Nature-Based Ecological Restoration And Management For Coastal Wetlands:A Coupled Modelling Approach

The precipitous degradation and loss of coastal wetlands globally has endangered critical functions and ecosystem services in coastal zones.Currently,the management and restoration of critical regions have become important measures to curb wetland ecosystem degradation,restore and protect its ecological service functions and biodiversity.Traditional coastal wetland restoration generally fights natural forces to overcome environmental stress and achieve wetland conservation,but the ultimate success has been limited.A more recent researchers and coastal management recognizes that"Nature-based Solutions（Nb S）"based on multiple ecological processes and natural forces can help with coastal protection,greatly promote the restoration and management of coastal zones,and achieve comprehensive and beneficial wetland protection.Taking the Chongming Dongtan wetland at Shanghai as a study case,the model systems for wetland plant grows and saltmarsh dispersal were developed respectively firstly by coupling the biotic-physical processes of wetland system for address the needs of ecological restored area optimization management and natural tidal flat saltmarsh vegetation restoration in Chongming Dongtan.The comprehensive management scheme for waterbird habitats and“Seed-Engine”technology for pioneer saltmarsh plant that achieve saltmarsh restoration by supplementing seed sources in suitable habitats were established based on these ecological model systems to provide a more economically-effective nature-based solution for coastal wetland ecological restoration and management.The main research content and results were as follows:1.The wetland vegetation biomass dynamic simulation based on water level and salinity response process in ecological restored areaTaking the Chongming Dongtan wetland ecological restored area as study object,the response of the biomass of three typical wetland plants,Phragmites australis,Typha angustifolia and Scirpus mariqueter,to water level and salinity was quantified through indoor controlled experiments under no-tide conditions.Subsequently,a wetland vegetation biomass dynamic model was developed to simulate biomass dynamics under changing water level and salinity conditions.The results showed that:（1）the biomass of all three wetland plants decreased as salinity increased,with different survival ranges for each plant.P.australis could grow at 20 ppt salinity,while the survived salinity thresholds of S.mariqueter and T.angustifolia were less than 20 ppt and 15 ppt,respectively.Additionally,each wetland plant had a different optimal water level,with P.australis,T.angustifolia,and S.mariqueter accumulating the most biomass at water levels of 20 cm,15 cm,and 5 cm,respectively.（2）The wetland plant biomass dynamic model was able to effectively simulate the spatiotemporal changes in the biomass of P.australis(RMSE=326.20 g dw m^-2),S.mariqueter(114.83 g dw m^-2),and T.angustifolia(RMSE=235.28 g dw m^-2),and had good predictive ability for the differences in wetland plant biomass under different water and salinity conditions（R²=0.79）.The model developed in this study can provide decision-making support for the nature-based optimized management scheme and technical support for wetland ecosystem management.2.Optimized waterbird habitat management based on coupled model in ecological restored areaBy coupling the wetland plant biomass dynamic model developed in this study with the Environmental Fluid Dynamics Code（EFDC）model for surface water environment fluid dynamics,we optimized the water level control ranges for each internal habitat unit in the ecological restored area based on the water level requirements of waterbirds and plants in different seasons,and developed a dynamic management scheme for the ecological restored area of Chongming Dongtan.The results showed that:（1）In the ecological restored area,the wetland plant growth was mainly affected by changes in water levels during the summer.Wetland comprehensive functions can be improved by prioritizing raising water level in the winter to meet the waterbird needs and reducing water level in the summer to promote beneficial plant growth.（2）A comprehensive optimized management scheme was proposed.Specifically,the water level in the open water area for waterfowl habitat is maintained at 40-60 cm by twice water pumping in June and September.The water level in the water area with P.australis community for waterfowl habitat is maintained at 10-30cm in the summer and increased to 30-40 cm in the winter,which scheme is conducted by three times water pumping in April,September and November,and once internal water supply in February.The water level in the floodplain with S.mariqueter community for shorebird habitat is maintained at 5-10 cm in the summer and increased to 10-20 cm in the winter,which scheme is conducted by four times water pumping in February,April,June,November and once water drainage in May.The water level in bare floodplain for shorebird habitat is maintained at 5-20 cm in the summer and increased to 5-30 cm in the winter,and water pumping is conducted twice in June and September.The model-based wetland dynamic management scheme used in this study can reduce the frequency of water adjustments and save costs,and provide an economic,effective,and nature-based management solution for the dynamic management of such controllable wetland ecosystems.3.The Seed-Engine model based on nature dispersal process and mechanism of saltmarsh plants in natural tidal flatIn this study,a Seed/seedling-based Saltmarsh Dispersal Model（SSDM）was developed based on the natural dispersal process and mechanisms of the saltmarsh pioneer plant on nature tidal flat.The SSDM model had been coupled to the Finite-Volume Coastal Ocean Model（FVCOM）subsequently to systematically develop a Seed-Engine Model（SEM）.The SEM simulated the natural dispersal and settlement process of saltmarsh pioneer S.mariqueter from seeds to newly established saltmarsh vegetation communities after supplementing seed sources in suitable intertidal habitats（suitable elevation,hydrodynamic and sediment）and appropriate period（Spring）.To verified the SEM applicability in saltmarsh restoration,a Seed-Engine based S.mariqueter community restoration experiment was conducted on the natural tidal flats of Chongming Dongtan,where seeds sources were lacking.The results demonstrated that the coupled Seed-Engine Model accurately simulated the natural dispersal process after supplementing seed sources,with the direction（R²=0.65,RMSE=3%）and distance（R²=0.59,RMSE=1.12%）of newly established S.mariqueter patches in SEM closely matching the results of experimental observation,thereby indicating its good predictive ability.The coupled SEM developed in this study contributes to our understanding of the natural dispersal process and mechanism of saltmarsh pioneer plants,and provides a nature-based innovative alternative for saltmarsh vegetation ecological restoration on natural tidal flats that lack seed sources but have suitable habitats for salt marsh plant dispersal and settlement.4.Optimization scheme for seeds source supplement based on coupled Seed-Engine model in in natural tidal flatThe sedimentary dynamic and geomorphological monitoring of four cross sections of natural tidal flat was conducted to determine range of suitable habitats for S.mariqueter natural dispersal in Chongming Dongtan.The coupled SEM developed in this study was employed to simulate the restoration pattern of S.mariqueter under various scenarios involving the placement of seed sources at varying locations and quantities.This aimed to compare the restoration effects of S.mariqueter communities under various scenarios and to propose an optimized seed source placement scheme for implementing the Seed-Engine restoration technology.The results showed that:（1）Placing seed sources on higher elevation tidal flats that are closer to the dike（simulating the natural seed source site of S.mariqueter communities）can improve the restoration efficiency of S.mariqueter communities.In contrast,placing seed sources on lower elevation tidal flats may lead to a significant loss of seeds and seedlings,resulting in restoration failure.（2）Increasing the number of seed source placement points in various directions does not significantly improve the restoration efficiency of S.mariqueter communities.（3）In light of these findings,an application scheme for the Seed-Engine restoration technology of S.mariqueter communities can be established.The scheme involves selecting natural tidal flat habitats suitable for the ecological restoration of S.mariqueter populations and setting up a seed source placement point on a natural tidal flat closer to the dike in early spring（around April）.Placing pre-vernalized S.mariqueter seeds to promote the dispersal and establishment of seeds/seedling using natural forces.The optimized saltmarsh pioneer vegetation restoration scheme proposed in this study based on coupled SEM select suitable locations to place seed sources placement in Spring and utilize natural forces to achieve saltmarsh dispersal and settlement,and provides a novel solution for low-cost,high-efficiency,and nature-based ecological restoration for saltmarsh pioneer vegetation.In summary,the development of ecological models based on ecological processes and mechanisms can deepen our comprehension of the environmental thresholds influencing plant growth in ecological restored area and the underlying mechanisms that control the dispersal of pioneer plant species in nature tidal flat.This study designed and developed nature-based ecological restoration and management solutions to address the optimized management needs in ecological restored areas and vegetation communities’restoration needs in natural tidal flat,which possess profound theoretical value and practical significance for the conservation and safeguarding of coastal wetlands.The research results can provide a theoretical foundation and technical support for the ecological management and restoration of coastal wetlands in China.