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2014 | Book

Nitrogen Deposition, Critical Loads and Biodiversity

Editors: Mark A. Sutton, Kate E. Mason, Lucy J. Sheppard, Harald Sverdrup, Richard Haeuber, W. Kevin Hicks

Publisher: Springer Netherlands

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About this book

This volume brings together extended reviews and papers of new scientific research on atmospheric nitrogen deposition impacts globally. While there is a wealth of evidence on the magnitude, components and effects of nitrogen disposition on floral biodiversity in Europe and North America, there is an obvious lack of information on impacts on above- and below-ground fauna, and all impacts in other parts of the world, with no clear overview of how the different strands of evidence fit together. This overall synthesis is targeted at the international conventions, but is equally readable for scientists, environmental managers, conservation agencies and policy makers. 'This timely book highlights the global nitrogen deposition problem. Major regions of the world are exceeding sustainability thresholds for adverse effects on ecosystem function and biodiversity. This highlights the importance of ongoing work, including under the Convention on Biological Diversity, in developing indicators and monitoring nitrogen deposition effects to enable appropriate measures. This book presents a milestone towards this global goal as the international community works toward meeting the Aichi Biodiversity Targets, especially Target 8: "By 2020, pollution, including from excess nutrients, has been brought to levels that are not detrimental to ecosystem function and biodiversity". Braulio Ferreira de Souza Dias, Executive Secretary, Convention on Biological Diversity “This key volume highlights the global challenge to reduce atmospheric nitrogen pollution resulting from energy production, transport and agricultural activities. It takes forward the agenda recently launched in the UNEP commissioned report ‘Our Nutrient World”. Dr. Anjan Datta, UNEP.

Table of Contents

Frontmatter
1. Nitrogen Deposition, Critical Loads and Biodiversity: Introduction

Human activities, related primarily to agricultural practices and the combustion of fossil fuels for energy and transport, have caused steep increases in global emissions of reactive nitrogen (N

r

) over the last 50 years (e.g., Galloway et al.

Biogeochemistr

y

, 70

(2), 153–226, 2004,

Science, 320,

889–892, 2008). Atmospheric nitrogen (N) deposition derived from these sources represents a major threat to natural ecosystems around the world, leading to changes in structure, function and the associated biodiversity (e.g. Phoenix et al.

Global Change Biology, 12,

470–476, 2006; Bobbink et al.

Ecological Applications, 20,

30–59, 2010). Although substantial progress has been made in past decades, especially in Europe and North America, major uncertainties remain regarding the global perspective. In the last 30 years, Europe and North America have made great progress in assessing the problem, although the knowledge base is greater for impacts on flora than fauna; in many other parts of the world, however, the required datasets and assessments in many cases do not yet exist. This chapter summarizes the approach taken in the Workshop on Nitrogen Deposition, Critical Loads and Biodiversity and outlines the contents and structure of the book.

W. Kevin Hicks, Richard Haeuber, Mark A. Sutton

Monitoring and Modelling Atmospheric Nitrogen Deposition

Frontmatter
2. Progress in Monitoring and Modelling Estimates of Nitrogen Deposition at Local, Regional and Global Scales

This chapter discusses the status and progress of activities around the world to measure and model dry and wet deposition of reactive nitrogen (N

r

), i.e. the final removal processes from the atmosphere, at the local, regional and global scales. It gives an overview of present status and developments in networks and techniques for measuring deposition of N

r

. We describe recent developments in the modelling of emissions and deposition, and finish by giving research and policy recommendations regarding N-deposition measurement and modelling, including the need for;

an increase in the number of regional-scale, long-term monitoring sites for the routine measurement/estimation of wet and particularly dry deposition worldwide;

an increase in the number of N species routinely measured, especially dissolved organic N (DON), ammonia (NH

3

) and nitrogen dioxide (NO

2

);

global and regional models to improve their estimation of dry deposition and their resolution, especially in situations with complex topography.

Frank Dentener, Robert Vet, Robin L. Dennis, Enzai Du, Umesh C. Kulshrestha, Corinne Galy-Lacaux
3. Gaseous Nitrogen Emissions from Australian Cattle Feedlots

At any one time, close to 700,000 beef cattle are raised intensively in Australian feedlots. This chapter describes measurements of emissions of the greenhouse gas N

2

O and the reactive nitrogen gases NH

3

and NO

x

from two Australian beef cattle feedlots made over two years with open- and closed-path concentration measurement systems and backward Lagrangian stochastic dispersion modelling. Emissions of all three gases exhibited marked diurnal cycles with maxima close to mid-day and minima over night. The average emission rate for N

2

O was 1.3 ± 1.65 (s.d) kg N ha−

1

d−

1

, that for NH

3

was 95 ± 36 kg N ha−

1

d−

1

, and for NO

x

1.20 ± 0.58 kg N ha−

1

d−

1

. Extrapolating these figures to all the feedlots in the country and accepting the estimate by Mosier et al. (

1998

) that 1 % of the NH

3

and NO

x

would be converted to N

2

O after eventual deposition, the direct emissions of N

2

O from feedlots amount to 241 kt CO

2

-e year−

1

and those from NH

3

plus NO

x

to 181 kt CO

2

-e year−

1

, or 43 % of the total N

2

O emissions. These direct and indirect emissions are substantial, amounting to 60 % in terms of CO

2

-e of the CH

4

emissions measured in the project.

O. Tom Denmead, Deli Chen, Doug Rowell, Zoe Loh, Julian Hill, Stephanie Muir, David W.T. Griffith, Travis Naylor, Mei Bai, Frances Phillips, Sean McGinn
4. Ammonia Emissions in the US: Assessing the Role of Bi-directional Ammonia Transport Using the Community Multi-scale Air Quality (CMAQ) Model

A pilot study assessing bi-directional ammonia (NH

3

) transport using the Community Multi-scale Air Quality (CMAQ) Model for the Eastern United States (US) is underway. The study develops and tests bi-directional flux algorithms, explores methods of providing agricultural fertilizer information into CMAQ, and clarifies possible NH

3

, and overall one-atmosphere, chemical budget changes with the full implementation of the bi-directional flux option planned for the 2011 CMAQ release. One focus area is the adjustment of the current CMAQ bi-directional flux module to include a dynamic soil emission potential component. The soil emission potential (Γ

g

) is calculated offline using commercial fertilizer application survey data from the National Nutrient Loss & Soil Carbon (NNLSC) Database and is then input to CMAQ for computation of the NH

3

air-soil compensation point and subsequent NH

3

flux. A full 2002 year model run over the standard CMAQ (v. 4.7) Eastern US domain incorporating the revised bi-directional flux module is planned.

Megan L. Gore, Ellen J. Cooter, Robin L. Dennis, Jon E. Pleim, Viney P. Aneja
5. Regional Scale Modelling of the Concentration and Deposition of Oxidised and Reduced Nitrogen in the UK

The Fine Resolution Atmospheric Multi-pollutant Exchange model (FRAME) was applied to model the spatial distribution of air concentration and deposition of nitrogen (N) compounds between 1990 and 2005. Modelled wet deposition of N was found to decrease more slowly than the emissions reductions rate. This is attributed to a number of factors including increases in NO

x

emissions from international shipping and changing rates of atmospheric oxidation. The modelled deposition of NO

y

and NH

x

to the United Kingdom (UK) was estimated to fall by 52 % and 25 % between 1970 and 2020. The percentage of the UK surface area for which critical loads for sensitive ecosystems are exceeded was estimated to fall from 73–49 % for nutrient N deposition. Comparison with model simulations at 1 km and 5 km resolution demonstrated that fine scale simulations are important in order to spatially separate agricultural source regions from sink areas (nature reserves) for ammonia dry deposition.

Anthony J. Dore, Małgorzata Werner, Jane R. Hall, Christopher J. Dore, Stephen Hallsworth, Maciej Kryza, Ron I. Smith, Ulrike Dragosits, Y. Sim Tang, Massimo Vieno, Mark A. Sutton
6. High Rates of Wet Nitrogen Deposition in China: A Synthesis

Anthropogenic reactive nitrogen emissions (especially NH3 and NOx) have been increasing rapidly since the late 1970s in China and may lead to increased atmospheric input of reactive nitrogen to the Earth's surface through wet and dry deposition. Analyzing the temporal and spatial patterns of nitrogen (N) deposition is a high priority in order to assess environmental impacts of N deposition on a national scale. To this end, we have established a database for China, based on wet N deposition measured between 1995 and 2007. High rates of wet N deposition have been observed in large areas, particularly in central and eastern China. Average rates of wet deposition for dissolved inorganic nitrogen (DIN), NH

4

 +

-N

and NO

x−

-N were 17.36 ± 10.53, 10.66 ± 6.54 and 6.57 ± 4.93 kg N ha

−1

year

−1

. The average ratios of NH

4

+

-N/NO

x

-N in wet deposition were as high as 1.96 ± 1.27 and showed no significant difference among urban, rural and remote sites. Average wet deposition for DON was 4.84 ± 2.80 kg N ha

−1

year

−1

accounting for 25.4 ± 13.5 % of the total dissolved nitrogen (TDN) deposition. Wet N deposition exceeded 15 kg N ha

−1

year

−1

at 52 % of the rural sites. The high rates of wet N deposition in central and eastern China suggest heavy atmospheric reactive nitrogen pollution and substantial negative effects on the terrestrial and aquatic ecosystems of China.

Enzai Du, Xuejun Liu
7. Enrichment of Atmospheric Ammonia and Ammonium in the North China Plain

Atmospheric ammonia and ammonium in PM

10

were measured at six sites (two suburban sites and four rural sites) in the North China Plain (NCP) between August 2006 and September 2009, i.e. for 3 years. The annual mean concentrations of ammonia and ammonium were 7.3–19.9 μg N m

−3

with an average of 12.8 μg N m

−3

and 5.6–13.1 μg N m

−3

with an average of 9.6 μg N m

−3

respectively, at the sampling sites. Both ammonia and ammonium concentrations were higher at the rural sites than at the suburban sites, highlighting the importance of agricultural sources for atmospheric ammonia and ammonium. Higher ammonia concentrations were observed in the nitrogen (N) fertilization seasons, indicating that ammonia emission from N fertilizer application was an important source of atmospheric ammonia in the NCP. Based on the measured ammonia and ammonium concentrations and their deposition velocities taken from literatures, the annual mean NH

x

(NH

3

plus NH

4

 +

) dry deposition rate was 25.6 kg N ha

−1

year

−1

among the six sampling sites. The high NH

x

concentrations and dry deposition rates in the NCP indicated agricultural sources were a large contributor to air pollution, and should be taken into account in the control of regional air pollution.

Jianlin Shen, Xuejun Liu, Andreas Fangmeier, Fusuo Zhang
8. Nitrogen Deposition within the Littoral-Highlands County of Croatia Between 1996 and 2008

Temporal trends in bulk nitrogen (NH

4

+

 + NO

3

) deposition at four sites within the Littoral-highlands County of Croatia are discussed. The selected sites included: the remote island Site 1, an urban and industrial coastal Site 2 (Rijeka), Site 3 which is a settlement and Site 4 a hunting resort located in the highlands area, claimed to suffer from acidic deposition. The lowest deposition of nitrogen (N) was measured at the remote Site 1 (5.6–11.2 kg N ha

−1

year

−1

), while higher values were obtained at the urban Site 2 (7.6–17.9 kg N ha

−1

year

−1

) due to the local washout of the atmosphere, and at the highlands Sites, 3 (10.3–32.1 kg N ha

−1

year

−1

) and 4 (5.6–24.9 kg N ha

−1

year

−1

) because of higher precipitation. The bulk nitrogen (N) deposition at the highlands Sites 3 and 4 is below the critical load for the corresponding soil-vegetation type (CL = 64.4 kg N ha

−1

year

−1

). In the period 1996–2003 NH

4

-N made up 66 % of the N deposition at all sites, but since 2004 this ratio has diminished to 50 %, due to the increase in NO

3

-N deposition. Overall there has been almost no change in N deposition at all except Site 4, where N deposition has increased, reflecting an increase in NO

3

-N deposition but no significant decline in NH

4

-N.

Ana Alebic-Juretic
9. Atmospheric Deposition of Reactive Nitrogen in India

The increasing demand of food and energy of the global population is contributing excess reactive nitrogen (N

r

) in the atmosphere primarily in the form of ammonium and nitrate compounds. Subsequently, through wet and dry deposition processes, these compounds are deposited onto the ground, vegetation, soils, water bodies etc. enriching these systems with excess nitrogen (N). Knowledge about N deposition in North America and Europe is quite advanced because of systematic studies. But the present knowledge about N deposition in India and the south Asian region is very limited due to a lack of systematic measurements dedicated to nitrogenous compounds. Though a number of wet deposition studies have been reported by various groups for different sites and years in India, only a few of these are considered as having good quality data. This chapter reports quality controlled wet deposition fluxes of N

r

at rural (2006–2008) and urban (2005–2008) sites in south India as part of the RAPIDC-CAD programme. The rural site Hudegadde is located in the reserve forest area of Western Ghats by the south-west coast of India while the urban site Hyderabad, the capital of Andhra Pradesh State is located in south-central India. In general, at both the sites, wet deposition of N through NH

4

 + 

was observed to be higher than NO

3

. Fluxes of NH

4

 + 

showed an increasing pattern at Hudegadde, while those of NO

3

showed an increasing pattern at Hyderabad. The possible reason for increasing NH

4

 +

 at Hudegadde may be an increase in biomass burning and vegetation decay in the forest areas, which contribute higher ammonia to the atmosphere, together with transboundary pollution due to air-masses from nearby continental areas. The increasing pattern of NO

3

fluxes at Hyderabad might be due to an increase in population, vehicular density and other urban activities. Projections using the MATCH model coupled with rain chemistry measurements showed that the Indo-Gangetic region experiences very high wet deposition of NH

4

 + 

which might be due to a prevailing higher density of ammonia sources in the region. This chapter also highlights the importance of dry deposition of N

r

species for the Indian region.

Umesh C. Kulshrestha, Monika J. Kulshrestha, Jetta Satyanarayana, Loka Arun K. Reddy
10. Dry and Wet Atmospheric Nitrogen Deposition in West Central Africa

This work is part of the IDAF (IGAC/DEBITS/AFrica) programme which started in 1995 with the establishment of 10 measurement sites representative of major African ecosystems. The objectives of the programme are to study wet and dry deposition fluxes, to identify the relative contribution of natural and anthropogenic sources and factors regulating these fluxes. This study presents an estimation of the atmospheric nitrogen (N) deposition budget in Africa based on a long term monitoring measurements database including gaseous, precipitation and aerosols chemical composition. Annual nitrogen fluxes including wet and dry processes are estimated to be around 6 kg N ha−

1

year

−1

, 6.5 kg N ha−

1

year

−1

and 13 kg N ha−

1

year

−1

respectively over dry savanna, humid savanna and over the forest.

Corinne Galy-Lacaux, Claire Delon, Fabien Solmon, Marcellin Adon, Véronique Yoboué, Jonas Mphepya, Jacobus J. Pienaar, Babakar Diop, Luc Sigha, Laouali Dungall, Aristide Akpo, Eric Mougin, Eric Gardrat, Pierre Castera
11. Interannual Variability of the Atmospheric Nitrogen Budget in West African Dry Savannas

Surface emission and deposition fluxes of reactive nitrogen compounds have been studied in three sites of West Africa during the year 2006, representative of dry savannas ecosystem, and part of the IDAF network: Agoufou (Mali, 15.3°N, 1.4°W), Banizoumbou (Niger, 13.3°N, 2.4°E) and Katibougou (Mali, 12.5°N, 7.3°W). Dry deposition fluxes are calculated from surface measurements of NO

2

, HNO

3

and NH

3

concentrations (from passive samplers) and simulated deposition velocities, and wet deposition fluxes are calculated from NH

4

+

and NO

3

concentration in samples of rain. Emission fluxes are evaluated including simulated NO biogenic emission from soils, emissions of NO

x

and NH

3

from biomass burning and domestic fires, and volatilization of NH

3

from animal excreta. From these 3 sites, the average deposition flux, attributed to dry savanna ecosystems in Sahel, is 7.5 (± 1.8) kg N ha

−1

year

−1

, and the average emission flux is from 8.5 ± 3.8 kg N ha

−1

year

−1

. This budget is dominated by the NH

3

contribution (due to volatilization of animal excreta). Biogenic emissions from soils are the second most important contribution in emission fluxes. Total estimated deposition is 1.84 ± 0.44 Tg N year

−1

and the estimated emission is 2.0 ± 0.9 Tg N year

−1

for the Sahel region. Limited interannual variability (between 2002 and 2007) in precipitation is responsible for small variability in local emission sources and hence deposition fluxes.

Claire Delon, Corinne Galy-Lacaux, Marcellin Adon, Catherine Liousse, Aaron Boone, Dominique Serça, Babakar Diop, Aristide Akpo, Eric Mougin
12. Assessment and Characterisation of the Organic Component of Atmospheric Nitrogen Deposition

The organic component of atmospheric reactive nitrogen is known to be important for biogeochemical cycles, climate and ecosystems, but it is still not routinely assessed in atmospheric deposition studies, and most worldwide air quality monitoring networks disregard it. The available jigsaw puzzle pieces of knowledge from diverse sources can now give a richer picture of global patterns of organic nitrogen deposition. This effort at data synthesis highlights the need for more data, but also suggests where those data gathering efforts should be focused. The development of new analytical techniques allows long-standing conjectures about the nature and sources of the organic matter to be investigated, with tantalising indications of the complex interplay between natural and anthropogenic sources, and links between the nitrogen and carbon cycles. Atmospheric emission and deposition models are needed, along with new chemical process models, to let us explore questions about the role and dynamics of organic nitrogen.

Sarah E. Cornell
13. Wet Deposition of Nitrogen at Different Locations in India

The wet deposition data for Pune (2000–2007), for the other locations representing different environments (i.e., urban, rural, industrial, high altitude, marine, traffic etc.) for different time periods during 2001–2007, and for ten Global Atmospheric Watch (GAW) locations in India for a period of 8 years (2000–2007) are considered in this chapter. All the rain water samples were analyzed for pH, conductivity, anions (Cl, SO

4

and NO

3

) and cations (NH

4

, Na, K, Ca and Mg). In general, in India the rain water was found to be in the alkaline range. Out of ten GAW stations, the 8 years average pH was slightly acidic (pH 5.15–5.36) at only three locations. At the remaining seven locations the pH was alkaline (pH > 5.65). This alkaline nature is due to high dust levels. Neutralization factors indicated that calcium (Ca) is the major neutralizing cation in wet deposition. Calcium concentrations were higher in north and northwestern regions and lower in southern and northeastern regions. Non-sea salt component and back trajectory analyses showed that Ca and SO

4

aerosols were transported to the Indian sub-continent from North African and Gulf countries. The wet deposition fluxes were estimated for all the ionic components including nitrogen (N). The 8 year average annual wet deposition of N for ten locations varied between 4.7 and 34.3 kg N ha

−1

year

−1

and yearly depositions varied between 1.8 and 57 kg N ha

−1

year

−1

. At all the locations, the NO

3

-N depositions were higher compared to NH

4

-N. At some of the locations, even though the concentrations are low, the depositions were higher due to the high rainfall amounts. In regional perspective, the excess SO

4

-S deposition was higher at an industrial location and the N deposition was higher at a traffic junction in Pune region. At a high altitude rural location (Sinhagad) nearby Pune, the concentrations of excess SO

4

, NO

3

and NH

4

were lower but their depositions were higher due to higher rainfall amounts. The total N deposition at four different locations in Pune region varied from 10.4 to 13.2 kg N ha

−1

year

−1

.

P. S. P. Rao, P. D. Safai, Krishnakant Budhavant, V.K. Soni

Nitrogen Impacts on Terrestrial and Aquatic Ecosystems

Frontmatter
14. Factors Affecting Nitrogen Deposition Impacts on Biodiversity: An Overview

The main mechanisms of nitrogen (N) deposition impacts on terrestrial biodiversity, mainly from studies in Europe, are identified as: direct foliar impacts; eutrophication; acidification; negative effects of reduced N; and increased susceptibility to secondary stress and disturbance factors such as drought, frost, pathogens or herbivores. The relation of several of these mechanisms to aquatic ecosystems is also described, as is the relative lack of N impact studies on faunal species/communities compared to floral ones. The factors that moderate N impacts on ecosystems are also considered and are categorized as: (1) the duration and total amount of the N inputs; (2) the chemical and physical form of the airborne N input; (3) the intrinsic sensitivity to the changes in N availability of the plant and animal species present; (4) the abiotic conditions (such as the ability of soils and waters to neutralize acidification effects); and (5) the past and present land use or management. The increased susceptibility of plants (or animal) species to stresses and disturbances, induced by enhanced atmospheric N loads, is highly dependent of the large differences in the physiological functioning of individual species. Therefore, the generalization of the effects of N deposition over a range of ecosystems is hardly, if at all, possible, although these impacts have been demonstrated to be of major importance in some ecosystems.

Roland Bobbink, W. Kevin Hicks
15. What Happens to Ammonia on Leaf Surfaces?

The exchange of ammonia between leaf surfaces and the atmosphere is bi-directional, and depends on the relative solution concentrations in or on the leaf, and concentrations in the atmosphere. The amount of ammonia (as ammonium ions) present at equilibrium in solution on leaf surfaces depends on temperature, and on the presence of other gases such as carbon dioxide and sulphur dioxide, which act as acids to neutralise the hydroxide ions formed when ammonia dissolves. Under ambient conditions, with low concentrations of ammonia and sulphur dioxide, equilibrium may not be achieved even over many hours, because of aerodynamic limitations in the transfer between the air and the surface. Unless chemical reactions occur to ‘fix’ ammonium on the surface, for example as involatile ammonium sulphate or organic nitrogen, any deposited ammonia will be returned to the atmosphere as surface water evaporates. Results from a simple model are presented to show the effects of different atmospheric components and temperature, and also of the rate of oxidation of dissolved sulphur dioxide, on the retention of ammonium on leaf surfaces.

J. Neil Cape
16. Effects of Nutrient Additions on the Diversity of the Herbaceous-Subshrub Layer of a Brazilian Savanna (Cerrado)

The anthropogenic increase of nutrient availability in natural ecosystems is related to different impacts as soil acidification and loss of biodiversity. The present work investigated the effects of nutrient additions on the diversity of the herbaceous-subshrub layer of a Brazilian savanna. The experimental design consisted of an unfertilized control and four fertilization treatments as follows: + N (100 kg N ha

−1

year

−1

as (NH

4

)

2

SO

4

), + P (100 kg of P ha

−1

year

−1

as Ca(H

2

PO

4

)

2

 + CaSO

4

.2H

2

O), + NP (100 kg of N + 100 kg of P ha

−1

year

−1

as (NH

4

)

2

SO

4

plus Ca(H

2

PO

4

)

2

 + CaSO

4

.2H

2

O) and + Ca (4,000 kg of dolomitic limestone and CaSO

4

.2H

2

O). Nutrient treatments were applied twice yearly between 1998 and 2006. Soil physic-chemical analyses were performed and related to the results of vegetation surveys performed in April 2009. Calcium (Ca) addition increased the soil pH in all Ca fertilized plots, while the additions of nitrogen (N), nitrogen and phosphorus (NP) and phosphorus (P) decreased soil pH. The floristic diversity was high in all treatments but differed significantly between them (

p

 < 0.01). NP plots presented the lowest richness and the control plots showed the highest richness. Species cover and environmental variables were correlated to axes 1 and 2 in the Canonical Correspondence Analysis (

F

 = 1.14;

p

 = 0.035). In our study the invasive grass

Melinis minutiflora

(African C4 grass) responded to P and N + P treatments but was absent in the N plots, probably due to P limitation. The low cover of

M. minutiflora

in control and in Ca plots may be due to competition with native species, since these plots had a high H’ index for the herbaceous-subshrub layer and were probably also P limited. The combination of N + P was especially detrimental to diversity, inducing the invasion by

M. minutiflora

. The invasion seems to be strongly limited by P and interespecific competition with native species.

Thiago R. B. de Mello, Cássia B. R. Munhoz, Mercedes M. C. Bustamante
17. Leaf Litter Decomposition and Nutrient Release Under Nitrogen, Phosphorus and Nitrogen Plus Phosphorus Additions in a Savanna in Central Brazil

The aim of this study was to determine leaf decomposition rates and nutrient release in a cerrado

sensu stricto

under nitrogen (N), phosphorus (P) and N plus P additions. The experiment was carried out in an area located in the Ecological Reserve of the Instituto Brasileiro de Geografia e Estatística, near Brasília (15° 56’ S, 47° 53’ W). Between 1998 and 2006, 100 kg ha

−1

year

−1

of N (N treatment), P (P treatment) and N plus P (NP treatment) were applied to 16 225 m

2

plots, arranged in a completely randomized design. Litterfall was collected at the end of dry season (September 2006) and oven dried (60 °C) for 72 h. Litter bags with 10 g of leaf litter were incubated in situ for 453 days to determine decomposition rate. Nitrogen and P concentrations and mass loss were measured during the incubation process. Decomposition rates of leaf litter in N plots did not differ in relation to those in control plots. Leaf litter decomposition rates increased in P (+ 18.6 %) and NP (+ 27.4 %) plots, where there was a greater N (in NP plots) and P (in P and NP plots) initial concentration in litter relative to the control plots (

p

 < 0.05). Leaf litter in the N treatment had the highest N mass loss, and together with NP treatment, the smallest P mass loss. Nitrogen addition increased N mass loss, while the combined addition of N and P resulted in an immobilization of N in leaf litter. When the nutrients are supplied separately, there is greater mass loss of N with N addition, and greater mass loss of P with P addition compared to that observed when N and P are supplied together. The results indicate that if the availability of P is not increased proportionally to the availability of N, the losses of N are intensified during the decomposition process.

Tamiel K. B. Jacobson, Mercedes M. C. Bustamante
18. Diversity of the Shrub-tree Layer in a Brazilian Cerrado Under Nitrogen, Phosphorus and Nitrogen Plus Phosphorus Addition

The aim of this study was to compare the diversity of the shrub-tree layer in fertilized and unfertilized plots in a cerrado

stricto sensu

area in Central Brazil. The experiment was conducted in 16 plots of 15 m × 15 m arranged in a completely randomized design with tree fertilization treatments (+ N, + P, + NP), and an unfertilized treatment (control) in the Ecological Reserve of the Instituto Brasileiro de Geografia e Estatística (RECOR-IBGE), Federal District, near Brasília. Treatments were applied from 1998 to 2006. Vegetation surveys were performed during January and July 2008 on all trees and shrubs with circumference > 5 cm at ground level. Indices of diversity of Shannon (H′), evenness of Pielou (J′) and similarity of Sørensen were calculated. Control plots contained 479 individuals of 47 species, belonging to 29 families. In the nitrogen (N) plots, 461 individuals were registered, belonging to 53 species and 34 families while 448 individuals of 54 species from 31 families were registered in phosphorus (P) plots and 336 individuals of 40 species, belonging to 24 families in nitrogen + phosphorus (NP) plots. The N (H′ = 3.20; J′ = 0.80) and NP (H′ = 2.89; J′ = 0.78) plots showed lower Shannon (H′) and Pielou (J′) indices relative to the control plots (H′ = 3.40; J′ = 0.88). The Sørensen floristic similarity was high between fertilized and control plots but decreased in the following order: P plots (0.81), N (0.78) and NP (0.76) plots. Fertilization shifted species density and dominance patterns in comparison to unfertilized plots. Nitrogen and NP addition decreased the evenness, species diversity and provided the least floristic similarity relative to the control plots. Density and dominance changes resulted in differences in species importance values among treatments. Simultaneous addition of N and P affected density, dominance, richness and diversity patterns more significantly than addition of N or P separately.

Tamiel K. B. Jacobson, Mercedes M. C. Bustamante
19. Model Predictions of Effects of Different Climate Change Scenarios on Species Diversity with or without Management Intervention, Repeated Thinning, for a Site in Central European Russia

The EFIMOD-ROMUL soil-vegetation dynamic model of carbon and nitrogen cycles in forest ecosystems and a static ground vegetation model BioCalc were used for simulating the dynamics of forest ecosystem parameters and prognosis of plant species biodiversity under two management and two climate change scenarios. A large forested area occupying approximately 1,800 km

2

on the Central Russian Plain (in Kostroma administrative region) was taken as a case study. Natural forest development (forest reservation) and clear cutting regime were taken as the management scenarios. The most dramatic climate change based on HadCM3 model and A1Fi emission scenario and ‘stationary climate’ were taken as the climatic scenarios. The simulation results showed that clear cutting impacts on forest biodiversity are very strong in the study area and climate warming has minimal effect on biodiversity under the clear cutting regime but climate changes lead to a slight decrease in species diversity under the forest natural development.

Larisa G. Khanina, Maxim V. Bobrovsky, Alexander S. Komarov, Vladimir N. Shanin, Sergey S. Bykhovets
20. Seasonal Changes in Photosynthetic Nitrogen of Tree Species Differing in Leaf Phenology in a South-eastern Brazilian Savanna

Dominant tree species from a south-eastern Brazilian savanna showing different leaf phenologies (evergreen, semi-deciduous and deciduous) were characterized regarding photosynthetic potential (A), leaf nitrogen content (% N), specific leaf area (SLA), photosynthetic nitrogen (PN) and photosynthetic nitrogen use efficiency (PNUE). The ecophysiological traits evaluated seasonally (dry and wet season) characterized a gradient of strategies among three species: the evergreen species that dominates lower strata, showed low % N, SLA, Amax and Amass and high PNUE; the semi-deciduous species that dominates intermediate strata, showed medium leaf nitrogen and SLA and high Amax, Amass and PNUE; the deciduous species that dominates the canopy, showed high leaf N, SLA, Amax and Amass and low PNUE. Non deciduous species invested relatively more nitrogen in photosynthesis during the wet season, while the deciduous species maintained higher PN in the dry season. Photosynthetic N and PNUE appear to be the key to a better understanding of the relations among leaf traits, N content and photosynthetic potential in species with different leaf phenologies and subjected to climatic seasonality.

Sabrina R. Latansio-Aidar, Luciana D. Colleta, Jean P.H.B. Ometto, Marcos P.M. Aidar
21. Atmospheric Nitrogen Deposition can Provide Supplementary Fertilization to Sugar Cane Crops in Venezuela

Acidic rain, loaded with ammonium is characteristic of Central Northern Venezuela, a region dominated by sugarcane plantations. Nitrogen (N) inputs in precipitation are crucial to the N economy of natural ecosystems; in agro-systems these inputs are of less importance. However, in some polluted areas, atmospheric deposition loaded with N as a consequence of industrial and agricultural activities can contribute significantly to crop nutrition. The N and other nutrients present in both precipitation and dry deposition can originate from a variety of natural and anthropogenic sources, including air pollution. Canopies of forest and agricultural crops can modify the chemistry of rainfall in different ways: through uptake, leaching and removal of ions from the canopy in throughfall. In this contribution we analyzed the chemical changes in N enriched acid rain as it passed through a sugarcane canopy. The study site was located on a sugarcane farm near San Felipe, Yaracuy state, Venezuela. Four plots of 300 m

2

within an experimental area of 4.5 ha, planted with

Saccharum

officinarum

had rain and throughfall collectors installed. The study corresponds to the analysis of the second and third ratoons of two sugarcane varieties. Rain water was quite acidic ranging from 3.54 to 4.52, a situation that is common in Northern Central Venezuela as a consequence of the high industrial and agricultural activities. The pH of the acid rain in the sugar cane system increased after passing through the canopy. The magnitudes of the changes were important and related to the significant amount of cations leached from the leaves or washed out from dry deposition to the leaves and cane stems. Ammonium was the dominant N form in wet deposition. N inputs for wet and dry deposition in the agro-system were high compared with other ecosystems (26.3 kg ha 

−1

year

−1

, mostly in the ammonium form). This is probably due to: the high agricultural activity in the area, the local burning of the sugarcane before cropping, and the location of the experimental area close to petrochemical industrial activities and fertilizer producer industries. Although nitrates were leached and wash out in throughfall, the balance accounted for a significant N fertilization of the canopy through ammonium uptake.

Danilo López-Hernández, Diego Sequera, Oswaldo Vallejo, Carmen Infante
22. Competition Alters Responses of Juvenile Woody Plants and Grasses to Nitrogen Addition in Brazilian Savanna (Cerrado)

The Cerrado, Brazilian savanna, is characterized by high radiation and dystrophic soils. Seedlings of woody species must compete effectively for resources belowground in order to establish in the herbaceous matrix. Few studies focus on the dynamics of herbaceous and woody juvenile plants and their competitive strategies, especially under increasing nitrogen (N) availability. In the present study, seedlings of three woody species,

Eugenia dysenterica,

Magonia pubescens

and

Enterolobium gummiferum

were grown with or without the dominant grass in Cerrado areas of central Brazil,

Echinolaena inflexa

. Half of the pots were exposed to N additions equivalent to a deposition of 20 kg N-NO

3

NH

4

ha

−1

year

−1

. The N induced responses of plants growing under intra and interspecific competition were analyzed, with special attention to plasticity of root biomass and morphology. One year after the beginning of the experiment, the fresh and dry biomass of roots and shoots were weighted. Before drying, total length, surface area and diameter of roots were determined. Interspecific competition tended to reduce root and shoot biomass of all plants. However, effects of competition with

E. inflexa

were more obvious on root morphology, being total root and fine root length diminished in two of the woody species in the absence of N addition. The enhancement of N availability, in general, minimized the effects of competition, increasing the potential competitiveness of some woody species due to changes in total fine root length and biomass. The results provide indication that competition between saplings of woody plants and grasses could be an important factor driving plant allometry and morphology during the first stages of development in Cerrado environments. The responsiveness of plants to N deposition seemed to depend, in part, on the type of competition (intra- or interspecific), what should be taken into account in models of vegetation dynamics in response to nutrient deposition.

Viviane T. Miranda, Alessandra R. Kozovits, Mercedes M.C. Bustamante
23. Pigment Ratios of the Mediterranean Bryophyte Pleurochaete squarrosa Respond to Simulated Nitrogen Deposition

Nitrogen (N) deposition alters ecosystem structure and functioning. To study potential impacts on Mediterranean ecosystems, we designed a field fertilization experiment where NH

4

NO

3

was added at four rates (0, 10, 20 and 50 kg N ha

−1

year

−1

). The terricolous moss

Pleurochaete squarrosa

was sampled and pigments extracted in spring-autumn 2008 and spring 2009. Simulated N deposition increased lutein and

VAZ

pigments to chlorophyll ratios in autumn 2008; β-carotene to chlorophyll ratio was reduced in spring 2009; (neoxantin + lutein) to β-carotene increased with N supply and this was explained as higher investment in light-harvesting complexes than in reaction centres. Response of carotene to chlorophylls and of (neoxantin + lutein)/β-carotene to N enrichment were only evident when soil NH

4

and Mn, respectively, were used as covariates. Thus, covariance analyses are highly recommended to detect N fertilization effects on terricolous species when field experiments are set up in highly heterogeneous environments.

Raúl Ochoa-Hueso, Cristina Paradela, M. Esther Pérez-Corona, Esteban Manrique
24. Calibrating Total Nitrogen Concentration in Lichens with Emissions of Reduced Nitrogen at the Regional Scale

The impact of nitrogen (N) on ecosystem functioning and biodiversity is currently recognized to be increasing worldwide. For that reason, there is an urgent need for strategies aimed at identifying and mitigating N mediated effects. Most studies undertaken at a regional scale regarding N deposition are based on models. However, there is a missing link between the predictions made by N emission models at broad spatial scales, and the actual atmospheric N deposition. Our aim was to use biomonitors to provide that link. More specifically our objective was to present clear evidence that N concentrations measured in lichen thalli can be used as an ecological tool to assess the deposition of atmospheric reduced N in ecosystems. To do so we have related N concentrations measured in lichens thalli to ammonia emissions estimated from cattle numbers and the cover of agricultural land. This was done in two areas with a Mediterranean climate in south-west Portugal. The results have shown that N concentrations in lichens could be significantly correlated with reduced-N emissions. There was a very close relationship between N concentrations in lichens and the main regional sources of reduced nitrogen. This lichen variable can thus be used as an ecological tool to map with high resolution and at a regional scale, N deposition in ecosystems. Measurement of lichen thallus N concentration will help identify areas of high N deposition where further monitoring may be required to help safe-guard against Critical Load exceedance and Biodiversity impacts.

P. Pinho, Maria-Amélia Martins-Loução, Cristina Máguas, Cristina Branquinho
25. The Impact of the Rural Land-Use on the Ecological Integrity of the Intermittent Streams of the Mediterranean 2000 Natura Network

The main objective was to understand the impact of the neighbouring land-use and of water pollution on the integrity of the riparian vegetation in intermittent Mediterranean streams of the 2000 Natura network in a rural area. The ecological integrity of the riparian vegetation of intermittent streams in the Mediterranean was negatively associated with the aquatic NH

4

 +

concentration, which might a consequence of direct and indirect effects. There was a significant increase in frequency of exotic shrub species with increasing PO

4

3−

concentration in stream waters and high NO

3

concentrations in stream waters did not affected the QBR index or its components. Despite occupying a large area, pastures were not a source of eutrophication elements to the stream waters. Agricultural practices close to streams i.e. < 200 m, should be avoided. When the latter is not possible a well established native vegetation buffers should surround such areas.

Cristina Branquinho, Carla Gonzalez, Adelaide Clemente, Pedro Pinho, Otília Correia
26. Biodiversity of Acid Grasslands in the Atlantic Regions of Europe: The Impact of Nitrogen Deposition

Reduction in the species richness of acid grasslands along a gradient of atmospheric nitrogen (N) deposition has previously been demonstrated in the UK (Stevens, Dise, Mountford, Gowing, Science 303:1876–1879, 2004). Further surveys of acid grasslands in the UK confirm this relationship. This chapter reports an examination of the relationship across the Atlantic region of Europe. Examining the cover of functional groups across this gradient reveals that forb cover is strongly reduced along the gradient of N deposition.

Carly J. Stevens, Cecilia Duprè, Edu Dorland, Cassandre Gaudnik, David J. G. Gowing, Albert Bleeker, Martin Diekmann, Didier Alard, Roland Bobbink, David Fowler, Emmanuel Corcket, J. Owen Mountford, Vigdis Vandvik, Per Arild Aarrestad, Serge Muller, Nancy B. Dise
27. Effects of Increased Nitrogen Availability in Mediterranean Ecosystems: A Case Study in a Natura 2000 Site in Portugal

Nitrogen (N) enrichment has been pinpointed as a main driver for biodiversity change. Most of our knowledge of effects of increased N availability on ecosystems comes from northern Europe and America. Most other ecosystem types have been neglected. Although Mediterranean ecosystems are N-limited biodiversity hotspots, very little is known about the effects of N enrichment in these systems. In contribution to filling this gap, our study examined the short-term effects of N enrichment in a N-manipulation (doses and forms) field study of a severely nutrient-limited Mediterranean ecosystem located in a Natura 2000 site in Portugal. N availability (dose and forms) was modified by the addition of 40 and 80 kg N ha

−1

year

−1

as NH

4

NO

3

or 40 kg N as NH

4

 +

ha

−1

year

−1

(control plots are not fertilized) since January 2007. The studied ecosystem was highly N responsive, i.e., visible changes were seen within one year of N additions: vascular plant and soil microbial diversity (soil bacteria and arbuscular mycorrhizal fungal spores) increased. Also the N concentration in leaves and litter increased, while the carbon-to-nitrogen (C/N) ratio of leaves and litter decreased.

Teresa Dias, Sandra Chaves, Rogério Tenreiro, Maria-Amélia Martins-Loução, Lucy J. Sheppard, Cristina Cruz
28. Species of Arbuscular Mycorrhizal Fungal Spores can Indicate Increased Nitrogen Availability in Mediterranean-type Ecosystems

Mycorrhizal fungi form ecologically important connections between plants and soils, and although nitrogen (N) enrichment has been implicated in the decline of ectomycorrhizal fungal diversity, they are rarely considered in studies investigating the effects of increased N availability on plant species diversity. This chapter describes the effects of N enrichment on the soil fungal community and in particular on arbuscular mycorrhizal fungal (AMF) spores, in a Mediterranean ecosystem in a Natura 2000 site in southern Portugal (PTCON0010 Arrábida/Espichel). Soil fungal community structure was affected by the addition of 80 kg N ha

−1

year

−1

as NH

4

NO

3

within 2 years. The effects of N addition on AMF diversity (richness and evenness) appear to depend on the form of N, since the addition of 40 kg N ha

−1

year

−1

as ammonium increased AMF spore richness and evenness proportionally more than the addition of 40 kg N ha

−1

year

−1

as ammonium plus nitrate. The composition of AMF species may serve as a sensitive indicator of N enrichment.

Teresa Dias, Sidney Luiz Stürmer, Sandra Chaves, Cátia Fidalgo, Rogério Tenreiro, Patrícia Correia, Luís Carvalho, Maria-Amélia Martins-Loução, Lucy J. Sheppard, Cristina Cruz
29. Nitrogen Biogeochemistry Research at Fernow Experimental Forest, West Virginia, USA: Soils, Biodiversity and Climate Change

Nitrogen (N) saturation arises when atmospheric inputs of N exceed biological N demand, resulting in loss of NO

3

-

in streams, accompanied by the loss of nutrients (Ca and Mg) that are essential to forest health. Previous studies have shown that some watersheds the Fernow Experimental Forest (FEF), West Virginia, USA, are among the more N-saturated sites in North America. Research from the Gilliam laboratory at Marshall University (West Virginia, USA) began focusing specifically on N biogeochemistry in 1993 with establishment of plots at FEF to carry out long-term

in situ

(“buried bag”) incubations in three watersheds: two control (WS4, WS7) and one treatment (WS3). This was done in conjunction with the Fernow Watershed Acidification Study, established by the USDA Forest Service in 1989 to treat an entire watershed (WS3) with aerial applications of 35 kg N ha 

–1

year  –

1

. The initial period (1993–1995) exhibited increases in rates for all watersheds, but especially in treated WS3. This period has been followed by declines in net nitrification, which is consistent with current declines in stream NO

3

and has been especially pronounced in WS3 since 1998. Also during this time, sampling of the herbaceous layer (vascular plants ≤ 1 m in height) has revealed pronounced changes in response to N treatments on WS3, especially in the increase of the shade-intolerant

Rubus

spp. Future work will investigate the effects of freezing on soil N dynamics. Preliminary results indicate that freezing exacerbates the symptoms of N saturation already seen in soils at FEF, further increasing already high rates of net nitrification.

Frank S. Gilliam

Critical Loads and Levels Approaches and Regional Upscaling

Frontmatter
30. Development of the Critical Loads Concept and Current and Potential Applications to Different Regions of the World

The chapter addresses whether the critical load of nutrient nitrogen (N) is a relevant, necessary and sufficient indicator to address adverse effects of reactive nitrogen (N

r

) on biodiversity in different regions of the world. Based on a description of the critical loads concept for nutrient N, and the relationship to biodiversity endpoints, applications of the critical load for nutrient N are summarized in the context of policies under the Long-range Transboundary Air Pollution (LRTAP) Convention. Potential applications of critical loads are addressed with respect to the relevance of adverse effects of N under the Convention on Biological Diversity (CBD). The chapter considers the prospects for effect-based applications in different regions of the world and poses some questions that need to be addressed. Finally, the potential for a broader indicator for N (a ‘threshold’ rather than a ‘load’) that could apply to all forms and impacts of N is considered, as it could potentially increase the coherence between CLRTAP and CBD.

Jean-Paul Hettelingh, Wim de Vries, Maximilian Posch, Gert Jan Reinds, Jaap Slootweg, W. Kevin Hicks
31. Nitrogen Deposition as a Threat to the World’s Protected Areas Under the Convention on Biological Diversity (CBD)

This chapter combines information on the world’s protected areas (PAs) under the Convention on Biological Diversity (CBD), common classification systems of ecosystem conservation status, and current knowledge on ecosystem responses to nitrogen (N) deposition, to determine areas most at risk. The results show that 2,600 PAs located in both the G200 Ecoregions and Biodiversity Hotspots are exposed to a deposition > 10 kg N ha

−1

year

−1

with projections for 2030 indicating that this situation is expected to continue. Furthermore, 62 PAs are projected to receive > 30 kg N ha

−1

year

−1

by 2030; with forest and grassland ecosystems in Asia particularly at risk. Many of these sites are known to be sensitive to N deposition effects, both in terms of biodiversity changes and ecosystem services they provide. Urgent assessment of high-risk areas identified in this study is recommended to inform the conservation efforts of the CBD.

Albert Bleeker, W. Kevin Hicks, Frank Dentener, James N. Galloway, Jan Willem Erisman
32. How Much is too Much? Nitrogen Critical Loads and Eutrophication and Acidification in Oligotrophic Ecosystems

Ecosystem impacts from nitrogen (N) deposition are related to (1) the degree to which plant growth responds to increases in N supply and (2) soil buffering capacity. Herbaceous communities dominated by plants adapted to low nutrient supply typically have low capacity to take up inputs of N. As a result they are more highly susceptible to loss of base cations, acidification, and increased production of toxic aluminium, manganese, and iron. Here we show that alpine ecosystems with acidic parent material display loss of biotic uptake together with soil acidification at relatively low inputs of N deposition, and can possibly reach extreme levels of acidification as indicated by a shift from an aluminium to an iron dominated soil buffering system.

William D. Bowman, L’uboš Halada, Juraj Hreško, Cory C. Cleveland, Jill S. Baron, John Murgel
33. Predicting Lichen-based Critical Loads for Nitrogen Deposition in Temperate Forests

Critical loads (CLs) define the quantitative exposure to one or more pollutants below which significant harmful effects on sensitive elements of the environment do not occur, according to present knowledge. Management according to CLs generated for epiphytic lichens, a highly nitrogen (N)-sensitive indicator, should protect forested ecosystems from N deposition effects. We tested the hypothesis that epiphytic lichen community composition, specifically the relative contribution of oligotrophs vs. eutrophs to species richness, can be predicted from mean annual precipitation and N deposition. We applied a multiple linear regression model developed for the North American Marine West Coast Forests to dry, mesic, and wet deciduous forests in California and Scotland. Replication of previously published CLs using this model validated our hypothesis, implying that lichen-based CLs for N can be estimated for other temperate forests where natural lichen community composition and mean annual precipitation are known.

Linda H. Geiser, Sarah E. Jovan, Douglas A. Glavich, Mark E. Fenn
34. Using Fire Risk and Species Loss to set Critical Loads for Nitrogen Deposition in Southern California Shrublands

Southern California deserts and coastal sage scrub (CSS) are undergoing vegetation-type conversion to exotic annual grassland, especially in regions downwind of urban areas that receive high nitrogen (N), primarily as dry deposition. To determine critical loads (CLs) of N that cause negative impacts, we measured plant and soil responses along N deposition gradients, fertilized vegetation at different N levels, and used biomass production output from the DayCent model. Nitrogen deposition gradients were identified from the CMAQ model and compared with measured N deposition values. Coastal sage scrub receives N deposition as high as 30 kg ha

− 1

year

− 1

, while the desert has levels up to 16 kg ha

− 1

year

− 1

. These ecosystems are subject to increases in exotic species production, loss of native species diversity, and increased fire risk at relatively low CLs. For instance, a gradient survey in CSS showed that exotic grass cover increased and native plant species richness declined by almost 50 % above 10 kg N ha

 − 1

year

− 1

. Fertilization studies in desert creosote bush scrub showed a significant increase in exotic species biomass with 5 kg N ha

− 1

year

− 1

in a wet year, and biomass output from DayCent modelling indicated an increased fire risk from exotic grasses with 1 t per ha production during years with moderate to high precipitation at 2.2–8.8 kg N ha

− 1

year

− 1

. The difference in CL between desert and CSS is related to the different criteria used (diversity loss in CSS, productivity and fire risk in desert), as well as responsiveness of native vs. exotic plant species to N and the degree to which precipitation and soil N limits plant growth in the two vegetation types.

Edith B. Allen, Leela E. Rao, Gail Tonnesen, Robert F. Johnson, Mark E. Fenn, Andrzej Bytnerowicz
35. Empirical Critical Loads of Nitrogen in China

For supplying the scientific basis of future nitrogen (N) emission control, the empirical critical loads of some forests and grasslands in China were determined by using reported field observations of N effects. Results showed that the critical loads of forest varied from 10~30 kg N ha

−1

year

−1

for temperate deciduous forest to 170~300 kg N ha

−1

year

−1

for subtropical coniferous plantation, and those of grassland varied from < 50 kg N ha

−1

year

−1

for typical temperate steppe and alpine steppe to 150~250 kg N ha

−1

year

−1

for subtropical grassland. These critical loads were much higher than 10–15 kg N ha

−1

year

−1

and 10–30 kg N ha

−1

year

−1

, the common values of natural forest and grassland respectively in Europe. The critical load map, based on the median of critical load range of each vegetation type, indicated that the empirical critical loads were lower in the northwest part of China, and higher in the southeast. Although the critical loads of N in the southeast part of China, where high nitrogen deposition existed, were relatively high to very high, critical loads occurred in some areas in north China and the south of northeast China, and sporadically in southwest China and east China. Nitrogen emission abatement is required in these areas to avoid exceedance of the estimated critical loads.

Lei Duan, Jia Xing, Yu Zhao, Jiming Hao
36. Challenges in Defining Critical Loads for Nitrogen in UK Lakes

It is now widely recognised that the deposition of nitrogen (N) compounds can lead to both acidification and eutrophication impacts in upland lakes. While major reductions in sulphur (S) emissions and deposition in the UK have been largely matched by chemical recovery from acidification in surface waters, reductions in emissions of N compounds have not been matched by corresponding reductions in deposition. Here we explore two related issues in the use of critical loads for N in upland waters:

1.

Identifying potential impacts of nutrient N in naturally nutrient poor systems of conservation importance and links to biodiversity, and

2.

Problems in defining critical chemical limits with respect to reference conditions in upland lakes.

Empirical critical loads for nutrient N have been recommended to protect macrophyte communities of shallow softwater lakes in Europe. The recommended range of 5–10 kg N ha

−1

year

−1

is exceeded across most of the UK, but most oligotrophic lakes are of a different habitat type to those for which empirical critical loads have been recommended. Furthermore, while there is widespread evidence from nutrient bioassay work for N limitation of phytoplankton production in oligotrophic lakes there is little direct evidence to date of impacts on other biological groups in the UK, including macrophytes. A major problem is the lack of data on reference communities in unimpacted lakes and lack of identified “harmful ecological effects” required by the definition of critical loads. There are also fundamental differences in approach between the critical loads employed under the UNECE Gothenburg Protocol and the EU Water Framework Directive. We show that there are major challenges in application of critical loads for nutrient N which must be overcome if we are to protect designated sites of conservation interest and maintain, or allow recovery to, the good ecological status required by the EU Water Framework Directive.

Chris J. Curtis, Gavin L. Simpson, Rick W. Battarbee, Stephen Maberly
37. Proposing a Strict Epidemiological Methodology for Setting Empirical Critical Loads for Nitrogen Deposition

Currently empirical critical loads are derived from manipulation experiments and field survey data and more recently these data have come under scrutiny as our understanding of how ecosystems respond to reactive nitrogen (N

r

) deposition evolves. The importance of background nitrogen (N) deposition and the significance of the starting N capital, cumulative N, are now recognized. This has led to a credibility rating against which experimental data can be evaluated. However, there is still no robust and transparent system in place for setting empirical critical loads for nitrogen deposition. This chapter discusses some of the issues involved in the evaluation of the available data and proposes a testable approach to carry the system forward.

Harald Sverdrup, Bengt Nihlgård, Salim Belyazid, Lucy J. Sheppard
38. A Comparison of Empirical and Modelled Nitrogen Critical Loads for Mediterranean Forests and Shrublands in California

Nitrogen (N) deposition is impacting a number of ecosystem types in California. Critical loads (CLs) for N deposition determined for mixed conifer forests and chaparral/oak woodlands in the Sierra Nevada Mountains of California and the San Bernardino Mountains in southern California using empirical and various modelling approaches were compared. Models used included the Simple Mass Balance (SMB) model for nutrient N and acidification (both site-specific and regional approaches) and the Daycent process-based biogeochemical simulation model. Empirical CLs reported herein were based on responses across N deposition gradients of lichen community functional groups and streamwater nitrate (NO

3

) leaching. Broad scale CL mapping for the San Bernardino Mountains using the SMB model resulted in nutrient N CL values that were on average approximately 50 % lower than the empirical CL value for NO

3

leaching (17 kg ha

−1

year

−1

) in California mixed conifer forests. Over the range of elevations and vegetation types in the San Bernardino Mountains, SMB CL values ranged from 5.1 to 13.0 kg ha

−1

year

−1

for nutrient N. For both the empirical NO

3

leaching CL and the SMB estimate, the CL was generally lower for chaparral vegetation than for forests. The estimated CL for NO

3

leaching derived from the Daycent model was equal to the empirical CL (17 kg ha

−1

year

−1

), but the severity and frequency of elevated NO

3

leaching was underestimated by Daycent. Statewide empirical CL exceedance maps indicate that 3.3 and 4.5 % of the chaparral and forested areas in California are in excess of the NO

3

leaching CL. Likewise, 23.4, 41.2 and 52.9 % of the mixed conifer forest, oak woodland and chaparral areas are in excess of the empirical N CL for epiphytic lichen community effects, respectively. Eutrophication effects in terrestrial ecosystems of California are widespread, while significant acidification effects are limited to the more polluted sites in southern California.

Mark E. Fenn, Hans-Dieter Nagel, Ina Koseva, Julian Aherne, Sarah E. Jovan, Linda H. Geiser, Angela Schlutow, Thomas Scheuschner, Andrzej Bytnerowicz, Benjamin S. Gimeno, Fengming Yuan, Shaun A. Watmough, Edith B. Allen, Robert F. Johnson, Thomas Meixner
39. Source Attribution of Eutrophying and Acidifying Pollutants on the UK Natura 2000 Network

Atmospheric nitrogen (N) and sulphur (S) deposition from industrial, transport and agricultural sources may exert a range of different types of impacts on Natura 2000 sites in Europe. The FRAME (Fine Resolution Atmospheric Multi-pollutant Exchange) model, incorporating emission point sources and sectors, was used to provide footprints of N and S deposition across the UK from 160 sources or groups of sources. The resulting matrix of source attribution by sector, and exceedance statistics for each site, provide a means of impact assessment for the whole UK’s Natura 2000 network. For 2005 80 % of Special Areas of Conservation (SACs) in the UK have at least one feature exceeding their minimum N critical load, while the figure for acidity exceedance is 75 %. By 2020, the values are estimated at 74 and 62 %, respectively, indicating that current policies are insufficient to avoid exceedance of the critical loads. Although NO

x

emissions are projected to decrease substantially, the modest reduction in exceedance is a consequence of the contribution of NH

3

from agricultural sources, which is projected to decrease only slightly between 2005 and 2020. Future analysis should address the spatial importance of source location and site proximity to a source, and examine the relationship between dry and wet deposition by source sector.

William J. Bealey, Anthony J. Dore, Clare P. Whitfield, Jane R. Hall, Massimo Vieno, Mark A. Sutton
40. Mapping Critical Loads for Nitrogen Based on Biodiversity Using ForSAFE-VEG: Introducing the Basic Principles

This chapter describes the basic principles inside the VEG extension to the ForSAFE model system. It allows changes in ground vegetation to be calculated, an important part of biodiversity. In the VEG model, the basis for modelling ground vegetation dynamics is a competition strength model based on soil chemistry promoting and retarding factors, nutrients, water and light. The strength is used in a competition model to assign ground area to each plant type considered. The ForSAFE-VEG is freely available from the authors and is used for assessing critical loads for acidity and nitrogen in Europe and United Sates, based on biodiversity criteria.

Harald Sverdrup, Bengt Nihlgård, Salim Belyazid

Nitrogen Deposition, Ecosystem Services and Policy Development

Frontmatter
41. Impacts of Nitrogen Deposition on Ecosystem Services in Interaction with Other Nutrients, Air Pollutants and Climate Change

Nitrogen (N) deposition affects many ecosystem services, ranging from: (i) provisioning services such as timber/wood fuel production, (ii) regulating services such as carbon sequestration and pollutant filtering leading to the provision of clean air and water, (iii) supporting services such as nutrient cycling and primary production, and (iv) cultural services such as recreation and landscape features or species with aesthetic or spiritual value. This chapter presents discussion of the major relationships between N deposition and ecosystem services as distinguished in the Millennium Ecosystem Assessment. An important issue is how other factors, such as changes in climate, CO

2

and tropospheric ozone exposure and other nutrients, such as phosphate, affect those ecosystem services, and how they should be taken into account in critical load assessments, while accounting for regional differences. Another important issue is the linkage between plant species diversity changes, being the main indicator for critical N loads, and ecosystem services, including faunal species diversity and biodiversity-based products, such as impacts on edible wild plants and medicinal plants. Consideration is also given to the implications of these issues for the CBD and LRTAP Conventions.

Wim de Vries, Christine Goodale, Jan Willem Erisman, Jean-Paul Hettelingh
42. The Form of Reactive Nitrogen Deposition Affects the Capacity of Peatland Vegetation to Immobilise Nitrogen: Implications for the Provision of Ecosystem Services

Peatlands represent significant carbon (C) reserves accumulated over millennia, as a consequence of slow decomposition rates conditioned by the acidity and anoxia that define these ecosystems. Such conditions are maintained largely through climate but also the activities of peatland ‘engineers’, vegetation such as

Sphagnum

mosses. Peatlands are hugely valued for C sequestration and the distinct communities they support. However, increased nitrogen (N) availability, from anthropogenic deposition, has been linked to detrimental changes in the vitality of

Sphagnum

and species active in perpetuating peatland processes. The effects of manipulating the form and dose of N to an ombrotrophic peatland, Whim bog in the Scottish Borders, UK, have been studied since 2002. Ammonia is provided by free air release, in response to wind direction and wind speed, and wet deposition, comprising nitrate or ammonium, in response to rainfall. Manipulation has increased the background deposition of 8 kg N ha

−1

year

−1

by 2, 4 and 8 times. Responses to the different N forms in terms of species cover, importance of component species in maintaining low nutrient availability through N immobilisation and the implications of breakdown in vegetative cover and species replacement for peatland function are discussed in relation to N fluxes. All forms of N were not equally detrimental: ammonia deposition significantly reduced the vegetative cover, removing the sink for N, leading to increased nitrate in soil pore water and nitrous oxide emission whereas effects of wet N deposition, though still detrimental, were more modest. Nitrogen driven reductions in the cover of the keystone

Sphagnum

species and other characteristic mosses and their ability to immobilise incoming N can affect soil chemistry and lead to changes that could compromise C sequestration.

Lucy J. Sheppard, Ian D. Leith, Sanna K. Kivimaki, Jenny Gaiawyn
43. Quantification of Impacts of Nitrogen Deposition on Forest Ecosystem Services in Europe

Important forest ecosystem services are the provision of a habitat for a diversity of plants and wildlife (habitat service), pollutant filtering relevant for an adequate water quality (regulating service) and wood production with the related carbon (C) storage (provisioning/regulating service). Nitrogen (N) deposition affects these ecosystem services as it has an impact on: (i) the habitat for wild plants, reducing plant species diversity, (ii) water/soil quality by its impact on acidity (pH) and on the soil accumulation and leaching of N as nitrate, aluminium (Al) and metals to ground water and surface water and (iii) net primary production and C sequestration. In this chapter, we describe the application of the Very Simple Dynamic (VSD) model, extended with relationships between nitrogen (N) deposition and greenhouse gas emissions, on a European-wide scale to quantify the impact of N deposition on these forest ecosystem services. This includes: (i) potential impacts of N deposition on plant species diversity in terms of excess N deposition compared to critical loads for N, (ii) excess nitrate (NO

3

) and Al concentrations in leachate to groundwater and surface water compared to critical limits, (iii) soil acidification, in terms of the depletion of the pools of base cations (BC) and Al, and (iv) C sequestration and related emissions of the greenhouse gases carbon dioxide (CO

2

), nitrous oxide (N

2

O) and methane (CH

4

). Results show that the N deposition reduction measures that have been taken since 1980 have led to a reduction between 10 and 15 % in the areas exceeding critical N loads and critical limits for NO

3

and Al in groundwater or surface water, but the estimated CO

2

uptake is nearly 20 % lower under a reduced N deposition scenario as compared to a constant 1980 N deposition scenario. The N induced N

2

O emissions however counteract the N induced C sequestration.

Wim de Vries, Maximilian Posch, Gert Jan Reinds, Jean-Paul Hettelingh
44. Implications of Current Knowledge on Nitrogen Deposition and Impacts for Policy, Management and Capacity Building Needs: CLRTAP

The Convention on Long-range Transboundary Air Pollution (CLRTAP), linking North America, Europe, and large parts of Central Asia, has achieved considerable reductions in air pollution emissions and effects. In addition, CLRTAP has also facilitated political cooperation, international law development, and the use of science to develop and implement policy. For instance, regionalized emission reduction targets of the CLRTAP Gothenburg Protocol minimize environmental effects and abatement costs. However, reductions of nitrogen (N) emissions causing eutrophication effects have not been sufficient to prevent widespread critical load exceedances. CLRTAP has increasingly assessed links between N emissions/effects, climate change and biodiversity but more research is needed. To achieve enhanced capacity building and further emission reduction of N compounds challenges have to be overcome in science (e.g., regarding N effects on ecosystems and feedbacks with climate), policy (e.g., linking CLRTAP with other multilateral and global environmental agreements), and communication between science, policy and the public.

Till Spranger, Keith Bull, Thomas A. Clair, Matti Johansson
45. The Convention on Biological Diversity: How does Nitrogen fit into the Plans?

The Convention on Biological Diversity (CBD) recognises five direct drivers of biodiversity loss: habitat change, climate change, invasive species, over-exploitation, and pollution, including by excessive nitrogen (N) and phosphorus (P) nutrients. Nitrogen was part of the flexible framework of indicators, under the ‘threats’ focal area, established to measure progress towards the CBDs target of achieving a ‘significant reduction in the current rate of biodiversity loss’ at global, regional and national level by 2010. Nitrogen indicators were established at various scales, including N deposition at global scale and critical loads at European scale. The target was not reached for almost all the indicators. Measuring, and addressing changes in, ecosystem services is likely to be a key aspect of any post-2010 target, and is an area in which this workshop could help the CBD: by providing ideas on how N inputs can be effectively measured at a variety of scales, and critically, what the impact of different levels of N (in its various forms) is on biodiversity, at a variety of scales.

James M. Williams
46. Agriculture and the Nitrogen Problem in India: Environmental Implications

Much of the excess nitrogen (N) inputs in the Indian region are from agriculture. We quantified soil surface N loads for agro-ecological zones (AEZs) in India using a mass balance approach. We estimate nearly 35.0 Tg of N inputs from different sources, with output N from harvested crops of about 21.0 Tg. The soil surface N balance, estimated as inputs minus outputs, is found to be about 14.4 Tg surpluses from the agricultural land of India. Livestock manure constituted a major percentage of total inputs (44 %), followed by inorganic fertilizer (32.4 %), atmospheric deposition (11.86 %) and N fixation (11.58 %). Nitrogen balance varied from deficit to surplus for different Indian states and AEZs. The lowest N loads were found for AEZs in the Eastern Himalaya, with 19 kg ha

−1

surplus, and highest surplus in AEZs with >111 kg ha

−1

in areas such as the Deccan plateau and southern India. Environmental implications of these excess N loads in India are discussed, in addition to some best management practices to reduce the loads from agricultural sources.

Krishna P. Vadrevu, K.V.S. Badarinath
47. Mitigating Increases in Nitrogen Deposition: The Challenge of Extending Symbiotic Nitrogen Fixation to Cereals and Other Non-legume Crops

Extending the symbiotic nitrogen-fixing capability of legume crops with nitrogen-fixing bacteria to non-legume crops, particularly the cereals, would increase the extent of biological nitrogen (N) fixation and reduce the need for synthetic N fertilizers; excess N from N fertilizers causes many environmental impacts including a contribution to the greenhouse effect, acid rain and biodiversity loss. The first step required to achieve symbiotic N fixation in non-legume crops is to establish N-fixing bacteria intracellularly within cytoplasmic vesicles in their roots. By inoculating seedlings of maize, rice, wheat, oilseed rape and tomato grown aseptically in sucrose-containing culture media with very low numbers of

Gluconacetobacter diazotrophicus

we have shown that this N-fixing bacterium is able to intracellularly colonise the meristematic cells of their roots. Dark blue histochemically stained

G. diazotrophicus

were visible within the cytoplasm of meristematic cells of root tips and also within their cell walls. Electron microscopy confirmed that

G. diazotrophicus

was within membrane-bound vesicles in the cytoplasm. Field trials of cereals and other major non-legume crops will now be required. Within a timeframe of 5–10 years it should be possible to determine the extent to which symbiotic N fixation resulting from this bacterial intracellular colonisation will enable reductions in the use of synthetic nitrogen fertilizers.

Edward C Cocking, Philip J Stone

Conclusions and Outlook

Frontmatter
48. Progress in Nitrogen Deposition Monitoring and Modelling

The chapter reviews progress in monitoring and modelling of atmospheric nitrogen (N) deposition at regional and global scales. The Working Group expressed confidence in the inorganic N wet deposition estimates in U.S., eastern Canada, Europe and parts of East Asia. But, long-term wet or dry N deposition information in large parts of Asia, South America, parts of Africa, Australia/Oceania, and oceans and coastal areas is lacking. Presently, robust estimates are only available for inorganic N as existing monitoring generally does not measure the complete suite of N species, impeding the closing of the atmospheric N budget. The most important species not routinely measured are nitrogen dioxide (NO

2

), ammonia (NH

3

), organic N and nitric acid (HNO

3

). Uncertainty is much higher in dry deposition than in wet deposition estimates. Inferential modelling (combining air concentrations with exchange rates) and direct flux measurements are good tools to estimate dry deposition; however, they are not widely applied. There is a lack of appropriate parameterizations for different land uses and compounds for input into inferential models. There is also a lack of direct dry deposition flux measurements to test inferential models and atmospheric model estimates.

Wenche Aas, Silvina Carou, Ana Alebic-Juretic, Viney P Aneja, Rajasekhar Balasubramanian, Haldis Berge, J. Neil Cape, Claire Delon, O. Tom Denmead, Robin L. Dennis, Frank Dentener, Anthony J. Dore, Enzai Du, Maria Cristina Forti, Corinne Galy-Lacaux, Markus Geupel, Richard Haeuber, Carmen Iacoban, Alexander S. Komarov, Eero Kubin, Umesh C. Kulshrestha, Brian Lamb, Xuejun Liu, D. D. Patra, Jacobus J. Pienaar, Pedro Pinho, P. S. P. Rao, Jianlin Shen, Mark A. Sutton, Mark R. Theobald, Krishna P. Vadrevu, Robert Vet
49. The Effects of Atmospheric Nitrogen Deposition on Terrestrial and Freshwater Biodiversity

This chapter reports the findings of a Working Group on how atmospheric nitrogen (N) deposition affects both terrestrial and freshwater biodiversity. Regional and global scale impacts on biodiversity are addressed, together with potential indicators. Key conclusions are that: the rates of loss in biodiversity are greatest at the lowest and initial stages of N deposition increase; changes in species compositions are related to the relative amounts of N, carbon (C) and phosphorus (P) in the plant soil system; enhanced N inputs have implications for C cycling; N deposition is known to be having adverse effects on European and North American vegetation composition; very little is known about tropical ecosystem responses, while tropical ecosystems are major biodiversity hotspots and are increasingly recipients of very high N deposition rates; N deposition alters forest fungi and mycorrhyzal relations with plants; the rapid response of forest fungi and arthropods makes them good indicators of change; predictive tools (models) that address ecosystem scale processes are necessary to address complex drivers and responses, including the integration of N deposition, climate change and land use effects; criteria can be identified for projecting sensitivity of terrestrial and aquatic ecosystems to N deposition. Future research and policy-relevant recommendations are identified.

Jill S. Baron, Mary Barber, Mark Adams, Julius I. Agboola, Edith B. Allen, William J. Bealey, Roland Bobbink, Maxim V. Bobrovsky, William D Bowman, Cristina Branquinho, Mercedes M.C. Bustamente, Christopher M. Clark, Edward C. Cocking, Cristina Cruz, Eric Davidson, O. Tom Denmead, Teresa Dias, Nancy B. Dise, Alan Feest, James N. Galloway, Linda H. Geiser, Frank S. Gilliam, Ian J. Harrison, Larisa G. Khanina, Xiankai Lu, Esteban Manrique, Raúl Ochoa Hueso, Jean P.H.B. Ometto, Richard Payne, Thomas Scheuschner, Lucy J. Sheppard, Gavin L. Simpson, Y. V. Singh, Carly J. Stevens, Ian Strachan, Harald Sverdrup, Naoko Tokuchi, Hans van Dobben, Sarah Woodin
50. The Critical Loads and Levels Approach for Nitrogen

This chapter reports the findings of a Working Group to review the critical loads (CLs) and levels approach for nitrogen (N). The three main approaches to estimating CLs are empirical, mass balance and dynamic modelling. Examples are given of recent developments in Europe, North America and Asia and it is concluded that other countries should be encouraged to develop basic assessments using soil, land cover, and deposition map overlays in order to determine what regions might exceed nitrogen CLs. There is a need for increasing the certainty of critical load (CL) estimates by focusing on empirical data needs, especially for understudied ecosystems such as tropical or Mediterranean, high elevation environments, and aquatic systems. There is also a need to improve steady-state mass balance parameters, especially soil solution terms, such as nitrate leaching, used to determine the CL, and denitrification, which is an equation parameter. Improved dynamic models are needed for predicting plant community changes, and work should continue on existing models to determine CL values. Dynamic models require more data and are more complex than simple calculated CLs but offer more information and allow the development of ‘what if?’ scenarios. Optimal use of CLs requires expert knowledge of ecosystem values to provide reference states so that safe deposition amounts can be determined. Increased interaction between CL and biodiversity specialists to identify critical biodiversity limits would help provide better CL assessments.

Thomas A. Clair, Tamara Blett, Julian Aherne, Marcos P. M. Aidar, Richard Artz, William J. Bealey, William Budd, J. Neil Cape, Chris J. Curtis, Lei Duan, Mark E. Fenn, Peter Groffman, Richard Haeuber, Jane R. Hall, Jean-Paul Hettelingh, Danilo López-Hernández, Scot Mathieson, Linda Pardo, Maximilian Posch, Richard V. Pouyat, Till Spranger, Harald Sverdrup, Hans van Dobben, Arjan van Hinsberg
51. Nitrogen Deposition Effects on Ecosystem Services and Interactions with other Pollutants and Climate Change

Ecosystem services are defined as the ecological and socio-economic value of goods and services provided by natural and semi-natural ecosystems. Ecosystem services are being impacted by many human induced stresses, one of them being nitrogen (N) deposition and its interactions with other pollutants and climate change. It is concluded that N directly or indirectly affects a wide range of provisioning, regulating, supporting and cultural ecosystem services, many of which are interrelated. When considering the effects of N on ecosystem services, it is important to distinguish between different types of ecosystems/species and the protection against N impacts should include other aspects related to N, in addition to biodiversity. The Working Group considered the following priorities of ecosystem services in relation to N: biodiversity; air quality/atmosphere; ecosystem changes; NO

3

leaching; climate regulation and cultural issues. These are the services for which the best evidence is available in the literature. There is a conflicting interest between greenhouse gas ecosystem services and biodiversity protection; up to some point of increasing N inputs, net greenhouse gas uptake is improved, while biodiversity is already adversely affected.

Jan Willem Erisman, Allison Leach, Mark Adams, Julius I. Agboola, Luan Ahmetaj, Didier Alard, Amy Austin, Moses A. Awodun, Simon Bareham, Theresa L. Bird, Albert Bleeker, Keith Bull, Sarah E. Cornell, Eric Davidson, Wim de Vries, Teresa Dias, Bridget Emmett, Christine Goodale, Tara Greaver, Rick Haeuber, Harry Harmens, W. Kevin Hicks, Lars Hogbom, Paul Jarvis, Matti Johansson, Zoe Russell, Colin McClean, Bill Paton, Tibisay Perez, Jan Plesnik, Nalini Rao, Susanne Schmidt, Yogendra B. Sharma, Naoko Tokuchi, Clare P. Whitfield
52. Workshop on Nitrogen Deposition, Critical Loads and Biodiversity: Scientific Synthesis and Summary for Policy Makers

It is clear that nitrogen (N) deposition impacts on the biodiversity and ecosystem services provided by natural and semi-natural ecosystems have been experienced in Europe, North America and Asia over the last 50 years. Impacts are also estimated to increase in line with increasing rates of N deposition in coming decades across the globe, especially in Asia. To improve the assessment of impacts progress is required in the following key areas: the extent of monitoring networks and the measurement of dry and organic deposition; the modelling of N deposition in areas with complex topography; the assessment of impacts on fauna generally and impacts on flora in areas outside the relatively well studied temperate ecosystems; the application of critical load (CL) and level approaches outside of Europe; and the linkage between impacts on biodiversity and important ecosystem services. New indicators are required, in addition to N deposition and critical loads, to demonstrate the wider impacts and to help integrate the biodiversity, air pollution and climate change policy communities.

W. Kevin Hicks, Richard Haeuber, Mark A. Sutton, Wenche Aas, Mary Barber, Jill S. Baron, Tamara Blett, Silvina Carou, Thomas Clair, Jan Willem Erisman, Allison Leach, James N. Galloway
Backmatter
Metadata
Title
Nitrogen Deposition, Critical Loads and Biodiversity
Editors
Mark A. Sutton
Kate E. Mason
Lucy J. Sheppard
Harald Sverdrup
Richard Haeuber
W. Kevin Hicks
Copyright Year
2014
Publisher
Springer Netherlands
Electronic ISBN
978-94-007-7939-6
Print ISBN
978-94-007-7938-9
DOI
https://doi.org/10.1007/978-94-007-7939-6