The use of critical load exceedances in abatement strategy planning

Critical loads for sulphur and nitrogen are defined to produce effective control strategies over Europe, such as those of the new sulphur protocol. To determine the critical load exceedances on the European scale it is necessary to simplify and generalize. The spatial variation on a scale smaller than the 150 × 150 km EMEP grid squares is considered for critical loads, via a cumulative frequency distribution and the 95 percentile for the grid square is determined. The deposition is assumed to be uniform over the area and the exceedance over the 95 percentile critical load is determined. In reality, the spatial variation is considerable for critical loads as well as for deposition. Calculations based on the frequency of local critical load exceedances have been made for two grid squares in southern Sweden. Local critical loads for acidity are compared to local deposition. Deposition variations due to pollution gradients within the square and to ecosystem structure have been considered. The results are similar for the two squares. The calculations based on local exceedances on 50×50 km grid squares and consideration to landuse variability, indicate that in order to protect 95% of the ecosystems in the square, emission reductions 25% greater than the large-scale European approach are needed. The effect of enhanced deposition at forest edges is of relatively small importance for the total exceedance.     

Critical loads of sulfur and nitrogen for lakes II: Regional extent and variability in Finland

The concept of critical loads has been developed to assist in the design of environmentally sound abatement strategies for the emissions of acidifying compounds. In this paper the critical loads of S and N for lakes in Finland are computed and mapped, based on methods presented in an accompanying paper. The employed steady-state mass balance model allows the simultaneous evaluation of the reductions required of S and N deposition exceeding these critical loads. Special emphasis has been put on the presentation of the spatial variability and the uncertainty of the critical loads and their exceedances. The derived critical loads of S and N for lakes in Finland show a substantial spatial variability. The highest exceedance of critical loads is presently estimated in the south-east of the country, where up to 80% of the lakes show an exceedance of the critical loads of S. The evaluation of two emission scenarios shows that only “maximum feasible reductions” would be sufficient for protecting most Finnish lakes from the impacts of acidic deposition. The results of this study form a basis for setting national targets for emission reductions in Finland.     

Critical loads of sulfur and nitrogen for lakes I: Model description and estimation of uncertainty

Presently considerable effort is devoted to the development of methods for estimating critical loads of acidic deposition. In this paper a steady-state mass balance model for lakes is presented, allowing the simultaneous calculation of critical loads of acidifying S and N deposition and their exceedance. Special emphasis is given to the derivation of model inputs and parameters and the quantification of their uncertainties. The inclusion of rate-limited processes in the model leads to the dependence of the critical loads not only on catchment properties but also on the loading to the ecosystem. As a consequence, critical load values have to be re-calculated whenever deposition patterns change. The methods presented in this study are used in an accompanying paper to derive regional distributions of critical loads of S and N for lakes in Finland and to quantify their uncertainties.     

Evidence for recent acidification of lentic soft waters in the Netherlands

During 1983–1984 about 90% of the Dutch soft waters appeared to be acid, and 35% of them showed pH-values below 4.0. The alkalinity of most waters (70%) was less than 0.1 meq. L^?1. Evidence for recent acidification is derived from temporal trends in water quality, fish population status, shifts in aquatic biota and application of current empirical models for lake acidification. It has been concluded that at least 59% of the Dutch soft waters have been recently acidified. This is a conservative estimate. Depending on the criterion used for assessment of acidification this percentage might be as high as 96%.     

The use of critical loads in emission reduction agreements in Europe

Critical loads have been used in the revision of the Sulphur Protocol of the Convention on Long Range Transboundary Air Pollution (LRTAP) of the United Nations Economic Commission for Europe (UN/ECE). Critical loads, i.e. maximum allowable depositions which do not increase the probability of damage to forest soils and surface waters, have been computed and mapped for Europe by means of the Steady-state Mass Balance Method, using national data and, if national data were unavailable, using a European database. Results show that areas with low critical loads are located mostly in northern and central Europe. The reduction of the excess of sulfur (S) deposition over critical loads was a starting point for negotiations leading to the Oslo Protocol on Further Reduction of Sulphur Emissions (the “Second Sulphur Protocol”). The new protocol protects about 81%, 86% and 90% of the ecosystems' area in 2000, 2005 and 2010, respectively. In addition, the total European area in which sulphur deposition exceeds critical loads by more than 500 eq ha^?1 yr^?1 will be reduced from about 19% in 1980 to practically zero in 2010. Besides these results, a methodology is presented which allows the combined assessment of the acidifying effects of S and N as well as the eutrophying effects of N deposition on ecosystems (so-called critical load functions and the protection isolines derived from them). This methodology is well suited to integrate ecosystem sensitivities into future negotiations on the reductions of nitrogen (N) compounds, taking into account present or anticipated S emissions.     

Effect of soil acidification on the growth and nitrogen use efficiency of maize in Ultisols

Purpose

To examine the effect of soil acidification on growth and nitrogen (N) uptake by maize in Ultisols.

Materials and methods

A clay Ultisol derived from Quaternary red earth and a sandy Ultisol derived from tertiary red sandstone were used in this study. A pot experiment was conducted with maize growing in the two Ultisols acidified to different pH values. Urea with ¹⁵N abundance of 10.11% was used to investigate the distribution of N fertilizer between soil and plant. Total N content and ¹⁵N abundance in plant and soil samples were determined by elemental analysis-isotope mass spectrometry.

Results and discussion

Critical soil pHs of 4.8 and 5.0 were observed for maize growing in the clay and sandy Ultisols, respectively. Below the critical soil pH, increasing soil pH significantly increased maize height and the yield of maize shoots and roots (both P < 0.05), but changes in soil pH showed no significant effect on maize growth above the critical soil pH in both Ultisols. Maize growing in the sandy Ultisol was more sensitive to changes in soil pH than in the clay Ultisol. Increase in the pH in both Ultisols also increased N accumulation in maize, the N derived from fertilizer in maize, physiological N use efficiency, and N use efficiency (NUE) by maize. Changes in soil pH had a greater effect on these parameters below the critical soil pH, compared to above. The change in soil pH had a greater effect on N accumulation in maize, the N derived from fertilizer in maize, and NUE in the sandy Ultisol than in the clay Ultisol. The NUE increased by 24.4% at pH 6.0, compared with pH 4.0 in the clay Ultisol, while the NUE at pH 5.0 was 4.8 times that at pH 4.0 in the sandy Ultisol. The increase in soil pH increased the ratio of N accumulation in maize/soil residue N and decreased the potential loss of fertilizer N from both Ultisols.

Conclusions

Soil acidification inhibited maize growth, reduced N uptake by maize, and thus, decreased NUE. To maintain soil pH of acidic soils above the critical values for crops is of practical importance for sustainable food production in acidic soils.

     

氮、硫配施对冬小麦氮素利用效率及产量的影响

【目的】氮(N)、硫(S)是生物所必需的营养物质,对小麦籽粒产量和品质起着重要作用。硫素供应不足,特别是在当前大量氮素供应情况下引起的作物生理性缺硫将导致作物产量和含硫氨基酸蛋白质含量下降。本文旨在探索氮、硫配施对冬小麦氮素利用效率和籽粒产量的促进效果并提出合理的区域氮、硫施肥技术。【方法】20122013年,在河南温县以国审冬小麦品种豫麦49-198为供试材料,进行大田试验。设置不同施氮量0、120、180、240和360 kg/hm2(分别以N0、N120、N180、N240和N360表示)和施硫0和60 kg/hm2(S0和S60)试验,调查氮、硫对冬小麦干物质积累、氮素积累分配、籽粒产量和氮素利用效率的影响。【结果】对冬小麦生育后期干物质积累分析表明,干物质积累随施氮量增多而提高,相同施氮量条件下施硫较不施硫小麦干物质积累量显著提高,其中成熟期干物质积累量N180S60、N240S60和N360S60分别较N180S0、N240S0和N360S0提高2225、3607和3120 kg/hm2,而且氮素低的处理添加硫后干物质积累量高于氮素高不加硫处理,如N180S60N240S0、N240S60N360S0,处理间差异均达显著水平。随施氮量增多,冬小麦植株氮素积累总量增加,在N 240和360 kg/hm2水平,硫素供应显著增加小麦植株氮素积累。不同施氮量条件下施硫较不施硫均显著提高了小麦籽粒产量,分别提高了10.5%、18.3%、5.2%、5.6%和4.9%。随施氮量增多,氮肥偏生产力下降,氮回收效率、生理效率和农学效率则均以N 180达最高值。不同施氮水平下,施硫均显著提高了冬小麦氮素回收效率,但对氮生理效率影响不显著,其中在施N量为120、180和240kg/hm2时,施硫较不施硫氮肥偏生产力和农学效率均显著提高。【结论】在当前小麦生产中,采用控氮或减氮增硫技术措施,可实现小麦氮利用效率和籽粒产量的同步提高。在本试验地区小麦生产中,达到冬小麦稳产高效或增产高效的适宜施氮量为180 240 kg/hm2配合60 kg/hm2硫肥施用。     

Mapping critical levels of ozone,sulfur dioxide and nitrogen dioxide for crops,forests and natural vegetation in the United States

Air pollution abatement strategies for controlling nitrogen dioxide, sulfur dioxide, and ozone emissions in the United States focus on a ‘standards-based’ approach. This approach places limits on air pollution by maintaining a baseline value for air quality, no matter what the ecosystem can or cannot withstand. In this paper, we present example critical levels maps for the conterminous U.S. developed using the ‘effects-based’ mapping approach as defined by the United Nations Economic Commission for Europe's Convention on Long-Range Transboundary Air Pollution, Task Force on Mapping. This approach emphasizes the pollution level or load capacity an ecosystem can accommodate before degradation occurs, and allows for analysis of cumulative effects. We present the first stage of an analysis that reports the distribution of exceedances of critial levels for NO₂, SO₂, and O₃ in sensitive forest, crop, and natural vegetation ecosystems in the contiguous United States. We conclude that extrapolation to surrounding geographic areas requires the analysis of diverse and compounding factors that preclude simple extrapolation methods. Pollutant data depicted in this analysis is limited to locationally specific data, and would be enhanced by utilizing spatial statistics, along with converging associated anthropogenic and climatological factors. Values used for critical levels were derived from current scientific knowledge. While not intended to be a definitive value, adjustments will occur as the scientific community gains new insight to pollutant/receptor relationships. We recommend future analysis to include a refinement of sensitive receptor data coverages and to report relative proportions of exceedances at varying grid scales.     

Predicting freshwater critical loads from national data on geology,soils and land use

Using information on geology, soils and land use, a map has been generated for Great Britain which indicates five classes of sensitivity of surface waters to acidification. This map has been used for designing sampling strategies for mapping critical loads of acidity for freshwaters. This paper evaluates the freshwater sensitivity map using a data set of water chemistry collected as part of the UK critical loads programme. Discriminant analysis was used to predict five critical load classes from information on geology and soil sensitivity for freshwater sites. This showed geology and soil information can correctly predict approximately 50% of all critical loads classes. In addition, 77% of sites fall within one critical loads class of that predicted. Predictions may be improved by including other variables eg altitude and geographical location. Differences between lake, stream and reservoir sites are also examined. Ranges of critical loads values were determined for each of the five classes of surface water sensitivity. While a trend in critical load values was evident between classes, there was significant overlap. A simplified sensitivity map with only three classes related more closely to critical loads values. The paper demonstrates the usefulness of the surface water sensitivity map for assessing acidification at a national scale, but highlights the difficulties of predicting critical loads for individual sensitive catchments using national data.     

Atmospheric sulfur and nitrogen in West Java

Wet-only rainwater composition on a weekly basis was determined at four sites in West Java, Indonesia, from June 1991 to June 1992. Three sites were near the extreme western end of Java, surrounding a coal-fired power station at Suralaya. The fourth site was ～100 km to the east in the Indonesian capital, Jakarta. Over the 12 months study period wet deposition of sulfate at the three western sites varied between 32–46 meq m^?2 while nitrate varied between 10–14 meq m^?2. Wet deposition at the Jakarta site was systematically higher, at 56 meq m^?2 for sulfate and 20 meq m^?2 for nitrate. Since sulfate and nitrate wet deposition fluxes in the nearby and relatively unpopulated regions of tropical Australia are both only ～5 meq m^?2 anthropogenic emissions of S and N apparently cause significant atmospheric acidification in Java. It is possible that total acid deposition fluxes (of S and N) in parts of Java are comparable with those responsible for environmental degradation in acid-sensitive parts of Europe and North America.     

Developing optimal abatement strategies for the effects of sulphur and nitrogen deposition at European scale

Integrated Assessment Models were successfully used to provide input to the negotiations for the Oslo Protocol on Further Reductions of Sulphur Emissions, finalized within the United Nations Economic Commission for Europe Convention on Long-range Transboundary Air Pollution in Oslo in June 1994. The techniques developed within this framework will be extended now to the simultaneous analysis of sulphur and nitrogen deposition. In addition to acidification, atmospheric deposition of nitrogen contributes to eutrophication of certain ecosystems, through a nutrient effect, and originates from the long-range transport of emissions of both oxidised and reduced nitrogen (NO_x and NH₃). Modelling reductions in nitrogen deposition thus introduces a need to establish multi-pollutant multi-effect modelling techniques. This paper investigates the development of a model set up to examine reductions of these pollutants in an economically and environmentally efficient manner. The control of nitrogen deposition encompasses action across several economic sectors, particularly the power, transport and agricultural sectors. Combining sulphur and nitrogen deposition limits on a European scale will require a flexible modelling approach and the issues governing possible approaches are presented.     

Uncertainty analysis of critical loads for terrestrial ecosystems in Russia

The goal of this study is to give a comprehensive and quantitative estimation of the uncertainty of computed in different scale nitrogen (N) and sulphur (S) critical loads (CL) values for terrestrial ecosystems of the Northern Asia, European part and the North-Western regions of Russia. The CL values are used to set goals for future deposition rates of acidifying compounds so that the environment is protected. In this research CL values for terrestrial ecosystems are determined using the expert-modelling geoinformation system (EM GIS) approach. UNCSAM software package is used as the tool for uncertainty analysis. The analysis presented here focuses on the estimation and effect of the input source uncertainties and sensitivities on the CL values in various regions under study. In spite of the region, nitrogen uptake by vegetation, nitrogen leaching from terrestrial ecosystems and the difference between deposition and uptake by plants of base cations (BC) are the most influential factors for all terrestrial ecosystems of Russia.     

Estimating uncertainty in the current critical loads exceedance models

The critical loads approach to quantifying areas at risk of damage requires deposition and critical loads data at the same spatial scale to calculate exceedance. While maps of critical loads for soil acidification are available at a 1 km scale no monitoring networks in Europe measure wet and dry inputs at this scale and, further, the models currently used to estimate deposition incorporate a number of assumptions which are not valid at the 1 km scale. Simulations of 1 km deposition from 20 km data show that the uncertainty introduced by using 20 km scale estimates of deposition is small, except in mountain areas where it can give misleading results, but a major problem is the uncertainty in estimates of deposition at the 20 km scale produced by the current models.     

Application of the critical loads approach in South Africa

South Africa is the most industrialised country in southern Africa and stands at some risk from negative pollution impacts. To the authors' knowledge, this paper presents the first attempt to apply the critical loads approach on the African continent; although sensitivity mapping has been performed for Africa and the rest of the world (Kuylerstierna et al, this conference). Actual sulphate and base cation deposition loads in Mpumalanga (formerly the Eastern Transvaal province of South Africa) were mapped from 16 monitoring sites. The region is characterised by long, dry periods with little rain, high evaporation (up to 8 mm per day) and low run-off (15% of MAP). Provisional critical load and exceedance maps were produced for the surface waters using the Steady-State Water Chemistry Model and the Diatom model. Maps of soil sensitivity to acid deposition, based on bedrock lithology, soil chemical characteristics and land cover, were produced. A weathering rate of 0.39–0.86 keq/ha/year was calculated for the most sensitive sites and taken as the critical load, based on the assumption that the weathering rate represents the buffering ability of the system. The critical loads were contrasted with measures of actual deposition to examine potential scenario's for critical load exceedances. Akey factor in refining the sensitivity maps, and allowing estimation of the critical loads, is the accurate calculation of weathering rates under the warmer and more arid environmental conditions prevalent in South Africa. In a developing country such as South Africa, where research resources are limited, the critical loads approach is a valuable means of assessing the risk of potential impacts of atmospheric deposition.     

作物临界氮浓度稀释模型研究述评

作物临界氮浓度是作物达到最大生长的植株最小氮浓度。临界氮浓度随地上部植株干物质积累量增加而下降,可以用幂函数模型N_c=a×W_max^-b表示。已建立了数十种作物临界氮稀释模型,根据作物收获器官的特点,分为收获籽粒、收获鲜果实、收获块根块茎和收获地上部营养体4类,不同类型临界氮浓度稀释模型在模型参数和氮素诊断应用方面各有特点。临界氮浓度稀释模型除了植株临界氮浓度-植株干重这一典型形式外,还有器官临界氮浓度-器官干重、植株临界氮浓度-器官数量指标(叶片干重、茎鞘干重、LAI、叶面积持续期)等形式。因此,提出评价选择临界氮浓度稀释模型类型的基本原则。由于不同气候条件、不同作物类型,甚至同一作物不同品种的生育特性、氮素营养特性和干物质生产力差异很大,建立某一大类作物甚至某一种作物在各个气候区域的通用模型是困难的,应以一定生态区域某一作物特征相近品种类型作为建模基本单元。作物临界氮浓度稀释模型的应用包括计算氮营养指数(NNI)进行氮素营养诊断,计算临界氮积累量、亏缺量和氮肥需要量,预测作物产量和品质等。分析了以植株干物质重驱动的氮素...     

Calculating critical loads for acidity with the simple mass balance method

The critical load for acid deposition to forest soils, groundwater and surface water can be calculated using a simple mass balance model, taking into account all sources of acidity and alkalinity in the system. The model is very simple to apply, and the major difficulty lies primarily in the estimation of reasonable values for the required input data such as the weathering rate. Methods for its estimation are indicated here. Examples are given for the application of the simple mass balance method (SMB) to Dutch and Swedish forest soils, lakes and shallow groundwater. This work outlines and explains the actual application of the consept as it is being carried out regionally for all European nations.     

氮硫配施对冬小麦氮硫吸收转运及利用效率的影响

采用二元二次正交旋转组合设计,通过田间试验研究了陕西关中地区氮硫配施对冬小麦氮硫素吸收、转运及利用效率的影响。试验施氮量[kg(N)·hm-2]设75(N1)、108(N2)、187.5(N3)、267(N4)和300(N5)5个水平,施硫量[kg(S)·hm-2]设75(S1)、97.5(S2)、150(S3)、202.5(S4)和225(S5)5个水平,组成N4S4、N4S2、N2S4、N2S2、N5S3、N1S3、N3S5、N3S1、N3S3 9个处理。结果表明:拔节期至开花期是冬小麦干物质和氮、硫积累的高峰期,积累量分别占全生育期内干物质和氮、硫积累量的43.33%~48.42%、28.71%~44.77%和40.11%~50.43%。氮素向籽粒的转运率(63.61%~70.64%)远高于硫素向籽粒的转运率(10.63%~30.98%);氮硫配施促进了小麦花后营养器官氮硫向籽粒的运转,同时增加了总转运量对籽粒氮硫的贡献率。在N2(108 kg·hm-2)和S2(97.5 kg·hm-2)水平,氮硫积累量及转运量随施硫量或施氮量的增加而增加;在N3(187.5 kg·hm-2)和S3(150 kg·hm-2)水平,则随施硫量或施氮量的增加先增加后趋于稳定。植株体内的氮素和硫素吸收累积量具有极显著相关关系。综合考虑氮素(硫素)表观利用率及生理效率,在施氮量(170.64~204.52 kg·hm-2)与施硫量(97.35~139.32 kg·hm-2)水平下,氮硫肥利用率较高。因此,在冬小麦栽培过程中,可以通过调节施氮量和施硫量,充分利用氮硫交互效应,提高氮硫的吸收、分配及利用效率。     

Validation of the UK critical loads for freshwaters: Site selection and sensitivity

Critical loads maps for UK freshwaters have been produced on a 10×10 km grid square basis, and used to map critical load exceedances under various deposition scenarios. A single lake or stream site was selected to represent the most sensitive water body in each grid square using predefined criteria. In the UK a major programme of data screening and validation has been undertaken in order to address issues of accuracy and validity. A major part of this validation exercise, the within-square variability study, is designed to test the extent to which the site chosen for mapping represents the most sensitive water body within each grid square or mapping unit. Sampling of all lake sites in thirty-two randomly chosen 10 × 10 km grid squares has shown that in two thirds of cases, the selection exercise has identified a site in the lowest critical load class within a square. However, up to a third of all sites selected to represent grid squares could be replaced by more sensitive sites with a critical load smaller by at least one Skokloster class. The mean overestimate of diatom model critical loads for sulphur in the within-square variability study is 0.188 keq ha^–1 yr^–1. This means that current critical load maps show overestimates for some grid squares. In order to determine where the most sensitive site has not been identified, further work on catchment scale classification of freshwater sensitivity is being carried out.     

Improvement in nitrogen availability, nitrogen uptake and growth of aerobic rice following soil acidification

A yield decline and increase in soil pH under continuous cropping of aerobic rice have been reported in previous studies. However, the underlying mechanisms governing the poor growth and low yield of aerobic rice following an increase in soil pH are unknown. The objective of the present study was to determine the effect of soil acidification on the soil nutrient availability, plant nutrition and growth of aerobic rice grown in continuously cropped aerobic soil. Two pot experiments were conducted using soil from a field where aerobic rice had been grown for 13 consecutive seasons. Soil was acidified by adding 50–300 mL of 0.05 mol L^–1 sulfuric acid to 3.0 kg of air-dried soil to achieve a range of soil pH levels. Rice was grown aerobically with N rates of 0–1.2 g per pot using urea or ammonium sulfate. Soil chemical properties were measured as were leaf nutrient concentrations, plant growth parameters, and the above-ground N uptake. A 5.5-fold and 1.5-fold increase in soil ammonium and nitrate were observed, respectively, after adding sulfuric acid. Plant growth and N uptake improved significantly with soil acidification, regardless of N rates or N sources, and were associated with an improvement in plant N nutrition. The application of N had greater positive effects on plant growth and N uptake than soil acidification. The growth response to soil acidification reduced as the rate of N application increased. These results suggest that the yield decline of continuous aerobic rice is probably associated with a reduction in soil N availability and plant N uptake as a result of a gradual increase in soil pH.     

Effects of nitrogen deposition on the acidification of terrestrial and aquatic ecosystems

The concentration of ammonium and nitrate in precipitation has increased during this century. The deposition of N compounds (wet + dry) is reaching 30 to 40 kg ha^?1yr^?1 in many areas in Central Europe and above 20 kg in the southern parts of Scandinavia. In extreme situations throughfall data indicate depositions above 60 kg ha^?1yr^?1 in Central Europe and above 40 kg ha^?1yr^?1 in south Sweden. Very high depositions are observed on slopes at forest edges and adjacent to areas with animal farms and manure spreading. In areas with low N deposition almost all deposited N (>95%) will be absorbed in the tree canopies or in the soil. In areas with high deposition an increased outflow is observed which in some cases reach 10 to 15 kg ha-lyr-1. The increased output is an indication of N saturation of the ecosystem and it leads to acidification effects in soils, soilwater, groundwater and surface waters.