Mathematical modeling of nitrous oxide emissions from an agricultural field during spring thaw

Confidence in regional estimates of N2O emissions used in national greenhou se gas inventories could be improved by using mathematical models of the bi ological and physical processes by which these emissions are known to be co ntrolled. However these models must first be rigorously tested against fiel d measurements of N2O fluxes under well documented site conditions. Spring thaw is an active period of N2O emission in northern ecosystems and thus pr esents conditions well suited to model testing. The mathematical model ecos ys, in which the biological and physical processes that control N2O emissio ns are explicitly represented, was tested against N2O and CO2 fluxes measur ed continuously during winter and spring thaw using gradient and eddy covar iance techniques. In the model, ice formation at the soil surface constrain ed soil-atmosphere gas exchange during the winter, causing low soil O-2 con centrations and consequent accumulation of denitrification products in the soil profile. The removal of this constraint to gas exchange during spring thaw caused episodic emissions of N2O and CO2, the timing and intensities o f which were similar to those measured in the field. Temporal variation in these emissions, both simulated and measured, was high, with those of N2O r anging from near zero to as much as 0.8 mg N m(-2) h(-1) within a few hours . Such variation should be accounted for in ecosystem models used for tempo ral integration of N2O fluxes when making long-term estimates of N2O emissi ons.