Inorganic Nitrogen Deposition Research Articles

Isotopic composition of water-soluble nitrate in bulk atmospheric deposition at Dongsha Island: sources and implications of external N supply to the northern South China Sea

Abstract. Increased reactive nitrogen (Nr, NO3− + NH4++ + dissolved organic nitrogen) emission from the Asian continent poses profound threats to ecosystem safety from terrestrial throughout the ocean proper. To quantify atmospheric Nr input, diagnose its sources, and evaluate influence on marine nitrogen cycle of the South China Sea (SCS), an oligotrophic marginal sea adjacent to the emission hot spot China, we conducted measurements of concentrations of nitrate and ammonium as well as other major ions and dual isotopes of nitrate (δ15NNO3 and δ18ONO3) in atmospheric deposition collected from Dongsha Island off southern China. The δ15NNO3 and δ18ONO3 for dry deposition averaged at −2.8‰ and +58.8‰, ranging from −7.5 to +3.7‰ and from ∼ +17 to +88‰, respectively. Wet deposition, although with limited samples, showed a similar flux-weighted mean in δ15NNO3 (−2.6‰) yet a significantly higher mean in δ18ONO3 (+78.8‰). The dual isotope ratios showed an anti-correlation and an inverse seasonality; the δ15NNO3 values were higher in summer compared to those in winter, while the δ18ONO3 values were higher in winter than those in summer. In winter, not only dual isotopic compositions of nitrate but also the ammonium and nitrate dry deposition fluxes were relatively uniform, demonstrating a persistent influence of fossil fuel combustion sourced from Asian continental outflows via the northeasterly monsoon winds. More variable isotopic values in summer likely suggest varying sources and dynamical formation processes of dry deposition nitrate. Biomass burning and lightning are suggested to be responsible for the observed higher δ15NNO3 values in summer. Atmospheric nitrate and ammonium deposition together was estimated to be ∼50 mmol N m−2 year−1, with the dominance of nitrate in dry deposition but ammonium slightly higher in wet deposition. If not including this additional fertilization of atmospheric inorganic nitrogen deposition to enhance the carbon sequestration, CO2 release out of the SCS would be double than that of the present amount, 460 ± 430 mmol C m−2 year−1. Our study demonstrates that atmospheric deposition may serve as an important external Nr supplier to the SCS; however it is difficult to separate the isotopic signal from N2 fixation (−2–0‰) due to their similarity in δ15NNO3. More studies related to isotopic composition of nitrogen speciation in atmospheric Nr deposition, their relative contributions and source identification, and the role of typhoons in the SCS are required.

Sinks for inorganic nitrogen deposition in forest ecosystems with low and high nitrogen deposition in China.

We added the stable isotope 15N in the form of (15NH4)2SO4 and K15NO3 to forest ecosystems in eastern China under two different N deposition levels to study the fate of the different forms of deposited N. Prior to the addition of the 15N tracers, the natural 15N abundance ranging from −3.4‰ to +10.9‰ in the forest under heavy N deposition at Dinghushan (DHS), and from −3.92‰ to +7.25‰ in the forest under light N deposition at Daxinganling (DXAL). Four months after the tracer application, the total 15N recovery from the major ecosystem compartments ranged from 55.3% to 90.5%. The total 15N recoveries were similar under the (15NH4)2SO4 tracer treatment in both two forest ecosystems, whereas the total 15N recovery was significantly lower in the subtropical forest ecosystem at DHS than in the boreal forest ecosystem at DXAL under the K15NO3 tracer treatment. The 15N assimilated into the tree biomass represented only 8.8% to 33.7% of the 15N added to the forest ecosystems. In both of the tracer application treatments, more 15N was recovered from the tree biomass in the subtropical forest ecosystem at DHS than the boreal forest ecosystem at DXAL. The amount of 15N assimilated into tree biomass was greater under the K15NO3 tracer treatment than that of the (15NH4)2SO4 treatment in both forest ecosystems. This study suggests that, although less N was immobilized in the forest ecosystems under more intensive N deposition conditions, forest ecosystems in China strongly retain N deposition, even in areas under heavy N deposition intensity or in ecosystems undergoing spring freezing and thawing melts. Compared to ammonium deposition, deposited nitrate is released from the forest ecosystem more easily. However, nitrate deposition could be retained mostly in the plant N pool, which might lead to more C sequestration in these ecosystems.

陕西省不同生态区大气氮素干湿沉降的时空变异

PDF HTML阅读 XML下载 导出引用 引用提醒 陕西省不同生态区大气氮素干湿沉降的时空变异 DOI: 10.5846/stxb201211011517 作者: 作者单位: 西北农林科技大学资源环境学院,西北农林科技大学资源环境学院,陕西省长安区气象局,中国农业大学,陕西省气象局,西北农林科技大学资源环境学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（40675006） Spatial-temporal variability of dry and wet deposition of atmospheric nitrogen in different ecological regions of Shaanxi Author: Affiliation: College of Resources and Environmental Sciences,Northwest A F University,Yangling Shaanxi,College of Resources and Environmental Sciences,Northwest A F University,Yangling Shaanxi,Weather Bureau of Changan District,Xi’an,China Agricultural University,Weather Bureau of Shaanxi Province,Xi’an,College of Resources and Environmental Sciences,Northwest A F University,Yangling Shaanxi Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为研究陕西省不同生态区大气氮素干湿沉降的时空变化规律，于2009年11月至2010年10月对4个生态区5个监测点的干湿沉降输入量进行为期1a的观测。结果表明：监测期内，榆林、洛川、西安、杨凌和安康地区总N沉降量分别为4.7、11.9、25.8、31.9和19.2 kg/hm2，其中N湿沉降量分别为2.9、10.4、24.8、27.7和16.3 kg/hm2，占总沉降的62%-96%，N干沉降量分别为1.8、1.5、1.0、4.1和2.9 kg/hm2，占4%-38%，且湿沉降与降雨量之间呈正相关关系，干沉降与之相反；各地区NH4+-N沉降量分别为2.0、6.4、17.0、17.2和11.9 kg/hm2，占总沉降的44%-66%，NO3--N沉降量分别为2.6、5.5、8.8、14.7和7.3 kg/hm2，占34%-56%，除榆林地区外，其他地区以NH4+-N沉降为主。 Abstract:The objective of this experiment was to study the spatial-temporal variability of dry and wet deposition of atmospheric nitrogen in different ecological regions of Shaanxi Province. Measurements were made at five monitoring sites in four different ecological regions from November 2009 to October 2010. The amounts of total inorganic nitrogen (TIN) deposition were 4.7 kg/hm2 at Yulin, 11.9 kg/hm2 at Luochuan, 25.8 kg/hm2 at Xi'an, 31.9 kg/hm2 at Yangling, and 19.2 kg/hm2 at Ankang. Wet deposition accounted for 62 to 96% of the TIN deposition, ranging from 2.9 kg/hm2 at Yulin, 10.4 kg/hm2 at Luochuan, 24.8 kg/hm2 at Xi'an, 27.7 kg/hm2 at Yangling, and 16.3 kg/hm2 at Ankang. Dry deposition accounted for 4 to 38% of the TIN deposition, ranging from 1.8 kg/hm2 at Yulin, 1.5 kg/hm2 at Luochuan, 1.0 kg/hm2 at Xi'an, 4.1 kg/hm2 at Yangling, and 2.9 kg/hm2 at Ankang. Wet deposition and rainfall were positively correlated, whereas dry deposition and rainfall were negatively correlated. Ammonium nitrogen (NH4+-N) deposition amounts were 2.0 kg/hm2 at Yulin, 6.4 kg/hm2 at Luochuan, 17.0 kg/hm2 at Xi'an, 17.2 kg/hm2 at Yangling, and 11.0 kg/hm2 at Ankang. These amounts accounted for 44 to 66% of the TIN deposition. Nitrate nitrogen (NO3--N) amounts were 2.6 kg/hm2 at Yulin, 5.5 kg/hm2 at Luochuan, 8.8 kg/hm2 at Xi'an, 14.7 kg/hm2 at Yangling, and 7.3 kg/hm2 at Ankang. These amounts made up 34 to 56% of the TIN deposition. Nitrogen deposition is mainly in the form of NH4+-N in all regions except Yulin. 参考文献 相似文献 引证文献

Nitrogen deposition and its spatial pattern in main forest ecosystems along north-south transect of eastern China

A continuous three-year observation (from May 2008 to April 2011) was conducted to characterize the spatial variation of dissolved inorganic nitrogen (DIN) deposition at eight main forest ecosystems along the north-south transect of eastern China (NSTEC). The results show that both throughfall DIN deposition and bulk DIN deposition increase from north to south along the NSTEC. Throughfall DIN deposition varies greatly from 2.7 kg N/(ha·yr) to 33.0 kg N/(ha·yr), with an average of 10.6 kg N/(ha·yr), and bulk DIN deposition ranges from 4.1 kg N/(ha·yr) to 25.4 kg N/(ha·yr), with an average of 9.8 kg N/(ha·yr). NH4 -N is the dominant form of DIN deposition at most sampling sites. Additionally, the spatial variation of DIN deposition is controlled mainly by precipitation. Moreover, in the northern part of the NSTEC, bulk DIN deposition is 17% higher than throughfall DIN deposition, whereas the trend is opposite in the southern part of the NSTEC. The results demonstrate that DIN deposition would likely threaten the forest ecosystems along the NSTEC, compared with the critical loads (CL) of N deposition, and DIN deposition in this region is mostly controlled by ag- ricultural activities rather than industrial activities or transportation.

Indications of nitrogen-limited methane uptake in tropical forest soils

Abstract. It is estimated that tropical forest soils contribute 6.2 Tg yr−1 (28%) to global methane (CH4) uptake, which is large enough to alter CH4 accumulation in the atmosphere if significant changes would occur to this sink. Elevated deposition of inorganic nitrogen (N) to temperate forest ecosystems has been shown to reduce CH4 uptake in forest soils, but almost no information exists from tropical forest soils even though projections show that N deposition will increase substantially in tropical regions. Here we report the results from two long-term, ecosystem-scale experiments in which we assessed the impact of chronic N addition on soil CH4 fluxes from two old-growth forests in Panama: (1) a lowland, moist (2.7 m yr−1 rainfall) forest on clayey Cambisol and Nitisol soils with controls and N-addition plots for 9–12 yr, and (2) a montane, wet (5.5 m yr−1 rainfall) forest on a sandy loam Andosol soil with controls and N-addition plots for 1–4 yr. We measured soil CH4 fluxes for 4 yr (2006–2009) in four replicate plots (40 m × 40 m each) per treatment using vented static chambers (four chambers per plot). CH4 fluxes from the lowland control plots and the montane control plots did not differ from their respective N-addition plots. In the lowland forest, chronic N addition did not lead to inhibition of CH4 uptake; instead, a negative correlation of CH4 fluxes with nitrate (NO3–) concentrations in the mineral soil suggests that increased NO3– levels in N-addition plots had stimulated CH4 consumption and/or reduced CH4 production. In the montane forest, chronic N addition also showed negative correlation of CH4 fluxes with ammonium concentrations in the organic layer, which suggests that CH4 consumption was N limited. We propose the following reasons why such N-stimulated CH4 consumption did not lead to statistically significant CH4 uptake: (1) for the lowland forest, this was caused by limitation of CH4 diffusion from the atmosphere into the clayey soils, particularly during the wet season, as indicated by the strong positive correlations between CH4 fluxes and water-filled pore space (WFPS); (2) for the montane forest, this was caused by the high WFPS in the mineral soil throughout the year, which may not only limit CH4 diffusion from the atmosphere into the soil but also favour CH4 production; and (3) both forest soils showed large spatial and temporal variations of CH4 fluxes. We conclude that in these extremely different tropical forest ecosystems there were indications of N limitation on CH4 uptake. Based on these findings, it is unlikely that elevated N deposition on tropical forest soils will lead to a rapid reduction of CH4 uptake.

Atmospheric Nitrogen Deposition at Two Sites in an Arid Environment of Central Asia

Arid areas play a significant role in the global nitrogen cycle. Dry and wet deposition of inorganic nitrogen (N) species were monitored at one urban (SDS) and one suburban (TFS) site at Urumqi in a semi-arid region of central Asia. Atmospheric concentrations of NH3, NO2, HNO3, particulate ammonium and nitrate (pNH4 + and pNO3 −) concentrations and NH4-N and NO3-N concentrations in precipitation showed large monthly variations and averaged 7.1, 26.6, 2.4, 6.6, 2.7 µg N m−3 and 1.3, 1.0 mg N L−1 at both SDS and TFS. Nitrogen dry deposition fluxes were 40.7 and 36.0 kg N ha−1 yr−1 while wet deposition of N fluxes were 6.0 and 8.8 kg N ha−1 yr−1 at SDS and TFS, respectively. Total N deposition averaged 45.8 kg N ha−1 yr−1at both sites. Our results indicate that N dry deposition has been a major part of total N deposition (83.8% on average) in an arid region of central Asia. Such high N deposition implies heavy environmental pollution and an important nutrient resource in arid regions.

Exploring the long-term response of undisturbed Mediterranean catchments to changes in atmospheric inputs through time series analysis

The aim of this study was to gain insights on the potential hydrological and biogeochemical mechanisms controlling the response of two nested Mediterranean catchments to long-term changes in atmospheric inorganic nitrogen and sulphate deposition. One catchment was steep and fully forested (TM9, 5.9ha) and the other one had gentler slopes and heathlands in the upper part while side slopes were steep and forested (TM0, 205ha). Both catchments were highly responsive to the 45% decline in sulphate concentration measured in atmospheric deposition during the 1980s and 1990s, with stream concentrations decreasing by 1.4 to 3.4μeqL−1y−1. Long-term changes in inorganic nitrogen in both, atmospheric deposition and stream water were small compared to sulphate. The quick response to changes in atmospheric inputs could be explained by the small residence time of water (4–5months) in these catchments (inferred from chloride time series variance analysis), which was attributed to steep slopes and the role of macropore flow bypassing the soil matrix during wet periods. The estimated residence time for sulphate (1.5–3months) was substantially lower than for chloride suggesting unaccounted sources of sulphate (i.e., dry deposition, or depletion of soil adsorbed sulphate). In both catchments, inorganic nitrogen concentration in stream water was strongly damped compared to precipitation and its residence time was of the order of decades, indicating that this essential nutrient was strongly retained in these catchments. Inorganic nitrogen concentration tended to be higher at TM0 than at TM9 which was attributed to the presence of nitrogen fixing species in the heathlands. Our results indicate that these Mediterranean catchments react rapidly to environmental changes, which make them especially vulnerable to changes in atmospheric deposition.

Concentration, solubility and deposition flux of atmospheric particulate nutrients over the Yellow Sea

Satellite images showed that two large dust storms swept over the Yellow Sea from 31 Mach to 1 April 2007; both were accompanied by precipitation. Three to four days after the dust episodes, blooms occurred in the Yellow Sea. As an important and potential controlling factor of the bloom, nutrients in the total suspended particle (TSP) and size-segregated particle samples during the cruise campaign were measured and their atmospheric deposition fluxes of nutrients are reported in this paper. Concentrations of total P and TIN (NH4+, NO2− and NO3−) in TSP varied from 0.01 to 1.05μgm−3, and from 1.21 to 22.28μgm−3, with the maximum occurring concurrently with the dust storm events. In addition, the measured solubility of Fe in these particles varied from 1.0 to 20.1%, while it ranged from 0.8 to 15% for Al. The total deposition fluxes of Asian dust as well as the contained nutrients were estimated on the basis of an episodic increment of the measured concentration of dissolved Al in the surface ocean during the dust events. The estimated fluxes of atmospheric deposition of soluble Fe, P and inorganic nitrogen over the Yellow Sea during the dust episodes were 42.5±10.9, 10.3±2.6 and 772.0±198.0mgm−2, respectively. The estimated fluxes of nutrients via dry atmospheric deposition accounted for only ~2% of the total fluxes. The deposition fluxes of particulate Fe and P during the two dust storm events associated with precipitation were about 500–1000 times of that daily averaged flux during non-dust days, indicating the importance of the episodic inputs to the annual budget of these metals deposited into the ocean.

Soil microbial community indices as predictors of soil solution chemistry and N leaching in Picea abies (L.) Karst. forests in S. Sweden

High rates of inorganic nitrogen (N) deposition or internal N turnover increases the risks of N loss from forests with negative effects on stream water quality. We hypothesized that soil fungi may be more important N sinks than bacteria, and thus examined the impact of soil microbial community composition on N leaching from forests. We studied 19 spruce stands to examine relationships between microbial community composition, stem growth, soil-, and lysimeter-collected soil solution characteristics, and N leaching. We used nitrate concentration in the soil solution below the rooting zone as an N leaching index and phospholipid fatty acid (PLFA) analysis for characterisation of microbial communities. Microbial community composition in the organic horizon and soil solution chemistry below the rooting zone was highly correlated. Stands with low concentrations of nitrate (NO3 −) and aluminium (Al) had higher fungi: bacteria ratio compared with stands with higher concentrations of NO3 − and Al. Stem growth and fungi: bacteria ratio explained 70 % of the variation in N and Al leaching. We identified three microbial predictors of variation in soil solution chemistry, of which the fungi: bacteria was the strongest. The other two were putative indicators of microbial C limitation, a condition known to stimulate N mineralisation and nitrification.

Atmospheric deposition of nitrogen and sulfur and preferential canopy consumption of nitrate in forests of the Pacific Northwest, USA

Wet, dry and throughfall deposition of N and S were measured for 2years in three national parks in Washington State: Olympic, Mount Rainier, and North Cascades. Throughfall was measured using ion exchange resin (IER) collectors. A major objective of the study was to evaluate the effectiveness of IER throughfall measurements for monitoring deposition inputs, including cloudwater deposition, to forest stands in national parks and other protected areas. Wet deposition (0.9–2.0kgNha−1yr−1) and throughfall (0.5–1.2kgNha−1yr−1) deposition of inorganic N in the three parks were relatively low. Wet deposition of sulfur (1.0–3.2kgha−1yr−1) was similar to wet deposition of inorganic nitrogen except at OLYM where wet deposition of S was higher than for N because of marine sources of SO4–S. Throughfall N deposition was lower than wet deposition of N because of strong preferential canopy consumption of nitrate (NO3–N), particularly during the wet winter periods. This phenomenon was previously reported for forests in this region, but its apparent near ubiquity in the region had not been recognized. Data on preferential canopy retention of NO3–N from wet-deposited N is shown for 38 stands in the Pacific Northwest of which 21 are newly-reported data. Deposition of NO3–N in throughfall at MORA and NOCA was reduced by 87% and 93% compared to wet deposition over the 2years. In contrast, wet deposition of NH4–N was generally increased by passage through the canopy. This strong preferential canopy retention of wet-deposited NO3–N limits the usefulness of throughfall measurements as a N deposition monitoring approach in forests of the Pacific Northwest region of North America and in some other regions with low to moderate N deposition. As a potential remedy to this limitation, a simple method is proposed for estimating total N deposition in the study sites based on S/N ratios in wet deposition and throughfall S deposition.

Inorganic Nitrogen Deposition and Its Impacts on N:P-Ratios and Lake Productivity

The pronounced increase in the cycling and deposition of biologically reactive dissolved inorganic nitrogen (DIN) over large areas globally not only cause increased concentrations of DIN in surface waters, but it will also affect nutrient ratios in rivers, lakes and coastal areas. This review addresses the flux and fate of DIN, focusing NO3 in lakes of boreal and alpine catchments. Not only DIN-deposition, but also catchment properties strongly affect the concentrations of NO3 in lakes, as well as NO3:total P (TP) ratios. This ratio displays an extreme variability, and does also serve as an indicator of shift between N and P-limitation of aquatic autotrophs. A high share of forests and bogs in the catchment generally decreases NO3:total P ratios, while alpine and subalpine catchments with sparse vegetation cover may have high NO3:total P ratios, especially in regions with high DIN-deposition. Several empirical and experimental studies indicate a shift from an initial N to P-limitation, but for N-limited lakes, an increased growth of phytoplankton, periphytes and macrophytes may be accredited to elevated inputs of DIN. An intensified P-limitation may also be a consequence of elevated DIN-deposition. This P-limitation may again yield higher C:P-ratios in autotrophs with negative impacts on grazers and higher trophic levels.

Responses of soil microbial biomass and enzymatic activities to different forms of organic nitrogen deposition in the subtropical forests in East China

AbstractNumerous studies reported that inorganic nitrogen (N) deposition strongly affected forest ecosystems. However, organic N is also an important component of atmospheric N deposition. The influence of organic N deposition on soil microbial biomass and extracellular enzymatic activities (EEA) in subtropical forests remains unclear. Coniferous forest (CF) and broad‐leaved forest (BF) were chosen from the Zijin Mountain in China. Five forms of organic N (urea, glycine, serine, nonylamine, and a mixture of all four) were used to fertilize the soils in CF and BF every month for 1 year. Soil samples were collected every 2 months. Subsequently, soil microbial biomass and EEA were assayed. Results showed that the microbial biomass and EEA of soils fertilized with urea and amino acids increased significantly, whereas those fertilized with nonylamine and mixed N decreased significantly. Urea and amino acid fertilizations had a more positive influence on EEA of BF than on those of CF. Nonylamine fertilization had a more negative influence on EEA of CF than on those of BF. Organic N fertilization shifted soil microbial biomass away from the excretion of N‐degrading enzymes and toward the excretion of C‐degrading enzymes. These results suggest that organic N type is an important factor that affects soil microbial biomass, EEA, and their relationship. Organic N deposition may seriously affect soil C and N cycling, as well as carbon dioxide releasing from the soils by influencing microbial activities and biomass. This study thereby provides evidence that soil microorganisms have strong feedback to different forms of organic N deposition.

Evaluation of deposition fluxes in two mountain Norway spruce stands with different densities using the extended Canopy Budget Model

The field study in a mountain forest at Bílý Kříž provides a comparison of element fluxes for two adjacent forest spruce stands of the same age (29 years in 2005) but with different stem densities. During five years (2001–2005), bulk and throughfall precipitation was sampled and analysed. Total deposition, dry deposition and canopy exchange fluxes were evaluated on the basis of the Canopy Budget Model. Highly significant differences in base cations, dissolved organic carbon, SO<sub>4</sub><sup>2−</sup>, F<sup>−</sup>, and Cl<sup>−</sup> throughfall concentrations were found between the sparser and denser spruce stands.  Throughfall, dry deposition and canopy exchange fluxes were also influenced by stand density. Annual throughfall fluxes of inorganic nitrogen were within 11.9–17.8 kg N·ha<sup>–1</sup>·yr<sup>–1</sup> on the sparser plot and within 15.4–20.6 kg N·ha<sup>–1</sup>·yr<sup>–1</sup> on the denser plot; annual throughfall fluxes of sulphur were within 15.3–20.3 kg S·ha<sup>–1</sup>·yr<sup>–1</sup> on the sparser plot and within 20.7–27.7 kg S·ha<sup>–1</sup>·yr<sup>–1</sup>on the denser plot. The critical load for nitrogen (11.2 kg N·ha<sup>–1</sup>·yr<sup>–1</sup>) was exceeded on both plots in all evaluated years 2002–2005.  Total annual inorganic nitrogen deposition was higher by up to 37.5% (in 2002) on the denser plot than on the sparser one.

Impact of declining atmospheric deposition on forest soil solution chemistry in Flanders, Belgium

Throughout Europe and the USA, forest ecosystem functioning has been impacted by long-term excessive deposition of acidifying compounds. In this study, we report on trends in stand deposition and soil solution fluxes of inorganic nitrogen (N) and sulphur (S) compounds over a 17-year period (1994–2010) in five ICP Forests monitoring plots in Flanders, northern Belgium. Deposition was dominated by N, and primarily NH4+. Deposition of SO42− and NH4+ declined by 56–68% and 40–59% respectively. Deposition of NO−3 decreased by 17–30% in deciduous forest plots, but remained stable in coniferous forest plots. The decrease of N and S deposition was parallelled by a simultaneous decline in base cation (BC = Ca2+ + K+ + Mg2+) deposition, resulting in a 45–74% decrease of potentially acidifying deposition. Trends in soil solution fluxes of NH4+, NO3−, SO42− and BC mirrored declining depositions. Nitrate losses below the rooting zone were eminent in both coniferous forest plots and in one deciduous forest plot, while net SO42− release was observed in two deciduous forest plots. Critical limits for BC/Al ratio were exceeded at the three plots on sandy soils with lower cation exchange capacity and base saturation. Soil solution acid neutralizing capacity increased but remained negative, indicating that soil acidification continued, as the start of recovery was delayed by a simultaneous decrease of BC depositions and short-term soil buffering processes. Despite substantial reductions, current N deposition levels still exceed 4–8 times the critical load for safeguarding sensitive lichen species, and are still 22–69% above the critical load for maintaining ground vegetation diversity.

Impact of atmospheric nitrogen deposition on soil properties and herb-layer diversity in remnant forests along an urban–rural gradient in Guangzhou, southern China

Atmospheric nitrogen (N) deposition in subtropical metropolitan regions has increased greatly because of rapid urbanization, and such increase could lead to N-related changes in soil properties and plant diversity in remnant forests of urban ecosystems. To investigate the pattern of atmospheric N deposition along an urban–rural gradient in metropolitan Guangzhou, southern China, and to assess the potential influence of N deposition on soil properties and understory plant diversity in remnant forests, precipitation, and soil samples were collected and vegetation was surveyed from four forest sites between March 2010 and March 2011. The atmospheric inorganic nitrogen deposition (DIN) decreased with increasing distance from the urban center: DIN inputs were 43.3, 41.2, 35.2, and 30.1 kg N ha−1 year−1 in two urban sites, a suburban site and a rural site, respectively. However, forest soil N status (NH4 +-N, NO3 −-N, and total nitrogen) showed the opposite pattern. Understory herb-layer diversity was negatively correlated to DIN input and positively correlated to soil calcium (Ca) and potassium (K) concentrations and pH; with highest herb-layer diversity found in the rural site receiving the lowest amount of DIN input. These results indicated that higher DIN along with soil acidification and leaching of base cations (Ca and K) might change the current N status and increase nutrients leaching and thereby cause reductions in understory plant diversity. A regional policy linking atmospheric pollution and land protection is needed to protect the most N-sensitive herb species (e.g., forbs and ferns) in these remnant forests.

Monitoring nitrogen deposition in typical forest ecosystems along a large transect in China

The nitrogen (N) deposition fluxes were investigated in eight typical forest ecosystems along the North-South Transect of Eastern China (NSTEC; based on the ChinaFLUX network) by ion-exchange resin (IER) columns from May 2008 to April 2009. Our results demonstrated that the method of IER columns was both labor cost saving and reliable for measuring dissolved inorganic nitrogen (DIN) deposition at the remote forest stations. The deposition of DIN in the throughfall ranged from 1.3 to 29.5 kg N ha(-1) a(-1), increasing from north to south along NSTEC. The relatively high average ratio of ammonium to nitrate in deposition (1.83) indicated that the N deposition along the NSTEC in China mostly originated in farming and animal husbandry rather than in industry and vehicle activities. For seasonal variability, the DIN deposition showed a single peak in the growing season in the northern part of NSTEC, while, in the southern part, it exhibited double-peaks in the early spring and the mid-summer, respectively. On the annual scale, the DIN deposition variations of the eight sites could be mainly explained by precipitation and the distances from forest stations to provincial capital cities.

The role of nitrogen deposition in the recent nitrate decline in lakes and rivers in Northern Italy

Deposition of inorganic nitrogen (N) in north-western Italy is around 20–25kgNha−1y−1, and has remained constant during the last 30years. This flux of N caused saturation of terrestrial catchments and increasing levels of nitrate (NO3) in surface waters. Recently, monitoring data for both rivers and lakes have shown a reversal in NO3 trends. This change was widespread, affecting high-altitude lakes in the Alps and subalpine lakes and rivers, and occurred at almost the same time at all sites. The seasonal pattern of NO3 concentrations in running waters has shown a change in the last few years, with a tendency towards slightly lower leaching of NO3 during the growing season. Atmospheric input of N has also shown a recent decrease, mainly due to decreasing emissions and partly to the lower amount of precipitation occurring between 2003 and 2009. Surface waters are probably responding to these changing N inputs, but a further decrease of N deposition, especially reduced N, will be required to achieve full recovery from N saturation.

Modelling changes in nitrogen emissions into the Oder River System 1875–1944

Studies of nutrient emissions into surface waters are usually only performed for years in recent decades. However, estimating nutrient emissions for the more distant past enables us to identify the main factors responsible for the increasing nutrient contamination since the end of the nineteenth century. We focussed on the Oder River System for 1875–1944, divided into 10-year periods. Nutrient emissions into surface waters were calculated with the model MONERIS (MOdelling Nutrient Emissions in RIver Systems). For seven different pathways and eight sources, the total nitrogen (TN) emissions were quantified. The TN-emissions into the surface waters for 1880 amounted to 25,300 t year−1, and by 1940, this value had almost doubled to 46,600 t year−1. In 1880, 57% of TN-emissions into the surface waters derived from urban systems, due to the high amount of untreated waste water. In 1940, only 34% of TN-emissions into surface waters derived from urban systems, despite a population growth of about 27% since 1880; point sources via newly constructed waste water treatment plants (WWTPs) increased from 4% (1880) to 26% (1940). During the study period, the main changes in diffuse TN-emissions from agriculture were caused by inorganic fertilizer application and nitrogen deposition, while TN-emissions via urban sources were shifted to point sources due to population growth and the construction of new WWTPs. Furthermore, estimated TN-concentrations could make a contribution to construct benchmarks for nutrient concentrations according to the physiochemical properties to implement the European Water Framework Directive (WFD 2000).

Trends in atmospheric nitrogen and sulphur deposition in northern Belgium

Abstract Temporal trends (2002–2009) in air concentrations and wet and dry atmospheric deposition of inorganic nitrogen (N) and sulphur (S) were determined for nine stations in northern Belgium (Flanders). Wet deposition of NH 4 + , NO 3 − and SO 4 2− was measured with wet-only precipitation collectors and air concentrations of NH 3 , NO 2 and SO 2 with passive samplers. Dry deposition was calculated from the air concentrations and literature-based deposition velocities. Generalized additive models were used to assess seasonal and long-term trends of biweekly measurements. Kendall tests on annual data were also applied but found to be less powerful. There was no trend in wet N deposition, while wet deposition of SO 4 2− and air concentrations of NH 3 and SO 2 decreased significantly ( P 2 , no significant long-term trend was detected, but opposite to the other compounds, the NO 2 concentration tended to increase at all stations. Overall, inorganic N deposition and potentially acidifying deposition (N + S) to grassland decreased significantly at seven stations. The N and N + S deposition to grassland in 2009 was generally below deposition targets for 2010, but the difference was not significant when accounting for data uncertainty using a bootstrap resampling procedure. For most stations, atmospheric deposition to heathland and deciduous forest insignificantly exceeded the targets, while deposition to coniferous forest was significantly too high. Consequently, additional policy measures are needed to reach deposition targets in order to prevent further eutrophication and acidification of (semi)natural ecosystems and to protect groundwater layers in Flanders.

Atmospheric dry deposition of inorganic and organic nitrogen to the Bay of Bengal: Impact of continental outflow

The continental outflow from south and south-east Asia, persisting during January to March, dominates the widespread dispersal of pollutants over tropical Bay of Bengal. With a view to assess the impact of anthropogenic sources on surface ocean biogeochemistry, concentrations of water-soluble inorganic and organic nitrogen (N Inorg, N Org), their spatial variability and dry-deposition fluxes have been studied in two size fractions (PM 2.5 and PM 10) collected during Jan-2009 from the MABL of Bay of Bengal. The mass concentration of N Inorg (NH 4 + + NO 3 −, range: 18 to 565 nmol m − 3 ) dominates the total soluble nitrogen (N Tot = N Inorg + N Org,) in the fine mode (PM 2.5), and occurs mainly as NH 4 + (range: 16 to 561 nmol m − 3 ). The mass-ratio of N Inorg in PM 2.5 to PM 10 centers around 0.85, suggesting that contribution of coarse mode NO 3 − is relatively insignificant. The dominant contribution of N Inorg (as NH 4 +) to N Tot is also evident based on the data from earlier cruises (Feb–Mar-2001, Feb-2003 and Mar–Apr-2006) conducted in the Bay of Bengal. Water-soluble N Org also dominates the fine fraction and accounts for no more than 40% of N Tot, with relatively high concentrations along coastal regions. A significant linear relationship among N Org, NH 4 +, nss-K + and EC (p-value < 0.001) suggest their common source from biomass burning emissions and large-scale application of fertilizers (urea). The dry-deposition flux of nitrogen (N Inorg + N Org) to the Bay of Bengal ranges from 2 to 167 μmol m − 2 d − 1 . The upper estimate of N-deposition is somewhat comparable with the model based fluxes, and can support up to 13% of the Primary Production in the Bay of Bengal.