Nitrous Oxide Fluxes from Agricultural Streams in East-Central Illinois

Abstract

Indirect nitrous oxide (N2O) emissions account for the majority of uncertainty associated with the global N2O budget. Agricultural streams with subsurface (tile) drainage are potential hotspots of indirect N2O 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 N2O 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 N2O fluxes from the stream surface at 4 of the 10 sites. Dissolved N2O concentrations ranged from < 0.1 to 7.46 μg N2O-N L−1. Floating chamber N2O fluxes ranged from 0 to 13.84 μg N2O-N m−2 min−1. We found strikingly different patterns of nitrate (NO3−) concentrations at sites downstream of a wastewater treatment plant (WWTP) effluent. Data from sites not affected by the WWTP expressed seasonal variations of NO3− with elevated concentrations in winter and spring months when subsurface tile drains were flowing. Floating chamber N2O fluxes were strongly correlated (p value 0.001) with NO3− at sites not affected by the WWTP. All sites were correlated with flow (p value 0.01) and dissolved N2O (p value 0.02). Our data suggest flow and dissolved N2O are stronger indicators of N2O flux from stream surfaces than NO3− concentrations in agricultural watersheds. Furthermore, this study supports growing concerns of estimating N2O emissions using linear relationships between N2O and NO3−, such as those used in IPCC estimates.