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See detailNitrogen budget of the northwestern Black Sea shelf inferred from modeling studies and in situ benthic measurements
Grégoire, Marilaure ULg; Friedrich, Jana

in Marine Ecology. Progress Series (2004), 270

A 3D eddy-resolving coupled biogeochemical-hydrodynamical model and in situ observations are used to investigate benthic processes on the Black Sea's NW shelf. Measurements of benthic fluxes (oxygen ... [more ▼]

A 3D eddy-resolving coupled biogeochemical-hydrodynamical model and in situ observations are used to investigate benthic processes on the Black Sea's NW shelf. Measurements of benthic fluxes (oxygen, nutrients, redox compounds) with in situ flux chambers are analyzed in regard to sediment dynamics on the shelf. The seasonal/interannual and spatial variability of benthic processes is explained in terms of 3D ecohydrodynamics. The space/time distribution of benthic fluxes depended on the position of the river plume and the associated primary production, intensity of vertical mixing and water depth. Model results and in situ observations reveal the presence of a region of intense benthic recycling and high benthic nutrient fluxes nearshore and in the northern part of the shelf. The model estimates that this region covers about 15 % of the shelf area and is connected to the high productivity and high sedimentation caused by river input of organic matter. On the offshore shelf, covering about 85 % of the shelf area, benthic nutrient regeneration is low due to low productivity. Benthic mineralization pathways (aerobic respiration, denitrification, sulfate reduction, methanogenesis) are quantified. In the high flux region, more than 55 % and in the offshore low flux region more than 80 % of the organic matter is decomposed by aerobic respiration. In the high flux region, sulfate reduction is the main anaerobic pathway, whereas denitrification is more important on the low flux offshore shelf. At the shelf edge, under the influence of anoxic waters, more than 60 % of organic matter is remineralized by sulfate reduction. Little organic matter is decomposed by methanogenesis. A mass balance of particulate organic carbon (POC) and particulate organic nitrogen (PON), integrated over the whole shelf and year, shows that 3.7 to 4.2 x 10(6) t of POC reach the sediments, while model results give a value of 1.4 x 10(6) t C. The annual ammonium benthic outflux is estimated at 85 x 10(3) and 174 x 10(3) t N by in situ data and the model, respectively. The amount of nitrogen lost by burial and denitrification estimated from in situ observations is 57 x 10(3) and 324 x 10(3) t N, respectively. Therefore, NW shelf Black Sea sediments are an efficient sink for riverine nitrogen, trapping about 50 % of the annual river discharge in total inorganic N. [less ▲]

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See detailNitrogen budget on the shelf and slope area of the Back Sabasin as inferred from modeling experiments
Grégoire, Marilaure ULg; Beckers, Jean-Marie ULg; Friederich, J. et al

in Second International Conference on "Oceanography of the Eastern Mediterranean and Black Sea: Similarities and Differences of Two Interconnected Basins" (2002)

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See detailNitrogen deposition and nitrification in coniferous forests’
Carnol, Monique ULg

Doctoral thesis (1997)

The increased inorganic nitrogen (N) deposition in the last decades has become a major concern for the health of forest ecosystems. High anthropogenic N emissions, mainly from fossil fuel combustion and ... [more ▼]

The increased inorganic nitrogen (N) deposition in the last decades has become a major concern for the health of forest ecosystems. High anthropogenic N emissions, mainly from fossil fuel combustion and livestock agriculture, have resulted in both high gaseous concentrations and high deposition in rainfall and throughfall. In forest ecosystem, where N is no longer limiting to primary production due to high inputs, the excess N is thought to be related to forest decline and a concept of ‘N saturation ‘ has been developed. In particular, N in the form of NH4, in excess to plant and microbial demands could lead to soil acidification if nitrified in the soil and leached, causing loss of base cations or mobilisation of phytotoxic aluminium. Nutrient imbalances due to high soil solution NH4/cation ratios or damaged root systems may also occur. The fate of the incoming NH4 is central to determining the effects on the ecosystem, and is closely related to the controls of nitrification. Although this process has been intensely studied in pure cultures for some nitrifying bacteria, the organisms responsible and controlling factors in acid forest soils are still poorly understood. A better comprehension of the fate of NH4 deposition is necessary to determine ‘Critical Loads for N’, the threshold deposition not damaging to the ecosystem, which is used as a political tool for quantifying pollution limits. In this thesis, I focused on a) the effects of increased (NH4)2SO4 deposition on soil solution chemistry of six coniferous forest sites the presence of live roots, b) the impacts of (NH4)2SO4 deposition on Norway spruce (Picea abies [L.] Karst) and Scots pine (Pinus sylvestris L.) fine roots, and c) the controls of nitrification in an acid forest soil. The work was part of the CEC project ‘CORE’, investigating the effects of atmospheric pollution on nutrient turnover in soils. An identical field experiment was performed in six coniferous sites, situated in five European countries. Chronically increased NH4 deposition by 75 kg N ha-1 a-1 through (NH4)2SO4 application, demonstrated the contrasting responses of the different ecosystems. Soil solution concentrations and yearly ionic fluxes were analysed. (NH4)2SO4 treatment resulted in deposition of 79 to 93 kg N ha-1 a-1 at the different sites. In the two less acidic, clay/clay loam soils, only 6% of the added NH4 was lost through leaching. The two sandy soils lost up to 75% of the added NH4, and the two remaining sites lost ca. 25%. Leaching of added NH4 was thought to be related to soil physico-chemical characteristics, such as pH, C and N content and texture. NO3 leaching was increased at three sites, only 4-9 months after starting the (NH4)2SO4 treatment, with a maximum doubling of concentrations. One sandy soil failed to nitrify under any condition, and the other sandy soil showed high NO3 leaching under all treatments, but no increase due to increased N inputs. The presence of live roots reduced NO3 leaching in two sites, delaying the increase in soil solution NO3 concentrations in response to the (NH4)2SO4 deposition in one of them. In all nitrifying soils, soil solution NO3 concentrations were related to cation concentrations, with Al being the dominant cation in the more acid soils with low base saturation. This experiment demonstrated the importance of soil N storage capacity and nitrification potential in determining the consequences of increased NH4 deposition, and the strong relationship between NO3 and cation leaching. Ionic fluxes and soil solution chemistry were further analysed in one of the six sites (Grizedale, UK). In this Norway spruce stand on clay soil, NO3 fluxes were increased by increased (NH4)2SO4 deposition, and mainly balanced by increased Al losses. This soil had a pHH2O around 3.6, and was characterised by over 90% of the exchange complex being occupied by Al. Independent of treatment, soil solution changed from Ca to Al leaching during the 18 month field experiment, with a decrease in soil solution pH from 4.9 to 3.8. At the end of the experiment, soil solution Al concentrations were higher for the (NH4)2SO4 treatments. It was suggested that nitrification had caused the pH decrease, with a further lowering of the base saturation, linked to a abrupt increase in soil solution Al concentrations. The impacts of increased (NH4)2SO4 deposition and soil characteristics on Norway spruce root biomass and vitality, and on Norway spruce and Scots pine fine root chemistry, were investigated with an ingrowth core technique. The same experiment was performed in a Norway spruce stand on clay soil (Grizedale, UK) and a Scots pine stand on sandy soil (Wekerom, NL), using soil from each of the two sites. For Norway spruce, root biomass and numbers of fine root tips were higher in the organic than in the mineral horizon of the clay and sandy soils. This was related to higher fine root Al and lower Ca contents in the mineral horizon. Root biomass and the proportion of dead roots were higher in the clay soil, compared to the sandy soil, with higher root Al contents, despite lower soil solution Al concentrations than in the sandy soil. For Norway spruce, a negative correlation between root biomass and fine root Al content was established. Enhanced N deposition caused an increase in the total number of root tips and in the proportion of dead roots in the sandy soil. Effects of increased (NH4)2SO4 deposition on root biomass were not significant for the clay soil, yet caused increased fine root N content in the organic horizon for both species. Scots pine fine roots also showed higher Al and lower Ca contents in the mineral horizon. (NH4)2SO4 treatment caused increased fine root Al content and a decreased Mg/Al ratio in the mineral layer of the sandy soil, with opposite effects in the clay soil. This (NH4)2SO4 treatment effect in the sandy soil for Scots pine was the only indication of a potential adverse effect of (NH4)2SO4 deposition on fine roots. Results demonstrated the dominant importance of inherent soil characteristics and the stratification into soil horizons on fine root growth and chemical composition. The effects of temperature, throughfall volume and NH4 deposition on soil solution NO3 concentrations, N2O emissions and numbers of NH4 oxidisers were investigated for the Grizedale soil in a controlled laboratory experiment. Multiple regression and surface response analysis revealed temperature as the most important factor, with an optimum for NO3 leaching and numbers of NH4 oxidisers in the mineral horizon at 11°C. Volume acted independently of temperature with a minimum at 870 mm throughfall 2 weeks-1. The relatively low optimum temperature compared to other studies was explained by the minimum disturbance of the soil in the current study. NO3 fluxes increased quadratically with throughfall volume. N2O fluxes increased quadratically with temperature and throughfall volume, and showed high variability. It was suggested that the temperature optimum for net nitrification depended on the physico-chemical characteristics of the soil and on the activity of decomposers, by competition for O2 and NH4. Optimum temperatures may have been overestimated in previous studies using disturbed soils. The regression model for NO3 leaching derived from the laboratory experiment was applied to data from the previous field experiment and tested with different time intervals for temperature input parameters. A model including two-monthly mean temperatures yielded the best fit between measured and simulated values, as determined by correlation and minimum sum of squared residuals. Simulated NO3 leaching was over-estimated in the second part of the field study. The good correspondence between field temperature frequency distribution and the optimum temperature determined by the regression model, as well as the high correlation between measured and simulated values, demonstrated the adequacy of a quadratic model with a relatively low temperature optimum to describe field NO3 leaching, determined for the same soil with an identical sampling design. [less ▲]

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See detailNitrogen dynamics in Posidonia oceanica cuttings: implications for transplantation experiments
Lepoint, Gilles ULg; Vangeluwe, Denis; Eisinger, Michael et al

in Marine Pollution Bulletin (2004), 48(5-6), 465-470

A N-15 tracer study was performed during an experimental transplantation trial of natural Posidonia oceanica cuttings. The experiment was done in situ at 17 m depth in the Revellata Bay (Calvi, NW Corsica ... [more ▼]

A N-15 tracer study was performed during an experimental transplantation trial of natural Posidonia oceanica cuttings. The experiment was done in situ at 17 m depth in the Revellata Bay (Calvi, NW Corsica, France). Despite high survival rates of transplants (>90%) after one year, the weight and the N content of transplants are significantly lower than those of reference plants. In absence of roots, the transplants are not able to meet their N requirement because, leaf uptake is insufficient to replenish the N lost during the natural leaf decay. This could constitute a major cause of long-term failure for transplantation experiments or natural recolonisation processes. The increase of the N-15 content in the roots shows that the plant re-allocates the nitrogen of one organ (i.e. leaves, rhizomes) to ensure the growth of another (i.e. roots). (C) 2003 Elsevier Ltd. All rights reserved. [less ▲]

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See detailNitrogen enrichment, boron depletion and magnetic fields in slowly-rotating B-type dwarfs
Morel, Thierry ULg; Hubrig, S.; Briquet, Maryline ULg

in Astronomy and Astrophysics (2008), 481

Evolutionary models for massive stars, accounting for rotational mixing effects, do not predict any core-processed material at the surface of B dwarfs with low rotational velocities. Contrary to ... [more ▼]

Evolutionary models for massive stars, accounting for rotational mixing effects, do not predict any core-processed material at the surface of B dwarfs with low rotational velocities. Contrary to theoretical expectations, we present a detailed and fully-homogeneous, NLTE abundance analysis of 20 early B-type dwarfs and (sub)giants that reveals the existence of a population of nitrogen-rich and boron-depleted, yet intrinsically slowly-rotating objects. The low-rotation rate of several of these stars is firmly established, either from the occurrence of phase-locked UV wind line-profile variations, which can be ascribed to rotational modulation, or from theoretical modelling in the pulsating variables. The observational data presently available suggest a higher incidence of chemical peculiarities in stars with a (weak) detected magnetic field. This opens the possibility that magnetic phenomena are important in altering the photospheric abundances of early B dwarfs, even for surface field strengths at the one hundred Gauss level. However, further spectropolarimetric observations are needed to assess the validity of this hypothesis. [less ▲]

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See detailNitrogen excess in slowly-rotating beta Cephei stars: deep mixing or diffusion?
Morel, Thierry ULg; Butler, K.; Aerts, C. et al

in Communications in Asteroseismology (2007), 150

We present the results of an NLTE abundance study of a small sample of β Cephei stars, which point to the existence of a population of slowly-rotating B-type pulsators exhibiting a significant amount of ... [more ▼]

We present the results of an NLTE abundance study of a small sample of β Cephei stars, which point to the existence of a population of slowly-rotating B-type pulsators exhibiting a significant amount of nitrogen-enriched material at their surface. Although the origin of this nitrogen excess remains unclear, an overabundance preferentially occurring in stars with a detected magnetic field seems to emerge at this stage. Full details can be found in Morel et al. (2006). [less ▲]

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See detailNitrogen excretions in dairy cows on a rotational grazing system: effects of fertilization type, days in the paddock and time period.
Dufrasne, Isabelle ULg; Robaye, Vincent ULg; Istasse, Louis ULg et al

in Schnyder, Hans; Isselstein, J.; Taube, F. (Eds.) et al Grassland in a changing world (2010, September)

The present study aims to quantify nitrogen (N) excretions in dairy cows on a rotational grazing system with different types of fertilization (mineral N, slurry and compost) after 3 or 5 days in the ... [more ▼]

The present study aims to quantify nitrogen (N) excretions in dairy cows on a rotational grazing system with different types of fertilization (mineral N, slurry and compost) after 3 or 5 days in the paddock and during two different periods in June and September. Individual samples of faeces and urine were collected to assess N excretions from cows in the paddocks. The urea content in milk from the tank or from the individual cows was also measured. N intake was higher on day 3 compared to day 5 (465 vs 425 g d-1, P<0.001) and in September as compared to June (488 vs 425 g d-1, P<0.001) but was not influenced by the fertilization type. The amount of excreted urinary N was significantly higher in the mineral N group than in the two other groups (272 vs 226 g d-1; P<0.001). The N excretion in faeces and urines decreased with days (92 vs 84 g d-1, P<0.01; 256 vs 228 g d-1, P<0.001 respectively for days 3 and 5). Urinary N excretion was lower in June than in September (181 vs 302 g d-1, P<0.001) while the N excretion in the faeces was higher (96 vs 80 g d-1, P<0.01). [less ▲]

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See detailNitrogen fertilisation recommendations : could they be improved using stochastically generated climates in conjunction with crop models ?
Dumont, Benjamin ULg; Basso, Bruno; Meza Morales, Walter ULg et al

in Proceedings of the 12th ICPA (2014)

Accurate determination of optimal Nitrogen (N) recommendations which ensure maximization of farmer's revenue while minimizing the environmental constraint is maybe among the major challenges in ... [more ▼]

Accurate determination of optimal Nitrogen (N) recommendations which ensure maximization of farmer's revenue while minimizing the environmental constraint is maybe among the major challenges in agriculture. Crop models have the potential to deal with such aspects and could thus be used to develop decision support systems. However unknown future weather conditions remains the key point of accurate yield forecast. This paper presents the results of a preliminary study that aims to supply the unknown future with stochastically generated climatic conditions. Coupling the methodology with appropriate decision rules led to a generic decision support system able to guide the N management practices. [less ▲]

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See detailNitrogen flaring stages of novae
Swings, Polydore ULg

in Publications of the American Astronomical Society (1946)

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See detailThe nitrogen isotope ratio in a few Oort Cloud comets
Jehin, Emmanuel ULg; Arpigny, Claude ULg; Manfroid, Jean ULg et al

in 35th COSPAR Scientific Assembly (2004)

In the past few years, high-resolution (R ˜ 70,000) and high quality spectra of the CN B^2Sigma^+ - X^2Sigma^+ (0,0) band (at 388 nm) of several Oort Could comets have been collected by our team in ... [more ▼]

In the past few years, high-resolution (R ˜ 70,000) and high quality spectra of the CN B^2Sigma^+ - X^2Sigma^+ (0,0) band (at 388 nm) of several Oort Could comets have been collected by our team in different observatories and have allowed the first optical detections of [SUP]12[/SUP]C[SUP]15[/SUP]N. Observations with first class spectrographs on large 8m telescopes, such as UVES at the ESO VLT, have shown that such very efficient equipment are able to provide isotopic ratios for comets as faint as m_r ˜ 9 (heliocentric magnitude), opening up the possibility of carrying out a systematic analysis over a significant sample of comets. While the measured [SUP]12[/SUP]C/[SUP]13[/SUP]C isotope ratios in the different comets are in good agreement with the Solar system value (89), the derived [SUP]14[/SUP]N/[SUP]15[/SUP]N ratios are only about half the value in Earth's atmosphere (272), indicating an excess of [SUP]15[/SUP]N by a factor of about 2 with respect to the "cosmic" value. It is striking to note that the optical determinations of [SUP]14[/SUP]N/[SUP]15[/SUP]N in the different comets are consistent with each other (140 � 30), but not with the ratios derived for comet Hale-Bopp from sub-millimeter measurements on HCN, generally believed to be the main parent of CN. This discrepancy could indicate the existence of (an) other unknown parent(s) of CN, with an even higher [SUP]15[/SUP]N excess. Organic compounds like those found in interplanetary dust particles (IDPs) are good candidates. Further determinations from HCN are now badly needed in other comets. Obtaining the value of the N isotopic ratio in Jupiter-family short-period comets would be of great significance in view of their presumed different place of birth. Much is also expected in this respect, as in many others, from several space missions such as Deep Impact, Stardust, and Rosetta. [less ▲]

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See detailNitrogen Isotope Ratios in Comets. ESO Astrophysics Symposia
Cochran, Anita L; Jehin, Emmanuel ULg; Manfroid, Jean ULg et al

in Precision Spectroscopy in Astrophysics (2008)

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See detailNitrogen K-shell photoabsorption
Garcia, J; Kallman, T R; Witthoeft, M et al

in Astrophysical Journal Supplement Series (2009), 185

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See detailNitrogen leaching forecasting: modelling and measurements
Sohier, Catherine ULg; Vandenberghe, Christophe ULg; Dautrebande, Sylvia et al

in Bruthans, Jiri; Kovar, Karel; Hrkal, Zbynek (Eds.) International Interdisciplinary Conference on Predictions for Hydrology, Ecology and water Resources Management Using Data And Models To Benefit Society (2008)

European nitrate directive (CEE/91/676) imposes wide monitoring of Nitrogen in farmlands. The Walloon Region (South of Belgium – 750 000 ha of arable land) develops an original combination of methods to ... [more ▼]

European nitrate directive (CEE/91/676) imposes wide monitoring of Nitrogen in farmlands. The Walloon Region (South of Belgium – 750 000 ha of arable land) develops an original combination of methods to reach European objectives in this topic. On the one hand, water and nitrogen flows and balances are modelled, on the other hand, an Agricultural Surface Survey is put into practice to monitor nitrate nitrogen in the soil at the beginning of the leaching period. The Agricultural Surface Survey is constituted by a 30 reference farms network within more than 200 plots are monitored each in order to fix annual standards for nitrate profiles. Each year, about 1% of the Walloon farms are assessed about their good nitrogen management. Thanks to the existence of a useful database of nitrate profiles measured through six years in the whole Walloon Region, validation of the simulations in the vadose zone can be realised. The comparison of the measured data and the simulation shows a good accuracy of the EPICgrid model. [less ▲]

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See detailNitrogen-containing bisphosphonates can inhibit angiogenesis in vivo without the involvement of farnesyl pyrophosphate synthase.
Stresing, Verena; Fournier, Pierrick G; Bellahcene, Akeila ULg et al

in Bone (2011), 48(2), 259-66

Nitrogen-containing bisphosphonates (N-BPs) are widely used to block bone destruction associated with bone metastasis because they are effective inhibitors of osteoclast-mediated bone resorption. More ... [more ▼]

Nitrogen-containing bisphosphonates (N-BPs) are widely used to block bone destruction associated with bone metastasis because they are effective inhibitors of osteoclast-mediated bone resorption. More specifically, once internalized by osteoclasts, N-BPs block the activity of farnesyl pyrophosphate synthase (FPPS), a key enzyme in the mevalonate pathway. In addition to their antiresorptive activity, preclinical evidence shows that N-BPs have antiangiogenic properties. However, the exact reasons for which N-BPs inhibit angiogenesis remain largely unknown. Using different angiogenesis models, we examined here the effects of zoledronate, risedronate and three structural analogs of risedronate (NE-58025, NE-58051 and NE-10790) with lower potencies to inhibit FPPS activity. Risedronate and zoledronate were much more potent than NE-compounds at inhibiting both endothelial cell proliferation in vitro and vessel sprouting in the chicken egg chorioallantoic membrane (CAM) assay. In addition, only risedronate and zoledronate inhibited the revascularization of the prostate gland in testosterone-stimulated castrated rats. Moreover, as opposed to NE-compounds, risedronate and zoledronate induced intracellular accumulation of isopentenyl pyrophosphate (IPP) in endothelial cells by blocking the activity of the IPP-consuming enzyme FPPS. Thus, these results indicated that N-BPs inhibited angiogenesis in a FPPS-dependent manner. However, drug concentrations used to inhibit angiogenesis, both in vitro and in the CAM and prostate gland assays, were high. In contrast, a low concentration of risedronate (1 muM) was sufficient to inhibit blood vessel formation in the ex vivo rat aortic ring assay. Moreover, NE-58025 (which had a 7-fold lower potency than risedronate to inhibit FPPS activity) was as effective as risedronate to reduce angiogenesis in the rat aortic ring assay. In conclusion, our results suggest that low concentrations of N-BPs inhibit angiogenesis in a FPPS-independent manner, whereas higher drug concentrations were required to inhibit FPPS activity in vivo. [less ▲]

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