The imprint of agricultural ecosystems on trace gas emissions in the US Midwest

Agricultural ecosystems are having a profound influence on nitrous oxide (N₂O), ammonia (NH₃), and methane (CH₄) emissions in the US Midwest. Nitrous oxide, NH₃ and CH₄ have increased dramatically as a consequence of the production of synthetic nitrogen fertilizer and proliferation of intensive livestock systems. Nitrous oxide and CH₄ are radiatively important trace gases, while NH₃ is a chemical of significant environmental concern as it readily reacts with atmospheric acids to produce fine particulate matter linked to serious human health impacts. Here, we use over a decade of trace gas observations from a tall tower located within the US Corn Belt in combination with micrometeorological flux and atmospheric inverse analyses to constrain these trace gas emissions and to assess their sensitivity to climate variability and land management. Preliminary budget estimates indicate large inter-annual variability for each trace gas with N₂O emissions ranging from 300 to 600 Gg N₂O-N y^-1; NH₃ emissions ranging from 1100 to 1400 Gg NH₃-N y^-1, and anthropogenic CH₄ emissions ranging from 6 to 10 Tg CH₄ yr^-1. Our ongoing analyses are assessing the extent to which these emissions are enhanced by seasonal variations in temperature and precipitation, which is key to understanding how these emissions are likely to change as climate continues to become warmer and wetter within this region.