No description available.

Historically, whole stream open channel metabolism has been measured over short periods in conjunction with nutrient injections to assess nutrient dynamics within streams. The purpose of my study was to understand the seasonal changes in metabolism within and among streams as well as the impacts of different land use. This was addressed by monitoring nine different watersheds in the Little Tennessee River watershed in southwestern North Carolina.  The nine study watersheds were selected to represent a gradient of forested, agricultural, and developed land use / land cover types. Data loggers were deployed to collect continuous oxygen, temperature, conductivity, and stage height data from 2010-2011. I used these data to estimate gross primary production (GPP) and ecosystem respiration (ER). GPP and ER were compared to stream chemistry, light, land cover, and storms. I found that there is greater influence of local riparian land cover than watershed land cover on GPP and ER. Streams had varying annual GPP, but generally the peak in GPP occurred in late winter- early spring with lows in fall. GPP was most strongly influenced by the amount of available light, which is directly related to the amount of canopy cover. ER was much more variable than GPP within and among streams but generally peaked in summer and was lowest in the winter. ER was most strongly related to the proportion of agricultural land cover in the local riparian area. My results suggest that local riparian vegetation may have a greater impact on metabolism than mountainside development. / Master of Science

Understanding the mechanism of photosynthetic seasonality in Amazonian evergreen forests is critical for its formulation in global climate and carbon cycle models. However, the control of the unexpected photosynthetic seasonality is highly uncertain. Here we use eddy-covariance data across a network of Amazonian research sites and a novel evapotranspiration (E) and two-leaf-photosynthesis-coupled model to investigate links between photosynthetic seasonality and climate factors on monthly scales. It reproduces the GPP seasonality (R-2=0.45-0.69) with a root-mean-square error (RMSE) of 0.67-1.25gCm(-2)d(-1) and a Bias of -0.03-1.04gCm(-2)d(-1) for four evergreen forest sites. We find that the proportion of diffuse and direct sunlight governs the photosynthetic seasonality via their interaction with sunlit and shaded leaves, supported by a proof that canopy light use efficiency (LUE) has a strong linear relationship with the fraction of diffuse sunlight for Amazonian evergreen forests. In the transition from dry season to rainy season, incident total radiation (Q) decreased while LUE and diffuse fraction increased, which produced the large seasonal increase (similar to 34%) in GPP of evergreen forests. We conclude that diffuse radiation is an important environmental driver of the photosynthetic seasonality in tropical Amazon forests yet depending on light utilization by sunlit and shaded leaves. Besides, the GPP model simulates the precipitation-dominated GPP seasonality (R-2=0.40-0.69) at pasture and savanna sites. These findings present an improved physiological method to relate light components with GPP in tropical Amazon. Plain Language Summary Understanding the mechanism of photosynthetic seasonality in Amazonian evergreen forests is critical for its formulation in global climate and carbon cycle models. However, the control of the unexpected photosynthetic seasonality is highly uncertain. Here we use eddy-covariance data across a network of Amazonian research sites and a novel evapotranspiration (E) and two-leaf-photosynthesis-coupled model to investigate links between photosynthetic seasonality and climate factors on monthly scales. It reproduces the GPP seasonality (R2= 0.45-0.69) for four evergreen forest sites. We find that the proportion of diffuse and direct sunlight governs the photosynthetic seasonality via their interaction with sunlit and shaded leaves, supported by a proof that canopy light-use efficiency (LUE) has a strong linear relationship with the fraction of diffuse sunlight for Amazonian evergreen forests. We conclude that diffuse radiation is an important environmental driver of the photosynthetic seasonality in tropical Amazon forests yet depending on light utilization by sunlit and shaded leaves. Besides, the GPP model simulates the precipitation-dominated GPP seasonality (R2= 0.40 similar to 0.69) at pasture and savanna sites. These findings present an improved physiological method to relate light components with GPP in Amazon.

O gênero Pinus ocupa no Brasil uma área plantada de 1,59 milhão de hectares e tem uma ampla faixa de produtividade florestal (18 a 45 m3 ha-1 ano-1), em função das espécies utilizadas, das limitações edáficas, dos tipos de clima, melhoramento genético e, e alguns casos, pela ocorrência de pragas e doenças. Apesar do conhecimento de que o aumento da disponibilidade de recursos naturais (luz, água e nutrientes) eleva a produção de madeira, faz-se necessário compreender como estes recursos influenciam os processos de captura (produção primária bruta ou GPP) e alocação de carbono (C) para os diferentes compartimentos da floresta (raiz, lenho, galhos e folhas). Além disso, o grau de controle genético é de grande importância nesses processos e também deve ser analisado. Assim, este projeto objetivou quantificar as taxas de captura e alocação de carbono em uma espécie de Pinus tropical (P. caribaea var. hondurensis) e em uma subtropical (P. taeda), dos 6,5 aos 8,5 anos de idade, em parcelas controle (sem fertilização e sem irrigação) e parcelas fertilizadas e irrigadas. O experimento está localizado no município de Itatinga - SP e se utilizou o método do balanço de carbono para estimar a produtividade primária líquida da parte aérea (ANPP), o fluxo de carbono para o solo (TBCF), produtividade primária bruta (GPP) e produtividade líquida do ecossistema (NEP). Ao final do estudo, a biomassa do tronco foi 75% superior no P. caribaea var. hondurensis (126 Mg ha-1) do que no P. taeda (72 Mg ha-1), sendo que em ambas as espécies houveram ganhos significativos com a fertilização e irrigação. O primeiro ano avaliado foi mais seco do que o segundo (1195 contra 1487 mm), resultando em diferenças nos fluxos calculados. A produção de tronco do P. caribaea var. hondurensis variou de 722 a 1569 gC m-2 ano-1, enquanto do P. taeda foi de 221 a 452 gC m-2 ano-1. A espécie subtropical obteve os maiores valores de TBCF, variando de 1150 a 2197 gC m-2 ano-1, e para as duas espécies se encontrou relação do TBCF com a ANPP e GPP. Assim, encontrou-se que a maior produtividade da espécie tropical é resultado de seu maior GPP (4964 contra 3744 gC m-2 ano-1 no P. taeda), maior partição de carbono para incremento de tronco (22% contra 9% no P. taeda) e menor partição para TBCF (23% contra 45% no P. taeda). Já a fertilização e irrigação não mudaram a partição da GPP para a ANPP e TBCF comparado ao tratamento controle, e o ganho em produção de madeira foi explicado apenas pelo aumento na GPP (11%). A NEP para ambas as espécies foi positiva, mostrando que essas espécies estão atuando como drenos de carbono. Assim, o conhecimento de como a captura e alocação de C é afetada pela espécie, água e nutrição terá aplicação sobre o manejo florestal, além de propiciar valores de fluxos essenciais para a calibração de modelos ecofisiológicos de produção, ainda inexistentes para essas espécies no Brasil. / The genus Pinus in Brazil has a planted area of 1.59 million hectares and it has a wide range of forest productivity (18-45 m3 ha-1 yr-1) depending on the species, edaphic limitations, climate, breeding and, in some cases, the occurrence of pests and diseases. Despite knowing that the increased resources availability (light, water and nutrients) improves the production of wood, it is necessary to understand how these features influence the uptake processes (gross primary production or GPP) and carbon allocation (C) on the different forest compartments (root, bole, branch and leaf). Furthermore, the degree of genetic control is rather important in these processes and should also be analyzed. Thus, this project aimed to quantify carbon sequestration and allocation rates in a tropical pine (P. caribaea var. hondurensis) and a subtropical one (P. taeda), from ages 6.5 to 8.5 years old, in control plots (no fertilization and no irrigation) and fertilized and irrigated plots. The experimental site is located in Itatinga- SP and the carbon balance approach was used to estimate the above ground net primary production (ANPP), total belowground carbon flux (TBCF), gross primary production (GPP) and net ecosystem production (NEP). At the end of the study, the bole biomass was 75% higher in the P. caribaea var. hondurensis (126 Mg ha-1) than in P. taeda (72 Mg ha-1), and in both species there were substantial improvements with fertilization and irrigation. The first year evaluated was drier than the second (from 1195 to 1487 mm), resulting in differences in the calculated fluxes. The P. caribaea var. hondurensis bole production ranged from 722 to 1569 gC m-2 yr- 1, while the P. taeda showed values from 221 to 452 gC m-2 yr-1. The subtropical specie obtained the largest values of TBCF (from 1150 to 2197 gC m-2 yr-1), and on both species there was relationship between TBCF and ANPP and GPP.Thus, the higher productivity of tropical specie is a result of higher GPP (4964 versus 3744 gC m-2 yr-1 in the P. taeda), increased carbon partitioning to bole increment (22% versus 9% in the P. taeda) and smaller partitioning for TBCF (23% versus 45% in the P. taeda). Fertilization and irrigation have not changed the partitioning from GPP to ANPP and TBCF compared to the control plots, and increase in the production of wood it has been explained only by increased GPP (11%). The NEP for both species was positive, showing that these species are acting as carbon sinks. Therefore, the knowledge of how the carbon sequestration and allocation is affected by the species, water and nutrition will have application on forest management, besides providing values of essential fluxes for calibration of ecophysiological production models, still non-existent for these species in Brazil.

O gênero Pinus ocupa no Brasil uma área plantada de 1,59 milhão de hectares e tem uma ampla faixa de produtividade florestal (18 a 45 m3 ha-1 ano-1), em função das espécies utilizadas, das limitações edáficas, dos tipos de clima, melhoramento genético e, e alguns casos, pela ocorrência de pragas e doenças. Apesar do conhecimento de que o aumento da disponibilidade de recursos naturais (luz, água e nutrientes) eleva a produção de madeira, faz-se necessário compreender como estes recursos influenciam os processos de captura (produção primária bruta ou GPP) e alocação de carbono (C) para os diferentes compartimentos da floresta (raiz, lenho, galhos e folhas). Além disso, o grau de controle genético é de grande importância nesses processos e também deve ser analisado. Assim, este projeto objetivou quantificar as taxas de captura e alocação de carbono em uma espécie de Pinus tropical (P. caribaea var. hondurensis) e em uma subtropical (P. taeda), dos 6,5 aos 8,5 anos de idade, em parcelas controle (sem fertilização e sem irrigação) e parcelas fertilizadas e irrigadas. O experimento está localizado no município de Itatinga - SP e se utilizou o método do balanço de carbono para estimar a produtividade primária líquida da parte aérea (ANPP), o fluxo de carbono para o solo (TBCF), produtividade primária bruta (GPP) e produtividade líquida do ecossistema (NEP). Ao final do estudo, a biomassa do tronco foi 75% superior no P. caribaea var. hondurensis (126 Mg ha-1) do que no P. taeda (72 Mg ha-1), sendo que em ambas as espécies houveram ganhos significativos com a fertilização e irrigação. O primeiro ano avaliado foi mais seco do que o segundo (1195 contra 1487 mm), resultando em diferenças nos fluxos calculados. A produção de tronco do P. caribaea var. hondurensis variou de 722 a 1569 gC m-2 ano-1, enquanto do P. taeda foi de 221 a 452 gC m-2 ano-1. A espécie subtropical obteve os maiores valores de TBCF, variando de 1150 a 2197 gC m-2 ano-1, e para as duas espécies se encontrou relação do TBCF com a ANPP e GPP. Assim, encontrou-se que a maior produtividade da espécie tropical é resultado de seu maior GPP (4964 contra 3744 gC m-2 ano-1 no P. taeda), maior partição de carbono para incremento de tronco (22% contra 9% no P. taeda) e menor partição para TBCF (23% contra 45% no P. taeda). Já a fertilização e irrigação não mudaram a partição da GPP para a ANPP e TBCF comparado ao tratamento controle, e o ganho em produção de madeira foi explicado apenas pelo aumento na GPP (11%). A NEP para ambas as espécies foi positiva, mostrando que essas espécies estão atuando como drenos de carbono. Assim, o conhecimento de como a captura e alocação de C é afetada pela espécie, água e nutrição terá aplicação sobre o manejo florestal, além de propiciar valores de fluxos essenciais para a calibração de modelos ecofisiológicos de produção, ainda inexistentes para essas espécies no Brasil. / The genus Pinus in Brazil has a planted area of 1.59 million hectares and it has a wide range of forest productivity (18-45 m3 ha-1 yr-1) depending on the species, edaphic limitations, climate, breeding and, in some cases, the occurrence of pests and diseases. Despite knowing that the increased resources availability (light, water and nutrients) improves the production of wood, it is necessary to understand how these features influence the uptake processes (gross primary production or GPP) and carbon allocation (C) on the different forest compartments (root, bole, branch and leaf). Furthermore, the degree of genetic control is rather important in these processes and should also be analyzed. Thus, this project aimed to quantify carbon sequestration and allocation rates in a tropical pine (P. caribaea var. hondurensis) and a subtropical one (P. taeda), from ages 6.5 to 8.5 years old, in control plots (no fertilization and no irrigation) and fertilized and irrigated plots. The experimental site is located in Itatinga- SP and the carbon balance approach was used to estimate the above ground net primary production (ANPP), total belowground carbon flux (TBCF), gross primary production (GPP) and net ecosystem production (NEP). At the end of the study, the bole biomass was 75% higher in the P. caribaea var. hondurensis (126 Mg ha-1) than in P. taeda (72 Mg ha-1), and in both species there were substantial improvements with fertilization and irrigation. The first year evaluated was drier than the second (from 1195 to 1487 mm), resulting in differences in the calculated fluxes. The P. caribaea var. hondurensis bole production ranged from 722 to 1569 gC m-2 yr- 1, while the P. taeda showed values from 221 to 452 gC m-2 yr-1. The subtropical specie obtained the largest values of TBCF (from 1150 to 2197 gC m-2 yr-1), and on both species there was relationship between TBCF and ANPP and GPP.Thus, the higher productivity of tropical specie is a result of higher GPP (4964 versus 3744 gC m-2 yr-1 in the P. taeda), increased carbon partitioning to bole increment (22% versus 9% in the P. taeda) and smaller partitioning for TBCF (23% versus 45% in the P. taeda). Fertilization and irrigation have not changed the partitioning from GPP to ANPP and TBCF compared to the control plots, and increase in the production of wood it has been explained only by increased GPP (11%). The NEP for both species was positive, showing that these species are acting as carbon sinks. Therefore, the knowledge of how the carbon sequestration and allocation is affected by the species, water and nutrition will have application on forest management, besides providing values of essential fluxes for calibration of ecophysiological production models, still non-existent for these species in Brazil.

No description available.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The net exchange of CO2 between the atmosphere and the ecosystem (NEE), represent the balance of the ecosystem respiration (Reco) and gross primary production (GPP), which are directly related to temperature and photosynthetic active radiation (PAR) respectively. Studies related to the exchange of CO2 between ecosystems and atmosphere has been conducted in different ecosystems, with the objective of finding the contribution of different ecosystems to the atmospheric CO2. For this it is important to have a continuous data series. However, these series may fail causing gaps in time series data. Here, were studied gapfilling techniques( multiple linear regression , nonlinear regressions , Look-up Tables, Mean diurnal variation and Neural networks) and the technique of non-linear regressions excel the other, it is indicated to fill the gaps when available variables weather temperature and radiation, not available when these forcings , advise the use of Mean Diurnal variation . Three years of CO2 fluxes over irrigated rice were used to compare the techniques: two years at the Cachoeira do Sul site and one year at Paraiso do Sul site, both located at Rio Grande do Sul. As a result of gapfilling by nonlinear regression, NEE was estimated to be -92 ± 80gC / m² (2010/2011) and 429 ± 188gC / m² (2011/2012), for Cachoeira do Sul and -43 ± 72gC / m² (2003/2004), for Paraíso do Sul. / As trocas líquidas de CO2 entre a atmosfera e o ecossistema (NEE) representam o balanço entre a respiração do ecossistema (Reco) e a produção primaria bruta (GPP), que estão diretamente relacionados à temperatura e a radiação fotossinteticamente ativa (PAR), respectivamente. Estudos relacionados às trocas de CO2 entre ecossistemas e a atmosfera têm sido realizados em diferentes sítios experimentais com o objetivo de conhecer quanto cada ecossistema contribui para o CO2 atmosférico. Para tanto, é importante ter uma série de dados contínuos. Conquanto, estas séries podem apresentar falhas, gerando lacunas nas séries temporais dos dados, que devem ser preenchidas. Neste trabalho, foram estudas técnicas de preenchimento de dados (Regressões lineares múltiplas, Regressões não lineares, Look-up Tables, Mean diurnal variation), Redes neurais para estimativa do NEE anual sobre culturas de arroz irrigado no estado do Rio Grande do Sul. Foram utilizados três anos de dados de NEE coletados em dois anos para o sítio de Cachoeira do Sul e um ano para Paraíso do Sul. As diferentes técnicas foram avaliadas através da incerteza e do calculo do erro na estimativa do NEE para lacunas artificiais de cada técnica. A técnica de regressões não lineares mostrou-se mais adequada, sendo indicada para o preenchimento das falhas quando disponíveis as variáveis meteorológicas de temperatura e radiação. Quando não disponíveis, o uso da Mean diurnal variation é aconselhada. Como resultado do preenchimento de dados por meio da técnica de Regressão não linear, foram estimados os seguintes valores acumulados de carbono: -92 ± 80gC / m² (2010/2011) e 429 ± 188gC / m² (2011/2012), para Cachoeira do Sul e -43 ± 72gC / m² (2003/2004), para Paraíso do Sul.

No description available.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The turbulent fluxes of carbon dioxide (CO2 ) were investigated in two sites of irrigated rice in southern Brazil, using the eddy covariance technique over 385 days of analysis at the site of Paraiso do Sul and 683 days in site Cachoeira do Sul also used the model of filling the gaps in order to estimate the net ecosystem exchange CO2 -C (NEE). Throughout the growing season, rice fields, both for the site of Paraiso do Sul to the site of Cachoeira do Sul, acted as carbon sinks (C). During fallow periods, these fields were the source of C. The NEE accumulated at the site of Cachoeira do Sul was similar in both cycles and practically equal to the estimated site of Paraiso do Sul. The GPP accumulated during the crop cycle 2010-2011, the rice field of Cachoeira do Sul, was less than 12% of the 2011-2012 cycle and higher than 15% of the site of Paraiso do Sul. The Re accumulated was similar at the site of Paraíso do Sul in the 2010-2011 cycle Cachoeira do Sul, but less than the 2011- 2012 cycle. The values of NEE, GPP and R e for the site of Paraíso do Sul were - 270.53 gCm2 , -821.19gCm2 and 527.59gCm2 , respectively. To the site of Cachoeira do Sul, were -282,53 gCm2 , -933,40gCm2 and 597,05gCm2 for NEE, GPP and Re , respectively, in the 2010-2011 cycle. For the 2011-2012 cycle in the rice field of Cachoeira do Sul, the values of NEE, GPP and Re were -279,69gCm2 , - 1062,64gCm2 and 716,58gCm2 , respectively. The total C accumulated over the period analyzed for the site of Paraíso do Sul was -45,90gCm2 , considering this area of rice cultivation, as a sink for C. While the growing area of Cachoeira do Sul was considered a source of C (19,94 gCm2 ). Showing by this that long periods of fallow contribute significantly to the accumulated fluxes due to constant presence of vegetation. The contribution of this work will assist in the investigation of CO2 in these ecosystems. / Os fluxos turbulentos de dióxido de carbono (CO2 ) foram investigados em dois sítios de cultura de arroz irrigado no Sul do Brasil, utilizando a técnica de covariância de vórtices ao longo de 385 dias de análise no sítio de Paraíso do Sul e de 683 dias, no sítio de Cachoeira do Sul. Além disso, utilizou-se o modelo de preenchimento das lacunas com o objetivo de estimar a troca líquida de C-CO2 no ecossistema (NEE). Ao longo do período de cultivo, os campos de arroz, tanto para o sítio de Paraíso do Sul quanto para o sítio de Cachoeira do Sul, atuaram como sumidouros de carbono (C). Durante os períodos de pousio, esses campos foram fontes de C. O NEE acumulado, no sítio de Cachoeira do Sul foi semelhante em ambos os ciclos e praticamente igual ao estimado no sítio de Paraíso do Sul. A GPP acumulada durante o ciclo de cultivo de 2010-2011, no campo de arroz de Cachoeira do Sul, foi inferior a 12% do ciclo de 2011-2012 e superior em 15% a do sítio de Paraíso do Sul. A Re acumulada foi semelhante no sítio de Paraíso do Sul e no ciclo de 2010- 2011 de Cachoeira do Sul, mas inferior a do ciclo de 2011-2012. Os valores de NEE, GPP e Re para o sítio de Paraíso do Sul foram de -270,53 gCm2 , -821,19gCm2 e 527,59gCm2 , respectivamente. Para o sítio de Cachoeira do Sul, foram de - 282,53gCm2 , -933,40gCm2 e 597,05gCm2 para NEE, GPP e Re , respectivamente, no ciclo de 2010-2011. Para o ciclo de 2011-2012, no campo de arroz de Cachoeira do Sul, os valores de NEE, GPP e Re foram de -279,69gCm2 , - 1062,640gCm2 e 716,58gCm2 , respectivamente. O total de C acumulado ao longo do período analisado para o sítio de Paraíso do Sul foi de -45,90gCm2 , considerando esta área de cultivo de arroz, como um sumidouro de C. Enquanto que a área de cultivo de Cachoeira do Sul foi considerada fonte de C (19,94 gCm2 ). Mostrando com isso, que períodos longos de pousio contribuem consideravelmente para os fluxos acumulados devido a permanência constante de vegetação. A contribuição deste trabalho auxiliará na investigação das emissões de CO2 nesses ecossistemas.

Les zones côtières ne sont prises en compte dans les budgets globaux de CO2 atmosphérique que depuis peu. Il s’avère que bien qu’elles ne représentent globalement que de faibles superficies, les flux de carbone et de nutriments y sont très significatifs à l’échelle globale. On sait peu de chose sur le comportement des écosystèmes lagunaires vis-à-vis du CO2 et, encore moins des zones intertidales où les échanges avec l’atmosphère ont lieu alternativement avec l’eau et le sédiment. Les objectifs de cette étude ont été d’une part, d’établir le bilan de carbone échangé entre la lagune d’Arcachon, l’atmosphère et le milieu terrestre, et d’autre part de mettre en relation ces flux avec la production nette de l’écosystème (NEP) afin de mieux caractériser le statut métabolique de celle-ci ainsi que les facteurs environnementaux clés. Pour cela, nous avons mis en place pour la première fois et à différentes saisons et stations, des mesures directes de flux de CO2 par Eddy Corrélation, une méthode fonctionnant en continu pendant l’immersion et l’émersion. En parallèle, les apports de carbone terrestre sous ses différentes formes ont été quantifiés par un suivi annuel sur 9 rivières alimentant la lagune. L’export total de carbone par le bassin versant à travers les eaux de surface des rivières est estimé à 116 t C km-2 an-1 dont 39% est exporté à la lagune sous forme organique dissoute (DOC) du fait de la prédominance de podzols dans le bassin versant. La forte minéralisation de la matière organique terrestre dans les sols et eaux souterraines sursature largement les eaux en CO2 et l’export sous forme de carbone inorganique dissoute (DIC) représente environ 21%. La formulation d’un modèle mathématique, le « StreamCO2-DEGAS », basé sur les mesures de pCO2, de concentrations et de compositions isotopiques en DIC a permis de montrer que 43% de l’export total de carbone était dégazé sous forme de CO2 depuis les rivières vers l’atmosphère, réduisant alors le flux net entrant dans la lagune à 66 t C km-2 an-1. Concernant la mesure de flux verticaux, l’analyse cospectrale ainsi que les résultats obtenus en adéquation avec les contrôles physiques et biologiques aux différentes échelles tidale, diurne et saisonnières, ont permis de valider la méthode de l’Eddy Covariance en zone intertidale. Sur l’ensemble de la période de mesures, les flux de CO2 étaient faibles, variant entre -13 et 19 µmol m-2 s-1. Des puits de CO2 atmosphérique à marée basse le jour ont été systématiquement observés. Au contraire, pendant l’immersion et à marée basse la nuit, des flux positifs ou négatifs ou proche de zéro ont été observés suivant la saison et la station étudiées. L’analyse concomitante des flux de CO2 et des images satellites du platier à marée basse le jour a clairement permis de discriminer l’importance relative des deux cycles métaboliques distincts des principaux producteurs primaires avec (1) les herbiers de Zostera noltii à cycle annuel long, dominant la NEP en été et en automne à la station la plus centrale et (2) les communautés microphytobenthiques, dominant la production primaire brute (PPB) au printemps à la même station et en automne au fond du bassin. Un recyclage rapide de cette production durant l’immersion et l’émersion a aussi clairement été mis évidence. Au vue des différents résultats, la technique d’Eddy Covariance utilisée en zone intertidale laisse envisager d’intéressantes perspectives en termes de connaissances sur les budgets de carbone et les processus écologiques et biogéochimiques dans la zone côtière. / The coastal zone is only taken into account since recently in global carbon budgeting efforts. Although covering globally modest surface areas, carbon and nutrient fluxes in the coastal zone appear significant at the global scale. However, little is known about the CO2 behaviour in lagoons and even less in intertidal zones where exchanges with the atmosphere occur alternatively with the water and the sediment. The purposes of this work are, on one hand, to establish the carbon budget between the Arcachon lagoon, the atmosphere and the terrestrial watershed and on the other hand, to link these fluxes with the net ecosystem production (NEP) and better characterize its metabolic status along with the relevant environmental factors. For the first time, CO2 flux measurements by Eddy Correlation have been carried out at different seasons and stations in the tidal flat. In parallel, the total terrestrial carbon export from river waters has been quantified throughout a complete hydrological cycle in nine watercourses flowing into the lagoon. The total carbon export from the watershed through surface river waters is estimated at 116 t C km-2 yr-1 on which 39% is exported to the lagoon as dissolved organic carbon (DOC) owing to the predominance of podzols in the watershed. Intense organic matter mineralization in soils and groundwaters largely over-saturate river waters in CO2 on which export accounts for 21% as dissolved inorganic carbon (DIC). The mathematical “StreamCO2-DEGAS” model formulation based on water pCO2, DIC concentrations and isotopic composition measurements permits to show that 43% of the total carbon export was degassed as CO2 from the riverine surface waters to the atmosphere, lowering then this latter to 66 t C km-2 yr-1. With respect to the CO2 flux measurements in the lagoon, cospectral analysis and the well accordance of results with physical and biological controls at the tidal, diurnal and seasonal time scales permit to validate the Eddy Correlation technique over tidal coastal zone. CO2 fluxes with the atmosphere, during each period, were generally weak and ranged between -13 and 19 µmol m-2 s-1. Low tide and daytime conditions were always characterized by an uptake of atmospheric CO2. In contrast, during the immersion and during low tide at night, CO2 fluxes where either positive or negative, or close to zero, depending on the season and the site. The concomitant analysis of CO2 fluxes with satellite images of the lagoon at low tide during the day clearly discriminate the relative importance of the two distinct metabolic carbon cycling involving the main primary producers, i.e. (1) the Zostera noltii seagrass meadow predominance on the NEP in autumn and summer in the more central station, with an annual cycling and (2) the microphytobenthos community predominance on the gross primary production (GPP) in spring at the same station and in autumn in the inner part of the bay where a rapid carbon cycling during the immersion and the emersion was clearly highlighted. The different results obtained with the Eddy Correlation technique over tidal flats opens interesting perspectives on the knowledge of the carbon budget and the biogeochemical and ecological processes within the coastal zone.