks are deviations between the expected target and the actual result under certain conditions and in a specific period. In decision theory, risks are defined as uncertainty, meaning the possible losses stemming from certain choices when decision makers cannot be sure of structures, rules, and consequences of an event (Cao 2011). For insurance, risks refer to the uncertainly of losses.

Experts and scholars at home and abroad have different opinions on the definition of risks. Haynes, who first proposed the concept of risks, asserted that risks are the possibility of losses (Haynes 1895). Knight, a notable economist, the founder of the Chicago School, defined risks as uncertainty with quantifiable characteristics (Knight 1921). The International Organization for Standardization considered risks to be the impact of uncertainty (ISO 14001 2015). Wu et al. defined risks as the losses that stem from uncertainty, represented by the probability of an unfortunate event (Wu et al. 2004). Deng et al. considered risks to be the possibility of unfortunate events and the damages that might follow (Deng et al. 2011).

For multivariate analyses of risks, risks can be defined by the following: (1) risks are the deviation between the expected target and the actual result; (2) risks denote uncertainty, including the uncertainty of risk events occurring, as well as the uncertainty of their impacts; (3) risks indicate losses, encompassing the possibility and probability of losses. Based on these perspectives and for purposes of this study, risks are defined as the possibility and potential effects of uncertain events. In this study, the definitions of risks are primarily bound by events that may occur in the future and are primarily focused on the adverse consequences of urban ecological risks. Therefore, we primarily consider the negative effects of urban ecological risks.

Accordingly, ecological risks are defined as possible damage to ecosystems and their components stemming from uncertain events (inclusive of environmental pollution and disaster), including the probability of damage and the extent of the damage occurring.

In this framework, urban ecological risks were defined as adverse effects and possibility of impacts on urban ecosystem services resulting from urbanization. And the physical or material assessment of ecosystem services is adopted as the core method for the analysis of urban ecological risk, because it is believed that analysis of urban ecological risk should be based on the physical or material assessment of ecosystem services instead of the value assessment of ecosystem services (Zhao et al. 2000). The results of the single value assessment of urban ecosystem services will cause the deviation from the purpose of urban ecosystem services assessment. The purpose of urban ecosystem services assessment is to maintain and/or improve the capability of urban ecosystems of providing physical or material services, and further to reduce or avoid the occurrence risks of unsustainable cities.

2.2. Main components and definitions of urban ecological risks

To ascertain the ecological risks of urban areas, the following components must be defined: risk source, stressor, risk receptor, and assessment endpoint. The urban ecosystem is a complex ecosystem, and the urban ecological process is recognized as a continuous and circular process, making the relationship between the components of urban ecological risks ambiguous. Furthermore, there is no consensus with respect to the definition of these components. Therefore, the basic terms of urban ecological risks must be accurately defined and the boundaries of each component demarcated to better conduct assessments, simulations, and predictions of urban ecological risks and then better control ecological risks in urban planning, construction, and management.

2.2.1. Risk source

Risk sources are origins of risks that encompass both natural and artificial risk sources. Natural risk sources include meteorological, marine, biological, geological, and other aspects, for example, natural risk sources can be the earthquakes and other sudden disasters, pests and disease, global climate change, and water crises stemming from artificial activities. Artificial risk sources can include land use changes, haze, and other physical risk sources; heavy metals and other chemical risk sources (Li et al. 2008; Maanan et al. 2015); and biological risk sources such as invasive species and pathogens introduced through international tourism and trade (Anderson et al. 2004). Most scholars define a risk source as one or more chemical, physical, or biological of risk sources that exert an adverse effect on the ecological environment (Xu et al. 2012; Ren et al. 2013). These chemical, physical, or biological risk sources can be came down to entities or behaviors. Therefore, we define risk sources as entities or behaviors that damage an ecosystem or its components.

2.2.2. Stressor

The term ‘stressor’ first appeared in the field of physics (Tao and Heng 2009). This term has also been used in medicine, biology, geography, and other disciplines, and its connotation has been progressively enriched. According to the purpose of research, stress is considered adversity, pressure, or urgency, and the stressor is considered a pressure source. In medicine, stress comprises not only environmental stress but also a person’s feeling of pressure (Tao and Heng 2009). In ‘Ecological Risk Assessment’ (second edition), ‘stressor’ and ‘urgency’ are synonyms, and the definition of urgency is any physical, chemical, or biological entity or process capable of triggering a reaction (Suter 2006). This interpretation was adopted to define stressor in this study: physical, chemical, or biological entities and processes produced by various risk sources that may result in negative ecological effects. A stressor factor is defined as a quantitative description of a stressor.

2.2.3. Risk receptor

In biochemistry and pharmacology, the receptor is a protein that receives chemical signals from an extracellular source (Hall 2016). In ecology, the receptor has new meanings.

Yang et al. define a risk receptor as the receiver of risks, and, in a risk assessment, it denotes the components of an ecosystem that may be affected by the adverse effects of a source. These components may include people in this area, sensitive substances, and sensitive environmental factors such as water, soil, and air (Yang et al. 2006). Yang et al. consider a risk receptor to be a potential receiver of the risks of environmental pollution. It refers to a complex system that comprises society, economy, an ecological environment, and humans (Yang et al. 2015). Suter asserts that a risk receptor is an individual, population, or community exposed to contaminants (Suter 2006).

Given the foregoing definitions of ecological risk components and integrating various scholars’ views of risk receptors, we propose that a risk receptor is a receiver of risks. It is an individual, population, community, or ecosystem that is exposed to a stressor.

2.2.4. Assessment endpoint

An assessment endpoint is defined as an external expression of the environmental value that needs to be protected. Operationally, it refers to an ecological entity and its attributes (USEPA 1998a; Suter 2006). Wang et al. assert that an assessment endpoint is the ecological response of a risk receptor after facing a stressor. It usually refers to the structure, process, and function of an urban ecosystem that is closely associated with human health, the urban economy, and social development. It can also refer to the nature of an urban overall level and changes in function (Wang et al. 2014).

Synthesizing the preceding definitions, an assessment endpoint is defined as an attribute of an ecological entity exposed to a stressor. Additionally, an assessment endpoint indicator is defined as a measurable indicator that characterizes the status of an assessment endpoint.

2.3. Relationships among the components of urban ecological risks

The various types of stressors emanating from the risk source act on a risk receptor through various channels and change the properties of the risk receptor; that is, the assessment endpoint is changed, which is reflected in the assessment endpoint indicator. In this study, we considered urbanization to be the risk source and the urban ecosystem to be the risk receptor, and we chose 37 stressor factors to quantify the stressors stemming from various risk source types. In addition, to characterize the changes in urban ecosystem services arising from a stressor, we selected 21 assessment endpoint indicators. Assessment endpoint indicators may directly or indirectly characterize the status of multiple assessment endpoints. This study primarily established a link between assessment endpoints and indicators that have larger and more direct effects on these endpoints (Figure 1).

Figure 1. Components and their relationships with urban ecological risks.

Note: S stands for risk source; T stands for risk source type; ST stands for stressor; F stands for stressor factor; I stands for assessment endpoint indictor; E stands for assessment endpoint; R stands for risk receptor.Pink boxes indicate that their contents belong to regulating services; yellow boxes indicate that their contents belong to supporting services; green boxes indicate that their contents belong to provisioning services; purple boxes indicate that their contents belong to cultural services.

To deepen our understanding of urban ecological risk components and illuminate the relationship among these components, the following paragraph will describe an ecological risk assessment using space occupation as an example of an important eco-function area.

In urbanization, with the expansion of built land, important eco-function areas will be occupied to some extent. Some stressor factors can be adopted to quantify the extent of being occupied, including the amounts of occupied area in the important eco-function areas of water, soil, and biodiversity, and the amounts of occupied area in sensitive areas of soil and riverside. As one type of stressor, space occupation of important eco-function areas can affect urban ecosystems by affecting water purification and waste treatment, habitat provisioning, erosion regulation, recreation and ecotourism, water regulation, and other urban ecosystem services. To characterize the status of assessment endpoints, we used two assessment endpoint indicators: losses of ecological importance and increments of ecological sensitivity.

3. Urban ecological risk assessment and management framework

By comprehensive considering the definitions of urban ecological risk components and their relationships, we design a framework for the assessment of urban ecological risks (Figure 2).

Figure 2. Urban ecological risk assessment and management process.

3.1. Urban ecological risk identification

Urban ecological risk identification is the foundation of urban ecological risk management. It is a process that allows intra-regional ecological risk components to be identified and described. Urban ecological risk sources and risk receptors are complicated and various, and this study mainly identifies urban ecological risks that have a single risk source, a single risk receptor, multiple stressors, and multiple assessment endpoints (Figure 3).

Figure 3. Urban ecological risk identification.

Risk sources comprise natural risk sources and anthropogenic risk sources. Natural risk sources are characterized by contingency, low probability, and high intensity, whereas anthropogenic risk sources have a high probability, but their intensity can be estimated and controlled. As the key driver of urbanization, humans play a leading role in contributing to urban ecological risks. To estimate and control urban ecological risks conveniently, anthropogenic risk sources were the focus of this study. Anthropogenic risk sources comprise land use change, haze, heavy metals, and other sources. Urbanization is an important factor in the evolution of an urban ecological environment and, as an anthropogenic risk source, its complications are greater than those of a traditional single risk source. Considering urbanization as a risk source means that the key part of urban ecological risks has been defined. Therefore, in this study, urbanization is considered the macro risk source of urban ecological risks. Xu et al. indicate that urbanization covers at least four transformations: transformations in population structure, economic structure, geographical space, and lifestyle (Xu et al. 2009). In this study, we divide urban ecological risk sources into three types: population growth, industrial development, and expansion of built land.

With urbanization, unreasonable human activities cause various stressors in the urban ecological environment. To facilitate ecological risk management, stressors are subdivided into contamination accumulation, resource consumption, and space occupation, based on their forms and characteristics. Discharges of air, water, soil, solid waste, light, thermal, and noise pollutants all contribute to the accumulation of contaminants. Resource consumption includes the consumption of water and biological resources, as well as the exploration of energy. Space occupation includes landscape pattern changes and space occupation in important eco-function areas such as road network expansion, impervious surface increase, loss of croplands, and sea reclamation. We chose SO₂ and NO_X emissions and other stressor factors to measure them.

Based on the scale of a risk assessment and for research purposes, a risk receptor could be an individual, population, community, or whole ecosystem. With urbanization, stressors caused by various risk source types interact and overlap with each other, acting on biological, societal, economic, and natural environments through multiple channels, as well as affect the ability of these components to manage and repair themselves. Urban ecosystems encompass natural, economic, and social systems. To better reveal the nature of urban ecological risks, including the complexity, comprehensiveness, and dynamism of urban ecological risks (Yang et al. 2006), this study considered the urban ecosystem as the risk receptor at the urban regional level.

An urban ecosystem is an open and complicated ecosystem, and the stressors arising from an urban ecological risk source affect the structure and processes of an urban ecosystem, which are eventually reflected in urban ecosystem services. To facilitate the assessment of urban ecological risks, in this study, we divided the assessment endpoints into provisioning, regulating, cultural, and supporting services (Assessment ME 2003). Among these, provisioning services comprise the provisions of food, fresh water, and genetic resources; regulating services cover the regulations of air quality, climate, and erosion; cultural services embrace spiritual and religious values, aesthetic values, and recreation and ecotourism; supporting services include soil formation, provisioning of habitat, and primary production. To characterize the assessment endpoint, we adopted some measurable indicators such as air pollution load, an excess water pollutant coefficient, and a soil pollution concentration index.

3.2. Urban ecological risk assessment

Urban ecological risk assessments are based on the results of urban ecological risk identification, which quantitatively characterizes the negative ecological effects on risk receptors caused by risk sources. The steps of an urban ecological risk assessment include conducting an exposure and effects characterization; ascertaining the exposure-response relationship; assessing a single stressor, a single endpoint, and comprehensive ecological risks; and conducting a risk characterization.

Exposure characterization characterize the existing or potential associations between a stressor and a risk receptor by analyzing the stressor and its exposure medium, intensity, frequency, spatio-temporal distribution, and related uncertainty.

Effects characterization estimates the rules of spatio-temporal variation of an attribute of the risk receptor after exposure to stressors. That is, effects characterization estimates the rules of spatio-temporal variation in assessment endpoints.

The exposure-response relationship denotes the quantitative relationship between the exposure intensity and frequency of the stressor and the assessment endpoint.

In this study, urban ecological risks embrace multiple stressors and multiple assessment endpoints; therefore, a phased evaluation method was adopted for the evaluation. This method incorporates single stressor and single endpoint assessments, as well as a comprehensive ecological risk assessment. Single stressor assessments evaluate possible adverse ecological effects of a single stressor on an assessment endpoint. Single endpoint assessments evaluate the adverse ecological effects that are occurring or may occur as the result of a single assessment endpoint exposed to one or more stressor factors. Comprehensive ecological risk assessments evaluate the overall ecological risks of the risk receptor by combining the results of single stressor and single endpoint assessments. For single stressor and single endpoint assessments, the method of assessment varies from stressor to stressor. When assessing air pollution emissions, a long-range energy alternatives planning model and box model can be adopted (Shi et al. This issue). To assess water pollutant emissions, the methods of risk quotient, water environmental capacity, regression, and gray predication models can be employed (Yan et al. This issue). For an assessment of soil pollutant emissions, a regression model and Nemerow pollution index can be used (Huang et al. This issue). When it comes to a comprehensive ecological risk assessment, the valuation method, which intuitively quantifies the risk level in currency form, can be adopted to combine ecological risks with economic benefits and allow convenient comparison, analysis, and selection of optimal solutions (Xu et al. This issue).

Risk characterization converts possible changes in risk sources and the intensity, probability, and distribution of adverse ecological effects resulting from these changes into tables, values, pictures, reports, and other outputs. As the last step of an ecological risk assessment, risk characterization connects urban ecological risk assessments with urban ecological risk managements. It also lays a solid foundation for managers to develop risk averse, risk control, and risk emergency strategies. To fulfill the information requirements at different management stages and management layers, a method for multi-level characterization of urban ecological risks that has a complete information level, partial integration level, and complete integration information level has been proposed (Li et al. This issue). This method is used to present the results of an urban ecological risk assessment and provide managers with the most comprehensive, authentic, and core decision support information.

3.3. Urban ecological risk simulation and prediction

Ecological risk simulation is based on historical and actual data, which is used to train a model of the exposure-response relationship. It is carried out on the urban ecological risk management platform. In accordance with the requirement for risk management, the platform is divided into data, computing, and presentation layers (Wang et al. This issue). That is, before simulating urban ecological risks, an urban ecological risk database should be established first; and then a corresponding calculation process designed; finally, the benchmark scenario, combination scenario, and selection scenario are simulated to present the internal relationships and spatio-temporal variation between the ecological risk level and the components of urban ecological risks.

Ecological risk prediction is based on the results of an ecological risk assessment to analyze and predict stressor factors, as well as the intensity and probability of changes in risk receptors and assessment endpoints under the effects of stressor factors. Ecological risk prediction is the preparatory stage of risk management. It can be used to predict the trend, intensity, and speed of ecological risk changes, as well as the time to reach a certain risk threshold. These predictions facilitate the management of urban ecological risks in a timely and effective manner to make urban development sustainable.

3.4. Urban ecological risk management

The ultimate purpose of a risk assessment is to serve management and provide solid technical support for scientific decision-making (Nie et al. 2012). Urban ecological risk management encompasses ecological risk warning, ecological risk regulation, and an ecological risk management platform.

Ecological risk warning monitors the various stressor factors caused by a risk source to determine the status quo and changes in ecological risks and the strength of risks that deviate from the alert line. Based on the results of monitoring, ecological risk managers are alerted to implement control measures in advance of emerging ecological risks. When a stressor factor reaches a certain risk threshold, managers can be warned with a corresponding risk grade so that they have sufficient time to implement control measures.

Ecological risk regulation refers to the prompt implementation of measures to prevent or reduce the occurrence of ecological risk events or to mitigate the hazards of ecological risk events that might occur. When the urban ecological risk management platform sends out a warning signal, ecological risk managers should evaluate the ecological status and identify and prioritize barriers by adjusting the model parameters (Rausand 2011). Urban ecological risk managers should consider the greatest economic and environmental benefits to determine acceptable levels of risk damage, and thus formulate optimal control strategies and development plans. When the warning signal is caused by a single stressor, the most influential stressor factor should be preemptively controlled. When the warning signal is caused by multiple stressors, the stressor that has the maximum effect should be regulated first, and, from the perspective of urban planning, the risk source should be regulated using diverse management and policy systems and scientific and technological approaches, as well as by optimizing structures to prevent, eliminate, inhibit, or transfer risks (Ren et al. 2013).

An ecological risk management system is a system that incorporates information technologies to regulate ecological risks. By collecting information on relevant ecological risks, this system identifies, evaluates, and warns of ecological risks, so that risk managers can implement risk regulatory measures immediately to cope with actual or potential ecological risks and reduce the negative effects of ecological risks. At a technical level, an ecological risk management platform is established based on the landscape ecology and environmental internet of things technologies to identify, assess, and manage urban ecological risks through data input and model design. To address possible countermeasures, the system provides a variety of ecological risk cases and provides corresponding emergency control schemes, recovery plans, and effective macro-control polices as a reference for ecological risk managers to make decisions. As for the organization system, a platform administrator is installed to supervise, maintain, and develop platform functions, as well as to update the ecological risk database. Ecological risk evaluators use the platform to simulate, predict, and analyze the causes and trends of ecological risk. Finally, ecological risk managers use a login system with a password, consider the results of the assessment, and weigh the social, economic, and environmental benefits in formulating countermeasures that optimize the management of urban ecological risk.

4. Conclusion

Numerous domestic and overseas studies have been conducted on urban ecological risks; however, a unified understanding of the definitions and relationships between the components of urban ecological risks has not been attained. In this study, we systematically expounded on the definitions and boundaries of urban ecological risk components and described in detail the relationships between components of urban ecological risks. In addition, we provide a theoretical foundation for subsequent ecological risk research (identification-assessment-management) and provide specific methods for comparative study.

Reports on urban ecological risk assessment are scarce in China, and most of these focus on evaluations of single stressors or single assessment endpoints. Further, the processes of evaluation are so diverse that it is difficult to compare the results of different case studies. To contribute to the optimization of ecological risk assessment in our country and effective management of ecological environments, we examined urban ecological risks, with urbanization considered the risk source and an urban ecosystem considered the risk receptor. Furthermore, we designed a framework to provide a standardized process for the assessment of urban ecological risks. By constructing an urban ecological risk management platform, we can identify, assess, and manage urban ecological risks online. It is a new method for us to manage urban ecological risks conveniently.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Key R&D Program of China (2016YFC0502902) and the National Natural Science Foundation of China (71533003).