PRESENTATION NOT AVAILABLE
Christine Thibodeaux
Louisiana Department of Natural Resources
Coastal Restoration Division
635 Cajundome Blvd., Suite 203A
P.O. Box 62027
Lafayette, LA 70596-2027
Abstract
The Coastal Wetlands Planning, Protection, and Restoration Act (CWPPRA) authorized and constructed the Pecan Island Terracing (ME-14) project on the 7th annual Priority Project List in 1998. This project is located five miles north of the Gulf of Mexico in Vermilion Parish, Louisiana, south of the town of Pecan Island. Prior to construction, the project area comprised approximately 1,437 ha of brackish marsh and open water. The project area was classified in 1956 as 99.1% fresh marsh and 0.9% water. In the mid-1950s, continuous dikes were constructed and water was pumped off the marsh, transforming it into dry pastureland. As a result of oxidation, the soil elevation subsided 1 to 2 feet. Combined with the failure of the levees in the very late 1950's, the area became open water. The project goal is to increase land-water ratios and minimize wave fetch by constructing approximately 40 ha of earthen terraces.
Construction was complete in August 2003 using a track hoe on marsh buggy on approximately 60,046 linear meters of terraces in a staggered gap formation. Some terraces were planted with Spartina alterniflora and some terraces were left unplanted. Pre-construction engineering data detected a natural channel in the southeast portion of the project and terrace sizes were modified to accommodate the existing channel. Monitoring of this project includes aerial photography, emergent vegetation and submerged aquatic vegetation (SAV) over the 20 yr life of the project. Aerial photography was collected in 2001 (pre-construction) and in 2004 (post-construction). SAV data were collected pre-construction in the spring of 2001 and post-construction in the spring of 2005. The SAV data suggest an increase in species richness. Soil cores collected from three of the planted terraces and three of the unplanted terraces during the 2005 SAV monitoring revealed low percent organic matter and a moderately alkaline pH level, which may be responsible for the balding effect occurring on the crowns of the terraces. Emergent vegetation was compared on 15 planted terraces and 15 unplanted terraces in the fall of 2003 where percent cover, dominant plant heights, and species composition were documented. In the fall of 2004 ancillary emergent vegetation data were collected on two of the unplanted terraces and two of the planted terraces. Percent cover of emergent vegetation was significantly different among planted and unplanted terraces over two sampling periods (F1,1=6.286, p<0.05), suggesting that planting of vegetation accelerates the rate vegetative cover over natural succession. Colonization of vegetation on the planted terraces was predominantly composed of Spartina alterniflora. On the unplanted terraces sampled, S. alterniflora did not occur. Paspalum vaginatum, a native species dominant in the surrounding marsh, colonized both planted and unplanted terraces. |
|
|