The transport of particulate and dissolved matter on the surface of coastal marshes is controlled by the hydrodynamic characteristics of over-marsh flows. High-frequency (5 Hz) in situ measurements of flow speed were collected in Spartina alternijlora, Juncus roemerianus, and Di:-tichlis spicata canopies using hot-film anemometry sensor arrays. These data indicate that mean flow speed, turbulence intensity, and the shape of the vertical speed profile are influenced by variations in plant morphology and stem density.Mean flow speed and turbulence intensity are inversely related to stem density and to distance from the creek edge. Flow energies decrease by about one order of magnitude when flows encounter the vegetated marsh surface and continue to decrease as vegetation density increa,ses. Turbulent flow energy also decays exponentially with increasing distance from the creek edge. Reductions in flow speed coupled with energy decay provide a hydrologic mechanism for sediment deposition patterns commonly observed in marsh systems.Suspended matter transport is also affected by plant-flow interactions. Vertical flow structure is strongly influenced by canopy morphology (plant type and plant shape). Plant-flow interactions result in vertical speed profiles whose shapes deviate from the logarithmic profile typical in free-stream conditions and in the development of transitional flow regimes (i.e. neither laminar nor fully turbulent).

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Sedimentation on the surface of tidal marshes is a process that is controlled by the interactions of a complex set of variables. To adequately describe the patterns of sediment transport and deposition in any particular system requires extensive sampling of biological, physicM, sedimentological, and geomorphological parameters. In this study, measurements of sediment deposition, marsh elevation, water level, total suspended solid (TSS) loads, overmarsh current speeds, and vegetative cover were used to detern~ne which of these factors control sediment distribution patterns in a small marsh basin in southeastern North Carolina. The results of this study suggest that marsh elevation exerted significant control over deposition but that its effects were largely muted by other processes. Creek hydrology, sediment instability associated with areas of new creek development, plmnt/flow interactions, and tidal creek TSS concentrations also influenced sediment deposition in the study area. Flow patterns, resuking from the interaction between tidal stage and marsh topography, controlled the dispersal of particulate matter across the marsh surface and contributed to significant depositional differences among sampling sites as a function of tidal stage. The results of this study indicate that tidal creek geometry, creek channel position, and tidal stage interact synergistically to control sediment/particulate delivery on the surfaces of tidal wetlands.

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