NLOSS:: A mechanistic model of denitrified N2O and N2 evolution from soil

Soil microbial denitrification is a significant source of atmospheric nitrous oxide (N2O), a trace gas important in global climate change and stratospheric ozone depletion. In this paper we describe a mechanistic submodel, which is incorporated in the model NLOSS, designed to predict the soil biogenic source and efflux of N2O and N-2 during denitrification, NLOSS simulates transient soil moisture and temperature, decomposition, soil anaerobicity, denitrifying bacterial biomass, rates of soil nitrogen transformations, soil trace-gas transport, and gas efflux to the atmosphere. Uncertainty in predicted N gas effluxes is commuted using a Monte Carlo approach. We test NLOSS's denitrification estimates by comparing predictions with results from a N-15 tracer experiment in a Mexican agricultural system. The model accurately predicted the measured soil moisture and denitrified N2O and N-2 fluxes during the experiment. We also apply NLOSS to compute denitrified N trace-gas speciation curves as a function of soil hydrologic properties and moisture content. These speciation curves will be used in future work to extrapolate the plot-scale modeling results presented here to field and regional estimates of N trace-gas emissions. The results presented here suggest that NLOSS can be used to identify the processes most important for trace-gas losses and to facilitate efforts to scale plot-level modeling results to regional estimates of N trace-gas emissions.