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Abstract Bottom sediments in tidal estuaries influence organic matter and nutrient cycling, habitat suitability, and geomorphological processes. Characterizing the grain size distribution of bottom sediments is essential for predicting sediment transport, channel stability, and ecosystem health. However, this information can be challenging to acquire over large areas as traditional in situ approaches provide only point‐based observations that are spatially limited. This study addresses this limitation by applying the sediment balance equation to remotely sensed maps of total suspended solids concentration and numerical model outputs to derive a high‐resolution, spatially explicit sediment grain size distribution within a tidal channel of a New England mesotidal estuary. Results reveal a distinct gradient in sediment grain size, with coarse sediments near the inlet transitioning to finer sediments landward. Fine sand covers over 85% of the channel bottom, while medium and coarse sand occupy 14% and 1%, respectively. Peaks in settling velocity identify zones of sediment convergence controlled by tidal forcing and river inflows. The positive correlation between , estimated through the depth integrated suspended sediment continuity equation, and bottom grain size confirms the effectiveness of this approach for sediment classification in estuarine environments. 

Abstract Sediment budgets are diagnostic of saltmarsh resilience, yet quantifying net sediment fluxes remains constrained by limited, asynchronous observations of suspended sediment concentration (SSC) and water flux. Using high‐frequency observations from 15 U.S. saltmarsh stations, we combine phase folding and Monte Carlo simulations to assess whether sporadic sampling can reliably resolve net sediment exchange. We show that asynchronous SSC and water‐flux measurements spanning >8 full tidal cycles robustly identify sediment sources and sinks. High‐resolution optical satellite archives (Sentinel‐2) typically capture >30 tidal cycles in most saltmarshes, yielding 5%–41% uncertainty in net flux magnitude across systems. This accuracy is sufficient to distinguish saltmarshes functioning as sediment sources from those acting as sinks at regional to global scales, though local calibration could improve accuracy. Integrating optical remote sensing with emerging water‐flux technologies can therefore enable scalable assessments of tidal saltmarsh sediment budgets, providing a pathway for evaluating coastal resilience under accelerating sea‐level rise. 

Abstract Flooding and salinization triggered by storm surges threaten the survival of coastal forests. After a storm surge event, soil salinity can increase by evapotranspiration or decrease by rainfall dilution. Here we used a 1D hydrological model to study the combined effect of evapotranspiration and rainfall on coastal vegetated areas. Our results shed light on tree root uptake and salinity infiltration feedback as a function of soil characteristics. As evaporation increases from 0 to 2.5 mm/day, soil salinity reaches 80 ppt in both sandy and clay loam soils in the first 5 cm of soil depth. Transpiration instead involves the root zone located in the first 40 cm of depth, affecting salinization in a complex way. In sandy loam soils, storm surge events homogeneously salinize the root zone, while in clay loam soils salinization is stratified, partially affecting tree roots. Soil salinity stratification combined with low permeability maintain root uptakes in clay loam soils 4/5‐time higher with respect to sandy loam ones. When cumulative rainfall is larger than potential evapotranspiration ET_p(ET_p/Rainfall ratios lower than 1), dilution promotes fast recovery to pre‐storm soil salinity conditions, especially in sandy loam soils. Field data collected after two storm surge events support the results obtained. Electrical conductivity (a proxy for salinity) increases when the ratio ET_p/Rainfall is around 1.76, while recovery occurs when the ratio is around 0.92. In future climate change scenarios with higher temperatures and storm‐surge frequency, coastal vegetation will be compromised, because of soil salinity values much higher than tolerable thresholds. 

IntroductionSaltmarsh introduction has been widely implemented to restore ecosystem services and promote sedimentation in tidal mudflats, yet its effects on tidal network dynamics remain hard to predict. The interplay between saltmarsh extent and sediment availability in shaping long-term mudflat morphodynamics is not fully understood. MethodsWe develop a two-dimensional biomorphodynamic model to examine the individual and combined influences of saltmarsh presence and sediment availability on the evolution of tidal-flat channels. Results and discussionOur results demonstrate that sediment availability controls the long-term morphological change of mudflats, while the presence of saltmarshes exerts substantial short-term alterations in mudflat evolution. During the initial phase of saltmarsh introduction, vegetation promotes the development of tidal networks, characterized by channel elongation, narrowing and deepening. However, under higher sediment supply, saltmarshes restrict sediment deposition on landward and central mudflats compared to that on unvegetated flats. Furthermore, sediment availability primarily facilitates the extension of pre-existing channels, while saltmarshes play a dual role in both generating new channels and elongating existing ones. This distinction highlights the competing mechanisms driving channel network development. 

Abstract Ecological zonation in coastal forests is driven by sea level rise and storm‐surge events. Mature trees that can survive moderately saline conditions show signs of stress when soil salinity increases above its tolerance levels. As leaf burn, foliar damage, and defoliation reduce tree canopy cover, light gaps form within the crown. At the forest‐marsh edge, canopy cover loss is most severe; trunks of dead trees without canopies form “ghost forests.” Canopy thinning and light from the edge alter conditions for understory vegetation, promoting the growth of shrubs and facilitating establishment and spread of invasive species that were previously limited by light competition. In this research, we present an analysis of illuminance and temperature in a coastal forest transitioning to a salt marsh. Light sensors above the ground surface were used to measure light attenuation of trees and understory vegetation and to observe the effect of reduced canopies at the forest‐marsh edge. Farther from the marsh, where salinity is lower and trees are healthy, dense canopies attenuate light. We estimate that during the growing season, tree canopies intercept 50% of illuminance on average. Closer to the marsh, canopy thinning, and tree death allow greater light penetration from above, as well as from the adjacent marsh. These illuminance values are further increased by light penetration from the forest‐marsh edge (edge effect). Here, higher illuminance may permitPhragmites australisexpansion. At intermediate locations, trees intercept between 32% and 49% of light and the understory shrubMorella ceriferaintercepts a further 45% of penetrating light based on comparisons of illuminance above and below shrub canopies. Light penetration from the edge can also be felt. The presence ofM. ceriferareduces the air temperature close to the soil surface, creating a cooler summer microclimate. The tree health state is reflected in the canopy size. The canopy patterns and the edge effect are responsible for light availability distribution along forest‐marsh gradients, consequently affecting the understory vegetation biomass. We conclude that during forest retreat driven by sea level rise, tree dieback increases light availability favoring the temporary encroachment ofPh. australisandM. ceriferain the understory.