Relationship between critical load exceedances and empirical impact indicators at Integrated Monitoring sites across Europe

Critical loads for acidification and eutrophication and their exceedances were determined for a selection of ecosystem effects monitoring sites in the Integrated Monitoring programme (UNECE ICP IM). The level of protection of these sites with respect to acidifying and eutrophying deposition was estimated for 2000 and 2020. In 2020 more sites were protected from acidification (67%) than in 2000 (61%). However, due to the sensitivity of the sites, even the maximum technically feasible emission reductions scenario would not protect all sites from acidification. In 2000, around 20% of the IM sites were protected from eutrophication. In 2020, under reductions in accordance with current legislation, about one third of the sites would be protected, and at best, with the maximum technically feasible reductions, half of the sites would be protected from eutrophication. Data from intensively monitored sites, such as those in ICP IM, provide a connection between modelled critical thresholds and empirical observations, and thus an indication of the applicability of critical load estimates for natural ecosystems. Across the sites, there was good correlation between the exceedance of critical loads for acidification and key acidification parameters in runoff water, both with annual mean fluxes and concentrations. There was also evidence of a link between exceedances of critical loads of nutrient nitrogen and nitrogen leaching. The collected empirical data of the ICP IM thus allow testing and validation of key concepts used in the critical load calculations. This increases confidence in the European-scale critical loads mapping used in integrated assessment modelling to support emission reduction agreements.     

The sensitivity of Afromontane tarns in the Maloti-Drakensberg region of South Africa and Lesotho to acidic deposition

Despite their remoteness from sources of atmospheric pollutant emissions, the Afromontane tarns in the Maloti-Drakensberg region are perfect candidates to study the negative effects of acidifying atmospheric pollution, because mountain lakes are widely recognised as sentinel ecosystems, unimpacted by direct human disturbance within their catchments. Thirty-four tarns were sampled in the Maloti-Drakensberg region and most were found to be extremely sensitive to acidic deposition, as indicated by their low acid neutralising capacity. There are very few studies of freshwater critical loads for any region within South Africa. The steady-state water chemistry model (SSWC) was adapted and used to determine critical loads, whereas exceedance was estimated relative to modelled regional deposition data, in order to understand the risk of harmful effects to aquatic ecosystems. Seventy-six percent of sampled sites across the Maloti-Drakensberg would exceed critical loads even at the lowest modelled deposition levels, but there are no current measured deposition data for the region. The sensitivity of the Maloti-Drakensberg tarns needs to be considered in future policy formulation regarding acceptable levels of acidifying atmospheric pollution from South Africa’s energy sector and indicates the need for assessing aquatic ecosystem impacts in other regions of South Africa.     

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

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

Influence of canopy budget model approaches on atmospheric deposition estimates to forests

Accurate quantification of total nitrogen and acidifying deposition is a major source of uncertainty in determining the exceedance of critical loads in forest ecosystems. Monitoring of atmospheric deposition is frequently based on throughfall measurements in combination with the canopy budget model to calculate ion-exchange fluxes between the forest canopy and incident rainfall water. Various approaches for each step in the canopy budget model have been reported and compared, but combinations of different approaches were not yet assessed. Therefore, the present study quantified the range of estimated dry deposition and total deposition resulting from all possible combinations of canopy budget model approaches for three typical case studies: (i) total nitrogen and potentially acidifying deposition onto a forest canopy, (ii) the ratio of these deposition variables between adjacent coniferous and deciduous stands and (iii) the parameters of a deposition time trend analysis. The time step, type of precipitation data and tracer ion used in the model had a significant effect on the findings in the three case studies. In addition, including or excluding canopy leaching of weak acids and canopy uptake of nitrogen during the leafless season largely affected the results, while including or excluding canopy uptake of nitrate generally showed no effect. In general, the use of wet-only precipitation data can be recommended, along with sodium as a tracer ion and the inclusion of weak acids. We conclude that further research should focus on the assumptions of inertness of the tracer ion and the equal deposition efficiency of base cations and the tracer ion and on the quantification of weak acids in rainfall and throughfall water. Since local or tree-species specific effects might influence the results obtained in this study, a similar analysis is recommended for other tree species and regions when using the canopy budget model.     

Developing an indicator-modelling approach to forecast changes in nitrogen critical load exceedance across Europe arising from agricultural reform

Atmospheric nitrogen (N) deposition above the critical load causes eutrophication with adverse impacts on biodiversity. Average Accumulated critical load Exceedance (AAE) is a measure of the amount of critical load exceedance and the area of habitat which is affected, and has been adopted in Europe as a pressure indicator for biodiversity. In Europe, AAE is calculated by the Coordination Centre for Effects (CCE) of the United Nations Economic Commission for Europe based on modelled nitrogen deposition and country-level reporting of critical load thresholds and ecosystem area. Due to differences in country-level reporting, AAE values for semi-natural habitats may show large differences across Europe. This paper therefore describes the development of a simpler approach to the modelling of habitat eutrophication. The eutrophication indicator model is applicable to all habitats for which empirical critical loads for nutrient nitrogen have been defined and is easily configured to assess impacts of modelled policies or scenarios on AAE. Outputs from the model showed a high correlation with published AAE data (R² = 0.80) and replicated broad spatial patterns in AAE, but under-estimated actual values by a factor of 2.5. This variation was traced primarily to the use of habitat-specific nitrogen deposition by the CCE which calculates higher nitrogen deposition to forest areas, but also to differences between countries in the critical load thresholds used and the areas of sensitive ecosystems reported. Sensitivity testing showed that exceedance calculations were particularly sensitive to the critical load threshold used, since nitrogen deposition across Europe lies in the middle of most critical load ranges. The indicator model was used to forecast AAE under two scenarios: socio-economic changes under a business as usual scenario to 2025, and the additional effect of agricultural reform where both direct support to farmers and market support were removed. Ammonia emissions showed a net decrease by 2025, with strong regional differentiation. Emissions increased in former Soviet bloc countries and decreased mainly in south west Europe and Finland. Agricultural reform had little additional impact on ammonia emissions. AAE was forecast to decrease by 49% by 2025, due mainly to reductions in emissions of oxidised N from industry and transport, independent of agricultural reform. However, as oxidised N decreases, the relative contribution of N from agricultural sources will increase, and policy measures which reduce ammonia emissions will have increasing relevance for reducing AAE.     

离子树脂法测定森林穿透雨氮素湿沉降通量——以千烟洲人工针叶林为例

穿透雨是大气氮素输入森林生态系统的重要途径之一,穿透雨中氮素含量的定量评估在森林生态系统氮素循环研究中的作用不可忽视。穿透雨中氮沉降通量的空间异质性很强,传统降水收集法工作量大,且容易带来测定误差。分析了国产离子树脂测定大气氮素湿沉降的可行性,并以千烟洲人工针叶林为例探讨离子树脂法测定森林穿透雨的适用性。结果表明,离子交换树脂法和传统降水收集法测定值之间的相关性显著,离子交换树脂法可以很好的反映大气氮沉降通量和季节变化特征,并且在采样周期较长时也能准确测定氮沉降组分,是适用于野外站点林内穿透雨氮沉降通量的观测方法。千烟洲人工针叶林穿透雨的氮沉降通量为9.19 kgN?hm-2?a-1,夏季的5—7月份和冬季的1—2月份出现氮沉降通量高峰。夏季穿透雨氮沉降以铵态氮为主,而冬季以硝态氮为主。千烟洲人工针叶林的氮沉降通量与附近地区针叶林穿透雨氮沉降通量近似,低于临近区域阔叶林穿透雨的氮沉降通量水平,但已可能接近森林生态系统氮输出出现强烈反应的氮沉降临界值。     

Characterising the effects of high ammonia emission on the growth of Norway spruce

This paper studies the effects of high ammonia emissions and nitrogen deposition on tree growth. Wood cores of 125 Norway spruces were analysed along a transect (800 m) from forest edge to forest interior. The forest edge was exposed to a strong ammonia emission source (poultry farm, less than 50 m). Atmospheric nitrogen bulk deposition, ammonia concentration, soil solution concentration, soil nutrient content, foliar N concentration and C/N ratio of the humus layer were measured at five plots along the transect. The tree growth increment of two clusters of trees close to the forest edge and forest interior was compared. The results indicate extremely high nitrogen load at the forest edge. All nitrogen variables show an `edge effect' with increasing values from forest interior to the forest edge. The growth of nitrogen-influenced spruce trees generally increases. Trees with excessive long-term nitrogen load appear to loose increment after a long-term nitrogen impact. The average gain of increment at the edge appears to be related to the amount of nitrogen emission.     

Natural vegetation cover in the landscape and edge effects: differential responses of insect orders in a fragmented forest

Human activities have led to global simplification of ecosystems, among which Neotropical dry forests are some of the most threatened. Habitat loss as well as edge effects may affect insect communities. Here, we analyzed insects sampled with pan traps in 9 landscapes (at 5 scales, in 100–500 m diameter circles) comprising cultivated fields and Chaco Serrano forests, at overall community and taxonomic order level. In total 7043 specimens and 456 species of hexapods were captured, with abundance and richness being directly related to forest cover at 500 m and higher at edges in comparison with forest interior. Community composition also varied with forest cover and edge/interior location. Different responses were detected among the 8 dominant orders. Collembola, Hemiptera, and Orthoptera richness and/or abundance were positively related to forest cover at the larger scale, while Thysanoptera abundance increased with forest cover only at the edge. Hymenoptera abundance and richness were negatively related to forest cover at 100 m. Coleoptera, Diptera, and Hymenoptera were more diverse and abundant at the forest edge. The generally negative influence of forest loss on insect communities could have functional consequences for both natural and cultivated systems, and highlights the relevance of forest conservation. Higher diversity at the edges could result from the simultaneous presence of forest and matrix species, although “resource mapping” might be involved for orders that were richer and more abundant at edges. Adjacent crops could benefit from forest proximity since natural enemies and pollinators are well represented in the orders showing positive edge effects.     

Driving Factors Behind Litter Decomposition and Nutrient Release at Temperate Forest Edges

Forest edges have become important features in landscapes worldwide. Edges are exposed to a different microclimate and higher atmospheric nitrogen (N) deposition compared to forest interiors. It is, however, unclear how microclimate and elevated N deposition affect nutrient cycling at forest edges. We studied litter decomposition and release of N, phosphorus (P), total cations (TC) and C/N ratios during 18 months via the litterbag technique along edge-to-interior transects in two oak (Quercus robur L.) and two pine (Pinus nigra ssp. laricio Maire and ssp. nigra Arnold) stands in Belgium. Furthermore, the roles of edge conditions (microclimate, atmospheric deposition, soil fauna and soil physicochemical conditions), litter quality and edge decomposer community were investigated as underlying driving factors for litter decomposition. Litter of edge and interior was interchanged (focusing on the influence of edge conditions and litter quality) and placed in open-top chamber (OTC), which create an edge (warmer) microclimate. As the decomposer macrofauna was more abundant at the edge than in the interior, the OTCs were used to isolate the effects of warming versus soil fauna. Oak litter at the edge lost 87 and 37% more mass than litter in the interior. We demonstrated an edge effect on litter decomposition and nutrient release, caused by an interplay of edge conditions (atmospheric deposition of N and TC, soil pH and C/N ratio), litter quality and soil fauna. Consequently, edge effects must be accounted for when quantifying ecosystem processes, such as litter decomposition and nutrient cycling in fragmented landscapes.     

Are there edge effects on forest fungi and if so do they matter?

Fungi are vital within forest ecosystems through their mycorrhizal relationships with trees, and as the main agents of wood decomposition and thus carbon and nutrient cycling. Globally, forests are becoming increasingly fragmented, creating forest patches that are isolated, reduced in area, and exposed at edges. Edges are often ecologically distinct from the forest interior due to their exposure to the matrix habitat. This exposure can result in altered microclimatic conditions and flows of biotic and abiotic materials such as spores or inorganic nitrogen, respectively.Although fungi are known to be affected by microclimate and nitrogen deposition, knowledge of forest edge effects on fungi is extremely limited; however, a consideration of the factors known to regulate fungal activity in combination with known biotic and abiotic edge effects implies that forest edges are likely to strongly influence fungi. These include responses of fungi to the altered microclimate and nitrogen levels at forest edges, at both the individual and community level; interactions with plants and animals that have been influenced by edges; above–belowground feedback between mycorrhizal fungi and host trees. The small body of existing research focuses on fruit body presence and distribution; fungal biomass and community composition in soil have been touched upon. Positive, negative and neutral edge responses have been found, the majority of studies finding a significant effect on some of the parameters measured. Generally, abundance of fruit bodies and biomass in the soil is lower at the forest edge.Understanding how fungi respond to edges is essential to a more complete knowledge of carbon and nitrogen cycling in forest edges, influence of mycorrhizal species on vegetation, and conservation of rare fungi. As edges become increasingly dominant landscape features it is vital to investigate processes within them, to understand ecosystem function at a landscape scale.     

Plant–frugivore networks are less specialized and more robust at forest–farmland edges than in the interior of a tropical forest

Forest fragmentation and local disturbance are prevailing threats to tropical forest ecosystems and affect frugivore communities and animal seed dispersal in different ways. However, very little is known about the effects of anthropogenic forest edges and of local disturbance on the structure and robustness of plant–frugivore networks. We carried out focal tree observations to record the frugivore species feeding on eight canopy tree species in the forest interior and at forest–farmland edges in a little and a highly disturbed part of a Kenyan rain forest. For each frugivore species, we recorded its body mass and its forest dependence. We examined how forest edge and local disturbance affected the abundance, the richness and the composition of the frugivore community and tested whether forest edge and local disturbance affected plant frugivore networks. Abundance and species richness of frugivores were higher at edges than in the forest interior. Forest visitors and small‐bodied frugivores increased, while forest specialists decreased in abundance at forest edges. The changes in frugivore community composition resulted in plant–frugivore networks that were more connected, more nested and more robust against species extinctions at forest–farmland edges than in the forest interior. Network specialization was lower at forest edges than in the forest interior because at the edges plant specialization on frugivores was very low in small‐fruited species. In contrast, small‐fruited plants were more specialized than large‐fruited plants in the forest interior. Our findings suggest that forest‐visiting birds may stabilize seed‐dispersal services for small‐fruited plant species at rain forest margins, while seed‐dispersal services for large‐fruited plant species may be disrupted at forest edges due to the decrease of large‐bodied frugviores. To assess the ultimate consequences of bird movements from farmland to forest edges for ecosystem functioning, future studies are required to investigate the seed‐dispersal qualities provided by forest‐visiting bird species in the tropics.     

Tree species traits cause divergence in soil acidification during four decades of postagricultural forest development

A change in land use from agriculture to forest generally increases soil acidity. However, it remains unclear to what extent plant traits can enhance or mitigate soil acidification caused by atmospheric deposition. Soil acidification is detrimental for the survival of many species. An in‐depth understanding of tree species‐specific effects on soil acidification is therefore crucial, particularly in view of the predicted global increases in acidifying nitrogen (N) deposition. Here, we report soil acidification rates in a chronosequence of broadleaved deciduous forests planted on former arable land in Belgium. This region receives one of the highest loads of potentially acidifying atmospheric deposition in Europe, which allowed us to study a ‘worst case scenario’. We show that less than four decades of forest development caused significant soil acidification. Atmospheric deposition undoubtedly and unequivocally drives postagricultural forests towards more acidic conditions, but the rate of soil acidification is also determined by the tree species‐specific leaf litter quality and litter decomposition rates. We propose that the intrinsic differences in leaf litter quality among tree species create fundamentally different nutrient cycles within the ecosystem, both directly through the chemical composition of the litter and indirectly through its effects on the size and composition of earthworm communities. Poor leaf litter quality contributes to the absence of a burrowing earthworm community, which retards leaf litter decomposition and, consequently, results in forest‐floor build‐up and soil acidification. Also nutrient uptake and N₂ fixation are causing soil acidification, but were found to be less important. Our results highlight the fact that tree species‐specific traits significantly influence the magnitude of human pollution‐induced soil acidification.     

Arthropods on plants in a fragmented Neotropical dry forest: A functional analysis of area loss and edge effects

Loss and fragmentation of natural ecosystems are widely recognized as the most important threats to biodiversity conservation, with Neotropical dry forests among the most endangered ecosystems. Area and edge effects are major factors in fragmented landscapes. Here, we examine area and edge effects and their interaction, on ensembles of arthropods associated to native vegetation in a fragmented Chaco Serrano forest. We analyzed family richness and community composition of herbivores, predators, and parasitoids on three native plant species in 12 fragments of varying size and at edge/interior positions. We also looked for indicator families by using Indicator Species Analysis. Loss of family richness with the reduction of forest fragment area was observed for the three functional groups, with similar magnitude. Herbivores were richer at the edges without interaction between edge and area effects, whereas predators were not affected by edge/interior position and parasitoid richness showed an interaction between area and position, with a steeper area slope at the edges. Family composition of herbivore, predator, and parasitoid assemblages was also affected by forest area and/or edge/interior situation. We found three indicator families for large remnants and five for edges. Our results support the key role of forest area for conservation of arthropods taxonomic and functional diversity in a highly threatened region, and emphasize the need to understand the interactions between area and edge effects on such diversity.     

Edge responses are different in edges under natural versus anthropogenic influence: a meta‐analysis using ground beetles

Most edges are anthropogenic in origin, but are distinguishable by their maintaining processes (natural vs. continued anthropogenic interventions: forestry, agriculture, urbanization). We hypothesized that the dissimilar edge histories will be reflected in the diversity and assemblage composition of inhabitants. Testing this “history‐based edge effect” hypothesis, we evaluated published information on a common insect group, ground beetles (Coleoptera: Carabidae) in forest edges. A meta‐analysis showed that the diversity‐enhancing properties of edges significantly differed according to their history. Forest edges maintained by natural processes had significantly higher species richness than their interiors, while edges with continued anthropogenic influence did not. The filter function of edges was also essentially different depending on their history. For forest specialist species, edges maintained by natural processes were penetrable, allowing these species to move right through the edges, while edges still under anthropogenic interventions were impenetrable, preventing the dispersal of forest specialists out of the forest. For species inhabiting the surrounding matrix (open‐habitat and generalist species), edges created by forestry activities were penetrable, and such species also invaded the forest interior. However, natural forest edges constituted a barrier and prevented the invasion of matrix species into the forest interior. Preserving and protecting all edges maintained by natural processes, and preventing anthropogenic changes to their structure, composition, and characteristics are key factors to sustain biodiversity in forests. Moreover, the increasing presence of anthropogenic edges in a landscape is to be avoided, as they contribute to the loss of biodiversity. Simultaneously, edges under continued anthropogenic disturbance should be restored by increasing habitat heterogeneity.     

Forest floor vegetation response to nitrogen deposition in Europe

Chronic nitrogen (N) deposition is a threat to biodiversity that results from the eutrophication of ecosystems. We studied long‐term monitoring data from 28 forest sites with a total of 1,335 permanent forest floor vegetation plots from northern Fennoscandia to southern Italy to analyse temporal trends in vascular plant species cover and diversity. We found that the cover of plant species which prefer nutrient‐poor soils (oligotrophic species) decreased the more the measured N deposition exceeded the empirical critical load (CL) for eutrophication effects (P = 0.002). Although species preferring nutrient‐rich sites (eutrophic species) did not experience a significantly increase in cover (P = 0.440), in comparison to oligotrophic species they had a marginally higher proportion among new occurring species (P = 0.091). The observed gradual replacement of oligotrophic species by eutrophic species as a response to N deposition seems to be a general pattern, as it was consistent on the European scale. Contrary to species cover changes, neither the decrease in species richness nor of homogeneity correlated with nitrogen CL exceedance (ExCL_empN). We assume that the lack of diversity changes resulted from the restricted time period of our observations. Although existing habitat‐specific empirical CL still hold some uncertainty, we exemplify that they are useful indicators for the sensitivity of forest floor vegetation to N deposition.     

Interplay between nitrogen deposition and grazing causes habitat degradation

Abstract Increased atmospheric nitrogen (N) deposition has been held responsible for the large‐scale invasion of graminoids (grasses, sedges and rushes) in a wide range of habitats from forests to upland heaths, causing dramatic changes in plant species composition. Concurrently with an increase in N deposition over the last century, livestock grazing has intensified in many parts of the world following policy reform, leading to large‐scale degradation of natural and seminatural ecosystems. On the basis of a series of experiments conducted in a Scottish montane ecosystem, we discovered that grazing and N deposition do not operate independently, and the interplay between them is leading to the replacement of valuable moss‐dominated habitat by grasses and sedges. Our study indicates that in setting ‘critical loads’ of N, widely used to minimize habitat degradation, it is necessary to account for substantial amplification of N‐deposition effects by grazing.     

The role of atmospheric dispersion models and ecosystem sensitivity in the determination of characterisation factors for acidifying and eutrophying emissions in LCIA

Background, aim and scope  The methodological choices and framework to assess environmental impacts in life cycle assessment are still under discussion. Despite intensive developments worldwide, few attempts have been made hitherto to systematically present the role of different factors of characterisation models in life cycle impact assessment (LCIA). The aim of this study is to show how European average and country-dependent characterisation factors for acidifying and eutrophying emissions differ when using (a) acidifying and eutrophying potentials alone, (b) depositions from an atmospheric dispersion model or (c) critical loads in conjunction with those depositions. Furthermore, in the latter case, the contributions of emissions, an atmospheric transport model and critical loads to changes in characterisation factors of NO₂ are studied. In addition, the new characterisation factors based on the accumulated exceedance (AE) method are presented using updated emissions, a new atmospheric transport model and the latest critical loads. Materials and methods  In this study, characterisation factors for acidifying and eutrophying emissions are calculated by three different methods. In the ‘no fate’ (NF) methods, acidifying and eutrophying potentials alone are considered as characterisation factors. In the ‘only above terrestrial environment’ (OT) approach, characterisation factors are based on the deposition of the acidifying or eutrophying substances to terrestrial land surfaces. The third method is the so-called AE method in which critical loads are used in conjunction with depositions. The results of the methods are compared both at the European and the country level using weighted mean, weighted standard deviation, minimum and maximum values. To illustrate the sensitivity of the AE method, changes in European emissions, employed atmospheric dispersion model and the critical loads database are conducted step-by-step, and the differences between the results are analysed. Results and discussion  For European average characterisation factors, the three characterisation methods of acidification produce results in which the contributions of NH₃, NO₂ and SO₂ to the acidification indicator do not differ much within each method when 1 kg of each acidifying substance is emitted. However, the NF methods cannot describe any spatial aspects of environmental problems. Both OT and AE methods show that the spatial aspects play an important role in the characterisation factors. The AE method results in greater differentiations between country-dependent characterisation factors than does the OT method. In addition, the results of the AE and OT methods differ from each other for individual countries. A major shortcoming of the OT approach is that it does not consider the sensitivity of the ecosystems onto which the pollutants are deposited, whereas the AE approach does. In the case of the AE method, a new atmospheric dispersion model, new information on emissions and critical loads have a different influence on the characterisation factors, depending on the country. The results of statistics show that the change in the atmospheric dispersion model has a greatest influence on the results, since ecosystem-specific depositions are taken into account for the first time. Conclusions and recommendations  The simple NF methods can be used in a first approximation to assess the impacts of acidification and terrestrial eutrophication in cases where we do not know where the emissions occur. The OT approach is a more advanced method compared with the NF method, but its capability to describe spatial aspects is limited. The AE factors are truly impact-oriented characterisation factors and the information used here represents the current best knowledge about the assessment practice of acidification and terrestrial eutrophication in Europe. The key message of this study is that there is no shortcut to achieving advanced characterisation of acidification and terrestrial eutrophication: an advanced methodology cannot develop without atmospheric dispersion models and information on ecosystem sensitivity.     

森林土壤氮素转换及其对氮沉降的响应

近几十年人类活动向大气中排放的含氮化合物激增 ,并引起大气氮沉降也成比例增加。目前 ,氮沉降的增加使一些森林生态系统结构和功能发生改变 ,甚至衰退。近 2 0 a欧洲和北美有关氮沉降及其对森林生态系统的影响方面的研究较多 ,而我国少有涉及。森林土壤氮素转换是森林生态系统氮素循环的一个重要的组成部分 ,而矿化、硝化和反硝化作用是其核心过程 ,氮沉降作为驱动因子势必改变森林土壤氮素转换速度、方向和通量。根据国外近 2 0 a有关研究 ,首先介绍了森林土壤氮素转换过程和强度 ,论述森林土壤氮素在生态系统氮素循环中的作用 ,然后在此基础上 ,介绍了氮沉降对森林土壤氮素循环的研究途径 ,探讨了氮沉降对森林土壤氮素矿化、硝化和反硝化作用的影响及其机理     

Site-Dependent Life-Cycle Impact Assessment of Acidification

The lack of spatial differentiation in current life-cycle impact assessment (LCIA) affects the relevance of the assessed impact. This article first describes a framework for constructing factors relating the region of emission to the acidifying impact on its deposition areas. Next, these factors are established for 44 European regions with the help of the RAINS model, an integrated assessment model that combines information on regional emission levels with information on long-range atmospheric transport to estimate patterns of deposition and concentration for comparison with critical loads and thresholds for acidification, eutrophication via air; and tropospheric ozone formation. The application of the acidification factors in LCIA is very straightforward. The only additional data required, the geographical site of the emission, is generally provided by current life-cycle inventory analysis. The acidification factors add resolving power of a factor of 1,000 difference between the highest and lowest ratings, while the combined uncertainties in the RAINS model are canceled out to a large extent in the acidification factors as a result of the large number of ecosystems they cover The framework presented is also suitable for establishing similar factors for eutrophication and tropospheric ozone formation for regions outside Europe as well.     

Nitrogen Depletion and Redistribution by Free‐Ranging Cattle in the Restoration Process of Mosaic Landscapes: The Role of Foraging Strategy and Habitat Proportion

In a mosaic landscape in N‐Belgium (W‐Europe), consisting of forest, grassland, and wooded pasture on former agricultural land, we assessed nitrogen redistribution by free‐ranging cattle (±0.2 animal units ha^?1 yr^?1). We examined if the spatial redistribution of nitrogen among habitats by cattle could restore nutrient‐poor conditions in preferred foraging habitats, and conversely whether such translocation could lead to extreme eutrophication in preferred resting habitats. We used nitrogen content of different diet classes, habitat use, foraging and defecation behavior, weight gain, and nitrogen losses in the actual situation to explore four different habitat proportion scenarios and two different foraging strategies to calculate a net nitrogen balance per habitat. An atmospheric deposition of 30 kg N ha^?1 yr^?1 with varying interception factors according to the habitat types was included in an integrated nitrogen balance. All scenarios showed a net nitrogen transport from grassland and wooded pasture to forest habitat. We found that nitrogen redistribution strongly depends on habitat proportion. Nitrogen losses from preferred grassland habitat can be high, given its proportion is small. Depletion is only to be expected at excretion‐free areas and probably is of minor importance to trigger the establishment of woody species. In general, nitrogen transported by cattle was much lower than input by atmospheric deposition, but grazing can compensate for high N inputs in excretion‐free areas and maintain grassland types that support critical loads of 20–25 kg N ha^?1 yr^?1. In none of the scenarios, N transport by cattle resulted in the exceeding of critical nitrogen loads to vulnerable forest ground vegetation.