ECOSYSTEM RESPONSE TO 9 YEARS OF NITROGEN ADDITION AT SOGNDAL, NORWAY

Since 1983, 7 kg N ha(-1) year(-1) as nitric acid has been added to a 1940 m(2) pristine alpine catchment (SOG4) at Sogndal, central Norway, as part of the RAIN project (Reversing Acidification In Norway). Duri ng 9 years of treatment SOG4 has retained 90% of the NO3 inputs, about the same fraction as the adjacent untreated control catchments which received ambient N inputs of 2 kg N ha(-1) year(-1). Runoff from SOG4 contains elevated concentrations of nitrate only in conjunction with e vents of high flow and high concentrations of nitrate in incoming wate r. The 9 years of N deposition of 9 kg N ha(-1) year(-1) has not induc ed nitrogen saturation. A total of 63 kg N ha(-1) has been retained ov er the 9 year period. Retarded decomposition and higher total N concen tration indicate that part of this 63 kg N ha(-1) may be stored in the ectorganic (L+F+H) layer. Measurements of N contents in foliage do no t reveal differences that can be ascribed to the N addition.