Foliar Nitrogen as an Indicator of Nitrogen Deposition and Critical Loads Exceedance on a European Scale

The foliar N content of bryophytes and Calluna vulgaris (L.) has been shown to be an indicator of atmospheric N deposition in the UK at a regional scale (1000km) and more recently on a smaller scale in the vicinity of intensive livestock farms. This work extends the geographical scale of the relationship between foliar N concentration of Calluna vulgaris and other ericaceous shrubs and N deposition with 2 measurement transects, one extending from northern Finland to southern Norway (2000 km) and the other extending from central Sweden to Stockholm, south east Sweden (330 km). Included in the second transect is a region of complex terrain in the Transtrand uplands, where the variation in N deposition with altitude and canopy cover was quantified using ²¹⁰Pb inventories in organic soil. The relationship between foliar N (F_N) and N deposition was shown to increase linearly with N deposition (N_D) over the range 0.8% N to 1.4% N according to F_N = 0.040N_D + 0.793 (r² = 0.70). The data are entirely consistent with earlier studies which together provide a valuable indicator of critical loads exceedance, the threshold value being approximately 1.5% N, which is equivalent to a N deposition of 20 kg N ha^?1 y^?1.     

Critical Nitrogen Deposition Loads in High-elevation Lakes of the Western US Inferred from Paleolimnological Records

Critical loads of nitrogen (N) from atmospheric deposition were determined for alpine lake ecosystems in the western US using fossil diatom assemblages in lake sediment cores. Changes in diatom species over the last century were indicative of N enrichment in two areas, the eastern Sierra Nevada, starting between 1960 and 1965, and the Greater Yellowstone Ecosystem, starting in 1980. In contrast, no changes in diatom community structure were apparent in lakes of Glacier National Park. To determine critical N loads that elicited these community changes, we modeled wet nitrogen deposition rates for the period in which diatom shifts first occurred in each area using deposition data spanning from 1980 to 2007. We determined a critical load of 1.4 kg N ha^?1 year^?1 wet N deposition to elicit key nutrient enrichment effects on diatom communities in both the eastern Sierra Nevada and the Greater Yellowstone Ecosystem.     

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.     

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.     

Exploring Ground Vegetation Change for Different Deposition Scenarios and Methods for Estimating Critical Loads for Biodiversity Using the ForSAFE-VEG Model in Switzerland and Sweden

The ForSAFE-VEG model was used to investigate the impacts of climate change and air pollution scenarios on soil chemistry and ground vegetations composition. In particular, the model involves a ground vegetation model incorporating plant changes to ambient site conditions in terms of climate and chemistry, but the model also incorporate competition between the different plant groups. The model was validated against observed values and reproduced observations of tree growth, soil chemistry, and ground vegetation compositions to satisfaction. The results show that the ground vegetation reacts strongly to changes in air pollution, in particular nitrogen as well as to climate change with major shifts in plant composition. A procedure for estimating critical loads for nitrogen, using ground vegetation biodiversity as criterion, was tested and the method seems operable. It suggests that if we want to protect the present biodiversity of the ground vegetation, this will face significant difficulties because of permanent climate change that induced changes in the ecosystem. We conclude that the reference state for ground vegetation biodiversity is rather to be sought for in the future, hopefully using models, than in the past or present.     

A Literature Review of Uncertainties in Studies of Critical Loads for Acidic Deposition

Uncertainties in the assessment of critical loads for acidic deposition are caused by the choice of biological indicators (BI), critical chemical values (CCV), the current methods used to determine critical loads for an ecosystem, and deficient field data. This paper focuses on the present steady-state mass balance (SSMB) approach, dynamic models and the importance of changes in atmospheric base-cation deposition (BCD), particularly in China. It is argued that 1) for the SSMB approach much uncertainty may come from the choice of BI and the related CCV, and long-term and large-scale monitoring data on weathering rates and growth uptake are urgently needed, especially in China, 2) significant uncertainty may be caused by changes in BCD during SO₂ emission controls, particularly in China, 3) constructing a mechanistic Al submodel may be a promising direction for dynamic models, and 4) the nutrient cycle in the vegetation through biogeochemical processes should be incorporated into dynamic models but the input requirements should be moderate for broad application considerations. Generally higher BCD, different soil components and characteristics and different vegetation types in China compared to Europe and North America suggest that more field investigations on BI and their corresponding CCV be carried out before application of current approaches to specific areas, particularly in China.     

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

Critical loads of acid deposition for ecosystems in South China are derived by synthesizing the critical loads of acid deposition for soils, the critical loads of SO₂ dry deposition for ecosystems, as well their exceedance. The results show in the southeast of Sichuan province around Chongqing municipality, the central and north of Guizhou province around Guiyang municipality, and the most areas of Jiangsu province, both the critical loads for soils and critical loads of SO₂ dry deposition are exceeded. In Guangxi Zhuang Autonomous Region and some areas among Jiangxi, Zhejiang and Anhui provinces, the critical loads of SO₂ dry deposition is the only restricting factor. There is no area where the critical load for soil is the only restricting factor in South China, so only the critical load for soil is not enough to be the basis to make sulfur abatement scheme.     

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.     

An Overview of Nitrogen Critical Loads for Policy Makers, Stakeholders, and Industries in the United States

Critical load values are calculated to determine ecosystem responses to deposition in a given area; these values may act as a tool to identify sensitive ecosystems in further need of protection. This overview provides an introduction to nitrogen critical loads for policy makers and parties involved in managing nitrogen deposition including electric utility generators, transportation managers and automobile manufacturers, and large-scale agricultural operators in the United States. It examines the use of the critical loads concept in European nations for establishing policy guidelines, current research on nitrogen critical loads in the U.S., and the development of nitrogen critical loads modeling and mapping.     

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.     

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.     

Atmospheric Deposition and Inorganic Nitrogen Flux

Flux of dissolved inorganic nitrogen (DIN??primarily nitrate) from terrestrial ecosystems has been considered an important contributor to acidification of linked aquatic systems. The basis of this concern is the nitrogen (N) saturation hypothesis, positing that additions of N to terrestrial ecosystems in excess of biological requirements will result in DIN leaching. There is a consensus (implicit hypothesis) in the literature that atmospheric deposition of DIN in excess of a threshold of approximately 10?kg?ha^?1?year^?1 leads to significant flux. Diverse data from USA indicate that DIN flux is highly variable both in space and time; the spatial uncertainty as measured by the pooled coefficient of variation is about 0.95, and the temporal (inter-year) uncertainty is about 0.75. The relationship between atmospheric deposition of DIN and annual flux is near-linear within the range of current deposition for US sites (??8?kg?ha^?1?year^?1 wet deposition). If wet and dry depositions are approximately equal, over 85 % of total DIN deposition is retained. This is nearly equal to the retention reported by the US Geological Survey National Water-Quality Assessment Program, which considered all nonpoint sources of N as inputs and both DIN and organic N as fluxes. Although input?Coutput data have high uncertainty, the 85 % retention of atmospheric DIN by terrestrial watersheds casts doubt on its importance as a contributor to aquatic acidification. There is no obvious threshold of deposition leading to DIN leaching. The nitrogen saturation hypothesis may not fully explain N behavior in terrestrial ecosystems.     

Forest Damages by the Storm ‘Lothar’ in Permanent Observation Plots in Switzerland: The Significance of Soil Acidification and Nitrogen Deposition

In a network of permanent observation plots in Switzerland,the storm ‘Lothar’ uprooted 18.7% of Fagussylvaticaand 14.8% of Picea abies. The percentage of uprootingwas significantly inversely correlated with actual soil basesaturation (NH₄Cl-extract). At a base saturation of≤40% (calculated as an average over 0–40cm depth) uprootingwas increased by a factor of 4.8 in beech and by a factor of3.6 in Norway spruce compared to less acidic soils. In beech,the percentage of uprooted trees was also significantlycorrelated with nitrogen concentration in the leaves(positively) and with coarse pore volume in the soil(negatively). There was neither a relation with seasonalozone dose nor a relation with crown transparency, stemdiameter, crown size, slenderness, social position andposition within the stand. The results suggest thatanthropogenic stress factors play an important role in theextent of the ‘Lothar’ damages in Switzerland.     

Relative Contribution of Nitrogen and Sulphur to Deposition Acidity and Regional Modelling in Lake Maggiore Watershed (Southern Alps,Switzerland and Italy)

Water, Air, & Soil Pollution - Over the last 20 years wet deposition chemistry in the Lake Maggiore watershed has been studied at 13 sites distributed at different altitudes throughout the...     

Deposition and Atmospheric Nitrogen Concentrations Trends in Cuba

The NO₂, nitrate and ammonia sampling in aerosols and rainfall was carried out at five stations located along the Cuban Island from 1986 to 1991. The sampling and chemical analysis were made mainly on the basis of methodologies recommended by WMO for above mentioned compounds at regional level. The total deposition of these compounds varies from 0.706 to 3.317 g m^-2 yr^-1. The wet deposition is about of 60%, so that the dry one is 40%. The amount of both depositions depends on our tropical rainy climate features. For some of these compounds the trend is increasing.     

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 ANC_limit 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.     

土壤污染物临界负荷研究进展

随着城市化进程与工农业的快速发展,土壤污染形势也越来越严峻。土壤污染物临界负荷的研究,可获取土壤可持续发展质量指标,是一条实现土壤可持续管理的有效途径。我国土壤污染临界负荷研究不足,为了推动其发展,本文讨论了其研究进展、指导原则、应用、存在问题与发展趋势。动态的和基于风险的土壤污染物临界负荷估算已是国际发展趋势。当前,缺乏完善的动态临界负荷估算模型,估算过程具有较大不确定性。为了准确地估算土壤污染物的临界负荷,在未来研究中需要加强对临界浓度制定和动态模型构建的研究,主要包括土壤中污染物的迁移传输规律、污染物的剂量-效应关系等。     

Acid Deposition and Critical Load Map of Tokyo

Acid deposition has been monitored in the natural vegetation of the western part of Tokyo, especially in the Okutama Mountains and surrounding areas. However, it is difficult to grasp the condition of acid deposition and the possible impacts on the vegetation in the whole area. Therefore, we attempted to make gridded acidic deposition maps and critical load maps. The grid size was 30 seconds latitude and 45 seconds longitude. Monthly wet deposition in the fiscal year of 1997 was calculated by multiplying concentration of wet deposition and precipitation. Concentration of wet deposition was estimated by averaging the data monitored at the nearest three stations with the inverse of distance as the weight. Precipitation was estimated by step-wise multiple regression with geographical factors as explanatory variables. Critical loads were estimated using the steady-state mass balance model with some modifications. As result, it was found that sulfur deposition had exceeded in most of the western part of Tokyo.     

Multi-Effect Critical Loads Used in Multi-Pollutant Reduction Agreements in Europe

The scientific support of negotiations on emission reductions under the framework of the Convention on Long-range Transboundary Air Pollution of the UN Economic Commission for Europe has been based during the last decade on the integrated assessment of sources, including abatement costs, and risks to receptors (e.g. forests, lakes) quantified by critical loads. The shift from a single-pollutant (sulfur) protocol in 1994 to a multi-pollutant protocol in 1999 necessitated an extension of the methods by which critical loads were computed and mapped. Instead of a single critical load for acidification, methods were now developed to assess the risk of acidifying effects of both sulfur and nitrogen deposition as well as the eutrophying effects of nitrogen on sensitive elements of the environment. Collaboration with a scientific network of 24 national institutions ensured a successful implementation of the proposed methodology across countries. This paper summarizes the methodology, describes the latest input data and presents critical load maps on the basis of which about 98% and 78% of European ecosystems would be protected against acidification and eutrophication, respectively, by the year 2010 according to the multi-pollutant multi-effect protocol.