Abstract
Mangrove ecosystems are highly productive and can store disproportionate amounts of carbon in their sediment that may be metabolized to methane by methanogens. Methane can then be released to the atmosphere through outgassing. By evaluating the structure and function of microbial communities in mangrove sediments, more can be understood about the role mangrove systems play in the carbon cycle. We investigated the methane flux in mangrove-dominated, Spartina-dominated, and seagrass-dominated sediments at Mission-Aransas National Estuarine Research Reserve in South Texas. Atmospheric concentrations of methane, carbon dioxide, and sulfide were measured using a gas analyzer connected to a flux chamber. Mangrove-dominated and Spartina-dominated sediment had greater concentrations of methane than seagrass-dominated sediment. Complementary data for dissolved ammonium, nitrate, sulfate, and sulfide within the porewater showed similar trends. These results show that diurnal variability may have a significant impact on how methane emissions are modeled. Sediment from 2, 12, and 20 cm were sequenced using Illumina HiSeq for metagenomes and metatranscriptomes. The 16S rRNA genes and 16S rRNA transcripts from the metagenomes and metatranscriptomes, respectively, were investigated to compare community structure. Genes pertaining to geochemical pathways were compared between 54 metagenome samples. Sulfur cycling genes (soxZ, dsrC, dsrH) were expressed in August mangrove samples at 12 cm along with the increased expression of genes associated with carbon fixation. Further work will be done to investigate microbial community structure and function with regard to observed methane emissions.
