A Shift in Louisiana Salt Marsh Microbial Communities Reflecting Changes in Salinity and Biogeochemical Parameters

The relationship between microbial communities, salinity, soil depth, and time was evaluated using phospholipid fatty acids (PLFA) collected from coastal wetlands in Louisiana post hurricanes Katrina and Rita. The three marsh types studied included freshwater and intermediate marshes from the Jean Lafitte Preserve as well as two brackish marsh sites from the Caernarvon Basin. The Caernarvon Basin was heavily impacted from the hurricanes leaving the lower sites sampled remnant marsh. The goal of this study was to examine microbial community changes along a salinity gradient to further understand the impact of salinity on the wetland ecosystem. This was done using multivariate comparison analysis (CCA) in combination with descriptive analysis comparing water chemistry (pH, DOC, TDN, NO 2-, NO 3-, Cl-, and SO 4 3-) to PLFA data. This study finds a noticeable impact of salinity on PLFA as seen in an increased ratio of saturated to unsaturated PLFA as well as an increase the amount of cyclopropane PLFA in areas with a higher chloride content. The lower Caernarvon sites through exposure to the Caernarvon freshwater diversion and the recent hurricanes had salinity levels much closer to the intermediate marsh and proved to be an outlier on all findings. These findings mean that the microbial community is dynamic changing with season, depth, and salinity.