Regional mapping of nitrogen leaching from clearcuts in southern Sweden

Increased nitrogen leaching from forest soils is a potential environmental problem in areas with high nitrogen deposition. In Sweden nitrogen is strongly retained in the forests, and high nitrogen leaching is not common from growing forests. However, soil water measurements on clearcuts along a deposition gradient in Sweden showed a positive correlation between increased concentration of inorganic nitrogen and the deposition. In this paper nitrogen leaching from clearcuts in southern Sweden was modelled on a municipality level, based on this correlation. Modelled deposition was used as input data together with runoff and forest statistics, e.g. clearcut areas from the municipalities. The calculations showed a clear leaching gradient on clearcuts from west (up to 35 kg ha(-1) year(-1)) to east (less than 5 kg ha(-1) year(-1)). This was in accordance with the deposition gradient. The leaching gradient was reinforced by the higher runoff in the west. The results indicated that, in southwestern Sweden with the highest nitrogen deposition, up to 30-40% of the total leaching of nitrogen from forest soils originates from clearcuts. These high amounts of nitrogen leaching from clearcuts in southwestern Sweden have not been included in previous national calculations of nitrogen leaching to surface waters. The contribution of nitrogen from clearcuts to the total nitrogen leaching from all land use classes varies between 1% in the southernmost part where agricultural land is highly dominating, to 11% in the forested central part of southern Sweden. (C) 2004 Elsevier B.V. All rights reserved.