Vertical accretion is growth in the total land mass of a wetland by natural processes; this is the natural counter weight to subsidence. Wetlands are created and maintained by a variety of natural processes. The most vital of these processes in the southeastern United States is vertical accretion. Periodic flooding is a necessary component of multiple types of vertical accretion. Wetlands provide many ecological and anthropogenic benefits.

Sedimentation is removal of particulate matter into the water column is essential for the redistribution of sediment, this is called Sediment Accumulation. This sediment is then deposited downstream of the eroded areas creating new land. This is the primary mechanism in one of the types of vertical accretion.

During flooding events certain species, such as Spartina patens, have been shown to sprout aquatic root systems. Aquatic roots are grown to increase the amount of nutrients the plant can take in from the flood waters. These roots are not used to anchor the plant only for nutrient absorption. The aquatic root growth happens continually through the flood period meaning the longer the waters are stagnant the more time the roots have to grow. Eventually, if the flooding persists for too long the roots will become over saturated with water and begin to rot.

Organic accumulation is the vertical accretion created by the decomposition and compression of aquatic roots during and after flood periods. As the flood waters recede the decomposing organic matter becomes new substrate. This raises the height of elevation and increasing the land mass of the marsh. Ecosystems where vegetative vertical accretion is the primary source of new substrate can be viewed as analogs to coral reefs. Both ecosystems are created and sustained by organic not physical processes.

Most coastal restoration projects only take into account vertical accretion via sedimentation. It is an important distinction to make when proposing management practices. In an organic accumulation dependent ecosystem period of flooding would be more important than the amount of sediment carried into the mash.

http://en.wikipedia.org/wiki/Wetlands

http://en.wikipedia.org/wiki/Wetlands_of_the_United_States

http://en.wikipedia.org/wiki/Wetlands_of_Louisiana

http://en.wikipedia.org/wiki/Salt_marsh

http://en.wikipedia.org/wiki/Spartina_patens

Wold, Amy. "Scientists Raise Questions over Diversions’ Effectiveness." The Advocate[Baton Rouge] 2011. Print.

Nyman, J., R. Walters, R. Delaune, and W. Patrickjr. "Marsh Vertical Accretion via Vegetative Growth." Estuarine, Coastal and Shelf Science 69.3-4 (2006): 370-80. Print.

Neubauer, S. "Contributions of Mineral and Organic Components to Tidal Freshwater Marsh Accretion." Estuarine, Coastal and Shelf Science 78.1 (2008): 78-88. Print.

"Wetland Loss In Louisiana." LaCoast.gov. Web. 29 Nov. 2011. http://lacoast.gov/reports/rtc/1997/5.htm. http://geography.about.com/od/physicalgeography/a/wetlands.htm