Factors controlling Nitrous Oxide emission from a spruce forest ecosystem on drained organic soil, derived using the CoupModel

AbstractHigh Nitrous Oxide (N2O) emissions have been identified in hemiboreal forests in association with draining organic soils. However, the specific controlling factors that regulate the emissions remain unclear. To examine the importance of different factors affecting N2O emissions in a spruce forest on drained organic soil, a process-based model, CoupModel, was calibrated using the generalized likelihood uncertainty estimation (GLUE) method. The calibration also aims to estimate parameter density distributions, the covariance matrix of estimated parameters and the correlation between parameters and variables information, useful when applying the model on other peat soil sites and for further model improvements. The calibrated model reproduced most of the high resolution data (total net radiation, soil temperature, groundwater level, net ecosystem exchange, etc.) very well, as well as cumulative measured N2O emissions (simulated 8.7±1.1kgN2Oha−1year−1 (n=97); measured 8.7±2.7kgN2Oha−1year−1 (n=6)), but did not capture every measured peak. Parameter uncertainties were reduced after calibration, in which 16 out of 20 parameters changed from uniform distributions into normal distributions or log normal distributions. Four parameters describing bypass water flow, oxygen diffusion and soil freezing changed significantly after calibration. Inter-connections and correlations between many calibrated parameters and variables reflect the complex and interrelated nature of pedosphere, biosphere and atmosphere interactions. This also highlights the need to calibrate a number of parameters simultaneously. Model sensitivity analysis indicated that N2O emissions during growing seasons are controlled by competition between plants and microbes for nitrogen, while during the winter season snow melt periods are important. Our results also indicate that N2O is mainly produced in the capillary fringe close to the groundwater table by denitrification in the anaerobic zone. We conclude that, in afforested drained peatlands, the plants and groundwater level have important influences on soil N availability, ultimately controlling N2O emissions