Exchange of gaseous nitrogen compounds between agricultural systems and the atmosphere

Crop and livestock agricultural production systems are important contributors to local, regional and global budgets of NH₃, NO_x (NO + NO₂) and N₂O. Emissions of NH₃ and NO_x (which are biologically and chemically active) into the atmosphere serve to redistribute fixed N to local and regional aquatic and terrestrial ecosystems that may otherwise be disconnected from the sources of the N gases. The emissions of NO_x also contribute to local elevated ozone concentrations while N₂O emissions contribute to global greenhouse gas accumulation and to stratospheric ozone depletion.Ammonia is the major gaseous base in the atmosphere and serves to neutralize about 30% of the hydrogen ions in the atmosphere. Fifty to 75% of the 55 Tg N yr^–1 NH₃ from terrestrial systems is emitted from animal and crop-based agriculture from animal excreta and synthetic fertilizer application. About half of the 50 Tg N yr^–1 of NO_x emitted from the earth surface annually arises from fossil fuel combustion and the remainder from biomass burning and emissions from soil. The NO_x emitted, principally as nitric oxide (NO), reacts rapidly in the atmosphere and in a complex cycle with light, ozone and hydrocarbons, and produces nitric acid and particulate nitrate. These materials can interact with plants and the soil locally or be transported form the site and interact with atmospheric particulate to form aerosols. These salts and aerosols return to fertilize terrestrial and aquatic systems in wet and dry deposition. A small fraction of this N may be biologically converted to N₂O. About 5% of the total atmospheric greenhouse effect is attributed to N₂O from which 70% of the annual global anthropogenic emissions come from animal and crop production.The coupling of increased population with a move of a large sector of the world population to diets that require more energy and N input, will lead to continued increases in anthropogenic input into the global N cycle. This scenario suggests that emissions of NH₃, NO_x and N₂O from agricultural systems will continue to increase and impact global terrestrial and aquatic systems, even those far removed from agricultural production, to an ever growing extent, unless N resources are used more efficiently or food consumption trends change.     

Policy implications of human-accelerated nitrogen cycling

The human induced input of reactive N into the globalbiosphere has increased to approximately 150 Tg N eachyear and is expected to continue to increase for theforeseeable future. The need to feed (125 Tg N) andto provide energy (25 Tg N) for the growing worldpopulation drives this trend. This increase inreactive N comes at, in some instances, significantcosts to society through increased emissions of NO_x,NH₃, N₂O and NO₃ ^– and deposition of NO_y and NH_x.In the atmosphere, increases in tropospheric ozone andacid deposition (NO_y and NH_x) have led toacidification of aquatic and soil systems and toreductions in forest and crop system production. Changes in aquatic systems as a result of nitrateleaching have led to decreased drinking water quality,eutrophication, hypoxia and decreases in aquatic plantdiversity, for example. On the other hand, increaseddeposition of biologically available N may haveincreased forest biomass production and may havecontributed to increased storage of atmospheric CO₂ inplant and soils. Most importantly, syntheticproduction of fertilizer N has contributed greatly tothe remarkable increase in food production that hastaken place during the past 50 years.The development of policy to control unwanted reactiveN release is difficult because much of the reactive Nrelease is related to food and energy production andreactive N species can be transported great distancesin the atmosphere and in aquatic systems. There aremany possibilities for limiting reactive N emissionsfrom fuel combustion, and in fact, great strides havebeen made during the past decades. Reducing theintroduction of new reactive N and in curtailing themovement of this N in food production is even moredifficult. The particular problem comes from the factthat most of the N that is introduced into the globalfood production system is not converted into usableproduct, but rather reenters the biosphere as asurplus. Global policy on N in agriculture isdifficult because many countries need to increase foodproduction to raise nutritional levels or to keep upwith population growth, which may require increaseduse of N fertilizers. Although N cycling occurs atregional and global scales, policies are implementedand enforced at the national or provincial/statelevels. Multinational efforts to control N loss tothe environment are surely needed, but these effortswill require commitments from individual countries andthe policy-makers within those countries.     

Policy implications of human-accelerated nitrogen cycling

The human induced input of reactive N into the globalbiosphere has increased to approximately 150 Tg N eachyear and is expected to continue to increase for theforeseeable future. The need to feed (125 Tg N) andto provide energy (25 Tg N) for the growing worldpopulation drives this trend. This increase inreactive N comes at, in some instances, significantcosts to society through increased emissions of NO_x,NH₃, N₂O and NO₃ ^– and deposition of NO_y and NH_x.In the atmosphere, increases in tropospheric ozone andacid deposition (NO_y and NH_x) have led toacidification of aquatic and soil systems and toreductions in forest and crop system production. Changes in aquatic systems as a result of nitrateleaching have led to decreased drinking water quality,eutrophication, hypoxia and decreases in aquatic plantdiversity, for example. On the other hand, increaseddeposition of biologically available N may haveincreased forest biomass production and may havecontributed to increased storage of atmospheric CO₂ inplant and soils. Most importantly, syntheticproduction of fertilizer N has contributed greatly tothe remarkable increase in food production that hastaken place during the past 50 years.The development of policy to control unwanted reactiveN release is difficult because much of the reactive Nrelease is related to food and energy production andreactive N species can be transported great distancesin the atmosphere and in aquatic systems. There aremany possibilities for limiting reactive N emissionsfrom fuel combustion, and in fact, great strides havebeen made during the past decades. Reducing theintroduction of new reactive N and in curtailing themovement of this N in food production is even moredifficult. The particular problem comes from the factthat most of the N that is introduced into the globalfood production system is not converted into usableproduct, but rather reenters the biosphere as asurplus. Global policy on N in agriculture isdifficult because many countries need to increase foodproduction to raise nutritional levels or to keep upwith population growth, which may require increaseduse of N fertilizers. Although N cycling occurs atregional and global scales, policies are implementedand enforced at the national or provincial/statelevels. Multinational efforts to control N loss tothe environment are surely needed, but these effortswill require commitments from individual countries andthe policy-makers within those countries.     

What Have Stable Isotope Studies Revealed About the Nature and Mechanisms of N Saturation and Nitrate Leaching from Semi-Natural Catchments?

Various studies over the last 15 years have attempted to describe the processes of N retention, saturation and NO₃ ⁻ leaching in semi-natural ecosystems based on stable isotope studies. Forest ecologists and terrestrial biogeochemists have used ¹⁵N labelled NO₃ ⁻ and NH₄ ⁺ tracers to determine the fate of atmospheric deposition inputs of N to terrestrial ecosystems, with NO₃ ⁻ leaching to surface waters being a key output flux. Separate studies by aquatic ecologists have used similar isotope tracer methods to determine the fate and impacts of inorganic N species, leached from terrestrial ecosystems, on aquatic ecosystems, usually without reference to comparable terrestrial studies. A third group of isotopic studies has employed natural abundances of ¹⁵N and ¹⁸O in precipitation and surface water NO₃ ⁻ to determine the relative contributions of atmospheric and microbial sources. These three sets of results often appear to conflict with one another. Here we attempt to synthesize and reconcile the results of these differing approaches to identifying both the source and the fate of inorganic N in natural or semi-natural ecosystems, and identify future research priorities. We conclude that the results of different studies conform to a consistent conceptual model comprising: (1) rapid microbial turnover of atmospherically deposited NO₃ ⁻ at multiple biologically active locations within both terrestrial and aquatic ecosystems; (2) maximum retention and accumulation of N in carbon-rich ecosystems and (3) maximum leaching of NO₃ ⁻, most of which has been microbially cycled, from carbon-poor ecosystems exposed to elevated atmospheric N inputs.     

LUCAS - A New LCIA Method Used for a Canadian-Specific Context

Goal, Scope and Background Canadian LCA practitioners currently use European or American methodologies when conducting comprehensive impact assessments, despite the fact that these methods may not be appropriate for Canadian conditions. Due to the lack of suitable models that are currently available, work has been undertaken to develop an LCIA method by adapting existing LCIA models to the Canadian context. This new method allows the characterization of 10 impact categories. Methods This project is strongly based on preliminary outcomes from SETAC recommendations for the best available practices in LCIA. Models from 3 recent LCIA site-dependent methods, EDIP2003, IMPACT2002+ and TRACI, were used in this midpoint Canadian-specific method. Characterization models were chosen based on their level of comprehensiveness, scientific sophistication and the possibility of integrating site-specific values in the models. Results and Discussion All regional and local impact categories in the method are site-differentiated. For aquatic eutrophication, (eco)toxicity and land-use impact categories, regionally-differentiated models taking into account fate and effect were already available: the parameters of these models were modified for the Canadian context. For acidification, aquatic and terrestrial eutrophication, existing models were spatially differentiated for fate: regionalization of the effect factor was also included, based on the level of sensitivity of each ecozone assessed with vulnerability factors. The default spatial resolution selected for this method was Canadian ecozones, which define spaces in an ecologically meaningful way where organisms and their physical environment evolve as a system. For each ecozone, 2334 site-dependent characterization factors have been calculated. Conclusion This LCIA methodology proposes an attractive and useful set of site-dependent characterization factors for the 15 Canadian terrestrial ecozones. Recommendation and Outlook Efforts are being carried out to extend the specificity of some factors used in eutrophication modelization. Finally, the transparency of the methodology will allow to re-calculate site-dependent characterization factors for different regions and for additional substances.     

Contemporary and pre-industrial global reactive nitrogen budgets

Increases and expansion of anthropogenic emissions of both oxidized nitrogen compounds, NO_x, and a reduced nitrogen compound, NH₃, have driven an increase in nitrogen deposition. We estimate global NO_x and NH₃ emissions and use a model of the global troposphere, MOGUNTIA, to examine the pre-industrial and contemporary quantities and spatial patterns of wet and dry NO_y and NH_x deposition. Pre-industrial wet plus dry NO_x and NH_x deposition was greatest for tropical ecosystems, related to soil emissions, biomass burning and lightning emissions. Contemporary NO_y+NH_x wet and dry deposition onto Northern Hemisphere (NH) temperate ecosystems averages more than four times that of preindustrial N deposition and far exceeds contemporary tropical N deposition. All temperate and tropical biomes receive more N via deposition today than pre-industrially. Comparison of contemporary wet deposition model estimates to measurements of wet deposition reveal that modeled and measured wet deposition for both NO ₃ ^– and NH ₄ ⁺ were quite similar over the U.S. Over Western Europe, the model tended to underestimate wet deposition of NO ₃ ^– and NH ₄ ⁺ but bulk deposition measurements were comparable to modeled total deposition. For the U.S. and Western Europe, we also estimated N emission and deposition budgets. In the U.S., estimated emissions exceed interpolated total deposition by 3-6 Tg N, suggesting that substantial N is transported offshore and/or the remote and rural location of the sites may fail to capture the deposition of urban emissions. In Europe, by contrast, interpolated total N deposition balances estimated emissions within the uncertainty of each.Abbreviations EMEP European Monitoring and Evaluation Program - GEIA Global Emissions Inventory Activity - NADP/NTN National Atmospheric Deposition Program/National Trends Network in the US - NH Northern Hemisphere - NH_x=NH₃+NH ₊ ⁴ NO_x=NO+NO₂ NO_y total odd nitrogen=NO_x+HNO₃+HONO+HO₂NO₂+NO₃+radical (NO₃ ^.)+Peroxyacetyl nitrates+N₂O₅+organic nitrates - SH Southern Hemisphere - Gg 10⁹ g - Tg 10¹² g     

Uncertainty and spatial variability in characterization factors for aquatic acidification at the global scale

Purpose

Characterization factors (CFs) quantifying the potential impact of acidifying emissions on inland aquatic environments in life cycle assessment are typically available on a generic level. The lack of spatial differentiation may weaken the relevance of generic CFs since it was shown that regional impact categories such as aquatic acidification were influenced by the surroundings of the emission location. This paper presents a novel approach for the development of spatially differentiated CFs at a global scale for the aquatic acidification impact category.

Methods

CFs were defined as the change in relative decrease of lake fish species richness due to a change in acidifying chemicals emissions. The characterization model includes the modelling steps linking emission to atmospheric acid deposition (atmospheric fate factor) change, which lead to lake H⁺ concentration (receiving environment fate factor) change and a decrease in relative fish species richness (effect factor). We also evaluated the significance of each factor (i.e. atmospheric fate, receiving environment fate and effects) to the overall CFs spatial variability and parameter uncertainty.

Results and discussion

The highest CFs were found for emissions occurring in Canada, Scandinavia and the northern central Asia because of the extensive lake areas in these regions (lake areas being one of the parameters of the CFs; the bigger the lake areas, the higher the CFs). The CFs’ spatial variability ranged over 5, 6 and 8 orders of magnitude for NO_x, SO₂ and NH₃ emissions, respectively. We found that the aquatic receiving environment fate factor is the dominant contributor to the overall spatial variability of the CFs, while the effect factors contributed to 98 % of the total parameter uncertainty.

Conclusions

The resulting characterization model and factors enable a consistent evaluation of spatially explicit acidifying emissions impacts at the global scale.     

Impact of nitrogen and climate change interactions on ambient air pollution and human health

Nitrogen oxides (NO_x) are important components of ambient and indoor air pollution and are emitted from a range of combustion sources, including on-road mobile sources, electric power generators, and non-road mobile sources. While anthropogenic sources dominate, NO_x is also formed by lightning strikes and wildland fires and is also emitted by soil. Reduced nitrogen (e.g., ammonia, NH₃) is also emitted by various sources, including fertilizer application and animal waste decomposition. Nitrogen oxides, ozone (O₃) and fine particulate matter (PM_2.5) pollution related to atmospheric emissions of nitrogen (N) and other pollutants can cause premature death and a variety of serious health effects. Climate change is expected to impact how N-related pollutants affect human health. For example, changes in temperature and precipitation patterns are projected to both lengthen the O₃ season and intensify high O₃ episodes in some areas. Other climate-related changes may increase the atmospheric release of N compounds through impacts on wildfire regimes, soil emissions, and biogenic emissions from terrestrial ecosystems. This paper examines the potential human health implications of climate change and N cycle interactions related to ambient air pollution.     

The role of the atmosphere in nitrogen cycling

In this work an analysis of the sources, atmospheric concentration, chemical reactions and sinks of the principal atmospheric nitrogen compounds is made. Atmospheric emissions of N₂O and NH₃ are almost entirely due to biological activity on the continents and in the oceans. The combustion of fossil fuels and biomass is the principal source of NO_x. The only relevant chemical transformations in the troposphere are the oxidation of NO_x to NO₃ ^? and the formation of ammonium salts. Only 10% of the NH₃ emitted is oxidized. Washout of NH₄ ⁺ and NO₃ ^? by rainfall is the principal mechanism for removing nitrogen compounds from the atmosphere. Part of the N₂O enters the stratosphere and part must be removed in the biosphere by processes not yet established. NO_x produced in the atmosphere by the burning of fossil fuels and biomass and by lightning represents between 30 and 40% of the total nitrogen fixed. A complete nitrogen balance for the troposphere is presented. Since the photochemical oxidation of NO_x is rapid and atmospheric transport is relatively slow with respect to the cycling of water in the troposphere, nitrogen compounds return to the earth's surface close to where they were emitted. Fixed-nitrogen inputs to the continents and oceans due to biological and industrial fixation are slightly greater than those due to rain water. However, since rain falls everywhere, input from this source is only important on soils not subject to intensive agriculture.     

Photochemical ozone creation potentials

Goal, Scope and Background

Photochemical ozone creation potentials (POCPs) typically used in life cycle impact assessment (LCIA) to address the impact category ‘photo-oxidant formation’ only provide factors for particular volatile organic compounds and do not take into account background concentrations and meteorological conditions. However, the formation of ozone from volatile organic compounds (VOCs), carbon monoxide (CO) and nitrogen oxides (NOx) is highly dependent on the background pollutant concentrations and meteorological conditions. Some LCIA manuals therefore recommend working with potentials for high background concentrations of NOx (Derwent 1998), and potentials for low background concentrations of NOx (Andersson-Sköld 1992).

Objectives

This study has introduced an improved set of POCPs independently of meteorological and emission conditions specific to a given period or location. Whereas current POCP values may be relevant to estimate the photo-oxidant formation over a certain (temporally and spatially well-defined) domain, this study has further introduced more relevant values with respect to potential impacts of ozone on human health and environment.

Methods

For the computation of POCP values on the scale of Western Europe, independently of meteorological and emission conditions specific to a given period or location, a Eulerian chemistry-transport numerical model (CHIMERE-continental) has been implemented over three summer seasons. POCPs have been evaluated for ten VOC species (including the whole VOC group), CO and NOx. The coherence of this new set of POCP values with previous studies has been checked. The spatial representa-tivity of POCP values over the simulation domain in Europe has also been addressed. The robustness of these POCP values to changes in the implemented chemical mechanism used in our model has been checked.

Results and Discussion

The POCPs computed in this study were generally lower than the POCPs calculated in previous studies. In the previous studies, but not here, the POCPs have been calculated with particular meteorological conditions (during anti-cyclonic, fair weather conditions) or emission levels (high polluted backgrounds) known to be optimal with respect to ozone formation. Despite the quantitative variations in the POCP values, we have found a good agreement in the relative ranking of the pollutant species between this study and previous studies. It was also shown that POCP values display significant spatial variability over Western Europe (the largest spatial differences were obtained for NO_x where the sign of the POCP value even changes from region to region).

Conclusions

Finally, the temporally and spatially averaged values obtained here for the POCP index update previous values and represent an attempt to generate the most appropriate and accurate scale for European conditions independently of meteorological and emission conditions specific to a given period or location.

Recommendations and Outlook

These new PCOPs should be useful to LCIA-practitioners in further life cycle impact assessment. However, for the NO_x species, we do not recommend the use of the POCP value for LCIA.

     

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.     

Seasonal Photochemical Transformations of Nitrogen Species in a Forest Stream and Lake

The photochemical release of inorganic nitrogen from dissolved organic matter is an important source of bio-available nitrogen (N) in N-limited aquatic ecosystems. We conducted photochemical experiments and used mathematical models based on pseudo-first-order reaction kinetics to quantify the photochemical transformations of individual N species and their seasonal effects on N cycling in a mountain forest stream and lake (Plešné Lake, Czech Republic). Results from laboratory experiments on photochemical changes in N speciation were compared to measured lake N budgets. Concentrations of organic nitrogen (N_org; 40–58 µmol L⁻¹) decreased from 3 to 26% during 48-hour laboratory irradiation (an equivalent of 4–5 days of natural solar insolation) due to photochemical mineralization to ammonium (NH₄ ⁺) and other N forms (N_x; possibly N oxides and N₂). In addition to N_org mineralization, N_x also originated from photochemical nitrate (NO₃ ⁻) reduction. Laboratory exposure of a first-order forest stream water samples showed a high amount of seasonality, with the maximum rates of N_org mineralization and NH₄ ⁺ production in winter and spring, and the maximum NO₃ ⁻ reduction occurring in summer. These photochemical changes could have an ecologically significant effect on NH₄ ⁺ concentrations in streams (doubling their terrestrial fluxes from soils) and on concentrations of dissolved N_org in the lake. In contrast, photochemical reactions reduced NO₃ ⁻ fluxes by a negligible (<1%) amount and had a negligible effect on the aquatic cycle of this N form.     

Interactive Effects of Vegetation Type and Topographic Position on Nitrogen Availability and Loss in a Temperate Montane Ecosystem

Determining the fate of deposited nitrogen (N) in natural ecosystems remains a challenge. Heterogeneity of vegetation types and resulting plant–soil feedbacks interact with topo-hydrologic gradients to mediate spatial patterns of N availability and loss, yet net effects of variation in these two factors together across complex terrain remain unclear. Here we measured a suite of N-cycle pools and fluxes in sites that differed factorially in vegetation type (mixed forest vs. herbaceous) and topographic position (upslope vs. downslope) in a protected montane watershed near Salt Lake City, UT. Vegetation type was associated with large variation in N availability—herbaceous sites had larger NO₃ ^? pools, higher NO₃ ^?:NH₄ ⁺ ratios, higher nitrification potentials, lower soil C:N values, enriched δ¹⁵N values, and lower microbial biomass compared to forests, especially those upslope. Downslope sites tended to exhibit higher N availability and indicators of N-cycle openness, but patterns were moderated by vegetation type. In downslope forest, soil NO₃ ^? depth profiles and higher foliar N content suggested trees were accessing deep soil N and transferring it to the surface via litterfall, while more deep soil NO₃ ^? but no change in surface or foliar N suggested herbaceous cover was not N limited or deeper N pools were not accessible. Soil NO₃ ^? leaching from below the rooting zone closely tracked N availability, revealing a link between N status and hydrologic loss as well as an important role for roots in N retention. NO₃ ^? isotopes did not reveal a similar link for gaseous losses (that is, denitrification), instead reflecting nitrification and/or transport dynamics. Together, these results suggest a coupled ecological, topo-hydrologic perspective can help assess the fate of N in complex landscapes.     

Eutrophication of aquatic ecosystems a new method for calculating the potential contributions of nitrogen and phosphorus

Aim, Scope and Background  

Aquatic eutrophication is a widespread problem in inland and coastal waters around the world and it should therefore be one of the impact categories to be considered in LCA studies of products and services. In LCAs there are several impact assessment methods to determine characterisation factors for eutrophying nutrients, but few methods have been developed to model fate and spatial aspects. One such method was developed as part of an LCA application of the Finnish forest industry. The aim of this study was to present this characterisation method in which the potential contributions of nitrogen and phosphorus to eutrophication of aquatic ecosystems are calculated. The use of the method was demonstrated by producing site/sector-specific characterisation factors and by constructing a reference value of aquatic eutrophication for Finland. A discussion of sensitivity and uncertainty aspects related to input data is also presented.     

Country-specific damage factors for air pollutants

An integrated impact assessment model is used to calculate the impact per tonne of SO₂, NO_x, fine particles, and NMVOC emitted from different source countries on human health, acidification, eutrophication, and the man-made environment (crop yield and building materials). Indicators on the endpoint level are used to measure the effects resulting from a marginal change in emission levels. While the assessment of impacts on ecosystems and the man-made environment is limited to Europe, damage factors for health effects are also derived for Asia and South America. For Europe, emission scenarios for the years 1990 and 2010 are considered to analyse the influence of changing background conditions on the resulting impacts. Results show that there is a significant variation in the damage resulting from a unit emission for some of the impact categories, both between countries and between base years. Depending on the scope of the study and the information available from the life cycle inventory, results from the paper can be used to consider site dependent conditions in life cycle impact assessment as a complement to the current site-independent (or global) approach.     

DETECTION OF LIMITING OR SURPLUS NITROGEN IN ALGAE AND AQUATIC WEEDS1

The rate of NH₄+-N absorption by algae and aquatic weeds in the dark has been shown to be 4-5 times greater for plants which are N-limited as compared to plants with sufficient available N. Eight species of green algae, 2 blue-green algae, 2 diatoms, and 3 aquatic weeds were used to demonstrate the usefulness of the test in determining if available N was in surplus or limited supply in a particular environment. The test was shown not to differentiate between blue-green algae capable of fixing N (4 species) from media with NO₃-N or without combined nitrogen. The factors influencing the results of NH4⁺-N absorption tests have been investigated. In order to differentiate between plants with sufficient available N and those which are N limited, the rate of NH₄⁺-N absorption (0.1 mg N) over 1-hr incubation in the dark by 10-20 mg of algae or aquatic weed tissues is measured. The relatively simple analysis for NH₄⁺-N in the samples makes it very easy to follow the changing N nutrition of plants in cultures with a limited N supply or in the presence of possible N sources.     

The kinetics of ammonium and nitrate uptake by young rice plants

Summary An important process which affects the fate of fertilizer nitrogen (N) applied to a rice crop is crop N uptake. This uptake rate is controlled by many factors including the N-ion species and its concentration. In this study the relation between N concentration at the root surface and N uptake was characterized using Michaelis-Menten kinetics. The equation considers two parameters, Vmax and Km, which are measures of the maximum rate of uptake and the affinity of the uptake sites for the nutrient, respectively. Uptake rates of intact rice plants growing in a continuously flowing nutrient solution system were fitted to the Michaelis-Menten model using a weighted regression analysis. For NH₄−N the Km values for 4- and 9-week-old rice plants indicated a high affinity for the ammonium ions relative to concentrations reported for rice soils after fertilization. The Vmax values expressed on a unit-root-mass basis decreased with plant age, indicating a reduction in the average density of uptake sites on the root surface. The kinetics of NO₃−N uptake was similar to that of NH₄−N when NO₃−N was the only N source. However, if NH₄−N and NO₃−N were present simultaneously in the solution the Vmax for the uptake of NO₃−N was severely reduced, while the Km was affected very little. This inhibition appears to be noncompetitive. Fertilization of young rice plants leading to concentration of N at the root surface above approximately 900 μM will not increase crop uptake and may contribute to inefficient N recovery by the crop. The existence of NH₄−N and NO₃−N simultaneously at the root surface may also lead to inefficient N recovery because of reduced uptake of NO₃−N.     

A global budget for atmospheric NH3

We provide an assessment of the global sources of NH₃ in the atmosphere, which indicates an annual flux of about 75 Tg of N as NH₃. The emissions from land are dominated by the release of NH₃ during the hydrolysis of urea from the urine of domestic animals (32 TgN/yr) and by emanations from soils in unmanaged ecosystems (10 TgN/yr) and from fertilized agricultural soils (9 TgN/yr). Emissions from the sea surface may approach 13 TgN/yr. The total annual source of NH₃ is in reasonable agreement with estimates of global NH ₄ ⁺ deposition from the atmosphere, the major fate of atmospheric NH₃. As an alkaline atmospheric species, NH₃ emitted to the atmosphere each year can neutralize only about 32% of the annual production of H⁺ in the atmosphere from natural and anthropogenic sources.     

Nitrogen Transport and Retention in an Arid Land Watershed: Influence of Storm Characteristics on Terrestrial–aquatic Linkages

Arid ecosystems experience prolonged dry periods, as well as storms that vary in size, intensity and frequency. As a result, nitrogen (N) retention and export patterns may be a function of individual storm characteristics. Our objective was to determine how seasonal patterns in rainfall as well as individual storm characteristics influence N transport and retention on terrestrial hill slopes in a Sonoran Desert watershed. Regression models indicated that variation in runoff ammonium (NH₄⁺) was best explained by antecedent conditions (cumulative seasonal rainfall, days since last storm) while variation in runoff nitrate (NO₃⁻) was best explained by single storm characteristics, primarily rain NO₃⁻. Increases in runoff NO₃⁻ along overland surface flowpaths were balanced by decreases in NH₄⁺ during summer, with no change in dissolved inorganic nitrogen (DIN) concentration; a pattern consistent with nitrification. Nitrate increases along flowpaths were not as strong during winter storms. Results indicate that NH₄⁺ is transported from hillslopes to other parts of the catchment, including streams, and that nitrification occurs along surface flowpaths, particularly during summer storms. These findings suggest that the extent to which a receiving patch is supplied with NH₄⁺ or NO₃⁻ depends on the distance runoff has traveled (flowpath length) and the length of the antecedent dry period. The extent and configuration of fluvial reconnection amongst patches in the landscape following long drought periods likely determines the fate of available N, whether N is processed and retained in the terrestrial or in the aquatic component of the watershed, and the mechanisms involved. The nature of this fluvial reconnection is driven by the size, intensity and sequence of storms in space and time.     

东北有机及常规大豆对环境影响的生命周期评价

选择我国主要有机出口农产品之一——大豆作为研究对象,采用生命周期评价、DNDC模型、实地调研等方法建立大豆生命周期资源消耗和环境排放清单,分析比较了出口型有机大豆、国内消费型有机大豆以及国内消费型常规大豆的生命周期环境影响.结果表明:3种不同生产消费型大豆生命周期中资源消耗、酸化以及全球变暖对综合环境影响贡献最明显,基本上占到综合环境影响评价的30％左右,而富营养化和生态毒性的贡献率较低,小于10％.从生命周期的不同阶段分析,3种消费模式的大豆其运输阶段对于各分类环境影响的贡献率最大,都在50％以上,对资源消耗的贡献率更是在80％以上.从2种不同的生产模式看无论是全球变暖、酸化、资源消耗还是生态毒性都是有机大豆的环境影响综合指数小于常规大豆,对环境产生的负面影响较小.综合比较3种不同生产消费型大豆,国内消费的有机大豆生命周期综合环境影响最小,其环境影响综合指数比常规大豆的减少31％.但是出口有机大豆由于出口使运输距离延长,其生命周期综合环境影响最大.因此,环境管理关键是提倡有机产品本地消费以缩短运输距离,或者采用环保型能源以减少环境排放.