Pattern-regulated wave attenuation by salt marshes in the Yangtze Estuary, China

Abstract

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.