Technical methodologies for the assessment of the impacts of reclamation projects on marine ecology

The present article introduces the concept of ecological assessment of reclamation projects. In addition, we built a framework that considers structure, function, and ecosystem services for the assessment of the impact of reclamation projects on marine ecology. Moreover, this study explored different technical methods for the ecological assessment of reclamation projects, with an emphasis on those that evaluate the impacts of reclamation on marine ecosystems structure. The present research provides technical support for the recognition and diagnosis of marine ecology problems that are the result of reclamation projects, introduces a guideline for the development of ecological restoration projects, assists in protecting coastal wetland ecosystems, promotes the scientific and reasonable management and control of reclamation, and helps in maintaining the regional marine ecological security pattern.


Introduction
Coastal areas are transition zones between ocean and land. Apart from natural geographical features such as rich resources and ecological fragility, coastal zones display unique social and economic characteristics. These regions present intensive human activities including industrial, commercial, residential, tourism, military, fisheries, and transportation. The coastal economy has been playing a pivotal role in the economic growth and modernization in China. In 2019, the national marine product was 8,941.5 billion yuan, accounting for 9.0% of the gross domestic product (GDP) and 17.1% of the coastal area's GDP (Beijing: Department of Marine Strategy, Planning and Economy, Ministry of Natural Resources 2020). The rapid development of the marine economy, the acceleration of urbanization processes, and the rapid population growth have greatly stimulated infrastructure construction and the development of coastal industries and at the same time have aggravated the shortages of land resources in coastal areas. In this context, the primary solution to relieve this situation is land reclamation (Wang et al. 2015;Ma et al. 2015;Sengupta et al. 2018). Between 2002 and 2018, China reclaimed 2976.1 km 2 from the sea, of which 910.8 km 2 was used for urbanization and industrialization purposes (Li et al., 2020a). Since 2002, China has gained 163,000 hm 2 reclamation lands with warrants, with a peak period in 2005-2015 at a rate of approximately 10,000 hm 2 per year and a peak value of 18,000 hm 2 in 2009. The reclamation lands are mainly used for port projects, coastal industries, and urban construction, activities that accounted for approximately 90% of the total reclamation lands (Yu et al., 2019a).
Human beings greatly benefit from reclamation projects since they result in the protection of arable lands that increases food supply (Peng et al. 2005). In addition, economic aggregates increase, providing proper space and ensuring the implementation of strategic plans for major development of coastal urban areas and industries (Chinese Academy of Sciences 2016). However, reclamation has also caused permanent changes in the natural characteristics of sea areas (Hou et al. 2018). Unreasonable reclamation projects have also introduced a series of ecological and environmental problems, resulting in reduced coastal wetlands and declined natural purification capacity of seawater. As a consequence, marine ecosystems have been threatened because of a decreased repairability, reduced stability, or even loss of islands. Most land reclamation projects have transformed the natural coastlines into artificial areas, changed the natural characteristics of the coastline, blocked the exchange of material and energy between the sea and land, altered the ecosystem structure of the reclamation areas, damaged the ecosystem stability, reduced the ecological service, and also increased the risk of alien species invasion. In order to solve these problems, coastal areas have engaged with some success in active ecological restoration projects including the construction of ecological seawalls, reverse reclamation, coastal wetlands restoration, and marine breeding and releasing, among others.
Currently, there is a significant amount of research about the impacts of reclamation on (a) marine hydrodynamics (Hou et al., 2018;Chen et al. 2021;Yang & Chui 2017); (b) marine ecology, including potential impacts on intertidal habitats and intertidal benthos (Yang et al. 2018), plankton and benthos (Li et al. 2010(Li et al. , 2020b, fish habitats (Ding et al. 2020), birds (Muller et al. 2020), and landscape (Ma et al. 2009); (c) compensation standard and compensation mechanisms for ecological damage (Peng et al. 2005;Li et al. 2014;Yu et al., 2015Yu et al., , 2019aZhang et al. 2020), and (d) ecological risk ), among others. For the purpose of analysis and optimization of reclamation, the impacts of reclamation have been determined considering single environmental or ecological factors. In order to provide references for quantitative eco-compensations, several researchers have used different methods to assess the ecological loss or ecosystem service loss. In addition, other experts have reported different methods for the comprehensive ecological assessment of reclamation projects. However, only a few studies have focused on the assessment of ecological damages in the reclamation area for the purpose of ecological restoration, that is, ecological assessment. This concept is the scientific basis of ecological restoration goals and plans, and it plays an essential role in ecological restoration processes. Considering the composition of the marine ecosystem and taking the reference system as the goal, the present study established an ecological assessment method for reclamation projects. This method can be used to obtain a comprehensive assessment and determine the extent of ecological damage or degradation in areas where reclamation projects are located. With this information, the scientific implementation of ecological restoration in reclaimed areas will be possible.

Concepts of marine ecological assessment for reclamation projects
At present, there is no specific definition for ecological assessment. Commonly related concepts include ecosystem assessment (Zhao and Zhang, 2004;Millennium Ecosystem Assessment 2005;Zhao 2001), ecological impact assessment (Ministry of Environmental Protection, PRC 2011), ecological damage assessment (General Administration of Quality Supervision, Inspection and Quarantine, PRC 2017), and others. However, most of them are formulated from a management perspective and are useful in assisting relevant management departments for decision-making purposes. The concepts previously presented differ from those related to ecological assessment in terms of assessment purpose, assessment objectives, assessment scope, and assessment methods. Previous studies have focused on solving scientific questions related to ecosystem structure, dynamics, processes, services, and sustainability management, as well as ecological diversity, ecosystem management, ecological risk and security, ecological response, and the effects of global change (Fu 2010).
In order to properly define these concepts, we must first clarify the purpose of the marine ecological assessment of reclamation projects. Generally, the marine ecosystem is present in a stable equilibrium state, which is the normal ecosystem. It is a self-sustaining system with biological communities and a natural environment in a state of equilibrium (Li & Ju 2005). When various components are disturbed, they follow certain rules and fluctuate around the position of equilibrium, reaching a state of dynamic equilibrium. After the implementation of reclamation projects, the normal ecosystem may be degraded due to disturbance and become a degraded marine ecosystem. In other words, a marine ecosystem formed under natural and/or human disturbance deviates from its original state (Li & Tang 2016). Therefore, the purpose of marine ecological assessment of reclamation projects is to evaluate the extent to which the marine ecosystem deviates from the normal ecosystem. The results are used in the formulation of ecological restoration plans. Through the implementation of different ecological restoration measures, the damaged or degraded marine ecosystems will be gradually restored.
The original ecosystem before degradation or the undamaged natural ecosystem is used as the reference object for the marine ecological assessment of reclamation projects. He Nianpeng et al. He et al. (2020) proposed that the ideal reference frame is composed of specific values for a series of key indicators, which provide information about the quality of the ecosystem under specific conditions for suitable environments and with no or few human activities. It can also be called an authentic reference frame.
Therefore, the concept of marine ecological assessment of reclamation projects refers to the assessment of damaging pathways, damaging processes, and the degree of damage in marine ecosystems that are under the impact of reclamation with respect to the reference ecosystem.
Marine ecological assessment of reclamation projects should consider (a) the degraded marine ecosystem affected by the already implemented reclamation projects and (b) the marine ecosystem that might be degraded because of planned reclamation projects.
Marine ecological assessment of reclamation projects should consider different scenarios and disturbance conditions, including the extent of reclamation, location, construction time, construction methods, as well as ecological and environmental protection measures, among others.
Design of the framework for marine ecological assessment of reclamation projects Ecosystem refers to an interconnected and interacting natural entirety with an automatic adjustment mechanism that is the result of energy flow and material circulation between organisms (one or more biological communities) and abiotic environment within a certain time and space (Shen et al. 2010). The marine ecosystem is a natural organic entirety that is interdependent and interrelated and displays an automatic mechanism of adjustment. This ecosystem is formed by the marine biological community (marine plants, animals, and microbial communities) and the marine abiotic environment that interacts through energy flow and material circulation (Wang 2009). Depending on the concept of ecological assessment of reclamation projects and the definition of marine ecosystem, ecological assessment needs to consider the direct impacts of reclamation on marine abiotic environments and marine communities, as well as the indirect impacts of changes in marine abiotic environments on marine biological communities ( Fig. 1).
Marine ecosystems display a specific structure and function and provide a variety of services to human beings. Reclamation affects the structure of the marine ecosystem, which in turn affects functions and services causing different types of damages to the entire marine ecosystem. When the damage exceeds a certain level, it causes the degradation of marine ecosystems. Therefore, reclamation projects should be evaluated taking into account the following three aspects: (a) structure; (b) function; and (c) services of the marine ecosystem. Among them, the impact on the structure of marine ecosystem plays a key role, since it determines the degree of damage to function and services. Thus, evaluating the impact of reclamation on marine system structure should be the focus of the assessment. The ecological assessment framework of reclamation projects is shown in Fig. 2.

Methods of marine ecological assessment in reclamation projects
Assessment regarding the changes in marine ecosystem structure

Marine hydrodynamics
In planned reclamation projects, the hydrodynamic environmental ecological assessment may be conducted through digital and physical prediction models. For previously implemented reclamation projects, the hydrodynamic environmental ecological assessment should include a before-and-after comparative analysis of the actual measurements in addition to a comparison of the digital model (Wang 2010;Sun et al. 2014). In the analysis of the loss of tidal capacity caused by the Gulei reclamation project performed in Zhangzhou, Fujian, the author used a numerical simulation method. In this case, results indicated that the loss of tidal capacity was about 1.22×10 7 m 3 , which accounted for 1.62% of the total tidal capacity of the bay.
Indirect effects of hydrodynamic changes on marine biological communities, with emphasis on targets that are especially sensitive, are also important. Feature points for prediction or comparative analysis should be selected at the protected area border around the construction site and at the borders of important ecosystems. For example, in high flow velocities, coral reef ecosystems and coral larvae would fail to attach to the reef and reduce their ability to survive from predators. In contrast, too slow flow velocities would reduce the exchange rate of dissolved oxygen and nutrients in the water body diminishing favorable conditions for the growth of coral reefs. In mangrove forests impacted by tidal scouring and sea tides, the mangrove foundations are prone to erosion and collapse. Therefore, for ecological assessment purposes after the implementation of a reclamation project, the changes in water flow velocity (the maximum change in flow velocity and the range of flow velocity change) at the boundaries of the coral reef and the mangrove area should be considered.

Marine geomorphology and deposition-erosion
The ecological assessment of the ocean surface topography is usually carried out through on-site field survey, remote sensing, and unmanned aerial methods. In our investigation on planned reclamation projects, numerical simulations were used to predict the scouring and silting degree of seabed and shore. For previously implemented reclamation projects, in addition to using numerical simulations, a before-and-after comparative analysis of water depth was also conducted. Data on water depth was obtained through field measurements.
In the present research, changes in ocean surface topography and scouring and silting environments, as well as indirect impacts on marine biological communities caused by reclamation projects, were investigated. For this purpose, we considered the validated numerical simulation results obtained for bank and seabed deposition and erosion. Using spatial analysis methods including Kriging interpolation and Tyson polygon construction, shore and seabed scouring, and silting, Fig. 1 Impact of reclamation on marine ecosystems Fig. 2 Ecological assessment framework in reclamation projects spatial distribution data was generated. Analysis was performed for the whole sea area. Combined with data on the distribution and characteristics of sensitive objects, the impacts of the reclamation project on seabed topography, shoreline, and surrounding ecologically sensitive objects were quantified. The assessment plan is shown in Fig. 3.
In the present research, changes in the sedimentary environment were explored. For this purpose, we combined results on changes in hydrodynamic conditions and analysis of sedimentation process and sediment source. Finally, the indirect impacts of sedimentary environment characteristics on marine biological communities, mainly those regarding benthic organisms, were further studied. During the ecological assessment of the project developed for the new airport of the artificial island of Sanya located in the Hainan Province, the author analyzed bank deposition-erosion superimposed with seabed deposition-erosion in five different working conditions. Also, they determined the impact of superimposed results on coastal coral reefs. In this case, the authors concluded that the direct death of coral reefs was caused by sediment deposition, and the direct death area was more than 50% of the total coastal coral reef area. About 3 km 2 of coral reefs died due to sediment deposition. In addition, the appearance of scour in the sea may have also affected the growth and development of coral reefs.

Marine water quality
The impacts of reclamation projects on marine water quality were evaluated considering two aspects. The first aspect considers the impact of suspended sediments originated from construction activities on seawater quality. Analyses were performed to determine indirect impacts on marine biological communities including plankton, benthos, and fishery resources, as well as the impacts on sensitive objects such as coral reefs and lancelets. The second aspect considers changes in the pollution carrying capacity of the area (especially the bay) caused by the reclamation project. Using a validated numerical simulation model, changes in the environmental carrying capacity can be determined. Results were used to determine the indirect impacts on marine biological communities, primarily focusing on pollution-sensitive organisms. Moreover, the status of marine ecology may be combined with sensitive object surveys to perform a qualitative analysis of changes in biological species (such as pollution-tolerant species and invasive species). During the ecological assessment of the reclamation project of Xiamen New Airport in Fujian Province, the author performed numerical simulation analysis considering the presence and absence of antifouling curtains. It was concluded that the diffusion and silt deposition of suspended sediments increased the silt content in local areas. This process probably changed the sedimentary environment originally suitable for amphioxus survival, affecting a total area of approximately 1.7 km 2 . When antifouling measures were taken, the affected area was extremely small, about 0.3 km 2 .

Marine sediments
The marine ecological assessment of reclamation projects should consider the coverage of suspended sediments originated from construction activities on the seabed. Results may be used to further explore the indirect impacts of the quality of sediments on marine biological communities, particularly the benthos.

Marine ecological environment
The direct impact of reclamation on the marine environment occurs on benthic habitats, significantly affecting the benthos component. In addition, the impacts of reclamation projects on the hydrodynamic environment, ocean surface topography, and scouring and silting environment indirectly affect marine Fig. 3 An assessment plan for the indirect impact of changes in ocean surface topography and scouring and silting in marine biological communities communities, especially their habitats, causing changes in marine biological species, resources, and biodiversity.

Marine ecological sensitive objects
The impacts of reclamation projects on marine ecological sensitive objects should be assessed considering important coastal wetlands (including estuaries, mangroves, coral reefs, etc.), marine protected areas, concentrated areas for rare and endangered marine species, important fishery waters (spawning grounds, feeding grounds, wintering grounds, and migratory passages for commercially important fishes), marine natural historical artifacts, and natural landscapes.
For reclamation projects involving migratory and foraging grounds for birds, the assessment of impacts on birds should also be carried out. For this purpose, it is important to identify changes in the number and species of birds, as well as distribution areas. The author investigated the distribution and species of birds before and after the reclamation project developed in the Industrial Zone of Sanyu, located in the Ningde City in the Fujian Province. Data showed that the impact of this reclamation project on birds mainly involved the disappearance of herons, wild ducks, and a small number of wader foraging sites. These birds are common species in the region, and the original distribution density in the reclamation area was not high. Therefore, it did not produce a significant reduction of bird diversity in the Ningde coastal area.

Assessment regarding changes in marine ecosystem functions
To the best of our knowledge, only a few studies regarding the impact of reclamation projects on marine ecosystems have been reported. The three major functions of an ecosystem include energy flow, material circulation, and information transmission (Shen et al. 2010). The main impacts of reclamation projects on the energy flow of marine ecosystems result in the transformation of natural ecosystems into artificial ecosystems, reducing trophic levels and reducing energy utilization efficiency. At the same time, material circulation and information transmission may be hindered. Thus, it is extremely important to investigate further changes in ecosystem functions caused by reclamation projects. These modifications can be analyzed considering primary productivity before and after the implementation of a reclamation project, as well as variations in the stability of marine ecosystems (Gray 1977;Vallina et al. 2017;Valdivia et al., 2021). However, there are limited studies on this topic.

Assessing changes in marine ecosystem services
Currently, there is a significant amount of data on the impact of reclamation projects on marine ecosystem services. In addition, assessment methods are reasonably mature. Marine ecosystems provide a wide range of services to human society. Costanza et al. (1997) divided the services into 17 types, while Wang and Tang (2009) categorized them into 15 types. Taking into account the United Nations Millennium Ecosystem Assessment framework, these services were classified into four categories: (a) provisioning; (b) regulating; (c) cultural; and (d) supporting services (Millennium Ecosystem Assessment 2005). The marine ecological assessment of reclamation projects also considers these four service functions. Market price, participation willingness in surveys, cost method, shadow engineering, alternative market, and result-based reference are among the commonly used assessment methods. For example, Su Hongyan established a comprehensive profit and loss evaluation index system for construction reclamation considering the loss cost of ecosystem services (Su & Li 2020). Sui Yuzheng used cost method, market price, and result-based reference methods to calculate the loss of marine ecosystem service value caused by island reclamation (Sui et al. 2013). Wang Xuan et al. used the characteristics of various coastal ecosystem services to propose a monetization model for the assessment of the damage caused by reclamation to coastal ecosystem services ). These researchers applied direct market, alternative market, investigation and evaluation, and result-based references, to study the Tong' an Bay in Xiamen. Also, Jingzhu Shan et al. proposed a random parameter logit model to calculate the average willingness to pay for the restoration of marine ecosystem services in Jiaozhou Bay . Liu Ruiqing et al. used result-based references to determine the changes in ecological service value of 12 main bays located in the eastern coast of China during the period 1990 to 2015 (Liu et al. 2020). The existing assessment methods for the loss of marine ecosystem services caused by reclamation projects are relatively mature, and the appropriate assessment method can be selected according to particular conditions and the potential difficulty involved during data collection.

Conclusions
The present paper introduced the concept of ecological assessment of reclamation projects and proposed a marine ecological assessment framework that includes structure, function, and ecosystem services. Furthermore, we explored different methodologies for the ecological assessment of reclamation projects, with a focus on the impacts of reclamation on the structure of marine ecosystems. In addition, considering biotic factors, we identified different methods that can be used to determine the effects of abiotic variations on marine biological communities. Ecological assessment of reclamation projects on marine abiotic environments is performed using numerical simulation. With the use of this tool, experts are able to determine the tidal capacity, water exchange capacity, tidal current velocity and the range and degree of flow regime change, the extent of erosion and deposition, the level of suspended sediment diffusion and deposition, and the degree of changes in environmental capacity, among others. In addition, the tidal current velocity and flow pattern changes can be estimated and compared before and after the project is implemented. In order to understand the impact of reclamation projects on marine biological communities, it is necessary to identify the ecological factors that affect marine abiotic environments, clarify the mechanisms of action, and quantify the degree of damage to the marine biological community. In order to determine the direct impact of reclamation projects on marine biological communities, different aspects including project occupation and resource reduction can be considered.
The results of the present investigation provide technical support for the recognition and diagnosis of marine ecological problems caused by reclamation projects. In addition, information may also be helpful for the subsequent development of problem-oriented marine ecological restoration projects that may reduce the negative impacts of reclamation. The present research may stimulate the protection of coastal wetland ecosystems, strengthen the scientific and reasonable management and control of reclamation, and assist in maintaining regional marine ecological security patterns.

Prospect
To the best of our knowledge, the assessment of marine ecosystem structures is still in the development stage, where few studies involve basic theoretical research and a few more focus on applications and case studies. We consider that future research should include the elucidation of the mechanisms of reclamation projects on marine ecological environment and further optimize and improve the methods and techniques that are used for the assessment of marine ecosystem structures. The current ecological assessment of reclamation projects focuses on the marine ecosystem structure and ecosystem service values. In particular, methodologies for the evaluation of ecological service value are relatively mature. In the future, we should pay more attention to other technical methods that may be used for the evaluation of marine ecosystem functions, in order to further improve the technical method system used in this area. In addition, current studies are mostly conducted on single reclamation projects. However, in specific regions, particularly in estuaries and bays, the cumulative effect of multiple reclamation projects has drawn an increasing attention of scholars, and it is very likely that it will become the focus of future research. Moreover, managers and researchers should pay more attention to marine ecological restoration. In the case of planned reclamation projects that will be carried out in the future, we suggest taking into account the positive benefits of ecological restoration projects and adding the corresponding scenario design to the ecological assessment plan.
Acknowledgements Thanks to the Ministry of Natural Resources of the People's Republic of China and the Third Institute of Oceanography, Ministry of Resources for providing fund support and research platforms Author contribution OYY defined the concept of marine ecological assessment for reclamation projects and designed an ecological assessment framework. LW discussed current domestic and international research status, as well as existing problems of marine ecological assessment for reclamation projects. JD participated in the marine ecological assessment framework for reclamation projects. He designed and studied the evaluation of changes in marine ecosystem functions. YW studied the impact assessment of sea reclamation projects on marine ecologically sensitive targets. LC investigated marine ecological environment assessment methods. QL conducted research about seawater quality environmental assessment methods. JW studied marine landforms and scouring and silting environment assessment methods. SJ studied hydrodynamic environment assessment methods.

Funding Study on Ecological Restoration Technology of Reclamation of Ministry of Natural Resources of the People's Republic of China
Data availability Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.

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