Study On The Change Of The Wetland Ecosystem Pattern In The Yangtze Estuary

The Yangtze estuarine wetland provides various ecosystem services.However,affected by human activities（upstream sediment reduction）and natural background（sea-level rise,SLR）,the saltmarsh of estuarine wetland is undergoing dramatically changes in recent years.Exploring the historical evolution of ecosystem structure and driving mechanism of Yangtze estuarine wetlands,and predicting its future changes,have become the concern of resources sustainable utilization of Yangtze estuarine wetland and ecological environment protection.Two national nature reserves in the Yangtze Estuary（Chongming Dongtan National Nature Reserve for Birds and Jiuduansha Wetland Nature Reserve）are selected as objects of this study.Through the analysis of historical data,remote sensing interpretation,chart digitization,and field monitoring,we analyzed the changes of wetland ecological system at the Yangtze estuary in the past 30 years（1985-2020）.To evaluate future changes of the wetland pattern in the Yangtze estuarine,we employed the SLAMM（Sea-Level Rise Affecting Marshes Model）model to predict the short-term and long-term evolution of the wetland habitat under different scenarios of SLR and sedimentation reduction.Finally,we put forward the protection countermeasures of wetland ecological system in the Yangtze estuary.Our results showed that（1）the saltmarsh area of Chongming Dongtan decreased from 110.23 km~2 in 1985 to 25.2 km~2 in 2020.The area decrease of Phragmites australis（P.australis）is affected by the implementation of the coastal reclamation project at Chongming Dongtan,and the area decrease of Scirpus mariquete（S.mariquete）indicates that the current upstream sediment is decreasing.However,the saltmarsh area of Jiuduansha Wetland increased from 2.63 km~2 in 1990 to 96.65 km~2 in 2020.This is mainly due to the development of fresh wetlands,and the area of Spartina alterniflora（S.alterniflora）significantly increased from 0.47 km~2 in 2000 to 66.15 km~2 in 2020.And P.australis spread to the northwest in Upper Shoal.The reasons for the dynamic change of the saltmarsh area in the Yangtze Estuary are enclosure activities,the decrease of sediment inflow from the upper reaches and the invasion of alien organisms.（2）Under the scenario of PC（Present sea-level rise and current sedimentation）,the area of mudflat with erosion risk in Chongming Dongtan is about 138-140 km~2,and the saltmarsh decreases about 0.6-2.8 km~2.In Jiuduansha Wetland,the area of mudflat with erosion risk is about 18-24 km~2,and 5.6-6.6 km~2 of P.australis in Upper Shoal and Jiangya Shoal is occupied by S.alterniflora community;Under the scenario of H5（High sea-level rise and-50%of current sedimentation）,the trend of mudflat and S.alterniflora community diffusion will be further intensified.The area of mudflat with erosion risk in Chongming Dongtan is about 140-142 km~2 and the saltmarsh decreases about 3.1-7.1 km~2.In the north of Chongming Dongtan,0.2-0.3 km~2 of P.australis area was occupied by S.alterniflora.In Jiuduansha Wetland,the south of Jiangya Shoal,Upper Shoal and Lower Shoal will be seriously eroded,and about 36-41 km~2 of mudflat will be exposed to erosion risk.In Upper Shoal,about 5.3-5.7 km~2 of saltmarsh degenerated into mudflat.P.australis and Scirpus mariquete（S.mariqueter）communities occupied 17.9-18.8 km~2 of S.alterniflora community.（3）For Chongming Dongtan Bird National Nature Reserve,this study suggested that the estuary wetland should be controlled for high intensity reclamation and the native saltmarsh（P.australis）should be protected.For S.alterniflora in the north of Chongming Dongtan,it is suggested to form a joint force with Jiangsu province（Nantong）to carry out regional joint prevention and control.Secondary invasion of S.alterniflora should be prevented and controlled in ecological control areas.In view of the spreading trend of S.alterniflora population in Jiuduansha National Nature Reserve,it is suggested to carry out S.alterniflora control project and carry out ecological restoration project of native saltmarsh（S.mariqueter）.For potential erosion areas,making full use of channel dredged soil resources and carrying out erosion management combined with channel project（Phase II of south Channel Project）.At the same time,ecological engineering was adopted to cultivate new wetland（Jiangya Shoal）.According to the results of this research,wetland protection and tidal flat utilization in the revision of Yangtze Estuary Comprehensive Regulation and Development Plan could be scientifically supported.