|TURNER, P - University Of Minnesota|
|GRIFFIS, TIMOTHY - University Of Minnesota|
|LEE, X - Yale University|
|CRAWFORD, J - Us Geological Survey (USGS)|
|LOKEN, L - Us Geological Survey (USGS)|
|Venterea, Rodney - Rod|
Submitted to: Geophysical Research Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2016
Publication Date: 5/6/2016
Citation: Turner, P.A., Griffis, T.J., Baker, J.M., Lee, X., Crawford, J.T., Loken, L.C., Venterea, R.T. 2016. Regional-scale controls on dissolved nitrous oxide in the Upper Mississippi River. Geophysical Research Letters. 43:4400-4407.
Interpretive Summary: Nitrous oxide (N2O) is a potent greenhouse gas, and also contributes to depletion of stratospheric ozone. The Intergovernmental Panel on Climate Change (IPCC) has developed emission factors that are used to estimate emissions from all major sources of N2O in order to determine where improvements can be made. Recent research has shown that the emission factor used for estimating emissions from streams, which is solely based on stream nitrate concentration, leads to substantial underestimates. Data presented in this paper, which were collected on the Mississippi River, show that the emission process depends not only on nitrate concentration, but also on carbon availability, dissolved oxygen, and pH. These results were used to develop a more accurate model for predicting N2O emissions from large streams. This model, when used in conjunction with forecasted increases in nitrate loading and eutrophication, indicates that N2O emission from the Mississippi River could increase substantially in the future.
Technical Abstract: Bottom-up estimates of riverine nitrous oxide (N2O) emissions developed by the Intergovernmental Panel on Climate Change (IPCC) assume a constant emission factor (EF5r) that predicts N2O production from anthropogenic nitrogen inputs. This relation ignores any direct stream water biochemical characteristics that may enhance or limit the production of N2O. We present a high frequency, near-continuous data set of surface water N2O measurements in the Upper Mississippi River. Although N2O was primarily dependent on the nitrate concentration, production was also limited by carbon availability, dissolved oxygen, and pH. This caused riverine N2O to follow a Michaelis-Menten type relation in response to increasing nitrate concentrations rather than the linear relationship implied by the EF5r. Growing evidence indicates that the EF5r overestimates N2O emissions from large rivers in the US Corn Belt. However, considering forecasted increases in nitrate loading and greater eutrophication, we suggest that Mississippi River N2O emissions could increase by 70%.