Effects of diatoms on erosion and accretion processes in saltmarsh inferred from field observations of hydrodynamic and sedimentary processes

Abstract

Microphytobenthos influence sediment dynamics via their growth and covering on the surface sediment of saltmarshes. To understand the sediment transport and morphological changes resulting from microphytobenthos in a saltmarsh, two parallelly located sites were established to measure the hydrodynamic forces, sediment characteristics and microphytobenthos properties both in winter and summer. Diatoms were not observed at any of the two sites in winter because of their growth cycles. In summer, however, diatoms were found in both sites, with a chlorophyll a (Chl-a) concentration of 4.1 μg/g in the surficial sediment at the unvegetated site and a Chl-a concentration of 1.4 μg/g at the vegetated site. Interactions between diatoms and fine particle accumulation induced positive feedbacks between the seabed stable states and the growth of diatoms. Furthermore, the critical erosion threshold value in the vegetated area was 0.33 N/m 2 , whereas the value in the adjacent unvegetated area reached up to 0.43 N/m 2 because of the dense diatom armouring in summer, which increased 50% and 126% critical erosion threshold values than those at the corresponding sites in winter. Consequently, net sediment accumulation occurred in the unvegetated area in summer but opposite to that in winter. These results reveal that high coverage of diatoms contributes to substantial impacts on bed erodibility and sedimentary processes, which is vital for the understanding of the morphological evolution in saltmarshes, and provide valuable suggestions for coastal saltmarsh reconstruction.

The Hummocky Patches and Associated Sediment Dynamics Over an Accretional Intertidal Flat

“…We infer that the accurate critical erosion shear stress of cohesive sediments with active biological activities can only be obtained by field measurements, therefore, the results from CSM observation are more reliable. Previous studies show that the critical erosion threshold of substrate sediments in the salt marsh zone of this study area ranges from 0.3 to 0.4 N/m 2 based on CSM measurement (Chen et al, 2020), much smaller than our results, this may due to the dissipative and trapping effects of salt marsh that allow the settling of fine-grained sediments (sediment fraction is relatively homogeneous), resulting in a small critical erosion threshold. In summary, the above results indicated that the uneven spatial distribution of erosion threshold caused by physical characteristics of sediments and biological activities provide the foundation of patches formation, while hydrodynamics is the crucial driving force in determining the development, distribution, and destruction of hummocky patches (Figure 11).…”

Seagrass Meadows Reduce Wind-Wave Driven Sediment Resuspension in a Sheltered Environment

“…τ m is expected to be greater than τ c , and τ max to be greater than the vector sum of τ c and τ w (Soulsby and Clarke, 2005). These methods have been successfully applied to estimate mean and maximum bed shear stresses accounting for the attenuation of the near-bed flows by the canopy, including coral reefs (Pomeroy et al, 2017(Pomeroy et al, , 2021, saltmarsh (Chen et al, 2020) and benthic feeding tubes (Egan et al, 2020(Egan et al, , 2021.…”

Mapping the most heavily reclaimed shorelines of the Yangtze River delta urban agglomerations

“…Shorelines, as well as the new reserved land brought about by the shoreline expansion, are the most valuable natural resource in the land-ocean interaction areas (Temmerman et al, 2013). As the value provider for ecosystem services (Chen et al, 2020), they could ensure the land demand for increased human survival and development space, provide habitat for fish, birds and benthic organisms, and serve as the buffer zone and natural barrier against marine disasters such as storm surges (Allen, 2000;Costanza, 2006). Therefore, investigating the changes in the key areas of shoreline expansion is necessary for coastal zone environmental planning and ecological conservation (Wang et al, 2012;Addo, 2013;Li et al, 2014).…”

“…The hydrodynamic environment in estuaries and coasts determines the direction and destination of suspended sediment transport (Wang et al, 2013;Xiong et al, 2017;Li et al, 2018). Hence, the physical processes of local hydrodynamic-sediment coupling and the corresponding biological responses affect the seaward/ landward trend of coastal wetlands and, therefore, shoreline changes (Chen et al, 2020).…”

“…The internal salt marsh systems attenuate hydrodynamics and reduce erosion, with more significant accumulation rates than bare flats. Thus, regions with vegetation cultivation, such as salt marshes, become the main reclamation targets (Chen et al, 2020). Therefore, an urgent requirement for the rational use of new land is to better understand the coastal hydrodynamic-sediment coupling process and ecological response under the influence of anthropogenic activities at spatial and temporal scales.…”