Application of the model niccce to the Solling spruce site

A model for turnover of C and N in coniferous ecosystems has been applied to the long-term data set available for the Solling spruce site in Germany. The model (niccce; NItrogen Isotopes and Carbon Cycling in Coniferous Ecosystems) simulates water and heat transport, primary production, and turnover of C and N for coniferous forest on a multi-layer soil profile. Application of the model to the Solling site involved calibration to the specific soil conditions and tree species present at this site. Observed amounts of throughfall, pressure heads of soil water, and chloride concentrations at various depths were satisfactory reproduced by the model, as well as concentrations and fluxes of C and N in various tree compartments. Leaching of nitrate below the rooting zone, amounting to 18 kmol ha−1 over a 17-year period, was simulated well, but some annual and seasonal variations of nitrate concentrations could not be reproduced by the model. In particular the large annual variations in nitrate concentrations observed below the litter layer were not satisfactory reproduced.