Short-term sedimentation dynamics in mesotidal marshes

Area of Science:

• Coastal geomorphology
• Wetland ecology
• Sea-level rise adaptation

Background:

• Wetland resilience to sea-level rise hinges on sufficient sediment supply.
• Identifying marsh survival tipping points is critical for coastal management.

Purpose of the Study:

• To characterize sediment fluxes between tidal flats and salt marshes in Ria Formosa, Portugal.
• To assess factors influencing sediment delivery and deposition for marsh accretion.

Main Methods:

• Field data collection on sediment fluxes during neap and spring tides.
• Measurement of flow magnitude, shear velocities, and suspended sediment concentrations.
• Linking deposition rates with near-bed velocities and theoretical formulas.

Main Results:

• Sediment deposition rates varied across the marsh, ranging from 20 to 45 g/m²/hr.
• Maximum currents (0.20 m/s) were flood-dominated in the low marsh due to flow-plant interactions.
• Mid-upper marsh areas exhibited higher deposition rates; hydroperiod was not the primary driver.

Conclusions:

• Sediment transport is tidally driven and significantly influenced by marsh vegetation.
• Spatio-temporal variability in vegetated platforms is essential for assessing marsh bed level changes.
• Findings highlight the need for site-specific data in coastal wetland management strategies.