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1.
Critical loads for N, S and total acidity, and amounts by which they are exceeded by present atmospheric loads, were derived for coniferous and deciduous forests in Europe using the one-layer steady-state model START. Results indicated that present acid loads exceed critical values in approximately 45% of the forested area i.e. 52% of all coniferous forests and 33% of all deciduous forests. The area exceeding critical loads was nearly equal for N (50%) and S (52%). However, the maximum exceedances were much higher for S (up to 12000 molc ha?1 yr?1 in Czechoslovakia, Poland and Germany) than for N (up to 3500 molc ha?1 yr?1 in the Netherlands, Belgium and Germany). Furthermore, the critical N loads derived refer to the risk of increased vegetation changes. Higher values, i.e. lower exceedances, were found for N when it was related to an increased risk in forest vitality decrease. The uncertainty in the area exceeding critical loads was estimated to be about ±50% of the given value. This is mainly due to uncertainties in the chemical criteria that have been used. However, despite the uncertainties involved it is clear that large exceedances in critical N and S loads occur in Western and Central Europe. This coincides with the area where a decrease in forest vitality has been reported.  相似文献   

2.
Planning advice for forest planting in acid sensitive areas suggests that, where calculated critical loads for acidity are exceeded at a catchment level, new conifer planting may not be appropriate. In south west Scotland, acid waters are currently found in areas where critical loads are not exceeded. The rivers Cree and Bladnoch show a decline in pH of about one unit since 1970, when major afforestation of the headwaters began. No equivalent decline in pH was observed in the adjacent Water of Luce, although it receives similar inputs and has similar geology and soils. Little of the Luce catchment is afforested. Recent surveys of water quality, invertebrate fauna and salmonid fish reveal a picture of widespread acid conditions, impoverished benthos and absence of young salmon. 25 streams (total catchment >150km2) recorded pH <4.5 in high flow conditions. Critical loads for acidity were >1.5keqha?1yr?1 for 12 and >2keqha?1yr?1 for 6 of the 25 streams. Published deposition data suggested that one stream with pH <4.5 and 7 streams with pH < 5 were in areas where critical load was not exceeded. In 22 catchments, forestry was a major land use. To be effective as planning and management tools, systems must be robust and easy to operate. Critical load exceedance calculations remain research tools at the catchment level where deposition data is generally inadequate. The uncertainties inherent in critical load exceedances render them sources of argument and not beacons of enlightenment.  相似文献   

3.
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.  相似文献   

4.
Atmospheric deposition of N and S on terrestrial and aquatic ecosystems causes effects induced by eutrophication and acidification. Effects of eutrophication include forest damage, NO3 pollution of groundwater and vegetation changes in forests, heathlands and surface waters due to an excess of N. Effects of acidification include forest damage, groundwater pollution, and loss of fish populations due to Al mobilization. Critical loads (deposition levels) for N and S on terrestrial and aquatic ecosystems in the Netherlands related to these effects have been derived by empirical data and steady-state acidification models. Critical loads of N generally vary between 500 and 1500 mol c ha?1 yr?1 for forests, heathlands and surface waters and between 1500 and 3600 for phreatic groundwaters. Critical loads of total acid (S and N) vary between 300 to 500 mol c ha?1 yr?1 for phreatic groundwaters and surface waters and between 1100 to 1700 mol ha?1 yr?1 for forests. On the basis of the various critical loads a deposition target for total acid of 1400 mol c ha?1 yr?1 has been set in the Netherlands from which the N input should be less than 1000 mol c ha?1 yr?1. This level, to be reached in the year 2010, implies an emission reduction of 80–90% in SO2, NO x and NH3 in the Netherlands and of about 30% in neighboring countries compared to 1980 emissions.  相似文献   

5.
Chemical composition of soil solution provides information on the availability of nutrients and potentially toxic substances to plant roots and mycorrhizas. It is therefore used to monitor impacts of air pollutants on soils. In this study we examined two soil solution parameters, base cations/aluminium ratio (Bc/Altot ratio) and inorganic nitrogen concentration (N), in samples collected at 300 intensive monitoring plots of the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) from the early 1990s to 2006 in order to detect possible critical limit exceedances (CLimE). CLimE for Bc/Altot ratio indicating negative effects for tree growth were only rarely detected. Quite the contrary was observed in CLimE for inorganic N concentrations where the safety limits were frequently exceeded in parts of Europe. Especially noteworthy is the number of the plots where leaching of N from forest soils occurred over the studied period. With ongoing high atmospheric N input into forest soils, we expect critical limits to be exceeded in the future as well.  相似文献   

6.
Significant areas of temperate forests in Central Europe, NE America and E Asia receive high amounts of N deposition. According to the few studies available, suspension of the N load leads to reductions in both inorganic soil N and leaching of N within a few years. We report that, surprisingly, N is still mineralized at high rates 14 yr after suspension of a previous N-load of >100 kg N/ha yr for 20 yr. In this treatment, gross N mineralization rates exceeded those in control plots by a factor 3, but equaled those in still on-going (34 yr of) treatments with 30 and 60 kg N/ha yr, in which levels of extractable NH4+ were up to 10 times higher.  相似文献   

7.
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.  相似文献   

8.
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.  相似文献   

9.
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.  相似文献   

10.
This study shows that it is questionable if critical load modelling can contribute in the search for harmful effects of acid deposition on forest health at present. Critical loads forS and N deposition were calculated using the MAGIC and PROFILE models for more than 100 monitoring plots in Norway spruce forestin south-east Norway. The two models gave different results, likely due to differences in the models, including differences in the time spans applied. The PROFILE model gave considerably more plots with exceedance than the MAGIC model.At plots where the CL was exceeded, calcium/aluminium (Ca/Al) ratios in the soil solutions were low. However, very few of theseplots had possible harmful values of the Ca/Al-ratio. More than 50 yr seems in most cases to be needed to bring Ca/Al ratios below 1.0. Present deposition was better correlated with measured forest condition variables such as crown condition and needle chemistry,than with modelled exceedance according to any of the two methods. The deposition of S and N was weakly, negatively correlated to foliar concentrations of P and Ca, and positivelyto foliar N concentrations and crown density.  相似文献   

11.
In the natural forest communities of Central Europe, beech (Fagus sylvatica L.) predominates in the tree layer over a wide range of soil conditions. An exception with respect to the dominance of beech are skeleton‐rich soils such as screes where up to 10 broad‐leaved trees co‐exist. In such a Tilia‐Fagus‐Fraxinus‐Acer‐Ulmus forest and an adjacent mono‐specific beech forest we compared (1) soil nutrient pools and net nitrogen mineralization rates, (2) leaf nutrient levels, and (3) leaf litter production and stem increment rates in order to evaluate the relationship between soil conditions and tree species composition. In the mixed forest only a small quantity of fine earth was present (35 g l—1) which was distributed in patches between basalt stones; whereas a significantly higher (P < 0.05) soil quantity (182 g l—1) was found in the beech forest. In the soil patches of the mixed forest C and N concentrations and also concentrations of exchangeable nutrients (K, Ca, Mg) were significantly higher than in the beech forest. Net N mineralization rates on soil dry weight basis in the mixed forest exceeded those in the beech forest by a factor of 2.6. Due to differences in fine earth and stone contents, the volume related soil K pool and the N mineralization rate were lower in the mixed forest (52 kg N ha—1 yr—1, 0—10 cm depth) than in the beech forest (105 kg N ha—1 yr—1). The leaf N and K concentrations of the beech trees did not differ significantly between the stands, which suggests that plant nutrition was not impaired. In the mixed forest leaf litter fall (11 %) and the increment rate of stem basal area (52 %) were lower than in the beech forest. Thus, compared with the adjacent beech forest, the mixed forest stand was characterized by a low volume of patchy distributed nutrient‐rich soil, a lower volume related K pool and N mineralization rate, and low rates of stem increment. Together with other factors such as water availability these patterns may contribute to an explanation of the diverse tree species composition on Central European screes.  相似文献   

12.
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.  相似文献   

13.
Critical acid loads for Dutch forests were derived using a multi-layer steady-state model that includes canopy interactions, nutrient cycling, mineral weathering and N transformations. Values were calculated for combinations of 12 tree species and 23 soil types for a 10×10 km grid. Critical acid loads thus derived increased with decreasing soil depth. Nearly 90% of the values varied approximately between 1500 and 4000 molc ha?1 yr?1 at 10 cm soil depth and between 750 and 2000 molc ha?1 yr?1 at the bottom of the rootzone. Separate critical loads calculated for N and S at the bottom of the rootzone varied between approximately 300 and 1000 molc ha?1 yr?1 for N and between 150 and 1250 molc ha?1 yr?1 for S. Using deposition data of 1990, a median reduction of the deposition by approximately 75% was calculated to achieve the critical loads at the bottom of the rootzone. The overall uncertainty in this value was estimated to be about 10%, although it can be much larger for specific soil types such as clay and peat soils. For N a larger reduction deposition percentage was calculated than for S, especially for coniferous forests with a high present N input.  相似文献   

14.
Critical loads for N and S on Dutch forest ecosystems have been derived in relation to effects induced by eutrophication and acidification, such as changes in forest vegetation, nutrient imbalances, increased susceptibility to diseases, nitrate leaching, and Al toxicity. The criteria that have been used are N contents in needles, nitrate concentrations in groundwater (drinking water), and NH4/K ratios, Ca/Al ratios, and Al concentrations in the soil solution. Assuming an equal contribution of N and S, all effects seem to be prevented at a total deposition level below 600 molc ha?1 yr?1 due to N uptake by stemwood and acid neutralization by base cation weathering. The most serious effects will probably be prevented at total deposition levels between 1500 and 2000 molc ha?1 yr?1. The current average deposition in the Netherlands is 4900 molc ha?1 yr?1.  相似文献   

15.
Measurements were made of NO3-N and NH4-N in bulk deposition, throughfall and soil solution on six permanent plots in pine and spruce stands located along a transect from the south to the north of Poland. Location differed both in the level of air pollution level and in climatic parameters. The total N load calculated from throughfall ranged from 12.5 to 34 kg-1a -1. The load of NH4-N exceeded the NO3-N contribution. Differences in total N load were not reflected in foliar N concentration. Present forest health status of stands determined by defoliation class, and do not appear to be related to their N deposition.  相似文献   

16.
Nitrous oxide (N2O) is a high‐impact greenhouse gas. Due to the scarcity of unmanaged forests in Central Europe, its long‐term natural background emission level is not entirely clear. We measured soil N2O emissions in an unmanaged, old‐growth beech forest in the Hainich National Park, Germany, at 15 plots over a 1‐year period. The average annual measured N2O flux rate was (0.49 ± 0.44) kg N ha–1 y–1. The N2O emissions showed background‐emission patterns with two N2O peaks. A correlation analysis shows that the distance between plots (up to 380 m) does not control flux correlations. Comparison of measured data with annual N2O flux rates obtained from a standard model (Forest‐DNDC) without site‐specific recalibration reveals that the model overestimates the actual measured N2O flux rates mainly in spring. Temporal variability of measured N2O flux was better depicted by the model at plots with high soil organic C (SOC) content. Modeled N2O flux rates were increased during freezing only when SOC was > 0.06 kg C kg–1. The results indicate that the natural background of N2O emissions may be lower than assumed by most approaches.  相似文献   

17.
The results of mapping critical loads, areas where they have been exceeded and steady state (Ca+Mg+K)/Al ratios of soils in Sweden, has been used to assess the order of magnitude of the ecological and economic risks involved with acid deposition for Swedish forests. The results of the calculations indicate that 81% of the Swedish forested area receive acid deposition in excess of the critical load at present. Under continued deposition at 1990 level, forest die-back is predicted to occur on approximately 1% of the forested area, and significant growth rate reductions are predicted for 80% of the Swedish forested area. For Sweden, growth losses in the order of 17.5 million m?3 yr?1 is predicted, equivalent to approximately 19% of current growth. Comparable losses can be predicted for other Nordic countries. The soil acidification situation is predicted to deteriorate significantly during the next 5–15 years, unless rapid emission reductions can be achieved. A minimum deposition reduction over Sweden of 85% on sulphur deposition and 30% on the N deposition in relation to 1990 level is required in order to protect 95% of the Swedish forest ecosystems from adverse effects of acidification. A minimum reduction of 60% on sulphur deposition and 30% on the N deposition is required to keep forest harvest at planned levels.  相似文献   

18.
Temperate forests dominated by Quercus spp. cover large parts of Central Mexico and rural communities depend on these forests for wood and charcoal. The impacts of charcoal production on selected chemical properties including C and N dynamics, and populations of ammonifiers, nitrifiers and denitrifiers were investigated on surface soils (0–15 cm) collected during the dry and rainy season of these forests. Organic C was halved in soil at the kiln sites compared to undisturbed forest soil. Concentrations of exchangeable Ca2+, K+ and Mg2+ increased >1.6 times at kiln sites and pH increased from 4.5 in undisturbed soil to 7.0 at kiln sites. The kiln sites had 1.3 times and 2.4 times lower microbial biomass C and N, respectively, than undisturbed forest sites during the rainy season. Although the effect of charcoal production on NH4+, NO2? and NO3? concentrations was small, the ammonifying, nitrifying and denitrifiers were 16 times lower at the kiln sites than in the undisturbed forest soil. This research found that the charcoal production had a negative effect on the cultivable microorganisms involved in N cycling and the soil microbial biomass C and N compared to undisturbed forest soil. Differences in inorganic N dynamics were more affected by seasonality, i.e. precipitation, than by charcoal production.  相似文献   

19.
One of the major threats to the structure and the functioning of natural and semi-natural ecosystems is the recent increase in air-borne nitrogen pollution (NHy and NOx). Ecological effects of increased N supply are reviewed with respect to changes in vegetation and fauna in terrestrial and aquatic natural and semi-natural ecosystems. Observed and validated changes using data of field surveys, experimental studies or, of dynamic ecosystem models (the empirical approach), are used as an indication for the impacts of N deposition. Based upon these data N critical loads are set with an indication of the reliability. Critical loads are given within a range per ecosystem, because of spatial differences in ecosystems. The following groups of ecosystems have been treated: softwater lakes, wetlands & bogs, species-rich grasslands, heathlands and forests. In this paper the effects of N deposition on softwater lakes have been discussed in detail and a summary of the N critical loads for all groups of ecosystems is presented. The nitrogen critical load for the most sensitive ecosystems (softwater lakes, ombrotrophic bogs) is between 5–10 kg N ha–1 yr–1, whereas a more average value for the range of studied ecosystems is 15–20 kg N ha–1 yr–1. Finally, major gaps in knowledge with respect to N critical loads are identified.  相似文献   

20.
Elevated atmospheric inputs of NH4+ and NO3– have caused N saturation of many forest ecosystems in Central Europe, but the fate of deposited N that is not bounded by trees remains largely unknown. It is expected that an increase of NO3– leaching from forest soils may harm the quality of groundwater in many regions. The objective of this study was to analyze the input and output of NH4+ and NO3– at 57 sites with mature forest stands in Germany. These long‐term study sites are part of the European Level II program and comprise 17 beech, 14 spruce, 17 pine, and 9 oak stands. The chloride balance method was used to calculate seepage fluxes and inorganic N leaching below the rooting zone for the period from 1996 to 2001. Nitrogen input by throughfall was significantly different among most forest types, and was in the order: spruce > beech/oak > pine. These differences can be largely explained by the amount of precipitation and, thus, it mirrors the regional and climatic distribution of these forest types in Germany. Mean long‐term N output with seepage was log‐normal distributed, and ranged between 0 and 26.5 kg N ha–1 yr–1, whereby 29 % of the sites released more than 5 kg N ha–1 yr –1. Leaching of inorganic N was only significantly lower in the pine stands (P < 0.05) compared with leaching rates of the spruce stands. Median N output : input ratio ranged between 0.04 and 0.11 for the beech, oak, and pine stands, while the input : output ratio of the spruce stands was 0.24, suggesting a higher risk of NO3– leaching in spruce forests. Following log‐transformation of the data, N input explained 38 % of the variance in N output. The stratification of the data by the C : N ratio of the O horizon or the top mineral soil revealed that forests soils with a C : N ratio < 25 released significantly more NO3– (median of 4.6 kg N ha–1 yr–1) than forests with a C : N ratio > 25 (median of 0.8 kg N ha–1 yr–1). The stratification improved the correlation between N input and N output for sites with C : N ratios < 25 (r2 = 0.47) while the correlation for sites with C : N ratios > 25 was weaker (r = 0.21) compared with the complete data set. Our results suggest that NO3– leaching may increase in soils with wide C : N ratios when N deposition remains on a high level and that the potential to store inorganic N decreases with C : N ratios in the O horizons becoming more narrow.  相似文献   

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