Friday, August 7, 2009

PS 76-14: Are restored marshes as good as natural marshes?

Chuan-Kai Ho, Michael Bell, Amanda Thronson, Eric Madrid, Antonietta Quigg, and Anna Armitage. Texas A&M University at Galveston


Coastal wetlands are productive habitats that have been greatly threatened by anthropogenic impacts.  As restoration efforts increase in scale and scope, ensuring the ecological success of restoration methods is increasingly important.  To examine whether and which restoration methods have the highest ecological success and might produce habitat that is similar to natural marshes, we are monitoring the development of plant and animal communities and ecosystem functions in restored brackish marshes in the Lower Neches Wildlife Management Area in Port Arthur, Texas, USA.  This study site includes native marshes and 4 types of restored marshes that were completed in spring 2008: 1) mounds created using soil excavated from adjacent subtidal habitat, 2) mounds excavated then surrounded by dredge fill to decrease surrounding water depth, 3) mounds created from dredge material pumped in directly from a nearby canal, and 4) terraces constructed from an upland dredge disposal site.


Plant community surveys conducted in April 2009 showed that restored marshes approached or exceeded reference marsh conditions in some respects.  In particular, compared to reference marshes, excavated mounds and terraces canopies were > 50% taller, Spartina alterniflora was 47% taller in excavated mounds, and S. alterniflora canopies were nearly twice as complex in excavated and filled mounds.  In contrast, reference marshes had higher plant stem density (83% to 165% increase) and plant species richness (N=2.9) than all restored marshes (N<1.9).  Although S. alterniflora, one of the most abundant marsh plants, was shorter and less dense in reference than restored marshes, we found no difference in total plant aboveground biomass among these marshes.  This is likely due to compensation from other plant species, S. patens in particular, in reference marshes.  In fact, S. patens also contributed to higher plant stem density and overall plant structure complexity in reference marshes, suggesting some structure benefits to having higher species richness.  Although our surveys suggest that restored marshes could quickly match or outperform reference marshes in terms of S. alterniflora performance, it is possible that the differences in plant structure complexity and species richness among these marshes could directly and/or indirectly result in different trophic structure and ecosystem functions.  We will examine herbivores, predators, and nutrient retention in summer 2009 and continue monitoring the trajectory of restored marshes.  Our findings should provide useful information in predicting the ecological efficacy of future coastal restoration projects.