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10 results for “atmospheric nitrogen deposition”
International Long-Term Ecological Research Network (ILTER) Atmospheric Deposition and Stream Nitrogen Synthesis
We identified variables controlling stream nitrogen concentrations and fluxes, and how they have changed over time, by synthesizing 20 time series ranging from 5 to 51 years of data collected from forest and grassland dominated watersheds across Europe, North America, and East Asia and across four climate types (tropical, temperate, Mediterranean, and boreal) using the International Long-Term Ecological Research Network. We found declining trends in bulk ammonium and nitrate deposition, with ammonium contributing significantly more to atmospheric nitrogen deposition over time. Among sites, there were significant positive relationships between (1) precipitation and stream ammonium and nitrate fluxes and (2) atmospheric nitrogen inputs and stream nitrogen concentrations and fluxes. There were no significant relationships between air temperature and stream nitrogen export. Our long-term data shows that although nitrogen deposition is declining over time, atmospheric nitrogen inputs and precipitation remain the main predictors for nitrogen exported from forested and grassland watersheds. Overall, we also demonstrate that long-term monitoring provides understanding of ecosystems and biogeochemical cycling that would not be possible with short-term studies alone. Acknowledgements: We thank the organizers and funders of the ILTER Nitrogen Initiative Training Course and Workshop in Hokkaido, Japan in June 2016, which brought together many of the participants in this project. Templer was supported by a US National Science Foundation LTER grant NSF DEB 1637685. McDowell was supported by US National Science Foundation LTER grant NSF DEB 1831592. We are grateful to the EU Horizon 2020 funded eLTER PLUS project (Grand Agreement No. 871128) for financial support to Haase and Dirnböck. Dirnböck was also funded by the LTER-CWN project (FFG project number 858024). This study was partly supported by the Research Initiative Grants of the ILTER, Grants-in-Aid for Scientific Research (1
Denitrification rates in lake sediments of mountains affected by high atmospheric nitrogen deposition
<p>During the last decades, atmospheric nitrogen loading in mountain ranges of the Northern Hemisphere has increased substantially, resulting in high nitrate concentrations in many lakes. Yet, how increased nitrogen has affected denitrification, a key process for nitrogen removal, is poorly understood. We measured actual and potential (nitrate and carbon amended) denitrification rates in sediments of several lake types and habitats in the Pyrenees during the ice-free season. Actual denitrification rates ranged from 0 to 9 μmol N<sub>2</sub>O m<sup>−2</sup> h<sup>−1</sup> (mean, 1.5 ± 1.6 SD), whereas potential rates were about 10-times higher. The highest actual rates occurred in warmer sediments with more nitrate available in the overlying water. Consequently, littoral habitats showed, on average, 3-fold higher rates than the deep zone. The highest denitrification potentials were found in more productive lakes located at relatively low altitude and small catchments, with warmer sediments, high relative abundance of denitrification nitrite reductase genes, and sulphate-rich waters. We conclude that increased nitrogen deposition has resulted in elevated denitrification rates, but not sufficiently to compensate for the atmospheric nitrogen loading in most of the highly oligotrophic lakes. However, there is potential for high rates, especially in the more productive lakes and landscape features largely govern this.</p>
Data and code for: Influence of atmospheric nitrogen deposition on soil greenhouse gas fluxes from forests in China and the world
<p><span>Since the industrial revolution, greenhouse gas emissions (particularly CO<sub>2</sub>, CH<sub>4</sub>, and N<sub>2</sub>O) caused by human activities have accelerated global climate change. To avoid catastrophic transitions in the Earth system, many countries including China have set goals to achieve “net zero emission” (or “carbon neutrality”) by mid-21<sup>st</sup> century. Forestland-related practices are among the most preferred “natural climate solutions”. However, high uncertainties remain in the greenhouse gas fluxes from forest soils, because of the limited capability to observe soil dynamics at a large spatial scale. Meanwhile, forest soil greenhouse gas fluxes are influenced by multiple anthropogenic environmental changes including enhanced atmospheric nitrogen deposition, which further complicates the interactions between forest ecosystem and the atmosphere. During the past half century, simulated nitrogen deposition (or “nitrogen addition”) experiments have been conducted in various forest sites worldwide, founding a basis for quantifying the spatially-varying responses of soil greenhouse gas flux to nitrogen deposition. </span></p> <p><span>In this research, we systematically synthesized global nitrogen addition experiment data from published literature and public databases, using which we explored the responses of the three major greenhouse gases to N input. Derived sensitivity of soil N<sub>2</sub>O emission to N deposition allowed for determining the N saturation (or limitation) status of global forests. Using process-augmented data-driven approach and random forest regression models, we estimated soil greenhouse gas budgets on regional and global levels. On the basis, we quantified the varying effects of N deposition on soil greenhouse gas fluxes in N-limited and N-saturated forests across biomes. </span><span> </span></p> <p><span>The produced global map of N-saturated forests in this research could facilitate studies on carbon and nitrogen cycles and improve forest nitrogen management. The revealed response patterns and response factors of soil greenhouse gases to N input could help improve the structure and parameters of ecosystem models. Furthermore, the localized N<sub>2</sub>O emission factors for 145 countries could be used to reduce the uncertainties in their national greenhouse gas inventories. The “process-augmented data-driven” approach could potentially bridge the gap between site-level manipulative experiments and the demand for regional greenhouse gas budgets, allowing manipulative experiments to play a more important role in global change research. </span></p>
Data from: Patterns and drivers of atmospheric nitrogen deposition retention in global forests
<p>Forests are the largest carbon sink in terrestrial ecosystems, and the impact of nitrogen (N) deposition on this carbon sink depends on the fate of external N inputs. However, the patterns and driving factors of N retention in different forest compartments remain elusive. In this study, we synthesized 408 observations from global forest <sup>15</sup>N tracer experiments to reveal the variation and underlying mechanisms of <sup>15</sup>N retention in plants and soils. The results showed that the average total ecosystem <sup>15</sup>N retention in global forests was 63.04 ± 1.23%, with the soil pool being the main N sink (45.76 ± 1.29%). Plants absorbed 17.28 ± 0.83% of <sup>15</sup>N, with more allocated to leaves (5.83 ± 0.63%) and roots (5.84 ± 0.44%). In subtropical and tropical forests, <sup>15</sup>N was mainly absorbed by plants and mineral soils, while the organic soil layer in temperate forests retained more <sup>15</sup>N. Additionally, forests retained more <sup>15</sup>NH<sub>4</sub><sup>+</sup> than <sup>15</sup>NO<sub>3</sub><sup>−</sup>, primarily due to the stronger capacity of the organic soil layer to retain <sup>15</sup>NH<sub>4</sub><sup>+</sup>. The mechanisms of <sup>15</sup>N retention varied among ecosystem compartments, with total ecosystem <sup>15</sup>N retention affected by N deposition. Plant <sup>15</sup>N retention was influenced by vegetative and microbial nutrient demands, while soil <sup>15</sup>N retention was regulated by climate factors and soil nutrient supply. Overall, this study emphasizes the importance of climate and nutrient supply and demand in regulating forest N retention and provides data to further explore the impacts of N deposition on forest carbon sequestration.</p>
Soil protist functional composition shifts with atmospheric nitrogen deposition in subtropical forests
<p><span>1. </span><span>Soil protist plays a key role in ecological functions through predation and parasitism. However, little is known about how nitrogen (N) deposition and seasonal variations influence soil protist function in forest soils. </span></p> <p><span>2. </span><span>Here, we assessed firstly the impacts of N deposition (control, 50 kg N ha<sup>-1</sup> yr<sup>-1</sup>, 100 kg </span><span>N ha<sup>-1</sup> yr<sup>-1</sup></span><span>, and 150 kg </span><span>N ha<sup>-1</sup> yr<sup>-1</sup></span><span>) on the functional composition of the soil protist community in summer and winter, using amplicon sequencing of environmental DNA from a subtropical natural forest. </span></p> <p><span>3. </span><span>We found that soil protists were dominated by consumers (42.6–51.6%), followed by parasites (32.9–40.9%) and phototrophs (3.2–13.1%), implying a predominant role of consumers and potential top-down effects on the other trophic groups in subtropical forest soils. The functional composition of soil protists was greatly influenced by N deposition, but these responses were dependent on seasonal variations. The diversity of phototrophs was lower in summer than in winter. Instead, an opposite pattern was observed for consumers, resulting in a significantly higher protist diversity in summer than in winter, which indicates a greater sensitivity of soil protists to seasonal variations. Furthermore, low and high N deposition simplified the structural complexity of soil protist communities, suggesting a nonlinear response of the protist structural stability to N deposition.</span></p> <p><span>4. <em>Synthesis and applications.</em></span><span><em> </em>This study provides unprecedented evidence that season variation plays an important role in regulating responses of soil protist functional composition to N deposition, and highlights the nonlinear effects of rising N deposition levels on the soil food web. </span></p>
Data from: Patterns and drivers of atmospheric nitrogen deposition retention in global forests
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Soil protist functional composition shifts with atmospheric nitrogen deposition in subtropical forests
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Data from: Conditional vulnerability of plant diversity to atmospheric nitrogen deposition across the United States
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Supplementary material 1 from: Balestrini R, Delconte C, Buffagni A, Fumagalli A, Freppaz M, Calvo E, Buzzetti I (2019) Dynamic of nitrogen and dissolved organic carbon in an alpine forested catchment: atmospheric deposition and soil solution trends. In: Mazzocchi MG, Capotondi L, Freppaz M, Lugliè A, Campanaro A (Eds) Italian Long-Term Ecological Research for understanding ecosystem diversity and functioning. Case studies from aquatic, terrestrial and transitional domains. Nature Conservation 34: 41-66. https://doi.org/10.3897/natureconservation.34.30738
: Data type: statistical data
Global Maps of Atmospheric Nitrogen Deposition, 1860, 1993, and 2050
This data set provides global gridded estimates of atmospheric deposition of total inorganic nitrogen (N), NHx (NH3 and NH4+), and NOy (all oxidized forms of nitrogen other than N2O), in mg N/m2/year, for the years 1860 and 1993 and projections for the year 2050. The data set was generated using a global three-dimensional chemistry-transport model (TM3) with a spatial resolution of 5 degrees longitude by 3.75 degrees latitude (Jeuken et al., 2001; Lelieveld and Dentener, 2000). Nitrogen emissions estimates (Van Aardenne et al., 2001) and projection scenario data (IPCC, 1996; 2000) were used as input to the model. The model output grids were subdivided into 50 km x 50 km sub-grids to create spatially defined deposition maps. The gridded data were assigned to continental and marine regions using boundaries delineated on a world data coverage from ESRI (1993).The data are stored as ASCII text files (.txt), in tab delimited format. The data can be used to produce maps that illustrate both the temporal and spatial variability of atmospheric deposition of N, NHx, and NOy as well as the degree of alteration and regional heterogeneity in deposition through time. Nine data files are provided to produce the following maps:Global N Deposition (1860, 1993, and 2050)Global NHx Deposition (1860, 1993, and 2050)Global NOy Deposition (1860, 1993, and 2050).
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