Master of Science (MS)
Oceanography and Coastal Sciences
In wetland sediments, organic matter provides a substrate for microbial activity. During metabolism, microbes release extracellular polymeric substances, which accumulate to bind soil particles. A similar concept can be implemented on a large scale to reduce wetland loss in Louisiana. Hypothetically, hydraulically dredged sediment can be amended with polymer and deposited on subsiding marshes as a restoration method where the polymer increases sediment stabilization until plants become established. This lab study focused on investigating the influence of natural polymer additions on particle aggregation to increase sediment stability and the effects on microbial activity. Sediments from three sites (i.e. freshwater, intermediate, and marine) were used, which varied in moisture content, organic matter content, salinity, and texture. The soil amendments were xanthan gum, a microbially produced polymer, and guar gum, a plant polysaccharide. Following polymer application, sediment-polymer mixtures were incubated for 1, 8, 16, or 26 weeks before analysis. Response variables included moisture content, redox potential, pH, dewatering, consolidation, aggregate size, microbial biomass, and basal respiration. Polymer addition increased microbial activity in the first week. Lower redox potentials indicate that more carbon substrates were available to serve as electron donors for microbial use. High respiration rates suggest a microbial response to polymer addition with increased activity and growth, followed by rapid turnover of the biomass. At the 0.5% polymer concentration level, microbes assimilated carbon as indicated by respiration similar to control samples. At the 1% polymer concentration level, increased respiration indicates a transition to an increasing biomass pool. Microbial response to added polymer carbon indicates that microbial communities degraded the polymers within one week of application. No evidence of increased aggregation was found, supported by no polymer effects on dewatering and consolidation. Natural polymer additions may not achieve the goal of increasing sediment stability, due to their water-solubility and simple structure, which contributed to rapid degradation by microbes. High moisture content of wetland sediments may require the use of synthetic polymers for aggregation. A material that maintains structure in water and resists microbial activity may be more successful in stabilizing wetland sediments.
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Land, Lauren, "Physical and microbial responses of dredged sediment to two-soil-stabilizing amendments, xanthan gum and guar gum, for use in coastal wetland restoration" (2010). LSU Master's Theses. 3942.