The deposition of acidifying nitrogen and sulphur compounds from agriculture and fossil fuel combustion has drastically altered the chemical balance of forest soils in many regions of the world, leading to soil acidification with negative impacts on nutrient availability and thus also on tree vitality. The change of nutrient concentrations in the soil solution can be assessed by long-term investigations, however meaningful indicators, reflecting environmental changes, are needed to compare the current nutrient status with past values. We used dendrochemical indicators in stem wood of different tree species to access the impact of acidifying depositions on soil quality and tree nutrition. We selected 328 stem wood samples from 96 trees of Norway spruce (Picea abies), European beech (Fagus sylvatica), Sessile oak (Quercus petrea) and English oak (Quercus robur) from 22 forest sites, which are part of the long-term Intercantonal Forest Observation Program in Switzerland. Four time periods of 20 years were defined according to the emissions of air pollutants between 1910 and 2017. Our results showed a trend of increasing Al concentrations in tree rings of spruce peaking in the most recent time period (2000–2017). Mn and Ca concentrations in spruce and beech wood have decreased significantly throughout the time period 1910–2017. These dendrochemical indicators depended on the soil pH, with higher Al and lower Mn and Ca concentrations for soils with a low pH (pH<4.2). In oak trees the observed dendrochemical changes are confounded with dendrochemical differences between heartwood and sapwood. K and Mg showed inconsistent patterns in all three tree species, which are probably caused by translocation within the stem discs. With the use of piecewise structural equation models (SEM) we highlighted the direct and indirect influences of N deposition on element concentrations in stem wood. The data suggest a relation between increased N deposition and lower base saturation values in the forest soils for all three tree species, which were linked to higher Al concentrations in spruce and lower Mn concentrations in spruce and beech. The relation between Al concentrations in tree rings of Norway spruce and measured base saturation was used to reconstruct past soil base saturation values. It revealed a progressive soil acidification in the long-term forest observation sites. These reconstructed base saturation values were further used to validate modelled values from dynamic biogeochemical models such as SAFE/ForSAFE. This comparison pointed out possible shortcomings such as the lack of organic complexation in those models. Taken together, our analyses showed that element concentrations of Al, Mn, Ca in Norway spruce and European beech stem wood were suitable dendrochemical indicators of environmental change due to soil acidification, as they reflect both direct and indirect effects of air pollutants and chemical soil properties.

Im Rahmen einer im Auftrag des Bundesamts für Umwelt (BAFU) durchgeführten Machbarkeitsstudie wurde erstmalig eine Verwitterungskarte für Schweizer Waldböden mit einer Auflösung von 100 m berechnet. Auf der Grundlage gut untersuchter Bodenprofile konnte die Beziehung zwischen der Verwitterungsrate und dem chemisch-physikalischen Milieu des Bodens sowie des Ausgangssubstrates der Bodenbildung statistisch erfasst werden. Da viele dieser Informationen flächenhaft vorhanden sind, liess sich damit eine schweizweite Karte der Verwitterung berechnen. Sie zeigt eine Abschätzung der jährlich freigesetzten basischen Kationen bis zu einer Bodentiefe von 60 cm, die für die Aufnahme von Nährstoffen durch die Baumwurzeln relevant ist. Die Karte bietet sich für waldbauliche Planungen sowie für die Modellierung grösserer Naturräume an.

Abstract. The PROFILE model, now incorporated in the ForSAFE model can accurately reproduce the chemical and mineralogical evolution of the soil unsaturated zone. However, in deeper soil layers and in groundwater systems, it appears to overestimate weathering rates. This overestimation has been corrected by improving the kinetic expression describing mineral dissolution by adding or upgrading breaking functions. The base cation and aluminium brakes have been strengthened, and an additional silicate brake has been developed, improving the ability to describe mineral-water reactions in deeper soils. These brakes are developed from a molecular-level model of the dissolution mechanisms. Equations, parameters and constants describing mineral dissolution kinetics have now been obtained for 102 different minerals from 12 major structural groups, comprising all types of minerals encountered in most soils. The PROFILE and ForSAFE weathering sub-model was extended to cover two-dimensional catchments, both in the vertical and the horizontal direction, including the hydrology. Comparisons between this improved model and field observations is available in Erlandsson Lampa et al. (2019, This special issue). The results showed that the incorporation of a braking effect of silica concentrations was necessary and helps obtain more accurate descriptions of soil evolution rates at greater depths and within the saturated zone.

This chapter presents four geochemical dynamic models (VSD, MAGIC, ForSAFE and SMARTml) that have been used to assess impacts of nitrogen and acidity inputs on soil and soil solution chemistry. These models differ in their complexity and description of some processes. Some models can be used to calculate effects on surface waters as well. For all models this chapter shows examples of site-scale applications at intensively monitored forested plots in the UK, Germany, Switzerland and Norway, illustrating the adequacy of the model behaviour. Impacts of legislated emission reductions and forest harvest scenarios on soil solution chemistry are illustrated with a MAGIC model application. Besides scenario analyses, dynamic models can also be used to determine target loads, i.e. the deposition to reach a prescribed condition within a given time frame. This chapter introduces the target load concept and presents target load calculations with the MAGIC and the VSD model.

Base cation weathering (BCw) rate is one of the most influential yet difficult to estimate parameters in the calculation of critical acid loads of nitrogen (N) and sulfur (S) deposition for terrestrial systems. Only the clay correlation–substrate method, a simple empirical model, has been used for estimating BCw rates for forest ecosystems in the conterminous USA and may not be suitable for application at all sites without calibration or revision. An alternate model, PROFILE, may offer an improved method to estimate BCw rates. It is a transferable, process-based model that simulates the weathering rates of groups of minerals. The objective of this study was to evaluate PROFILE using national datasets as a method to estimate BCw rates for forests in the USA, focusing on Pennsylvania (PA) as the first test state. The model paired with national datasets was successfully applied at 51 forested sites across PA. Weathering rates ranged from 119 to 9,245 eq ha−1 year−1 and were consistent with soil properties and regional geology. Comparisons of terrestrial critical acid loads with 2002 N and S deposition showed critical load exceedances at 53 % of the sites. This trial evaluation of PROFILE paired with national datasets in PA establishes that there are sufficient data to support the estimation of BCw rates and determination of critical acid loads for forests in the USA. However, the paired method should be applied in other locations to further evaluate the performance of the model in different regions of the country.

The ForSAFE-VEG model was used to investigate the impacts of climate change and air pollution scenarios on soil chemistry and ground vegetations composition. In particular, the model involves a ground vegetation model incorporating plant changes to ambient site conditions in terms of climate and chemistry, but the model also incorporate competition between the different plant groups. The model was validated against observed values and reproduced observations of tree growth, soil chemis- try, and ground vegetation compositions to satisfac- tion. The results show that the ground vegetation reacts strongly to changes in air pollution, in particular nitrogen as well as to climate change with major shifts in plant composition. A procedure for estimating critical loads for nitrogen, using ground vegetation biodiversity as criterion, was tested and the method seems operable. It suggests that if we want to protect the present biodiversity of the ground vegeta- tion, this will face significant difficulties because of permanent climate change that induced changes in the ecosystem. We conclude that the reference state for ground vegetation biodiversity is rather to be sought for in the future, hopefully using models, than in the past or present.

Information on soil mineralogy is essential for weathering rate calculations. Quantitative mineralogical analyses are expensive and time-consuming, and thus indirect methods of determining the mineralogical composition are important, for example estimating the composition based on the elemental content in till (total concentrations), or based on information about the underlying bedrock. The mineralogical composition and the elemental content in till were analysed in two areas in southern Sweden, at 10 sites in each area. There were significant differences between the areas regarding both elemental content and optically determined mineralogy. The content of calcium was significantly higher in one area, 5ESV, and there were tendencies in this direction also for magnesium and iron. The potassium content was significantly higher in the other area, 6FNV. The variation in soil chemistry between the areas can be explained by higher contents of the minerals biotite, hornblende and epidote in the first area (5ESV) and higher contents of K-feldspar in the second (6FNV). Normative mineralogy was determined based on the elemental content. A comparison between the normative mineralogy and the optically determined mineralogy showed great similarities which indicates that there is good potential for using elemental content for estimating the mineralogical composition. The difference in till composition between the areas could not be explained by the underlying bedrock, which indicates that the information available on the bedrock is not sufficient for estimation of the till mineralogical composition.

A2M (‘Analysis to Mineralogy’) is a computer program to determine, for given total chemical analyses, all possible mineral modes from an arbitrary but pre-specified set of minerals. A2M is specifically designed to address the case in which the number of minerals is greater than the number of analysed elements (oxides). Since in this case the solution is not unique, all extreme mineral modes are determined. They span a finite convex polyhedron in the solution space with dimension ‘number of minerals’ minus ‘number of elements’. Every possible solution can be obtained as linear combination of the extreme modes; and the arithmetic mean of all extreme modes (i.e. the centre of gravity of the solution polyhedron) is a routine output of A2M, which can be regarded as the ‘best’ solution in the absence of any additional information. The use of A2M is illustrated with several examples.

Weathering rates of base cations are crucial in critical load calculations and assessments of sustainable forestry. The weathering rate on a single site with detailed geological data can be modelled using the PROFILE model. For environmental assessments on a regional scale, the weathering rates for sites are scaled into regional maps. The step from sites to regional level requires focus on the spatial variation of weathering rates. In this paper, a method is presented by which weathering rates are calculated for 25589 Swedish sites with total elemental analysis for the soil. Based on a part of the results, a methodology for creating area covering maps by geostatistical analysis and kriging is described. A normative reconstruction model was used to transform total elemental analysis to mineralogy. Information from the Swedish Forest Inventory database and other databases were used to derive texture and other important information for the sites, e.g. climate, deposition and vegetation data. The calculated weathering rates show a regional pattern that indicates possibilities for interpolation of data in large parts of Sweden. Geostatistical analysis of an area in southern Sweden shows different properties for different base cations. Kriging was performed for potassium to demonstrate the method. It was concluded that different base cations and different regions have to be analysed separately, in order to optimise the kriging method.

The European steady-state Simple Mass Balance (SMB) model and the dynamic soil acidification model SAFE were used to assess the risk of future forest soil acidification in Switzerland. 2010 deposition forecasts on a 150×150 km grid resolution as well as corresponding ecosystem protection levels were obtained from RAINS model runs based on the 1999 Gothenburg Protocol obligations under the UN/ECE LRTAP Convention. Deposition values for 2010 on the national resolution were derived by scaling down present 1×1 km deposition values according to the deposition trends at the 150×150 km grid resolution. Meeting the Protocol obligations will reduce the percentage of Swiss forest ecosystems not protected against acidification between 1990 and 2010 from 41 to 4% according to the RAINS assessment and from 63 to 16% according to the assessment with the SMB at the 1×1 km resolution. The dynamic approach indicates, however, that soil conditions may not improve as much as these steady-state models suggest. By 2010, 39% of the sites considered will still have soil solution Bc/Al molar ratios below 1 at least in one soil layer. Nevertheless, deposition reductions obtained from the implementation of the new protocol will prevent the major part of Swiss forest soils from further acidification. Aiming at recovery of the more sensitive forest ecosystems would require emission reductions beyond the Protocol's obligations.

The steady-state soil chemistry model PROFILE was used to calculate the chemical status of forest soils under present deposition loads for two areas with dissimilar ecosystem properties. Two regions in Switzerland, with contrasting bedrock geology were selected to be investigated in detail: 88 locations in the Jura Mountains, representative for carbonate bedrock and 91 locations in the Ticino Area dominated by metamorphic crystalline host rocks. Weathering rates calculated for the key regions cover the tremendous range between 0.013 and 25 keq ha−1 yr−1. In the Ticino Area, the effect of increased abundance of relatively fast weathering silicates (epidote, hornblende and plagioclase) on the weathering rate is apparently masked by the total effects of the physical conditions applied and by the variation in the deposition load. In the Jura Mountains, generally high weathering rates occur with about 50% of the sites yielding rates above 1 keq ha−1 yr−1. In many of the sites investigated, however, carbonates have already been dissolved completely in the soil horizons of interest resulting in very low weathering rates. The critical load of actual acidity was calculated according to: CLAcidity=RWeathering−ANCLeaching, where alkalinity leaching is estimated by keeping the base cation to aluminum molar ratio at the critical limit of 1 at steady-state. The minimum critical load calculated was 0.2 keq ha−1 yr−1 and the maximum was 6.2 keq ha−1 yr−1. Comparing the cumulative frequency distributions of critical loads of actual acidity for forest soils in the individual areas it can be seen that the differences between the key regions are less substantial than with the weathering rates. Critical loads of acidity for the Ticino Area range from 1 to 3.9 keq ha−1 yr−1. Sites yielding the lowest critical loads of acidity are observed in the Jura Mountains. Among these apparent sensitive soils are soils with intermediate or high weathering rates, although it has depleted topsoil layers. Within the context of this model application, it becomes apparent that the sensitivity of these soils with respect to acidification is also governed by the alkalinity leaching term and not only by the susceptibility of its minerals to weathering.

A variant of the European modelSimple Mass Balance (SMB) and the regionalizedPROFILE model have been used to calculate critical loads of acidity for Swiss forest soils. The single layer SMB has been applied to 11,800 receptor points and the multi-layer PROFILE to 720 forest sites. Weathering rates used in SMB calculations were assessed by means of a modified de Vries soil classification, and calculated from physical properties of the soil system with PROFILE.