Water Resources Research Act Program

Details for Project ID 2011OH205B

The Constructed Wetland Dilemma: Nitrogen Removal at the Expense of Methane Generation?

Institute: Ohio
Year Established: 2011 Start Date: 2011-03-01 End Date: 2013-08-31
Total Federal Funds: $29,953 Total Non-Federal Funds: $63,308

Principal Investigators: Paula Mouser, Gil Bohrer

Project Summary: Fixed nitrogen (N) is required for the growth for all biological organisms, and agriculture is dependent upon nitrogen for fertilizer. When present at elevated levels in water resources, however, nitrate-N concentrations present human and environmental health risks, including contributing to the eutrophication of some water bodies and coastal zones. Ohio exports significant levels of nitrogen in its surface waters and groundwater to Lake Erie and the Mississippi Basin due to its geology and agricultural land management techniques. Constructed wetlands can be used for nitrogen removal through the biologically-mediated process of denitrification, where nitrite is reduced to nitrogen gas and released to the atmosphere. Unfortunately, denitrification in wetlands comes with the tradeoff of increased Green House Gas (GHG) production. Wetlands sequester large amounts of carbon (C) from the atmosphere, removing the most common GHG - CO2 but produce another and more potent GHG – methane (CH4). In order to allow development of wetlands as a solution for N removal without concerns of GHG emissions, it is critical to understand what factors control methane production, and how they relate to wetland aquatic conditions. The proposed work will examine the in situ metabolic condition of dominant bacteria and archaea responsible for denitrification and methanogenesis in a wetland by quantifying the mRNA transcript abundance for two key microbial genes catalyzing these processes: nitrate reductase (nirS) and methyl coenzyme M reductase (mcrA). By linking microbial activity to biogeochemical conditions, gas chamber measurements, and atmospheric gas fluxes measured concurrently at the site, this work will elucidate the factors controlling denitrification and methane production (and ultimately the GHG budget) in a constructed wetland ecosystem.