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Invasive Spartina alterniflora has become a global management challenge in coastal wetlands. China has decided to eradicate it completely, but the high costs and its provision of beneficial ecosystem functions (EF, in the form of blue carbon and coastal protection) have raised concerns about its removal. Here, using the Yangtze Estuary as a case study, we explore a reasonable pathway of S. alterniflora management that balanced control of invasive species and EF. We simulated the spatial patterns of two key EF – blue carbon storage and wave attenuation – and identified appropriate zones for eradicating S. alterniflora based on their trade-offs. We observed contrasting patterns along the land-sea gradient for S. alterniflora community, with a decrease in blue carbon storage and an increase in wave attenuation. Notably, pioneer S. alterniflora near the foreshore displayed a high cluster of blue carbon storage (63.61 ± 7.33 Mg C ha−1) and dissipated nearly 70% of wave energy by a width of 163 m. The trade-offs between the two EF indicated that the eradication project should be implemented along the seawall rather than the foreshore. Even in the scenario of prioritized shore defense with the largest eradication zone, S. alterniflora still stored 43.1% more carbon (10.67 Gg C) compared to complete eradication and dissipated over 70% of wave energy in extreme events. Our study innovatively integrates eradication and reservation in S. alterniflora management, providing a sustainable and flexible spatial strategy that meets the needs of stakeholders. • Quantified coastal ecosystem functions with complex processes from space. • Invasive Spartina significantly enhances ecosystem functions in the foreshore. • Eradication project of Spartina should be implemented towards landward side. • Setting optimal Spartina zone width enhances coastal wetlands' ecosystem function. • Wise management of Spartina with eradication and reservation. [ABSTRACT FROM AUTHOR]

Due to the increasing risk of coastal disasters and climate change, the traditional gray sea dikes may become unsustainable. Coastal wetlands provide natural protection for shoreline areas and have wave attenuation capacities as green dikes. In this study, we developed a new assessment approach to evaluate comprehensive dike risk for coastal gray-green defense systems, based on the dike characters and the wave attenuation capacity of coastal wetlands for the Chongming Island. The risk assessment system consists of nine indicators of dike constructure standards, dike-top height, land subsidence, wetland vegetation width, wave attenuation capacity of vegetation, mean high water level, storm frequency, rain intensity, and annual rainfall, to determine the dike risk index (RI). The information of dike and meteorological conditions were obtained by carrying out a field survey and referring to construction bulletins and domestic statistical yearbooks. The wave attenuation effect of wetland vegetation was characterized by plant morphology and seasonality. The results indicated that, without the coastal wetland indicators, the RI values of most parts of the dike ring of the island were high. The high-risk regions were mainly located in the south and north shores, consisting of several old dikes that did not meet the constructure standard. The risk level was higher in summer and autumn than in winter and spring, due to seasonal variations (typhoon or storm frequency and intensity). When the coastal wetland indicators were included, the presence of coastal wetland vegetation reduced the dike RI values by an average of 13.6% around the Chongming Island. During the flourishing periods of the vegetation, a high rate of wave attenuation reduced the RI levels considerably. We provide a reliable framework to carry out large-scale and high-resolution dike risk assessment to be applied for wetland vegetation restoration, green dike construction, and risk management in coastal areas. • A dike risk assessment method was established for coastal gray-green defense system. • Wetland vegetation width and wave attenuation are embedded into risk assessment. • Wave attenuation of wetland are characterized by vegetation types and seasonality. • Framework carried out spatiotemporal and high-resolution dike risk assessment. • We discussed green dike management strategies for the Chongming Island. [ABSTRACT FROM AUTHOR]

Frequently, large-scale typhoon-induced casualties and financial losses in global mega-delta cities can be buffered to a large extent by the presence of mangrove wetlands occurring in tropical coastal zones. However, there is little information about how mangrove wetland dynamics induce wave energy damping. Here, a series of biomorphodynamic field data was acquired during a storm period induced by Typhoon Sinlaku over a mangrove wetland in the Nanliu Delta, the largest delta of the northern Beibu Gulf in China; these data revealed the wave attenuation process of native Aegiceras corniculatum (AC). The results indicated that the wave damping coefficient of AC was higher during the storm period than during normal weather conditions. Sapling and adult AC were densely distributed in the field and had a greater effect on reducing wave height than seedlings, which were sparsely distributed, even though seedlings might have a stronger damping ability. Moreover, wave height was linearly attenuated with landward wave propagation distance along a transect of AC plots of different ages. Our work further indicated that the slopes and intercepts of the linear fits between wave height and landward wave propagation distance under storm and normal conditions were closely related to incident wave height, the water level and submerged vegetation volume. These results highlight the role of AC trees of different ages and densities under distinct weather conditions in the wave attenuation process. • Wave damping was determined based on mangrove structures and water level. • Mangroves of different ages produced distinctive drag forces. • Mangrove band design for wave attenuation depends on local ecohydrodynamic conditions. [ABSTRACT FROM AUTHOR]

To quantify wave attenuation by (introduced) Spartina alterniflora vegetation at an exposed macrotidal coast in the Yangtze Estuary, China, wave parameters and water depth were measured during 13 consecutive tides at nine locations ranging from 10 m seaward to 50 m landward of the low marsh edge. During this period, the incident wave height ranged from <0.1 to 1.5 m, the maximum of which is much higher than observed in other marsh areas around the world. Our measurements and calculations showed that the wave attenuation rate per unit distance was 1 to 2 magnitudes higher over the marsh than over an adjacent mudflat. Although the elevation gradient of the marsh margin was significantly higher than that of the adjacent mudflat, more than 80% of wave attenuation was ascribed to the presence of vegetation, suggesting that shoaling effects were of minor importance. On average, waves reaching the marsh were eliminated over a distance of ∼80 m, although a marsh distance of ≥100 m was needed before the maximum height waves were fully attenuated during high tides. These attenuation distances were longer than those previously found in American salt marshes, mainly due to the macrotidal and exposed conditions at the present site. The ratio of water depth to plant height showed an inverse correlation with wave attenuation rate, indicating that plant height is a crucial factor determining the efficiency of wave attenuation. Consequently, the tall shoots of the introduced S. alterniflora makes this species much more efficient at attenuating waves than the shorter, native pioneer species in the Yangtze Estuary, and should therefore be considered as a factor in coastal management during the present era of sea-level rise and global change. We also found that wave attenuation across the salt marsh can be predicted using published models when a suitable coefficient is incorporated to account for drag, which varies in place and time due to differences in plant characteristics and abiotic conditions (i.e., bed gradient, initial water depth, and wave action). [ABSTRACT FROM AUTHOR]

With the increase in coastal hazards induced by global change, estuarine deltas are urgently required to enhance nature-based coastal defenses. This study sets an example at the Nanhui nearshore salt marshes in the Yangtze Estuary, China, with a one-dimension wave attenuation empirical model and Landscape Resistance Index (LRI). We explored wave attenuation by salt marshes at site and transect scale, and put forward potential approaches to improve coastal defenses. Results showed that 1) the two 10 m-wide stripes of typical vegetation (Spartina alterniflora and Scirpus mariqueter) could attenuate wave height mostly when incident wave height was 0.22 m and 0.20 m, respectively; 2) under the condition of 0.6 m initial wave height, wave attenuation rate among all transects ranged from 32.50% to 98.30% (71.30 ± 16.09% on average); and 3) Land cover-Position-Length weighted LRI was an effective indicator for the relationship between wave attenuation and landscape pattern. Wave attenuation by salt marshes differ in various environments and are species specific. Wave attenuation along transects was also affected by both land cover and spatial configuration. Thus, we proposed some salt marsh restoration strategies, such as preferential restoration of long transects, differentiation of vegetation configuration, and engineering protections like low levees or breakwaters in front of salt marsh edges. These findings could be used to promote ecological functions in the Yangtze Estuary and other coastal marshes in the world. [Display omitted] • Wave attenuation by vegetation was species-specific and varied with environments. • Landscape Resistance Index was an effective indicator for wave attenuation by salt marshes. • Wave attenuation was influenced by both land cover and spatial configuration. • Transect landscape pattern should be considered in nature-based coastal defense. [ABSTRACT FROM AUTHOR]