Salt Marsh Restoration with Sediment-Slurry Amendments Following a Drought-Induced, Large-Scale Disturbance
A large-scale, drought-induced disturbance occurred in Louisiana during the spring and summer of 2000. Approximately 100,000 acres of Spartina dominated marshes died-back and turned brown. This die-off caused considerable concern because in the absence of recovery dieback marshes can transform to mudflats, which can subside leading to open ponds. The state of Louisiana is attempting to restore some of the dieback marshes through the addition of sediment-slurries. The sediment-slurry generated significantly different marsh elevations: high elevation (mean and 95 % confidence interval: 29, 26 to 32 cm above ambient marsh), medium elevation (21, 19 to 24 cm), low elevation (14, 11 to 16 cm), pop-up (36, 32 to 40 cm), and vegetated (20, 17 to 22 cm), which were compared to reference marshes: healthy marshes (4, -1 to 9 cm) and dieback marshes (?2, -6 to 3 cm). High and medium elevations had minimal recovery two years following the slurry addition. These areas had plant cover similar to the reference dieback marshes, which did not receive the sediment-slurry amendment. The low elevation, popup (highly organic sections of the original substrate that detached during slurry application and settled on top of the sediment-slurry), and vegetated (dieback areas that recovered by the start of the study) areas that received the sediment-slurry had rapid plant recovery. Two years following the slurry addition, vegetation structure in the low and vegetated areas was the most similar to reference healthy marshes in plant cover (~100 %) and species richness (~1.25); pop-ups had the highest species richness (2.35, 1.8 to 2.9). Marshes that did not receive the sediment-slurry amendments were more frequently flooded and had higher sulfide concentrations (~1 mM) than marshes that received the sediment-slurry. Soil salinity was similar throughout the study site and did not limit plant recruitment. Rapid recovery was governed by optimal inundation, high organic matter content concurrent with high elevation, and/or rhizome survivability following burial. If applied appropriately, sediment-slurry amendments can restore salt marshes that have subsided as a result of a drought-induced disturbance or other events that cause a lowering of marsh surface elevation.
Advisor:Robert Gambrell; Jaye Cable; Irving Mendelssohn
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Keywords:oceanography coastal sciences
Date of Publication:06/02/2006