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1
Burgoyne, Calum K. "Parameterisation of a nitrogen cycle model". Thesis, University of Aberdeen, 2012. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=191768.
Testo completo
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Cioncoloni, Giacomo. "Towards an anthropogenic nitrogen cycle based on nitrite". Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/30717/.
Testo completoAbstract (sommario):
The overall goal of this thesis was to investigate the feasibility of a new route to anthropogenic nitrogen fixation based on the oxidation of nitrogen (to give primarily nitrite), and then electrocatalytic conversion of nitrite to other N-containing species of interest, such as nitrate and nitric oxide (NO). In pursuit of this goal, the synthesis of metal-ligand coordination complexes that could act as electrocatalysts for the oxidation of nitrite to nitrate was attempted, as was the synthesis of metal-ligand coordination complexes that could act as electrocatalysts for the reduction of nitrite to NO. As a corollary to this, routes for the initial fixation reaction were also investigated, of which the ultrasonic generation of nitrite from aerated aqueous solutions was found to be the most promising. The work detailed in this thesis is organized in the following manner: In Chapter 1 we discuss coordination complexes that mimic the enzymes promoting the redox reactions of the nitrogen cycle involving nitrite as a substrate or product. During this introduction we will also give an overview of topics that are relevant to the following chapters, such as proton-coupled-electron transfer and basic kinetic treatment of catalytic reactions. Chapter 2 is a description of the different techniques used throughout this thesis. Once having set the bases, we shall start with the actual research, which corresponds to Chapters 3 to 6. Chapter 3 deals with the synthesis, characterization and catalytic properties of a copper coordination compound mimicking the active site of the copper nitrite reductase (CuNiR) class of enzymes. This chapter includes a detailed study of the kinetics and electrocatalytic properties of this complex towards the mono-electronic reduction of nitrite to nitric oxide. Chapters 4 and 5 deal with the unusual structures and spectroscopic properties of a number of new cobalt complexes that we isolated whilst trying to develop Mo(bis-dithiolene) coordination complexes that might act as analogues of the molybdenum nitrite oxidoreductase (MoNiOR), which oxidises nitrite to nitrate in nature. Our original Mo-containing targets proved impossible to obtain and are not discussed in this thesis. However, we found that cobalt readily makes coordination complexes with these bis-dithiolene ligands, which allowed us to isolate the compounds we present in Chapters 4 and 5. Hence in Chapter 4 we show the synthesis and the solvatochromic properties of mixed-ligand mono-nuclear Co-diimine o-catecholato complexes and compare these complexes with the analogous compounds prepared with o-benzenedithiolato ligands. Chapter 5 then discusses the synthesis and redox properties of a mixed-ligand di-cobalt coordination complex in which the two cobalt centres have (unprecedented) inequivalent metal coordination environments. Finally, in Chapter 6 we describe a much-underexplored way to fix nitrogen based on a sonochemical reaction. After a brief introduction we describe the optimisation of the procedure and comparisons with previous reports.
3
Rahn, Thomas A. "Enrichment of ¹⁵N and ¹⁸O in stratospheric nitrous oxide : observations, experimental results, and implications /". Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1998. http://wwwlib.umi.com/cr/ucsd/fullcit?p9907828.
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Parolari, Anthony Joseph. "The nitrogen cycle and ecohydrology of seasonally dry grasslands". Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/79491.
Testo completoAbstract (sommario):
Thesis (Ph. D. in the Field of Hydrology)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 2013."February 2012." Cataloged from PDF version of thesis.
Includes bibliographical references (p. 155-172).
This thesis addresses the coupling of hydrologic and biogeochemical processes and, specifically, the organization of ecosystem traits with the water, carbon, and nitrogen cycles. Observations from a factorial irrigation-fertilization experiment in a seasonally dry annual grassland are combined with a simple ecosystem model to identify relationships between vegetation, nitrogen availability, and hydrology. Assuming primary productivity is water-limited, data analysis indicates that soil moisture and canopy conductance are insensitive to nitrogen supply, owing to a trade-off between canopy density and leaf conductance that maximizes efficient use of available water. That is, fertilization-induced increases in leaf area index are offset by reduced leaf area-based stomatal conductance. When primary productivity is assumed to be co-limited by water and nitrogen availability, total surface conductance is estimated to be insensitive to nitrogen supply, but added nitrogen increases the ratio of transpiration to evaporation. This coupled water-carbon-nitrogen model is then extended to predict ecosystem sensitivity across independently varied gradients of water and nitrogen supply rates. This analysis reveals two distinct regimes of plant-resource organization. In arid climates, rooting depths decrease with increasing aridity, while in humid climates, rooting depths increase with aridity. In all climates, rooting depths increase with increased nitrogen supply. Further, relative root-carbon allocation always increases with aridity and decreases with nitrogen supply. These resource use strategies result in an efficient use of available water in arid climates and efficient use of available nitrogen in humid climates. The associated ecosystem process rates indicate that nitrogen supply is an important determinant of surface water and carbon fluxes in humid climates, but only of carbon fluxes in arid climates.
by Anthony Joseph Parolari.
Ph.D.in the Field of Hydrology
5
Monteiro, Maria Rovisco Correia Gonçalves. "Dynamic of estuarine prokaryotic communities and the nitrogen cycle". Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/12738.
Testo completoAbstract (sommario):
Mestrado em MicrobiologiaEstuaries are highly dynamic aquatic systems, having steep physical and chemical gradients, such as salinity, influencing microbial communities in terms of their abundance and diversity. The analysis of microbial responses and adaptations to those environmental fluctuations became essential to understand the biogeochemical cycles that regulate these ecosystems, which have been undergoing progressive anthropogenic pressures. In this study, we investigated the dynamics of Archaea and Bacteria diversity along the salinity gradient of the Douro River estuary (NW Portugal). Samples were collected at four locations covering the salinity gradient, ranging from 4.9 - 21.7 ppt. The application of denaturing gradient gel electrophoresis (DGGE) showed a variation of Bacteria and Archaea diversity along the salinity gradient. The diversity of ammonia oxidizing Archaea (AOA) was also assessed by the analysis of amoA diversity. Simultaneously, were measured net fluxes of inorganic nitrogen (NH4+, NO3-, NO2-) and nitrification rates by using acetylene and 15N isotope analysis. The results showed that although there was an increase in the diversity of AOA with the decrease of salinity, the highest magnitudes of nitrification rates were registered at intermediary saline sites, where there was a higher availability of NH4+. This study revealed important insights on the effect of salinity on estuarine prokaryotic diversity structure as well on the dynamics of key processes of the nitrogen cycle.
Estuários são ecossistemas aquáticos altamente dinâmicos, possuindo grandes gradientes físicos e químicos, como é o caso da salinidade, influenciando as comunidades microbianas em termos de diversidade e abundância. A análise das respostas e adaptações destas comunidades às flutuações ambientais torna-se essencial para a compreensão dos ciclos biogeoquímicos que regulam estes ecossistemas, que tem vindo nos últimos anos a sofrer pressões ambientais devido à crescente atividade antropogénica. Neste estudo, investigámos a dinâmica da diversidade de Archaea e Bacteria ao longo de um gradiente de salinidade no estuário do Rio Douro (NW, Portugal). As amostras foram recolhidas em quatro locais cobrindo um gradiente de salinidade que variou entre 4.9 - 21.7 ppt. A aplicação da técnica de electroforese em gel com gradiente desnaturante (DGGE), revelou uma variação na diversidade de Bacteria e Archaea ao longo do gradiente salino. A diversidade das comunidades de Archaea com a capacidade de oxidar a amónia (AOA) foi também avaliada através da análise de diversidade do gene funcional amoA. Paralelamente, foram avaliados os fluxos líquidos dos compostos de azoto inorgânico (NH4+, NO3-, NO2-) bem como as taxas de nitrificação através da utilização do método do acetileno e da análise isotópica de 15N. Os resultados mostraram que apesar de ter ocorrido um aumento da diversidade das AOA com a diminuição da salinidade, as maiores magnitudes das taxas de nitrificação foram registadas nos locais com salinidades intermédias, onde se registou maior disponibilidade de NH4+. Este estudo permitiu-nos obter importantes conhecimentos sobre o efeito da salinidade na estrutura das comunidades procariotas estuarinas bem como na dinâmica de processos chave do ciclo do azoto.
6
Agrella, Karen. "Nitrogen transformations in South African soils". Diss., University of Pretoria, 2001. http://hdl.handle.net/2263/23565.
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Moschonas, Grigorios. "Dissolved organic nitrogen dynamics and influence on phytoplankton". Thesis, University of Aberdeen, 2015. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=228584.
Testo completoAbstract (sommario):
A balanced nitrogen (N) cycle is paramount for the ecology and biogeochemistry of planet Earth. Human activities are now causing an imbalance in the N cycle, with several negative effects on the marine environment. However, our knowledge of the marine N cycle remains incomplete, especially with regards to the role of dissolved organic N (DON). Therefore, there is need to study the role of DON more extensively to aid in restoring balance to Earth's ecosystems and biogeochemical cycles. This project investigated DON dynamics and influence on phytoplankton in coastal and shelf seas (CSS) to the west of Britain where DON was understudied. First, selected methods for the measurement of N uptake rates, urea and dissolved free amino acid (DFAA) concentrations were reviewed and tested. Then, they were used to study the spatial and temporal DON dynamics in the shelf region to the west of Britain (Irish Sea and adjacent shelf), the in-situ seasonal DON dynamics and N uptake in relation to phytoplankton community composition and abundance in Loch Creran, and the influence of DON on the phytoplankton community composition and abundance in controlled nutrient uptake kinetics and growth experiments and ecosystem modelling. The main findings were: DON was important in the N dynamics of the Irish Sea and adjacent shelf waters; DON was correlated with changes in phytoplankton community composition in Loch Creran; its seasonal cycle suggested its importance as an N source for the development of the spring bloom; these ideas were further supported by controlled laboratory experiments and ecosystem modelling.
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Tekin, Elif. "Anaerobic Ammonium Oxidation in Groundwater Contaminated by Fertilizers". Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/23956.
Testo completoAbstract (sommario):
Anaerobic ammonium oxidation (anammox) is a pathway that has been known for almost 2 decades, but few studies have investigated its importance in natural groundwaters. This thesis investigated the presence of anammox cells and the groundwater geochemistry of 2 sites (Elmira and Putnam) in southwestern Ontario where groundwaters are contaminated with high levels of nitrate and ammonium. Fluorescence in situ hybridization (FISH) was used to quantify the relative abundance of anammox cells in these waters. Our results showed that anammox cells could be detected in many wells at both sites and that their relative abundance varied between 0.45 and 4.81 % at the Putnam site, whereas it ranged between 0.8 to 8.4 % at the Elmira site. These values are within the same range as those obtained for marine and freshwater environments where anammox cells have been detected. In addition, indirect observations point to the fact that N cycling at the 2 sites might be linked to Fe and Mn reduction, but additional experiments are needed. In summary, our results corroborate the findings of N-labeled microcosm experiments which demonstrated that anammox was an important pathway of N cycling in those groundwaters and molecular analyses that detected important anammox organisms at the same sites.
9
Franklin, Oskar. "Plant and forest dynamics in response to nitrogen availability /". Uppsala : Swedish University of Agricultural Sciences, 2003. http://diss-epsilon.slu.se/archive/00000345/.
Testo completoAbstract (sommario):
Thesis (doctoral)--Swedish University of Agricultural Sciences, 2003.Appendix consists of reprints of three papers and a manuscript, three of which are co-authored with others. Includes bibliographical references. Also partially issued electronically via World Wide Web in PDF format; online version lacks appendix.
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Mielke, Nora. "The role of nitrogen and phosphorus in carbon and nutrient cycling of bryophyte-dominated exosystems". Thesis, University of Aberdeen, 2016. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=231758.
Testo completoAbstract (sommario):
Bryophytes form an important component of northern vegetation communities. Mosses efficiently capture aerially deposited nutrients, restricting nutrient availability to the soil. Given that key ecosystem processes of northern ecosystems are nutrient-limited, understanding nutrient cycling of the moss layer is key to understanding ecosystem nutrient and C cycling in these systems. However, the role of the moss layer in regulating ecosystem-scale nutrient and C cycling, while potentially significant, is largely unknown. The aim of this thesis is to investigate the effect of the relative availability of N and P on aspects of bryophyte nutrient uptake, retention and C acquisition. The hypothesis investigated is that the availability of one nutrient will influence the demand for the other and thereby moss nutrient acquisition and retention mechanisms. To test this hypothesis, various aspects of moss nutrient cycling in response to the relative availability of N and P were investigated. As the C cycle is tightly linked to the N and P cycles, the hypothesis extended to include bryophyte C assimilation and decomposition processes of an arctic tundra. Bryophyte nutrient demand was chiefly governed by the tissue N:P ratio. Consequently, nutrient uptake, both from aerially deposited nutrients and through moss-cyanobacteria N2 fixation, and nutrient losses after a simulated rainfall event were mostly in response to the relative availability of N and P rather than the availability of one nutrient alone. This thesis provides novel evidence that ectohydric mosses have the ability to internally translocate nutrients. In conjunction with efficient nutrient capture, this trait makes mosses strong nutrient sinks which are likely to exert considerable control over ecosystem nutrient cycling. The relative availability of N and P played a role in C uptake of mosses. Through the production of recalcitrant litter and their insulating effect on soil microclimate mosses exerted an influence over ecosystem C cycling.
11
Koikkalainen, Riitta Katariina. "Influence of nitrogen on below ground dynamics in improved grasslands". Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources, 2009. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=33591.
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12
Coles, Simon Philip. "Automated flow injection instrumentation for monitoring nitrogen species in natural waters". Thesis, University of Plymouth, 1999. http://hdl.handle.net/10026.1/2144.
Testo completoAbstract (sommario):
The provision of high quality analytical data is an essential prerequisite for understanding the biogeochemical cycling of nutrients in the aquatic environment. Due to the instability of samples collected for nutrient determinations however, in situ analysis is preferred. This approach also allows for high temporal and spatial resolution of the data and alteration of the sampling frequency to meet local environmental needs. Chapter One describes the role of nitrogen species, particularly ammonia and nitrate, in the aquatic environment, their sources, and possible environmental effects and summarises analytical techniques for their determination. Solid state miniaturised detectors and their suitability for in situ monitoring are also discussed. The characterisation and evaluation of a miniature Ocean Optics PSD - 1000 spectrometer and its suitability for field deployment is described in Chapter Two. Parameters investigated were optical resolution, wavelength repeatability, photometric linearity and instrumental noise and drift. The incorporation of the Ocean Optics PSD - 1000 miniature spectrometer into a gas diffusion Flow Injection (Fl) manifold for the determination of ammonia in natural waters is detailed in Chapter Three. Optimisation of the Fl parameters and analytical performance are discussed in detail. The development of an immobilised pH indicator and adaptation to a laminar Fl manifold is also considered. Chapter Four describes the use of the miniature spectrometer in a Fl manifold for the determination of nitrate and nitrite, with analytical figures of merit detailed. The increased information potential of the spectrometer (i.e. full spectral acquisition) facilitated the removal of the refractive index problem using dual wavelength correction. Miniaturisation and automation of the optimised nitrate manifold using micro-solenoid pumps and LabView™ graphical programming is described in Chapter Five. Field deployment of the automated system was assessed during a six week British Schools Exploring Society Expedition to Lesotho, S. Africa (in which an intensive biogeochemical survey of the Sehlabathebe National Park was conducted) and a three day campaign on the River Frome, Dorset, U.K. Chapter Six details the ion chromatographic analysis of major anions and cations (including ammonium and nitrate) in precipitation samples. Two sampling campaigns were conducted. One was at an urban site (Plymouth City Centre) from 27/01/98 - 11/05/98, and the influence of aerosol source on the chemical composition of Plymouth precipitation is discussed. The other involved the Austrian precipitation network and wet deposition trends for nitrate, ammonium and sulphate are discussed. The multivariate analysis technique of PCA was applied to both environmental datasets and the interpretation and merits of this statistical approach are considered.
13
Warren, Victoria. "The temperature dependence of the gaseous products of the nitrogen cycle". Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/25983.
Testo completoAbstract (sommario):
The nitrogen cycle is one of the key macronutrient cycles that controls the distribution of life on Earth. The nitrogen cycle is composed of a series of distinct microbially mediated processes which may be affected differently with warming. Climate change is likely to affect all components of the nitrogen cycle. However, the extent to which each component will be affected and how this will alter interactions in natural systems is unknown. Here we used laboratory and field experiments to investigate the effect of warming on nitrogen cycling. We used a combination of pure cultures, in-situ measurements and laboratory manipulations of environmental samples to explore responses in freshwater and marine systems. In pure cultures of denitrifying bacteria, denitrification rates increased by 117-164%, with a 4oC temperature increase (11.5-15.5oC). In freshwater mesocosms, long term warming rates of sediment denitrification increased by 247%, with no significant thermal response of sediment nitrification within these systems. Marine sediment rates of denitrification and anammox increased by 4.69-16.23% and 3.71-35.39% respectively, depending on N substrate. Whereas a 3oC temperature increase in the water of the ETNP OMZ increased denitrification and anammox rates by 52.5% and 52.9% respectively, with no significant thermal response of nitrogen fixation in the OMZ surface waters. From this study, nitrogen removal processes increase with increasing temperature across systems but internal transformation and fixation of N show little to no thermal response. Further investigation into the causes of the observed variation in responses, such as substrate limitation and identification of microbes involved, will allow us to better understand and therefore better predict cross-system responses of the nitrogen cycle to global warming.
14
Widener, Andrew Scott. "A mathematical model of the nitrogen cycle in a constructed wetland". Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-12172008-063133/.
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Emmett, Bridget A. "The effects of harvesting on soil nitrogen transformations in a Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation at Beddgelert forest (N. Wales)". Thesis, University of Exeter, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253559.
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Burns, Lisa C. "Cycling of fertiliser-derived N in a Sitka spruce ecosystem after 15N-urea application". Thesis, University of Aberdeen, 1992. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU545404.
Testo completoAbstract (sommario):
Low recovery rates of fertiliser N in tree biomass are frequently reported due to the inefficiency of N fertilisers in afforested ecosystems. At Culloden (North East Scotland), only 13&'37 of 15N-urea fertiliser applied to Sitka spruce could be recovered in the above-ground tree biomass two years after fertilisation. Fertiliser N not taken up by trees was largely 'locked-up' in stable organic forms of N within the LFH layers of the soil profile. 15N-labelled litter was used in both field and microcosm experiments, the release and fate of litter-derived-N (LDN) being traced over the course of two growing seasons. In both experiments, the microbial biomass acted as a major sink for LDN. Measurement of soil microbial biomass was calibrated for Culloden soil samples by determination of a kEN-factor. Tree uptake of LDN, in the field, occurred within one month of labelled-litter application, with the foliage being the largest sink for LDN. Approximately 30&'37 of the N within the labelled-litter layer was taken up by the trees over the course of two growing seasons and was equivalent to 5.4 kg LDN ha-1 y-1. There was considerable mixing of the LFH and peat layers in Sitka spruce microcosm soil profiles. This was probably due to elevated soil animal population densities. After 18 months, approximately 83&'37 of LDN had been redistributed to other N pools in the microcosm. Uptake of LDN by seedlings accounted for 15.7&'37 of LDN after 12 months, the largest sink being the foliage, equivalent to 6.16 kg LDN ha-1 y-1. Again, the microbial biomass was a major sink for LDN. Measurement of availability (NH4+) N in Culloden soil samples incubated at different matric potentials and temperatures, appeared not to reflect N mineralisation rates. There was a strong interaction between temperature and soil matric potential, seedling uptake of N being greatest at 15oC and -16.0 kPa. The rate of turnover of the microbial biomass pool was identified as the key determinant of the rate of processing of LDN in forest soils.
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Jamieson, Nicola. "Competition between roots and soil micro-organisms for fertiliser N". Thesis, University of Aberdeen, 1992. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU548165.
Testo completoAbstract (sommario):
Low fertiliser recoveries are often found for temperate coniferous forests and appear to be associated with the 'locking-up' of residual fertiliser N in stable organic forms. This phenomenon may well be caused by strong microbial immobilisation, out competing uptake by tree roots. This thesis investigates root/microbe competition for fertiliser-derived N (FDN) in microcosms of coniferous forest soil (supporting Sitka spruce seedlings) as well as in re-seeded blanket peat (supporting a mixed grass pasture). Combinations of selective microbial inhibitors, both with and without either 15N-labelled urea or NH4NO3, were applied to microcosms to selectively inhibit target microbial groups which may be competing with roots for FDN and determine the role of microbial immobilisation as a mechanism controlling N flow to seedlings/herbage. The dynamics of FDN novement into microcosm N pools was also studied in microcosms to which 15N-labelled urea was applied alone. At harvest, plant and soil N pools were analysed for 15N and total N (15 N &'43 14N). The impact of biocide and fertiliser N treatments on concentrations of target and non-target soil organisms were also determined. Biocidal (benlate and to a lesser extent streptomycin) inhibition of soil micro-organisms (particularly fungi) increased the uptake of both urea-derived N and NH4O3 N by Sitka spruce seedlings. Increases were associated with reduced percentages of FDA active hyphae and concentrations of FDN immobilised in the microbial biomass of LFH layer and peaty mineral soil. The results suggest that roots were competing with soil microbes for both fertiliser N forms. In conclusion this study has demonstrated the role of microbial biomass, particularly the dominant fungal component as a major competitive sink for fertiliser N and a major factor contributing to the low efficiency of fertiliser N in temperate coniferous forests. The study also has identified selective biocidal manipulation as a powerful technique for characterising competition between roots and microbes for nutrients in soil.
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Nave, Lucas Emil. "Nitrogen cycling in the northern hardwood forest soil, plant, and atmospheric processes /". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1196187071.
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Sarkodie-Addo, Joseph. "Nitrogen dynamics in a green manure - maize rotation system". Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368885.
Testo completo
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Sakaguchi, K., X. Zeng, LR Leung e P. Shao. "Influence of dynamic vegetation on carbon-nitrogen cycle feedback in the Community Land Model (CLM4)". IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/624742.
Testo completoAbstract (sommario):
Land carbon sensitivity to atmospheric CO2 concentration (bL) and climate warming (gL) is a crucial part of carbon-climate feedbacks that affect the magnitude of future warming. Although these sensitivities can be estimated by earth system models, their dependence on model representation of land carbon dynamics and the inherent model assumptions has rarely been investigated. Using the widely used Community Land Model version 4 as an example, we examine how bL and gL vary with prescribed versus dynamic vegetation covers. Both sensitivities are found to be larger with dynamic compared to prescribed vegetation on decadal timescale in the late twentieth century, with a more robust difference in gL. The latter is a result of dynamic vegetation model deficiencies in representing the competitions between deciduous versus evergreen trees and tree versus grass over the tropics and subtropics. The biased vegetation cover changes the regional characteristics of carbon-nitrogen cycles such that plant productivity responds less strongly to the enhancement of nitrogen mineralization with warming, so more carbon is lost to the atmosphere with rising temperature. The result calls for systematic evaluations of land carbon sensitivities with varying assumptions for land cover representations to help prioritize development effort and constrain uncertainties in carbon-climate feedbacks.
21
Horak, Rachel Elizabeth Ann. "Controls on nitrogen fixation and nitrogen release in a diazotrophic endosymbiont of shipworms". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37238.
Testo completoAbstract (sommario):
Nitrogen fixation is an ecologically important microbial process that can contribute bioavailable combined N to habitats low in N. Shipworms, or wood-boring bivalves, host N2-fixing and cellulolytic symbiotic bacteria in gill bacteriocytes, which have been implicated as a necessary adaptation to an N-poor C-rich (wooden) diet. Shipworm symbionts are known to fix N within the gill habitat and newly fixed N is subsequently incorporated into non-symbiont containing host tissue. The presence of N2-fixation in gill bacteriocytes presents a conundrum because N2-fixation is tightly regulated by oxygen in most other diazotrophic microbes. Also, the direct evidence of new N being incorporated into the host tissue indicates that there are potentially complex nutrient cycles in this symbiosis, which have not been investigated. We used the cultivated symbiont Teredinibacter turnerae, which has been isolated from many shipworm species, as a model organism to elucidate controls on N2-fixation and N release in the shipworm symbiosis. Our results indicate that headspace oxygen concentration does not control biomass specific N2-fixation and respiration activity in T. turnerae, but it does influence the magnitude of the growth rate and timing of culture growth. Also, we examined the controls of oxygen on inorganic nutrient uptake rates, and documented a small amount of dissolved inorganic nitrogen release. While the N budget is only partially balanced, we provide indirect evidence for the allocation of fixed N to the excretion of exopolymeric substances and dissolved organic nitrogen; future studies that measure these additional N sinks are necessary to close the N budget. Although there are limitations of using pure cultures to investigate a complex symbiotic system, this study provides direct experimental evidence that T. turnerae has adaptations that are conducive to N2-fixation in gill bacteriocytes.
22
Zuliani, Filippo. "Nitrogen footprint: development and testing of new methodologies for the assessment of environmental impact related to the nitrogen cycle". Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3422430.
Testo completoAbstract (sommario):
The research work addresses the topic of the assessment of environmental impact related to the nitrogen cycle. Starting from an analysis of the environmental effects derived from the alteration of the nitrogen cycle caused by human intervention and of the tools currently available to evaluate these effects, the objective of the research is to develop a new impact assessment methodology, based on an whole Life Cycle Assessment (LCA) approach and to verify its effectiveness in accounting and detailing the environmental impacts caused by a product system and by the related processes.
The proposed methodology overcomes some of the weaknesses identified in existing assessment tools, in particular by proposing a comprehensive LCA approach, applied at both methodological and operational level, and an orientation to the identification and accounting of environmental impacts. In particular, the methodology provides for a multistep approach that, starting from the identification of the nitrogen-containing substances of a product systems, first allows to account for reactive nitrogen and then, through specific characterization models, to assess the environmental effects for different impact categories to finally calculate, after normalization and weighting, a single stand-alone impact indicator. This approach allows identifying and accounting the environmental impacts related to the nitrogen cycle for a product system, quantifying also the contribution of the different processes and activities in the life cycle.
After the design phase, the methodology has been successfully tested in four different application cases, two based on database and two on real data collected on the field, demonstrating the validity and applicability of the proposed model and obtaining results consistent with the targets set for each application.
The proposed methodology has been defined and applied in all its phases and steps, with some computational shortcuts specially modeled on the application cases addressed in the research work: some further adaptations may therefore be required for applications in fields different from those proposed.Il lavoro di ricerca affronta il tema della valutazione degli impatti ambientali collegati al ciclo dell'azoto. A partire dall'analisi degli effetti sull'ambiente derivanti dalle alterazioni del ciclo dell'azoto provocate dall'intervento umano e dagli strumenti attualmente disponibili per la loro valutazione, l'obiettivo della ricerca è quello di sviluppare una nuova metodologia per la valutazione degli impatti, basata su un approccio LCA (Life Cycle Assessment) e verificarne l'efficacia per identificare e valutare gli impatti ambientali sul ciclo dell'azoto causati da un sistema prodotto e dai processi collegati. La metodologia proposta intende superare alcuni dei punti di debolezza degli attuali strumenti di valutazione, proponendo in particolare un completo approccio di tipo LCA, applicato sia a livello metodologico sia a livello operativo, e un orientamento all'identificazione e valutazione degli impatti ambientali. Nello specifico, la metodologia prevede un approccio multifase che, partendo dall'identificazione delle sostanze contenenti azoto riconducibili ad un sistema prodotto, permette in primo luogo di quantificare l'azoto reattivio emesso e successivamente, attraverso l'applicazione di modelli di caratterizzazione, di valutare gli impatti ambientali per diverse categorie di impatto e di calcolare un indicatore finale attraverso operazioni di normalizzazione e pesatura. Dopo la fase di progettazione, la metodologia è stata testata con esito positivo in quattro applicazioni, due basate su database e due basate su dati reali raccolti sul campo, dimostrando la validità e l'applicabilità del modello proposto e ottenendo risultati consistenti con gli obiettivi fissati per ogni applicazione. La metodologia proposta è stata definita e applicata in tutte le singole fasi con alcune semplificazioni di calcolo specificamente adottate per ciascuno dei casi applicativi proposti: ulteriori adattamenti potrebbero pertanto essere necessari per applicazioni in ambiti differenti da quelli proposti.
23
Kim, Ok-Sun [Verfasser]. "Diversity of functional genes in the aquatic nitrogen cycle / Ok-Sun Kim". Kiel : Universitätsbibliothek Kiel, 2010. http://d-nb.info/101995213X/34.
Testo completo
24
Arfken, Ann. "The Eastern Oyster Microbiome and its Implications in the Marine Nitrogen Cycle". W&M ScholarWorks, 2017. https://scholarworks.wm.edu/etd/1516639592.
Testo completoAbstract (sommario):
Microbial communities associated with a particular space or habitat, or microbiomes, play significant roles in host health and the regulation of biogeochemical cycles. In oysters these microbiomes may be important contributors in the removal of biologically available nitrogen (N) from the coastal and marine environment through the process of denitrification. Denitrification is the microbially mediated step-wise reduction of nitrate (NO3-) or nitrite (NO2-) to N2 gas. Excess nitrogen in the Chesapeake Bay has been implicated in the increase of eutrophication and other detrimental effects including harmful algal blooms, hypoxia, and loss of benthic communities. Oyster reefs have been shown to enhance the rates of denitrification in nearby sediments, but little is known about the oyster microbiomes or associated microbes responsible for denitrification (denitrifiers). Furthermore, the identification of the oyster core microbiome, or set of resident microbes continually present in the oyster, is relatively unknown. Assessing the stable underlying core is necessary to evaluate and predict the effect of varying environmental conditions on the oyster microbiome and oyster denitrification. A combined 16S targeted metagenomic and metabolic inference approach was used in this study to investigate the gill, gut and shell microbiomes of the eastern oyster (Crassostrea virginica) and their associated denitrifiers in response to spatial and temporal changes. Denitrification activity was linked to community structure using methods such as quantitative PCR of nitrous oxide reductase genes (nosZ) and 15N isotope pairing technique with experimental flow-through design. The oyster gill, gut, and shell microbiomes all showed distinct and unique core microbiomes, suggesting an importance of the core to oyster function or health. Denitrifier abundance and activities were most consistent in the shell microbiomes indicating a stable, pool of potential denitrifiers for oyster denitrification. In comparison, oyster gill and gut denitrifier abundances and activities were highly variable and likely related to transient denitrifiers ingested with food particles. Additionally, denitrifiers demonstrated niche differentiation between the different oyster microbiomes, indicating different groups of denitrifiers are responsible for performing denitrification in the oyster. Assessing the stability and variability of the oyster microbiome and associated denitrifiers provides a greater understanding of the oyster’s role in denitrification and the mitigation of excess N in marine and coastal environments.
25
Yeatman, Stuart Gregory. "Major-ion and isotopic studies of aerosol nitrogen species in the marine atmosphere". Thesis, University of East Anglia, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327281.
Testo completo
26
Hall, Cynthia Adia. "Insights into marine nitrogen cycling in coastal sediments". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28228.
Testo completoAbstract (sommario):
Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2009.Committee Chair: Ellery Ingall; Committee Member: Andrew Stack; Committee Member: Greg Huey; Committee Member: Joseph Montoya; Committee Member: Judith Curry.
27
Chapman, Jasmin. "The study of the dissolved nitrogen containing macromolecules in the marine environment". Thesis, University of Plymouth, 1988. http://hdl.handle.net/10026.1/1888.
Testo completo
28
Farmer, Ryan Michael. "Coordination of Carbon Dioxide and Nitrogen Metabolism in Rhodobacter sphaeroides". The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1365519943.
Testo completo
29
Stroud, Joanne. "Dinuclear copper complexes with planar, neutral, N-donor, bridging ligands". Thesis, University of Nottingham, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282624.
Testo completo
30
Brandes, Jay Allen Gregory. "Isotopic effects of denitrification in the marine environment /". Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/11051.
Testo completo
31
Kreibich, Heidi. "N₂ fixation and denitrification in a floodplain forest in central Amazonia, Brazil". Connect to this title online (Marburg Universität site) Connect to this title online (Deutsche Nationalbibliothek site), 2002. http://archiv.ub.uni-marburg.de/diss/z2002/0398/.
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32
Dale, Olivia R. "Detection, diversity, and activity on anaerobic ammonium oxidizing bacteria (Anammox) in the Cape Fear River Estuary /". Electronic version (PDF), 2007. http://dl.uncw.edu/etd/2007-1/r1/daleo/oliviadale.pdf.
Testo completo
33
Bohlen, Lisa [Verfasser]. "Regional and global scale modeling of the benthic marine nitrogen cycle / Lisa Bohlen". Kiel : Universitätsbibliothek Kiel, 2012. http://d-nb.info/1020284021/34.
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34
Parent, Serge. "The role of meiofauna in the nitrogen cycle of a cold marine mesocosm". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ48110.pdf.
Testo completo
35
Hamersley, Michael Robert. "The role of denitrification in the nitrogen cycle of New England salt marshes". Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/29055.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), February 2002.Vita.
Includes bibliographical references (leaves 153-161).
I used direct measurements of nitrogen gas (N₂ fluxes and a ¹⁵N stable isotope tracer to determine the contribution of denitrification to salt marsh sediment N cycling. Denitrification in salt marsh tidal creekbottoms is a major sink for groundwater nitrate of terrestrial origin. I studied creekbottom denitrification by direct measurements of N₂ fluxes in closed chambers against a low-N₂ background. I undertook experiments and simulation modeling of sediment N₂ fluxes in closed chambers to optimize the key experimental parameters of this approach. Denitrification in these sediments was driven by the degradation of labile organic matter pools which are depleted during long incubations. Sediment thickness was the most important parameter controlling the required incubation time. Errors of up to 13% with gas headspaces and 80% with water headspaces resulted from headspace N2 accumulation and the resulting collapse of the sediment-water diffusion gradient. These errors could be eliminated by using headspaces of sufficient thickness. Headspace flushing to reduce ammonium accumulation did not affect denitrification rates, but caused transient disturbance of N₂ flux rates. Direct measurements of 0₂, C0₂, N₂, and inorganic N fluxes from the sediments of a salt marsh tidal creek were made in order to examine the interaction of denitrification with the carbon, oxygen, and N cycles. Organic carbon concentration and lability were the primary controls on metabolic rates. C0₂/N flux ratios averaged 6.1, indicating respiration driven by algal biomass.
(cont.) Allochthonous denitrification accounted for 39% of total sediment denitrification (2.7 mol N m⁻² yr⁻¹). 46% of remineralized ammonium was denitrified, while the contribution of autochthonous denitrification to 0₂ and C0₂ fluxes was 18% and 10%, respectively. A ¹⁵N-ammonium tracer was used to study competition between plants and nitrifying bacteria for remineralized ammonium. In undisturbed sediments of Spartina alterniflora, plant uptake out-competed nitrification-denitrification, with plant uptake accounting for 66% of remineralized ammonium during the growing season. Under N fertilization (15.5 mol m⁻² yr⁻¹), both plant N uptake and denitrification increased, but denitrification dominated, accounting for 72% of the available N. When plant uptake was hydrologically suppressed, nitrification-denitrification was stimulated by the excess N, shifting the competitive balance toward denitrification.
by Michael Robert Hamersley.
Ph.D.
36
Sjöberg, R. Michael. "Carbon and nitrogen turnover in the humus layer of coniferous forests with emphasis on immobilisation, stabilisation and uptake processes /". Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 2000. http://epsilon.slu.se/avh/2000/91-576-5887-0.pdf.
Testo completo
37
Fraser, Fiona C. "Temperature responses of nitrogen transformations in grassland soils". Thesis, University of Stirling, 2013. http://hdl.handle.net/1893/17055.
Testo completoAbstract (sommario):
The current literature shows that global climate is changing with temperatures generally increasing, precipitation patterns becoming less predictable and extreme weather events becoming more frequent. However, the literature is often unclear not only about how changes in temperature will affect soil processes but even about how soil temperatures themselves are changing. This thesis has found that soil temperatures over recent decades have increased at rates comparable to air temperatures (average mean of 0.71 in soil and 0.93 °C in air over the total length of the data sets used). There were differences in seasonal trends between soil and air, for example, winter air temperatures increased twice as quickly as spring air temperatures whereas in soil winter and spring temperatures were increasing at similar rates. This highlights potential problems for predicting how soil functions such as biogeochemical cycling will respond to realistic temperature change. In order to assess the effects of changing soil temperatures on particular reactions involved in soil Nitrogen cycling incubation experiments, both short and longer term in the laboratory as well as soil warming in the field were carried out. Realistic warming was found to increase the rates of protease and urease activity during all tests; however, amidase activity was only measurable after the addition of labile carbon and even then showed no temperature sensitivity. This thesis also considered the effect of temperature change on the size and structure of the soil microbial community at these realistic soil temperatures. Both in the lab and the field changes in rates of soil processes (enzyme activity) as a result of temperature change are not accompanied by a change in either size or structure of the microbial community as measured by phospholipid fatty acid analysis, suggesting high levels of functional redundancy within the soil microbial community. The effects of organic matter input in the field were found to have only small effects on the rates of enzyme activity although this was more important during laboratory incubations. Organic matter quality was also important during lab incubations where lower quality organic matter provoked greater enzyme activity in accordance with q-theory; however, there was no evidence for greater temperature sensitivity of low quality organic matter. The size and structure of the microbial community, both in the field and in the lab, were not affected by either the rate of organic matter input (in the field) or they quality of organic matter (in the lab). The size of the microbial community, however, decreased over time in both situations, the ratio of bacteria to fungi in the soil seemed to increase over time also.
38
Gaige, Elizabeth. "Throughfall Dynamics and Canopy Processes in a Nitrogen Fertilized Forest". Fogler Library, University of Maine, 2005. http://www.library.umaine.edu/theses/pdf/GaigeES2005.pdf.
Testo completo
39
Currey, Pauline M. "Interactions between atmospheric nitrogen deposition and carbon dynamics in peatlands". Thesis, University of Aberdeen, 2009. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=165545.
Testo completoAbstract (sommario):
Most undisturbed peatlands sequester carbon, and rising levels of atmospheric nitrogen deposition may have the potential to destabilize this function, possibly resulting in an increased release of carbon dioxide into the atmosphere. It is therefore of vital importance to investigate further the link between atmospheric nitrogen deposition and carbon dynamics in exposed ecosystems such as peatlands. The work described in this thesis aimed to elucidate the impact of increasing nitrogen on aspects of carbon turnover in peatlands. Using a long-term field-based experiment, I tested the effects of 4 years of ammonium and nitrate addition (8, 24 and 56 kg N ha-1 y-1) on the fate of newly photosynthesised carbon by plants and the turnover of labile and recalcitrant carbon. A second set of experiments undertaken in the laboratory assessed the use of plant wax analysis as potential biomarkers of past changes in vegetation and carbon status in peat. Overall, this work has shown that the form of nitrogen (ammonium versus nitrate) is a crucial component of atmospheric pollution and must be taken into consideration when investigating or predicting effects of reactive nitrogen on peatlands. In addition, nitrogen addition affected the fate of newly synthesised carbon differently in Eriophorum vaginatum and Calluna vulgaris, revealing the importance of considering plant traits when investigating environmental changes in terrestrial ecosystems. Furthermore, it has led to the development of an investigative tool for further exploration of the historical effects of atmospheric nitrogen deposition on vegetation an carbon content in peatlands.
40
Au, William R. "Relationships between microbial physiological status and nitrogen availability in forest soils". Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21506.
Testo completoAbstract (sommario):
Although the physiological nitrogen demand of the soil microbial biomass is a major determinant of N mineralization in forest soils, the exact nature of the relationship is unclear. This study investigated the relationships between a respiration-based indicator of microbial physiological N demand (NIR) and N availability in forest soils. NIR was found to correlate significantly with net mineralized N in the field and annual foliar litterfall N fluxes. In a laboratory incubation, NIR was shown to be sensitive to changes in soil available C and N pools. These results demonstrated that microbial physiological N demand is determined by relative availabilities of labile C and N, and that it is significantly related to N cycling in forest soils. Results from a seasonal study of a forested watershed suggest that nutrient availability determined tree production and soil C availability, which in turn determined microbial physiological N demand and nitrogen dynamics in the forest.
41
Kim, Dong Yeob. "Municipal wastewater effects on nitrogen cycling in a mature hardwood forest". Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/40072.
Testo completoAbstract (sommario):
Land disposal of municipal wastewater is considered ecologically acceptable and cost effective. The success of land treatment systems, however, requires proper functioning of all ecosystem components. The impact of municipal wastewater irrigation on the structure and function of an Appalachian hardwood forest in Virginia was investigated. Four irrigation rates (17.5, 35, 70, and 140 em yr⁻¹ ) were applied in this hardwood forest, and their effects on forest nutrient cycling were monitored for two years. Tree growth, seedling reproduction, tree mortality, species diversity, and N sequestering by vegetation were not changed significantly. Herbaceous ground cover increased due to irrigation, except for the 140 cm yr⁻¹ treatment where the heavy spray caused physical damage to the cover. Depending on the rate applied, the mature hardwood forest system sequestered only -3.4 to 8.2 kg N ha yr⁻¹ in the above ground biomass. Therefore, the fate of added N to the system became a function of N transformation processes in the soil. Nitrogen mineralization and nitrification increased as irrigation increased. Denitrification rates were not affected by irrigation; the process of denitrification did not constitute a significant N output from the forest system. The additional soil nitrate (N0₃) was left to leach because of the low assimilation by the plant/soil system and the low denitrification rate. Nitrogen storage decreased in the forest floor due to the increase in litter decomposition, and increased in the surface soil due to the increase in microbial N assimilation. Total soil N increased on the low irrigation sites and decreased on the high irrigation sites, indicating that high rates of irrigation stimulated N loss from the soil by enhancing soil N transformations. The health of the forest ecosystem was not adversely affected during this period, but the forest did not serve as a net sink for N. There was little opportunity for N sequestering in this mature hardwood forest. Without harvesting and regeneration, the system is likely to lose system N when wastewater is applied. When wastewater is applied to lands, N sequestering and denitrification should be maximized in order to minimize the pollution potential of N0₃ leaching to groundwater systems.Ph. D.
42
Eliasson, Peter. "Impacts of climate change on carbon and nitrogen cycles in boreal forest ecosystems /". Uppsala : Swedish University of Agricultural Sciences, 2007. http://diss-epsilon.slu.se/archive/00001525/.
Testo completoAbstract (sommario):
Thesis (doctoral)--Swedish University of Agricultural Sciences, 2007.Thesis documentation sheet inserted. Includes appendix of four papers and manuscripts, three co-authored with others. Includes bibliographical references. Also issued electronically via World Wide Web in PDF format; online version lacks appendix.
43
Persson, Jörgen. "Organic nitrogen uptake by boreal forest plants /". Umeå : Dept. of Forest Genetics and Plant Physiology, Swedish Univ. of Agricultural Sciences, 2003. http://epsilon.slu.se/s265-ab.html.
Testo completo
44
Rattle, Jean. "Dissolved nitrogen dynamics in an ombrotrophic bog". Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=98773.
Testo completoAbstract (sommario):
Research for a dissolved nitrogen budget was conducted at Mer Bleue bog near Ottawa, ON, from May 20, 2003 to May 21, 2004. Mer Bleue is located within an area experiencing the highest levels of atmospheric nitrogen deposition in North America, although these levels are only low to moderate compared to those in Europe. Continuous measurements of precipitation, evapotranspiration, bog water table level and outflow water depth were used in conjunction with discrete measurements of precipitation and outflow to determine the hydrologic budget. Water samples were taken from precipitation collectors, piezometers at various depths and locations throughout the bog, and an outflow point in order to gauge changes and patterns in chemical concentrations at various points throughout the bog. The nature of the bog morphology and landscape allowed for collection of water samples from a single outflow point.Chemical analysis combined with the water budget revealed that the majority of the dissolved nitrogen is entering the bog as NO3-N and NH 4-N (inorganic nitrogen), and leaving the bog as dissolved organic nitrogen (DON). Export of nitrogen was generally low relative to the input, and was only a very small fraction of the huge amount of nitrogen stored in the bog. Bog porewater concentrations were dominated by DON and did not show spatial patterns in relation to the bog edge. When comparing the annual accretion of nitrogen at the bog to the long-term storage numbers, it was apparent that there is a missing source of nitrogen. From the literature and patterns in the bog, it appears that this missing input at Mer Bleue is likely due to a combination of previously unmeasured nitrogen fixation and more diverse usage of DON by bog vegetation.
45
Le, Noë Julia. "Biogeochemical functioning and trajectories of French territorial agricultural systems : carbon, nitrogen and phosphorus fluxes (1852-2014)". Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS159/document.
Testo completoAbstract (sommario):
Cette thèse décrit les systèmes de production agricole en termes de flux biogéochimiques d’azote (N), de phosphore (P) et de carbone (C) dans les territoires français de 1852 à 2014 suivant une approche socio-écologique qui permet d’appréhender les logiques qui les gouvernent. Les résultats obtenus mettent en lumière à l’échelle des territoires français le lien systémique entre structures de production, bilans N et P et variations des stocks de C organique dans les sols agricoles. Les systèmes agricoles intensifs et spécialisés engendrent les pertes environnementales et les consommations de ressources par unité de surface agricole les plus considérables et accentuent l’ouverture des cycles d’N et de P. Cependant, c’est seulement après la seconde guerre mondiale que certaines régions françaises se sont spécialisées dans la grande culture ou, à partir des années 1980, dans l’élevage intensif. La période des années 1950 à 1980 est marquée par l’accélération des rendements des cultures végétales, de la densité de cheptel et de l’usage des fertilisants minéraux. Les conséquences en ont été une augmentation des bilans N et P et des apports de C aux sols agricoles, causant des pertes considérables d’N vers l’hydrosphère et l’atmosphère et l’augmentation des stocks de P et de C dans les sols. Néanmoins, l’accumulation du C n’a été rendue possible que par le recours aux fertilisants minéraux et au machinisme agricole consommant des énergies fossiles. Ainsi, le stockage du C dans les sols représente un effet secondaire du passage d’un métabolisme énergétique dépendant de l’énergie solaire à un métabolisme fondé sur la combustion d’énergie fossileThis work investigates agricultural systems from the angle of nitrogen (N), phosphorus (P) and carbon (C) fluxes in French regions from 1852 to 2014, following a socio-metabolic approach stressing out the underlying logic behind these material fluxes. Results brought out by this research highlight the systemic relation between production pattern and N and P balances, and changes in soil organic C stocks in agricultural soil. Intensive specialized agricultural systems generate high environmental losses and resource consumption per unit agricultural surface and present largely open nutrient cycles due to substantial trade flows. Conversely, integrated crop and livestock farming have more limited N and P consumption and lead to lower air and water contamination. Long-term analysis shows that only after the Second World War, under the pressure of strong interventionist policies, some French regions specialized into crop or livestock farming. Particularly, the period from the 1950’s to the 1980’s was marked by a concomitant acceleration in crops yields, livestock production and use of mineral fertilizers. This resulted in increased N and P balances over cropland and grassland and growing C inputs to cropland, causing important losses of N to the hydrosphere and atmosphere, together with the accumulation of P and C stocks in soils. However, C accumulation resulting from increased crop production was permitted by the increased recourse to mineral fertilizers and agricultural machinery which consumes fossil-fuel energy. Therefore, C storage in cropland was a side-effect of the shift from an energy metabolism based on solar energy to one based on fossil-fuel combustion
46
Lowman, Guy Russell Pollock. "Deposition of nitrogen to grassland versus forested areas in the vicinity of sabie, Mpumalanga, South Africa". Thesis, University of the Witwatersrand, 2003. http://hdl.handle.net/10539/20112.
Testo completoAbstract (sommario):
Nitrogen deposition to adjacent grassland and forested areas in the vicinity of Sabie,
Mpumalanga, South Africa was studied. Total deposition amounts to the forested area are
calculated to be 7l.2 kg N ha-1 yr1 and to the grassland area, 25 kg N ha· 1 yr1. The
average deposition amounts are similar to or at least approach nitrogen mineralisation
amounts at nearby sites of 50-70 kg N ha-1 yr1. The deposition amounts are made up of
21.4 kg N ha-1 yr1 dry deposition, 7.8 kg N ha-1 yr1 wet deposition and 42 kg N ha-1 yr1
cloud droplet deposition for the forest. For the grassland, the amounts are 7 kg N ha-1 yr1
dry deposition, 7.8 kg N ha-1 yr1 wet deposition and 10.5 kg N ha-1 yr1 cloud droplet.
deposition. For both wet and cloud droplet deposition, the amount attributable to nitrate
was greater than that attributable to ammonium. For wet deposition, nitrate contributed
4.1 kg N ha-1 yr1 and ammonium contributed 3.7 kg N ha-1 yr1 to both forests and
grasslands. For cloud droplet deposition to forests, the amounts were 28 kg N ha-1 yr1
attributable to nitrate and 14 kg N ha-1 yr1 attributable to ammonium. For grasslands the
amounts were 7 and 3.5 kg N ha-1 yr1. In both forests and grasslands, the component of
dry deposition contributing the most to deposition was ammonia gas, the amounts being
14.2 and 4.3 kg N ha-1 yr1 respectively. Nitric acid contributes 3.7 and 1.9 kg N ha-1 yr1
respectively and is followed by the nitrogen dioxide component that contributes 1.6 and
0.5 kg N ha- I yr1. Ammonium and nitrate particles contribute the least to deposition. For
the forests the amounts are 1 and 0.9 kg N ha-1 yr1 and for the grasslands they are 0.2 and
0.1 kg N ha-1 yr1. A strong seasonal variance in deposition amounts is apparent with
maximum deposition amounts occurring in Summer and minimum amounts in Winter.
Intermediate amounts are deposited in Autumn and Spring, with the latter season having
slightly larger deposition amounts. The seasonal variance is strongly linked to the
seasonal rainfall and cloud droplet deposition patterns. Biomass burning is indicated as a
possible important factor in influencing the chemical composition of rainfall during
Spring. Of the deposition amounts obtained in this study, the deposition from cloud
droplets is high compared to other studies and is probably overestimated. Further
research into this area is needed.
47
McCaig, Allison E. "16S ribosomal DNA analysis of marine ammonia-oxidising bacteria". Thesis, University of Aberdeen, 1995. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU543307.
Testo completoAbstract (sommario):
Nitrification is central to the global cycling of nitrogen and is important for primary production and other processes in marine systems, where nitrogen is generally the limiting nutrient. The majority of studies on nitrification, however, have focused on terrestrial systems, where this process can cause significant losses of N-based fertilisers from agricultural land. Comparatively little is known of nitrification in marine systems and the organisms involved. In addition, technical difficulties in isolation of pure cultures of ammonia-oxidising bacteria have severely restricted studies of species diversity and community structure of these organisms. In this study, molecular technology, based on the 16S ribosomal RNA (rRNA) molecule was applied to the characterisation of marine communities of ammonia-oxidising bacteria. PCR primers were designed for specific amplification of the rRNA gene (rDNA) from ammonia-oxidisers belonging to the beta-subdivision of the Proteobacteria. These primers were used to characterise both enrichment cultures and communities within polluted and unpolluted sediment samples. These studies indicated considerable diversity of beta-subgroup ammonia-oxidisers within marine systems which has not previously been detected. It was also shown that enrichment and isolation techniques select for strains belonging to the genus Nitrosomonas while the majority of sequences obtained by direct analysis of rDNA amplified from total genomic extracts belonged to the genus Nitrosospira. In addition, novel isolation methods were developed which considerably reduced the level of heterotrophic contamination and greatly facilitated isolation of pure cultures. In situ probing, using fluorescently labelled rRNA oligonucleotide probes, indicated that CCD microscopy is less sensitive than UV microscopy alone due to quenching of the signal.
48
Graham, Taylor B. "Nitrate recycling versus removal in the Cape Fear River estuary". View electronic thesis, 2008. http://dl.uncw.edu/etd/2008-3/grahamt/taylorgraham.pdf.
Testo completo
49
Thanapakpawin, Porranee. "Spatially-distributed modeling of hydrology and nitrogen export from watersheds /". Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/9850.
Testo completo
50
Röing, Kristina. "Soil nitrogen fluxes in Swedish and Nigerian agricultural systems /". Uppsala : Dept. of Soil Sciences, Swedish University of Agricultural Sciences, 2005. http://epsilon.slu.se/200557.pdf.
Testo completo