Identifier

etd-11102011-172016

Degree

Master of Science (MS)

Department

Environmental Sciences

Document Type

Thesis

Abstract

Coastal wetlands, long recognized to be among the most productive ecosystems on the planet, are being lost at a disturbingly high rate in coastal Louisiana due to both eustatic sea-level rise and land subsidence. A number of approaches have been proposed for reducing wetland loss and restoring deteriorated wetlands, among which the addition of sediment to increase marsh surface elevation is promising. However, little is known about how the added sediment affects the biogeochemistry of marsh sediment. The objective of this study was to determine the effects of sediment slurry addition on sulfur, iron, and manganese biogeochemistry in a subsiding Spartina patens dominated marsh in coastal Louisiana. The study site was located inside the Paul J. Rainey Wildlife Sanctuary in Vermillion Parish, Louisiana where low, medium, or high levels of sediment slurry were added to each study plot in July of 2008. Sediment and porewater samples were collected from the control (i.e. no sediment addition), low, medium, and high sediment treatment plots approximately on a seasonal basis from February 2009 to June 2011. Laboratory incubation of sediment using the radioisotope 35S technique showed that there was no significant difference (p=0.2201) among the treatments in the rate of sulfate reduction 3 years after sediment slurry addition. However, significant increases (p=0.0007) in average concentrations of sulfate in sediment and decreases (p<0.0001) in sulfide in porewater with sediment addition over the 3 years’ measurements indicate that there likely was a decrease in sulfate reduction rate with increasing sediment addition during the preceding 3 years. Concentrations of sediment and porewater iron and manganese significantly increased when sediment addition increased, which was primarily attributed to the high levels of these two elements in the added sediment. The increased iron and manganese concentrations could, in part, explain the lower level of sulfide observed in the sediment-treated plots over the 3 year study. Additionally, average pH and redox increased significantly with sediment addition (p<0.0001 and p=0.0084, respectively). More samplings are needed to better understand the long-term impacts of sediment slurry addition on the rate of sulfate reduction in marsh sediment.

Date

2011

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Hou, Aixin

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