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In this study, lignin-derived phenols, stable carbon isotopes and bulk elemental compositions were determined along the length of two sediment cores (C1 and C2) from the Andong salt marsh, which is located southwest of Hangzhou Bay, China. The purpose of this study was to determine the short-term changes and their implications along sediment profiles. The 1997 high tide had caused an increase in the terrestrial organic matter (OM) signal from 1996/1997 to 2000 in both cores, which was indicated by a high Λ (total lignin in mg/100 mg OC), TOC, C/N and more negative δ 13 C values. The slight increases in terrestrial OM along the length of the cores between 2003 and 2006 were most likely attributable to the construction of the Hangzhou Bay Bridge. Both events have likely caused an increase in erosion, and thus, these events have increased the input of terrestrial OM to nearby areas. The effects of the distinctively dry year of 2006 can be observed along C2 between 2006 and 2008 in the steadily declining terrestrial OM signal. The overall slight decrease in terrestrial OM and the distinct increase in TOC along the length of both cores toward the present were most likely because of the overall reduced sediment caused by the trapping of materials within reservoirs. These results show that the reduction in terrestrial OM in the Andong salt marsh for the past 30 years was due to reservoirs and the 2006 drought, but this was counterbalanced by the 1997 high tide event and construction of the Hangzhou Bay Bridge, which resulted in increased erosion and terrestrial OM input. [ABSTRACT FROM AUTHOR]

Seasonal variability in the sediment dynamics of a Bay of Fundy tidal creek and salt marsh system was analyzed to better understand the ecomorphodynamics of a high suspended sediment concentration intertidal habitat. Data were collected over 62 tides for velocity, suspended sediment concentration, deposition, and grain size at four stations from the creek thalweg to the marsh surface. Five topographic surveys were also conducted throughout the 14-month study. Deposition rates per tide varied spatially from 56.4 g m -2 at the creek thalweg to 15.3 g m -2 at the marsh surface. Seasonal variations in deposition in the creek and marsh surface were from 38.0 g m -2 to 97.7 g m -2 and from 12.2 g m -2 to 19.6 g m -2 respectively. Deposition and erosion were greatest in late fall and winter. This seasonal change, led by higher suspended sediment concentrations, was observed in the creek and at the marsh bank but notably absent from the marsh edge and marsh surface. Sediments were predominantly deposited in floc form (76–83%). Because of high floc content, higher suspended sediment concentrations led to more rapid loss of sediment from suspension. With increasing sediment concentration, deposition increased in the tidal creek and at the marsh bank but not at the marsh edge or marsh surface. This suggests that in highly flocculated environments the water column clears fast enough that very little sediment remains in suspension when the water reaches the marsh and that the sediment concentration during marsh inundation is independent of the initial concentration in the creek. [ABSTRACT FROM AUTHOR]

A field study was conducted on a tidal flat intersected by small tidal channels (depth <0.1 m, width <2 m) within a tidal marsh. Data were collected in the channels, and on the adjacent tidal flat that encompasses approximately 1600 m 2 in planform area. Hydrodynamic processes and sediment suspension between the channels and adjacent flat were compared. Shear stress and turbulent kinetic energy were computed from high frequency velocity measurements. Maximum water depth at the field site varied from 0.11 m during the lowest neap high tide to 0.58 m during a storm event. In the channel intersecting the tidal flat, the shear stress, turbulence and along-channel velocity were ebb dominant; e.g. 0.33 m/s peak velocity for ebb compared to 0.19 m/s peak velocity for flood. Distinct pulses in velocity occurred when the water level was near the tidal flat level. The velocity pulse during flood tide occurred at a higher water level than during ebb tide. No corresponding velocity pulse on the tidal flat was observed. Sediment concentrations peaked at the beginning and end of each tidal cycle, and often had a secondary peak close to high tide, assumed to be related to sediment advection. The influence of wind waves on bed shear stress and sediment suspension was negligible. Water levels were elevated during a storm event such that the tidal flat remained inundated for 4 tidal cycles. The water did not drain from the tidal flat into the channels during the storm, and no velocity pulses occurred. Along-channel velocities, turbulent kinetic energy, and shear stresses were therefore smaller in the channels during storm conditions than during non-storm conditions. [ABSTRACT FROM AUTHOR]

An understanding of erosional and depositional processes in intertidal wetland environments is of great importance to coastal geomorphologists, ecologists, and engineers. To evaluate the morphodynamic response of intertidal mudflats and saltmarshes to tidal inundation, we measured water depth, wave activity, current velocity profiles, suspended sediment concentration (SSC), and sediment composition at a dynamic mudflat–saltmarsh transition on eastern Chongming Island, at the Yangtze delta front, China. Based on these data, we calculated bed shear stresses generated by the combined current–wave action ( τ cw ), and the critical shear stress required to erode the surface sediments ( τ ce ), and so were able to calculate the erosional ( E ) and depositional ( D ) fluxes. The erodibility parameter ( M E ) and settling velocity ( w s ) used in the calculations of E and D were calibrated using daily measurements of bed-level change. Our results showed that the mudflat experienced alternating phases of net erosion and net deposition during tidal inundation. The burst-based changes in bed level ranged from −0.92 (net erosion) to +0.43 mm/10 min, and the cumulative bed-level changes over an entire tidal cycle ranged from approximately 0 to −5.4 mm (net erosion), with an average change of −3.4 mm/tide (net erosion) over five consecutive spring tides. In contrast, only net deposition was recorded on the saltmarsh during our observations. The burst-based changes in bed level ranged from around 0 to +0.56 mm/10 min, and the cumulative changes over a tidal cycle ranged from around 0 to +5 mm, with an average of +2.6 mm/tide for the five consecutive spring tides. We conclude that net erosion and net deposition during tidal cycles alternate on the mudflat, but that only net deposition occurs on the saltmarsh. [ABSTRACT FROM AUTHOR]

Abstract: The stability of cohesive sediments of a saltmarsh in Southern England was measured in the field and the laboratory using a Cohesive Strength Meter (CSM) and a shear vane apparatus. Cores and sediment samples were collected from two tidal creek banks, covered by Atriplex portulacoides (Sea Purslane) and Juncus maritimus (Sea Rush), respectively. The objectives of the study were to examine the variation of sediment stability throughout banks with cantilevers present and investigate the influence of roots and downcore consolidation on bank stability. Data on erosion threshold and shear strength were interpreted with reference to bank depth, sediment properties and biological influences. The higher average erosion threshold was from the Sea Purslane bank whilst the Sea Rush bank showed higher average vane shear strength. The vertical variation in core sediment stability was mainly affected by roots and downcore consolidation with depth. The data obtained from the bank faces revealed that vertical variations in both erosion threshold and vane shear strength were affected primarily by roots and algae. A quantitative estimate of the relative contributions of roots and downcore consolidation to bank sediment stability was undertaken using the bank stability data and sediment density data. This showed that roots contributed more to the Sea Purslane bank stability than downcore consolidation, whilst downcore consolidation has more pronounced effects on the Sea Rush bank stability. [Copyright &y& Elsevier]

Abstract: Ice rafting is an important secondary sedimentation process that redistributes sediment form tidal flats, channel beds, and ponds to the vegetated marsh surface in northern temperate climates. Source location of ice-rafted sediment is identifiable based on distinct sediment properties. In New England salt marsh systems, ice raft thickness and entrained sediment load vary both during the season and interannually as a function of severity and duration of winter conditions; however, 97% of ice rafts carry measurable sediment loads. Thick rafts move sand or peat up to 100m from source areas, whereas thinner rafts tend to transport mud still further onto the marsh platform, sometimes reaching the upland border. Based on these observations, we present relationships defining the theoretical sediment-carrying potential of ice rafts as well as empirical parameterizations for ice-rafted sediment with respect to ice volume. Our results suggest that ice-rafting deposits a volume of sediment contributing up to 5% of annual vertical accretion, an important input in a region where rates of vertical accretion barely compensate for sea-level rise. We provide conceptual models of ice-raft formation and sediment entrainment linking these processes to the general geomorphic evolution of northern temperate marshes, which must be understood in light of the modern acceleration in rates of sea-level rise. [Copyright &y& Elsevier]

Estuaries are considered one of the most dynamic ecosystems in the world, ensuring high production and transfer of large quantities of organic matter (OM) from continents to the ocean. Despite the large influence of estuaries in the functioning of coastal ecosystems, our understanding of OM dynamics in these buffering coastal environments remains fragmented. In this frame, our study was carried out to describe and understand the main drivers of OM distribution in two estuaries (Canche, Authie) of the eastern English Channel, based on descriptive and quantitative approaches. For this purpose, in February and March 2018, surface sediments were sampled at low tide along cross-shore transects in the intertidal zone of each estuary. Analysis of sediment grain size, porosity, proportion of aggregated particles, total carbonate content and organic geochemical characteristics (total OM content, atomic TOC/TN ratio, δ13C value) of surface sediments allowed identifying four biosedimentary facies: sand flat, mud flat, low and high salt marshes. In parallel, the elemental and isotopic characterization of the suspended particulate OM inputs by the rivers, the surface biofilms and the halophytic vegetation was performed to trace the three major sources contributing to sedimentary OM in both estuaries. Spatial distribution of OM in surface sediments (ranging between 0.6 and 26.9% dry weight) evidenced higher contents along marsh platforms than in sand and mud flats. and the OM pool was mainly constituted of a mixing of C 3 terrestrial vascular plants, marine and riverine phytoplankton. The comparison between both estuaries highlighted that the geomorphology impacted by natural and anthropic factors plays a preponderant role in the distribution and the sources of sedimentary OM by influencing vegetation communities and hydrodynamic processes. In the context of sea level rise, an improved understanding of the OM dynamics within each biosedimentary facies is crucial to better constrain and assess the role of macrotidal estuaries in carbon cycle. • Field observation and physico-chemical analyses of exhaustive surface sediment samples used for determining biosedimentary facies. • Source of sedimentary organic matter defined by elemental and isotopic proxies. • Influence of the structure and texture of surface sediments on OM distribution. • Principal Components Analysis highlighted two contrasted geomorphological stages. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the development of a model for prediction of local changes in morphodynamics resulting from managed realignment, undertaken as part of a UK project funded by Defra. The methodology builds on the conceptual modelling approach to habitat development employed successfully by , and others for lagoon environments. The overall approach can be described as hybrid – combining bottom-up (process-based) and top-down (simplified and/or empirical) predictive techniques – to describe the essential inlet functioning. The model described in this paper is used to predict the evolution of a managed realignment site under the action of tides and waves and sediment supply. Validation of the managed realignment model is undertaken using the available survey data from before the realignment and from several years afterwards. The performance of the model is promising in this respect, producing the right magnitude and the main qualitative features of bathymetric change. Longer simulations are used to see how the growth of saltmarsh itself affects the evolution of the setback field and how sea level rise would affect the development of saltmarsh. [Copyright &y& Elsevier]