The Applicability of National Critical Loads Data in Assessing Designated Sites

Critical loads have been successfully used within Europe in the development of effects-based policies for pollution abatement, including the Second Sulphur Protocol and the Protocol to abate acidification, eutrophication and ground-level ozone (CLRTAP, 1979). This success has encouraged the UK Environment Agency and Conservation Agencies to use the national critical load maps as a screening tool in assessing the threats from acidification and eutrophication to designated (Natura 2000) sites. The UK maps of critical loads are based on national-scale data sets appropriate for national-scale assessments, and were never intended for use at the site-specific level. Site-based assessments are often targeted at Special Areas of Conservation, a sub-set of the UK Natura 2000 sites. The spatial data available includes the boundaries of the sites but not the location of the designated features. Ancillary data is variable from one site to another; habitat types may be described in detail with cross-reference to classes of the National Vegetation Classification (NVC: Rodwell, 1991 et seq), but information available on soils and geology is generalised and has not been related to the habitats or species being protected. Hence it can be difficult to relate the individual sites to the national maps, even where appropriate to do so. This paper examines the underlying uncertainties in the national critical load maps showing how the maps could give misleading results if used for site-specific assessments. It also includes advice on how to determine when the national data may be appropriate as a policy-tool at the site-level.     

The Development of a GIS-based Inventory of Standing Waters in Great Britain together with a Risk-based Prioritisation Protocol

An inventory of standing waters (freshwater lakes and lochs) wasderived from Ordnance Survey digital map data at a scale of 1:50 000 and represents the most comprehensive survey of its kind for Great Britain. The inventory includes 43 738 water bodies in England, Scotland, Wales and the Isle of Man and contains basic physical data such as location, surface area, perimeter and altitude. Catchment areas were computed for water bodies with a surface area larger than 1 ha from a digital terrain model (DTM) using customised routines in a geographical information system (GIS). The resulting polygons were then used to derive catchment-related information from a variety of national datasets including population density, livestock density, land cover, solid and drift geology, meteorological data, freshwater sensitivity status, acid deposition and conservation status. Using data derived from the inventory a risk-based prioritisation protocol was developed to identify standing waters at risk of harm from acidification and eutrophication. This information is required by the Environment Agency, Scottish Environmental Protection Agency and the U.K. statutory conservation bodies to co-ordinate actions and monitor change under international, European and national legislation.     

Uncertainties in Large Scale Assessments of Critical Load Exceedances

In the 1999 Gothenburg protocol to the UN/ECE LRTAP Convention andin the negotiations for an EU acidification strategy the area withexceedances of critical loads has been the preferred measure forenvironmental impacts. The aim of this study has been to assessthe influence of the uncertainty and spatial variation of both thecritical loads and deposition values on the calculated area withexceedances of critical loads. This has been done on a nationalscale for Denmark and on the European scale based on the dataincluded in the RAINS model. It is demonstrated that includinguncertainty and spatial variation in exceedance calculations, ingeneral gives larger exceeded area for the critical load ofacidity, CL(A). The picture for the critical load of nutrientnitrogen, CL_nut(N), is more mixed because of the higherproportion of exceeded areas. A further point of interest is thepossibility of validating relationships between critical loadexceedances and observable damage based on large scale monitoringand model data. It is demonstrated that it will probably not bepossible to use exceedance calculations on European scale as basisfor validation exercises, linking exceedances to observable 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.     

The Link Between the Exceedance of Acidity Critical Loads for Freshwaters,Current Chemical Status and Biological Damage: A Re-Interpretation

Critical loads have for several years been employed bypolicymakers to aid in the development of strategies for aciddeposition abatement. They provide an effects-based approachwhereby an acid deposition flux greater than the critical load(known as critical load exceedance) implies that long-termharmful effects on a selected target organism will occur.Implicit in this approach are two assumptions: first, theexceedance of a critical load will harm the target organism,and second, the severity of biological impact is related to themagnitude of exceedance. However, static models give noindication of when the predicted damage might occur. One suchmodel, the Steady-State Water Chemistry (SSWC) model, employs aseries of empirical relationships to derive the pre-industrial,baseline leaching rate of base cations from measured waterchemistry using the so-called `F-factor'. The SSWC model setsthe critical load relative to pre-industrial base cationleaching (a permanent buffer of acid deposition) and a selectedacid neutralizing capacity (ANC) value which corresponds with aknown likelihood of damage to a biological target organism.Here we interpret the meaning of critical load exceedance as aprediction of steady-state ANC, and explore the relationshipbetween exceedance of the critical load and current chemistry. We demonstrate that a critical loadexceedance with the SSWC model does not necessarily indicatethat the critical chemical threshold (zero ANC) has alreadybeen crossed, and there may be no correlation betweenexceedance and biological status. A reformulation of the SSWCmodel is proposed which provides a direct link between currentdeposition and current chemical conditions, and is thereforemore likely to indicate current biological damage. Thereformulation illustrates the discrepancy between currentchemical status and that predicted by the SSWC model atsteady-state, which is a function of the `F-factor'.     

Deposition Loads of Sulphur and Nitrogen in Germany

High spatial resolution maps of deposition loads in Germanyare produced as an input for abatement strategy research andfor critical loads exceedance calculations on a nationalscale. In this paper methods ofmapping total deposition loads in Germany and preliminarymaps of nitrogen and sulphur deposition loads for the year1993 are presented. A comparison of these mapping resultswith EMEP deposition mapping results has been carried out.The differences in the results of the German national and theEuropean EMEP mapping, due to different databases anddifferent methods, are quantified and discussed. Highresolution maps of deposition loads are compared to Europeanlow resolution maps on the same temporal and spatial scale,assuming that on average both should lead to similar results.However, the average differencescalculated for 23 EMEP 150 × 150 km² grid cells over Germanywere found to be 33% higher for sulphur (S) total depositionby the German method 65% higher for S dry deposition and1% lower for S wet deposition. The German results fornitrogen (N) total deposition are 2% higher than the EMEPresult 22% higher for N dry deposition and 10% lower for Nwet deposition.     

The Use of a GIS-based Inventory to Provide a Regional Risk Assessment of Standing Waters in Great Britain Sensitive to Acidification from Atmospheric Deposition

Previous attempts to identify regions of Britain vulnerable to acidification have used sensitivity maps based on the distributionof soils, geology, and land cover across Great Britain. Additionally, a systematic survey of freshwaters undertaken as partof the U.K. critical loads mapping programme provides a regional assessment of both sensitivity (critical loads) and, in tandem withdeposition data, potential impact (critical load exceedance). Both approaches, while useful for identifying regional patterns, do not enable estimates of the number of affected water bodies to be made. Recent EU legislation (e.g., The Water Framework Directive) requires member states to set water quality objectives for all water bodies. We developed a GIS-based inventory of standing water bodies in response to the need for legislation-driven assessments of the status of the U.K. lake population. This paper describes how the inventory can be used to assess the number of standing water bodies in Britain that are vulnerable to acid deposition (at current levels), building on the sensitivity mapping undertaken previously. Using this approach, approximately 31% of all standing waters in Great Britain (excluding the Shetlands and Orkney) larger than 0.02 ha are identified as `at risk' from acidification. Higher proportions are vulnerable in Scotland and Wales. Additionally, large numbers of standing waters in areas designated for environmental protection purposes are also vulnerable.     

Critical Loads and Exceedances of Acid Deposition and Associated Forest Growth in the Northern Hardwood and BorealConiferous Forests in Québec,Canada

We used the Québec forest monitoring network (`Réseaud'Étude et de Surveillance des Écosystèmes Forestiers' or RESEF)along with its atmospheric monitoring stations to assess criticalS and N loads and their combined soil acidification exceedancesfor natural ecosystems of the northern hardwood and borealconiferous forests in Québec, Canada. Critical loads (CL) forforest soil acidification were calculated using the simple mass-balance (SMB) approach and with the steady-state PROFILE model.Atmospheric deposition rates for water, S, N, Ca, Mg, Na, and K,for the years 1989–1993, and detailed, plot-specific forest andsoil characteristics were used as input. The SMB model alsorequired information regarding nutrient uptake and storage in theaboveground woody biomass. The CL calculations indicated that,from the 31 RESEF plots, 18 received atmospheric acidic inputs inexcess of their CL (55 and 61% of the hardwood and coniferousplots, respectively). The range of CL exceedance varied from 60to 470 eq ha^-1 yr^-1 for the hardwood stands, and from 10to 590 eq ha^-1 yr^-1 for the coniferous stands. The standswith CL exceedance were mainly located in the western and centralpart of the province. Stand growth associated with exceedanceclass of acidity was determined using the RESEF plots along withselected permanent forest survey plots having similar sitecharacteristics, but for which longer growth records wereavailable. We found a significant negative correlation betweenforest growth rates and critical soil acidification exceedancefor both the northern hardwood and the boreal conifer sites.Specifically, plots with critical load exceedances were found tohave a growth reduction of about 30% during the 1974–1982 andthe 1972–1990 measurement (plots with no soil acidificationexceedance served as a control). While this correlation is notnecessarily causal, it is nevertheless consistent with theexpectation that increased losses of soil base cations on accountof increased soil acidification should and could lead todeteriorating forest health conditions.     

The UN/ECE International Programme on Mapping Critical Loads and Levels

Critical Loads and levels have played a centralrole in the successful development of effect-based emissionreduction strategies for Europe in the fields of acidification,eutrophication and ground-level ozone. The aim of theInternational Programme on Mapping Critical Loads and Levelsled by Germany, with participation of 24 countries, is todetermine critical loads and levels for forest, crops, naturalvegetation, soils, water and materials. The exceedances ofcritical loads and critical levels are used to quantify the riskfor environmental damage by air pollution and tosupport the development of optimised abatement strategies.     

Critical Loads of Acidity for Forest Soils: Tentative Modifications

We reviewed the current methods for calculatingcritical loads of acidity for forest soils. The consequencesof four sets of assumptions concerning the soil modelstructure, parameter values and the critical loads criterionwere explored by comparing the values of the averageaccumulated exceedance (AAE) calculated for Finland withdeposition values for the year 1995. The AAE index is given inthe unit of deposition and is a measure of how far a region isfrom being protected in terms of fulfilling a certaincriterion, taking into account the size of the ecosystem areas.Using a critical limit for the molar ratio of theconcentrations of base cations to aluminium in soil solutiongave the lowest average accumulated exceedance. Assumingorgano-aluminium complexes and leaching of organic anions gaveAAE = 4 eq ha^-1 a^-1, which was close to the valueobtained with the standard approach used in Finland, assuminggibbsite equilibrium and no leaching of organic anions,yielding AAE = 5 eq ha^-1 a^-1. With a critical basesaturation limit, instead of the concentrations criterion, theAAE index was 17 eq ha^-1 a^-1. The highest averageaccumulated exceedance (AAE = 25 eq ha^-1 a^-1),corresponding to the lowest critical load, was obtained whenthe effects-based criterion (critical concentration or criticalbase saturation) was substituted with one restricting thedeterioration of the neutralizing capacity of the soil, ANC _le(crit) = 0. These tests illustrate the variabilityof the critical load values for acidity that can be introducedby changing the criterion or by varying the calculation method,without, however, representing the extreme values of criticalloads that could be derived.     

Freshwater Critical Loads in Wales

The Steady State Water Chemistry (SSWC) modeland the Diatom model have been used to calculate criticalloads for acidity using annual mean chemistry for 102 acidupland streams in Wales sampled as part of the Welsh AcidWaters Survey (WAWS) in 1995. Diatom critical loads werelower than SSWC values reflecting the higher effective[ANC]_limit of the Diatom model compared to the[ANC]_limit of zero used in the SSWC model. The WAWSstream sites were all located within 41 10 × 10 km squares andeach square was assigned the lowest critical load value fromamongst the sites located within it. Comparison with valuesassigned under the UK national critical loads mappingprogramme (UKCLMAP) showed that WAWS critical loads were lowerthan UKCLMAP values in approximately 40% of squares.Differences in critical load class were variable, but exceeded2 keq ha^-1 yr^-1 in up to a maximum of seven squares.It cannot be assumed, therefore, that reducing acid depositionto the currently mapped UKCLMAP critical load will protect allstreams occurring within a given 10 × 10 km grid square inWales. The limited number of sample sites means that even inthose squares where all WAWS sites will be protected, theremay be other, more acid sensitive freshwaters with lowercritical loads. This has important implications for theinterpretation and use of critical loads data for regional andlocal environmental planning.     

A Novel Method for Mapping Critical Loads Across a River Network: Application to the River Dart,Southwest England

To date, estimates of freshwater critical loads have beenbased on a single sample site within a given area, in theUK the `most sensitive' surface water in each 10 km gridsquare. The critical loads obtained are thus highlydependent on the sites chosen, and at a relatively coarsespatial resolution. To produce a higher resolutioncritical load assessment, the PEARLS (Prediction ofAcidification and Recovery on a Landscape Scale)procedure has been used to estimate critical loads acrossa large (248 km²), partially acid-sensitivecatchment in Southwest England. PEARLS utilises availablesoils and land-use databases, and sampled streamchemistry data, to derive characteristic runoffcompositions for a set of landscape types. Mixingequations are then used to calculate runoff chemistry,and subsequently critical loads, throughout the streamnetwork. Results show major spatial variability, withcritical loads lowest in streams draining peat-moorlandheadwaters, and generally increasing downstream asagricultural land contributes an increasing proportion ofrunoff. The 5th percentile freshwater critical loadfor the catchment is estimated at 0.29 keq H⁺ ha^-1yr^-1,and critical loads are exceeded for around 40% of totalstream length. The PEARLS methodology provides a novelopportunity to assess the spatial variability infreshwater critical loads, and to provide estimates ofexceedance at whole catchment scale. It has potentialapplication in the assessment of surface watersensitivity to acidification across wider areas in the UKand elsewhere.     

Application of the operating window concept to remediation‐option selection

An Erratum has been published for this article in Remediation 14(4) 2004, 141. The selection of remediation options for the management of unacceptable risks at contaminated sites is hindered by insufficient information on their performance under different site conditions. Therefore, there is a need to define “operating windows” for individual remediation options to summarize their performance under a variety of site conditions. The concept of the “operating window” has been applied as both a performance optimization tool and decision support tool in a number of different industries. Remediation‐option operating windows could be used as decision support tools during the “options appraisal” stage of the Model Procedures (CLR 11), proposed by the Environment Agency (EA) for England and Wales, to enhance the identification of “feasible remediation options” for “relevant pollutant linkages.” The development of remediation‐option operating windows involves: 1) the determination of relationships between site conditions (“critical variables”) and option performance parameters (e.g., contaminant degradation or removal rates) and 2) the identification of upper‐ and lower‐limit values (“operational limits”) for these variables that define the ranges of site conditions over which option performance is likely to be sufficient (the “operating window”) and insufficient (the “operating wall”) for managing risk. Some research has used case study data to determine relationships between critical variables and subsurface natural attenuation (NA) process rates. Despite the various challenges associated with the approach, these studies suggest that available case study data can be used to develop operating windows for monitored natural attenuation (MNA) and, indeed, other remediation options. It is envisaged that the development of remediation‐option operating windows will encourage the application of more innovative remediation options as opposed to excavation and disposal to landfill and/or on‐site containment, which remain the most commonly employed options in many countries. © 2004 Wiley Periodicals, Inc.     

On the Calculation and Interpretation of Target Load Functions

In this study critical load functions and target load functions of nitrogen and sulphur deposition with respect to acidity and minimum base cation to aluminium ratio were calculated with the SAFE model using three different averaging strategies: (1) averaging based on current forest generation, (2) averaging based on next generation and (3) averaging based on the entire simulation period. From the results it is evident that although target load calculation and indeed critical load calculation is straight forward, there is a problem in translating a predicted recovery according to the target load calculation back to a site-specific condition. We conclude that a policy strategy for emission reductions that ensures recovery, according to calculated target load functions, is likely to be beneficial from an ecosystem point of view. However, such a strategy may not be sufficient to achieve actual non-violation of the chemical criteria throughout the seasonal or rotational variations. To address this issue we propose a method for calculating dynamic critical loads which ensures that the chosen criteria is not violated.     

Application of Static Critical Load Models for Acidity to High Mountain Lakes in Europe

Critical load models for acidityprovide a measure of the sensitivity of surfacewaters to acid deposition, and can be used todetermine critical load exceedance and potentiallong-term harmful effects. Three static models,the Steady-State Water Chemistry model, diatommodel and First-order Acidity Balance model, arehere applied to 11 high mountain lakes in Norway,Scotland, the Alps, the Pyrenees and the Tatras.Between five and seven of the lakes show criticalload exceedance, depending on the model used.Nitrogen as well as sulphur deposition isimportant in causing exceedance. Since soil andvegetation cover are generally sparse, geologyand lake retention time appear to be key factorsin the determination of critical load. Retentionof nitrogen is observed, but it is unclearwhether this occurs within the lake or theterrestrial part of the catchment.     

An Analysis of the Structure of the Simple Mass Balance Equation: Implications for Testing National Critical Loads Maps

The critical loads concept is used by the UN-ECEConvention on Long Range Transboundary Air Pollution(CLRTAP) for setting pollution reduction targets.Increasing numbers of countries are adopting the SimpleMass Balance equation (SMB) to calculate critical loads ofacidifying S and N for forest soils. The equation is madeup of a series of mass balances each of which is used tocalculate a leaching flux. The assumptions in the SMBequation were investigated by testing its ability topredict current sulphur load and by comparing each of thecalculated leaching fluxes to measured rates. It was notpossible to predict current sulphur load at our sites usingthe SMB equation. The leaching tests demonstrated that,primarily due to its steady state assumptions, the SMBequation generates critical loads that are theoretical longterm estimates of risk, and are untestable. Thesimplifying assumptions sometimes lead to illogicalresults. Some of these can be improved by adding a final,simple but dynamic, calculation step to determine theexpected time until effects are observed. Theacceptability of combining annual average data, which bestapproximates steady state, with a biological indicator isquestionable. It is not possible to test critical loadscalculated using the SMB equation when applied with all ofits assumptions but it is possible to test its fundamentalapproach using non steady state data.     

Modeling Acidification Recovery on Threatened Ecosystems: Application to the Evaluation of the Gothenburg Protocol in France

To evaluate the acid deposition reduction negotiated for 2010 within the UNECE LRTAP Gothenburg Protocol, sulphur and nitrogen deposition time-series (1880–2100) were compared to critical loads of acidity on five French ecosystems: Massif Central basalt (site 1) and granite (2); Paris Bassin tertiary sands (3); Vosges mountains sandstone (4) and Landes eolian sands (5). The SAFE model was used to estimate the response of soil solution pH and ratio to the deposition scenario. Among the five sites, critical loads were exceeded in the past at sites 3, 4 and 5. Sites 3 and 4 were still expected to exceed in 2010, the Protocol year. Further reduction of atmospheric deposition, mainly nitrogen, would be needed to achieve recovery on these ecosystems. At sites 3, 4 and 5, the delay between the critical load exceedance and the violation of the critical chemical criterion was estimated to be 10 to 30 years in the top soil and 50 to 90 years in the deeper soil. At site 5, a recovery was expected in the top soil in 2010 with a time lag of 10 years. Unexpectedly, soil pH continued to decrease after 1980 in the deeper soil at sites 2 and 5. This time lag indicated that acidification moved down the soil profile as a consequence of slow base cation depletion by ion exchange. This delayed response of the soil solution was the result of the combination of weathering rates and vegetation uptake but also of the relative ratio between base cation deposition and acid compounds.     

Comparison of first-order-decay modeled and actual field measured municipal solid waste landfill methane data

The first-order decay (FOD) model is widely used to estimate landfill gas generation for emissions inventories, life cycle assessments, and regulation. The FOD model has inherent uncertainty due to underlying uncertainty in model parameters and a lack of opportunities to validate it with complete field-scale landfill data sets. The objectives of this paper were to estimate methane generation, fugitive methane emissions, and aggregated collection efficiency for landfills through a mass balance approach using the FOD model for gas generation coupled with literature values for cover-specific collection efficiency and methane oxidation. This study is unique and valuable because actual field data were used in comparison with modeled data. The magnitude and variation of emissions were estimated for three landfills using site-specific model parameters and gas collection data, and compared to vertical radial plume mapping emissions measurements. For the three landfills, the modeling approach slightly under-predicted measured emissions and over-estimated aggregated collection efficiency, but the two approaches yielded statistically equivalent uncertainties expressed as coefficients of variation. Sources of uncertainty include challenges in large-scale field measurement of emissions and spatial and temporal fluctuations in methane flow balance components (generated, collected, oxidized, and emitted methane). Additional publication of sets of field-scale measurement data and methane flow balance components will reduce the uncertainty in future estimates of fugitive emissions.     

Environmental effects of heavy metals derived from the e-waste recycling activities in China: A systematic review

As the world’s leading manufacturing country, China has become the largest dumping ground for e-waste, resulting in serious pollution of heavy metals in China. This study reviews recent studies on environmental effects of heavy metals from the e-waste recycling sites in China, especially Taizhou, Guiyu, and Longtang. The intensive uncontrolled processing of e-waste in China has resulted in the release of large amounts of heavy metals in the local environment, and caused high concentrations of metals to be present in the surrounding air, dust, soils, sediments and plants. Though the pollution of many heavy metals was investigated in the relevant researches, the four kinds of heavy metals (Cu, Pb, Cd and Cr) from e-waste recycling processes attracted more attention. The exceedance of various national and international standards imposed negative effects to the environment, which made the local residents face with the serious heavy metal exposure. In order to protect the environment and human health, there is an urgent need to control and monitor the informal e-waste recycling operations.     

The Role of Mineral Weathering Rate Determinations in Generating Uncertainties in the Calculation of Critical Loads of Acidity and their Exceedance

Current legislation within Europe aimed at limitingecosystem damage resulting from inputs of atmosphericpollution is based on the critical load concept. Mineralweathering rates are central to the calculation ofcritical loads (acceptable levels) of acid deposition.The authors have undertaken a number of studies whichillustrate the complications and limitations inherent inpredicting mineral weathering rates and the implicationswhich these have for critical loads calculations andmapping. Calculated weathering rates and critical loadsfor two acid-sensitive parent materials (greywackes andgranites) are presented and are used to illustrate theimpact that uncertainty can have on critical loadexceedances. The results have obvious implications forportraying the uncertainties of critical loads to policy makers.