Observations of Tidal Flat Sedimentation within a Native and an Exotic Spartina Species

Field measurements of bed elevation and related wave events were performed within a tidal marsh, on two cordgrass species, Spartina anglica (exotic) and Spartina maritima (native), in the Bay of Arcachon (SW France). Bed- and water-level time series were used to infer on the sediment behavior patterns from short to long term. A consistent response was found between the bed-level variation and the wave forcing, with erosion occurring during storms and accretion during low energy periods. Such behavior was observed within the two species, but the magnitude of bed-level variation was higher within the native than the exotic Spartina. These differences, in the order of millimeters, were explained by the opposite allocation of biomass of the two species. On the long term, the sedimentation/erosion patterns were dominated by episodic storm events. A general sediment deficit was observed on the site, suggested by an overall bed-level decrease registered within both species. However, further verification of within species variation needs to be considered when drawing conclusions. Despite possible qualitative limitations of the experimental design, due to single point survey, this work provides original and considerable field data to the understanding the different species ability to influence bed sediment stabilization and their potential to build marsh from the mudflat pioneer stage. Such information is valuable for coastal management in the context of global change.

Automated summary

Field measurements were conducted on two cordgrass species, exotic and native, in a tidal marsh in Bay of Arcachon, revealing consistent responses between bed-level variation and wave forcing. The native cordgrass exhibited higher bed-level variation compared to the exotic species, likely due to opposite biomass allocation. Long-term sedimentation/erosion patterns were primarily influenced by episodic storm events, leading to an overall sediment deficit at the site. Further verification of within species variation is necessary for drawing conclusions. Despite potential limitations, this study provides valuable field data on the species' ability to influence bed sediment stabilization and marsh building potential.