Total deposition of nitrogen on Swiss long-term forest ecosystem research (LWF) plots: comparison of the throughfall and the inferential method

The total deposition of nitrogen was estimated at 10 plots in the Swiss Long-Term Forest Ecosystem Research Programme for 1 year (1999/2000) using two methods: (1) the throughfall method, using bulk precipitation and throughfall measurements as input data for the canopy budget model; and (2) the inferential method, based on measurements of ammonia and nitrogen dioxide with passive samplers and deposition velocities taken from literature. The inferential method was coupled with a regression model deriving the other terms of the total deposition of nitrogen (wet deposition, dry deposition of nitric acid and dry deposition of particulate nitrogen) from measurements of the bulk deposition of nitrogen. The two methods gave estimates of the total deposition that correlated significantly with each other, in the range of 5-38 kg ha−1 a−1, but the inferential method tended to yield higher estimates than those obtained with the throughfall method (median difference +2.4 kg ha−1 a−1). In view of the overall agreement of the two methods, the use of passive samplers in the open, coupled with the measurement of bulk deposition, appears, under certain conditions, to be an interesting alternative to the throughfall method.