1. Ecosystem Health (EH)
Currently, there is no general consensus among academics on the definition of ecosystem health (EH). The EH concept is evolving as scientific research and understanding continue to advance 
. However, different organizations and scholars have explored and defined the EH concept from different perspectives and contexts.
1.1. Definition by Scholars
The term “health” was originally used in the medical field to refer to a dynamic equilibrium state in which an organism is free from disease and able to maintain normal function 
. Since the Stockholm Conference on the Human Environment in 1972, ecologists have given close attention to the study of the response of natural ecosystems to anthropogenic stress. In 1788, Scottish physician and the father of modern geology James Hutton first connected ecosystems with health in Theory of the Earth, likening the Earth to an organic organism capable of maintaining its own healthy functioning 
. In 1979, Rapport et al. 
studied common symptoms and stages of adaptation to stress in the mammalian community through subjective identification to measure the ecosystem responses to stress, but they did not study the symptoms of ecosystem dysfunction. This constituted the prototype of the EH concept, where the physiological approach was innovatively introduced into ecological studies 
. Furthermore, Canadian scholar Brenda J. Lee also introduced the EH concept, linking it to ecosystem resilience and persistence 
. Karr et al. 
emphasized EH as focusing on ecological integrity, suggesting that the ecosystem can maintain its integrity with minimal external support even when disturbed and has the ability for self-repair. Aldo Leopold, a renowned ecologist in the United States, was the first to identify symptoms of land sickness, such as soil erosion, decreased productivity, and declining quality of agricultural and forestry products. He viewed the land as a living organism with the same health characteristics as living organisms, including humans 
In the 1970s, D.J. Rapport, a well-known ecologist at the University of Guelph in Canada, proposed the concept of ecosystem medicine based on the health diagnosis of individual organisms, providing a clear and comprehensive definition of the EH concept. He believed that an ecosystem with the ability to maintain its organizational structure, self-regulation, and resilience over time is a healthy ecosystem, with an emphasis on stability and sustainability overall 
. Therefore, evaluating the health of an ecosystem requires considering three aspects: whether the stability and integrity of the internal structure, function, and process of the system can be maintained; whether the system provides a certain self-recovery ability when facing external stress; and whether the system’s service functions can adequately meet the reasonable needs of social development.
In 1992, ecological economist Robert Costanza described the importance of EH and its assessment (Ecological Economics: The Science and Management of Sustainability), which has profoundly impacted the adoption and application of the EH concept. Furthermore, he proposed that EH can be measured by assessing the capacity of ecosystems to provide services and support human well-being, which he referred to as the ecosystem service capacity 
. In 1995, Maguau et al. 
defined EH from the perspective of ecosystem services, suggesting that a healthy ecosystem should meet human ecological needs and provide necessary ecological services. In 1998, ecologist Daniel Simberloff defined EH as the ability of an ecosystem to persist in the face of disturbance and to retain the components, structures, and processes necessary for continued existence 
In contrast, in the 1990s, extensive critical discussions occurred among scholars regarding the EH concept. Early criticisms focused primarily on the argument that ecosystems do not possess the attributes of organisms in terms of their structure and function; therefore, they lack the properties of health possessed by organisms 
. Meanwhile, scholars have contended that the EH concept is not objectively scientific. Specifically, using the term “health” to describe an ecosystem suggests the existence of a state that is either good or bad for the system, and yet the evaluation of such states of ecosystems can only be based on the type of ecosystem expected by society 
. Further, EH is a term that involves value judgments, and these judgments can change as our understanding of nature evolves. Therefore, it is inappropriate to use the EH concept as a scientific basis for environmental management 
In general, most ecologists currently consider EH the normal state of ecosystem processes and functions, aimed at diagnosing the health level of ecosystems similar to human health diagnosis 
. However, as argued by Costanza 
, EH is a normative concept, suggesting specific social goals rather than constituting an objective scientific concept. Ecological balance may not be a shared attribute of organisms and ecosystems, which is not a reason to discard the useful EH concept.
1.2. Definition by Institutions
Furthermore, the normative term of EH has been institutionalized in national and international policies and laws 
. For instance, the EH concept was used in the Rio Declaration on Environment and Development, setting a global agenda for ecosystem management by the United Nations General Assembly in 1992. Additionally, ecosystem services have been incorporated into environmental management in various organizations and countries. For example, in 1992, the United Nations Conference on Environment and Development (UNCED) held in Rio de Janeiro, Brazil, proposed that countries should strengthen cooperation to protect and restore the health and integrity of the Earth’s ecosystems, indicating that there was a preliminary global EH consensus. Unfortunately, the UNCED has not provided a specific or formal definition of EH because of its primary focus on broader environmental issues, sustainable development, and the need for global cooperation to address these challenges.
In addition, the Society for Ecological Restoration (SER) has defined EH as the capacity of an ecosystem to sustain ecological processes, functions, biodiversity, and productivity over time. The Millennium Ecosystem Assessment (MA) considers EH to be the ability of an ecosystem to maintain its structure and function over time in the face of stresses, disturbances, and other external influences. The United States Environmental Protection Agency (EPA) defines EH as the condition of an ecosystem based on the extent to which it can support resilience, stability, and sustainability over time. The Resilience Alliance (RA) has described EH as the capacity of an ecosystem to maintain its desired functions, processes, and structures and to adapt to change and disturbance.
Furthermore, in the United Kingdom, the National Ecosystem Assessment (2011) has provided a foundation for advocating the transition toward a more sustainable state. In China, national programs such as the Natural Forest Conservation Program (NFCP) and the Grain to Green Program (GTGP), which involve payments for ecosystem services, have improved ecosystem conditions and generated positive socioeconomic effects 
Based on the aforementioned aspects, researchers believe that EH is widely regarded as a broad concept primarily used to assess the condition and functioning of the entire ecosystem. The EH concept emphasizes species diversity and the ecological processes, biogeochemical cycles, and services and resources provided by the ecosystem. EH evaluation typically involves examining biodiversity, ecological functions, and resilience and stability of the ecosystem 
2. Landscape Ecological Health (LEH)
2.1. Concept Definition of the Landscape Ecological Health
Distinguished from the discipline of ecosystems, the International Association for Landscape Ecology (IALE) Executive Committee considers landscape ecology as an interdisciplinary field that connects natural sciences and related human sciences, focusing on landscape spatial changes across different scales, including biotic, geographic, and social factors that contribute to landscape heterogeneity 
. As we have known, the difference between landscape ecological health (LEH) and EH lies in the research scale. EH mainly captures the self-sustaining and renewing ability of an ecosystem, whereas LEH primarily entails the spatial differences in the self-sustaining ability among ecosystems. As the object of study in landscape ecology, the landscape is considered a spatially heterogeneous (or patchy) attribute of ecosystems within an ecosystem region through the interconnection of its structural, functional, and process components 
and a suitable scale for studying the impact of human activities on the environment 
. Therefore, LEH can reflect the dynamic balance of ecosystems. In other words, if the system can maintain near equilibrium during frequent or minor disturbances or can quickly recover from a larger disturbance, the ecological landscape can be considered very healthy.
The LEH concept is based on EH and draws on ideas from natural health 
, land health 
, and ecological medicine 
, describing the health issues of landscapes. Currently, due to the lack of a consensus among scholars regarding the appropriate definition of EH 
, the LEH concept still lacks an authoritative meaning. Currently, many scholars have defined LEH from different research perspectives 
. For example, Ferguson 
first extended the concept of health to the landscape level, considering LEH to be a dynamic equilibrium where regulating and feedback mechanisms maintain the self-regulating function of the entire landscape. Rapport et al. 
suggested that a healthy landscape needs to provide a satisfactory range of ecological services. Cao et al. 
argued that, on the one hand, active human intervention should not cause damage to the maintenance of the stable landscape structure and normal functions, while on the other hand, over time, landscape evolution and development should not affect or disrupt the orderly, healthy, and sustainable development of adjacent landscapes and human socioeconomic systems. Fu et al. 
, however, considered LEH to be the stability and sustainability of different types of ecosystems in providing a diverse range of ecosystem services within a certain temporal and spatial range while maintaining their own health.
Numerous studies have shown that healthy landscapes possess the ability for self-regulation and renewal, thereby maintaining spatial structure, ecological processes, and stress recovery and ensuring the sustainable and optimal provision of ecosystem services 
. Therefore, researchers argue that LEH focuses on patterns, ecological processes, and ecosystem functions within a given geographic area, emphasizing the consideration of the effects of different habitat types and land uses on ecosystems on a larger scale, such that LEH assessment typically involves the analysis of landscape diversity, connectivity, fragmentation, habitat quality, and landscape service functions 
2.2. Research Progress of the Landscape Ecological Health
In the 1960s, Leopold further refined the concept of land health into EH and landscape health components, proposing land self-renewal capacity as a criterion for landscape health evaluation. Initially, Leopold and others believed that the evaluation criteria for health should be based on the performance or basic data provided by healthy land because the self-renewal capacity of fallow land is unaffected or damaged by human activities 
. With the deepening of related research, Leopold and others acknowledged the important role played by humans as part of the landscape in maintaining the ecological system’s landscape processes and structures, but the impact of landscape changes caused by humans on its fundamental ecological functions was not considered. Therefore, the degree to which the landscape meets human needs should be a component of landscape health evaluation 
. Costanza 
studied EH from an ecological perspective and believed that it refers to the ability of all organizational structures of the ecosystem to function normally and achieve self-recovery. To evaluate whether an ecosystem is healthy, it should meet six criteria: stability, disease-free state, diversity, vitality, recoverability, and balance. Therefore, the internal health status of the landscape refers to the absence of ecological diseases or stress factors caused by human activities, also referred to as ecosystem distress syndrome (EDS). A healthy ecological landscape should provide ecological services that include benefits for both humans and other organisms 
With the deepening of research on human health, the meaning and extension of health have continuously evolved. The concept of landscape health has been extended from a simple medical environment to various levels of social landscapes, derived from the basis of the comprehensive EH, as a deep form of expression of sustainable landscapes. For example, Cao et al. 
, from a human-interest perspective, proposed that a healthy ecosystem should provide ecological services such as healthy food, clean drinking water, and clean air needed by human society. Xie 
argued that the health state that merely satisfies the needs for providing ecological or landscape services may be a static and external pseudo-health phenomenon that does not reflect the essence of EH. They also studied the content of the LEH concept from a landscape ecology perspective and proposed that LEH includes the healthy structure and pattern of landscapes, healthy ecological processes, and healthy ecological functions. Further, Li et al. 
conducted research based on D.J. Rapport’s work and noted that EH should include an appropriate landscape structure and pattern, efficient ecological processes, and necessary ecological service functions.
In recent years, scholars have also assessed the EH status at different landscape scales. For example, Wu et al. 
demonstrated a conceptual model for the impact of a large open-pit coal mine site on the LEH of a semiarid grassland and established a landscape index-pattern evolution–driver–spatial statistics (IEDS) research system based on the Shengli coal mine in the Xilinguole grassland, Inner Mongolia, China. Their results showed that coal mining led to a gradual increase in landscape patches, landscape fragmentation, a gradual decrease in landscape connectivity, complex and irregular landscape shapes, increased landscape heterogeneity and complexity, a gradual decrease in landscape stability, a gradual decrease in grassland landscapes, and a yearly increase in unhealthy grassland landscapes. In conclusion, the grassland LEH basically indicated a state of slight deterioration. Currently, assessments of urban forest health at the landscape scale are still lacking. Zhao et al. 
used the Southern Peach Orchard in China as an LEH case study to show that there exists a close relationship between LEH and the internal structure of the forest landscape when both the patch area and the number ratio of forest/nonforest remain relatively stable and constant, indicating that the urban forest landscape is healthy; the healthiest forest landscapes were distributed mainly in the forest and nonforest transition zone, and unhealthy forest landscapes were distributed mainly in single natural forests.
In summary, it is generally accepted that the LEH concept is interdisciplinary in nature and that research must combine the fields of landscape ecology, health medicine, habitat environment, and socioeconomics 
. With the continuous health concern in the whole society, the current intense discussion of the LEH concept, especially in specific scopes such as wetlands, cities, and grasslands, has continuously deepened its connotation, despite the varying degrees of LEH research by scholars worldwide 
3. Wetland Landscape Ecological Health (WLEH)
Studies have shown that wetland landscapes are highly governed landscapes that are directly influenced by human activities 
. Bertollo 
defined highly governed landscapes as those where human management measures can maintain a relatively stable landscape structure, adapt to traditional land use practices, balance biophysical integrity and human cultural elements, and maintain the ability of the landscape system to provide basic biophysical resources and processes for humans and other organisms 
. Based on this definition, introducing the concept of landscape health into wetland landscape research has important theoretical and practical significance in coordinating the relationship between wetland protection and utilization under active human management conditions.
In regard to wetland or WLEH research, numerous research institutions and scholars worldwide have conducted extensive studies. For example, as early as the 1970s, the Commonwealth Scientific and Industrial Research Organization of Australia (CSIRO) established a diagnostic indicators of catchment health (DICH) system to evaluate the quality of the basin ecological environment. This system can be employed to analyze changes in the quality or health of aquatic ecosystems 
. In 2000, the EU Water Framework Directive (WFD) was officially implemented by the European Parliament and the Council of the European Union. It established an indicator system based on biological, hydrological, and physicochemical factors, providing a guiding framework for the evaluation, management, and protection of wetland aquatic ecosystems 
. In 1992, the University of Lund in Sweden developed the Riparian, Channel, and Environmental (RCE) Inventory with the hypothesis that natural river and shore structure disturbances constitute the main cause of river biological structure and function degradation. An effective method was provided for the evaluation of the physical and biological health statuses of small rivers in agricultural landscapes 
. In 1997, the UK Environment Agency developed the River Habitat Survey (RHS), focusing on river morphology, topographic features, and cross-sectional morphology, emphasizing the irreversibility of river ecosystems. The RHS is suitable for large-scale human-modified rivers 
. Additionally, Victoria, Australia, developed the Index of Stream Conditions (ISC), which assesses health through comparisons between the current and original states, emphasizing long-term evaluation of the major environmental characteristics that affect river health. ISC-based evaluation studies mainly include hydrology, river physical morphology, riparian zones, water quality, and aquatic organisms. The river health status is divided into five grades based on the total score, revealing the degree of river disturbance.
Significant studies have been conducted in the United States to determine the health of wetland ecosystems within watersheds. For example, the National Sanitation Foundation (NSF) developed the NSF Water Quality Index (WQI) to reflect the water quality characteristics of a region or area by considering the weight of the impact of each parameter on the water quality 
. In 1995, the US Army Corps of Engineers developed the hydrogeomorphic (HGM) method, which focuses on evaluating the functional value of river ecosystems. In this method, riverine wetlands are divided into four categories and fifteen functions, including animal habitats (four functions), hydrology and water quality (five functions), biogeochemistry (four functions), and plant habitats (two functions), and ratios are calculated to measure the degree of functionality on a scale from 0 (indicating complete loss of function) to 1 (indicating ideal conditions). In 2001, the Oregon Water Quality Index (GWQI) integrated eight water quality parameters, including temperature, dissolved oxygen, pH, ammonia–nitrogen, nitrate–nitrogen, total phosphorus, total suspended solids, biochemical oxygen demand, and fecal coliform, and converted these parameters into a dimensionless secondary index with a rating ranging from 10 to 100 to reveal the extent of their impact on the water quality 
. Furthermore, the US EPA comprehensively evaluated the wetland EH throughout the country based on hydrological, soil, and biological scales, which resulted in the development of three levels of wetland EH assessment systems 
Level I: Landscape development intensity (LDI) and synoptic method;
Level II: Rapid evaluation method;
Level III: HGM method and index of biological integrity (IBI).
After years of research, a theoretical system for the sustainable development, restoration, and evaluation of wetlands has been established overseas. However, the current research on wetlands focuses more on evaluation indices, ecological protection, public education, and ecotourism and less on landscape ecological system health, particularly the research on wetland landscape ecological processes and functions based on ecological theory.
In China, a search for “wetland” or “wetland park” in the China National Knowledge Infrastructure (CNKI) yielded over 4000 research articles, but there were only 15 studies on wetland landscape health. Most wetland landscape studies focus on structure and function, such as health concepts, diagnostic indicators, health recovery, wetland system spatial scale, and ecological design 
, with a clear bias toward wetland landscape health assessment research. There are few case studies that focus on specific wetland landscape ecological processes. Liu et al. 
believed that the WLEH concept encompasses the spatial heterogeneity of the wetland ecosystem landscape structure, landscape process, and landscape function at the landscape scale. Wetland landscape processes include material flow processes, information flow processes, and species movement processes. Information flow processes mainly involve the flow of water in the landscape and habitat use by birds in the landscape. In addition, Chinese scholars have shifted their research on wetland landscape health from macrolevel holistic to microlevel specific studies (or particular cases). For example, Wu et al. 
used remote sensing (RS) technology to study the spectral characteristics of wetland plants in an estuary delta and summarized the WLEH research progress. To compensate for the inability of wetland evaluation to reveal the spatial heterogeneity within wetlands, Wu and Chen 
constructed a wetland health index system consisting of five level 1 indicators (including water, soil, vegetation, landscape, and society) and 12 level 2 indicators based on RS technology and the landscape index and applied the analytic hierarchy process (AHP) to calculate corresponding weights. Their study showed that the health index of the edge of Hongze Lake was relatively low, whereas the interior was relatively healthy (a whole health index value of 5.63). Other scholars have also studied the LEH of riverine wetlands 
and coastal wetlands in depth 
, among which the Xixi National Wetland in Hangzhou, Zhejiang Province, as the first national wetland established by the State Forestry and Grassland Administration of China in 2005, has been studied several times 
. During different development periods, the conceptual definition, research content, and research methods for the WLEH have differed among academics (refer to Table 1
). Therefore, introducing the concept of landscape health into wetland landscape research to explore the LEH issues of wetlands under active management is highly important for the protection and utilization of wetlands and for achieving sustainable wetland development.
From a landscape ecology perspective, the study of wetland landscape health includes three aspects: landscape ecological structural health, landscape ecological functional health, and landscape ecological process health 
. Therefore, the study of WLEH should evaluate the LEH of the structures and processes based on the classification of functions. Due to different types of wetlands, the indicators, standards, and content used to measure their health status also vary. Therefore, WLEH can be considered a subset of LEH, and LEH is a specific EH perspective. They share a common focus on the condition, functioning, and services of ecosystems while considering ecological processes and habitat characteristics. However, their differences lie in the scope and specific types of ecosystems considered (refer to Table 2
). From the perspective of wetland types, the WLEH research content includes two aspects: natural wetland ecosystems (including watershed-scale natural wetlands, lake and swamp area natural wetlands, and estuarine and river mouth natural wetlands) and artificial or restored wetlands (including urban wetlands, reservoir surrounding areas, and artificial terraced wetlands) 
. Researchers therefore focused primarily on the LEH of artificial and restored wetlands.