Reduction Of Nitrogen Deposition Research Articles

The latest status of nitrogen saturation on Kureha Hill, Toyama, Japan, based on 20‐year observations

AbstractExcessive anthropogenic nitrogen fixation alters the nitrogen cycle and increases nitrogen deposition, leading to nitrogen saturation, which in turns leads to forest decline and nitrate leaching into stream waters. Kureha Hill in Toyama Prefecture, Japan, is considered to be in nitrogen saturation, since many streams have contained high concentrations of nitrate for more than 20 years. In this study, the latest status of nitrogen saturation was verified by comparing most recent data with 20 years observational data, focusing on various indicators of nitrogen saturation, such as stream water quality, nitrogen budget of the watershed, and soil nitrification and mineralization potential. Both the nitrogen deposition on the Hyakumakidani watershed on Kureha Hill and the amount of nitrate leaching to the stream tended to decrease. The reduction in nitrate leaching could be attributed to the reduction in nitrogen deposition and other factors, such as nitrogen pools in the soil. Despite the recent decline in nitrate concentration of the Hyakumakidani stream, the pH level has remained unchanged. This may be due to decreased concentrations of sulfate and acid neutralizing capacity (ANC). The C/N ratio of the soil ranged from 12 to 18 from 2000 to 2023, which was lower than the nitrogen saturation threshold of 25. The net nitrification rate and net mineralization rate showed no significant changes between 2002 and 2023, indicating that the potential to produce nitrate has been unchanged. Similar values in net nitrification and net nitrogen mineralization rates reflected that the Hyakumakidani watershed remained in Stage‐3 nitrogen saturation.

Airborne nitrogen deposition to the Baltic Sea: Past trends, source allocation and future projections

Despite significant reductions in nitrogen emissions achieved in Europe during the last three decades, eutrophication remains an environmental concern in the Baltic Sea basin. Recently, a number of comprehensive modelling studies have been conducted for the HELCOM Commission to inform the 2021 update of the Baltic Sea Action Plan. The calculations have focused on trends in airborne nitrogen deposition to the Baltic Sea and its nine sub-basins during the 2000–2017 period, the identification and ranking of the main contributors to deposition, as well as future projections for 2030, assuming compliance with the Gothenburg Protocol and the EU NEC Directive. This paper synthesizes the main results from these studies and puts them into the context of maximum allowable nutrient inputs to the Baltic Sea.According to our results, the airborne annual deposition to the Baltic Sea in 2017 amounted to 122.6 Gg(N) of oxidized nitrogen and 105.3 Gg(N) of reduced nitrogen, corresponding to a decrease since 2000 by, respectively, 39% and 11%. In order to filter out the large inter-annual variability due to meteorology and to better reflect trends in emissions, weather-normalized depositions of nitrogen have been calculated as well, according to which the decreases since 2000 amount to 35%, 7% and 25% for oxidized, reduced and total nitrogen, respectively.In 2017, Germany, Poland and Denmark were the most important contributors to airborne deposition of total (oxidized + reduced) nitrogen to the Baltic Sea. Agriculture contributed most to reduced nitrogen deposition, while the transport sector contributed most to oxidized nitrogen deposition. Agriculture in Germany was the single-most important contributor to nitrogen deposition to the Baltic Sea in 2017 (accounting for about 15% of the total), but there are numerous other important sectoral contributions. Emissions of nitrogen from the nine HELCOM Contracting Parties contributed 49%, 76% and 61% to oxidized, reduced and total nitrogen deposition, respectively.Assuming full compliance with the EU NEC Directive and the Gothenburg Protocol, significant further reductions in nitrogen deposition can be achieved by 2030, down to an annual deposition of 72.7 Gg(N) and 84.7 Gg(N) of oxidized and reduced nitrogen, respectively.

Woodland ectomycorrhizal fungi benefit from large‐scale reduction in nitrogen deposition in the Netherlands

Abstract Woodland ectomycorrhizal (ECM) fungal species declined considerably in the Netherlands in the late 20th century, mainly due to raised levels of atmospheric nitrogen deposition. Environmental measures have been taken to reduce this deposition, but it remains unclear whether and to what extent ECM species have benefitted from these. We hypothesized that ECM species, especially those species that are known to be nitrophobic, that is, sensitive to nitrogen loading, have recovered to some extent from the reduction in nitrogen deposition after 1994. We further hypothesized that, due to legacy effects of deposition, recovery has been stronger in regions where deposition levels have previously been lower. To test these hypotheses, we analysed long‐term opportunistic data, that is, observations collected without standardized field method. We applied data filtering and a modified List Length method to adjust for potential biases in these data. The removal of bias left us with two periods to examine ECM species trends: before (1965–1985) and after (1994–2013) deposition reduction started [in 1994]. We compared trends in ECM species in 1965–1985 with those in 1994–2013. Multispecies indicators were used to summarize the findings of ECM species, and to compare these with results of litter saprotrophic species and wood saprotrophic and wood parasitic species. We found that (1) most trends switched in direction from negative to positive after the reduction in nitrogen deposition began; (2) these trends were more pronounced for nitrophobic ECM species than for nitrotolerant ECM species; (3) trends for ECM species differed from those of the other functional groups; and (4) recovery was stronger in the region with a history of lower deposition. Policy implications. Our results suggest that woodland ectomycorrhizal species benefit substantially from environmental measures to reduce nitrogen deposition. Our study is one of few scientific studies to date documenting evidence of success of large‐scale (nation‐wide) environmental measures. We have demonstrated that opportunistic citizen science data can be used for the detection of species trends, but it is essential to examine and control for potential bias in the data.

Modelling the impact of climate change and atmospheric N deposition on French forests biodiversity

A dynamic coupled biogeochemical–ecological model was used to simulate the effects of nitrogen deposition and climate change on plant communities at three forest sites in France. The three sites had different forest covers (sessile oak, Norway spruce and silver fir), three nitrogen loads ranging from relatively low to high, different climatic regions and different soil types.Both the availability of vegetation time series and the environmental niches of the understory species allowed to evaluate the model for predicting the composition of the three plant communities. The calibration of the environmental niches was successful, with a model performance consistently reasonably high throughout the three sites.The model simulations of two climatic and two deposition scenarios showed that climate change may entirely compromise the eventual recovery from eutrophication of the simulated plant communities in response to the reductions in nitrogen deposition. The interplay between climate and deposition was strongly governed by site characteristics and histories in the long term, while forest management remained the main driver of change in the short term.

The potential for tree planting strategies to reduce local and regional ecosystem impacts of agricultural ammonia emissions

Trees are very effective at capturing both gaseous and particulate pollutants from the atmosphere. But while studies have often focussed on PM and NOx in the urban environment, little research has been carried out on the tree effect of capturing gaseous emissions of ammonia in the rural landscape. To examine the removal or scavenging of ammonia by trees a long-range atmospheric model (FRAME) was used to compare two strategies that could be used in emission reduction policies anywhere in the world where nitrogen pollution from agriculture is a problem. One strategy was to reduce the emission source strength of livestock management systems by implementing two ‘tree-capture’ systems scenarios – tree belts downwind of housing and managing livestock under trees. This emission reduction can be described as an ‘on-farm’ emission reduction policy, as ammonia is ‘stopped’ from dispersion outside the farm boundaries. The second strategy was to apply an afforestation policy targeting areas of high ammonia emission through two planting scenarios of increasing afforestation by 25% and 50%. Both strategies use trees with the aim of intercepting NH3 emissions to protect semi-natural areas. Scenarios for on-farm emission reductions showed national reductions in nitrogen deposition to semi-natural areas of 0.14% (0.2 kt N–NHx) to 2.2% (3.15 kt N–NHx). Scenarios mitigating emissions from cattle and pig housing gave the highest reductions. The afforestation strategy showed national reductions of 6% (8.4 kt N–NHx) to 11% (15.7 kt N–NHx) for 25% and 50% afforestation scenarios respectively. Increased capture by the planted trees also showed an added benefit of reducing long range effects including a decrease in wet deposition up to 3.7 kt N–NHx (4.6%) and a decrease in export from the UK up to 8.3 kt N–NHx (6.8%).

The influence of long term trends in pollutant emissions on deposition of sulphur and nitrogen and exceedance of critical loads in the United Kingdom

Abstract In the United Kingdom, as with other European countries, land-based emissions of NO x and SO 2 have fallen significantly over the last few decades. SO 2 emissions fell from a peak of 3185 Gg S in 1970 to 344 Gg S in 2005 and are forecast by business-as-usual emissions scenarios to fall to 172 Gg by 2020. NO x emissions were at a maximum of 951 Gg N in 1970 and fell to 378 by 2005 with a further decrease to 243 Gg N forecast by 2020. These large changes in emissions have not been matched by emissions changes for NH 3 which decreased from 315 Gg N in 1990 to 259 in 2005 and are forecast to fall to 222 by 2020. The Fine Resolution Atmospheric Multi-pollutant Exchange model (FRAME) has been applied to model the spatial distribution of sulphur and nitrogen deposition over the United Kingdom during a 15-year time period (1990–2005) and compared with measured deposition of sulphate, nitrate and ammonium from the national monitoring network. Wet deposition of nitrogen and sulphur was found to decrease more slowly than the emissions reductions rate. This is attributed to a number of factors including increases in emissions from international shipping and changing rates of atmospheric oxidation. The modelled time series was extended to a 50-year period from 1970 to 2020. The modelled deposition of SO x , NO y and NH x to the UK was found to fall by 87%, 52% and 25% during this period. The percentage area of sensitive habitats in the United Kingdom for which critical loads are exceeded is estimated to fall from 85% in 1970 to 37% in 2020 for acidic deposition and from 73% to 49% for nutrient nitrogen deposition. The significant reduction in land emissions of SO 2 and NO x focuses further attention in controlling emissions from international shipping. Future policies to control emissions of ammonia from agriculture will be required to effect further significant reductions in nitrogen deposition.

Effect of nitrogen deposition reduction on biodiversity and carbon sequestration

Global warming and loss of biodiversity are among the most prominent environmental issues of our time. Large sums are spent to reduce their causes, the emission of CO 2 and nitrogen compounds. However, the results of such measures are potentially conflicting, as the reduction of nitrogen deposition may hamper carbon sequestration and thus increase global warming. Moreover, it is uncertain whether a lower nitrogen deposition will lead to a higher biodiversity. We applied a dynamic soil model, a vegetation dynamic model and a biodiversity regression model to investigate the effect of nitrogen deposition reduction on the carbon sequestration and plant species diversity. The soil and vegetation models simulate the carbon sequestration as a result of nitrogen deposition and they provide the biodiversity model with information on the soil conditions groundwater table, pH and nitrogen availability. The plant diversity index resulting from the biodiversity model is based on the occurrence of ‘red list’ species for the tree soil conditions. Based on the model runs we forecast that a gradual decrease in nitrogen deposition from 40 to 10 kg N ha −1 y −1 in the next 25 years will cause a drop in the net carbon sequestration of forest in The Netherlands to 27% of the present amount, while biodiversity remains constant in forest, but may increase in heathland and grassland.

Ecosystem recovery: heathland response to a reduction in nitrogen deposition

AbstractAtmospheric deposition of nitrogen is responsible for widespread changes in the structure and function of sensitive seminatural ecosystems. The proposed reduction in emissions of nitrogenous pollutants in Europe under the Gothenburg Protocol raises the question of whether affected ecosystems have the potential to recover to their previous condition and, if so, over what timescale. Since 1998, we have monitored the response of a lowland heathland in southern England following the cessation of a long‐term nitrogen addition experiment, and subsequent management, assessing changes in vegetation growth and chemistry, soil chemistry and the soil microbial community. Persistent effects of earlier nutrient loading on Calluna growth and phenology, and on the abundance of lichens, were apparent up to 8 years after nitrogen additions ceased, indicating the potential for long‐term effects of modest nutrient loading (up to 15.4 kg N ha−1 yr−1, over 7 years) on heathland ecosystems. The size and activity of the soil microbial community was elevated in former N‐treated plots, 6–8 years after additions ceased, suggesting a prolonged effect on the rate of nutrient cycling. Although habitat management in 1998 reduced nitrogen stores in plant biomass, effects on belowground nitrogen stores were small. Although some parameters (e.g. soil pH) recover pretreatment levels relatively rapidly, others (e.g. vegetation cover and microbial activity) respond much more slowly, indicating that the ecological effects of even small increases in nitrogen deposition will persist for many years after deposition inputs are reduced. Indeed, calculations suggest that the additional soil nitrogen storage associated with 7 years of experimental nitrogen inputs could sustain the observed effects on plant growth and phenology for several decades. Carry over effects on plant phenology and sensitivity to drought suggest that the persistence of vegetation responses to nitrogen deposition should be integrated into long‐term assessments of the impact of global climate change on sensitive ecosystems.

Quantification of nitrate leaching from forest soils on a national scale in The Netherlands

Abstract. To evaluate the effects of nitrogen (N) emission policies, reliable information on nitrate concentrations and leaching fluxes from forest ecosystems is necessary. Insight into the regional variability of nitrate concentrations, to support local policy on emission abatement strategies is especially desirable. In this paper, three methods for the calculation of a spatial distribution of soil nitrate concentrations in Dutch forest ecosystems are compared. These are (i) a regression model based on observed nitrate concentrations and additional data on explanatory variables such as soil type, tree species and nitrogen deposition (ii) a semi-empirical dynamic model WANDA, and (iii) a process-oriented dynamic model SMART2. These two dynamic models are frequently used to evaluate the effects of reductions in nitrogen deposition at scales ranging from regional to countrywide. The results of the regression model evaluated the performance of the two dynamic models. Furthermore, the results of the three methods are compared with the steady-state approach currently used for the derivation of nitrogen critical loads. Both dynamic models, in the form of cumulative distribution functions, give similar results on a national scale. Regional variability is predicted differently by both models. Discrepancies are caused mainly by a difference in handling forest filtering and denitrification. All three methods show that, despite the high nitrogen inputs, Dutch forests still accumulate more N than they release. This implies that, in respect of groundwater quality, presently acceptable nitrogen deposition is higher than the (long-term) critical loads. However, in areas with high atmospheric nitrogen input, all three methods indicate that the EU standard for nitrate in groundwater (50 mg NO3 l–1) is exceeded. Steady-state with nitrogen deposition seems to have been reached in about 10% of the forested area, with a nitrate concentration greater than 50 mg NO3–1. Keywords: soil modelling, up-scaling, model validation, critical load

Acidic loadings in South Korean ecosystems by long-range transport and local emissions

Exceedances of sulfur and nitrogen critical loads in South Korean ecosystems caused by long-range transport and local emissions of sulfur and nitrogen have been estimated using the maximum critical load of sulfur and the critical load of nutrient nitrogen. The long-term-averaged deposition of sulfur and nitrogen is estimated with a simplified chemical model and the K -mean clustering technique. The three consecutive days of gridded daily mean National Center for Environmental Protection (NCEP) reanalyzed 850 hPa geopotential height fields with and without precipitation on the last day over South Korea are used for clustering of synoptic patterns for the period of 1994–1998. Two emission conditions are simulated for each cluster to estimate long-term averaged depositions of sulfur and nitrogen by long-range transport and local emissions over South Korea. One condition takes all emissions within the simulated domain into account as a base case and the other condition excludes all South Korean emissions but includes all of the other emissions, as a control case. The results of the present study indicate that the contribution of long-range transport to the annual total deposition over South Korea is found to be about 40% ( 530 eq ha - 1 yr - 1 ) for sulfur and 49% ( 650 eq ha - 1 yr - 1 ) for nitrogen, of which 55% for sulfur and 58% for nitrogen are contributed by wet deposition. This suggests the importance of wet deposition through the transformed acidic precursors for long-range transport to South Korea's total deposition of sulfur and nitrogen. The estimated exceedance for South Korean ecosystems indicates that the current estimate of total sulfur deposition affects about 42% of the South Korean ecosystems adversely, of which 14% is attributed to South Korean source only and the rest 28% is attributed to long-range transport together with South Korean source. Long-range transport of sulfur itself does not exceed the maximum critical load of sulfur. On the other hand, the current estimate of total nitrogen deposition is found to affect all South Korean ecosystems adversely. About 65% and 15% of the Korean ecosystems are, respectively, found to be affected adversely by South Korean nitrogen emissions and by long-range transport, suggesting that the reduction of nitrogen deposition from both South Korean sources and long-range transport is a prerequisite to ensure South Korean ecosystem sustainability.

Habitat management: a tool to modify ecosystem impacts of nitrogen deposition?

Atmospheric nitrogen deposition has been shown to affect both the structure and the function of heathland ecosystems. Heathlands are semi-natural habitats and, as such, undergo regular management by mowing or burning. Different forms of management remove more or less nutrients from the system, so habitat management has the potential to mitigate some of the effects of atmospheric deposition. Data from a dynamic vegetation model and two field experiments are presented. The first involves nitrogen addition following different forms of habitat management. The second tests the use of habitat management to promote heathland recovery after a reduction in nitrogen deposition. Both modelling and experimental approaches suggest that plant and microbial response to nitrogen is affected by management. Shoot growth and rates of decomposition were lowest in plots managed using more intensive techniques, including mowing with litter removal and a high temperature burn. Field data also indicate that ecosystem recovery from prolonged elevated inputs of nitrogen may take many years, or even decades, even after the removal of plant and litter nitrogen stores which accompanies the more intensive forms of habitat management.

A dynamic model for assessing the impact of coupled sulphur and nitrogen deposition scenarios on surface water acidification

MAGIC-WAND (Model of Acidification of Groundwaters In Catchments—With Aggregated Nitrogen Dynamics) has been specifically developed for wide application and scenario assessment. It maintains the sulphur driven acid/base chemistry dynamics of MAGIC, and considers in addition the impacts of changes in nitrogen deposition from the atmosphere and changes in nitrogen utilisation within the catchment. The model uses estimates of nitrification, mineralisation, N fixation and denitrification and changes in these soil processes through time. Plant uptake is nonlinear and dependant upon inorganic nitrogen concentrations in soil solution. Calibration of the model requires specification of values for the soil N fluxes and for the parameters which describe the hyperbolic uptake function. Literature data can provide ranges for these values but specific catchment related values are not obtainable since the model is conceptual. Selection of uptake parameters must reflect current catchment vegetation and vegetation change through time, and this has been investigated at a catchment in SW Scotland. Changes in soil processes through time are also important to model functioning, but are not considered in this study. The model has been applied to 25 acid sensitive (Acid Neutralising Capacity (ANC)<50 μeq l −1) lochs in SW Scotland to examine the interaction of afforestation and changes in nitrogen deposition, assuming recently agreed reductions in sulphur deposition. The model results suggest that a 50% reduction in nitrogen deposition coupled with agreed sulphur reductions is not sufficient to promote reversibility of acidification at the most sensitive sites within 15 years. Increased nitrogen deposition in conjunction with agreed sulphur reductions will most likely cause continued acidification at afforested lochs in the region.

Developing optimal abatement strategies for the effects of sulphur and nitrogen deposition at European scale

Integrated Assessment Models were successfully used to provide input to the negotiations for the Oslo Protocol on Further Reductions of Sulphur Emissions, finalized within the United Nations Economic Commission for Europe Convention on Long-range Transboundary Air Pollution in Oslo in June 1994. The techniques developed within this framework will be extended now to the simultaneous analysis of sulphur and nitrogen deposition. In addition to acidification, atmospheric deposition of nitrogen contributes to eutrophication of certain ecosystems, through a nutrient effect, and originates from the long-range transport of emissions of both oxidised and reduced nitrogen (NOx and NH3). Modelling reductions in nitrogen deposition thus introduces a need to establish multi-pollutant multi-effect modelling techniques. This paper investigates the development of a model set up to examine reductions of these pollutants in an economically and environmentally efficient manner. The control of nitrogen deposition encompasses action across several economic sectors, particularly the power, transport and agricultural sectors. Combining sulphur and nitrogen deposition limits on a European scale will require a flexible modelling approach and the issues governing possible approaches are presented.