Determination and Mapping Critical Loads of Acidity and Exceedances for Upland Forest Soils in Eastern Canada

Critical loads of acidity were estimated for upland forests in Eastern Canada using the steady-state Simple Mass Balance (SMB) Model. A consistent methodology was applied to the entire region, although critical loads were estimated separately for the Atlantic provinces (New Brunswick, Nova Scotia, Prince Edward Island and Newfoundland), Quebec and Ontario using different data sources. In this project, critical load estimates and steady-state exceedance values did not include the effect of forest fire and forest harvesting, which could have a considerable impact on critical loads in Eastern Canada. The observed soil pH – base saturation relationship for forest soils indicated that the constants used into the calculation of alkalinity leaching should be set to 10 (M/M) for the molar Bc/Al ratio in soil leachate and 10⁹ (mol L^?1)² for the gibbsite dissolution constant. The area-weighted median critical load for each province varied between 519 (Quebec) and 2063 eq ha^?1 y^?1 (Prince Edward Island), with a median critical load value for Eastern Canada of 559 eq ha^?1 y^?1. It is estimated that approximately 52% of the mapped area is exceeded in terms of acidity according to the 1994–1998 average total (wet + dry) atmospheric deposition. Greatest exceedances occurred in Ontario and Quebec and in the south of Nova Scotia, due to low critical loads and high loads of acid deposition.     

Critical Loads of Sulphur and Nitrogen for Terrestrial Ecosystems in Europe and Northern Asia Using Different Soil Chemical Criteria

A critical load data base was developed for Europe and Northern Asia using the latest data bases on soils, vegetation, climate and forest growth. Critical loads for acidity and nutrient nitrogen for terrestrial ecosystems were computed with the Simple Mass Balance model. The resulting critical loads are in accordance with critical loads from previous global empirical studies, but have a much higher spatial resolution. Critical loads of acidity are sensitive to both the chemical criterion and the critical limit chosen. Therefore a sensitivity analysis of critical loads was performed by employing different chemical criteria. A critical limit based on an acid neutralizing capacity (ANC) of zero resulted in critical loads that protect ecosystems against toxic concentrations of aluminium and unfavourable Al/Bc ratios, suggesting that ANC could be an alternative to the commonly used Al/Bc ratio. Critical loads of nutrient nitrogen are sensitive to the specified critical nitrate concentration, especially in areas with a high precipitation surplus. If limits of 3–6 mg N l^?1 are used for Western Europe instead of the widely used 0.2 mg N l^?1, critical loads double on average. In low precipitation areas, the increase is less than 50%. The strong dependence on precipitation surplus is a consequence of the simple modelling approach. Future models should explore other nitrogen parameters (such as nitrogen availability) instead of leaching as the factor influencing vegetation changes in terrestrial ecosystems.     

Calculation and Mapping of Sulfur Critical Loads for Terrestrial Ecosystems of Thailand

The essential parameters needed for the calculation of critical load of sulfur, CL(S), are base cation weathering rate, base cation uptake, acid neutralizing capacity leaching and base cation deposition. These parameters are estimated and mapped for the most area of terrestrial ecosystems of Thailand using data of national data soil survey. The values of CL(S) range from <200 to 2,225 eq.ha^?1yr^?1 and about 70% of terrestrial ecosystems are characterized by low values (<200 eq.ha^?yr^?1). These CL values reflect the sensitivity of Thai ecosystems to sulfur deposition.     

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 CL_maxN 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.     

Critical Loads of Acidity to Protect and Restore Acid-Sensitive Streams in Virginia and West Virginia

The purpose of the research described here is to apply a new approach for generating aquatic critical load (CL) and exceedance calculations for an important acid-sensitive region of the eastern USA. A widespread problem in regional aquatic acidification CL modeling for US ecosystems has been the lack of site-specific weathering data needed to derive accurate model CL estimates. A modified version of the steady-state water chemistry CL model was applied here to estimate CL and exceedances for streams throughout acid-sensitive portions of Virginia and West Virginia. A novel approach for estimating weathering across the regional landscape was applied, based on weathering estimates extracted from a well-tested, process-based watershed model of drainage water acid?Cbase chemistry and features of the landscape that are available as regional spatial data coverages. This process allowed extrapolation of site-specific weathering data from 92 stream watersheds to the regional context in three ecoregions for supporting CL calculations. Calculated CL values were frequently low, especially in the Blue Ridge ecoregion where one-third of the stream length had CL?<?50?meq/m²/year to maintain stream ANC at 50???eq/L under steady-state conditions. About half or more of the stream length in the study region was in exceedance of the CL for long-term aquatic resource protection under assumed nitrogen saturation at steady state. Land managers and air quality policy makers will need this information to better understand responses to air pollution emissions reductions and to develop ecoregion-specific air pollution targets.     

Dynamic Modelling of Spatially Variable Catchment Hydrochemistry for Critical Loads Assessment

Concern about acidification in upland areas has brought about the need to model the stream hydrochemical response to deposition and land-use changes and calculate critical loads. Application of dynamic models such as MAGIC are preferable to steady-state methods, since they are able to produce an estimate of the time scale required to meet some water chemistry target given a reduction in acid deposition. These models typically consider annual changes in stream chemistry at one point. However, in order to protect biota from 'acid episodes', quantification of temporal variability needs to encompass event responses; in addition spatial variability across the catchment also needs to be considered. In this paper, modelling of both spatial and temporal variability is combined in a new framework which enables quantification of catchment hydrochemical variability in time and space. Both low and high flow hydro-chemical variability are quantified in terms of statistical distributions of ANC (Acid Neutralisation Capacity). These are then input as stochastic variables to an EMMA (End-Member Mixing Analysis) model which accounts for temporal variability and ANC is hence predicted as a function of time and space across the whole catchment using Monte-Carlo simulation. The method is linked to MAGIC to predict future scenarios and may be used by iteration to calculate critical loads. The model is applied to the headwaters of the River Severn at Plynlimon, Wales, to demonstrate its capabilities.     

Deposition and Critical Loads of Nitrogen in Switzerland

Many ecosystems in Switzerland suffer from eutrophication due to increased atmospheric nitrogen (N) input. In order to get an overview of the problem, critical loads for nutrient N were mapped with a resolution of 1×1 km applying two methods recommended by the UN/ECE: the steady state mass balance method for productive forests, and the empirical method for semi-natural vegetation, such as natural forests, (sub-)alpine or species-rich grassland and raised bogs. The national forest inventory and a detailed atlas of vegetation types were used to identify the areas sensitive to N input. The total N input was calculated as the sum of NO₃ ^?, NH₄ ⁺, NH₃, NO₂ and HNO₃ wet and dry deposition. Wet deposition was determined on the basis of a precipitation map and concentration measurements. Dry deposition was calculated with inferential methods including land-use specific deposition velocities. The concentration fields for NH₃ and NO₂ were obtained from emission inventories combined with dispersion models. Reduced N compounds account for 63% of total deposition in Switzerland. As indicated by exceeded critical loads, the highest risk for harmful effects of N deposition (decrease of ecosystem stability, species shift and losses) is expected on forests and raised bogs in the lowlands, where local emissions are intense. At high altitudes and in dry inner-alpine valleys, deposition rates are significantly lower.     

Assessing Potential Impacts on Biodiversity Using Critical Loads

In many countries there has been much concern over maintaining biodiversity in natural ecosystems in the face of pressures such as changing land use and pollution. The 1992 UN Convention on Biodiversity calls upon signatories to develop national strategies for the conservation and sustainable use of biodiversity. In the UK, the potential impacts of sulphur and nitrogen deposition at the national level are being assessed using national critical loads and modelled deposition maps, together with available information on the occurrence of habitats and plant species. This simple approach gives an indication of the areas where atmospheric deposition may have impacts on biodiversity. The results of the analyses are presented and the strengths and weaknesses of the methods used are discussed. This first approach to considering the effects on biodiversity shows the importance of including the effects of atmospheric deposition in any biodiversity action plan. It also highlights those areas where more or improved information is required for the national strategy. With the modelled deposition data available, it would seem that reduced impacts are to be expected by 2010. However, higher resolution deposition data, better estimates of ammonium deposition, consideration of temporal aspects and the dynamics of change, and the use of higher resolution biological data sets are likely to suggest greater impacts than current predictions.     

Nitrogen Leaching of Two Forest Ecosystems in a Karst Watershed

Karst watersheds are a major source of drinking water in the European Alps. These watersheds exhibit quick response times and low residence times, which might make karst aquifers more vulnerable to elevated nitrogen (N) deposition than non-karst watersheds. We summarize 13 years of monitoring NO ₃ ^? , NH ₄ ⁺ , and total N in two forest ecosystems, a Norway spruce (Picea abies (L.) Karst.) forest on Cambisols/Stagnosols (IP I) and a mixed beech (Fagus sylvatica L.) spruce forest on Leptosols (IP II). N fluxes are calculated by multiplying concentrations, measured in biweekly intervals, with hydrological fluxes predicted from a hydrological model. The total N deposition in the throughfall amounts to 26.8 and 21.1 kg/ha/year in IP I and IP II, respectively, which is high compared to depositions found in other European forest ecosystems. While the shallow Leptosols at IP II accumulated on average 9.2 kg/ha/year of N between 1999 and 2006, the N budgets of the Cambisols/Stagnosols at IP I were equaled over the study period but show high inter-annual variation. Between 1999 and 2006, on average, 9 kg/ha/year of DON and 20 kg/ha/year of DIN were output with seepage water of IP I but only 4.5 kg/ha/year of DON and 7.7 kg/ha/year of DIN at IP II. Despite high DIN leaching, neither IP I nor IP II showed further signs of N saturation in their organic layer C/N ratios, N mineralization, or leaf N content. The N budget over all years was dominated by a few extreme output events. Nitrate leaching rates at both forest ecosystems correlated the most with years of above average snow accumulation (but only for IP I this correlation is statistically significant). Both snow melt and total annual precipitation were most important drivers of DON leaching. IP I and IP II showed comparable temporal patterns of both concentrations and flux rates but exhibited differences in magnitudes: DON, NO ₃ ^? , and NH ₄ ⁺ inputs peak in spring, NH ₄ ⁺ showed an additional peak in autumn; the bulk of the annual NO ₃ ^? and DON output occurred in spring; DON, NO ₃ ^? , and NH ₄ ⁺ output rates during winter months were low. The high DIN leaching at IP I was related to snow cover effects on N mineralization and soil hydrology. From the year 2004 onwards, disproportional NO ₃ ^? leaching occurred at both plots. This was possibly caused by the exceptionally dry year 2003 and a small-scale bark beetle infestation (at IP I), in addition to snow cover effects. This study shows that both forest ecosystems at Zöbelboden are still N limited. N leaching pulses, particularly during spring, dictate not only annual but also the long-term N budgets. The overall magnitude of N leaching to the karst aquifer differs substantially between forest and soil types, which are found in close proximity in the karstified areas of the Northern Limestone Alps in Austria.     

Transformation of Forest Ecosystems in Moscow Megapolis under Recreational Impacts

Eurasian Soil Science - A comprehensive quantitative assessment of the state of vegetation, soil invertebrate complex, litter horizons, and soddy-podzolic soils (Albic Retisols) in Moscow forest...     

亚热带区域几种典型人工林生态系统林地土壤质量评价

针对不同经营模式对林地土壤的物理性质、化学性质和生物学性质的影响,采用主成分分析方法直观定量地研究了亚热带区域几种典型人工林生态系统林地的土壤质量指数和土壤退化指数,揭示了土壤质量指数之间的相关性和差异性、以及土壤退化指数之间的相关性和差异性,并很好地识别出了土壤质量指数和土壤退化指数的主要成分。分析结果基本上反映了不同生态类型林地土壤质量状况,主成分分析土壤质量指数得分以常绿阔叶林最高,其次是混交林和阔叶纯林,连栽杉木纯林最低;主成分分析土壤退化指数表明,与次生常绿阔叶林比较,其中连栽杉木纯林退化幅度最大,而混交林和阔叶纯林次之。从而对其林地土壤质量进行了准确评价,为杉木人工林的可持续利用提供直接依据,并为亚热带区域人工林生态系统林地土壤质量评价提供参考。     

Effects of Natural Soil Acidification on Biodiversity in Boreal Forest Ecosystems

Variations in soil acidity and in biodiversity were analysed in the National Natural Park "Russian North", European Russia. Improving soil quality from podzol, podzolic soil, derno-podzolic soil, brown earth to pararendzina leads to increase in diversity and changes in floristical composition, followed by changing of pine and spruce forest to mixed and birch forests. In PCA ordination species diversity, richness and evenness of trees, shrubs and vascular plants are closely connected with each other, and are represented by the first principal component. They are strongly correlated to the thickness of Al horizon, pH_H20 and pH_CaC12 in organic, surface and subsurface mineral horizons. Only bryophyte species richness and diversity are directly related to the thickness and weight of organic horizon, soil exchangeable acidity, and inversely related to the thickness of Al horizon and pH. Thus, the ordination of the major species diversity variables is highly related to soil pH, suggesting that pH is the best soil related predictor of species diversity parameters. Our study shows that plants notably respond to soil acidification in boreal forest ecosystems.     

Critical Loads of Trace Metals in Soils: a Method of Calculation

Critical load of trace metals in soils is a function of biological uptake, leaching by percolating water, input of the trace metals due to bedrock weathering, and the norms set to protect soils from metal pollution. The exceedance of the critical load is a difference between the calculated load and the measured input of the metals by atmospheric deposition and by application of agrochemicals. A critical time is the time when the concentration of a trace metal in soil, which is the result of all inputs and outputs of the metal in the soil, reaches the value of the norm. Data on biologically important trace metals in a small agricultural catchment in the Czech Republic indicate that the soil concentrations of As, Cd and Pb will reach the norms set for the soils after 4.5, 61, and 980 years, respectively. The present mass balances of Cu and Zn in the soils indicate that their steady-state concentrations will be below the norms so that the atmospheric and agricultural inputs will never overshoot the calculated critical load.     

Quantifying Uncertainty in Critical Loads: (A) Literature Review

Critical loads are the basis for policies controlling emissions of acidic substances in Europe. The implementation of these policies involves large expenditures, and it is reasonable for policymakers to ask what degree of certainty can be attached to the underlying critical load and exceedance estimates. This paper is a literature review of studies which attempt to estimate the uncertainty attached to critical loads. Critical load models and uncertainty analysis are briefly outlined. Most studies have used Monte Carlo analysis of some form to investigate the propagation of uncertainties in the definition of the input parameters through to uncertainties in critical loads. Though the input parameters are often poorly known, the critical load uncertainties are typically surprisingly small because of a “compensation of errors” mechanism. These results depend on the quality of the uncertainty estimates of the input parameters, and a “pedigree” classification for these is proposed. Sensitivity analysis shows that some input parameters are more important in influencing critical load uncertainty than others, but there have not been enough studies to form a general picture. Methods used for dealing with spatial variation are briefly discussed. Application of alternative models to the same site or modifications of existing models can lead to widely differing critical loads, indicating that research into the underlying science needs to continue.     

Macroinvertebrate-Inferred Stream-Water Acidity in North Eastern Finland Along a Sulphur Deposition Gradient

Recently developed weighted averaging (WA) models and widely used tolerance-limit approaches for inferring stream minimum pH from macroinvertebrates were tested in northeastern Finnish Lapland. Surface waters there are threatened by large sulphur emissions in the Russian Kola Peninsula. The modelled sulphur deposition increases from west to east approximately parallel to longitude. The effect of deposition on stream minimum pH was assessed by relating the macroinvertebrate-inferred stream minimum pH to longitude. In a test set of 17 streams, the minimum pH inferred from pooled invertebrate samples of three seasons by WA models showed a strong correlation (r = 0.67–0.72) with the minimum pH (range 6.3–7.1) observed during the spring snow-melt period. The relationship was slightly weaker (r = 0.59–0.69) using autumn samples only. The tolerance-limit approaches assigned the streams into the correct acidity class, but the inferred pH was not related to the observed minimum pH. This further demonstrates the superiority of the WA approach, especially in detecting early signs of acidification. The minimum pH inferred by WA from autumn assemblages of 37 streams along the deposition gradient showed a significant negative correlation with longitude, suggesting that the emissions from the Kola region contribute to low pH events in streams of northeastern Finnish Lapland. The results demonstrate the potential of bioassessment and monitoring using invertebrates in detecting impacts and changes that could remain unnoticed by conventional water quality-analyses.     

Calculating Critical Loads of Sulfur Deposition for 100 Surface Waters in China Using the Magic Model

Although decades of acid deposition have apparently not resulted in surface water acidification in China, some surface waters may have the potential trend of being acidified, especially those in southern China. In this paper, a dynamic acidification model–MAGIC was applied to 100 surface waters in southern and northeastern China to evaluate the impact of acid deposition to surface waters and to determine their critical loads of S deposition, both regions having distinguishing soil, geological and acid deposition characteristics. Results indicate that most surface waters included in this paper are not sensitive to acid deposition, with critical loads of S for these waters comparatively high. On the other hand, surface waters in southern China, especially those in Fujian, Jiangxi and Guangdong provinces, are more susceptible to acidification than those in northeastern China, which coincides with their different patterns of soil, geological and acid deposition conditions. Among all the waters, a few small ponds, such as those on top of the Jinyun mountain and Emei mountain, are the most sensitive to acid deposition with critical loads of 1.84 and 3.70 keq·ha^?1·yr^?1, respectively. For the considerable ANC remaining in most 100 surface waters, it is not likely that acidification will occur in the near future for these waters.     

Are Indicators for Critical Load Exceedance Related to Forest Condition?

The aim of this study was to evaluate the suitability of the (Ca?+?Mg?+?K)/Al and the Ca/Al ratios in soil solution as chemical criteria for forest condition in critical load calculations for forest ecosystems. The tree species Norway spruce, Sitka spruce and beech were studied in an area with high deposition of sea salt and nitrogen in the south-western part of Jutland, Denmark. Throughfall and soil water were collected monthly and analysed for pH, NO₃-N, NH₄-N, K, Ca, Mg, DOC and Al_tot. Organic Al was estimated using DOC concentrations. Increment and defoliation were determined annually, and foliar element concentrations were determined every other year. The throughfall deposition was highest in the Sitka spruce stand (maximum of 40 kg N ha^?1yr^?1) and lowest in the beech stand (maximum of 11 kg N ha^?1yr^?1). The Sitka spruce stand leached on average 12 kg N ha^?1yr^?1 during the period 1988–1997 and leaching increased throughout the period. Only small amounts of N were leached from the Norway spruce stand whereas almost no N was leached from the beech stand. For all tree species, both (Ca?+?Mg?+?K)/Al and Ca/Al ratios decreased in soil solution at 90 cm depth between 1989 and 1999, which was mainly caused by a decrease in concentrations of base cations. The toxic inorganic Al species were by far the most abundant Al species at 90 cm depth. At the end of the measurement period, the (Ca?+?Mg?+?K)/Al ratio was approximately 1 for all species while the Ca/Al ratio was approximately 0.2. The lack of a trend in the increment rates, a decrease in defoliation as well as sufficient levels of Mg and Ca in foliage suggested an unchanged or even slightly improved health condition, despite the decreasing and very low (Ca?+?Mg?+?K)/Al and Ca/Al ratios. The suitability of these soil solution element ratios is questioned as the chemical criteria for soil acidification under field conditions in areas with elevated deposition rates of sea salts, in particular Mg.     

Proton Budgets of Forest Ecosystems on Volcanogenous Regosols in Hokkaido,Northern Japan

The proton budgets of deciduous and coniferous forest ecosystems on volcanogenous regosols in Hokkaido, northern Japan, were studied by measuring the biogeochemical fluxes (atmospheric deposition, canopy leaching, vegetation uptake and leaching from soil) at each site during a three year period. The proton budgets were developed for individual compartments of the ecosystem: vegetation canopy, organic and mineral soil layers. At both sites, atmospheric S deposition was the dominant proton source in the vegetation canopy. In organic horizons, dissociation of weak acids (bicarbonate and/or organic acids) and vegetation uptake of base cations were the dominant proton sources, and the net mineralization of base cations was the dominant proton sink. Atmospheric acid deposition was almost neutralized in the forest canopy and organic horizon. At both sites, weathering and/or ion exchange of base cations and protonation of weak acids (mainly bicarbonate) were the dominant proton sinks in the mineral soil. In both organic and mineral soil, internal proton sources (mainly vegetation uptake of base cations and dissociation of weak acids) exceeded external proton sources, indicating that acid deposition was not the main driving force of soil acidification in the studied forest ecosystems.     

Critical Loads of SO2 Dry Deposition and Their Exceedance in South China

The critical loads of SO₂ dry deposition in South China,which is transferred from critical level, as well the excess ofcritical loads are computed and mapped. The areas with thelowest critical load and the highest excess are, respectively,identified. The research is complementary to the previousresearches on critical loads for soils, and expected to beintegrated with them to make efficient sulfur emission abatement strategy.     

Consequences of N Deposition to Forest Ecosystems - Recent Results and Future Research Needs

Wet and dry deposition of atmospheric nitrogen (N) compounds into forest ecosystems and their effect on physical, chemical and microbial processes in the soil has attracted considerable attention for many years. Still the consequences of atmospheric N deposition on N metabolism of trees and its interaction with soil microbial processes has only recently been studied. Atmospheric N deposited to the leaves is thought to enter the general N metabolism of the leaves, but the processes involved, the interaction with different metabolic pathways, and the connection between injury by atmospheric N and its metabolic conversion are largely unknown. Laboratory and field experiments have shown that N of atmospheric NO₂ and NH₃, deposited to the leaves of trees, is subject to long-distance transport in the phloem to the roots. This allocation can result in considerable decline of N uptake by the roots. Apparently, the flux of N from the soil into the roots can be down-regulated to an extent that equals N influx into the leaves. This down-regulation is not mediated by generally enhanced amino-N contents, but by elevated levels of particular amino acids. Field experiments confirm these results from laboratory studies: Nitrate (NO₃) uptake by the roots of trees at a field sites exposed to high loads of atmospheric N is negligible, provided concentrations of Gln in the roots are high. At the ecosystem level, consequences of reduced N uptake by the roots of trees exposed to high loads of atmospheric N are (1) an increased availability of N for soil microbial processes, (2) enhanced emission of gaseous N-oxides from the soil, and (3) elevated leaching of NO₃ into the ground water. How recent forest management practices aimed at transforming uniform monocultures to more structured species-rich forests will interact with these processes remains to be seen. Possible implications of these forest management practices on N metabolism in trees and N conversion in the soil are discussed particularly in relation to atmospheric N deposition.