Tidal Wetland Sedimentation in the Yangtze Delta

Abstract

Based on the measurement on near-bed current, wave, suspended sediment concentration, sedimentary grain size, organic content, sediment trapped by plants and accretion rate, this article deals with hydrographic processes, accretion- erosion events, surficial deposit as well as their spatial and temporal changes. The near-bed current, wave energy and suspended sediment concentration were much lower on the marsh than on its adjacent bare flat with the same elevation. The median grain size in ф unit (ф₅₀) changed between 2.74 and 8.15. The bare flat sediment was mainly composed of very fine sand while the marsh sediment was dominated by silt. The organic content of the sediment was less than 3.0% and had a good correlation with sedimentary grain size. Although the sediment trapped by S. mariquete and S. triquiter amounted to 64.4mg/stem and 47.6mg/stem, their contribution to the accretion was much less than that by free settling. The annual accretion rate of the tidal marshes in the Yangtze Delta amounted to several decimeters because of the high suspended sediment concentration which was related to the great deal of riverine sediment supply. It is this feature that was responsible for the low organic content and the less contribution of biogenic deposition to accretion.