The influence of waves and seagrass communities on suspended particulates in an estuarine embayment

Resuspension of bottom sediments by waves, corresponding changes in suspended particulate material (SPM) concentrations in the overlying water column, and transport pathways of SPM were investigated in a shallow estuarine embayment colonized by seagrass communities in Chesapeake Bay. In shallow (<2 m), unvegetated regions significant resuspension of bottom sediments was evident when northerly winds exceeded 25 km h−1, increasing SPM concentrations up to 10-fold. High concentrations of SPM generated by resuspension dissipated rapidly (within 24 h) after winds became calm. Patterns of SPM along the embayment's depth gradient suggest that part of this resuspended material was transported offshore into deeper reaches of the estuary. In areas of the embayment colonized by seagrasses, wave energy was attenuated by the vegetation, suppressing resuspension and enhancing deposition. As a result, SPM concentrations were significantly lower inside seagrass beds than in adjacent unvegetated areas. During periods of high winds when wave induced resuspension occurred in unvegetated areas, SPM concentrations remained unchanged inside the bed at normal water levels. However, when water levels were elevated by spring tides or storm surges, plants were less effective at attenuating wave energy, and SPM concentrations increased inside the seagrass bed due to resuspension and advective processes. Calculations based on the results of this study indicate that sedimentation rates are substantially higher in seagrass communities than in unvegetated areas.

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