The Spatio-temporal Dynamics Of Estuarine Wetlands And The Scaling Effects Of The Influencing Factors

Estuarine wetland is an important component in coastal and estuarine areas.It provides various ecosystem services,including water purification and support,local climate regulation,habitat biodiversity,and coastal protection.As located at the transition zone between the land and the ocean,the estuarine wetland ecosystems are particularly sensitive to sea-level rise(hereinafter referred to as SLR).Moreover,estuarine wetlands are intensely influenced by human activities,since they are mostly located in highly developed areas.In the context of global climate change,studying the impacts of SLR and human activities on the coastal wetlands is the scientific basis for the protection and sustainable development of estuarine wetlands ecosystems.The study areas contain the estuaries of Yangtze in China and the Western Scheldt in the Netherlands.The main studies are as follows:(1)The spatial distributions and area of the estuarine wetlands of 1990,2000 and 2011 in the Yangtze Estuary were obtained.The total area of salt marsh vegetation in the Yangtze Estuary declined during 1990-2000,and the area of P.australis saltmarsh reduced significantly.The reason of wetlands reduction was reclamation at the high marsh.The area of estuarine wetlands in the Yangtze Estuary increased during 2000-2011,and S.alterniflora expanding much faster than P.australis community and S.mariqueter community at the tidal flat.The reasons of saltmarsh vegetation dynamics mainly include massive reclamation,upstream sediment reduction,invasion species and sea-level rise.The combined threat risk from sea-level rise and sedimentation reduction to the estuarine wetlands by the Sea Level Affecting Marshes Model(SLAMM).The quantitative evaluation was performed for three sets of projections of short-term,mid-term and long-term.The results showed that in the scenarios of present SLR rate,the areas of high marsh vegetation,P.australis,were constant by 2025 and 2050,and slightly decrease in the scenario A1F1.Both the scenarios of present SLR and IPCC A1F1,the low marsh S.mariqueter would be inundated.The sediment starving scenario will affect P.australis,S.mariqueter and S.alterniflora communities.Tuanjiesha,the southern area of Chongming Dongtan estuarine wetland,would be under the threat of drown.(2)The distance and rate of marsh edge retreat in the Western Schelde Estuary during 2008-2012 were quantified.Linear relationships between marsh edge erosion rate,wind exposure and wave height were built.The more exposed marsh edge retreats faster.The sediment erodibility is significantly related with vegetation.The sediment volume loss rate is inversely proportional to the below-ground biomass of vegetation.Sediment samples with S.anglica showed the slowest erosion rate.Based on the studies on the physical and biological process of marsh edge erosion and the quantification of the external and internal factors on marsh edge erosion(in chapter 3 and 4),multi-scale factors analyzing was conducted to identify which factors play more important role than the other at a certain spatial scale.In this study,external factors include wind exposure,foreshore morphology parameters.Internal factors include sediment erodibility,sediment properties and vegetation traits.This study revealed that at the large scale,wind exposure and the presence of pioneer vegetation in front of the cliff were the key factors governing cliff retreat rates,at the intermediate scale,foreshore morphology was partially related to cliff retreat,at the local scale,the erodibility of the sediment itself at the marsh edge played a large role in determining the cliff retreat rate,and at the mesocosm scale,cliff erodibility was determined by soil properties and belowground root biomass.(3)According to the above chapters,measures to slow down the marsh edge erosion were also provided for the areas with sea-level rise and negative sediment budget,in order to protect the safety of coastal and estuarine ecosystem,which include wave damping measurements and engineering,scientific management of sediment and controlling land subsidence.