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1. Storm Impacts on Mineral Mass Accumulation Rates of Coastal Marshes

   https://doi.org/10.1029/2023JF007065  

   Cortese, L.; Zhang, X.; Simard, Marc; Fagherazzi, S. (February 2024, Journal of Geophysical Research: Earth Surface)

   Abstract Coastal marsh survival may be compromised by sea‐level rise, limited sediment supply, and subsidence. Storms represent a fundamental forcing for sediment accumulation in starving marshes because they resuspend bottom material in channels and tidal flats and transport it to the marsh surface. However, it is unrealistic to simulate at high resolution all storms that occurred in the past decades to obtain reliable sediment accumulation rates. Similarly, it is difficult to cover all possible combinations of water levels and wind conditions in fictional scenarios. Thus, we developed a new method that derives long‐term deposition rates from short‐term deposition generated by a finite number of storms. Twelve storms with different intensity and frequency were selected in Terrebonne Bay, Louisiana, USA and simulated with the 2D Delft3D‐FLOW model coupled with the Simulating Waves Nearshore (SWAN) module. Storm impact was analyzed in terms of geomorphic work, namely the product of deposition and frequency. To derive the long‐term inorganic mass accumulation rates, the new method generates every possible combination of the 12 chosen storms and uses a linear model to fit modeled inorganic deposition with measured inorganic mass accumulation rates. The linear model with the best fit (highestR²) was used to derive a map of inorganic mass accumulation rates. Results show that a storm with 1.7 ± 1.6 years return period provides the largest geomorphic work, suggesting that the most impactful storms are those that balance intensity with frequency. Model results show higher accumulation rates in marshes facing open areas where waves can develop and resuspend sediments. This method has the advantage of considering only a few real scenarios and can be applied in any marsh‐bay system. 

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2. Empirical observations and numerical modelling of tides, channel morphology, and vegetative effects on accretion in a restored tidal marsh

   https://doi.org/10.1002/esp.4646  

   Fleri, Jesse R.; Lera, Sara; Gerevini, Alessandro; Staver, Lorie; Nardin, William (July 2019, Earth Surface Processes and Landforms)

   Abstract Tidal marshes form at the confluence between estuarine and marine environments where tidal movement regulates their developmental processes. Here, we investigate how the interplay between tides, channel morphology, and vegetation affect sediment dynamics in a low energy tidal marsh at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island. Poplar Island is an active restoration site where fine‐grained material dredged from navigation channels in the upper Chesapeake Bay are being used to restore remote tidal marsh habitat toward the middle bay (Maryland, USA). Tidal currents were measured over multiple tidal cycles in the inlets and tidal creeks of one marsh at Poplar Island, Cell 1B, using Acoustic Doppler Current Profilers (ADCP) to estimate water fluxes throughout the marsh complex. Sediment fluxes were estimated using acoustic backscatter recorded by ADCPs and validated against total suspended solid measurements taken on site. A high‐resolution geomorphic survey was conducted to capture channel cross sections and tidal marsh morphology. We integrated simple numerical models built in Delft3d with empirical observations to identify which eco‐geomorphological factors influence sediment distribution in various channel configurations with differing vegetative characteristics. Channel morphology influences flood‐ebb dominance in marshes, where deep, narrow channels promote high tidal velocities and incision, increasing sediment suspension and reducing resilience in marshes at Poplar Island. Our numerical models suggest that accurately modelling plant phenology is vital for estimating sediment accretion rates. In‐situ observations indicate that Poplar Island marshes are experiencing erosion typical for many Chesapeake Bay islands. Peak periods of sediment suspension frequently coincide with the largest outflows of water during ebb tides resulting in large sediment deficits. Ebb dominance (net sediment export) in tidal marshes is likely amplified by sea‐level rise and may lower marsh resilience. We couple field observations with numerical models to understand how tidal marsh morphodynamics contribute to marsh resilience. © 2019 John Wiley & Sons, Ltd. 

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3. Impact of Hurricane Sandy on salt marshes of New Jersey

   https://doi.org/DOI 10.1016/j.ecss.2016.09.006  

   Elsey-Quirk, T. (January 2016, Estuarine, coastal and shelf science)

   Hurricane Sandy, one of the largest Atlantic hurricanes on record, made landfall as an extratropical cyclone on the coast of New Jersey (29 October 2012) along a track almost perpendicular to the coast. Ten days later a northeaster caused heavy precipitation and elevated water levels along the coast. Two years of pre-storm monitoring and research in marshes of Barnegat Bay and the Delaware Estuary provided an opportunity to evaluate the impacts of Hurricane Sandy and the succeeding northeaster across the region. Peak water levels during Sandy ranged from 111 to 184 cm above the marsh surface in Barnegat Bay and 75 to 135 cm above the marsh surface in the Delaware Estuary. Despite widespread flooding and damage to coastal communities, the storm had modest and localized impacts on coastal marshes of New Jersey. Measurements made on the marsh platform illustrated localized responses to the storms including standing biomass removal, and changes in peak biomass the following summer. Marsh surface and elevation changes were variable within marshes and across the region. Localized elevation changes over the storm period were temporary and associated with subsurface processes. Over the long-term, there was no apparent impact of the 2012 storms, as elevations and regression slopes pre- and several months post-storm were not significant. Vegetation changes in the summer following the fall 2012 storms were also variable and localized within and among marshes. These results suggest that Hurricane Sandy and the succeeding northeaster did not have a widespread long-term impact on saline marshes in this region. Possible explanations are the dissipation of surge and wave energy from the barrier island in Barnegat Bay and the extreme water levels buffering the low-lying marsh surface from waves, winds, and currents, and carrying suspended loads past the short-statured marsh grasses to areas of taller vegetation and/or structure. These findings demonstrate that major storms that have substantial impacts on infrastructure and communities can have short-term localized effects on coastal marshes in the vicinity of the storm track.   

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4. Biogeomorphic patterns emerge with pond expansion in deteriorating marshes affected by relative sea level rise

   https://doi.org/10.1002/lno.11661  

   Qi, Man; MacGregor, Jessica; Gedan, Keryn (December 2020, Limnology and Oceanography)

   Abstract Interior marsh pond formation has been commonly observed in tidal marshes affected by high rates of relative sea level rise (RSLR). However, it is difficult to conclude whether an accretion deficit (accretion which does not keep pace with RSLR) or natural ice and wrack disturbance has driven pond formation. We propose that marsh deterioration caused by accretion deficit can be differentiated from that caused by other disturbances based upon temporal vegetation changes and the spatial configuration of vegetation zones relative to tidal creeks and the marsh platform. We tested this hypothesis in six newly ponded sites within RSLR‐affected marshes in Deal Island, Chesapeake Bay. At each site, we used field surveys and remote sensing to study spatiotemporal dynamics of marsh vegetation, marsh topography, and tidal creek incision. We found flood tolerant plants displaced flood intolerant species over time in the landward direction, or upslope, of ponds. A reverse species transition was observed seaward of ponds because tidal creek incision alleviated interior marsh inundation. The landscape‐scale biogeographic pattern we have recognized sheds light on how plants adapt to chronically reshaped geomorphological configurations of the marsh platform, which differentiates ponding caused by accretion deficit from ponding caused by natural and artificial disturbances. Furthermore, our results point to vegetation patterns that can be used as early warning signals of interior marsh loss to ponding. As ponding has been a major driver of tidal marsh habitat loss in microtidal marshes around the world, early indicators of decline are sorely needed to direct conservation activities. 

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5. Storm Dynamics Control Sedimentation and Shelf‐Bay‐Marsh Sediment Exchange Along the Louisiana Coast

   https://doi.org/10.1029/2024GL111344  

   Georgiou, Ioannis Y; FitzGerald, Duncan M; Sakib, Md Mohiuddin; Messina, Francesca; Kulp, Mark A; Miner, Michael D (November 2024, Geophysical Research Letters)

   Hurricanes can benefit wetland accretion by augmenting the delivery of mineral sediment, an essential process allowing marshes to offset submergence during rising sea levels. Using Hurricane Gustav (2008, Louisiana) as a control, we examined eight synthetic storms with varying characteristics (track, speed, intensity, size) to evaluate sediment exchange between the inner shelf and bay and bay‐to‐marsh interfaces. All storms showed net landward sediment exchange from the inner shelf to the bay to the marsh—storms with closer proximity, higher intensity, and slower forward speed positively correlated with net sediment exchange; storm size had little impact. Except for slow‐moving storms (½ speed of Gustav), our analyses suggest that most hurricane scenarios cause net bay erosion, because more sediment is conveyed to landward wetlands than is replenished from erosion of the inner shelf. Our results suggest that the ongoing deepening of the bay will likely worsen because of rising sea levels 

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