Do plants really reduce salt marsh erosion in Galveston Bay


Jan. 24, 2007


Feagin, R
Lozada-Bernard, S
Ravens, T

Journal Title

Journal ISSN

Volume Title


Galveston Bay Estuary Program


The results of this study challenge our conception of the traditional paradigm that plant roots directly prevent erosion along the coast. Previous studies have focused solely upon the ability of above-ground plant stems and leaves to reduce wave forces in the water column, yet these studies have ignored the physical mechanism that results in the majority of salt marsh erosion in Galveston Bay- undercutting of the marsh edge by waves. To investigate marsh edge erosion, we placed extracted marsh cores into a wave flume and sent waves at them. The waves simulated a typical windy 24 hour period in Galveston Bay. We tested for differences in erosion rates between cores with plants and without plants, for differences among plant species, and for differences in soil types. The results showed that the soil type was the master variable that determined the erosion rate, rather than the plants. In particular, bulk density and sediment particle size provided the best predictors for erosion rate. The presence of plants or live plant roots made no significant difference upon the erosion rate. Rather than the living plants and roots, we suggest that it is the indirect input of plant detritus in the form of finely-grained organic particles that lends cohesiveness to the soil, along with the associated changes in bulk density and particle size. As plant-produced detritus becomes incorporated into the matrix, the soil becomes less dense, finer, and more resistant to erosion. Thus, plants do not directly reduce erosion, but do so indirectly through modification of the soil parameters. Of all the extracted cores that we tested, the dense, coarse, inorganic, and sandy sediment from the terraces at Galveston Island State Park (a restored salt marsh) eroded the quickest. This study is important because it suggests that salt marsh restoration efforts should place the highest priority upon getting the soil right.




erosion, marsh cores, marsh edge, marsh restoration, plant roots, soil types, waves