Thesis (Ph. D.)--University of Colorado at Boulder, 2005. / Source: Dissertation Abstracts International, Volume: 66-02, Section: B, page: 0671. Director: Russell K. Monson.

Thesis (M. Sc.)--Lakehead University, 1996. / Includes bibliographical references.

Carbon (C) as a driver of soil denitrification was investigated in a series of four laboratory incubation experiments employing stable nitrogen (N) and C isotope approaches. The research addressed the lack of knowledge on mechanisms through which the quantity and quality of organic‐C containing substrates interact with denitrification. The amount of organic matter added to soil was manipulated to relate C respiration with process rates of denitrification. Respiration derived from dissolved organic matter C was linearly related to denitrification but the direction of the relationship was variable in time. This may be most likely an effect of changing quality of the C available and possibly microbial community structure. Nitrous oxide (N2O) emission from denitrification at the later stages of residue decomposition was driven by nitrate (NO3‐) accumulation in the soil rather than C provided by the residue. Denitrification across a vertical shallow soil profile formed in a laboratory microcosm was investigated. A surface hotspot formed immediately as a response to residue‐C addition and increased rates of N2O production. N2O reduction occurred at depth. The hotspot at depth was related to an indirect effect of residue‐C, which was depletion of O2. Further, to address the complexity of low molecular weight C substrate available to denitrifiers in the soil solution, denitrification rates in response to glucose, citric acid and glutamic acid supplied individually versus in mixture were characterised. Carbon substrate quality regulated N2O production rates via interactions within the soil microbial community and with the soil solid phase. Overall, the experiments showed that C stimulates strong N2O emission peaks and increase cumulative N2O emissions from arable soil along a gradient of varying C substrate complexity and quantity. Interaction in space and time play an important role when C containing inputs affected other proximal drivers of denitrification such as NO3‐ and O2.

Thesis (M.S.)--University of Toledo, 2009. / Typescript. "Submitted as partial fulfillment of the requirements for the Master of Science in Biology." "A thesis entitled"--at head of title. Bibliography: leaves 48-55.

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Made available in DSpace on 2014-06-11T19:28:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-02-28Bitstream added on 2014-06-13T19:16:24Z : No. of bitstreams: 1 bicalho_es_me_jabo.pdf: 503292 bytes, checksum: d2ce2166bc9f68e6b65aa37ca5a4615c (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A emissão de CO2 do solo (FCO2) é influenciada por processos físicos, químicos e biológicos que afetam a produção de CO2 no interior do solo e o seu transporte para a atmosfera, variando no tempo e no espaço em função das condições ambientais e do manejo agrícola da área. O objetivo deste estudo foi investigar a correlação existente entre os padrões de estrutura de variabilidade espacial e temporal de FCO2 e atributos do solo, em área de cana-de-açúcar sob sistema de manejo cana crua, por meio de dimensão fractal (DF), derivada a partir de variogramas isotrópicos e anisotrópicos em diferentes escalas espaciais. A área experimental constituiu-se de uma malha regular de 60 × 60 m contendo 141 pontos espaçados em distâncias mínimas que variaram de 0,5 a 10 m. A emissão de CO2, temperatura e umidade do solo foram avaliadas durante 7 dias, sendo determinados os atributos físico e químicos do solo em amostragem na profundidade de 0,0 a 0,1 m. A média de FCO2 variou de 1,26 a 1,77 μmol m-2 s-1 ao longo dos dias, com dependência temporal na média e longa escalas, em alcances superiores a 20 m. Apesar do comportamento isotrópico observado para FCO2, seus valores de DF, calculados para diferentes direções, evidenciaram maior variabilidade temporal na direção paralela à linha de plantio, indicando influência das práticas de manejo adotadas na área. A variabilidade espacial de FCO2 foi mais bem evidenciada na média (20 a 30 m) e longa (40 a 60 m) escalas, com sua estrutura de variabilidade, caracterizada pelo fractograma, correlacionando-se significativamente com a maioria dos atributos do solo e apresentando comportamento similar à observada para a temperatura do solo e volume total de poros. Além disso, os fractogramas permitiram observar o comportamento da dependência espacial e temporal de FCO2 e... / Soil CO2 emission (FCO2) is influenced by physical, chemical and biological factors that affect the production of CO2 in the soil and its transport to the atmosphere, varying in time and space as a function of environmental conditions and agricultural management. The aim of this study was to investigate the correlation between spatial and temporal variability patterns of FCO2 and soil properties in sugarcane area under green management by using fractal dimension (DF), derived from isotropic and anisotropic variogram at different spatial scales. The experimental area consisted of a regular grid of 60 × 60 m containing 141 points spaced at minimum distances ranging from 0.5 to 10 m. Soil CO2 emission, soil temperature and soil moisture were evaluated over a period of 7 days, and soil physical and chemical properties were determined by sampling at a depth of 0.0 to 0.1 m. The average of FCO2 ranged from 1.26 to 1.77 mol m-2 s-1 throughout the days, with temporal dependence in the medium and large scales, at ranges of more than 20 m. Despite the isotropic behavior observed for FCO2, their DF values, calculated for different directions, showed greater temporal variability in the direction parallel to the row, indicating the influence of area management. Spatial variability of FCO2 was better evidenced in the medium (20 to 30 m) and long (40 to 60 m) scales, with its variability structure, characterized by fractogram, significantly correlated with most soil properties and similar behaving to that observed for the soil temperature and total pore volume. In addition, fractograms allowed to observe the behavior of the spatial and temporal dependence... (Complete abstract click electronic access below)

Made available in DSpace on 2014-06-11T19:23:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-12-22Bitstream added on 2014-06-13T19:49:59Z : No. of bitstreams: 1 teixeira_db_me_jabo.pdf: 508270 bytes, checksum: 93d2af6f4bf67e9aab6a84ffe3f4ac1a (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A emissão de CO2 do solo (FCO2) apresenta alta variabilidade espacial, sendo devida a grande dependência espacial existente nas propriedades do solo que a influenciam. Neste estudo objetivou-se (i) caracterizar e relacionar a variabilidade e a distribuição espacial da FCO2, temperatura do solo, porosidade livre de água (PLA), teor de matéria orgânica do solo (MO) e densidade do solo (Ds), (ii) avaliar a acurácia dos resultados fornecidos pelo método da krigagem ordinária (KO) e simulação sequencial Gaussiana (SSG), e (iii) avaliar a incerteza na predição da variabilidade espacial das FCO2 e demais propriedades utilizando a SSG. O estudo foi conduzido em uma malha amostral regular de 60 x 60 m2 com 141 pontos, com espaçamento mínimo variando de 0,50 a 10 m, instalada em área de cana-de-açúcar. Nestes pontos foram avaliados a FCO2, temperatura do solo, PLA, determinadas com base na média de 07 dias de avaliação, MO e Ds. Todas as variáveis apresentaram estrutura de dependência espacial, sendo ajustados modelos Gaussianos, esféricos e exponenciais. A configuração da malha amostral e possivelmente a presença de espessa camada de resíduos da cultura sobre o solo influenciaram a estrutura de variabilidade espacial da FCO2, temperatura e MO. FCO2 apresentou correlações positivas com a MO (r = 0,25, p < 0,05) e PLA (r = 0,27, p < 0,01) e negativa com a Ds (r = - 0,41, p < 0,01). No entanto, quando os valores digitais estimados espacialmente (N=8.833) são considerados, a PLA passa a ser a principal variável responsável pelas características espaciais da FCO2, apresentando correlação de 0,26 (p < 0,01). As simulações individuais propiciaram, para todas as variáveis analisadas, melhor reprodução das funções de distribuição acumuladas (fdac), e dos variogramas em comparação... / The soil CO2 emission (FCO2) has high spatial variability, which caused due to the strong spatial dependence in soil properties that influence it. This study aimed to (i) to characterize the variability and spatial distribution of FCO2, soil temperature, air-filled pore space (AFPS), soil organic matter (OM) and soil bulk density (BD) and related properties, (ii) evaluate the accuracy of the results provided by the method of ordinary kriging (OK) and sequential Gaussian simulation (SGS), and (iii) evaluate the uncertainty in predicting the spatial variability of FCO2 and other properties using the SSG. The study was conducted on an regular sampling grid with 141 points, with spacing ranging from 0.50 to 10 m, installed in a sugarcane area. In this place were evaluated FCO2, soil temperature, AFPS, were based on the average of 07 days of evaluation, OM and BD. All variables showed spatial dependence structure, and models adjusted Gaussian, spherical and exponential. The configuration of the sampling grid and the presence of intense layer of crop residues in the soil influenced the structure of spatial variability of FCO2, temperature, and OM. The FCO2 showed positive correlations with OM (r = 0.25, p <0.05) and AFPS (r = 0.27, p <0.01) and negatively with Ds (r = - 0.41, p <0.01). However, when the estimated spatially values are considered, the AFPS becomes the main variable responsible for the spatial characteristics of FCO2, showing correlation of 0.26 (p <0.01). The individual simulations led to all variables, better reproduction of the cumulative distribution functions (cdf), and variograms compared to OK and E-type estimate. The analysis results show strong similarities between the E-type estimates to those generated by the procedure of OK. The major uncertainties in predicting FCO2 were associated with areas with the highest... (Complete abstract click electronic access below)

Coastal nutrient loading is a growing concern in urbanized communities and has led to alterations in above- and belowground processes throughout estuarine systems. Mangrove forests are highly productive coastal habitats that exhibit large carbon stocks contained mostly to the deep soils. Since nutrient enrichment has been found to increase mangrove aboveground growth, it’s presumed that nutrient enrichment will also increase belowground respiration rates. Disturbances in soil nutrient content may alter the mangrove carbon cycle by increasing the amount of CO2 lost to the atmosphere from enhanced microbial and root respiration. In this study, soil respiration responded greatest to nitrogen enrichment, but pneumatophore root respiration responded greatest to phosphorus enrichment. Nutrient limitation can shift between different ecological processes and responses to nutrient enrichment tend to be system specific in tidally influenced ecosystems. Understanding the implications of coastal nutrient loading will improve ecosystem models of carbon exchange and belowground processes. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2021. / FAU Electronic Theses and Dissertations Collection

Soil carbon (C) is the largest terrestrial carbon pool. While inputs to this system are fairly well constrained, the diverse factors driving soil C efflux remain poorly understood. Carbon in surface soils is mobilized via two distinct pathways: CO₂ gas flux and dissolved C flux. The goal of this study was to quantify the role of hydrologic variability in mobilizing carbon as gaseous and dissolved fluxes from near-surface soils, and to determine their relative magnitudes. Data were collected through 2010 and 2011 from two subalpine sites in Arizona and New Mexico. I observed no significant variability in dissolved fluxes, and these values were low at all sites. In contrast, CO₂ fluxes were large (from 0.22 g C m⁻² d⁻¹ to 5.27 g C m⁻² d⁻¹) and varied between sites and between years. My results suggest that in arid montane forests soil carbon flux is critically linked to water availability.

Rises in anthropogenic CO2 emissions are now widely acknowledged to be responsible for changes in the global climate, with potentially disastrous consequences if these rises continue unchecked. Although knowledge of ecosystem responses to climate change has improved, there are still large underlying uncertainties regarding their response to warming. Of all the ecosystems with the potential to mitigate rises in CO2, forests are arguably the most important because of their huge land area and store of carbon. A large proportion of the carbon stored in forests is found in the soil, and it is the response of this soil carbon to temperature that is the main determinant of a forest’s ability to act as a carbon sink, or indeed source. Understanding the response of soil carbon flux to temperature, as well as the contribution of soil carbon flux to the carbon balance of forests as a whole is crucial in helping to improve modelling approaches. In this thesis I first examined the temperature response of old and new soil organic carbon from a Sitka spruce plantation under controlled laboratory conditions. Both the old and new soil organic carbon showed similar temperature sensitivities after prolonged incubation at 20 °C, thus implying a similar response to increasing temperatures. Using a variety of different methods (root intensity, meshing and stable isotope analysis) I then studied the responses under field conditions. These methods showed that autotrophic respiration was responsible for up to 50 % of total soil respiration, and was more sensitive to temperature than heterotrophic respiration. Finally, I compared the contributions and determinants (particularly temperature and moisture) of soil respiration fluxes to ecosystem fluxes at a temperate (Sitka spruce) and Mediterranean (Maritime pine) forest. Temperature was found to be the dominant driver of soil respiration fluxes at the temperature forest, whilst soil respiration was limited by moisture at the Mediterranean forest. Statistically significant relationships between net ecosystem productivity and soil respiration (and the stable isotope signature of soil respiration) were found at both forests, indicating a close coupling between above-ground processes and soil respiration.