Trapping Effect of Tidal Marsh Vegetation on Suspended Sediment, Yangtze Delta

To quantify the trapping effect of tidal marsh vegetation on suspended sediment, we measured the amount of sediment adhering to three species of plants in different habitats in the Yangtze Delta. We also measured suspended sediment concentrations (SSC) and bed levels in the tidal marsh to examine their influence on the adherence of sediment to vegetation and the contribution of vegetation-trapped sediment to the local total deposition rate. The results include (1) the density of sediment trapped in the joints of leaves and stems and on fruits, which was 5 to 10 times higher than that on the stems and leaves; (2) the amount of sediment (18 to 559 g/m(2) in dry weight) trapped by vegetation, which increased with plant biomass (220 to 5408 g/m(2) in dry weight); (3) the dry weight of sediment adhering to plants, which drastically decreased from 10-15 g/m(2) to <2 g/m(2) upward from their base to their tip; (4) the amount of sediment trapped by vegetation per unit land area in the low marsh margin, which decreased at a rate of 1% to 3%/m with distance from the outer marsh edge, bordering the mudflat, or from the tidal creak, where the SSC was higher; and (5) the amount of vegetation-trapped sediment, which was likely responsible for >10% of the total depositional rate in the Spartina alterniflora marsh and <10% of the total depositional rate in the Scirpus mariqueter marsh. It was concluded that the amount of sediment trapped by the tidal marsh vegetation was related to plant properties, to the SSC, and to the bed level, which determines the tidal submergence; the introduced S. alterniflora is significantly more efficient in trapping suspended sediment than the native Scirpus and Phragmites plant species.