Wednesday, November 15, 2006

Emission of the Greenhouse Gas Nitrous Oxide (N2O) from Riparian Forest Buffers, Warm-Season and Cool-Season Grass Filters and Crop Fields.

Dong-Gill Kim1, Richard C. Schultz1, Thomas M. Isenhart1, Tim B. Parkin2, James W. Raich1, and Thomas E. Loynachan1. (1) Iowa State University, 339 Science 2, Ames, IA 50011-3221, (2) National Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011-4420

Denitrification is recognized as the major mechanism for reducing nitrate in riparian buffers coping with non-point source pollution (NPS) of surface water bodies.  However, there are still questions about the quantity and products of denitrification that different kinds of riparian buffer vegetation can support.  It has recently been hypothesized that the increased denitrification rates in riparian buffers may be trading the problem of NPS pollution of surface waters for atmospheric deterioration and global warming problems because denitrification produces both nitrogen gas (N2) and nitrous oxide (N2O), a greenhouse gas also involved in ozone depletion.  It is therefore important to compare the effects of different kinds of riparian buffer vegetation on the production of N2 and N2O from the denitrification process.  We measured denitrification rates, N2O emission, N2O in groundwater, N2O/ N2 emission ratios, and soil properties in riparian forest buffers, warm-season and cool-season grass filters, and a crop field all located in the Bear Creek watershed in central Iowa.  Preliminary results suggest that differences among crop fields, warm season grass filters, and forested buffers range between 3-8 μg m-2 h-1 N2O-N during the winter months in unfrozen soils with bursts up to 83 μg m-2 h-1 N2O-N as these soils thaw after being frozen.  These data further suggest as high as 10-fold differences in emissions in the unfrozen soils and 80-fold differences immediately following thawing between the various kinds of buffer plant communities.  In this presentation, we will discuss results of annual N2O emission and denitrification rates from riparian forest buffers, warm-season and cool-season grass filters, and crop fields.