No abstract

It is shown that by calibrating the simulation model BIOME-BGC with mandatory and optional Level II data, within the ICP Forest programme, a well-founded calculation of the carbon budget of forest stands is achievable and, based on succeeded calibration, the modified BIOME-BGC model is a useful tool to assess the effect of climate change on forest ecosystems

Almost all soil organic carbon turnover models rely on a partitioning of total organic carbon into an inert and a decomposable pool. The quantification of these pools has a large impact on modelling results. In this study several methods to estimate inert carbon in soils, based either on total soil organic matter or physical protection, were assessed with the objectives of (1) minimising errors in carbon and nitrogen dynamics and (2) ensuring usability for sites with marked differences in site conditions. CANDY simulations were carried out by varying solely the method for calculating the size of the inert carbon pool used to initialise the model. Experimental data from Bad Lauchsta¨dt and Mu¨ncheberg were used for the simulation. The data were made available for modellers at a workshop held at Mu¨ncheberg (Germany) in 2004. The results concerning not only carbon but also nitrogen dynamics were analysed by applying selected statistical methods. It was shown that even in short-term simulations model initialisation procedure may influence the simulation results considerably. Three methods of estimating inert carbon were identified as being the most appropriate. These methods are either based on soil texture or pore-space classes and therefore account for the physical protection of soil organic matter. Thus, physical protection seems to be of major importance. By extending the scope of the investigation into nitrogen dynamics, additional support for the applicability of a selected method was obtained.

No abstract

Calculation of solute flux into groundwater by recharge must account for the spatial variability of water flux and recharge solute concentration. Solute concentration of the recharge can be characterized by sampling the uppermost groundwater. In an earlier study under pine (Pinus silvestris L.) on sandy soil, solute concentrations at the water table along a transect fluctuated in a recurrent pattern, probably caused by heterogenous solute input via canopy throughfall. To obtain more insight into the spatial variability of deposition processes and solute concentrations in recharge, transect sampling of the uppermost groundwater was repeated in 1989, and again in 1993. Solute deposition by throughfall was also measured in 1993. The data were analyzed by spectral and time series methods. Sulfate (SO4) concentrations in canopy throughfall and uppermost groundwater showed recurrent fluctuations corresponding to canopy coverage of the ground. Sulfate maxima coincided with canopy edges. The dominant fluctuation frequency of SO4 concentrations in 1993 was lower than in 1989 because of canopy enlargement by pine tree growth. Detailed analysis of the 1993 SO4 concentrations revealed superimposed fluctuations with a frequency valid for the 1989 canopy edge distribution. This can be attributed to an actual patterned SO4 retrieval from solid aluminum‐hydroxo‐sulfate (Al‐OH‐SO4) phases, stored in the subsoil under previous higher SO4 deposition rates.