Reevaluating the wave power-salt marsh retreat relationship

Abstract

Salt marshes are threatened by rising sea levels and human activities, and a major mechanism of marsh loss is edge retreat or erosion. To understand and predict loss in these valuable ecosystems, studies have related erosion to marsh hydrodynamics and wave characteristics such as wave power. Across global studies, erosion is reported to be largely linearly related to wave power, with this relationship having implications for the resilience of marshes to extreme events such as storms. However, there is significant variability in this relationship across marshes because of marsh heterogeneity and the uniqueness of each physical setting. Here, we investigate the results of individual studies throughout the world that report a linear relationship and add a new dataset from the Great Marsh in Massachusetts (USA). We find that most marsh wave power and erosion data are not normally distributed and when these datasets are properly plotted to account for their distributions, the resulting relationships vary from previously published curves. Our Great Marsh data suggest that events from specific wind directions can have an outsized impact on edge erosion due to their larger fetch and wind speeds. We also find that factors other than wave attack such as edge erosion along tidal channels, can have a measurable impact on retreat rates. We show the importance of maintaining statistical assumptions when performing regressions, as well as emphasize the site-specificity of these relationships. Without calibration of a marsh erosion-wave power relationship using robust regressions for each individual marsh, such a relationship is not fully constrained, resulting in unreliable predictions of future marsh resilience and response to climate change.

Storm Impacts on Mineral Mass Accumulation Rates of Coastal Marshes

“…Wave power has generally been related to marsh lateral erosion (e.g., Houttuijn Bloemendaal et al., 2023; Leonardi et al., 2016; McLoughlin et al., 2015). Waves can deepen tidal flats facing marsh edges and consequently enhance wave energy (Fagherazzi et al., 2006).…”

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

“…In contrast, however, a wide range of field-based studies have identified a nonlinear fit between lateral erosion and wave power, with x = 1.10 to 1.37, e.g., (5)(6)(7)(8)(9)(10). These studies have shown a large amount of variability in erosion across field sites, caused by differences in soil properties, vegetation, and myriad other factors (11). 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.…”

“…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).…”

“…A longer duration field study generally will have (i) more of these nonwave effects embedded within the reported measurements as the duration of the study increases and (ii) a higher average wave power as the likelihood of encountering large wave events increases over time—with the net effect raising the exponent. These nonwave effects also occur in variable quantities depending on each unique study, which further induces scatter into the generalized nonlinear fit, particularly as the wave power increases ( 11 ). Both inherent site variation and these nonwave effects have complicated the discovery of a more universal relationship between lateral erosion and wave mechanics.…”

Expansion of Magallana Gigas Colonization: Northernmost and Southernmost Invasion on Saltmarsh Ecosystems in the SW Atlantic

“…Although physical factors like wind action, wave energy, and tides contribute significantly to marsh erosion rates [16,17], biological factors interacting with these physical forces also play an important role in geomorphological processes. Autogenic ecosystem engineers and allogenic ecosystem engineers, along with herbivores and their predators, influence primary production and the stability of these environments [4,[18][19][20][21]. Invasive species further complicate ecological systems by altering the evolutionary pathways of native species, modifying the structure of biological communities, and disrupting habitat complexity [22][23][24][25].…”