Estimation of net nitrogen flux between the atmosphere and a semi‐natural grassland ecosystem in Hungary

Abstract

The aim of this work is to estimate the net N balance (deposition – emission) between the atmosphere and a semi‐arid, semi‐natural grassland (Bugac station, Central Hungary, CarboEurope IP, NitroEurope IP level 3 site). Dry deposition of N compounds has been determined by the inferential method, based on continuous monitoring of NO2 gas and daily 24‐hour concentration measurements of HNO3 vapour, NH3 gas, and NH4+ and NO3− particles, using dry deposition velocities from the literature, measured above surfaces with the same characteristics as Bugac station. The bi‐directional flux of NH3 within the atmosphere and the canopy (excluding soil emission) has also been estimated by the inferential method. Wet deposition of nitrate and ammonium ions was calculated on the basis of daily precipitation sampling and concentration measurements of nitrate and ammonium ions. To estimate the soil‐atmosphere exchange of different gaseous N forms (N2, NO, N2O, NH3), the DNDC model was used as validated by the chamber measurements of NO and N2O soil emission fluxes. Soil emissions of NO and N2O have been determined by dynamic and static soil chamber methods, respectively. The measurement and modelling activity covers a complete year. Using the measured and modelled data, the calculated N balance at Bugac station between August 2006 and July 2007 is estimated at −8.8 kg N ha−1 year−1 (deposition) as a sum of the deposition and emission terms (−10.4 and 1.6 kg N ha−1 year−1, respectively). Due to the warm and dry weather during the examined period, wet fluxes were substantially lower than usual, which may also have altered the regular yearly course of dry deposition and emission.