M. Posch

A very simple dynamic soil acidification model for scenario analyses and target load calculations

A very simple dynamic soil acidification model, VSD, is described, which has been developed as the simplest extension of steady-state models for critical load calculations and with an eye on regional applications. The model requires only a minimum set of inputs (compared to more detailed models) and execution time is minimised by reducing the set of model equations to a single non-linear equation. To facilitate the exploration of model behaviour at individual sites, the model is linked to a graphical user interface (GUI). This GUI allows easy (Bayesian) calibration, forward simulation (scenario analyses) and can also be used to compute target loads and delay times between deposition reductions and ecosystem recovery. VSD compares well to other widely used more complex models and is currently used in several European countries in the support of effects-based emission reduction policies.

Dynamic modelling of metals - Time scales and target loads

Over the past decade steady-state methods have been developed to assess critical loads of metals avoiding long-term risks in view of food quality and eco-toxicological effects on organisms in soils and surface waters. However, dynamic models are needed to estimate the times involved in attaining a certain chemical state in response to input (deposition, fertilizers or manure) scenarios. Starting from a mass balance, a universal dynamic model was developed by defining appropriate dimensionless quantities, which depend only on the metal under consideration. For any given metal, the model (differential equation) is characterised by the interplay of four (dimensionless) variables: the initial condition, i.e. the concentration at the start of the simulation, the input (driving force), time, and the concentration of the metal at any given point in time. Depending on the question asked, one of these quantities is fixed and the functional relationship between the other three provides the answer. The model allows to investigate the time development of the soil chemical status under a constant future input of the metal to predict (i) the future metal concentration as a function of time (scenario analysis), (ii) the time when a prescribed chemical state (e.g., a critical concentration or steady state) is reached (delay times), and (iii) which future input (reduction) is needed to reach a prescribed chemical state within a prescribed time period (target loads). The general solutions are illustrated with concrete examples, using (average) data from the Netherlands for four metals: cadmium, lead, copper and zinc. The modelling approach set out in this paper illustrates the potential use of dynamic models in the support of policies aimed at reducing emissions of metals by providing an understanding of the structural properties of the model, independent of site-specific parameters. It thus allows assessing temporal behaviour and time scales before embarking on detailed modelling for individual sites.

Modelling the long-term soil response to atmospheric deposition at intensively monitored forest plots in Europe

The dynamic soil chemistry model SMART was applied to 121 intensive forest monitoring plots (mainly located in western and northern Europe) for which both element input (deposition) and element concentrations in the soil solution were available. After calibration of poorly known parameters, the model accurately simulated soil solution concentrations for most plots as indicated by goodness-of-fit measures, although some of the intra-annual variation especially in nitrate and aluminium concentrations could not be reproduced. Model evaluations of two emission-deposition scenarios (current legislation and maximum feasible reductions) for the period 1970-2030 show a strong reduction in sulphate concentrations between 1980 and 2000 in the soil due to the high reductions in sulphur emissions. However, current legislation hardly reduces future nitrogen concentrations, whereas maximum feasible reductions reduces them by more than half. Maximum feasible reductions are also more effective in increasing pH and reducing aluminium concentrations, mostly below critical values.

Critical loads of nitrogen and sulphur to avert acidification and eutrophication in Europe and China

IntroductionForests and other (semi-)natural ecosystems provide a range of ecosystem services, such as purifying water, stabilizing soils and nutrient cycles, and providing habitats for plants and wildlife. Critical loads are a well-established effects-based approach that has been used for assessing the environmental consequences of air pollution on large regional or national scales.Materials and methodsTypically critical loads of sulphur (S) and nitrogen (N) have been derived separately for characterizing the vulnerability of ecosystems to acidification (by S and N) and eutrophication (by N). In this paper we combine the two approaches and use multiple criteria, such as critical pH and N concentrations in soil solution, to define a single critical load function of N and S.Results and conclusions The methodology is used to compute and map critical loads of N and S in two regions of comparable size, Europe and China. We also assess the exceedance of those critical loads under globally modelled present and selected future N and S depositions. We also present an analysis, in which the sensitivity of the critical loads and their exceedances to the choice of the chemical criteria is investigated. As pH and N concentration in soil solution are abiotic variables also linked to plant species occurrence, this approach has the potential for deriving critical loads for plant species diversity.

Assessment of Critical Loads of Sulphur and Nitrogen and Their Exceedances for Terrestrial Ecosystems in the Northern Hemisphere

In this chapter an assessment of critical loads of sulphur and nitrogen for forests and (semi-)natural vegetation and their exceedances in the boreal and temperate region of the Northern Hemisphere (excluding the contiguous USA) is reported. Critical loads were estimated using steady-state mass balance methods (see Chap. 6). The influence of different chemical criteria on critical loads and their exceedances was also evaluated.

Assessing the impacts of nitrogen deposition on plant species richness in Europe

Dose-Response (D-R) relationships derived from nitrogen (N) addition experiments and N deposition gradient studies are extrapolated over natural and (semi-)natural grasslands in Europe, using a European land cover map. Based on emissions of oxidized and reduced N in 2000 and 2020, ecosystem-specific depositions of total N are computed over Europe. For 2020 two scenarios are applied, i.e. one according agreed emission reductions under national and European legislation and the other based on the (hypothetical) application of best available emission control techniques. Results show that the impact of N deposition on plant species diversity computed over European (semi-)natural grasslands is less when N addition based dose-response relationships are used than when a N deposition gradient based alternative is applied. Using the latter approach, the species richness is computed to be reduced by more than 40 % in about 5 % of European grasslands in 2000. This reduction in species richness becomes less than 25 %, when N emissions are cut back using maximum feasible abatement technologies.

Assessment of Critical Loads of Acidity and Their Exceedances for European Lakes

Lake acidification in northern Europe provided some of the key impetus for the development of the critical loads approach during the 1980s. While major reductions in acidic deposition have been achieved during the last 20 years, through the application of this approach, regions with continued acidification and critical load exceedance persist around Europe. This chapter describes regional applications of the First-order Acidity Balance (FAB) model in five European countries, highlighting national approaches to lake surveys and regional representation, and how the model has been adapted in each of these countries. We discuss the implications of interpreting critical load exceedances, and provide an overall synthesis of freshwater exceedance in Europe using common European deposition data. Despite uncertainties within the FAB model, such as the parameterisation of nitrogen immobilisation and denitrification, a coherent picture of the spatial extent of acidification within European lakes is evident. The ongoing failure to meet critical loads by 2020 demonstrates that lake acidification is still a current, not a historical, problem in Europe, and under current legislation many lakes will remain more acidic than their pre-industrial reference condition.

Geochemical Indicators for Use in the Computation of Critical Loads and Dynamic Risk Assessments

This chapter provides an overview of geochemical indicators for nitrogen (N), acidity, and metals in soil and water (soil solution, ground water and surface water) in view of their impacts on different endpoints (tree growth/health, human health, soil biodiversity etc.). Relevant indicators for N are the soil C/N ratio, nitrate (NO3) concentration in ground water and total N concentration in soil and surface water. For acidity the most relevant endpoint indicators are the exchangeable base cation pool or base saturation in the soil, the ratio of aluminium (Al) to base cation (Bc) in soil solution, the total Al concentration in ground water and the acid neutralizing capacity (ANC) in surface water. Relevant indicators for metals are the total or reactive metal concentration in the soil and the free or total metal ion concentration in water. Using critical limits for those endpoint indicators, it is possible to assess critical loads for both terrestrial and aquatic ecosystems based on geochemical modelling. An overview is given of the derivation of those limits, mostly under laboratory circumstances, and a critical evaluation of their relevance in the field situation.

Dynamic Geochemical Models to Assess Deposition Impacts and Target Loads of Acidity for Soils and Surface Waters

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.

The History and Current State of Critical Loads and Dynamic Modelling Assessments

This book focuses on knowledge and methods for the assessment of indirect, soil mediated effects of the deposition of sulphur dioxide, oxidized nitrogen and reduced nitrogen on terrestrial and aquatic ecosystems. The emphasis is on the science behind no-effect deposition thresholds (critical loads) and methods to understand future consequences of atmospheric depositions that exceed these thresholds. First, background information is given on drivers and impacts of air pollution and the philosophy behind the critical load approach is pointed out. Then, the history and current state of critical load assessments for sulphur (S), nitrogen (N) and metals is presented. This is followed by recent developments and use of dynamic models, for the assessment of future impacts of excessive deposition and the chapter finalizes with a reading guideline to this book and the logic of its organization.