Canopy and soil retention of nitrogen deposition in a mixed boreal forest in eastern Finland

Nitrogen deposition, leaching, and retention were monitored in a mature spruce (Picea abies Karsten) dominated mixed boreal forest in eastern Finland. Bulk precipitation, throughfall, stemflow, and percolation through the podzolic soil profile were monitored from 1993 to 1996. Mean annual bulk deposition of total N was 3.83 kg ha(-1), of which 33 % was NH4+-N, 26 % was NO3--N, and 41 % was organic N. Throughfall+stemflow flux of total N was 2.93 kg ha(-1) yr(-1). Sixty-four % of NH4+-N and 38 % of NO3--N in bulk precipitation was retained by the tree canopy. Organic N was released (0.27 kg ha(-1) yr(-1)) from the tree canopy. Nitrate-N was retained and organic N was leached as the water passed through the ground vegetation and soil O-horizon. Ammonium-N and organic N were retained mainly in the E-horizon. The output of total N from the E-horizon was only 5 % of the total N deposition in the forest stand during the study period and it was mainly as organic N. The output of inorganic N forms from under B-horizon was seasonal and occurred mainly at spring snowmelt.