Input-output budget of nitrogen and the effect of experimentally changed deposition in the forest ecosystems in central Japan

To evaluate the current nitrogen (N) status in Japanese forests, field measurements of rainfall, throughfall, litter layer percolation, and soil solution percolation were conducted in a red pine stand (Kannondai) and a deciduous stand (Yasato) located in central Japan. N input via throughfall was 31 and 14 kg ha(-1) year(-1) and output below rooting zone was 9.6 and 5.5 kg ha1 year(-1) in Kannondai and in Yasato, respectively. Two thirds of input N were retained in plant-soil systems. Manipulation of N input was carried out. Ionic constituents were removed from throughfall with ion exchange resin at removal sites and ammonium nitrate containing twice the N of the throughfall was applied at N addition sites periodically. SO4(2-) output below 20-cm soil layer changed depending on the input, while NO3- output was regulated mainly by the internal cycle and effect of manipulation was undetected. These Japanese stands were generally considered to have a larger capacity to assimilate N than NITREX sites in Europe. However, N output fluxes had large spatial variability and some sites in Kannondai showed high N leaching below rooting zone almost balanced with the input via throughfall.

Implementation of sulfate adsorption in the SAFE model

An SO4(2-) adsorption submodel has been implemented in the dynamic soil chemistry model SAFE. The submodel calculates pH-dependent SO4(2-) and H+ adsorption to the soil, as well as the net surface charge development due to uneven adsorption of SO4(2-) and H+, using the empirical equations derived from an electrostatic model (Extended Constant Capacitance Model, ECCM) of SO4(2-) adsorption. The resulting new SAFE model was applied on a roof experiment plot in the Norway spruce [Picea abies (L.) H. Karst.] stand at Solling, Germany, where atmospheric S and N deposition was artificially reduced by the roof construction. The model performance was compared with the previous versions that used a pH-independent Freudlich model of SO4(2-) adsorption or assumed no SO4(2-) adsorption. With the ECCM-based SO4(2-) adsorption submodel, SAFE simulated soil solution SO4(2-) concentration and base saturation better, in comparison with measured data, than with the previous SO4(2-) adsorption formulations. Through the model application, also, need of additional improvement was suggested, such as calibration of mass transfer coefficients.