Sediment transport in a cold climate salt marsh (St. Lawrence Estuary, Canada), the importance of vegetation and waves

Salt marshes in the St. Lawrence Estuary are subjected to strong seasonal variations with sub-arctic winter conditions. The present paper explores sedimentary processes in the Pointe-aux-Épinettes marsh during the ice-free period. Currents, waves, suspended sediment, and sedimentation rates have been measured in June, August and October 2009. Vegetation growth was monitored during one year on a monthly basis to understand the seasonal impact on the marsh. Vegetation attenuates currents and waves, but this attenuation changes over the year as vegetation disappears along winter. Results show that suspended sediment transport and deposition are controlled by vegetation, wave height, currents, distance from the marsh edge and distance from sediment sources. Suspended sediment concentrations and sedimentation rates were significantly correlated to wave height, highlighting the importance of waves for sediment resuspension transport. Transport was lowest in August when vegetation was high and wave occurrence low. However, vegetation growth didn't change fundamentally sediments dynamic of the marsh. Within one tide, an important part of sediment transport is only local within the marsh, as shown by the maximum sedimentation rates occurring near unvegetated areas of the marsh. Data provide a spatial understanding of summer sedimentology on cold climate marshes.

► Currents, waves, sediment transport were measured at different stages of vegetation growth.
► Sediment dynamic is controlled by vegetation, wave, distance from marsh edge and altitude.
► Waves are attenuated by vegetation and drive resuspension on unvegetated areas.
► Local intra-marsh transport is significant in this spatially heterogeneous environment.