Microbial Response to Carbon Input From Soil-Stabilizing Amendments Used with Dredged Sediment for Coastal Wetland Restoration.

Microbial mineralization of organic matter invokes production of extracellular polymeric substances, which accumulate to bind soil particles. This concept can be implemented on a large scale to reduce wetland loss in Louisiana. Hypothetically, dredged sediment can be amended with a polymer to increase stabilization of coastal marshes until plants become established. This study determined how the microbial community responds to polymer input using sediments from three sites that vary in texture, organic matter content, salinity, and moisture content. Following application of varying concentrations of xanthan gum and guar gum, sediments were incubated at room temperature for 1, 8, 16, or 26 weeks before analysis. Redox potential and pH were monitored. Chloroform fumigation-extraction was used to examine differences in the pool of microbial biomass carbon (MBC). Basal respiration rates were monitored on samples from week one to determine differences in microbial activity from polymer addition. Indices such as Cmic:Corg ratio and metabolic quotient were used to indicate use of available substrates. Polymers significantly reduced redox potential in the silty clay and sandy loam sediments. There was no significant affect on pH. Polymers had no significant impact on MBC but significantly increased respiration. For the clay sediment, tight associations between clay particles and the polymer led to mediated release of carbon. Indices suggest that K-strategists make up the microbial community. For the silty clay sediment, lower redox potential caused microbes to shift from facultative to obligate anaerobes. Over time, the activity stabilizes, and the community increases in size. For the sandy loam sediment, the significant increase in MBC by week 8 suggests that r-strategist species quickly utilize all available substrate. Overall, microbial community activity returns to equilibrium after additional carbon input.