Controls on spatial patterns of sediment deposition across a macro-tidal salt marsh surface over single tidal cycles

A field study was conducted to determine the controls on spatial patterns of sediment deposition across a salt marsh surface in the Bay of Fundy. Approximately 670 surface-mounted sediment traps were deployed over 28 different tidal cycles in a variety of spatial configurations and environmental conditions. Spatial patterns of deposition were derived using spatial interpolation procedures in ArcView GIS 3.2. Suspended sediment concentration, flow characteristics and water depth were measured using co-located optical backscatterance sensors, electromagnetic current meters and a pressure transducer. Sediment deposition was a complex function of variables controlling the availability of sediment and the opportunity for this sediment to be deposited. The relative importance of inundation time, distance from source material, relative roughness and suspended sediment concentration varied across the marsh surface. Wave activity, however, exerted a significant influence on both the temporal and spatial patterns of sediment deposition, particularly through an increase in suspended sediment concentrations and through transport of suspended sediment further up into the mid and high marsh during spring tides. In addition, the region around the mean high water level appears to form a transition zone for processes of sediment transport and deposition, with most deposition taking place around this region. This study also emphasizes the importance of knowing precisely where one’s sample stations are within the tidal frame. Modelling exercises must therefore consider spatial and temporal variability in sedimentary processes across a salt marsh surface. In addition, this study suggests sedimentation models developed for sheltered coastal marshes cannot necessarily be applied to open coastal marshes exposed to wave activity.