Critical Loads Of Acid Deposition Research Articles

An Assessment of Critical Loads of Acid Deposition in Kanpur Region, India

An Assessment of Critical Loads of Acid Deposition in Kanpur Region, India

Critical Loads of Acid Deposition for Wilderness Lakes in the Sierra Nevada (California) Estimated by the Steady-State Water Chemistry Model

Major ion chemistry (2000–2009) from 208 lakes (342 sample dates and 600 samples) in class I and II wilderness areas of the Sierra Nevada was used in the Steady-State Water Chemistry (SSWC) model to estimate critical loads for acid deposition and investigate the current vulnerability of high elevation lakes to acid deposition. The majority of the lakes were dilute (mean specific conductance = 8.0 μS cm−1) and characterized by low acid neutralizing capacity (ANC; mean = 56.8 μeq L−1). Two variants of the SSWC model were employed: (1) one model used the F-factor and (2) the alternate model used empirical estimates of atmospheric deposition and mineral weathering rates. A comparison between the results from both model variants resulted in a nearly 1:1 slope and an R 2 value of 0.98, suggesting that the deposition and mineral weathering rates used were appropriate. Using an ANClimit of 10 μeq L−1, both models predicted a median critical load value of 149 eq ha−1 year−1 of H+ for granitic catchments. Median exceedances for the empirical approach and F-factor approach were −81 and −77 eq ha−1 year−1, respectively. Based on the F-factor and empirical models, 36 (17 %) and 34 (16 %) lakes exceeded their critical loads for acid deposition. Our analyses suggest that high elevation lakes in the Sierra Nevada have not fully recovered from the effects of acid deposition despite substantial improvement in air quality since the 1970s.

Long-term Changes in Sulfate Concentrations and Soil Acidification of Forested Umbrisols and Andosols of Japan

Long-term changes in sulfate concentrations and soil acidification in two adjacent forest soils (Andosols and Umbrisols) were investigated using soil samples archived from 1967 to 2009. The amounts of phosphate-extracted sulfate in Andosols (≤51.0 mmol kg) were generally higher than that in Umbrisols (≤13.7 mmol kg). Both soils contained extremely high amounts of sulfate compared with the soils of polluted regions of Europe and North America in the 1980s and 1990s. A strong positive correlation was obtained between iron oxide minerals (acid oxalate–extractable Fe minus pyrophosphate-extractable Fe [Feo - Fep]) and phosphate-extracted sulfate, whereas soil organic matter was suggested to inhibit sulfate adsorption especially by allophane (acid oxalate–extractable Al minus pyrophosphate-extractable Al [Alo - Alp]). The amounts of phosphate-extracted sulfate in Umbrisols have gradually decreased by about one third between 1967 and 2009, resulting from the decline of sulfur emissions. However, those in Andosols have remained at high levels, indicating the very slow or irreversible equilibration of adsorbed sulfate in these soils. In addition, surface soils of Andosols from 1994 and 2009 showed soil acidification indicated by the decrease in soil pH, the dissolution of aluminum, and the formation of the precipitates, such as aluminum hydroxysulfate and basic iron sulfate. It is considered that irreversible adsorption of sulfate is an important factor contributing to the decrease in acid-neutralizing capacity. Although acidification in Andosols is slow to appear because of their high acid-neutralizing and sulfate adsorption capacities, acidification persists for a long time once the critical loads of acid deposition have occurred.

Ecological ranges for the pH and NO3 of syntaxa: a new basis for the estimation of critical loads for acid and nitrogen deposition

AbstractQuestion: Can the abiotic ranges of syntaxonomic units (associations) in terms of pH and nitrate concentration be estimated and then in principle be used to estimate critical loads for acid and nitrogen deposition?Location: Europe.Methods: Using splines, abiotic ranges of syntaxonomic units were estimated on the basis of measured soil pH and nitrate concentration and vegetation relevés. Owing to limited calibration data, this yielded responses for only a few syntaxa. In a second attempt, we used a 160 000‐relevé training set; the syntaxon of each relevé was known but not their soil pH values and soil nitrate concentrations, so for each relevé, the soil pH and nitrate concentration were estimated by inference from species composition. We again estimated abiotic ranges using the spline method, including the 5th and 95th percentiles as a proxy for the ecological range.Results: The second (indirect) method yielded ranges for soil pH and for nitrate concentration for many of the associations. The means and percentiles were corrected for regression to the mean.Conclusions: It is not yet possible to directly estimate ranges for syntaxa for pH and nitrate on a large scale from the data available. However, indirectly estimated soil pH and nitrate concentrations are sufficiently available to derive ranges for many associations. The lower (5th) percentile of the indirectly estimated pH ranges for associations may be used as the starting point for the estimation of critical loads for acid deposition. The 95th percentile should still be regarded as a rather uncertain estimate of the maximum nitrate concentration.

Sulfate adsorption properties of acid-sensitive soils in the Athabasca oil sands region in Alberta, Canada

The risk of soil acidification is high in the Athabasca oil sands region (AOSR) in Alberta, Canada, due to elevated SO 2 emission and the resultant acid deposition to sensitive, coarse-textured soils. Understanding the sulfate adsorption characteristics of soils sensitive to acidification will help establish critical loads of acid deposition in AOSR. Sulfate adsorption properties were evaluated and relationships between sulfate adsorption and soil properties were examined for soils in two contrasting watersheds (NE7 and SM8) in AOSR. The experimental data fitted well to both the Langmuir and the Freundlich models. The sulfate adsorption capacity was greater for soils in SM8 than in NE7 ( p < 0.01), even though it was relatively low in both watersheds as compared to other acid-sensitive soils in eastern North America. Based on the additional sulfate adsorbed when a soil was treated with 40 mL of 200 mg SO 4 2 - L −1 solution, the weakly developed Podzolic B horizon (Bfj)in NE7 could adsorb more sulfate than the Ae horizon while no difference was found among other horizons. In SM8, the Bfj and illuviated B (Bt) horizons had greater ability to adsorb sulfate than the other horizons, likely caused by the presence of muscovite in the Bfj and Bt horizons. The additional sulfate adsorbed accounted for about 80% of the total sulfate adsorption capacity and was correlated with pH NaF (soil pH extracted with 1 MNaF) and ΔpH NaF(the difference between pH NaF and pH measured with deionized water), with the following relationships: sulfate adsorption (mg SO 4 2 - kg −1) = exp(2.03 pH NaF – 18.0) + 50.2 ( R 2 = 0.63, p < 0.001) and sulfate adsorption (mg SO 4 2 - kg −1) = exp(1.83 ΔpH NaF – 6.57) + 48.9 ( R 2 = 0.70, p < 0.001). The ΔpH NaF was likely a better indicator of the soil’s sulfate adsorption capacity than pH NaF as the former excludes the effect of soil acidity. Our study indicates that the soil’s capacity to adsorb sulfate should be considered in determining the critical load for acid deposition in AOSR in Alberta.

Dissolved Al reduces Mg uptake in Norway spruce forest: Results from a long-term field manipulation experiment in Norway

Dissolved aluminium (Al) in soils, mobilized by acid deposition, is considered a threat to forest health through hampering root growth and nutrient uptake. Since the end of the 1980s dissolved Al in forest soil water plays a key role in the assessment of critical loads of acid deposition. So far, most evidence for toxicity of dissolved Al in forest soil water is based on nutrient solution studies and pot experiments. Here, we present results from one of the few in situ ecosystem-scale forest manipulation experiments to study the effect of Al on mature forest trees. A plotwise addition of dilute AlCl 3 was conducted during seven years in an even-aged spruce forest ( Picea abies) in an area in Norway with low acid deposition. Soil solution concentrations of Al were increased to potentially toxic levels (up to 500 μmol L −1) and base cation (Ca + Mg + K) to inorganic Al ratios in the soil solution in the root zone were mostly below 1 in the Al-addition treatments. In the control treatment (only water addition) Al concentrations did not exceed 15 μmol L −1 and base cation to inorganic Al ratios were above 1. The toxic effects of Al on fine root growth and plant growth found in hydroponic studies and pot trials are not confirmed by this field manipulation. However, magnesium (Mg) contents in needles decreased significantly and persistently in plots with elevated Al concentrations, whereas the needle Ca content did not respond. The depletion of the Mg content in needles is suggested to be due to antagonistic effects of high Al concentrations at the root surface, consistent with observed reductions in Mg to Al ratio of inner bark. This study clearly supports a role for Al in critical load functions for forests as dissolved Al causes a decrease in uptake of Mg. However, other signs of reduced forest vitality were not observed. Soil base cation status may need to be included in risk evaluations of forest health under acid deposition.

Evaluation of the Sensitivity of European Soils to the Deposition of Acid Compounds: Different Approaches Provide Different Results

Analysis of the sensitivity of soils to acidification caused by the deposition of atmospheric pollutants has been one of the major scientific issues in Europe during the past few decades. In the present study, critical loads of acid deposition were calculated using the most accurate datasets available at present for European soils, by the “Simple Mass Balance” method. The results show that the soils most sensitive to acid deposition are Histosols, Cryosols and Podzols in cold areas in northern countries, followed by Lithic and Haplic Leptosols (Dystric) developed on acid parent materials. The highest critical loads corresponded to soils developed over calcareous rocks and soils in areas subject to high precipitation, even those dominated by poorly weatherable primary mineral. In the latter case critical alkalinity leaching is the main variable that determines the value of critical loads, because of the buffering action of the dissolution of aluminium compounds. The results were compared with those obtained by the Stockholm Environmental Institute in the same area, but with a different method of analysis. It was found that the results are highly dependent on the method used to perform the analysis.

Quantifying Uncertainty in Critical Loads: (B) Acidity Mass Balance Critical Loads on a Sensitive Site

This paper reports an uncertainty analysis of critical loads for acid deposition for a site in southern England, using the Steady State Mass Balance Model. The uncertainty bounds, distribution type and correlation structure for each of the 18 input parameters was considered explicitly, and overall uncertainty estimated by Monte Carlo methods. Estimates of deposition uncertainty were made from measured data and an atmospheric dispersion model, and hence the uncertainty in exceedance could also be calculated. The uncertainties of the calculated critical loads were generally much lower than those of the input parameters due to a “compensation of errors” mechanism – coefficients of variation ranged from 13% for CLmaxN to 37% for CL(A). With 1990 deposition, the probability that the critical load was exceeded was > 0.99; to reduce this probability to 0.50, a 63% reduction in deposition is required; to 0.05, an 82% reduction. With 1997 deposition, which was lower than that in 1990, exceedance probabilities declined and uncertainties in exceedance narrowed as deposition uncertainty had less effect. The parameters contributing most to the uncertainty in critical loads were weathering rates, base cation uptake rates, and choice of critical chemical value, indicating possible research priorities. However, the different critical load parameters were to some extent sensitive to different input parameters. The application of such probabilistic results to environmental regulation is discussed.

Growth, net photosynthesis and leaf nutrient status of Fagus crenata seedlings grown in brown forest soil acidified with H2SO4 or HNO3 solution

To obtain basic information for evaluating critical loads of acid deposition for protecting Japanese beech forests, growth, net photosynthesis and leaf nutrient status of Fagus crenata seedlings grown for two growing seasons in brown forest soil acidified with H2SO4 or HNO3 solution were investigated. The whole-plant dry mass of the seedlings grown in the soil acidified by the addition of H2SO4 or HNO3 solution was significantly less than that of the seedlings grown in the control soil not supplemented with H+ as H2SO4 or HNO3 solution. However, the degrees of reduction in the whole-plant dry mass and net photosynthetic rate of the seedlings grown in the soil acidified by the addition of H+ as H2SO4 solution at 100 mg l−1 on the basis of air-dried soil volume (S-100 treatment) were greater than those of the seedlings grown in the soil acidified by the addition of H+ as HNO3 solution at 100 mg l−1 (N-100 treatment). The concentrations of Al and Mn in the leaves of the seedlings grown in the S-100 treatment were significantly higher than those in the N-100 treatment. A positive correlation was obtained between the molar ratio of (Ca+Mg+K)/(Al+Mn) in the soil solution and the relative whole-plant dry mass of the seedlings grown in the acidified soils to that of the seedlings grown in the control soil. Based on the results, we concluded that the negative effects of soil acidification due to sulfate deposition are greater than those of soil acidification due to nitrate deposition on growth, net photosynthesis and leaf nutrient status of F. crenata, and that the molar ratio of (Ca+Mg+K)/(Al+Mn) in soil solution is a suitable soil parameter for evaluating critical loads of acid deposition in efforts to protect F. crenata forests in Japan.

Acidification sensitivity and critical loads of acid deposition for surface waters In China

Although decades of severe acid deposition have not resulted in serious surface water acidification in China, at present, the risk of some freshwaters becoming acidified cannot be neglected. To know more clearly about the possible impact acid deposition would have on Chinese surface waters, it is necessary to study the sensitivity of those surface waters to acidification and their critical loads of acid deposition on a national scale. Here we assess the acidification sensitivity of Chinese surface waters using an approach based on geology, soils, land use and hydrological conditions. Critical loads of S, N and acidity were also evaluated by a first-order acidity balance (FAB) model. Results show that most surface waters in China have very high critical loads of S and acidity and are not susceptible to acidification. Surface waters can be divided into three groups according to both sensitivity classes and critical loads. The few most sensitive surface waters are located in the northern part of Daxinganling region, with critical loads of S deposition and acidity lower than 2 keq ha −1 year −1. Surface waters in the northeastern region draining dark brown forest soils and in southern China belong to the second class of acidification sensitivity and their critical loads of S and acidity are generally between 2 and 15 keq ha −1 year −1, indicating they are not likely to be acidified under any flow conditions. Surface waters in other parts of China will not be acidified to any degree, with critical loads much higher than 15 keq ha −1 year −1. The magnitude and spatial distribution pattern of acidification sensitivity have significant similarity to the critical loads of S and acidity for Chinese surface waters. Although most surface waters are not likely to be acidified, attention should still be paid to the possible adverse impact acid deposition would have, especially in northeastern China, where the surface waters are the most sensitive, and the southern region, where acid pollution is among the most severe in China.

Critical Loads of Acid Deposition for Ecosystems in China South Derived by a New Method

Critical Loads of Acid Deposition for Ecosystems in China South Derived by a New Method

Derivation and mapping of critical loads for nitrogen and trends in their exceedance in Germany.

The term “critical load” means a quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur, according to present knowledge. In the case of nitrogen, both oxidised and reduced compounds contribute to the total deposition of acidity, which exceeds critical loads in many forest ecosystems. These also cause negative effects through eutrophication. Critical loads of nitrogen were derived for forest soils (deciduous and coniferous forest), natural grassland, acid fens, heathland, and mesotrophic peat bogs. In Germany, a decrease in sulphur emissions over the past 15 years resulted in a reduced exceedance of critical loads for acid deposition. In the same period it was noted that reduction in the emissions of nitrogen oxides and ammonia remained insignificant. Therefore, emissions of nitrogen compounds have become relatively more important and will continue to threaten ecosystem function and stability. The risk of environmental damage remains at an unacceptable level. The German maps show the degree to which the critical loads are exceeded, and they present current developments and an expected future trend. Results indicate that recovery from pollutant stress occurs only gradually.

Impacts of uncertainties in base‐cation deposition on the assessment of critical loads for acid deposition

Less attention has been paid to changes in the concentration and the deposition amounts of base cations. This has brought about great uncertainty in the determination of critical loads for acid deposition. The paper utilized a newly developed long‐term soil acidification model (LTSAM), to simulate the effects of atmospheric base cations on the critical load of red earth in Wenzhou, Zhejiang Province. Results showed that great changes in atmospheric base‐cation deposition decreased the critical load by 68%. This suggested that by only reducing S deposition without considering changes in the atmospheric base‐cation deposition, would substantially overestimate the critical load of soils. Therefore, more attention should be focused on changes in base cations during reductions of SO2 emissions, and the long‐term monitoring of base cation deposition needs to be strengthened, especially in China.

Critical loads of acid deposition on soil in China.

Critical loads of acid deposition havebeen mapped for Chinese soils using a modifiedsemi-quantitative method, which is based on theminerals controlling weathering and soil development,and corrected by introducing an Arrhenius relationshipto describe the effect of temperature and a weightedaveraging approach to evaluate the effect of soiltexture, land use and precipitation. As a consequenceof these modifications, the method has been quantifiedand can be more widely used. Results from this studyshow that the lowest critical loads of acid depositionin China, i.e., those areas most sensitive to aciddeposition, occur in the Podzolic soils in theNortheast, followed by Latosol, Dark brown forest soiland Black soil areas. The Ferralsol areas in SouthChina are intermediate, tolerating about 0.8–1.6 g m-2 yr-1 sulfur deposition. The highestcritical loads of acid deposition are mainly locatedin the Alpine soil areas on the Plateau of Tibet andareas of Xerosol and Podocal soil in Northwest China.The reason for lower critical loads in the Northeastrelative to South China can be attributed to thedifference of temperature, soil moisture and soiltexture. Comparison of critical loads with the sulfurdeposition in 1995 identifies almost one fourth of theland area in southeast China to be subject to risk of acidification.

Uncertainty in the estimation of critical loads: A practical methodology

Critical loads of acid deposition for forest soils, ground and surface water resources are calculated utilising a variety of mathematical models. The estimation of the predictive uncertainty inherent in these models is important since the model predictions constitute the cornerstone of the development of emissions abatement policy decisions in Europe and the United Kingdom. The Generalised Likelihood Uncertainty Estimation (GLUE) approach is presented here as a tool for estimating the predictive uncertainty of PROFILE, a steady-state geochemical model that is widely applied within the critical loads community. GLUE is based on Monte Carlo simulation and explicitly recognises the possible equifinality of parameter sets. With this methodology it is possible to make an assessment of the likelihood of a parameter set being an acceptable simulator of a system when model predictions are compared to observed field data. The methodology is applied to a small catchment at Plynlimon, Mid-Wales. The results highlight that there is a large amount of predictive uncertainty associated with the model at the site: three of the six chosen field characteristics lie within the predicted distribution. The study also demonstrates that a wide range of parameter sets exist that give acceptable simulations of site characteristics as well as a broad distribution of critical load values that are consistent with the site data. Additionally, a sensitivity analysis of model parameters is presented.

Climate change and pollutant impacts on Scottish vegetation

Summary By the 2050s the UK is projected to be about 1.6°C warmer, when the atmospheric CO2 concentration will be 525 ppmv. These changes will have profound effects on the Scottish flora and fauna. Vegetation primary productivity will increase, except in dry regions, and the productivity of upland forest plantations may increase by several Yield Classes. The spread of plant species may be less than expected, but a number of slow-growing ‘stress-tolerant’ species, including montane/alpine species, are likely to be lost. Nitrogen deposited as a result of emission of NOX from vehicles and NH3 from agriculture is now a major source of acidity, and problems of acidification and eutrophication are linked. Despite reductions in sulphur emissions, critical loads of acid deposition are likely to be exceeded for soils in most of the Scottish uplands until at least 2005. Critical levels affecting tree growth may be exceeded where forests are in cloud for 10% of the time in areas of the Great Glen. Much of the Scottish uplands receives 25–30 kg N ha-1 yr-1, which may be causing change in species composition. Background tropospheric ozone concentrations are increasing. Much of the Scottish uplands experiences mean summer ozone concentrations exceeding those in southern England, but with fewer exceedances of critical levels. However, many crops and some sensitive native species are probably being adversely affected.

Critical loads of acid deposition for forest ecosystems in the Kola Peninsula

We assessed critical loads of acid deposition and their exceedance for soils in the Kola Peninsula using a simple balance method and mapped them within 1.0° × 0.5° longitude/latitude grid cells. Critical loads of acidity vary from 200 to 800 molc/ha/y with the type of soil, parent rock, vegetation and climatic conditions. The critical deposition values are dominated by S contribution. Present sulphur depositions are higher than critical values in the large part of the Kola Peninsula (about 40% of total area). The greatest excess (800–1200 molc/ha/y) occur in north-western and western parts, especially in surroundings of nickel smelter in Nickel. Terrestrial ecosystems in the north-western Kola Peninsula are particularly susceptible to acid deposition damage due to relatively high soil sensitivity and heavy sulphur deposition.

Assessment of critical loads in liuzhou, China using static and dynamic models

The project Comprehensive Control and Demonstration for Acid Deposition in Liuzbou area is a national key project in the 8th Five-year-plan, and the study on critical loads will provide scientific and quantitative accordance for formulating control strategy. In this paper, critical loads of acid deposition to soil in Lirzhou area, China, were calculated using the Steady State Mass Balance method (SMB and PROFILE) and dynamic modeling methods(MAGIC), based on data obtained from field investigations and physiochemical properties measured through experiments such as the organic content, cation exchange capacity, base saturation, sulfate adsorption capacity, gibbsite coefficient, biomass base cation uptake and selectivity coefficient for cations. Weathering rates necessary to calculate soil chemistry in applying SMB and MAGIC model were determined by computation with PROFILE using independent geophysical properties such as soil texture and mineralogy as the input data, or by the total soil base cation content correlation. The results have shown that the critical loads of acidity in this area are in the range of 0.7–6.0 keq ha−1 yr−1, indicating sulfur deposition should be cut down by 50–90 percent of the present level. The upper soil layer is the most sensitive. The maximum allowable deposition loading of this area is also presented in the paper.

Evaluation of estimation methods and base data uncertainties for critical loads of acid deposition in Japan

Simplified steady state mass balance model for critical load (CL) estimation was applied to a test area in Japan to evaluate applicability of the model. Three different criteria for acidification limits (1: [Al3+]<0.2 eq. m−3, 2: Al/BC<1.0 mol mol−1, 3:Al depletion criterion) were used. Mean values and spatial distribution patterns of CL values calculated by these criteria were extremely different from each other. The first criterion produced much higher CL than the second criterion in the Japanese condition with high annual precipitation. Improvements including definition of the criterion were considered necessary. As quantitative data of the base cation weathering rate (BCw) was lacking, the rate was specified based on surface geology and the soil type of each site. To evaluate uncertainty of BCw used for CL calculation, ion content and particle-size distribution were measured for the soils collected from the test area, and BCw was estimated with PROFILE model based on these measurements. It appeared that BCw estimates by surface geology were adequate as a mean value, but they had uncertainty of about 50% of the average values due to variability of ion contents within the same surface geology group.

Rates and processes of mineral weathering in soils developed on greywackes and shales in the Southern Uplands of Scotland

Critical loads of acid deposition are exceeded in parts of the Southern Uplands of Scotland where base saturation in the topmost mineral horizons in many soils developed on greywackes and shales is 4.3. The base cation least depleted is Ca and this is in sharp contrast to current weathering rates calculated from input-output budgets where Ca is the main base cation being exported. This discrepancy may be due to a contribution to the output from easily soluble Ca-bearing minerals (e.g. calcite) in narrow veins and fractures in the bedrock.