THE IMPACTS OF ATMOSPHERIC N-INPUTS ON THROUGHFALL, SOIL AND STREAM WATER INTERACTIONS FOR DIFFERENT AGED FOREST AND MOORLAND CATCHMENTS INWALES

A study of inorganic-N concentrations in streams, soil waters, through fall and rainfall was conducted for one year in five moorland and 20 S itka spruce plantation catchments in upland Wales. The forest ages ran ged from 10 to 55 yr. Highly significant positive relationships with f orest stand age existed for inorganic-N concentrations in streamwater, B and O horizon soil waters and throughfall. Inorganic-N in streams a nd B horizon waters was entirely NO3-. Inorganic-N fluxes in throughfa ll also showed a significant, positive relationship with stand age. Th roughfall flux of inorganic-N in the oldest stand was 25.1 kgN ha-1 yr -1, double that in incident rainfall. The older forest stands appear u nable to utilise the available N. Nitrification is very active in the soils of these older stands, resulting in significant soil acidificati on. The processes responsible for the observed NO3- leaching losses, a nd the implications for the debate on Nitrogen Critical Loads are disc ussed.