Restoration Success of Backfilling Canals in Coastal Louisiana Marshes

• Main Author: Baustian, Joseph
• Other Authors: Irving A. Mendelssohn
• Format: Others
• Language: en
• Published: LSU 2005
• Subjects: Oceanography & Coastal Sciences
• Online Access: http://etd.lsu.edu/docs/available/etd-04132005-180725/

The need for effective marsh restoration techniques in Louisiana is a pressing issue as the state continues to lose coastal wetlands. Returning spoil banks to canals, known as "backfilling", is an attractive restoration option because it restores marsh, prevents future wetland loss, and is cost effective. The direct conversion of marsh to canals and spoil banks accounted for over 22% of Louisiana's wetland loss from 1930 to 1990, and the indirect losses associated with canal dredging are even larger. The restoration success of 30 canals, backfilled twenty years ago, was examined in this study and compared to restoration success shortly after backfilling. Ultimately, the success of backfilling was controlled by the amount of spoil returned to the canal and the position of the canal in the marsh. Up to 95% of the spoil area was restored to marsh when the spoil banks were adequately removed, but only 5% of the spoil area was restored at sites where spoil removal was poor. Restoration of organic matter, bulk density, and water content of the former spoil areas was also constrained by the adequacy of spoil removal. Backfilling restored 80% of the organic matter and 94% of the bulk density and water content after twenty years at sites where spoil was properly removed. The plant species on the former spoil areas often did not match those of the surrounding marsh, and the differences were directly correlated with the amount of spoil removed. Canals backfilled in areas of more intact marsh showed greater restoration success than canals backfilled in highly degraded marshes. This study indicates that the benefits of backfilling continue to increase over time, although complete restoration will take longer than twenty years, particularly for soils. Improving the completeness of spoil removal, coupled with appropriate site selection, could speed up the restoration process and enhance the success of future backfilling projects.