Declining Sediments and Rising Seas: an Unfortunate Convergence for Tidal Wetlands
The availability of suspended sediments will be a dominant factor influencing the stability of tidal wetlands as sea levels rise. Watershed-derived sediments are a critical source of material supporting accretion in many tidal wetlands, and recent declines in wetland extent in several large river delta systems have been attributed in part to declines in sediment delivery. Little attention has been given, however, to changes in sediment supply outside of large river deltas. In this study, significant declines in suspended sediment concentrations (SSCs) over time were observed for 25 of 61 rivers examined that drain to the East and Gulf Coasts of the USA. Declines in fluvial SSC were significantly correlated with increasing water retention behind dams, indicating that human activities play a role in declining sediment delivery. There was a regional pattern to changes in fluvial sediment, and declines in SSCs were also significantly related to rates of relative sea level rise (RSLR) along the coast, such that wetlands experiencing greater RSLR also tend to be receiving less fluvial sediment. Tidal wetlands in the Mid-Atlantic, Mississippi River Delta, and Texas Gulf especially may become increasingly vulnerable due to rapid RSLR and reductions in sediment. These results also indicate that past rates of marsh accretion may not be indicative of potential future accretion due to changes in sediment availability. Declining watershed sediment delivery to the coastal zone will limit the ability of tidal marshes to keep pace with rising sea levels in some coastal systems.
KeywordsSuspended sediment Tidal wetlands Dams Land use change Accretion Sea level rise
I thank Guillaume Turcotte for his assistance with GIS analysis, Craig Diziki for assistance with data analysis, and Steven Goldsmith, Simon Mudd, and Mark Stacey for constructive comments on the manuscript. I am grateful to the United States Geological Survey, the Permanent Service for Mean Sea Level, the Army Corps of Engineers, the U.S. Census Bureau, the U.S. Agricultural Census, the National Atlas, and the U.S. Department of Agriculture for collection and dissemination of data that makes studies of this nature possible (no endorsement of the data or conclusions is implied). This research was partially supported by National Science Foundation grant DEB-0919173 and by Villanova University.
- Cahoon, Donald R., Philippe F. Hensel, Tom Spencer, Denise J. Reed, Karen L. McKee and Neil Saintilan. 2006. Coastal wetland vulnerability to relative sea-level rise: Wetland elevation trends and process controls. In Wetlands and Natural Resource Management: Ecological Studies, Vol. 190, ed. J.T.A. Verhoeven, B. Beltman, R. Bobbink and D.F. Whigham, 271-292. Berlin: Springer.Google Scholar
- 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.Google Scholar
- Day, John W., Robert R. Christian, Donald M. Boesch, Alejandro Yáñez-Arancibia, James Morris, Robert R. Twilley, Larissa Naylor, Linda Schaffner, and Court Stevenson. 2008. Consequences of climate change on the ecogeomorphology of coastal wetlands. Estuaries and Coasts 31: 477–491.CrossRefGoogle Scholar
- Day, John W., G. Paul Kemp, Denise J. Reed, Donald R. Cahoon, Roelof M. Boumans, Joseph M. Suhayda, and Robert Gambrell. 2011. Vegetation death and rapid loss of surface elevation in two contrasting Mississippi delta salt marshes: The role of sedimentation, autocompaction and sea-level rise. Ecological Engineering 37: 229–240.CrossRefGoogle Scholar
- Fagherazzi, Sergio, Matthew L. Kirwan, Simon M. Mudd, Glenn R. Guntenspergen, Stijn Temmerman, Andrea D’Alpaos, Johan van de Koppel, John M. Rybczyk, Enrique Reyes, Chris Craft, and Jonathan Clough. 2012. Numerical models of salt marsh evolution: Ecological, geomorphic, and climatic factors. Reviews of Geophysics. doi: 10.1029/2011RG000359.Google Scholar
- Gesch, Dean B. 2007. The National Elevation Dataset. In Digital elevation model technologies and applications: The DEM users manual, 2nd ed, ed. David Maune, 99–118. Bethesda: American Society for Photogrammetry and Remote Sensing.Google Scholar
- Gesch, Dean, Michael Oimoen, Susan Greenlee, Charles Nelson, Michael Steuck, and Dean Tyler. 2002. The national elevation dataset. Photogrammetric Engineering and Remote Sensing 68: 5–11.Google Scholar
- Homer, Collin, Jon Dewitz, Joyce Fry, Michael Coan, Nazmul Hossain, Charles Larson, Nate Herold, J. Alexa McKerrow, Nick VanDriel, and James Wickham. 2007. Completion of the 2001 national land cover database for the conterminous United States. Photogrammetric Engineering and Remote Sensing 73: 337–341.Google Scholar
- Krone, R.B. 1985. Simulation of marsh growth under rising sea levels. In In Hydraulics and hydrology in the small computer age, ed. W.R. Waldrop, 106–115. Reston: Hydraulics Division, ASCE.Google Scholar
- National Atlas. 2009. Major dams of the United States. http://www.nationalatlas.gov/mld/dams00x.html. Accessed 18 Oct 2009.
- Natural Resources Conservation Service, United States Department of Agriculture. U.S. General Soil Map (STATSGO2). http://soildatamart.nrcs.usda.gov. Accessed 1 Dec 2009.
- Permanent Service for Mean Sea Level (PSMSL). Tide Gauge Data. http://www.psmsl.org/data/obtaining/. Accessed 11 Jan 2012.
- Schwarz, G.E. 2008. A preliminary SPARROW model of suspended sediment for the conterminous United States. U.S. Geological Survey Open-File Report 2008–1205.Google Scholar
- Syvitski, James P.M., and John D. Milliman. 2007. Geology, geography, and humans battle for dominance over the delivery of fluvial sediment to the coastal ocean. Journal of Geology 115: 1–19.Google Scholar
- Syvitski, James P.M., Charles J. Vörösmarty, Albert J. Kettner, and Pamela Green. 2005. Impact of humans on the flux of terrestrial sediment to the global coastal ocean. Science 308: 376–380.Google Scholar
- Syvitski, James P.M., Albert J. Kettner, Irina Overeem, Eric W.H. Hutton, Mark T. Hannon, G. Robert Brakenridge, John Day, Charles Vörösmarty, Yoshiki Saito, Liviu Giosan, and Robert J. Nicholls. 2009. Sinking deltas due to human activities. Nature Geoscience 2: 681–686.Google Scholar
- Törnqvist, Torbjörn E., Davin J. Wallace, Joep E.A. Storm, Jakob Wallinga, Remke L. Van Dam, Martijn Blaauw, Mayke S. Derksen, Cornelis J.W. Klerks, Camiel Meijneken, and Els M.A. Snijders. 2008. Mississippi Delta subsidence primarily caused by compaction of Holocene strata. Nature Geoscience 1: 173–176.Google Scholar
- Turner, R.E., E.M. Swenson, and C.S. Milan. 2000. Organic and inorganic contributions to vertical accretion in salt marsh sediments. In Concepts and controversies in tidal marsh ecology, ed. Michael P. Weinstein and Daniel A. Kreeger, 583–595. Dordrecht: Kluwer Academic Publishers.Google Scholar
- U.S. Bureau of the Census. 1952. United States Census of Agriculture: 1950. Washington: U.S. Government Printing OfficeGoogle Scholar
- U.S. Bureau of the Census. 1964. U.S. Census of Population: 1960. Washington: U.S. Government Printing OfficeGoogle Scholar
- U.S. Census Bureau. 2002. 2000 Census of Population and Housing. Washington: U.S. Government Printing Office.Google Scholar
- U.S. Department of Agriculture. 1999. 1997 Census of Agriculture. Washington: U.S. Government Printing Office.Google Scholar
- Wahl, Kenneth. L. and Tony L. Wahl. 1988. Effects of regional ground-water declines on streamflows in the Oklahoma Panhandle. Symposium on Water-Use Data for Water Resources Management, American Water Resources Association, Tucson, Arizona, pp. 239–249.Google Scholar
- Woodworth, P.L., and R. Player. 2003. The Permanent Service for Mean Sea Level: An update to the 21st century. Journal of Coastal Research 19: 287–295.Google Scholar