Indirect nitrous oxide (N2O) emissions from drainage ditches and headwater streams are poorly constrained. Few studies have monitored stream N2O emissions and fewer modeling studies have been conducted to simulate stream N2O emissions. In this study, we developed direct and indirect N2O emission modules and a corresponding calibration module for use in the Soil and Water Assessment Tool (SWAT) model, and implemented the expanded SWAT model (termed SWAT-N2O) to a representative fourth-stream-order catchment (210 km2) and six first-order stream catchments (0.22–1.83 km2) in southeastern Minnesota. We simulated the spatial and temporal fluctuations of the indirect emissions from streams, identified emission “hot spots” and “hot moments,” and diagnosed the correlations between direct and indirect emissions. We showed that zero-order streams and first-order streams could contribute 0.034–0.066 and 0.011 nmol N2O m−2 s−1 (expressed on the basis of unit catchment area) to the total surface emissions, respectively. Emissions from zero-order and first-order streams equal 24–41% of direct emissions from soil, which may explain the emission gap between calculations using top-down and bottom-up methods. Clear spatial patterns were identified for both direct and indirect emissions and their spatial variations were negatively correlated. Our results suggest that the IPCC N2O emission factor for streams in the Corn Belt should be increased by 3.2–5.7 times. Increasing precipitation and streamflow in the Corn Belt may potentially increase frequencies of soil anoxic conditions and nitrate leaching to streams, and subsequently increase N2O emissions from both soils and streams.
Bibliographical noteFunding Information:
This study was funded by grants supported by the United States Department of Agriculture grant USDA-NIFA 2013–67019-21364 and the Pioneer Hundred Talent Program, Chinese Academy of Sciences (Y7BR021001). This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract DE-AC02–05CH11231. The Digital Elevation Model (DEM) is obtained from the National Elevation Dataset (https://nationalmap.gov/ 3DEP/3dep_prodserv.html). The meteorological forcing data are obtained from the National Centers for Environmental Prediction (NCEP) (http://globalweather.tamu.edu/). The streamflow and nitrate concentration data at the outlet of LCRC are obtained from the Minnesota Department of Natural Resources (http://www.dnr. state.mn.us/waters/csg/index.html). The stream N2O emission data are hosted at http://www.biometeorology. umn.edu/research/data-archives.
- Corn Belt
- Little Cannon River
- hot moments
- hot spots
- nitrous oxide