Fluxes of oxidised and reduced nitrogen above a mixed coniferous forest exposed to various nitrogen emission sources

Concentrations of nitrogen gases (NH3, NO2, NO, HONO and HNO3) and particles (pNH4 and pNO3) were measured over a mixed coniferous forest impacted by high nitrogen loads. Nitrogen dioxide (NO2) represented the main nitrogen form, followed by nitric oxide (NO) and ammonia (NH3). A combination of gradient method (NH3 and NOx) and resistance modelling techniques (HNO3, HONO, pNH4 and pNO3) was used to calculate dry deposition of nitrogen compounds. Net flux of NH3 amounted to −64 ng N m−2 s−1 over the measuring period. Net fluxes of NOx were upward (8.5 ng N m−2 s−1) with highest emission in the morning. Fluxes of other gases or aerosols substantially contributed to dry deposition. Total nitrogen deposition was estimated at −48 kg N ha−1 yr−1 and consisted for almost 80% of NHx. Comparison of throughfall nitrogen with total deposition suggested substantial uptake of reduced N (±15 kg N ha−1 yr−1) within the canopy.