Abstract
Salt marsh evolution is strongly affected by tidal processes and ecology, which regulate sediment accretion and erosional rates. A balance between marsh erosion and deposition in a restored tidal wetland is crucial for analyzing restoration strategies to adopt in a natural context. Here, we present an integrated approach monitoring salt marsh seasonal changes over several months in a microtidal restored salt marsh of the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island (MD, USA). The project is undertaken at a restoration site where sediment dredged from the shipping channels in the upper Chesapeake Bay is being used to restore a tidal marsh habitat in mid-Chesapeake Bay. We flew an Unmanned Aerial Vehicle (UAV) with an RGB and a multispectral camera to obtain a high-resolution map of the planimetric position of vegetation and to monitor the health of the marsh vegetation in diverse seasons. Due to its extension of 400 m by 400 m, a total of four flight plans were necessary to cover the entire marsh flying at a 40 m altitude obtaining a 2 cm Ground Sample Distance (GSD). This technique provides reliable results at a very low cost, enabling an accurate assessment of the marsh platforms to be conducted over time, due to both the very high spatial resolution and the precise georeferencing of the images for the comparisons. Our results show seasonal variability in the two dominant species colonizing the low marsh, Spartina alterniflora, and high marsh, Sporobolus pumilus. While the lower marshes showed a higher variability along seasons, the up-land vegetation showed persistent green foliage during cold seasons. Detecting salt marsh evolution and seasonality coupled with field measurements can help to improve the accuracy of hydrodynamic and sediment transport models. Understanding the drivers of salt marsh evolution is vital for informing restoration practices and designs, in order to improve coastal resilience, and develop and coastal management strategies.
Highlights
Coastal regions are affected by a multitude of phenomena that significantly modify the dynamics of sediment transportation, such as storm surges, tidal processes and sea level rise [1,2,3,4]
Tidal wetland ecosystems, which are an integral part of many coastal systems, can impact sediment dynamics, as well as promote biodiversity, enhance water quality, buffer coastal communities against sea level changes and storms, promote recreation and tourism and are recognized as an important blue carbon sink globally [5,6]
Sarbanes Ecosystem Restoration Project at Poplar Island (Poplar Island) is an ecosystem restoration site constructed of sediment that is dredged from the navigation channels approaching Baltimore Harbor, intended to restore remote island habitat in the Chesapeake Bay
Summary
Coastal regions are affected by a multitude of phenomena that significantly modify the dynamics of sediment transportation, such as storm surges, tidal processes and sea level rise [1,2,3,4]. Tidal wetland ecosystems, which are an integral part of many coastal systems, can impact sediment dynamics, as well as promote biodiversity, enhance water quality, buffer coastal communities against sea level changes and storms, promote recreation and tourism and are recognized as an important blue carbon sink globally [5,6]. The loss of hundreds of low-lying islands in the Chesapeake Bay (Maryland) are attributed to the action of inundation, wave erosion and historic SLR, and thousands more acres of coastal wetlands are projected to be eroded in the coming decades as SLR accelerates [8,9]. In recent decades, creating and restoring tidal wetlands has been undertaken to replace important habitat associated with these lost islands, but understanding the complex dynamics in tidal wetlands will be important to insure resilience
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