Critical Loads Approach Research Articles

Assessment of the potential for soil acidification in North India using the critical load approach and locally derived data for acidic and basic inputs

Major ions (Cl −, NO 3 −, SO 4 2−, Ca 2+, Mg 2+, Na +, K + and NH 4 +) were analysed in wet and dry deposition samples collected for 2 years using a polyethylene bottle and funnel collector at Agra in India. The deposition of ionic components (Ca 2+ and Mg 2+) derived from natural sources i.e. soil were higher than those of anthropogenic origin. In rainwater samples, non-sea-salt fraction was found to be 60–90%. In both wet and dry deposition Ca 2+ was found to be the dominant ion which may be due to its large particle diameter. Results suggest that most of the acidity, which occurs due to NO 3 −, SO 4 2− and Cl − is neutralized by alkaline constituents, which originate from airborne local soil and dust transported from the Thar desert. Acid neutralizing capacity of soil has also been quantified and found to be 33 × 10 3 neq g −1. Using deposition data, the critical load for acidity of soil with respect to Ashoka and Eucalyptus was evaluated. The present level of deposition of S and N was found to be much lower than critical loads calculated for S and N. Critical load of exceedance in terms of deposition acidity was also calculated and found to be negative. This indicates that with respect to these species, the ecosystem is protected at the current level of deposition.

Recent research advances on ECBL approach.: Part I: Plastic–elastic interactive buckling of cold-formed steel sections

The objective of this two parts paper is to present some recent developments and applications of erosion of critical bifurcation load (ECBL) approach for the interactive buckling. Two different types of problems are analysed: (1) plastic–elastic interactive buckling which implements into the Ayrton–Perry interaction formula the plastic strength of the stub columns evaluated by means of local plastic mechanism analysis, and (2) elastic–elastic interactive buckling for members with perforations. The first part of the paper analyses the occurrence of local plastic mechanisms in cold-formed steel sections in compression, and how they can be implemented in the ultimate limit state analysis of the members. Actually, the failure of thin-walled cold-formed members in compression always occurs with a local plastic mechanism. Starting from this observation, the authors suggest to use in the interactive local-overall buckling analysis the sectional plastic mechanism strength instead of traditional ‘effective section’. The ECBL approach is used to implement the proposed interactive buckling model. Results are compared with those of other two recent methods, namely the direct strength method and plastic effective width approach. Relevant tests are used to evaluate the three methods. Comparisons with European and American design codes are also presented in the paper.

Critical loads for lead in France: First results on forest soils

Within the framework of the United Nation Convention on Long Range Transboundary Air Pollution, France is part of the Working Group on Effect which aims at evaluating the impact of atmospheric deposition on ecosystems by calculating critical loads. The critical loads are the highest deposition of compounds that will not cause chemical changes in soil leading to long-term harmful effects on ecosystem structure and function. A guidance manual for calculation of critical loads for heavy metals (lead and cadmium) has been proposed by the Coordination Center for Effects (executive body of the WGE). French National Focal Center (CNRS and ADEME) aims in this study at evaluating the accuracy of the european methodology for calculation of critical loads for french forest soils. It appears that critical load approach is adapted for France but need to be calibrated at least for calculation of weathering fluxes and determination of critical limits. Stand-still on the contrary is not adequate because of inherent contradictions in the method and too much uncertainties in the transfer functions.

The impact of acid deposition and forest harvesting on lakes and their forested catchments in south central Ontario: a critical loads approach

Abstract. The impact of acid deposition and tree harvesting on three lakes and their representative sub-catchments in the Muskoka-Haliburton region of south-central Ontario was assessed using a critical loads approach. As nitrogen dynamics in forest soils are complex and poorly understood, for simplicity and to allow comparison among lakes and their catchments, CLs (A) for both lakes and forest soils were calculated assuming that nitrate leaching from catchments will not change over time (i.e. a best case scenario). In addition, because soils in the region are shallow, base cation weathering rates for the representative sub-catchments were calculated for the entire soil profile and these estimates were also used to calculate critical loads for the lakes. These results were compared with critical loads obtained by the Steady State Water Chemistry (SSWC) model. Using the SSWC model, critical loads for lakes were between 7 and 19 meq m-2yr-1 higher than those obtained from soil measurements. Lakes and forests are much more sensitive to acid deposition if forests are harvested, but two acid-sensitive lakes had much lower critical loads than their respective forested sub-catchments implying that acceptable acid deposition levels should be dictated by the most acid-sensitive lakes in the region. Under conditions that assume harvesting, the CL (A) is exceeded at two of the three lakes and five of the six sub-catchments assessed in this study. However, sulphate export from catchments greatly exceeds input in bulk deposition and, to prevent lakes from falling below the critical chemical limit, sulphate inputs to lakes must be reduced by between 37% and 92% if forests are harvested. Similarly, sulphate leaching from forested catchments that are harvested must be reduced by between 16 and 79% to prevent the ANC of water draining the rooting zone from falling below 0 μeq l-1. These calculations assume that extremely low calcium leaching losses (9–27 μeq l-1) from forest soils can be maintained without any decrease in forest productivity. Calcium concentrations in the three lakes have decreased by between ∼10 and 25% over the past 20 years and calculations assume that calcium concentrations in lakes can fall to around 30% of their current values without any harmful effects on biota. Both these assumptions require urgent investigation. Keywords: acid deposition, calcium, critical loads, forests, harvesting, lakes

Steady state critical loads of acidity for sulphur and nitrogen: a multi-receptor, multi-criterion approach

The critical load approach to emission reductions has become an important element of the United Nations Economic Commission for Europe (UNECE) Convention on Long-Range Transboundary Air Pollution (CLRTAP). The steady state mass balance approach (SSMB) is the most widely used method in Europe for estimating critical loads, typically applied to forest ecosystems on mineral soils in conjunction with a base cation to aluminium (Bc:Al) ratio using a default critical limit of 1.0. The ‘typical’ approach has been expanded in this paper by: inclusion of a broader range of natural and semi-natural receptor ecosystems; inclusion of multiple chemical criterion for each receptor; and an attempt to include organic soils (peatlands). Critical loads of acidity were estimated for the Republic of Ireland using four receptor ecosystems (coniferous forest, deciduous forest, natural grasslands and moors and heathlands) and seven chemical criteria. The dominant chemical criteria, in the determination of critical loads, were based on a critical pH limit for mineral soils or a critical pH shift in relation to pristine conditions for organic soils. Approximately 68 and 26% of the final distribution of critical loads were estimated using these criteria, respectively. The 5th-percentile critical loads of acidity were more sensitive than those previously estimated for Ireland due to the inclusion of organic soils. Furthermore, coniferous ecosystems had the lowest critical loads due to the high percentage occurring on organic soils, and the removal of base cations through harvesting. The results demonstrate that it may be more appropriate to use multiple criteria and receptors to ensure adequate protection of biological indicators. However, it is important that appropriate critical limits are chosen to protect the biological indicators and receptor ecosystems from long-term damage.

Dynamic cost-effective reduction strategies for acidification in Europe : An application to Ireland and the United Kingdom

This paper describes the application of an optimisation model for calculating cost-effective abatement strategies for the reduction of acidification in Europe while taking into account the dynamic character of soil acidification in a number of countries. Environmental constraints are defined in terms of soil quality indicators, e.g., pH, base saturation or the aluminium ion concentration in the soil solution within an optimisation model for transboundary air pollution. We present a case study for Ireland and the United Kingdom. Our results indicate that reduction of sulphur dioxide emission is more cost-effective than that of nitrogen oxides or ammonia. The reduction percentages for sulphur dioxide are highest, for two reasons: (i) marginal sulphur dioxide reduction costs are relatively low compared to marginal reduction costs of nitrogen oxides and ammonia and (ii) sulphur dioxide reduction is more effective in reducing acidification in physical terms than nitrogen oxides or ammonia abatement. Our dynamic analysis shows that a (fast) improvement of soil quality requires high emission reduction levels. These reduction levels are often higher than reduction levels that are typically deduced from the static critical loads approach. Once soil quality targets are reached, in our model, less stringent emission reductions are required to maintain the soil quality at a constant and “good” target level. Static critical load approaches that ignore dynamic aspects therefore may underestimate the emission reductions needed to achieve predefined soil quality targets.

Some phenomena for lateral flutter of beams under follower load

Abstract Simple model of a slender beam loaded by a transverse follower force and undergoing a lateral flutter is used to demonstrate the following phenomena: 1. If an analysis does not include any damping, an extraction of only two lowest eigenvalues can lead to a wrong conclusion that the critical load is infinite. This is so because, when the ratio of two principal rigidities of a beam is not small, the eigenvalue with a positive real part emerges first not at the very beginning of the spectrum. 2. For the Kelvin-type material, and with no external damping, the critical load becomes infinitely small when the damping in the normal stress vanishes while the shear stress damping is finite. 3. When the external damping is increased, the critical load approaches the value calculated with no internal damping. The nonlinear equilibrium is presented in the closed form and the eigenvalues of the torsional–flexural dynamic perturbed equations are found by the finite element approach and subdomain collocation method.

The role of forest management in controlling diffuse pollution in UK forestry

Forests and forest management practices have been identified as potentially important non-point sources of water pollution in upland areas of the United Kingdom. The major water quality concerns are recognised as being: increased turbidity and sedimentation due to the soil disturbance accompanying cultivation, drainage, road construction and harvesting operations; increased phosphate concentrations following aerial applications of fertiliser leading to eutrophication of standing waters; and the enhanced capture of acid deposition by forest canopies resulting in further acidification of surface waters. In order to address these concerns the UK Forestry Commission introduced their ‘Forests and Water Guidelines’ in 1988. The guidelines were prepared by a joint forest and water industry working group and provide advice on working methods and measures that should be taken to ensure that forests not only protect, but also enhance the freshwater environment. This paper reviews the evidence from recent studies in the UK designed to test the efficacy of the guidelines in practice. Results demonstrate that best management practices can be very effective in limiting soil erosion, and so preventing unacceptable increases in turbidity and sedimentation within watercourses. Technological improvements have allowed better targeting of aerial fertiliser applications and, when combined with protective measures such as riparian buffer strips, have helped to reduce the threat of nutrient enrichment. There has also been significant progress in tackling the acidification issue with the critical loads approach being used to identify those areas at risk from a forest acidification effect. Results to date from long-term studies provide support for this approach, although further testing is required. It is concluded that the ‘Forests and Water Guidelines’ appear to be effective in controlling the threat of diffuse pollution from forestry in the UK.

Acidification in developing countries: ecosystem sensitivity and the critical load approach on a global scale.

Acidification represents a growing threat to certain developing country ecosystems in tropical and subtropical climates. A methodology investigating the extent of acidification risks from sulfur emissions on a global scale is presented. Atmospheric transfer models have been used to calculate transfer and deposition of sulfur (using emissions for 1990 and a projection for 2050) and alkaline soil dust. A method to derive the relative sensitivity of terrestrial ecosystems is explained and preliminary critical load values are assigned. A range of values for critical loads and base cation deposition have been used to investigate uncertainty in maps depicting the excess of deposition above critical loads. These show an increasing risk of acidification in 2050 in extended regions of southern and eastern Asia, as well as parts of southern Africa, in comparison to 1990. Certain areas, especially in Asia, are shown at risk even when high values of critical load and base cation deposition are used.

Acidification in Developing Countries: Ecosystem Sensitivity and the Critical Load Approach on a Global Scale

Acidification in Developing Countries: Ecosystem Sensitivity and the Critical Load Approach on a Global Scale

Modelling Acidic Deposition in the United Kingdom at a Scale of 5 Km by 5 Km

This paper discusses the use of a long-term Lagrangian receptor-oriented trajectory model for assessing acidic deposition to the United Kingdom at high spatial resolution. Previously, a coarse resolution of 20 km was used. Impact assessments using the critical loads approach now require higher-resolutions of modelled data for future scenarios. In this paper, first results from a higher resolution of 5 km using a revised parameterization of orographic enhancement of the seeder-feeder effect. It was found that country budgets for the two different model resolutions were in good agreement and compared well with observations, except in the far north of Scotland where the straight-line trajectory approach is less valid.

Epistemic communities, collective entrepreneurship and European integration

This article investigates the conditions under which epistemic communities define the preferences of European Union (EU) policy-makers. The paper examines how one epistemic community, using the critical loads approach, has influenced EU acid rain policy.The article contends that actors seeking to change EU policy must pursue collective entrepreneurship. Epistemic communities can provide such entrepreneurship, but they only operate in very defined circumstances.

Using Multiple Chemical Criteria for Critical Loads of Acidity in Maritime Regions

Critical loads have become a well-establishedpart of the work programme of the UnitedNations Economic Commission for Europe (UNECE) Conventionon Long-Range Transboundary Air Pollution (CLRTAP). Thelinking of ecosystem response to deposition level is thecentral principal of the critical loads approach. Foreach ecosystem, a biological indicator is chosen, asuitable chemical criterion selected and a criticalchemical limit assigned. The Bc:Al ratio is the mostwidely used chemical criterion for setting criticalloads. However, critical loads based on this criterionare very sensitive to marine deposition. In regions whichreceive high depositions of marine-derived base cations,such as the Republic of Ireland (ROI) and the UnitedKingdom (UK), critical loads based on the Bc:Al criterionwill inevitably be high. Therefore, it is proposed thatcritical loads are estimated using multiple chemicalcriteria with appropriate critical limits to protect thechosen biological indicators. The range of publishedchemical criteria have been applied to the ROI and theUK. The chemical criterion corresponding to the mostsensitive critical load have been mapped and thecontribution of each to the final maps investigated. Thesimulations indicate that the most sensitive criteria forsetting critical loads are based on specifying critical Hor Al concentrations. However, the choice of critical limits andmodel parameters will ultimately effect the criticalloads. Therefore, it is important that appropriate criticallimits are chosen to protect the biological indicator andreceptor ecosystem from long-term damage.

VARIABILITY IN THREE FINNISH INTEGRATED ACIDIFICATION MODELS

Integrated assessment models have been used to support ofnegotiations for further emission reductions of acidifyingcompounds in Europe. More attention is being paid to theuncertainties in integrated models. Data from three Finnishintegrated acidification models were compiled to estimate thevariation and relative importance of different modules. Themodels included site-specific and regional dynamic simulationsand steady-state critical load calculations for forest soilsand lakes. The main emphasis was on the variability ofemissions and the uncertainties in ecosystem effects. Althoughmaximum technically feasible emission reduction measures cantheoretically result in very low deposition, the variabilitybetween realistic scenarios is rather restricted. Thevariability of deposition loading is largely determined byreductions in nearby emission sources. The dynamicsimulations, which are often based on detailed input data,seem to retain larger variability than steady-state criticalload approaches. This study suggests that the uncertainties ineffects seem to be larger generally than other modules ofintegrated acidification models. The results indicate the needfor further work on uncertainty analysis for integrated modelsand the availability of useful model systems for furtherconfirmation of ecosystem effects.

Modelling the spatial distribution of SO 2 and NO x emissions in Ireland

The spatial distributions of sulphur dioxide (SO 2) and nitrogen oxides (NO x ) emissions are essential inputs to models of atmospheric transport and deposition. Information of this type is required for international negotiations on emission reduction through the critical load approach. High-resolution emission maps for the Republic of Ireland have been created using emission totals and a geographical information system, supported by surrogate statistics and landcover information. Data have been subsequently allocated to the EMEP 50×50-km grid, used in long-range transport models for the investigation of transboundary air pollution. Approximately two-thirds of SO 2 emissions in Ireland emanate from two grid-squares. Over 50% of total SO 2 emissions originate from one grid-square in the west of Ireland, where the largest point sources of SO 2 are located. Approximately 15% of the total SO 2 emissions originate from the grid-square containing Dublin. SO 2 emission densities for the remaining areas are very low, <1 t km −2 year −1 for most grid-squares. NO x emissions show a very similar distribution pattern. However, NO x emissions are more evenly spread over the country, as about 40% of total NO x emissions originate from road transport.

00/03011 Residential end-use electricity demand: results from a designed experiment

The spatial distributions of sulphur dioxide (SO2) and nitrogen oxides (NOx) emissions are essential inputs to models of atmospheric transport and deposition. Information of this type is required for international negotiations on emission reduction through the critical load approach. High-resolution emission maps for the Republic of Ireland have been created using emission totals and a geographical information system, supported by surrogate statistics and landcover information. Data have been subsequently allocated to the EMEP 50×50-km grid, used in long-range transport models for the investigation of transboundary air pollution. Approximately two-thirds of SO2 emissions in Ireland emanate from two grid-squares. Over 50% of total SO2 emissions originate from one grid-square in the west of Ireland, where the largest point sources of SO2 are located. Approximately 15% of the total SO2 emissions originate from the grid-square containing Dublin. SO2 emission densities for the remaining areas are very low, <1 t km−2 year−1 for most grid-squares. NOx emissions show a very similar distribution pattern. However, NOx emissions are more evenly spread over the country, as about 40% of total NOx emissions originate from road transport.

U.S. report strengthens scientists' call for a critical load approach to controlling acid rain

U.S. report strengthens scientists' call for a critical load approach to controlling acid rain

Modeling, mapping, and managing critical loads for forest ecosystems using a geographic information system: Approach of Wallonia, Belgium, to the study of long-range transboundary air pollution effects on ecosystems in Europe

This critical load approach has been developed to guide policies aimed at reducing atmospheric pollutant emissions as part of the Geneva Convention on Long-Range Transhoundary Air Pollution (CLRTAP). Belgium, and more precisely the Walloon region, fit into this policy. To the best of our knowledge, the critical load for an ecosystem is defined as the maximal amount of one or more pollutant deposits below which no harmful impact appears in the ecosystem. The assessment method chosen for the Walloon region and tested during its forest ecosystem surveys is based on a simple mass balance model. This model involves management of much spatial data and, therefore, requires implementation of a geographic information system. This work has allowed the Walloon region to participate in ongoing CLRTAP negotiations and has provided an important tool with which to construct regional strategies to reduce the levels of acid pollutants.

Critical loads of sulphur and nitrogen for freshwaters in Great Britain and assessment of deposition reduction requirements with the First-order Acidity Balance (FAB) model

Abstract. The critical loads approach is widely used within Europe to assess the impacts of acid deposition on terrestrial and freshwater ecosystems. Recent work in Great Britain has focused on the national application of the First-order Acidity Balance (FAB) model to a freshwaters dataset of 1470 lake and stream water chemistry samples from sites across Britain which were selected to represent the most sensitive water bodies in their corresponding 10 km grid square. A ``Critical Load Function" generated for each site is compared with the deposition load of S and N at the time of water chemistry sampling. The model predicts that when catchment processes reach steady-state with these deposition levels, increases in nitrate leaching will depress acid neutralizing capacity (ANC) below the critical threshold of 0 μeql-1 at more than a quarter of the sites sampled, i.e. the critical load of acid deposition is exceeded at these sites. The critical load exceedances are generally found in upland regions of high deposition where acidification has been previously recognised, but critical loads in large areas of western Scotland are also exceeded where little biological evidence of acidification has yet been found. There is a regional variation in the deposition reduction requirements for protection of the sampled sites. The FAB model indicates that in Scotland, most of the sampled sites could be protected by sufficiently large reductions in S deposition alone. In the English and Welsh uplands, both S and N deposition must be reduced to protect the sites. Current international commitments to reduce S deposition throughout Europe will therefore be insufficient to protect the most sensitive freshwaters in England and Wales. Keywords: critical loads; acidification; nitrate; FAB model; acid deposition

Dynamics of soil acidification: an economic analysis

This paper studies the dynamic aspects related to the problem of acidification. It shows how accumulation of acidification in ecosystems can be studied in economic modelling by incorporating dynamic aspects of soil acidification. In contrast to the often applied critical loads approach which only focuses on the final state of a soil, the dynamic approach applied in this study gives information about the temporal development of the quality of a soil. Using an economic optimal control model containing these dynamic aspects the paper compares abatement policies based on static critical loads to abatement policies based on a dynamic analysis. It shows that soil dynamics play an essential role in identifying optimal policies. Based on numerical simulations cost-effective abatement strategies for combined reduction of sulphur dioxide (SO 2) and nitrogen oxides (NO x ) are determined. It is also shown that abatement cost savings may be realised when intertemporal cost efficiency is taken into account. The results indicate that current European policies which are based on a critical loads approach instead of dynamic analysis of soil quality, are non-optimal from both an ecological and an economic point of view.