Modelling future NO₃ leaching from an upland headwater catchment in SW Norway using the MAGIC model: II. Simulation of future nitrate leaching given scenarios of climate change and nitrogen deposition

Future nitrate (NO₃) leaching to surface water at an upland heathland catchment, Øygardsbekken, southwestern Norway, was simulated using the MAGIC model with monthly time steps. Øygardsbekken has high nitrogen (N) load and exhibits seasonally elevated NO₃ leaching. Future estimates for temperature, precipitation and N deposition were implemented. The climate scenarios were based on dynamically downscaled data from the Rossby Centre Regional Climate model (RCAO) driven by two scenarios of greenhouse gas emissions, A2 and B2, and run with two global climate models, HadAM3 and ECHAM4/OPYC3 from the Hadley Center and Max Planck Institute, respectively. Estimates of future rates of nitrogen (N) and carbon (C) processes in the catchment were based on the downscaled temperature scenarios and two different storylines, one assuming changes only in soil processes (mineralisation N, decomposition C, plant N uptake, N immobilisation, litterfall N) due to future warming and N deposition (SLsoil), and the other assuming changes in both vegetation (plant N uptake and litterfall C/N ratio) and soil processes (SLsoil + veg). Compared to the present, MAGIC simulated higher future NO₃ leaching for both storylines with much higher rates for SLsoil. The results suggest that differences between the two storylines were larger than differences between the different scenarios within each storyline. For the scenarios with the highest future leaching rates the pronounced seasonal NO₃ pattern levelled out, while for the scenarios with moderate projected NO₃ leaching the seasonal pattern prevailed but was skewed towards highest leaching during spring rather than in winter as at present.