N2O emission hotspots at different spatial scales and governing factors for small scale hotspots

Chronically nitrate-loaded riparian buffer zones show high N2O emissions. Often, a large part of the N2O is emitted from small surface areas, resulting in high spatial variability in these buffer zones. These small surface areas with high N2O emissions (hotspots) need to be investigated to generate knowledge on the factors governing N2O emissions. In this study the N2O emission variability was investigated at different spatial scales. Therefore N2O emissions from three 32 m2 grids were determined in summer and winter. Spatial variation and total emission were determined on three different scales (0.3 m2, 0.018 m2 and 0.0013 m2) at plots with different levels of N2O emissions. Spatial variation was high at all scales determined and highest at the smallest scale. To test possible factors inducing small scale hotspots, soil samples were collected for slurry incubation to determine responses to increased electron donor/acceptor availability. Acetate addition did increase N2O production, but nitrate addition failed to increase total denitrification or net N2O production. N2O production was similar in all soil slurries, independent of their origin from high or low emission soils, indicating that environmental conditions (including physical factors like gas diffusion) rather than microbial community composition governed N2O emission rates.