Nitrous Oxide Fluxes from Agricultural Streams in East-Central Illinois

Indirect nitrous oxide (N 2 O) emissions account for the majority of uncertainty associated with the global N 2 O budget. Agricultural streams with subsurface (tile) drainage are potential hotspots of indirect N 2 O emissions from streams and groundwater. However, there are only a limited number of studies with direct measurements from stream surfaces. Research presented here represents the first study of N 2 O emissions from agricultural streams in Illinois, USA. We measured water chemistry data from 10 sites in three watersheds in east-central Illinois. Additionally, floating chambers and gas transfer velocity models were used to measure N 2 O fluxes from the stream surface at 4 of the 10 sites. Dissolved N 2 O concentrations ranged from < 0.1 to 7.46 μg N 2 O-N L −1 . Floating chamber N 2 O fluxes ranged from 0 to 13.84 μg N 2 O-N m −2 min −1 . We found strikingly different patterns of nitrate (NO 3 −) concentrations at sites downstream of a wastewater treatment plant (WWTP) effluent. Data from sites not affected by the WWTP expressed seasonal variations of NO 3 − with elevated concentrations in winter and spring months when subsurface tile drains were flowing. Floating chamber N 2 O fluxes were strongly correlated ( p value 0.001) with NO 3 − at sites not affected by the WWTP. All sites were correlated with flow ( p value 0.01) and dissolved N 2 O ( p value 0.02). Our data suggest flow and dissolved N 2 O are stronger indicators of N 2 O flux from stream surfaces than NO 3 − concentrations in agricultural watersheds. Furthermore, this study supports growing concerns of estimating N 2 O emissions using linear relationships between N 2 O and NO 3 −, such as those used in IPCC estimates.