Abstract
The relationship between lateral erosion of salt marshes and wind waves is studied in Hog Island Bay, Virginia USA, with high-resolution field measurements and aerial photographs. Marsh retreat is compared to wave climate calculated in the bay using the spectral wave-model Simulating Waves Nearshore (SWAN). We confirm the existence of a linear relationship between long-term salt marsh erosion and wave energy, and show that wave power can serve as a good proxy for average salt-marsh erosion rates. At each site, erosion rates are consistent across several temporal scales, ranging from months to decades, and are strongly related to wave power. On the contrary, erosion rates vary in space and weakly depend on the spatial distribution of wave energy. We ascribe this variability to spatial variations in geotechnical, biological, and morphological marsh attributes. Our detailed field measurements indicate that at a small spatial scale (tens of meters), a positive feedback between salt marsh geometry and wave action causes erosion rates to increase with boundary sinuosity. However, at the scale of the entire marsh boundary (hundreds of meters), this relationship is reversed: those sites that are more rapidly eroding have a marsh boundary which is significantly smoother than the marsh boundary of sheltered and slowly eroding marshes.
Highlights
Salt marshes are among the most productive ecosystems on Earth and provide a variety of ecosystem services, such as storm protection of coastal cities, nutrients removal, and carbon storage [1,2,3]
Since pin measurements may underestimate erosion the average between the erosion rates calculated with the field survey and the aerial photographs is taken as the best estimate at each site (Table 1)
The erosion rates computed with erosion pins exhibit the same trend as the seven year (2002–2009) erosion rates derived from GIS and surveys (2008–2010): Matulakin marsh had the highest retreat rate at 0.74 m/year followed by Chimney Pole (0.71 m/year) and Hog Island (0.32 m/year) (Table 1)
Summary
Salt marshes are among the most productive ecosystems on Earth and provide a variety of ecosystem services, such as storm protection of coastal cities, nutrients removal, and carbon storage [1,2,3]. In spite of their important services, salt marshes are continuously threatened by external forcing such as wave action, sea-level rise, decrease in sediment supply, and land reclamation. Marsh erosion due to wind-waves attack has long been recognized as a mechanism for marsh loss and many studies have focused on the qualitative description of edge erosion and mechanics, and/or quantifying erosion rates through time [13,14,15,16,17,18,19,20,21]
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