Collaborative Research: Shifting pathways toward methane in nutrient impacted tropical and sub-tropical wetlands

点击翻译按钮获取中文摘要

Freshwater wetlands are the largest single source of methane to the atmosphere. Methane is a potent greenhouse gas (approximately 24 times more potent than carbon dioxide), such that the pathways that control the production of methane in wetlands have global implications. Most wetlands, including the Florida Everglades, are affected by human-derived nutrient additions. The goal of this research is to determine the enhancement of methane production caused by increased nutrient inputs, particularly phosphate. Phosphate and other nutrients result in increased inputs of plant derived-organic matter, which is then fermented to an array of small molecules in anoxic wetland soils, which are eventually converted to methane. There are two main pathways by which microbes form methane. Approximately 70% of global freshwater wetland-produced methane arises from the acetate fermentation pathway and 30% comes from reduction of carbon dioxide. Preliminary data indicate that pathways for methanogenesis are affected by phosphorus runoff from adjacent agricultural lands. Guiding this work is the hypothesis that in addition to increasing organic matter production by plants, excess phosphate also results in higher rates of methane production due to two additional factors affecting these pathways: provision of additional supply of hydrogen substrate from nitrogen fixation that is unrelated to organic production; and shunting of methane production from acetate-derived methane to fermentation of acetate by an unusual group of bacteria, the syntrophic acetate oxidizers. This shunting benefits the carbon dioxide reduction pathway which has higher rates of methane production, is less sensitive to competitive electron acceptors (such as sulfate), is less sensitive to phosphate and ammonium inhibition, and is affected differently by increased temperature. Thus predictions of methane emissions based on temperate wetlands may not accurately forecast methane emissions from warmer climates. A combination of microbiological, isotopic and biogeochemical approaches will be employed to determine how these pathways are affected by nutrient pollution. Wetlands in South Florida and Panama will be examined. An important component of this project is the education of future scientists and secondary school students in the United States and abroad. The investigators have long records of involvement in science education ranging from high schools to undergraduate, graduate and post doctoral education. High school students will be introduced to a variety of wetlands including those containing carnivorous plants. The project will aid not only in training the next generation of scientists at the University of Florida and Florida State University, but will also will involve students from Bethune-Cookman College, a small predominantly African American college, and local high schools.