TRACE GAS EXCHANGES IN MIDWEST CROPPING SYSTEMS
Location: Soil, Water, and Air Resources Research Unit
Title: Nitrous Oxide Emissions from Riparian Forest Buffers, Warm-Season and Cool-Season Grass Filters, and Crop Fields
| Kim, Dong-Gill - IOWA STATE UNIVERSITY |
| Isenhart, Thomas - IOWA STATE UNIVERSITY |
| Schultz, Richard - IOWA STATE UNIVERSITY |
| Loynachan, Thomas - IOWA STATE UNIVERSITY |
| Raich, James - IOWA STATE UNIVERSITY |
Submitted to: Biogeosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 15, 2008
Publication Date: January 13, 2009
Citation: Kim, D., Isenhart, T.M., Parkin, T.B., Schultz, R.C., Loynachan, T.E., Raich, J.R. 2009. Nitrous Oxide Emissions from Riparian Forest Buffers, Warm-Season and Cool-Season Grass Filters, and Crop Fields. Biogeosciences. 6:607-650.
Interpretive Summary: Establishment of grass, shrub, and tree buffer zones between agricultural lands and streams has been shown to be effective in reducing nitrate pollution of surface waters. Denitrification, a process carried out by soil bacteria, occurs in such buffer zones to remove nitrate in crop field runoff water and groundwater. However, the greenhouse gas, nitrous oxide, is a by-product of the denitrification process. Because of this, it has been suggested that vegetative buffer zones may serve to trade a water quality problem for an air quality one. To date, there is little information on the process of nitrous oxide production in buffer zones, so this study was done in order to measure how much nitrous oxide comes from buffer zones. It was found that nitrous oxide production in buffer zones was substantially less than in a nearby crop field. Also, the proportion of nitrogen emitted to the air as nitrous oxide was less in the buffer zone than in the crop field. These findings should be useful to land managers and scientists interested in developing strategies to reduce air and water pollution.
Increasing denitrification rates in riparian buffers may be trading the problem of nonpoint source (NPS) pollution of surface waters for atmospheric deterioration and increased global warming potential because denitrification produces nitrous oxide (N2O), a greenhouse gas also involved in stratospheric ozone depletion. The objectives of this study were to compare 1) the emissions of N2O from different kinds of riparian buffer systems and an adjacent crop field and 2) the measured N2O emissions with estimated ones using IPCC methodology. We measured soil properties, N inputs, weather conditions and N2O fluxes from soils in forested riparian buffers, warm-season and cool-season grass filters, and a crop field located in the Bear Creek watershed in central Iowa, USA. Cumulative N2O emissions from soils in all riparian buffers (5.8 kg N2O-N ha-1 in 2006-2007) were significantly less than those in the crop field (24.0 kg N2O-N ha-1 in 2006-2007), but no differences among different kinds of riparian buffers were observed. The ratio of N2O emission to N inputs was smaller in the riparian zones (0.02) than the crop field (0.07). These results indicate that N2O emissions from soils in the riparian buffers were significantly less than those in the crop field and suggest that the riparian buffers should not be considered a major source of N2O emission in the watershed. The observed large difference between measured N2O emission and estimated N2O emission by IPCC methodology (87% underestimation) in the crop field suggests that the IPCC methodology may underestimate N2O emissions in the regions where soil rewetting and thawing are common or potentially can be increased by future climate change.