Mattias Alveteg

Biogeochemical processes and mechanisms

The modelling adapted in the SUFOR programme attempts to take a large step forward. This chapter describes some of the biogeochemistry processes needed in the next step biogeochemical modelling taken in SUFOR. There are several models for nutrient dynamics and growth available, however, development of these have in some respects moved in old tracks for the last decade. We see several drawbacks in these older constructs with respect to operationality and several new steps are necessary, especially with respect to nitrogen and carbon cycling, but also with respect to developing models that operate on observable parameters. What is described in the following is the result of several theme groups that have been operative in the SUFOR Programme. The groups have been multidisciplinary, which was a great help for innovation.

Modeling Recovery of Swedish Ecosystems from Acidification

Abstract Dynamic models complement existing time series of observations and static critical load calculations by simulating past and future development of chemistry in forest and lake ecosystems. They are used for dynamic assessment of the acidification and to produce target load functions, that describe what combinations of nitrogen and sulfur emission reductions are needed to achieve a chemical or biological criterion in a given target year. The Swedish approach has been to apply the dynamic acidification models MAGIC, to 133 lakes unaffected by agriculture and SAFE, to 645 productive forest sites. While the long-term goal is to protect 95% of the area, implementation of the Gothenburg protocol will protect approximately 75% of forest soils in the long term. After 2030, recovery will be very slow and involve only a limited geographical area. If there had been no emission reductions after 1980, 87% of the forest area would have unwanted soil status in the long term. In 1990, approximately 17% of all Swedish lakes unaffected by agriculture received an acidifying deposition above critical load. This fraction will decrease to 10% in 2010 after implementation of the Gothenburg protocol. The acidified lakes of Sweden will recover faster than the soils. According to the MAGIC model the median pre-industrial ANC of 107 µ= L−1 in acid sensitive lakes decreased to about 60 µ= L−1 at the peak of the acidification (1975–1990) and increases to 80 µ= L−1 by 2010. Further increases were small, only 2 µ= L−1 between 2010 and 2040. Protecting 95% of the lakes will require further emission reductions below the Gothenburg protocol levels. More than 7000 lakes are limed regularly in Sweden and it is unlikely that this practice can be discontinued in the near future without adverse effects on lake chemistry and biology.

Reconstructing historic atmospheric deposition and nutrient uptake from present day values using MAKEDEP.

A model, MAKEDEP, was developed for reconstructing historic atmospheric deposition and nutrient uptake for forests using present day values. Deposition is reconstructed by separation of wet deposition and throughfall into five different categories. Dry deposition is assumed to depend linearly on needle biomass. Non-marine deposition is scaled using general European emission and deposition trends for sulphur, nitrate and ammonia. Historic nutrient uptake is reconstructed using current biomass and nutrient content, a logistic forest growth curve and information on historic land use.

Regional assessment of the temporal trends in soil acidification in Southern Sweden, using the safe model

The dynamic soil acidification model SAFE was applied to 44 forested sites in Skåne, southern Sweden, using available Swedish databases on present soil status, vegetation and deposition. Time series of deposition were derived for each site from present deposition in a generalized fashion by dividing deposition into different classes and scaling with deposition trends from the literature. This study connects the current status of the soil and the soil development with critical load maps calculated with the steady-state model PROFILE.The model was calibrated against measurements of present base saturation from the Swedish Forest Inventory. Model output was compared with available measurements of soil water chemistry.Model output was used to assess the time delay between changes in acidic input and system response in terms of exchangeable base cations and pH. The model was also used for scenario analysis, applying the reductions agreed in the Oslo Protocol to assess the environmental benefits of the agreement.

Parameterization and evaluation of sulfate adsorption in a dynamic soil chemistry model

Sulfate adsorption was implemented in the dynamic, multi-layer soil chemistry model SAFE. The process is modeled by an isotherm in which sulfate adsorption is considered to be fully reversible and dependent on sulfate concentration as well as pH in soil solution. The isotherm was parameterized by a site-specific series of simple batch experiments at different pH (3.8-5.0) and sulfate concentration (10-260 micromol 1(-1)) levels. Application of the model to the Lake Gardsj6n roof covered site shows that including sulfate adsorption improves the dynamic behavior of the model and sulfate adsorption and desorption delay acidification and recovery of the soil. The modeled adsorbed pool of sulfate at the site reached a maximum level of 700 mmol/m(2) in the late 1980s, well in line with experimental data.

Critical loads - is there a need for a new concept?

The concept of critical loads has been an important andsuccessful tool for the development of control strategiesfor transboundary air pollution in Europe. The use of theconcept has led us to a situation where very few areas inEurope will have an exceedance of critical loads foracidification in 2010, indicating that the benefits offurther control acidifying substances will be lessuseful. The critical loads concept does not, however,take into account the large benefits of further controlin damaged systems but where critical loads are nolonger exceeded. In this paper we discuss the importanceof widening the critical loads concept to include thesebenefits and we propose an additional effect-relatedmeasure, Dynamic Impact Analysis, to be included infurther control strategies and assessments. With such aconcept the actual situation and its further developmentwill be included in assessments and control strategies.

Integrated Assessment of Soil Chemical Status. 2. Application of a Regionalized Model to 622 Forested Sites in Switzerland

A regionalized version of the dynamic, process-oriented, multi-layer soil chemistry model SAFE was applied to 622 forest sites in Switzerland to assess effects of acidifying atmospheric deposition on the soil chemistry between 1850 and 2050. Simulation indicates that the present day chemical status of Swiss soils is a result of the last 50 years of acid deposition. Indicative soil parameters such as soil solution pH, acid neutralizing capacity, total Al concentration, base cation to total A1 molar ratio and base saturation consistently deteriorate since the beginning of the 1950s, when acid loads start to increase. The simulated adverse evolution of soil chemistry persists until some time between 1975 and 2010, and apart from being site-dependent, the turning-point is also dependent on which parameter is considered at which soil depth.

Developing a kinetic alternative in modeling soil aluminium

Soil chemistry models often use gibbsite solubility and similar equilibrium models to predict Al concentrations in soil solution. A kinetic alternative was developed with the goal of finding universal rate constants instead of the site- and depth-specific solubility constants usually associated with the equilibrium approach. The behavior of the two approaches was studied within the framework of the steady-state soil chemistry model PROFILE using data from Solling, Germany and Gårdsjön, Sweden, two sites with different mineralogy and land use history. The kinetic alternative uses a mass balance to predict Al concentrations. The sources of Al in soil water are deposition, weathering and mineralization. The sinks are leaching and the formation of an aluminosilicate precursor. The precursor slowly transforms into an ordinary clay mineral. Both formation and transformation of the precursor are treated as irreversible processes. The kinetic model introduces a new relationship between pH and Al and produces a systematic pattern of different apparent gibbsite equilibrium constants at different depths. Results show that the kinetic model systematically underestimates Al concentration in the upper horizons, which indicates that there may be additional sources of Al in the upper horizons not accounted for in the model. Predicted values of pH and Al concentrations are comparable with field observations.

Identifying potentials for reducing uncertainty in critical load calculations using the PROFILE model

A sensitivity analysis was performed testingweathering rates, critical loads andexceedances for Swedish forest soils using Monte Carlosimulations of the PROFILE model. Different subsetsof input data were investigated with respect to theirpotential to reduce data uncertainty at site level butalso for modified estimates of the 5%-ile critical load andthe 95%-ile exceedance on 150×150 kmresolution. Physical soil properties were of dominantimportance for all sites and yield up to 62%reduction of the output standard deviation in weathering rate.The study showed that the critical ratio ofbase cations to inorganic aluminium (Bc/Al ratio) in the soilsolution was of major importance for reducingdata uncertainty in critical loads and exceedance estimates.The critical Bc/Al ratio was found to beimportant for reducing data uncertainties in modifiedestimates of the 5%-ile critical load and the95%-ile exceedance, in particular in the northern part ofSweden. Atmospheric deposition, uptake andlitterfall were more important for reducing data uncertaintyin the southern part. Physical soil propertiesand especially mineral content were found to be less importantfor reducing data uncertainties in criticalloads and exceedance estimates. The greatest scope forreducing data uncertainties in an applied perspectiveis to improve estimates of atmospheric deposition of anionsand cations as well as uptake and litterfall ofbase cations and nitrogen.

Integrated Assessment of Soil Chemical Status. 1. Integration of Existing Models and Derivation of a Regional Database for Switzerland

A regional soil acidification model was developed by integration and adaptation of existing models. The regional model consists of the dynamic multi-layer soil chemistry model SAFE, its steady-state version INITSAFE, the atmospheric deposition and nutrient uptake reconstruction model MAKEDEP, and a routine with empirical relations concerning depth-dependent parameters. A scheme for the extraction of input to the regional model from available information of different geographical detail also was developed. Basic data sources considered were: 1) national surveys such as the National Forest Inventory, covering site specific information, 2) available point measurements of parameter values, and 3) literature sources. Not all parameters were available on a regional scale with sufficient resolution. Input required for the model calculations therefore was derived from the available data sources by means of transfer algorithms including spatial interpolation. Interpolation was done allocating parameter values determined at reference sites to conventionally mapped entities such as geological units, soil type, and other kinds of geographical information. The exercise resulted in a data base of the required 68 site-specific parameter values covering climatic, deposition and land use parameters, as well as stand characteristics and soil properties.