Differences in turbulence dissipation and sediment retention shape the coastal protection capacity of native and exotic saltmarsh species

Abstract

Spartina alterniflora (hereafter S. alterniflora), an exotic saltmarsh species, was introduced into intertidal flats of China in 1979 for its remarkable utility in hydrodynamic attenuation to protect the coasts. Against a background of national-scale removal of S. alterniflora along Chinese coasts, it is essential to investigate whether native saltmarsh species could provide a similar coastal protection function as the exotic one, particularly for coasts with great coastal defense pressure. Here, the hydrodynamic turbulence attenuation and sediment capture abilities of the native species Scirpus mariqueter (hereafter S. mariqueter) and S. alterniflora were compared through in situ observation in a typical macro-tidal estuary, Hangzhou Bay, China. Our results revealed that the turbulence attenuation by S. mariqueter and S. alterniflora varied with inundation depth and wave-current interactions. Under wave-dominated conditions, S. mariqueter had a turbulence dissipation rate of 0.04 J m ⁻⁴. This rate increased by approximately one order of magnitude under coupled wave-current conditions but remained one-third lower than that of S. alterniflora. Notably, the turbulence dissipation rate of S. mariqueter increased to three times that of S. alterniflora during the emergent stage. Nevertheless, sediment capture by S. mariqueter was only half that of S. alterniflora, primarily attributed to a greater tendency for sediment resuspension. This study suggested that short, flexible native saltmarsh species such as S. mariqueter alone are insufficient to restore the coastal protection capacity lost following the removal of S. alterniflora, necessitating the strategic introduction of other relatively tall and rigid native species to enhance coastal resilience.

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