Effects of Data Uncertainty in the Swedish Critical Load Assessment for Forest Soils

The effects of input data uncertainty on the critical loads andexceedance estimates for Swedish forest soils was assessed usingMonte Carlo simulations of the PROFILE model. The study focuseson the effects of data uncertainty on the 5%-ile critical loadat 150 × 150 km resolution and the 95%-ile exceedance at150 × 150 km and 50 × 50 km resolution.The results indicate that datauncertainty limits the possibility to differentiate grid cellson 150 × 150 km resolution. The confidence interval for agiven percentile can generally be reduced if the uncertaintiesin calculated critical loads are addressed simultaneously forall sites in a grid cell. The resulting best estimates of the5%-ile critical load were found to be lowered, therebyadvocating larger deposition reductions to comply with a givengap closure of exceedance. The results further indicate that thenumber of sites within the grid cells is important for the rangeof the confidence interval for a given percentile.Re-aggregation of exceedance estimate in 50 × 50 km gridcells showed that differentiation may be improved as compared to150 × 150 km resolution. For 70% of the grid cells on 50× 50 km resolution, the confidence interval forcalculated exceedance covers both negative and positive values.     

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.     

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.     

Modelling geochemistry and Lake pH since glaciation at Lake Gårdsjön

The soil acidification model SAFE was modified to calculate historical changes in geochemistry and runoff since the last glaciation ended at the Lake Gårdsjön F1 catchment 12 000 B.P. Changes in runoff pH and ANC, soil weathering rate, soil mineralogy, soil texture and base saturation was also calculated. The changes in mineralogy compared favorable to data. Modeled historic weathering rates were slightly higher than data suggest, while present weathering rate was somewhat to low, 37 mmol_c m^?2 yr^?1. The weathering rate was very high immediately after the last glaciation, and decreased as the smaller particles were consumed by weathering. The calculated runoff pH follows the pattern of the paleo-inferred pH. SAFE suggests a natural depletion of base cations in the C-layer.     

Magic,Safe and Smart Model Applications at Integrated Monitoring Sites: Effects of Emission Reduction Scenarios

Three well-known dynamic acidification models (MAGIC, SAFE, SMART) were applied to data sets from five Integrated Monitoring sites in Europe. The calibrated models were used in a policy-oriented framework to predict the long-term soil acidification of these background forest sites, given different scenarios of future deposition of S and N. Emphasis was put on deriving realistic site-specific scenarios for the model applications. The deposition was calculated with EMEP transfer matrices and official emissions for the target years 2000, 2005 and 2010. The alternatives for S deposition were current reduction plans and maximum feasible reductions. For N, the NOx and NHy depositions were frozen at the present level. For NOx, a reduction scenario of flat 30% reduction from present deposition also was utilized to demonstrate the possible effects of such a measure. The three models yielded generally consistent results. The ‘Best prediction’-scenario (including the effects of the second UN/ECE protocol for reductions of SO2 emissions and present level for NOx-emissions), resulted in many cases in a stabilization of soil acidification, although significant improvements were not always shown. With the exception of one site, the ‘Maximum Feasible Reductions’ scenario always resulted in significant improvements. Dynamic models are needed as a complement to steady-state techniques for estimating critical loads and assessing emission reduction policies, where adequate data are available.     

Integrated Assessment Modeling of Air Pollution in Four European Countries

The integrated assessment modeling on acid rain has incorporated several related effects and pollutants into a multi-pollutant/multi-effect approach, resulting in complex integrated models and policy assessments. The development and implementation of effects-oriented cost-effective emission reduction strategies in Europe are based on integrated assessment models. The project on national integrated assessment modeling in Finland, Denmark, Spain and Sweden aimed to support the national evaluation of European emission reduction strategies. The tasks covered the comparison of inventories and projections for emissions of sulfur, nitrogen oxides, ammonia and volatile organic compounds, assessment of control techniques and related costs, concentration and deposition scenarios to estimate environmental effects of acidification, eutrophication and ground-level ozone and their temporal aspects, uncertainty analyses on both individual modules and whole integrated models, and dissemination of results to stakeholders. The integrated assessment modeling provided a consistent framework for the harmonization of input data and in-depth scientific research tasks on emissions, pollutant loading and impacts including comprehensive uncertainty analyses, and facilitated the dissemination of knowledge to policy-makers.     

A Regional Perspective on Present and Future Soil Chemistry at 16 Swedish Forest Sites

Assessing the timescales of recovery, by the use of dynamic models, will be used as input to the policy process to abate acidification. In this study the multilayer dynamic soil chemistry model SAFE was applied to 16 forest sites in Sweden, covering a sulfur deposition gradient of 1.2–11 kg S/ha/yr. Soil samples were collected at all sites and the pH and sulfate concentration dependent isotherm, used for modeling sulfate adsorption in SAFE, was parameterized for every site. A new way of implementing the nutrient uptake distribution in SAFE was developed, which allows the uptake distribution between layers in the rooting zone to vary with time, depending on the availability of base cations in the individual layers. Model output was compared to measurements of base cation concentration, total inorganic Al, pH and Bc/Al both site-by-site and cumulatively for all sites, and the usefulness of these comparisons is discussed from a policy viewpoint. Future projections of recovery show that the overall recovery, expressed as minimum Bc/Al ratio > 1 in the rooting zone, is slow. Assuming full implementation of the UNECE LRTAP Gothenburg Protocol and no further emission reductions thereafter, 44% of the modeled sites still have a Bc/Al ratio below 1 in 2100 in some soil layer within the rooting zone.     

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.     

Steady-State and Dynamic Assessment of Forest Soil Acidification in Switzerland

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.     

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.