Next Article in Journal
Can ICZM Contribute to the Mitigation of Erosion and of Human Activities Threatening the Natural and Cultural Heritage of the Coastal Landscape of Calabria?
Next Article in Special Issue
Contrasting Considerations among Agricultural Stakeholders in Japan on Sustainable Nitrogen Management
Previous Article in Journal
Research on the Vehicle Emission Characteristics and Its Prevention and Control Strategy in the Central Plains Urban Agglomeration, China
Previous Article in Special Issue
Understanding N2O Emissions in African Ecosystems: Assessments from a Semi-Arid Savanna Grassland in Senegal and Sub-Tropical Agricultural Fields in Kenya
 
 
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

A National Nitrogen Target for Germany

1
German Environment Agency, Section II 4.3, Postfach 14 06, 06813 Dessau-Rosslau, Germany
2
INFRAS, Binzstr. 23, 8045 Zurich, Switzerland
3
Institute of Landscape Ecology and Resource Management (ILR), Research Centre for BioSystems, Land Use and Nutrition (iFZ), Justus Liebig University Giessen, Heinrich-Buff-Ring 26, 35392 Giessen, Germany
4
Centre for International Development and Environmental Research (ZEU), Justus Liebig University Giessen, Senckenbergstrasse 3, 35390 Giessen, Germany
*
Author to whom correspondence should be addressed.
Sustainability 2021, 13(3), 1121; https://doi.org/10.3390/su13031121
Received: 30 November 2020 / Revised: 15 January 2021 / Accepted: 18 January 2021 / Published: 21 January 2021
(This article belongs to the Special Issue Nitrogen: Too Much of a Vital Resource)

Abstract

:
The anthropogenic nitrogen cycle is characterized by a high complexity. Different reactive nitrogen species (NH3, NH4+, NO, NO2, NO3, and N2O) are set free by a large variety of anthropogenic activities and cause numerous negative impacts on the environment. The complex nature of the nitrogen cycle hampers public awareness of the nitrogen problem. To overcome this issue and to enhance the sensitivity for policy action, we developed a new, impact-based integrated national target for nitrogen (INTN) for Germany. It is based on six impact indicators, for which we derived the maximum amount of nitrogen losses allowed in each environmental sector to reach related state indicators on a spatial average for Germany. The resulting target sets a limit of nitrogen emissions in Germany of 1053 Gg N yr−1. It could serve as a similar means on the national level as the planetary boundary for reactive nitrogen or the 1.5 °C target of the climate community on the global level. Taking related uncertainties into account, the resulting integrated nitrogen target of 1053 Gg N yr−1 suggests a comprehensible INTN of 1000 Gg N yr−1 for Germany. Compared to the current situation, the overall annual loss of reactive nitrogen in Germany would have to be reduced by approximately one-third.

1. Introduction

Reactive nitrogen (Nr) is essential and beneficial for plant production. Our understanding of Nr includes and focuses on total nitrogen (N), ammonia (NH3), ammonium (NH4+), nitrogen monoxide (NO), nitrogen dioxide (NO2), nitrogen oxide (NOx), nitrate (NO3), and nitrous oxide (N2O) [1]. At present, the anthropogenic production of mineral fertilizer through industrial ammonia fixation ensures the feeding of about 50% of the global population [2]. However, through agricultural production and also through combustion processes, anthropogenic reactive nitrogen unintentionally also enters the environment, resulting in several severe environmental impacts [3]. Currently, about half of the year-to-year globally fixed nitrogen is resulting from anthropogenic sources [1]. The consequences of an increased availability of reactive nitrogen include biodiversity loss, health impacts, reduced air and water quality, and impacts on the climate [4]. Therefore, the urgent need for a sustainable nitrogen management has recently been identified by several institutions at the global level [5,6,7]. Rockström et al. [8] and Steffen et al. [9] included a planetary boundary for anthropogenic nitrogen fixation into their concept of keeping the earth system in a safe operating space and identified the alteration of the nitrogen cycle as one of the three most urgent fields of action. The current boundary for nitrogen, based on an original work by de Vries et al. [10], is currently clearly transgressed.
In contrast to the climate issue, nitrogen not only affects global biogeochemical pathways but also take effects on smaller scales nearby its source. Regional and local problems also suggest the search for solutions at smaller scales. That is why numerous assessments of the nitrogen cycle at the regional and national level, for example, in Europe, India, or California, have been published recently that included recommendations for better nitrogen management [11,12,13].
In Germany too, the release of reactive nitrogen to the environment poses different environmental threats. A quantification of the German nitrogen cycle with a description of the most urgent problems has been published by the German Environment Agency [14]. The agricultural sector is the major sector responsible for reactive nitrogen losses (67%), followed by industry and energy (16%), transports (11%), and urban runoff and wastewater disposal (6%) [15]. Among others, the loss of biodiversity through reduced and oxidized nitrogen species deposition, the pollution of groundwater and coastal ecosystems by nitrate, and the ongoing exceedances of health-oriented concentration limits for nitrogen dioxide at traffic-related monitoring sites result from these losses. This is reflected in recent infringement decisions against Germany’s insufficient implementation of the European Union’s Nitrate and Air Quality Directive [16,17]. To overcome the problems, the Federal Government launched the development of a national nitrogen strategy [18], which endorses the need for an integrated nitrogen action program.
However, the acknowledgement of a certain risk for humans and the environment and the acceptance of political measures and strategies by the general public and relevant stakeholders depend greatly on the tangibility of the problem to be solved. On the global level, the Planetary Boundary Concept [8] or the 1.5 °C target of the climate community [19] are examples that successfully illustrate complex problems in an easily understandable way.
For reactive nitrogen, such a comprehensive concept is missing so far on the national level [20], and the German Advisory Council on the Environment suggests the development of an integrated nitrogen strategy for Germany through the Federal Government [21]. These suggestions comprise the development of an integrated nitrogen target for Germany.
With this study, we present an attempt to develop such an integrated national target for nitrogen (INTN) for Germany. In line with the suggestions from Salomon et al. [20], we expect such a target to facilitate communications with the general public and policymakers and to be a core indicator for the success of political measures. Our objective is to develop a national complement to the nitrogen planetary boundary on the global level. To create confidence in such a value and to implement it most effectively in environmental policies, we are confident that relating a national nitrogen limit to existing environmental critical target values, such as concentration limits or deposition loads, for example, is a promising procedure.

2. Materials and Methods

To calculate the INTN, the six most relevant impact indicators affected by excessive amounts of reactive nitrogen were chosen: (1) vegetation affected by NH3- concentration, (2) terrestrial ecosystems affected by eutrophication, (3) surface water quality and (4) groundwater quality affected by nitrate, (5) nitrous oxide emissions affecting climate change, and (6) human health affected by NO2 concentration. For each of these impact indicators, critical target values exist for Germany. In most of the cases, these are concentration limits to protect air, water, and living beings from excessive nitrogen pollution. We selected those target values reflecting the current legislative situation in Germany or, where no legal value was available, those reflecting the latest scientific knowledge. Sectors and targets are shown in Table 1. Our basic approach was to calculate a maximum permitted nitrogen loss per year on the national level for each impact indicator, such that related quality targets, herein referred as state indicators, are met in Germany at the spatial average. Where such values for maximum loss rates were available from current legislation, we adopted those directly as target values. By the coverage of the six impact indicators, we obtained maximum loss rates for reactive nitrogen species, such as nitrate (NO3), nitrous oxide (N2O), nitrogen oxide (NOx), ammonia (NH3), and total nitrogen (Ntotal). Those rates were given uniformly in gigagram nitrogen per year (Gg N yr−1), converting species-related values into normalized nitrogen values by applying conversion factors related to the molecular weight per species.
To derive INTN, we calculated the sum of the lowest maximum allowable nitrogen loss rates per nitrogen species.

2.1. Vegetation Affected by NH3-Concentration

We calculated the maximum annual emission rate of NH3 to protect vegetation against a critical concentration of 3 µg m−3 (critical level, short CLev, recommended by the Geneva Convention on long-range transboundary air pollution [22]) from modelled NH3 emission and concentration data at a spatial resolution of 0.03125° longitude and 0.015625° latitude. Due to the high deposition velocity of NH3 [29], we assumed that the concentration in a grid cell is influenced primarily by the emission in the same grid cell. The emission data is based on the reported national submission of NH3 emissions to the European Environment Agency (EEA) in the year 2015 [30]. As the spatially resolved ambient concentrations and emissions are strongly correlated, the maximum allowable NH3 emission per grid cell (EmNH3max) can therefore be derived from a linear regression of the spatially resolved data (Equation (1))
Em NH 3 max = ( CLev b ) / a   [ Gg   yr 1 ]
with CLev = 3 µg m−3 NH3 and a, b regression parameters. The sum of the positive differences between the modelled emission (EmNH3,i) and the resulting maximum allowable emission (EmNH3max,i) per grid cell (N = number of grid cells = 6314) corresponds to the reduction of the related total NH3 emissions (RNH3) that is required to remain below the critical concentration in each grid cell (eq 2). To obtain a value for NH3–N, the CLev of 3 µg m−3 NH3 for vascular plants and the underlying concentration and emission data were converted to the fraction of nitrogen in the ammonia molecule with a factor of 14/17.
R N H 3 =   i = 1 N ( E m N H 3 ,   i   E m N H 3 m a x , i )   [ G g   y r 1 ]

2.2. Terrestrial Ecosystems Affected by Eutrophication

To protect terrestrial ecosystems from eutrophication and resulting loss of biodiversity, the deposition of reactive nitrogen from atmosphere into ecosystems needs to be reduced. Emission reduction requirements for NH3 and NOx for Germany are defined within the framework of the European Union’s directive on the reduction of national emissions of certain atmospheric pollutants, the so-called NEC Directive [24]. Assuming a successful implementation and compliance with the directive’s requirements until 2030, the area where critical loads for sensitive ecosystems are exceeded will decline by about 35% compared to the area in 2005 [23]. For the purpose of deriving a national nitrogen target, we adopted the current reduction requirements for Germany for NH3 (29%) and NOx (65%) between 2005 and 2030, and calculated maximum allowable NH3 and NOx emissions in 2030 based on the emission reporting submitted in 2017 [30].

2.3. Surface Water Quality

Increased inputs of reactive nitrogen put surface waters under severe pressure by unbalancing the ecosystem. The result is eutrophication, which can lead to hypoxia of surface waters and cause further release of toxic compounds [31]. However, primary production of fresh water ecosystems in Germany is predominantly controlled by phosphorous and only to a lesser extent by nitrogen [32]. In contrast, productivity of coastal and marine ecosystems is limited by nitrogen, which puts them at high risk for eutrophication by total nitrogen loads from rivers (Ntotal, mainly as nitrate). To reduce nitrogen inflow with rivers into coastal ecosystems, maximum allowable concentration levels to protect North Sea (2.8 mg N l−1) and Baltic Sea (2.6 mg N l−1) coastal ecosystems are defined for estuary areas in the German clean water legislation [25]. The German Federal States are the authorities responsible for reducing nitrogen inputs into rivers, such that the concentration limits mentioned above can be met. The river basin associations of the Federal State authorities calculated maximum allowable total nitrogen loads (Ntotal) for the river basins Rhine, Elbe, Ems, Weser, Eider, Schlei-Trave, and Warnow-Peene to meet these concentration limits for North Sea and Baltic Sea [33]. The given river basins cover most of the area, except south-eastern Germany, which is covered by the Donau-basin. The calculations were based on long-term measurement data of concentration and loads in the given river basins under the basic assumption that the annual mean of the total N concentration is proportional to the total annual N load in these surface waters. We added these river-related computed loads up and transferred the sum directly into our database for the purpose of deriving a national nitrogen target.

2.4. Groundwater Quality Affected by Nitrate Concentration

The Nitrate Directive of the European Union aims to protect groundwater from nitrate pollution from agricultural sources and defines a quality threshold of 50 mg NO3 l−1. Nitrogen budget surpluses from agricultural activities need to be reduced to diminish nitrate leaching with seepage water. To calculate the maximum permissible loss of nitrogen from agricultural land use through leaching to the groundwater, the Federal State data of nitrate monitoring in groundwater was evaluated in combination with regionalized modelled nitrogen soil surface budget surpluses. In a first step, a high-resolution Germany-wide map of nitrate concentrations in groundwater (1 × 1 km) was produced based on measured nitrate concentrations from some 5414 groundwater Federal State groundwater-monitoring stations, regionalized using the “Random Forest” modelling method based on spatial data (maps) for hydrogeology, land use, and further parameters [34]. As a simplification, we neglected the denitrification and retention potential and assumed that the nitrate concentration in groundwater equals nitrate concentration in seepage water and is predominantly due to inputs of nitrate through leachate from agricultural areas. The rationale behind this assumption is based on the precautionary principle. For each grid cell j with nitrate concentration cj > 50 mg NO3 l−1, the relative reduction of the NO3 concentration, ∆cj (%), necessary to comply with the quality standard of 50 mg NO3 l−1 was calculated. In a second step, these grid-specific relative reduction values were transferred to the gridded dataset of nitrogen budget surpluses [35], and we assumed that the necessary reduction in the nitrate concentration in seepage water and groundwater was proportional to the necessary relative reduction in the nitrogen surplus (ns) of the respective agricultural area (Equation (3)).
Δ ( n s ) j [ % ] =   Δ c j [ % ]
The reduction in the absolute nitrogen surplus per grid cell ∆(NS)j in kilogram nitrogen per year (kg N yr−1) for each grid cell can then be calculated from the absolute nitrogen surplus data, the necessary relative reduction and the used agricultural area per grid cell: the sum of the absolute necessary reductions per grid cell (N = number of grid cells = 357,582) corresponds to the required overall reduction of the nitrogen surpluses (RNS) to remain below the critical nitrate concentration in each grid cell (Equation (4)).
R N S =   j = 1 N N S j   [ G g   y r 1 ]

2.5. Nitrous Oxide Emissions Affecting Climate Change

We calculated maximum permissible N2O emissions based on targets defined in the national Climate Action Plan 2050 of the German Federal Environment Ministry [27]. All calculations were based on the reported greenhouse gas emission 2017 [36]. As a long-term objective for 2050, the Action Plan defines a reduction of total greenhouse gas emissions in Germany (in CO2 equivalents) by 80–95% as compared to 1990 and a corresponding interim reduction target for 2030 of 55%, which is also defined in terms of sectoral reduction targets. The action plan does, however, not define a specific target for nitrous oxide emissions. Therefore, we used the existing sectoral targets for 2030 to derive a target for nitrous oxide emissions in 2050. For N2O emissions from the energy sector, an average reduction in line with the long-term target for total greenhouse gas emissions is assumed (–87%, as compared to 1990). For N2O emissions from the waste sector, we assumed that the interim target corresponds to the long-term target (–87% as compared to 1990). For N2O emissions from agriculture, the interim target for 2030 (32.5%) was extrapolated linearly to 2050, resulting in a necessary reduction of 40% compared to 1990. Comparing these three sectoral reduction targets to the N2O emission situation in 2015 [36] provides a target for maximum allowable N2O emissions, which we included in the national nitrogen target. Since in the industrial sector nitrous oxide emissions were already reduced by 95% between 1990 and 2015, we assumed that the emissions remain at the level of 2015 in this sector.

2.6. Human Health Affected by NO2 Concentration

To protect human health from pollution by nitrogen dioxide, a concentration limit of 40 µg m−3 as an annual mean is defined in the European Air Quality directive [37]. However, this limit mainly addresses hotspots with heavy traffic. Background concentrations are well below this concentration limit. Deriving a maximum allowable NOx emission at the national scale from concentration measurements at hotspots that are strongly affected by local sources (i.e., traffic or industry) is therefore not adequate. At a measurement site exposed to heavy traffic, cutting local emission from traffic will likely lead to compliance with the concentration limit. Therefore, our approach for deriving a national emission target focusses on a limit value of 20 µg m−3 at background stations, proposed by the World Health Organization [28]. Measurements at background sites are influenced by emission sources at a wider range and are not exposed to specific local sources [38,39]. We therefore assume that they are representative of the emissions at the national scale and can therefore be used to derive a national target. We evaluated measurement data available for 179 background stations in Germany for the years 2002–2015. We assumed that the 98th percentile value of NO2 measurements from all background stations is approximately proportional to the national NOx emissions. The 98th percentile value was chosen, because the set of evaluated background stations should fulfil the requirement as far as possible to be unaffected by local emission sources. However, this requirement cannot be guaranteed for all background measurement sites over the entire time period considered, for which reason the choice of the 98th percentile acknowledges that some of the background measuring stations could also be affected by local emission sources. With A(t) being the 98th percentile of background concentrations measurements in the year t and E(t) as Germany’s national NOx emissions for the year t, the target emission Emax is calculated as follows:
E m a x =   A m a x   ( E ( t ) / A ( t ) ) [ G g   y r 1 ]
where Amax = 20 µg m−3 and (E(t))/A(t)) denotes the average proportion between NOx emissions and 98th percentile of NO2 concentration measurements over the time period 2002–2015.

3. Results

3.1. Vegetation Affected by NH3 Concentration

The maximum permissible NH3 emissions per grid cell for compliance with the critical level can be derived from a linear regression between ambient ammonia concentrations and ammonia emissions per grid cell. NH3 emission and NH3 concentration maps are shown in Figure 1. The linear regression between emission and concentration data is shown in Figure 2.
Figure 2 shows that to meet the critical level of 3 µg NH3 m−3 (2.47 µg NH3 m−3), the annual NH3 emissions per grid cell must not exceed a maximum of 0.12 Gg NH3–N yr−1. The sum and therefore the national total of the resulting maximum allowable emissions per grid cell therefore is 441 Gg NH3–N yr−1.

3.2. Terrestrial Ecosystems Affected by Eutrophication

The absolute target values for NH3 and NOx for the year 2030 are based on the reduction requirements for Germany under the NEC Directive between 2005 and 2030. The underlying emission data is based on the German emission report 2017. The report shows 558 Gg NH3–N yr−1 and 479 Gg NOx–N yr−1 for the year 2005 [30]. The reduction requirement for Germany of 29% NH3 between 2005 and 2030 [24] results in an absolute target value of 396 Gg N yr−1. The reduction requirement for Germany of 65% NOx [24] results in an absolute target value of 168 Gg N yr−1.

3.3. Surface Water Quality

Table 2 shows a total annual N load of 356.2 Gg N yr−1 from the inflows from Germany into the North Sea and Baltic Sea and the outflow of the Rhine into the Netherlands. Note the different reference periods for the individual river basins. To comply with the target values at the limnic/marine transition points and at the Bimmen/Lobith border point to the Netherlands, the associations of the river basins reported an overall necessary reduction by 42.2 Gg N yr−1.

3.4. Groundwater Quality Affected by Nitrate Concentration

The frequency distribution of the grid map of nitrate concentration in groundwater in Germany (Figure 3) shows that 8.8% of the area (grid cells) has a concentration above 50 mg NO3 l−1 (Figure 4). The mean NO3 concentration in grid cells that exceed the threshold is 59.4 mg NO3 l−1. Following that, for these cells, the mean necessary reduction of the N surplus is 15.8% or 9.1 kg N ha−1 yr−1. The sum for all these grid cells gives a necessary reduction of the N surplus in Germany of 21 Gg N yr−1. In comparison to the total soil surface balance N surplus (annual mean 2011–2014) of 148 Gg N yr−1, this leads to an overall reduction target of 127 Gg N yr−1.

3.5. Nitrous Oxide Emissions Affecting Climate Change

The assumptions made in chapter 2.5 lead to the fact that in 2050, compared with 1990 levels, nitrous oxide emissions have to be reduced by 66%. Relative to the nitrous oxide emissions in 2015, which is the basis for our calculation of our maximum permitted nitrogen loss rates, this corresponds to a reduction of 43%. In 2015, nitrous oxide emissions amounted to 83.4 Gg N2O–N yr−1. The resulting maximum annual nitrogen loss therefore is 48 Gg N2O–N yr−1.

3.6. Human Health Affected by NO2 Concentration

In Figure 5 the 179 background NO2 monitoring stations with complete data from 2002 to 2015 are shown. Of these, 78 stations are in urban areas, 47 in sub-urban areas, 23 in rural areas, 11 stations are rural/peri-urban, 14 stations are rural/regional, and 6 stations are remote rural. Figure 6 shows that the NO2 ambient concentrations show widespread compliance with the annual limit value (40 µg m−3), except at exposed locations, where values are still too high. The resulting mean target emission of NOx of 236 Gg NOx–N shown in Table 3 is based on equation 5, which gives the relation between yearly values of reported NOx–N emissions and the 98 percentile value of NO2 measurements from all background stations.

3.7. Summary of the Results

The maximum permissible nitrogen loss calculated for the six impact indicators is summarized in Table 4. The most sensitive (lowest) loss rates per nitrogen species were selected to derive the national nitrogen target by adding them up. Directly included indicators are “terrestrial ecosystems affected by eutrophication”, “surface water quality”, “groundwater quality”, and “nitrous oxide emissions affecting climate change”. The maximum loss rates for the impact indicators “vegetation affected by NH3 concentration” and “human health affected by NO2 concentration” based on quality targets set by the World Health Organisation (WHO) and the Convention on Long-Range Transboundary Air Pollution (CLRTAP) are only indirectly part of the national target, since the NOx and NH3 reduction rates required to meet the regional limit values for “terrestrial ecosystems affected by eutrophication” are more ambitious. The resulting integrated national target for nitrogen (INTN) amounts to 1053 Gg N yr−1 or 12.7 kg per capita and year accounting for 83 Million inhabitants in Germany.

4. Discussion

In Section 2 and Section 3, we showed an approach to calculate a national nitrogen target from pressure indicators, for which maximum permissible values are deduced from quality target values.
Our selection of indicators and our simplified methods used to calculate maximum permissible nitrogen loss are characterized by heterogeneity. Calculated nitrous oxide emissions are based on percental greenhouse gas emission reduction requirements. For NOx and NH3, proportionality between an approximation of quality targets and a related maximum emission was assumed. For eutrophication effects in terrestrial ecosystems, we relate our emission reduction requirements to results of the GAINS model [43], and the calculated N load into surface water is based on long-term correlation of concentration and N loads in rivers. We did not consider acidification of terrestrial ecosystems as a threat, because nitrogen-deposition-induced acidification is a minor threat in comparison with eutrophication [44], hence its consideration would lead to a minor reduction target in comparison with the “eutrophication target”.
The correlation between NH3 concentration and NH3 emission data was assumed on a spatial resolution of 0.03125° * 0.015625°, which is acceptable due to the high deposition velocity of NH3 [29]. However, the selection of the underlying emission data and of the critical level substantially influence the resulting maximum NH3–N loss rate. For example, picking the critical level of 1 µg m−3 (to protect most sensitive elements of the vegetation such as lichens and other cryptogams) instead the one of 3 µg m−3 for higher plants would lead to a much lower maximum NH3–N loss rate of 96 Gg N yr−1 instead of 441 Gg N yr−1.
Additionally, the resulting maximum NOx emission to protect human health from NO2 is influenced by our own assumptions: Picking, for example, a percentile value of 90 instead of 98 would lead to higher maximum NOx emissions. In contrast, calculating the maximum NOx emissions from a linear regression of the 98th percentile of the annual concentration measurement data at background stations and the annual NOx emission data, which show a high correlation, would lead to lower maximum NOx emissions.
Acknowledging the differences of the selected six different approaches, we are confident that integrating their results to our INTN is an acceptable simplification, comparable to the planetary boundary for N fixation by de Vries et al. [10]. We acknowledge that we face difficulties to prove our suggested value, but we are confident that the result is sufficiently robust for the purpose of an additional element for political communication.
Additionally, we admit that whereas five of our calculated maximum permissible nitrogen loss rates can be related to emission sources directly, in contrast, such a direct relationship to emission sources for the N load in surface waters cannot be established. This implies that necessary area-related emission reduction at the source is likely to be even larger than our load-related value. This denotes that our resulting INTN has to be interpreted as an interim target and that further in-depth assessments would lead to an even lower target value.
For human health effects of nitrogenous air pollutants, we focused only on the direct effects by NO2, although nitrogen in the atmosphere also influences the concentration of ozone and secondary inorganic particulate matter. We neglected those indirect effects and did not relate them to an acceptable nitrogen loss rate, as ozone concentrations and health effects of fine particulate matter are also driven by many other drivers and the establishment of a sound mathematical relationship to nitrogen emissions was not possible. However, by choosing a low-value background concentration of 20 µg m−3 as a state indicator, our approach is precaution-oriented, so that we are confident that our related maximum NOx emissions also improve human health exposition to those indirect effects.
The national nitrogen target is composed of independent targets, which we either calculated by applying a simplified approach or adopted from existing studies or directives. The methods applied are designed as such so that related state indicators or quality targets are met on a spatial average in Germany. Therefore, reaching the national nitrogen target does not guarantee that the six state indicators considered as spatial-dependent functions are reached everywhere. By integrating in the spatial dimension, our approach results in a target that only ensures compliance at the spatial average. The compliance with the nitrogen loss rate is therefore a necessary condition but is not sufficient to reach the environmental state indicators everywhere. For that, we recommend that neither our indicators nor the calculated national nitrogen target should fully replace existing indicators based on, for example, spatially resolved monitoring networks or detailed modelling approaches.
Against the background of the cascading mobility of reactive nitrogen, it cannot be excluded that a reduction of nitrate in groundwater will positively affect N concentration in surface waters, too. However, a double counting of nitrogen reduction requirements in a relevant order we believe is unlikely, because the groundwater-related quality target of 50 mg l−1 was neither designed to protect surface water downstream nor to protect marine and costal ecosystems from eutrophication. The assumption of long-lasting travel times of nitrate in groundwater justifies our hypothesis that double-counting of N in the groundwater and surface water indicators can be neglected. Therefore, it seems likely that compliance with our “groundwater indicator” will not lead to a substantial lower “surface water indicator”.
By combining the resulting maximum nitrogen loss rates per indicator to an integrated national nitrogen target, we aggregated the different nitrogen species to the uniform unit of total nitrogen and summed them up. In that sense, a future compliance with the national nitrogen target on that aggregated level will not give information on how much the different indicators contribute to the emission reduction. For that reason, it is not sufficient to achieve compliance with the national nitrogen target only. We suggest instead that all indicators need to be reduced to their maximum allowable loss rates independently in order to achieve the related state indicator.
In terms of robustness, we did not quantify the uncertainties of our maximum pressure indicators and the national nitrogen target. Nevertheless, we acknowledge the overall uncertainty of our approach, as we recognize a certain scope in the selection of target values in terms of types and units of limit values (concentration limits, area of critical load exceedance, critical levels, quality thresholds, and emission reduction targets) and methods to calculate maximum nitrogen losses. Note also that our results depend on the national nitrogen emissions and losses. Considering that emission estimates regularly change due to adjustments in inventorying emissions, it is possible that our target value of 1053 Gg N yr−1 will change in the future. To avoid this feature, a relative national nitrogen target could be a helpful complement in the future.
Finally, our selection of state indicators also determines the scope and level of our national nitrogen target. We selected the underlying six state indicators by focusing on the current political framework for Germany in combination with scientific limit values defined by international agreement within WHO and CLRTAP. Directly included indicators in the INTN are based on German legislation, indirectly enclosed indicators are science-based quality targets of the WHO and the CLRTAP. Available indicators are heterogenous and do not all imply an absolute good environmental status when reaching them. The state indicators implemented in the German legislative framework reflect action targets. For example, the state indicator for eutrophication of terrestrial ecosystems aims at reducing the area affected by eutrophication by 35% compared to the status in 2005. At the same time, compliance with the included state indicator to prevent coastal waters from eutrophication probably will not finish eutrophication automatically, as the changing climate and its effects on coastal ecosystems probably require a further lowering of the current quality targets. Lower N concentrations than the ones we include to prevent aquatic ecosystems from eutrophication in the range of 1 µg l−1 have been discussed by Camargo and Alonso [31]. Therefore, the proposed INTN reflects the heterogenous reduction required under the current legislation rather than the reduction required to achieve a good status of the environment everywhere in Germany. Thus, the proposed INTN should be interpreted more as a political interim target than a comprehensive environmental quality target, which means that a future lowering of the INTN should not be excluded.
In summary, we acknowledge that all of our own approaches are simple and the results deserve no more than to be characterized as good estimates. Full-chain iterative model calculations, for example, analysis of the agricultural surplus reduction in combination with accompanying nitrate, ammonia, and nitrous oxide reductions or even model combinations of sectoral activity and emission models, media distribution, and transfer models and last but not least, spatial-resolved impact analysis would have been more sophisticated alternatives. However, such models themselves, their combinations, and scenario back-calculations contain also uncertainties, which could increase by combining them. Furthermore, the simple set-up based on existing national indicators also is advantageous and suggests that our approach could be a role model for similar exercises in other countries or regions with a comparable data availability.
Despite our simplifications and the strong dependence of the results from our methods and assumptions, the resulting order of magnitude of our INTN is in a reasonable range with existing emission reduction commitments [45]. This is supported by the finding that our resulting per capita value of 12.7 kg is in the same order of magnitude as global, historical per capita reactive nitrogen creation in the early decades of industrial times until 1950 [46]. In summary, the chosen methods seem robust enough to use the national nitrogen target as a complementary means for communication. Rounding the calculated value 1053 Gg N yr−1 to a value of 1000 Gg N yr−1 does not change this order of magnitude. The suggested rounding makes the value more stable towards changes in input data and the selection of methods and limit values. Certainly, on the one hand, this rounding underlines that our result is not more than a good estimation, however, on the other hand a rounded value allows a better means of complementary political communication.

5. Conclusions

Environmental problems related to excessive loss of reactive nitrogen in Germany are manifold. A large variety of sectors and anthropogenic activities contribute to these problems. Fragmented measures taken so far show only limited success and bear the risk that nitrogen pollution is shifted from one medium of the nitrogen cycle to another (“pollution swapping”). To enhance awareness for this issue and to support political action on the way to an integrated approach to solve the nitrogen problem, we present an integrated national target for nitrogen (INTN). The selected methods allow us to derive a quantitative estimate of annual permitted nitrogen loss rates to the environment in Germany as an objective for political action that at the same time enhances the compliance with many of the media-related quality targets. Simultaneously it is as easily understandable and tangible for the addressed public and policy as the planetary boundary concept [8,9] or the 1.5 °C target of the climate community [19]. We are confident that the approach can be applied by other countries, although selected indicators might differ from one country to another and we suggest to use our findings as a role model for similar studies in countries or regions with comparable data availability.
Acknowledging the uncertainties and the scope of our approach and enhancing expressiveness of our concept, we propose to use 1000 Gg N yr−1 as a national nitrogen target for Germany when it is used in the political communication (instead of the calculated 1053 Gg N yr−1). As our target is linked to existing political reduction targets, which do not fully reflect the reduction requirements to achieve a good ecological status for all addressed impact indicators, it should be considered as an interim target. Comparing the result of our calculations under our selected assumptions to the current annual nitrogen losses to the environment in Germany amounting to 1574 Gg N yr−1 [34], the overall annual loss of reactive nitrogen in Germany would have to be reduced by more than 500 Gg N yr−1.

Author Contributions

Conceptualization, M.G. and J.H.; methodology, J.H.; validation, M.G., J.H. and B.S.; formal analysis, B.S.; investigation, M.B. and J.R.; resources, M.G.; data curation, L.K. (Lukas Knoll) and J.R.; writing—original draft preparation, M.G. and J.H.; writing—review and editing, L.B., U.H., L.K. (Lukas Knoll), L.K. (Laura Klement), B.S. and J.H.; visualization, B.S.; supervi-sion, M.G.; project administration, M.G. and J.H.; funding acquisition, M.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research received external funding by the German Federal Ministry for the Environment and the German Environment Agency, grant number RD-Project 371651200.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Generated data is publicly available.

Acknowledgments

The funding of the related RD-Project 3716512000 «German nitrogen fluxes, indicators and objectives» by the German Federal Ministry for the Environment and the German Environment Agency is kindly acknowledged. All project results are documented in the final report [34].

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Fowler, D.; Coyle, M.; Skiba, U.; Sutton, M.A.; Cape, J.N.; Reis, S.; Sheppard, L.J.; Jenkins, A.; Grizzetti, B.; Galloway, J.N.; et al. The global nitrogen cycle in the twenty-first century. Philos. Trans. R. Soc. B Biol. Sci. 2013, 368, 20130164. [Google Scholar] [CrossRef] [PubMed]
  2. Erisman, J.W.; Sutton, M.A.; Galloway, J.N.; Klimont, Z.; Winiwarter, W. How a century of ammonia synthesis changed the world. Nat. Geosci. 2008, 1, 636–639. [Google Scholar] [CrossRef]
  3. Galloway, J.N.; Leach, A.M.; Bleeker, A.; Erisman, J.W. A chronology of human understanding of the nitrogen cycle. Philos. Trans. R. Soc. B Biol. Sci. 2013, 368, 20130120. [Google Scholar] [CrossRef] [PubMed][Green Version]
  4. Erisman, J.W.; Galloway, J.N.; Seitzinger, S.; Bleeker, A.; Dise, N.B.; Petrescu, A.M.R.; Leach, A.M.; De Vries, W. Consequences of human modification of the global nitrogen cycle. Philos. Trans. R. Soc. B Biol. Sci. 2013, 368, 20130116. [Google Scholar] [CrossRef][Green Version]
  5. Sutton, M.A.; Bleeker, A.; Howard, C.M.; Bekunda, M.; Grizzetti, B.; de Vries, W.; van Grinsven, H.J.M.; Abrol, Y.P.; Adhya, T.K.; Billen, G.; et al. Our Nutrient World: The Challenge to Produce More Food and Energy with Less Pollution; On Behalf of the Global Partnership on Nutrient Management and the International Nitrogen Initiative; Centre for Ecology and Hydrology: Edinburgh, UK, 2013. [Google Scholar]
  6. OECD. Human Acceleration of the Nitrogen Cycle: Managing Risks and Uncertainty; OECD Publishing: Paris, France, 2018. [CrossRef]
  7. UNEP. Frontiers 2018/19–Emerging Issues of Environmental Concern. 2019. Available online: https://www.unenvironment.org/resources/frontiers-201819-emerging-issues-environmental-concern (accessed on 29 November 2020).
  8. Rockström, J.; Steffen, W.; Noone, K.; Persson, Å.; Chapin, F.S., III; Lambin, E.; Lenton, T.M.; Scheffer, M.; Folke, C.; Schellnhuber, H.J.; et al. Planetary boundaries: Exploring the safe operating space for humanity. Ecol. Soc. 2009, 14, 32. [Google Scholar] [CrossRef]
  9. Steffen, W.; Richardson, K.; Rockström, J.; Cornell, S.E.; Fetzer, I.; Bennett, E.M.; Biggs, R.; Carpenter, S.R.; De Vries, W.; De Wit, C.A.; et al. Planetary boundaries: Guiding human development on a changing planet. Science Express 2015, 347, 1259855. [Google Scholar] [CrossRef][Green Version]
  10. De Vries, W.; Kros, H.; Kroeze, C.; Seitzinger, S.P. Assessing planetary and regional nitrogen boundaries related to food security and adverse environmental impacts. Curr. Opin. Environ. Sustain. 2013, 5, 392–402. [Google Scholar] [CrossRef]
  11. Abrol, Y.P.; Adhya, T.K.; Aneja, V.P.; Raghuram, N.; Pathak, H.; Kulshrestha, U.; Sharma, C.; Singh, B. The Indian Nitrogen Assessment: Sources of Reactive Nitrogen, Environmental and Climate Effects, Management Options, and Policies; Elsevier: Duxford, UK, 2017. [Google Scholar]
  12. Tomich, T.P.; Brodt, S.B.; Dahlgren, R.A.; Scow, K.M. The California Nitrogen Assessment–Challenges and Solutions for People, Agriculture, and the Environment; University of California Press: Oakland, CA, USA, 2016. [Google Scholar] [CrossRef]
  13. Sutton, M.A.; Howard, C.M.; Erisman, J.W.; Billen, G.; Bleeker, A.; Grennfelt, P.; van Grinsven, H.; Grizetti, B. The European Nitrogen Assessment: Sources, Effects and Policy Perspectives; Cambridge University Press: Cambridge, NY, USA, 2011. [Google Scholar] [CrossRef]
  14. Umweltbundesamt. Reactive Nitrogen in Germany–Causes and Effects–Measures and Recommendations; Geupel, M., Frommer, J., Eds.; Umweltbundesamt: Dessau-Roßlau, Germany, 2015.
  15. Bach, M.; Häußermann, U.; Klement, L.; Knoll, L.; Breuer, L.; Weber, T.; Fuchs, S.; Heldstab, J.; Reutimann, J.; Schäppi, B. Reactive Nitrogen Flows in Germany 2010–2014 (DESTINO Report 2); Geupel, M., Ed.; Umweltbundesamt: Dessau-Roßlau, Germany, 2020.
  16. European Commission. Infringement Number 20132199 for Nitrate Directive–Germany. 2019. Available online: https://ec.europa.eu/atwork/applying-eu-law/infringements-proceedings/infringement_decisions (accessed on 21 November 2020).
  17. European Commission. Infringement Number 20152073 for Air Quality Directive–Germany. 2018. Available online: https://ec.europa.eu/atwork/applying-eu-law/infringements-proceedings/infringement_decisions (accessed on 21 November 2020).
  18. BMU–Federal Ministry for the Environment. Nitrogen Input in the Biosphere–First Nitrogen Report from the Federal Government; Federal Ministry for the Environment: Berlin, Germany, 2017.
  19. IPCC. Global Warming of 1.5 °C; An IPCC Special Report on the Impacts of Global Warming of 1.5 °C above Pre-Industrial Levels and Related Global Greenhouse Gas Emission Pathways, in the Context of Strengthening the Global Response to the Threat of Climate Change, Sustainable Development, and Efforts to Eradicate Poverty; Masson-Delmotte, V., Zhai, P., Pörtner, H.-O., Roberts, D., Skea, J., Shukla, P.R., Pirani, A., Moufouma-Okia, W., Péan, C., Pidcock, R., et al., Eds.; Intergovernmental Panel on Climate Change: Geneva, Switzerland, 2018; in press.
  20. Salomon, M.; Schmid, E.; Volkens, A.; Hey, C.; Holm-Müller, K.; Foth, H. Towards an integrated nitrogen strategy for Germany. Environ. Sci. Policy 2016, 55, 158–166. [Google Scholar] [CrossRef]
  21. SRU–German Advisory Council on the Environment. Nitrogen: Strategies for Resolving an Urgent Environmental Problem; Faulstich, M., Holm-Muller, K., Bradke, H., Calliess, C., Foth, H., Niekisch, M., Schreurs, M., Eds.; German Advisory Council on the Environment: Berlin, Germany, 2015. [Google Scholar]
  22. ICP Vegetation. Convention on Long-Range Transboundary Air Pollution (CLRTAP) Mapping critical levels for vegetation, Chapter 3. In Manual on Methodologies and Criteria for Modelling and Mapping Critical Loads and Levels and Air Pollution Effects, Risks and Trends; German Environment Agency: Dessau, Germany, 2017; Available online: https://www.umweltbundesamt.de/sites/default/files/medien/4292/dokumente/ch3-mapman-2017-10.pdf (accessed on 29 November 2020).
  23. European Commission. A Clean Air Programme for Europe–COM 2013; 918 final eds. European Commission; European Commission: Brussels, Belgium, 2013.
  24. European Union: Directive (EU) 2016/2284 of the European Parliament and of the Council of 14 December 2016 on the Reduction of National Emissions of Certain Atmospheric Pollutants, Amending Directive 2003/35/EC and Repealing Directive 2001/81/EC, European Union, 2016/2284; European Commission: Brussels, Belgium, 2016; Available online: http://data.europa.eu/eli/dir/2016/2284/oj (accessed on 29 November 2020).
  25. Bundesregierung: Ordinance on the Protection of Surface Waters (Oberflächengewässerverordnung–Verordnung zum Schutz der Oberflächengewässer) Bundesministeriums der Justiz und für Verbraucherschutz, BGBl. I S. 1373 vom 20. Juni 2016, 2016, Berlin. Available online: http://www.gesetze-im-internet.de/ogewv_2016/ (accessed on 29 November 2020).
  26. European Council: Council Directive of 12 December 1991 Concerning the Protection of Waters against Pollution Caused by Nitrates from Agricultural Sources European Council, 91/676/EEC, 1991, Brussels. Available online: http://data.europa.eu/eli/dir/1991/676/2008-12-11 (accessed on 29 November 2020).
  27. BMU–Bundesministerium für Umwelt Naturschutz und Reaktorsicherheit. Climate Action Plan 2050–Principles and Goals of the German Government’s Climate Policy; Bundesministerium für Umwelt Naturschutz und Reaktorsicherheit (BMU): Berlin, Germany, 2016.
  28. World Health Organization. Review of Evidence on Health Aspects of Air Pollution–REVIHAAP Project: Final Technical Report; World Health Organization: Geneva, Switzerland, 2013.
  29. Schrader, F.; Brümmer, C. Land use specific ammonia deposition velocities: A review of recent studies (2004–2013). Waterairsoil Pollut. 2014, 225, 1–12. [Google Scholar] [CrossRef] [PubMed][Green Version]
  30. Umweltbundesamt: German Informative Inventory Report 2017 (IIR 2017). Available online: https://iir-de-17.wikidot.com/ (accessed on 21 November 2020).
  31. Camargo, J.A.; Alonso, Á. Ecological and toxicological effects of inorganic nitrogen pollution in aquatic ecosystems: A global assessment. Environ. Int. 2006, 32, 831–849. [Google Scholar] [CrossRef] [PubMed]
  32. Kolzau, S.; Wiedner, C.; Rücker, J.; Köhler, J.; Köhler, A.; Dolman, A.M. Seasonal patterns of nitrogen and phosphorus limitation in four German lakes and the predictability of limitation status from ambient nutrient concentrations. PLoS ONE 2014, 9, e96065. [Google Scholar] [CrossRef] [PubMed][Green Version]
  33. LAWA. Associations of the River Basins to North-and Baltic Sea Nitrogen Reduction Targets of the German River Basins Association for the North-and Baltic Sea, 56. In Proceedings of the “Surface Water Board” of the Bund/Länderarbeitsgemeinschaft Wasser, Item 4.4.3, Integrated Nitrogen Strategy of the Federal Government, Wernigerode, Germany, 12–13 June 2018. [Google Scholar]
  34. Heldstab, J.; Schäppi, B.; Reutimann, J.; Bach, M.; Häußermann, U.; Knoll, L.; Klement, L.; Breuer, L.; Fuchs, S.; Weber, T. Integrated Nitrogen Indicator, National Nitrogen Target and the Current Situation in Germany (DESTINO Report 1); Geupel, M., Ed.; Umweltbundesamt: Dessau-Roßlau, Germany, 2020.
  35. Häußermann, U.; Klement, L.; Breuer, L.; Ullrich, A.; Wechsung, G.; Bach, M. Nitrogen soil surface budgets for districts in Germany 1995 to 2017. Environ. Sci. Eur. 2020, 32, 1–14. [Google Scholar] [CrossRef]
  36. UNFCCC CRF DEU Submission 2017 Reported by Umweltbundesamt. German Environment Agency. 2017. Available online: http://unfccc.int/files/national_reports/annex_i_ghg_inventories/national_inventories_submissions/application/zip/deu-2017-crf-11apr17.zip (accessed on 7 July 2017).
  37. European Union: Directive 2008/50/EC on Ambient Air Quality and Cleaner Air for Europe, European Union, 2008/50/EC, 2008, Brussels. Available online: https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX%3A32008L0050 (accessed on 29 November 2020).
  38. Henne, S.; Brunner, D.; Folini, D.; Solberg, S.; Klausen, J.; Buchmann, B. Assessment of parameters describing representativeness of air quality in-situ measurement sites. Atmos. Chem. Phys. Discuss. 2009, 9, 20019–20062. [Google Scholar] [CrossRef]
  39. Rattigan, O.; Carpenter, A.; Civerolo, K.; Felton, H. Pollutant measurements at near road and urban background sites in New York, USA. Atmos. Pollut. Res. 2020, 11, 859–870. [Google Scholar] [CrossRef]
  40. Stern, R.; Kerschbaumer, A.; Reimer, E. Description of the Chemical Transport Model ’REM-CALGRID; Freie Universität Berlin: Berlin, Germany, 2009. [Google Scholar]
  41. Umweltbundesamt. German Air Quality Data of the Federal States and the German Environment Agency; Feigenspan, S., Ed.; 2017. Available online: https://www.umweltbundesamt.de/en/data/air/air-data, personal communication (accessed on 30 May 2017).
  42. Umweltbundesamt. Map Server for Annual Data on Air Quality of the German Environment Agency; Feigenspan, S., Ed.; 2018. Available online: http://gis.uba.de/Website/luft/index.html (accessed on 31 August 2018).
  43. International Institute for Applied Systems Analysis (IIASA). The Final Policy Scenarios of the EU Clean Air Policy Package; TSAP Report #11; Amann, M., Ed.; IIASA: Laxenburg, Austria, 2014. [Google Scholar]
  44. de Vries, W.; Hettelingh, J.-P.; Posch, M. Critical Loads and Dynamic Risk Assessments. Nitrogen, Acidity and Metals in Terrestrial and Aquatic Ecosystems; Springer Science+Business Media: Dordrecht, The Netherlands, 2015. [Google Scholar] [CrossRef]
  45. BMU–Federal Ministry for the Environment: Nationales Luftreinhalteprogramm der Bundesrepublik Deutschland, Bundesministerium für Umwelt Naturschutz und nukleare Sicherheit (BMU), 22. Mai 2019 (Kabinettbeschluss), 2019, Berlin. Available online: https://www.bmu.de/download/nationales-luftreinhalteprogramm-der-bundesrepublik-deutschland/ (accessed on 29 November 2020).
  46. Galloway, J.N.; Winiwarter, W.; Leip, A.; Leach, A.M.; Bleeker, A.; Erisman, J.W. Nitrogen footprints: Past, present and future. Environ. Res. Lett. 2014, 9, 115003. [Google Scholar] [CrossRef]
Figure 1. Maps for 2015 of (a) ammonia emissions per grid cell (Gg NH3 yr−1) [30] and (b) ambient ammonia concentrations per grid cell (µg NH3 yr−1) modelled with the chemical transport model REM-CALGRID Model (RCG) [40].
Figure 1. Maps for 2015 of (a) ammonia emissions per grid cell (Gg NH3 yr−1) [30] and (b) ambient ammonia concentrations per grid cell (µg NH3 yr−1) modelled with the chemical transport model REM-CALGRID Model (RCG) [40].
Sustainability 13 01121 g001
Figure 2. Linear regression between NH3–N emission and NH3–N concentration based on the data shown in Figure 1.
Figure 2. Linear regression between NH3–N emission and NH3–N concentration based on the data shown in Figure 1.
Sustainability 13 01121 g002
Figure 3. Distribution of the nitrate concentration in groundwater in Germany (1 × 1 km grid), predicted using the random forest classification [34].
Figure 3. Distribution of the nitrate concentration in groundwater in Germany (1 × 1 km grid), predicted using the random forest classification [34].
Sustainability 13 01121 g003
Figure 4. Distribution according to the random forest classification, estimated nitrate concentration in groundwater in Germany [34].
Figure 4. Distribution according to the random forest classification, estimated nitrate concentration in groundwater in Germany [34].
Sustainability 13 01121 g004
Figure 5. Locations of NO2 background measurement stations with continuous data for 2002–2015 [41].
Figure 5. Locations of NO2 background measurement stations with continuous data for 2002–2015 [41].
Sustainability 13 01121 g005
Figure 6. Map of the modelled NO2 ambient concentrations 2015 (combination of measurements and distribution model). Circles mark measurements from stations that are only locally representative (annual means). The annual limit value is 40 µg NO2 m−3. The WHO response threshold for background concentrations is 20 µg NO2 m−3 [42].
Figure 6. Map of the modelled NO2 ambient concentrations 2015 (combination of measurements and distribution model). Circles mark measurements from stations that are only locally representative (annual means). The annual limit value is 40 µg NO2 m−3. The WHO response threshold for background concentrations is 20 µg NO2 m−3 [42].
Sustainability 13 01121 g006
Table 1. Overview of selected impact indicators and related state indicators to calculate the national nitrogen target as the sum of the related maximum permitted nitrogen losses per pressure indicator.
Table 1. Overview of selected impact indicators and related state indicators to calculate the national nitrogen target as the sum of the related maximum permitted nitrogen losses per pressure indicator.
NumberImpact IndicatorState IndicatorPressure Indicator (Nitrogen Loss Rate)
(1)Vegetation affected by ambient NH3 concentrationNH3 critical level for higher plants: 3 µg m−3 NH3 [22]NH3 emissions
(2)Terrestrial ecosystems affected by eutrophication (deposition)35% reduction of exceedance of the Critical Load for eutrophication from 2005–2030 [23,24]NH3 and NOx emissions
(3)Surface water quality (to prevent coastal water from eutrophication)Ntotal concentration to protect North Sea (2.8 mg N l−1) and Baltic Sea: (2.6 mg N l−1) [25]Ntotal load
(4)Groundwater quality affected by nitrate NO3 concentration in groundwater: 50 mg l−1 [26]NO3 leaching
(5)Nitrous oxide emissions affecting climate changeN2O emission: long-term goal reduction 80–95% [27]N2O emissions
(6)Human health affected by atmospheric NO2NO2 concentration: WHO effects level for the background: 20 µg m−3 [28]NOx emissions
Table 2. Nitrogen reduction requirement in German river basins flowing into the North Sea and Baltic Sea, to comply with target concentrations; various time periods (Gg N yr−1) [33].
Table 2. Nitrogen reduction requirement in German river basins flowing into the North Sea and Baltic Sea, to comply with target concentrations; various time periods (Gg N yr−1) [33].
River BasinCurrent LoadTarget LoadReduction
North Sea—target concentration 2.8 mg N l−1
Rhine 198.3 b196.6–1.7
Elbe78.8 b66.6–12.2
Ems15.1 c7.8–7.3
Weser44.4 b28.5–15.9
Eider5.7 b4.7–1.0
Sub-total North Sea 342.3304.2–38.1
Baltic Sea—target concentration 2.6 mg N l−1
Schlei/Trave6.3 b4.0–2.3
Warnow/Peene7.6 d5.8–1.8
Sub-total Baltic Sea13.99.8–4.1
Total356.2314.0–42.2
Note: b normalized mean nitrogen load 2012–2016; c mean nitrogen load 2008–2012; d mean nitrogen load 2012–2015.
Table 3. Relation between yearly values of reported NOx emissions, the 98th percentile value of NO2 measurements from all background stations, and the mean target emission of NOx based on Equation (5).
Table 3. Relation between yearly values of reported NOx emissions, the 98th percentile value of NO2 measurements from all background stations, and the mean target emission of NOx based on Equation (5).
Year20022003200420052006200720082009201020112012201320142015Mean
a538522501479474451429398406399386385371361
b2020202020202020202020202020
c3943414039383738373434333233
d274242243238246239234209222232229236234221236
Note: a: reported emission (Gg NOx–N yr−1) [30]; b: WHO threshold value (µg NO2 µm−3) [28]; c: 98th percentile value of NO2 measurements from all background stations [41]; d: resulting target emission (Gg NOx–N yr−1).
Table 4. Calculated maximum permitted pressure indicators (nitrogen loss rates per year) to comply with related concentration or impact targets in Germany for six impact indicators and the resulting national nitrogen target; selected indicators per species and INTN (integrated national target for nitrogen) shaded (in brackets, annual nitrogen losses for the year 2015 [34]).
Table 4. Calculated maximum permitted pressure indicators (nitrogen loss rates per year) to comply with related concentration or impact targets in Germany for six impact indicators and the resulting national nitrogen target; selected indicators per species and INTN (integrated national target for nitrogen) shaded (in brackets, annual nitrogen losses for the year 2015 [34]).
Method NumberImpact IndicatorMaximum Annual Pressure Indicator (Nitrogen Losses in 2015) (Gg N yr−1)
2.1.1Vegetation affected by NH3 concentration441 (625)     NH3–N
2.1.2Terrestrial ecosystems affected by eutrophication396 (625)     NH3–N
168 (361)     NOx–N
2.1.3Surface water quality (to prevent coastal waters from eutrophication)314 (356)     Ntotal
2.1.4Groundwater quality127 (148)     NO3–N
2.1.5Nitrous oxide emissions affecting climate change48 (83)     N2O–N
2.1.6Human health affected by NO2 concentration236 (361)     NOx–N
Integrated national target for nitrogen (INTN) as the sum of the lowest loss rates per nitrogen species (2.1.2 – 2.1.5)1053 (1574)     N
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Geupel, M.; Heldstab, J.; Schäppi, B.; Reutimann, J.; Bach, M.; Häußermann, U.; Knoll, L.; Klement, L.; Breuer, L. A National Nitrogen Target for Germany. Sustainability 2021, 13, 1121. https://doi.org/10.3390/su13031121

AMA Style

Geupel M, Heldstab J, Schäppi B, Reutimann J, Bach M, Häußermann U, Knoll L, Klement L, Breuer L. A National Nitrogen Target for Germany. Sustainability. 2021; 13(3):1121. https://doi.org/10.3390/su13031121

Chicago/Turabian Style

Geupel, Markus, Jürg Heldstab, Bettina Schäppi, Judith Reutimann, Martin Bach, Uwe Häußermann, Lukas Knoll, Laura Klement, and Lutz Breuer. 2021. "A National Nitrogen Target for Germany" Sustainability 13, no. 3: 1121. https://doi.org/10.3390/su13031121

Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop