GREENHOUSE GAS EMISSIONS FROM A RESTORED WETLAND IN CENTRAL ILLINOIS

Approximately 60 million ha of agricultural land in North America have been artificially drained. Much of this land was previously in wetlands. Field studies and modeling experiments have demonstrated that drainage of farm fields has been associated with significant changes in watershed hydrology and nutrient losses. Recent efforts to reduce sediment, nitrogen, and phosphorus loading of surface waters have focused on restoration of forested riparian buffer strips. Wetlands are capable of providing similar functions, but have been less widely applied.

Wetland systems have been shown to lower the concentration of many water contaminants, including nitrogen, phosphorus, suspended solids, biochemical oxygen demand, trace metals, trace organics, and pathogens. These processes are driven by diverse treatments: sedimentation, filtration, chemical precipitation and adsorption, microbial interactions, and uptake by vegetation.

Even though plant uptake of nitrogen occurs in wetlands, nitrogen is most effectively removed by nitrification-denitrification. In this process, ammonia is oxidized to nitrate by nitrifying bacteria in aerobic zones and nitrate is converted to free nitrogen in the anoxic zone by denitrifying bacteria. Nitrous oxide, a powerful greenhouse gas, is produced in both nitrification and dinitrification processes. Thus, as organic matter slowly becomes established in the soils of restored wetlands the rate of denitrification should increase.

As wetland restoration is a new and emerging land-use management practice to reduce nutrient loads from river water, the purpose of this research is to exam the impact of restoration on the methane (CH₄) and nitrous oxide (N₂O) components of the carbon and nitrogen cycles at the Hennepin-Hopper Lake wetland located near Hennepin, Illinois. Air samples were taken from soils of three different vegetation plots: willow, cattail, and native. Samples were analyzed for CH₄ and N₂O by gas chromatography. Preliminary results have indicated that Hennepin-Hopper wetlands can be both a source and sink of CH₄ and N₂O, with fluxes between -0.18 and 0.89 µmol ^-2 s^-1, and between -0.021 and 0.03 µmol m^-2 s^-1, respectively. [This work supported by The Wetlands Initiative and UIC's Institute for Environmental Science and Policy].