Scaling and Mapping Regional Calculations of Soil Chemical Weathering Rates in Sweden

Weathering rates of base cations are crucial in critical load calculations and assessments of sustainable forestry. The weathering rate on a single site with detailed geological data can be modelled using the PROFILE model. For environmental assessments on a regional scale, the weathering rates for sites are scaled into regional maps. The step from sites to regional level requires focus on the spatial variation of weathering rates. In this paper, a method is presented by which weathering rates are calculated for 25589 Swedish sites with total elemental analysis for the soil. Based on a part of the results, a methodology for creating area covering maps by geostatistical analysis and kriging is described. A normative reconstruction model was used to transform total elemental analysis to mineralogy. Information from the Swedish Forest Inventory database and other databases were used to derive texture and other important information for the sites, e.g. climate, deposition and vegetation data. The calculated weathering rates show a regional pattern that indicates possibilities for interpolation of data in large parts of Sweden. Geostatistical analysis of an area in southern Sweden shows different properties for different base cations. Kriging was performed for potassium to demonstrate the method. It was concluded that different base cations and different regions have to be analysed separately, in order to optimise the kriging method.     

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.     

Why Critical Loads of Acidity and N for Soils Should be Based on Pollutant Effective Concentrations Rather Than Deposition Fluxes

Numerous assumptions have been made over the past 17 years when calculating critical loads for soils, both for acidity (based upon base cation steady state mass balances (SMB)) and for N (eutrophication, based upon N mass balances), often without all the assumptions being explicitly stated. The tacit assumptions that the author believes to be implicit in the SMB approach are critically reviewed, with particular reference to upland regions where slope processes are highly significant. It is concluded that many of them cannot be justified, especially those that involve ignoring many key processes known to be important to biogeochemical cycling and soil evolution in upland catchments. The evidence presented suggests that critical loads of acidity and of N for soils should be based upon effective pollutant and, for acidity, also effective base cation deposition concentrations, rather than upon pollutant deposition fluxes. This is because of the dominant role of cation exchange equilibria, rather than weathering rate, in regulation of the pH and base status of the more acidification-sensitive soils, and because of the importance of transport down slope of base cations, alkalinity and N species.     

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.     

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.     

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.     

Critical Loads of Acidity for Surface Waters in South-Central Ontario, Canada: Regional Application of the First-Order Acidity Balance (FAB) Model

Major sulphur emission control programs have been implemented in North America, resulting in current emissions being ～30% less than those in 1980. However, the level of acidic deposition remaining is still unlikely to promote widespread recovery of aquatic ecosystems. The First-order Acidity Balance (FAB) model has been applied to south-central Ontario (285 lakes in the Muskoka River Catchment) to evaluate the need for further reductions in emissions. As a result of the past decline in deposition, the proportion of lakes with critical loads exceedance has dropped substantially; however, further reductions in sulphur and nitrogen emissions are required to eliminate critical loads exceedance. Based on bulk deposition of sulphate and nitrogen (41.1 mmol_c m^-2 yr^-1 and 62.5 mmol_c m^-2 yr^-1, respectively) for the period 1995–1999, 166 lakes (58.3%) exceedcritical loads. Even with full implementation of SO₂ abatementprograms in Canada (achieved in 1994) and the United States (legislated for 2010), critical loads will be exceeded in a large proportion (46.6%) of the study lakes.     

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.     

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.     

Critical Loads Exceedances in Germany and their Dependence on the Scale of Input Data

Critical load exceedances have been used as an effects-related parameter for guiding international air emission control negotiations. High-resolution critical load data are combined with low-resolution deposition data.This article shows that doing so systematicallyunderestimates `true' critical load exceedances as obtainedfrom combining critical load and deposition data of identicalhigh spatial resolution. 95th percentile critical loadexceedances in EMEP grids based on high resolution depositiondata are 60 and 150% higher (mean values for nutrientnitrogen and acidity, respectively) than critical loadexceedances based on the low resolution EMEP depositionmodel. The latter are used in international negotiations. Differences in individual EMEP grid squares vary betweeninsignificantly different from zero and 340%, depending onregional deposition and critical load characteristics andcritical load types (nutrient nitrogen versus acidity).Exceedances based on high-resolution deposition values arealso compared to EMEP grid averages of these values forforests only. This comparison excludes the effect ofsystematically higher depositions to forests. Still, thescale difference of (averaged, low-resolution) deposition and(high-resolution) critical loads data yields underestimatesof the 95th percentiles by on average ca. 20%.These systematic errors due to the scale dependence should beborne in mind when interpreting effects of internationalemission control measures.     

Predicting Freshwater Critical Loads from Catchment Characteristics using National Datasets

Maps of freshwater critical loads are used toguide emission strategies for sulphur and nitrogen bothnationally and internationally. Water chemistry data arerequired to calculate critical loads and the production ofnational maps therefore relies on the existence of extensivechemistry datasets. However, the data required to calculatecritical loads are not readily available for all sites. Thisarticle explores how empirical statistical models mightpotentially be used to predict critical loads using nationallyavailable datasets representing a range of catchmentcharacteristics. Initially a global regression model forexplaining freshwater critical load variation across a broadspectrum of catchment types (from lowland agricultural tomountain lakes) throughout mainland Britain is described. Whenattention is focused on more specific catchment types (i.e.upland and non-arable) it is shown that the global model hasless explanatory power. A regionalisation of Great Britain(based on 100 km grid squares) shows that the global modelcannot necessarily be applied successfully within a narrowerregional context. Separate analyses were undertaken on each ofthe regional subsets using backward selection regression. Thevariables emerging as significant predictors variedsubstantially across the regions, as did the explanatory powerof the models. This was also the case when the analysis wasconfined to upland and non-arable catchments. This approachcould be developed so that critical loads assessments can bemade for populations of standing waters rather than simplythose for which water chemistry is available.     

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.     

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.     

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.     

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.     

Removal of Oil from the Sea Surface through Particulate Interactions: Review and Prospectus

The fate of oil spilled in coastal zones depends in large part on the interactions with environmental factors existing within a short time of the spill event. In addition to weathering which produces changes in the chemistry of the hydrocarbon stock, physical interactions between oil and suspended particulate matter (SPM), both organic and inorganic, play a role in determining the dispersal and sedimentation rates of the spill. This in turn affects the degradation rate of the oil. This paper provides a comprehensive literature review of the role of oil–particle interactions in removal of petroleum hydrocarbons from the sea surface and provides estimates of the degree to which SPM may augment the deposition of oil. Both field and laboratory observations have shown widely varying rates of oil removal due to particulate interactions. The discussion covers the interaction between oil weathering, injection, sinking, adsorption, microbial processes, flocculation and ingestion by zooplankton, which all contribute to packaging oil and SPM into settling aggregates.     

Aluminium: The Need for a Re-Evaluation of Its Toxicity and Solubility in Mature Forest Stands

Aluminium (Al) is a key element in critical loadcalculations for forest. Here, we argue for re-evaluating theimportance of Al. Effects of two levels of enhanced Alconcentrations and lowered Ca:Al ratios in the soil solutionin a field manipulation experiment in a mature spruce stand(1996–1999) on tree vitality parameters were tested. Inaddition, Al solubility controls were tested. Various loads ofAl were added to forest plots by means of an irrigationsystem. Potentially toxic Al concentrations and criticalratios of Ca to inorganic Al were established. The ratio of Cato total Al was not a suitable indicator for unfavourableconditions for plant growth. No significant effects on crowncondition, tree growth and fine root production were observedafter three years of treatment. In 1999, foliar Mg content inthe highest Al addition treatment had declined significantly.This agreed with the known response to Al stress of seedlingsin nutrient solution experiments. No support was found forusing the chemical criterion Ca:Al ratio in soil solution,foliar and root tissue as an indicator for forest damage dueto acidification. Al solubility was considerably lower thanimplied by the assumption of equilibrium with gibbsite,particularly in the root zone. The gibbsite equilibrium iscommonly used in critical load models. Substitution of thegibbsite equilibrium with an Al-organic matter complexationmodel to describe Al solubility in soil water may have largeconsequences for calculation of critical loads. The resultsindicate that critical load maps for forests should bereconsidered.     

Physical Morphology and Quantitative Characterization of Chemical Changes of Weathered PVC/Pine Composites

This study investigated weathering effects on polyvinyl chloride (PVC) based wood plastic composites (WPC), with a focus on the color and structure that is attributed to the material composition. It is directed towards quantifying the main chemical modifications, such as carbonyl and vinyl groups which are formed during weathering. These composites were subjected to three weathering regimes: exterior, accelerated xenon-arc, and accelerated UVA. The change in color was monitored using colorimetry. Fourier transform infrared spectroscopy was used to identify and quantify the chemical modifications (carbonyl formation and vinyl propagation) due to weathering. Additionally, scanning electron microscopy was employed to observe the physical morphological changes that occurred. The results showed that exterior and accelerated xenon-arc and UVA weathering regimes increased the degree of lightness, total color change, carbonyl concentration, and wood loss on the surfaces of the weathered composites. The increased carbonyl concentration during weathering implied that degradation had occurred by oxidation process. Also, oxidation and lignin (from the wood) degradation influenced the color (lightness) of PVC based WPC upon weathering.