Sediment Exchange Between the Created Saltmarshes of Living Shorelines and Adjacent Submersed Aquatic Vegetation in the Chesapeake Bay

Iacopo Vona,Cindy M. Palinkas,William Nardin

doi:10.3389/fmars.2021.727080

Iacopo Vona, Cindy M. Palinkas + Show 1 more

Open Access

https://doi.org/10.3389/fmars.2021.727080

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Abstract

Rising sea levels and the increased frequency of extreme events put coastal communities at serious risk. In response, shoreline armoring for stabilization has been widespread. However, this solution does not take the ecological aspects of the coasts into account. The “living shoreline” technique includes coastal ecology by incorporating natural habitat features, such as saltmarshes, into shoreline stabilization. However, the impacts of living shorelines on adjacent benthic communities, such as submersed aquatic vegetation (SAV), are not yet clear. In particular, while both marshes and SAV trap the sediment necessary for their resilience to environmental change, the synergies between the communities are not well-understood. To help quantify the ecological and protective (shoreline stabilization) aspects of living shorelines, we presented modeling results using the Delft3D-SWAN system on sediment transport between the created saltmarshes of the living shorelines and adjacent SAV in a subestuary of Chesapeake Bay. We used a double numerical approach to primarily validate deposition measurements made in the field and to further quantify the sediment balance between the two vegetation communities using an idealized model. This model used the same numerical domain with different wave heights, periods, and basin slopes and includes the presence of rip-rap, which is often used together with marsh plantings in living shorelines, to look at the influences of artificial structures on the sediment exchange between the plant communities. The results of this study indicated lower shear stress, lower erosion rates, and higher deposition rates within the SAV bed compared with the scenario with the marsh only, which helped stabilize bottom sediments by making the sediment balance positive in case of moderate wave climate (deposition within the two vegetations higher than the sediment loss). The presence of rip-rap resulted in a positive sediment balance, especially in the case of extreme events, where sediment balance was magnified. Overall, this study concluded that SAV helps stabilize bed level and shoreline, and rip-rap works better with extreme conditions, demonstrating how the right combination of natural and built solutions can work well in terms of ecology and coastal protection.

Highlights

Human populations are concentrated in the coastal zone, with three-quarters of the global population living within 50 km of the sea and 50% of the US population living within 50 miles of the sea
Wave damping was positively correlated with wave height following a linear law (Figure 6A), while shorter waves were dampened more than longer ones, which suffered a slight increase in height due to the shoaling effect (Figure 6B)
The scenario with marsh, submersed aquatic vegetation (SAV), and rip-rap showed less deposition in the SAV compared with the case with marsh and SAV, but it was greater than the marsh-only scenario

Summary

Introduction

Human populations are concentrated in the coastal zone, with three-quarters of the global population living within 50 km of the sea and 50% of the US population living within 50 miles of the sea. More than one-third of the US gross national product is generated in the coastal zone (Marra et al, 2007) Recent catastrophic events such as Hurricanes Katrina in 2005, Sandy in 2012, and Florence in 2018 have shown that coastal communities are at great risk of coastal inundation caused by storm surges and sea-level rise (Li et al, 2020). As artificial structures, they do not take ecological aspects into account and result in generally, but not exclusively, negative ecosystem impacts (Bilkovic and Mitchell, 2013). In contrast to these interventions, the “living shoreline” technique takes ecology into account by incorporating natural habitat features, such as saltmarshes, into shoreline stabilization. Recent studies of living shorelines have highlighted the importance and effectiveness of these nature-based solutions in providing ecosystem services and enhancing coastal resilience by reducing wave energy and facilitating sedimentation (Currin et al, 2010; Manis et al, 2015; Sutton-Grier et al, 2015; Palinkas and Lorie, 2018; Bolton, 2020; Safak et al, 2020)

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