Long-Term Erosional Trends Along Channelized Salt Marsh Edges

Abstract

Salt marshes provide important habitats for many species in the estuaries along the east and Gulf coasts of North America. With many species dependent on these coastal marshlands and extensive documentation that these marshlands are disappearing, a clear understanding of the mechanisms causing loss is critical. Much of the salt marsh was lost to reclamation and construction before these activities were curtailed circa 1970; however, losses due to other causes have continued and multiple hypothesized causes have been proposed, not all mutually exclusive. Yet it remains unclear whether there are legacy effects from the reclamation projects. When the edges of salt marshes are cut into, and gentle vegetated slopes are replaced by sharp edges adjoining deep water of 2 m or more, erosion could accelerate and could continue for many years. One method that may help shed light on the relative importance of the various causes of salt marsh erosion would be to compare the erosion rates of specific edges within a marshland that are exposed to particular conditions. We therefore used several sets of aerial photography spanning 84 years to track the changes at specific edge locations along marsh edges and then make comparisons between anthropogenically created edges and naturally created edges, including comparisons within use and width categories of navigational channels. Erosion rates were found to remain significantly higher on channelized edges than along otherwise similar wetland edges even several decades after modification. Likely reasons include the continued exposure of underlying layers that lack reinforcing plant root systems, vertical edges that are more vulnerable to undermining from wave action, and increased erosion related to altered tidal flows.

An asymmetry in wave scaling drives outsized quantities of coastal wetland erosion

“…While these inherent differences among the sites can be partially accounted for by standardizing the individual erosion measurements by the mean quantity of erosion at each site (12), nonwave erosive effects still contaminate the field datasets and raise the exponent x. For example, mass wasting driven by gravity (13), tidal creek flows (14)(15), alongshore current velocity-driven erosion (11,16), precipitation-driven erosion (17), and soil cracking due to wetting and drying effects (18) each occur at different frequencies across time (19)(20)(21)(22)(23).…”

The effects of ship wakes in the Venice Lagoon and implications for the sustainability of shipping in coastal waters

“…It is well known that ship traffic can significantly damage vulnerable areas such as tidal creeks 11 , microtidal estuaries 12 , lakes 13,14 or wetlands 15,16 . The impact of vessel wakes can be the most significant factor for changes near fairways, such as on the channel edges in salt marshes 17 , on the shores of navigable delta channels 18 , and on river banks 19 .…”

Salt Marsh Peat Dispersal: Habitat for Fishes, Decapod Crustaceans, and Bivalves

“…One of the main causes of separation of marsh peat from the marsh platform is the bank being undercut by the current because the lower mud layer is less stable than the peat, and washes away first [12][13][14]. This leads to a peat overhang that then breaks off and falls away from the marsh edge into intertidal and subtidal waters.…”