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Coastal deltaic deposits are the primary locations for sediment storage on Earth, and quantifying their source contributions is a critical prerequisite for delineating S2S patterns in marginal seas. In most cases, quantification for the contribution by fine‐grained sediments (i.e. particle size < 63 μm) is considered to be representative to constrain the overall sediment supply. However, this approach may be inappropriate because large differences exist between the two quantities. Here we propose an approach to solve the problem, which is based on the maximum number of tracers from multiple sediment size fractions incorporating the content of all size fractions of sediment. Using this approach, absolute source contributions during the Holocene are reconstructed that provide a first‐order model for the S2S pattern of the central Jiangsu coast, China. The Huanghe River is the strongest driver for the Holocene sedimentation, with a mean contribution of ~72 ± 6% (1417 × 108 t). The absolute contributions from the Changjiang and offshore areas were of secondary importance, (i.e. ~17 ± 1% (330 × 108 t) and ~11 ± 5% (217 × 108 t), respectively). The results show that a large difference between the relative and absolute source contributions and the assumption that the relative contribution represents the absolute contribution is invalid in a coastal setting. The impact of the Huanghe is mainly based on episodic events, such as the event of 1128–1855 AD. The model also reveals that the offshore sediments are as important as the Changjiang sediments for the central Jiangsu coast during the Holocene. Thus, the model provides both the time series and overall quantities of sediment supply during the formation and evolution of the Holocene tidal flats on the Jiangsu coast. Our findings shed new light on quantitative analysis of sediment sources applicable to future S2S studies of marginal seas. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Understanding of bottom sediment erodibility is necessary for the sustainable management and protection of coastlines, and is of great importance for numerical models of sediment dynamics and transport. To investigate the dependence of sediment erodibility on degree of consolidation, we measured turbidity, waves, tidal currents, intratidal bed-level changes, and sediment properties on an exposed macrotidal mudflat during a series of tidal cycles. We estimated the water content of surface sediments (in the uppermost 2 cm of sediment) and sub-surface sediments (at 2 cm below the sediment surface). Bed shear stress values due to currents ( τ c ), waves ( τ w ), and combined current–wave action ( τ cw ) were calculated using a hydrodynamic model. In this study, we estimate the critical shear stress for erosion using two approaches and both of them give similar results. We found that the critical shear stress for erosion ( τ ce ) was 0.17–0.18 N/m 2 in the uppermost 0–2 cm of sediment and 0.29 N/m 2 in sub-surface sediment layers (depth, 2 cm), as determined by time series of τ cw values and intratidal bed-level changes, and values of τ ce , obtained using the water content of bottom sediments, were 0.16 N/m 2 in the uppermost 2 cm and 0.28 N/m 2 in the sub-surface (depth, 2 cm) sediment. These results indicate that the value of τ ce for sub-surface sediments (depth, 2 cm) is much greater than that for the uppermost sediments (depth, 0–2 cm), and that the τ ce value is mainly related to the water content, which is determined by the extent of consolidation. Our results have implications for improving the predictive accuracy of models of sediment transport and morphological evolution, by introducing variable τ ce values for corresponding sediment layers, and can also provide a mechanistic understanding of bottom sediment erodibility at different sediment depths on intertidal mudflats, as related to differences in the consolidation time. [ABSTRACT FROM AUTHOR]

Abstract: This paper focuses on the hydrodynamic and suspended sediment transport processes in response to sequential reclamations over the intertidal flat, Jiangsu coast, which used to be one of the widest intertidal flats in China. Investigations into the sediment transport patterns reveal that net suspended sediment fluxes increased from 102 kgm−1 on the upper intertidal flat to 103–4 kgm−1 on the lower intertidal flat, per tidal cycle. This variation was caused mainly by the phases of the current velocity, suspended sediment concentration (SSC), local bed geomorphology, inundation patterns, and extreme weather conditions. The longshore component of tidal currents intensifies seaward over the intertidal flat. Extreme weather conditions (e.g. storms) and strong winds were important factors affecting the current velocity structures, the intensity of residual currents, and the SSCs. The SSCs were characterized by several peaks throughout the tidal cycle. These peaks were associated with strong currents, combined wave-current interactions and intense turbulences due to the initial flood surge. Furthermore, the suspended sediment was finer and contained more clay materials during the flood phase of the tidal cycle, than during the ebb. Fine particles were transported within the upper water column by landward residual currents, but coarse particles were transported within the lower water column by seaward residual currents. Overall, residual currents were apt to transport fine-grained sediment landward and coarse-grained sediment seaward. This pattern indicates that the suspended sediment fluxes are highly variable in the water column, even for very shallow tidal environments. The cross-shore component accounted only for a small percentage of the total sediment flux. However, this part of sediment supply dominated accretion over the intertidal flat. The intertidal flat has become narrower and steeper, following sequential reclamations. A negative feedback process existed to maintain the convex profile shape, although the human activities (i.e. reclamation) could have modified the natural process. The surficial sediment tended to become finer on the mid-upper intertidal flat but coarser on the lower intertidal flat following reclamations, in response to a reduction in the tidal currents over the intertidal zone and enhancement of wave action over the lower intertidal flat. Accretion, with high rates, was maintained by landward transport of sediment. In such an accretional system with influences of reclamation, the width or slope of the intertidal flat is adjusted continuously. Before the cease of reclamation, the intertidal flat is unable to achieve an equilibrium shape. [Copyright &y& Elsevier]

The flocculation process of cohesive sediment impacts upon estuaries and tidal flats by affecting the sediment dynamics, modifying the biogeochemical exchanges, and playing an essential role in coastal ecosystems and geomorphologic evolution. To understand the roles of biological activity on flocculation processes in aquaculture areas, here we undertook in situ measurements over a bare tidal flat and a nearby clam aquaculture mudflat on the Jiangsu coast, China. Near-bed in situ floc size, the grain size distribution of suspended particles in seawater, suspended sediment concentration (SSC), and currents were obtained for nine consecutive semidiurnal tidal cycles simultaneously at the two sites. Correlation analysis indicated that the flocculation and its break-up process in this study appeared to be controlled by the variations in SSC and bottom shear stress due to combined wave and current. The floc sizes showed less difference between the two sites under calm conditions. However, the near-bed in situ floc size in the aquaculture mudflat was 23% larger than that in the bare tidal flat in the severe erosion events, suggesting modulation of the flocculation process due to the extracellular polymeric substances (EPS) eroded from the seabed sediments at the aquaculture site, as the hydrodynamics were very similar between the two sites. A higher EPS content was observed in the sediment layer below the surface seabed at the aquaculture site. We conclude that abundant filter feeders alter floc properties and enhance flocculation by excretion of exopolymer particles. • The higher EPS contents in sediment were observedat aquaculture site. • The near-bed in situ floc size in the aquaculture mudflat was much larger. • Negative relationships were found between SSC, turbulent and floc size. [ABSTRACT FROM AUTHOR]