3.1 Assessment regarding the changes in marine ecosystem structure
3.1.1 Marine hydrodynamics
Regarding the planned reclamation projects, the hydrodynamic environmental ecological assessment may be conducted through digital and physical prediction models. For the previously implemented reclamation projects, the hydrodynamic environmental ecological assessment should include a before-and-after comparative analysis of the actual measurements in addition to the digital model comparison(Wang 2010; Sun 2014).
Indirect effects of hydrodynamic changes on marine biological communities, with emphasis on targets that are especially sensitive. 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 distributed area should be considered.
3.1.2 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. For planned reclamation projects, numerical simulations predicting the scouring and silting degree of seabed and/or shore will be carried out. For the already implemented reclamation projects, in addition to numerical simulations, a before-and-after comparative analysis for water depth from field measurements will also be conducted.
Changes in ocean surface topography and scouring and silting environment, and indirect impacts on marine biological communities caused by reclamation projects will be investigated. For this purpose, the prediction results obtained for the scouring and silting of the shore and seabed will be considered. Using spatial analysis methods including Kriging interpolation and Tyson polygon construction, the spatial distribution data of the scouring and silting of the shore and seabed in the whole sea area will be generated. Later, including data on the regional water depth and terrain and the distribution and characteristics of sensitive objects, the impacts of the reclamation project on the seabed topography, shoreline, and surrounding ecologically sensitive objects will be quantified. The assessment plan is shown in Figure 3.
Taking into account our results for changes in hydrodynamic conditions, and combining them with the analysis of sedimentation process and sediment source, changes in the sedimentary environment will be explored. Finally, the indirect impacts of changes in the sedimentary environment on marine biological communities, primarily the benthos changes will be further studied.
3.1.3 Marine water quality
During marine ecological assessment of reclamation projects, the impacts of reclamation projects on marine water quality were evaluated considering two aspects. The first aspect focuses on 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 predictive modeling, changes in the environmental carrying capacity can be analyzed. Results were used to determine the indirect impacts on the marine biological community, primarily focusing on the impacts on pollution-sensitive organisms. Moreover, the status of marine ecology and sensitive object surveys may be combined to conduct qualitative analysis of changes in biological species (such as pollution-tolerant species and invasive species).
3.1.4 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 change of sediments on marine biological communities, particularly the benthos.
3.1.5 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 communities, especially their habitats, causing changes in marine biological species, resources, and biodiversity.
3.1.6 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, identifying the changes in the number, species, and bird distribution areas.
3.2 Assessment regarding changes in marine ecosystem functions
To the best of our knowledge, only few studies regarding the impact of reclamation projects on marine ecosystems have been reported. The three major functions of ecosystem are energy flow, materials circulation, and information transmission(Shen and Shi 2002). 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. 2020). However, there are limited studies on this topic.
3.3Assessing 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.(Costanza et al. 1997) divided the services into 17 types, while Wang Qixiang et al.(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, shadow engineering, alternative market, and result-based reference, are among the commonly used assessment methods. However, they are not discussed in detail in this article.