Salt marshes are among the most productive ecosystems on Earth, providing nurseries for fish species and shelter and food for endangered birds. Salt marshes also mitigate the impacts of hurricanes and tsunamis, and sequester large volumes of carbon in their peat soil. Understanding the mechanisms responsible for marsh stability or deterioration is therefore a key issue for society. Sea level rise is often viewed as the main driver of salt marsh deterioration. However, while salt marshes can reach equilibrium in the vertical direction, they are inherently unstable in the horizontal direction. Marsh expansion driven by sediment supply rarely matches lateral erosion by waves, creating a dynamic landscape. Recent results show that marsh collapse can occur in the absence of sea level rise if the rate at which sediment is eroded at marsh boundaries is higher than the input of sediment from nearby rivers or from the continental shelf. We propose that the horizontal dynamics and related sediment fluxes are key factors determining the survival of salt marshes. Only a complete sediment budget between salt marshes and nearby tidal flats can determine the fate of marshes at any given location, with sea level rise being only one among many external drivers. Ancient Venetians understood this dynamic very well. They manipulated the supply of sediment to the Venice lagoon, Italy, in order to control the long-term evolution of the intertidal landscape

Fagherazzi, S., G. Mariotti, P.L. Wiberg, and K.J. McGlathery. 2013. Marsh collapse does not require sea level rise. Oceanography 26(3):70–77, https://doi.org/10.5670/oceanog.2013.47.

Allen, J.R.L. 1989. Evolution of salt-marsh cliffs in muddy and sandy systems: A qualitative comparison of British west-coast estuaries. Earth Surface Processes and Landforms 14:85–92, https://doi.org/10.1002/esp.3290140108.

Allen, E.A., and H.A. Curran. 1974. Biogenic sedimentary structures produced by crabs in lagoon margin and salt marsh environments near Beaufort, North Carolina. Journal of Sedimentary Petrology 44:538–548, https://doi.org/10.1306/74D72A7C-2B21-11D7-8648000102C1865D.

Bertness, M.D. 1984. Ribbed mussels and Spartina alterniflora production in a New England salt marsh. Ecology 65:1,794–1,807, https://doi.org/10.2307/1937776.

Charlier, R.H., M.C.P. Chaineux, and S. Morcos. 2005. Panorama of the history of coastal protection. Journal of Coastal Research 21:79–111, https://doi.org/10.2112/03561.1.

Chen, X., and Y. Zong. 1998. Coastal erosion along the Changjiang deltaic shoreline, China: History and prospective. Estuarine, Coastal and Shelf Science 46:733–742, https://doi.org/10.1006/ecss.1997.0327.

Christiansen, T., P.L. Wiberg, and T.G. Milligan. 2000. Flow and sediment transport on a salt marsh surface. Estuarine, Coastal and Shelf Science 50:315–331, https://doi.org/10.1006/ecss.2000.0548.

Coops, H., N. Geilen, H.J. Verheij, R. Boeters, and G. van der Velde. 1996. Interactions between waves, bank erosion and emergent vegetation: An experimental study in a wave tank. Aquatic Botany 53:187–198, https://doi.org/​10.1016/0304-3770(96)01027-3.

D’Alpaos, A., S.M. Mudd, and L. Carniello. 2011. Dynamic response of marshes to perturbations in suspended sediment concentrations and rates of relative sea level rise. Journal of Geophysical Research 116, F04020, https://doi.org/​10.1029/2011JF002093. 

Day, J.W. Jr., F. Scarton, A. Rismondo, and D. Are. 1998. Rapid deterioration of a salt marsh in Venice Lagoon, Italy. Journal of Coastal Research 14:583–590, http://journals.fcla.edu/jcr/article/view/80638.

Deegan, L.A., D.S. Johnson, R.S. Warren, B.J. Peterson, J.W. Fleeger, S. Fagherazzi, and W.M. Wollheim. 2012. Coastal eutrophication as a driver of salt marsh loss. Nature 490:388–392, https://doi.org/10.1038/nature11533.

Escapa, M., G.M.E. Perillo, and O. Iribarne. 2008. Sediment dynamics modulated by burrowing crab activities in contrasting SW Atlantic intertidal habitats. Estuarine, Coastal and Shelf Science 80:365–373, https://doi.org/10.1016/​j.ecss.2008.08.020.

Fagherazzi, S., D.M. FitzGerald, R.W. Fulweiler, Z. Hughes, P.L. Wiberg, K.J. McGlathery, J.T. Morris, T.J. Tolhurst, L.A. Deegan, and D.S. Johnson. 2013. Ecogeomorphology of salt marshes. Pp. 182–200 in Treatise on Geomorphology, Vol. 12: Ecogeomorphology. J.F. Shroder, ed., Academic Press, San Diego, CA, https://doi.org/10.1016/B978-0-12-374739-6.00329-8.

Fagherazzi, S., M.L. Kirwan, S.M. Mudd, G.R. Guntenspergen, S. Temmerman, A. D’Alpaos, J. van de Koppel, J.M. Rybczyk, E. Reyes, C. Craft, and J. Clough. 2012. Numerical models of salt marsh evolution: Ecological and climatic factors. Reviews of Geophysics 50, RG1002, https://doi.org/​10.1029/2011RG000359.

Fagherazzi, S., and P.L. Wiberg. 2009. Importance of wind conditions, fetch, and water levels on wave-generated shear stresses in shallow intertidal basins. Journal of Geophysical Research 114, F03022, https://doi.org/​10.1029/2008JF001139.

Feagin, R.A., S.M. Lozada-Bernard, T.M. Ravens, I. Moller, K.M. Yeager, and A.H. Baird. 2009. Does vegetation prevent wave erosion of salt marsh edges? Proceedings of the National Academy of Sciences of the United States of America 106:10,109–10,113, https://doi.org/​10.1073/pnas.0901297106.

Kirwan, M.L., G.R. Guntenspergen, A. D’Alpaos, J.T. Morris, S.M. Mudd, and S. Temmerman. 2010. Limits on the adaptability of coastal marshes to rising sea level. Geophysical Research Letters 37, L23401, https://doi.org/​10.1029/2010GL045489.

Leonard, L.A., and A.L. Croft. 2006. The effect of standing biomass on flow velocity and turbulence in Spartina alterniflora canopies. Estuarine, Coastal and Shelf Science 69:325–336, https://doi.org/10.1016/j.ecss.2006.05.004.

Marani, M., A. D’Alpaos, S. Lanzoni, and M. Santalucia. 2011. Understanding and predicting wave erosion of marsh edges. Geophysical Research Letters 38, L21401, https://doi.org/10.1029/2011GL048995.

Mariotti, G., and S. Fagherazzi. 2013. Critical width of tidal flats triggers marsh collapse in the absence of sea-level rise. Proceedings of the National Academy of Sciences of the United States of America 110:5,352–5,356, https://doi.org/10.1073/pnas.1219600110. 

Mariotti, G., and S. Fagherazzi. 2010. A numerical model for the coupled long-term evolution of salt marshes and tidal flats. Journal of Geophysical Research 115, F01004, https://doi.org/10.1029/2009JF001326.

Mariotti, G., S. Fagherazzi, P.L. Wiberg, K.J. McGlathery, L. Carniello, and A. Defina. 2010. Influence of storm surges and sea level on shallow tidal basin erosive processes. Journal of Geophysical Research 115, C11012, https://doi.org/10.1029/2009JC005892.

McLoughlin, S.M. 2010. Erosional processes along salt marsh edges on the Eastern Shore of Virginia. MS Thesis, University of Virginia, Charlottesville, VA.

Meyer, D.L., E.C. Townsend, and G.W. Thayer. 1997. Stabilization and erosion control value of oyster cultch for intertidal marsh. Restoration Ecology 5:93–99, https://doi.org/​10.1046/j.1526-100X.1997.09710.x.

Micheli, E.R., and J.W. Kirchner. 2002. Effects of wet meadow riparian vegetation on streambank erosion: Part 2. Measurements of vegetated bank strength and consequences for failure mechanics. Earth Surface Processes and Landforms 27:687–697, https://doi.org/​10.1002/esp.340.

Montague, C.L. 1980. A natural history of temperate western Atlantic fiddler crabs (Genus Uca) with reference to their impact on the salt marsh. Contributions in Marine Science 23:25–55.

Morris, J.T., K. Sundberg, and C.S. Hopkinson. 2013. Salt marsh primary production and its responses to relative sea level and nutrients in estuaries at Plum Island, Massachusetts, and North Inlet, South Carolina, USA. Oceanography 26(3):78–84, https://doi.org/​10.5670/oceanog.2013.48.

Mudd, S.M., A. D’Alpaos, and J.T. Morris. 2010. How does vegetation affect sedimentation on tidal marshes? Investigating particle capture and hydrodynamic controls on biologically mediated sedimentation. Journal of Geophysical Research 115, F03029, https://doi.org/​10.1029/2009JF001566.

Nittrouer, J.A., J.L. Best, C. Brantley, R.W. Cash, M. Czapiga, P. Kumar, and G. Parker. 2012. Mitigating land loss in coastal Louisiana by controlled diversion of Mississippi River sand. Nature Geoscience 5, 534–537, https://doi.org/​10.1038/ngeo1525.

Phillips, J.D. 1986. Coastal submergence and marsh fringe erosion. Journal of Coastal Research 2:427–436, http://journals.fcla.edu/jcr/article/view/77487.

Piazza, B.P., P.D. Banks, and M.K. La Peyre. 2005. The potential for created oyster shell reefs as a sustainable shoreline protection strategy in Louisiana. Restoration Ecology 13:499–506, https://doi.org/​10.1111/j.1526-100X.2005.00062.x.

Redfield, A.C. 1965. Ontogeny of a salt marsh. Science 147:50–55, https://doi.org/10.1126/science.147.3653.50. 

Reed, D.J. 1995. The response of coastal marshes to sea-level rise: Survival or submergence? Earth Surface Processes and Landforms 20:39–48, https://doi.org/10.1002/esp.3290200105.

Riffe, K.C., S.M. Henderson, and J.C. Mullamey. 2011. Wave dissipation by flexible vegetation. Geophysical Research Letters 38, L18607, https://doi.org/10.1029/2011GL048773.

Schwimmer, R.A. 2001. Rates and processes of marsh shoreline erosion in Rehoboth Bay, Delaware, USA. Journal of Coastal Research 17:672–683, http://journals.fcla.edu/jcr/article/view/81397.

Scyphers, S.B., S.P. Pwers, K.L. Heck Jr., and D. Byron. 2011. Oyster reefs as natural breakwaters mitigate shoreline loss and facilitate fisheries. PLoS ONE 6(8):e22396, https://doi.org/10.1371/Journal.pone.0022396.

Syvitski, J.P.M., C.J. Vörösmarty, A.J. Kettner, and P. Green. 2005. Impact of humans on the flux of terrestrial sediment to the global coastal ocean. Science 308(5720):376–380, https://doi.org/​10.1126/science.1109454.

Taube, S.R. 2013. Impacts of fringing oyster reefs on wave attenuation and marsh erosion rates. MS Thesis, University of Virginia, Charlottesville, VA.

Temmerman, S., T.J. Bouma, G. Govers, and D. Lauwaet. 2005. Flow paths of water and sediment in a tidal marsh: Relations with marsh developmental stage and tidal inundation height. Estuaries 28(3):338–352, https://doi.org/10.1007/BF02693917. 

Tonelli, M., S. Fagherazzi, and M. Petti. 2010. Modeling wave impact on salt marsh boundaries. Journal of Geophysical Research 115, C09028, https://doi.org/​10.1029/2009JC006026.

Trembanis, A.C., O.H. Pilkey, and H.R. Valverde. 1999. Comparison of beach nourishment along the US Atlantic, Great Lakes, Gulf of Mexico, and New England shorelines. Coastal Management 27(4):329–340, https://doi.org/​10.1080/089207599263730.

Trevisan, B. 1715. Trattato della Laguna di Venezia. D. Lovisa, 129 pp.

van der Wal, D., and K. Pye. 2004. Patterns, rates and possible causes of saltmarsh erosion in the Greater Thames area (UK). Geomorphology 61:373–391, https://doi.org/10.1016/j.geomorph.2004.02.005.

van Eerdt, M.M. 1985. The influence of vegetation on erosion and accretion in salt marshes of the Oosterschelde, The Netherlands. Vegetatio 62:367–373, https://doi.org/10.1007/BF00044763.

Watts, C.W., T.J. Tolhurst, K.S. Black, and A.P. Whitmore. 2003. In situ measurements of erosion shear stress and geotechnical shear strength of the intertidal sediments of the experimental managed realignment scheme at Tollesbury, Essex, UK. Estuarine, Coastal and Shelf Science 58:611–620, https://doi.org/​10.1016/S0272-7714(03)00139-2.

Wilson, C.A., and M.A. Allison. 2008. An equilibrium profile model for retreating marsh shorelines in southeast Louisiana. Estuarine, Coastal and Shelf Science 80:483–494, https://doi.org/​10.1016/j.ecss.2008.09.004. 

Yang, S., P. Ding, and S. Chen. 2001. Changes in progradation rate of the tidal flats at the mouth of the Changjiang (Yangtze) River, China. Geomorphology 38:167–180, https://doi.org/​10.1016/S0169-555X(00)00079-9.

Yang, S., Q. Zhao, and I.M. Belkin. 2002. Temporal variation in the sediment load of the Yangtze river and the influences of human activities. Journal of Hydrology 263:56–71, https://doi.org/10.1016/S0022-1694(02)00028-8. 

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