La caféiculture représente 7,5% des cultures permanentes mondiales et utilise généralement de grandes quantités de fertilisants azotés (jusqu'à 350 kg N ha-1 an-1). La caféiculture est souvent pratiquée sous couvert d'arbres dont certains sont fixateurs d'azote. La contribution des plantes fixatrices d'azote aux émissions de N2O est un sujet prégnant dans le cadre du développement durable, avec des résultats dans la littérature qui peuvent parfois apparaître contradictoires. Dans ce contexte, nous avons étudié le bilan des gaz à effet de serre (GES) dans deux cultures caféières fortement fertilisées (250 kg N ha-1 an-1), au Costa Rica : une monoculture et une culture ombragée par l'espèce légumineuse fixatrice de N2 Inga densiflora. Nous avons mesuré périodiquement les flux de N2O, CH4 et CO2 à l'interface solatmosphère, leurs déterminants édaphiques (humidité gravimétrique, espace poral occupé par l'eau, température et teneur en azote minéral) et les taux de minéralisation de l'azote dans le sol. Par ailleurs, nous avons caractérisé, au laboratoire, les paramètres biologiques de nitrification-dénitrification et leur production associée de N2O et N2 pour simuler en continu les émissions de N2O avec les modèles NGAS et NOE sur une durée d'un an. Enfin, nous avons évalué la dynamique du C du sol et l'accumulation de C dans les biomasses et la litière. Nos mesures ont montré une très forte contribution de la fertilisation azotée aux émissions de N2O, soit une proportion moyenne de 77% des bilans annuels (4,3 ± 0,3 et 5,8 ± 0,5 kg N-N2O ha-1 an-1, respectivement dans la monoculture et la culture ombragée). Les fertilisations ont également augmenté temporairement la respiration du sol. Les valeurs faibles des activités biologiques (notamment des potentiels de dénitrification < 1 kg N ha-1 j-1) ont expliqué les flux toujours inférieurs à 300 g N ha-1 j-1 observés dans des conditions environnementales pourtant favorables à la production de N2O (température, humidité et teneur en nitrate du sol élevées). La similarité entre les activités biologiques mesurées sur les deux cultures de café ainsi que celle entre les bilans annuels de N2O établis à partir de mesures et de modélisation permettent de conclure sur un effet de faible ampleur de l'espèce légumineuse fixatrice de N2 sur les émissions de N2O. Le bilan des flux de GES hors CO2 à l'interface sol-atmosphère et du stockage de C de la culture ombragée (11,93 ± 2,17 Mg CO2-equivalent ha-1 an-1) a été 4 fois supérieur au bilan de la monoculture (2,67 ± 1,94 Mg CO2-equivalent ha-1 an-1). Nos résultats tendent donc à confirmer que la culture de café conduite en agroforesterie, sur un Andosol, augmente le puits de GES et que, dans le contexte présent, l'utilisation d'une légumineuse fixatrice de N2 comme espèce ombragère ne contredit pas cette observation.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2017-10-03T16:31:46Z No. of bitstreams: 1 _Dissertação-1.pdf: 1765644 bytes, checksum: 7e195b49bdd27dff996d76e75bbb6210 (MD5) / Made available in DSpace on 2017-10-03T16:31:46Z (GMT). No. of bitstreams: 1 _Dissertação-1.pdf: 1765644 bytes, checksum: 7e195b49bdd27dff996d76e75bbb6210 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / O aquecimento global provocado por gases como CO2, N2O e o CH4 resultantes de atividades agrícolas e por solos alagados tem motivado inúmeros estudos em diversos países, procurando quantificar a contribuição de diferentes sistemas na emissão desses gases. Os objetivos desse estudo foram elucidar o mecanismo de produção do gás do efeito estufa, óxido nitroso (N2O) em uma área de floresta secundária baixa localizada em Manguariba - Rio de Janeiro e determinar se estas emissões ocorrem acompanhadas por processos de nitrificação ou desnitrificação. Para que isso fosse possível, foram realizadas quatro campanhas de amostragens seguidas de experimentos de incubação do solo em laboratório e análises químicas deste solo antes e após as incubações. Medidas de variação de pressão em câmaras sob condições controladas de temperatura foram realizadas empregando-se um manômetro tubo em “U” em quatro experimentos e um barômetro/sensor/datalogger em outros dois experimentos. As concentrações de N2O, bem como as de CH4 no solo, foram determinadas antes e após as incubações por cromatografia gasosa. Na primeira campanha de amostragem foram coletadas também amostras de água em um curso de água que pode ser uma fonte de nitrogênio para este solo, pois em época de chuvas a água poluída com esgoto doméstico, deste riacho chega até os pontos de amostragem. Foram determinadas as concentrações de amônio e nitrato em amostras do solo, antes e após incubações, e na água do riacho. Através dos dados gerados pelas análises químicas determinamos as taxas líquidas de nitrificação, mineralização/assimilação ocorridas durante o período de incubação do solo e correlacionamos essas taxas com a produção de óxido nitroso. A nitrificação a uma taxa constante se mostrou dominante no experimento onde houve a maior produção de N2O. Nos demais experimentos a nitrificação permaneceu dominante, porém seguida por desnitrificação em outros dois experimentos, nos quais a produção do gás foi muito pequena e até mesmo nula, indicando a redução do óxido nitroso a N2. A desnitrificação ocorreu de forma dominante em apenas um dos experimentos e possivelmente foi seguida por nitrificação, pois houve uma pequena produção de N2O durante esta incubação. / The global warming caused by greenhouse gases like CO2, CH4 and N2O resulting from agricultural activities and flooded soils has motivated numerous studies in many countries, seeking to quantify the contribution of different systems on greenhouse gas emissions. The objectives of this study were to elucidate the mechanism of production of greenhouse gas, nitrous oxide (N2O) in a secondary forest area located in downtown Manguariba (Rio de Janeiro) and determines if these emissions occur accompanied by processes of nitrification and denitrification. To make this possible, there were four sampling campaigns followed by incubation experiments of soil in the laboratory and chemical analyses of soil before and after incubations. Measures of barometric pressure variation in PVC chambers under controlled temperature were carried out using a variation of a pressure gauge manometer tube into "U" for four incubation experiments and a sensor which measures the pressure variation barometer / sensor / datalogger (Baro Diver) during the third and fourth experiments. N2O concentrations were determined by gas chromatography. In the first year of sampling, samples of water were taken from a tributary of the Rio Guandu, which can be a source of sewage pollution for this soil, because in the rainy season the water in this tributary reaches the sampling points. Chemical analysis was performed for determination of NH4 + and for analysis of nitrate ions. Data generated by the chemical analysis determined the rate of net nitrification, mineralization / assimilation which occurred during the incubation periods and correlated these rates with the production of nitrous oxide. Nitrification at a constant rate proved to be dominant in the experiment where there was a greater production of N2O. In other experiments, however, nitrification remained dominant followed by denitrification in two other experiments, in which gas production was very small and even zero, indicating the reduction of nitrous oxide to N2. Denitrification was very dominant in only one experiment and was followed by nitrification possibly because there was a small N2O production during this incubation. The experiment with the barometer / sensor / datalogger (Baro Diver) was carried out to confirm what would be the dominant process along these incubations. With this sensor we observed nitrification-dominant production of nitrous oxide. There were no correlations between the flow of N2O emitting in situ and flow generated during the incubation periods. We also observed that the effluent water from the Rio Guandu sample showed high concentrations of nitrate and ammonia and can be considered as a source of inorganic N to this soil

No description available.

The area of vegetable production is growing rapidly world-wide, as are efforts to increase production on existing lands in these labor- and input-intensive systems. Yet information on nutrient losses, greenhouse gas emissions, and input efficiency is lacking. Sustainable intensification of these systems requires knowing how to optimize nutrient and water inputs to improve yields while minimizing negative environmental consequences. This work characterizes soil nitrogen (N) dynamics, nitrate (NO3¯) leaching, greenhouse gas emissions, and crop yield in five diversified vegetable systems spanning a gradient of intensification that is characterized by inputs, tillage and rotational fallow periods. The study systems included a low input organic system (LI), a mechanized, medium scale organic system (CSA), an organic movable high tunnel system (MOV), a conventional system (CONV) and an organic stationary high tunnel system (HT). In a three-year vegetable crop rotation with three systems (LI, HT and CONV), key N loss pathways varied by system; marked N2O and CO2 losses were observed in the LI system and NO3– leaching was greatest in the CONV system. Yield-scaled global warming potential (GWP) was greater in the LI system compared to HT and CONV, driven by greater greenhouse gas flux and lower yields in the LI system. The field data from CONV system were used to calibrate the Root Zone Water Quality Model version 2 (RZWQM2) and HT and LI vegetable systems were used to validate the model. RZWQM2 simulated soil NO3¯-N content reasonably well in crops grown on bare ground and open field (e.g. beet, collard, bean). Despite use of simultaneous heat and water (SHAW) option in RZWQM2 to incorporate the use of plastic mulch, we were not able to successfully simulate NO3¯-N data. The model simulated cumulative N2O emissions from the CONV vegetable system reasonably well, while the model overestimated N2O emissions in HT and LI systems.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2018-02-27T15:18:48Z No. of bitstreams: 1 Guimaraes GP 2005.pdf: 1398079 bytes, checksum: 2001454348415a2dbc540e659a2f4498 (MD5) / Made available in DSpace on 2018-02-27T15:18:48Z (GMT). No. of bitstreams: 1 Guimaraes GP 2005.pdf: 1398079 bytes, checksum: 2001454348415a2dbc540e659a2f4498 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / Em ambientes marinhos, a química do nitrogênio é controlada por reações redox, mediadas pelo fitoplâncton e por bactérias, que produzem gases trocados com a atmosfera devido ao desequilíbrio entre as concentrações do ar e do mar. Os dois principais gases de nitrogênio envolvidos neste processo são a amônia (NH3) e o óxido nitroso (N2O). O NH3 é a base dominante na atmosfera, possuindo grande importância como neutralizador dos ácidos presentes no ar. O N2O é um importante gás traço na atmosfera e absorve radiação infravermelha contribuindo para o efeito estufa, além de estar associado a diminuição de O3 na estratosfera. Na Baía de Guanabara cerca de 7,8 milhões de habitantes geram esgotos domésticos, que são lançados diretamente nas suas águas gerando elevadas concentrações de nitrogênio inorgânico, levando a acreditar que esta é uma importante fonte de NH3 e N2O para a atmosfera. Neste trabalho foi realizada uma estimativa preliminar dos fluxos de NH3 e N2O na interface ar-mar da Baía de Guanabara em dois tipos de abordagem: espacial e temporal. Para a abordagem espacial foram coletadas 37 amostras entre os dias 05 e 07 de abril de 2004. Para a abordagem temporal, foram coletadas amostras semanais em 10 praias da cidade do Rio de Janeiro, durante o período de julho de 2003 e fevereiro de 2004 (macrotemporal, n = 267), e amostras de 3 em 3 horas em um ponto central durante 9 a 12 de fevereiro de 2004 (microtemporal, n = 25). Em todas as análises a temperatura, salinidade e pH foram medidos in situ e o nitrogênio amoniacal analisado através do método do indofenol. Apenas na abordagem espacial foram analisados nitrito, nitrato (métodos espectrofotométricos) e N2O por cromatografia gasosa com ECD. Os fluxos foram calculados baseado no modelo de duas camadas (two-layer model) adotando concentrações atmosféricas de 1 e 5 μg m-3 para NH3 e de 325 ppb para N2O. Os fluxos de NH3 na interface ar-mar variaram de –31 a 3486 μg N m-2 h-1. Considerando as maiores concentrações na atmosfera (5 μg NH3 m-3), 92% dos fluxos na abordagem espacial, 68% na macrotemporal e 20% na microtemporal indicaram emissão de NH3 para a atmosfera. Os fluxos de N2O variaram entre -46 e 2123 ng N m-2 h-1 (média 306 ± 495 ng N m-2 h-1), dos quais 89% representaram emissão para a atmosfera. Foi verificada uma alta correlação do N2O com o nitrito (r=0,84) indicando que provavelmente o processo dominante de produção de N2O nas águas superficiais da Baía de Guanabara é a nitrificação. Todos os dados indicam uma maior contribuição orgânica no setor oeste da Baía de Gaunabara, contribuindo com altos fluxos de NH3 e N2O para a atmosfera. / In the marine environment, the chemistry of nitrogen is controlled by redox reactions, mediated by phytoplankton and bacteria, that produce gases exchanged with the atmosphere due to the desequilibrium between the concentrations of air and sea. The two main gases of nitrogen involved in this process are ammonia (NH3) and nitrous oxide (N2O). NH3 is the dominant base in the atmosphere and has great importance as neutralizer of the acids in the air. N2O is a trace gas that absorbs infrared radiation contributing to global warming and to ozone depletion in the stratosphere. Around Guanabara Bay about 7.8 million of habitants release domestic sewage directly in to the water elevating the concentrations of inorganic nitrogen, which leads us to believe that this is an important source of NH3 and N2O to atmosphere. A preliminary estimate of the fluxes of NH3 and N2O in the air-sea interface of Guanabara Bay were made using two approachs: spatial and temporal. For the spatial approach 37 samples were collected from 5 to 7 April 2004. For the temporal approach weekly samples were collected at 10 beaches of the city of Rio de Janeiro, during the period of July 2003 and February 2004 (macro temporal, n = 267), and samples in intervals of 3 hours in a central point from 9 to 12 February 2004 (micro temporal, n = 25). The temperature, salinity and pH were measured in situ and the ammoniacal nitrogen analyzed by the indophenol method. Only in the spatial approach were analyzed the nitrite, nitrate (spectrophotometer methods) and N2O by gaseous chromatography with ECD. The fluxes were calculated based on the two-lawyer model adopting atmospheric concentrations of 1 and 5 μg m-3 for NH3 and 325 ppb for N2O. The fluxes of NH3 in the air-sea interface varied from –31 to 3486 μg N m-2 h-1. Considering the greatest concentrations adopted in air (5 μg NH3 m-3), 92% of the fluxes in the spatial, 68% of macro temporal and 20% of micro temporal approaches indicated emission of NH3 to the atmosphere. The fluxes of N2O varied between –6 and 2123 ng N m-2 h-1, of which 89% indicated emission to the air. A high correlation of N2O with nitrite (r=0.84) was verified indicating that probably the dominant process of production of N2O in the surface waters of Guanabara Bay is nitrification. All data indicate a greater organic contribution in the West sector of Guanabara Bay, contributing with high fluxes of NH3 and N2O to the atmosphere.

No description available.

Nitrous oxide (N2O) is a greenhouse gas (GHG) with 300 times the radiative forcing in the atmosphere of carbon dioxide (CO2), and has recently become a subject of great concern because the nitrogen (N) fertilizers which have been necessary to increase agricultural productivity have also dramatically increased N2O emissions from agroecosystems. Many N control practices have been suggested and implemented in agroecosystems, but their ability to simultaneously remove reactive N from the environment and prevent the production of N2O is, at best poorly understood. The goal of this work is to characterize environmental controls on production of N2O in denitrifying bioreactors. The review portion of this work first discusses the geologic history of the N cycle, how its past and present processes differ, and how it is being affected by human activity. It then explores the N cycle's biochemical pathways, reviews the controls for each of its steps, and discusses the environmental drivers of these controls. The review closes with a discussion of environmental N management strategies. The experimental portion of this work further explores these concepts by observing how biochar amendment and the modification of pH affect N2O production in the denitrification pathway in denitrifying bioreactors. Both pH and biochar have previously been shown to affect N2O production and many N management practices utilize biochar or manipulate pH to increase N retention. The objectives of the experiment were to: 1) Examine headspace N2O concentration in sealed, biochar-amended, denitrifying bioreactors; 2) Determine if the effects of pH on N2O production differ in biochar-amended systems versus controls (under acidic, unbuffered, and buffered conditions); 3) Quantify key denitrification genes (nirK, nirS, nosZ) in each treatment combination. Experimental results showed biochar treatment to significantly increase N2O emissions, a result which runs contrary to most, but not all studies regarding its effects on N2O production. Differences between treatments decreased with increasing pH levels. Biochar did not exhibit significant effects on individual denitrification genes, but it did show influence on the ratios of their populations. On the other hand, pH was found to have significant effects on nirS and nosZ populations. Differences in N2O production between biochar and controls were thus explained by biochar's chemical effects, likely its ability to increase denitrification activity. Developing an understanding of the mechanisms behind these differences will require using a combination of isotope tracing, enzyme assays, and mass balance approaches. Future microbial work in biochar-amended systems should attempt to characterize differences in gene expression, overall community structure, and long-term population trends in the genes of interest. The combination of these approaches should allow researchers to better predict where N2O production will occur and develop strategies to mitigate it while simultaneously increasing food production to meet the demands of a growing population. / Master of Science

Le principal objectif de cette thèse est d'étudier les interactions entre l'océan côtier et l'océan ouvert dans la zone de l'upwelling du Benguela, située au large des côtes d'Afrique du Sud et de Namibie, à l'aide d'un outil numérique et de données satellites et in-situ. Un modèle biogéochimique adapté à la zone d'étude (BioBUS ; Biogeochemical model for the Benguela Upwelling System), prenant en compte les processus caractéristiques des systèmes d'upwelling de bord Est et des zones de minimum d'oxygène associées a été développé, puis couplé au modèle hydrodynamique ROMS, afin de mettre au point une configuration réaliste centrée sur le système de l'upwelling de Namibie (sous-système Nord du Benguela), zone d'étude de cette thèse. Ces travaux de thèse ont permis d'améliorer notre compréhension des systèmes d'upwelling de bord Est (EBUS), notamment leurs impacts locaux et régionaux, ainsi que les couplages physiques/biogéochimiques dans ces systèmes. A l'issue de ces travaux de thèse, les apports d'azote depuis la zone de l'upwelling vers le gyre oligotrophe de l'océan Atlantique Sud ont été estimés (0.38 molN.m-2.yr-1) et sont comparables aux autres sources d'azote (dépôts atmosphériques, fixation biologique, ...) possibles de soutenir la production primaire dans le gyre subtropical (de 0.01 à 0.24 molN.m-2.yr-1). Les pertes d'azote par dénitrification et anammox liées à la zone de minimum d'oxygène (2.2 108 molN.yr-1) sont du même ordre de grandeur que les pertes par émission de N2O vers l'atmosphère (5.5 108 molN.yr-1), mais sont sous-estimées par rapport aux quelques estimations in-situ dont nous disposons. Les flux de N2O à l'interface océan-atmosphère dans cette région sont clairement significatifs pour le budget atmosphérique de N2O. En effet, même si la surface de la zone ne représente pas plus de 1.2% des EBUS, ces émissions de N2O contribuent à 4% des émissions de N2O dans les EBUS. Enfin, ces travaux de thèse montrent l'importance des processus à mésoéchelle dans le transport total d'azote au large du plateau continental Namibien.

Les sols représentent environ 63% des émissions de N2O et à eux seuls les sols tropicaux représentent 23% de ce budget soit une contribution bien plus élevé que les sols tempérés. Ces sols sont connus pour abriter une grande biodiversité d'invertébrés dominés par quatre types i.e. termites, vers de terre, fourmis et larves de scarabaeid. Ces groupes macrofaunal sont considérés comme des ingénieurs des sols via notamment leurs actions de régulation de la disponibilité des ressources chimiques, tels que l'azote minéral pour les micro-organismes. Cette régulation est due à leurs capacités de digestion spécifiques de la matière organique ainsi que la création et/ou la modification des habitats des sols. Cette étude est basée sur l'hypothèse suivante (i) l'environnement digestif et les structures biogéniques de ces ingénieurs du sol sont considérées comme des « hot spot » d' émissions de N2O (ii) les taux d'émission de N2O varient en fonction de leurs régimes alimentaires, cette macrofaune ingérant des substrats avec différents C:N (iii) le taux d'émission de N2O de chaque invertébré est corrélé à la densité des communautés bactériennes digestives impliquées dans l'émission de N2O (bactéries nitrifiantes et dénitrifiantes) et à leur teneur en azote minéral dans leur tube digestif. Pour évaluer ces différentes hypothèses, des mesures des taux d'émission de N2O ont été effectuées in vitro en aérobiose pour la macrofaune (30 espèces différentes en provenance d'Afrique, d'Amérique du Sud et d'Europe) et leurs matériels biogéniques associées (nids, turricules). L'abondance des gènes fonctionnelles des bactéries nitrifiantes (AOA et AOB) et dénitrifiantes (nirK, nirS, nosZ) ont été quantifiés par PCR quantitative. Les termites humivores et champignonnistes ainsi que les larves de scarabaeid émettent des quantités significatives de N2O alors que les fourmis n'en émettent pas. Quand aux termites xylophages et litièrivore, ils absorbent le N2O. Les structures biogéniques des vers de terre (turricules) et des fourmis (nid) émettent des quantités importantes de N2O ce qui n'est pas le cas des nids de termites. La faune du sol et leurs structures biogéniques associées, sont donc, dans la majorité des cas étudiés, un lieu d'émission de N2O, confirmant ainsi notre première hypothèse. Ce travail a également démontré qu'il y a avait une étroite corrélation entre régime alimentaire et intensité de l'émission de N2O au sein de chaque type de macrofaune étudié. En revanche, l'abondance des gènes des communautés digestive nitrifiantes et dénitrifiantes et le contenu en N minéral au sein du tube digestif ne semblent pas être des proxies pertinents des émissions de N2O. A partir de ces mesures, des calculs ont été effectuées pour déterminer l'importance de ces émissions à l'échelle des écosystèmes tropicaux étudiés (forêt et savane). Ces calculs suggèrent que la macrofaune du sol dans ces écosystèmes pourrait contribuer entre 0,1 à 11,7% et 0,1 à 8,8% du budget total des émissions de N2O, respectivement. Les résultats de ces travaux devraient contribuer à une meilleure prise en compte de la composante biotique dans la modélisation des émissions de gaz à effet de serre provenant des sols en milieu tropical. / Soils account for about 63% of N2O emissions. Tropical soils are estimated to emit 23% of global N2O emission budget which is much higher than temperate soil N2O emissions. These soils also harbor a huge biodiversity of invertebrates dominated by four types of macrofauna i.e. termites, earthworms, ants and scarabaeid grubs. These macrofaunal groups are considered as soil engineers because they regulate the availability of chemical resources, like mineral nitrogen, for the microorganisms via their specific digestion capabilities and/or by creating and modifying soil habitats. This study is based on the following hypothesis (i) the gut environment or biogenic structures of these soil engineers are considered as hotspots of N2O emission (ii) the N2O emission rates will vary according to their feeding behavior as these macrofauna thrive on diverse substrates with different C:N ratio (iii) the rate of N2O emission in each soil fauna will also depend on the gut density of the bacterial communities involved in the N2O emission (nitrifiers and denitrifiers) and on the mineral nitrogen content within the gut. To assess these different hypotheses in-vitro short-term N2O emission rates were assessed for either live macrofauna (30 species collected from Africa, South America and Europe) or their biogenic materials or both under aerobic incubations. Genes abundance of nitrifiers (AOA and AOB) and denitrifiers (nirK, nirS, nosZ) were quantified by real time quantitative PCR. Soil-feeders and fungus-growing termites and scarabaeid grubs emitted in-vivo N2O while ants did not. Surprisingly, wood- and grass-feeding termites revealed an uptake of N2O. Biogenic structures of earthworms and ants emitted substantial amount of N2O while those of termites did not. The emission difference between macrofauna or their biogenic materials and their control materials was significant for most of the macrofaunal groups studied confirming our first hypothesis. We also confirmed that the feeding behavior (total N content and C:N ratio of food material) is the main factor explaining the observed N2O emission pattern of each macrofaunal group investigated whereas genes abundances, particularly of denitrifiers and gut N mineral content did not appear to be relevant proxies of the N2O emissions rates. A back-on-the-envelope data upscaling suggests that soil macrofauna could contribute from 0.1–11.7% and 0.1–8.8% of the total soil N2O emissions, respectively, for the tropical rainforest and dry savanna ecosystems. This work should contribute to a better estimation of the soil biotic compartment in the different models of greenhouse gas emissions from tropical soils.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2017-09-18T16:28:16Z No. of bitstreams: 1 Dissertação - Renato Ribeiro (Mestrado em Geoquímica Ambient.pdf: 1758942 bytes, checksum: 2ab97e8d9839edbd110b4bfbbc94fdc9 (MD5) / Made available in DSpace on 2017-09-18T16:28:16Z (GMT). No. of bitstreams: 1 Dissertação - Renato Ribeiro (Mestrado em Geoquímica Ambient.pdf: 1758942 bytes, checksum: 2ab97e8d9839edbd110b4bfbbc94fdc9 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Fundação de Amparo a Pesquisa do Estado do Rio de Janeiro / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / O óxido nitroso (N2O) é um dos principais gases do efeito estufa e a principal fonte de óxido nítrico na estratosfera, contribuindo de forma indireta para o consumo do ozônio estratosférico. O tratamento de esgotos é uma fonte antrópica de N2O, cuja contribuição é quantitativamente considerada de menor relevância, entretanto, pouco se sabe sobre a real contribuição dessas emissões em virtude da grande variabilidade reportada nos fatores de emissão (FEs), balizados na carga de nitrogênio total (NT) afluente, tanto oriundo de estudos realizados em escala real quanto laboratorial. As diretrizes de 2006 do Painel Intergovernamental sobre Mudanças Climáticas para inventários nacionais de gases do efeito estufa propõem como FE 3,2 (2-8) g N2O pessoa-1 ano-1 para o caso de Estações de Tratamento de Esgotos (ETEs) com processos de nitrificação e desnitrificação controlados. O objetivo do presente estudo foi avaliar a relação entre alguns parâmetros operacionais, tais como concentração de NT afluente à ETE (especialmente NH4+), demanda química de oxigênio (DQO) e concentração de oxigênio dissolvido (OD), com as emissões de N2O do tanque de aeração de uma ETE localizada na região metropolitana do Rio de Janeiro. O processo de tratamento de esgotos empregado é o sistema de lodos ativados convencional com aeração realizada de forma diferenciada por zonas. As emissões de N2O foram determinadas mensalmente, sempre na parte da manhã, no período de janeiro a junho de 2010 ao longo das seis zonas dos quatro tanques de aeração que a ETE possui em funcionamento. A média das emissões de N2O determinada durante o período de estudo foi 1,11 kg N dia-1, o que corresponde a 0,02% da carga de NT afluente. As emissões de N2O foram menores no período de verão do que no inverno e positivamente correlacionadas (r = 0,90; n = 6; P < 0,01) com as concentrações de NH4+ afluente à ETE. Em relação às concentrações de DQO e OD, as maiores emissões de N2O ocorreram em regiões de baixas concentrações de DQO e concentrações de OD superiores a 2,0 mg L-1, sendo a maior emissão média de N2O determinada em OD próximo a 3,0 mg L-1. A redução da carga orgânica ao longo das zonas e o aumento gradual da concentração de OD contribuem de forma direta para as maiores emissões de N2O, em razão da maior disponibilidade de OD para ambas as reações de oxidação da matéria orgânica e nitrificação e, consequentemente, maior produção e emissão de N2O. As eficiências de remoção de demanda bioquímica de oxigênio (DBO), DQO e NT foram 97%, 93% e 80%, respectivamente. O FE médio, balizado na população atendida, foi 2,5 vezes menor do que o proposto pelas diretrizes de 2006 do Painel Intergovernamental sobre Mudanças Climáticas para inventários de emissões de N2O em ETEs com processos de nitrificação e desnitrificação controlados. Portanto, os resultados sugerem que o processo de lodos ativados convencional empregado na ETE de estudo é bastante eficiente na remoção da carga orgânica e NT e, além disso, no que tange as menores emissões de N2O quando comparado a outros sistemas empregados nas ETEs estudadas no Brasil e em estudos desenvolvidos no exterior. Sugere-se que tal eficiência esteja relacionada à utilização de aeração suficiente e diferenciada por zonas, que proporciona condições favoráveis aos processos microbiológicos de oxidação da matéria orgânica e aos processos de nitrificação completos, mesmo nas condições de elevadas concentrações de DBO, DQO e de NT (especialmente NH4+), como observado no período de inverno. / Nitrous oxide (N2O) is a major greenhouse gas and the main source of nitric oxide in the stratosphere, contributing indirectly to consumption of the stratospheric ozone. Wastewater treatment is an anthropogenic source of N2O, whose contribution is considered to be quantitatively of minor importance. However, little is known about the actual contribution of these emissions due to the wide variability reported in the emission factors (EFs), based on amount of N2O emitted relative to the influent total nitrogen (TN) load, both from full-scale and laboratory-scale studies. The 2006 guidelines of the Intergovernmental Panel on Climate Change for national inventories of greenhouse gases as proposed EF 3.2 (2-8) g N2O person-1 yr-1 for the case of advanced centralized wastewater treatment plants (WWTPs) with controlled nitrification and denitrification steps. The aim of this study was to evaluate the relationship between some operational parameters, such as TN concentration (especially NH4+), chemical oxygen demand (COD) and dissolved oxygen (DO) concentrations, on N2O emissions from the aeration tank of a WWTP located in the metropolitan region of Rio de Janeiro, Southeast Brazil. The wastewater treatment employed is conventional activated sludge process with a differentiated aeration system. The entire aeration system consists of four adjacent aeration tanks with six zones each. N2O emissions were measured monthly in the period from January to June 2010, always in the morning, over the six zones of the four aeration tanks. The average N2O emission was 1.11 kg N day-1 corresponding to 0.02% of the influent TN load. N2O emissions were lower in summer than winter and were positively related (r = 0.90; n = 6; P < 0.01) with influent NH4+ concentrations. Regarding the COD and DO concentrations, the highest N2O emissions occurred in regions of low concentrations of COD and DO concentrations above 2.0 mg L-1, with the highest average emission of N2O in DO concentration close to 3.0 mg L-1. The reduction of the organic load along the zones and gradually increase the DO concentration, contributes directly to higher N2O emissions, due to the greater availability of DO for both the oxidation of organic matter and nitrification, and consequently higher production and emission of N2O. The removal efficiencies of biological oxygen demand (BOD), COD and TN were 97%, 93% and 80%, respectively. The average EF calculated from population served was 2.5 lower than that proposed by the IPCC for N2O emission inventories in WWTPs with controlled processes of nitrification and denitrification. Therefore, the results suggest that the process employed in the WWTP study is very efficient in removing the organic load and TN, and in addition, with smaller N2O emissions when compared to other systems studied in Brazil and those available in literature. It is suggested that this efficiency is related to the use of aeration sufficiently to promote conditions favorable for the microbial oxidation of organic matter and complete nitrification, even under conditions of high BOD, COD and TN concentrations (especially NH4+), as observed during winter.