Increased nitrogen in runoff and soil following 13 years of experimentally increased nitrogen deposition to a coniferous-forested catchment at Gårdsjön, Sweden

Beginning in 1991, we have added nitrogen (N) to the 0.5-ha, N-poor, coniferous-forested catchment G2 NITREX at Gårdsjön, Sweden, to investigate the consequences of chronic elevated N deposition. We have added 40 kg N ha −1 yr −1 in fortnightly doses of NH 4NO 3 to the ambient 15 kg N ha −1 yr −1 by means of a sprinkling system. NO 3 concentrations in runoff increased during 13 years from < 1 to 70 μeq L −1, and in 2004 comprised about 10% of N input. Inhibition of NO 3 immobilisation due to increased availability of NH 4 might explain the increased leaching of NO 3. C and N pools in the forest floor increased but C/N ratio has not changed. The increase in NO 3 leaching thus occurred independently of change in C/N ratio. The results from Gårdsjön demonstrate that increased leaching of inorganic N and decrease in C/N ratio respond to increased N deposition at greatly different time scales. NO 3 concentrations increased in runoff although the C/N ratio of forest floor has not changed.