Gruner, William E. M.S., Department of Biological Sciences, Wright State University, 2007. The community structure of Methanogens, Methanotrophs, and Ammonia Oxidizing Bacteria in vertical flow greenhouse wetland mesocosms exposed to PCE.
Chlorinated ethenes are among the top contaminants on the EPA National Priorities List due to their abundance in contaminated sites and their recalcitrant nature. These compounds, which are used in large scale degreasing and textile processes, are known liver and kidney toxins, and suspected carcinogens. Wetland ecosystems are capable of degrading PCE and its breakdown products TCE, DCE, and VC by providing anaerobic and aerobic growth conditions for microbes that express enzymes such as dehalogenases and monooxygenases with dual affinity for chlorinated solvents. Greenhouse mesocosms at Wright State University are used to mimic field conditions at a treatment wetland at W.P.A.F.B., while providing the ability to determine the influence of specific plant species. Functional gene analysis for methanogens, methanotrophs, and ammonia oxidizing bacteria shows the presence of these organisms at all locations, regardless of planting and depth. Rarefaction analysis shows that methanogens have the highest species richness and ammonia oxidizers have the lowest species richness. Ammonia oxidizers are influenced by port depth but not the presence or absence of plants, while methanogens and methanotrophs are influenced by both planting and port depth. The central portion of the columns, represented by port 3, support the lowest species richness overall. The community structure of all three functional groups combined is not significantly different between planted and non-planted columns, however there is a significant difference between the community structures in ports 2 and 3, and ports 2 and 5. Water nutrient analysis shows changes in ammonia, nitrate, nitrite, pH, and conductivity in the upper portions of the columns that demonstrate a switch from overall anaerobic conditions to overall aerobic conditions. Methane production primarily occurs in the lower portions of the columns, while methane and ammonia oxidation occur primarily in the upper portions of the columns. Column soil analysis shows an increase in soil and root organic content in the top portions or planted columns, and a decrease in bulk density and an increase in water content in all columns.