Intensive agriculture, coupled with an increase in nitrogen fertilizer use, has contributed significantly to the elevation of atmospheric greenhouse gases (GHGs), including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Rising GHG emissions usually mean a decrease in soil carbon. Currently, soil C is twice that of all standing crop biomass, making it an extremely important player in the C cycle. Fortunately, agricultural management practices have the potential to reduce agricultural GHG emissions whilst increasing soil C. Management practices that impact GHG emissions and soil C include various tillage practices, different N fertilization amounts and treatments (synthetic N, cattle manure, or a combination of both), the use of cover crops, aeration, and water levels. Employing agricultural best management practices (BMPs) can assist in the mitigation and sequestration of CO2, N2O and soil C. Measuring soil carbon storage and GHG emissions and using them as metrics to evaluate BMPs are vital in understanding agriculture's role in climate change. The objective of this research was to quantify soil carbon and CO2 and N2O emissions in agroecosystems (dairy, crop, and meat producing farms) under differing management practices. Three farms were selected for intensive GHG emissions sampling: Shelburne Farm in Shelburne, VT, a dairy in North Williston, VT, and Borderview Farm in Alburgh, VT. At each site, I collected data on GHG (CO2 and N2O) emissions and soil carbon and nitrogen storage to a depth of 1 meter. Soil emissions of CO2 and N2O were taken once every two weeks (on average) from June 2015 through November, 2015 using static flux chambers and a model 1412 Infrared Photoacoustic Spectroscopy (PAS) gas analyzer (Innova Air Tech Instruments, Ballerup, Denmark). Fluxes were measured on 17 dates at Shelburne Farms, 13 dates at the Williston site, and 13 dates in the MINT trial. Gas samples were taken at fixed intervals over a 10-14 minute time frame, with samples normally taken every one or two minutes. I also measured soil carbon to a depth of 1m in six BMPs at Borderview Farm. Overall, I found that manure injection increased N2O and CO2 emissions, but decreased soil C storage at depth. Tillage had little to no impact on N2O emissions, except at Shelburne Farms, where aeration tillage decreased N2O emissions (marginally significant, P < 0.1). No-till did, however, decrease CO2 emissions relative to other conservation tillage practices (strip and vertical tillage) but we were unable to detect a significant change in soil C due to tillage practices. At Borderview farm, N2O emissions increased with soil NO3 and soil moisture, while CO2 emissions increased with soil temperature and nitrate. At Williston, CO2 emissions only increased with temperature; at Shelburne CO2 emissions increased with nitrate. N2O fluxes at Shelburne and Williston were not associated with any of the measured covariates.

A emissão de gases de efeito estufa (GEE) é uma das principais causas do aquecimento global, sendo uma problemática mundial das últimas décadas. O dióxido de carbono (CO2), o metano (CH4) e oxido nitroso (N2O) são os principais GEE e os ruminantes são uns dos maiores contribuintes com a produção desses gases no mundo, devido ao processo digestivo de fermentação entérica. Na busca de estratégias para diminuir as emissões de metano e melhorar a produtividade animal, aditivos alimentares têm sido utilizados nas dietas dos animais. Assim, o objetivo deste trabalho foi avaliar a inclusão de aditivos alimentares sobre a produção de metano determinada pela técnica do gás traçador SF6, assim como, o consumo de matéria seca, a dinâmica ruminal e a contagem total e diferencial de protozoários do rúmen. Seis vacas não-gestantes e não-lactantes, com peso vivo médio de 784 &plusmn; 87 kg e canuladas no rúmen, foram distribuídas a uma das três dietas experimentais, seguindo-se delineamento experimental em quadrado latino 3x3 replicado (n= 18 unidades experimentais), sendo os tratamentos: 1) Controle (CON): Dieta basal sem inclusão de aditivo; 2) Monensina (MON): Dieta com adição de 300 mg de monensina sódica por animal por dia; 3) Tanino (TAN): Dieta com adição de 68 g de extrato de tanino condensado de Acácia-negra (Acacia mearnsii) por animal por dia. Os alimentos foram fornecidos duas vezes ao dia, na forma de ração completa. Cada período experimental foi constituído por 21 dias, sendo 10 dias de adaptação às respectivas dietas. A partir do dia 16 até o dia 21 foram coletados os dados de consumo de matéria seca e de produção de metano, sendo este último determinado a cada 24 horas, pela técnica do gás traçador de SF6. No dia 21, coletou-se conteúdo ruminal para determinação de protozoários. Quanto à dinâmica ruminal, foi realizado o esvaziamento ruminal nos dias 10 (3 horas após alimentação matinal) e 11 (imediatamente antes da alimentação matinal) de cada período experimental. Os resultados foram analisados através do procedimento MIXED onde o modelo incluiu o efeito de tratamento como fator fixo e os efeitos de animal dentro de quadrado, quadrado e período como fatores aleatórios. Não houve diferenças significativas (P&gt;0,05) entre os tratamentos para as variáveis do consumo de matéria seca, como também, para os parâmetros de dinâmica ruminal (P&gt;0,05) (matéria seca do conteúdo ruminal, massa líquida, massa sólida, massa total, assim como taxa de desaparecimento). A emissão de metano (expressa em g/d, g/kg PV, g/kg PV0,75 ou Mcal/Ani/d) com o tratamento com monensina foi menor em relação ao tratamento controle. Para a contagem total e diferencial de protozoários foi verificado efeito de aditivo para a subfamília Diplodiniinae, sendo que, o tratamento com monensina diminuiu em 27,5% a contagem desta subfamília em relação ao tratamento com tanino. Referente ao gênero Isotricha, foi observado que os tratamentos com monensina ou com tanino diminuíram em 31 e 30% respectivamente, este gênero em relação ao tratamento controle. A adição de monensina (17 mg/kg de MSI) revela-se uma alternativa para reduzir as perdas energéticas geradas na produção de metano, assim como também na redução de protozoários, que albergam microrganismos metanogênicos. Em relação ao tanino (0,4% na dieta) acredita-se que com doses mais elevadas na dieta possa resultar numa redução da emissão de metano / The emission of greenhouse gases (GHG) is a major cause of global warming, being a worldwide concern in recent decades. Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are the main greenhouse gases and ruminants are one of the major contributors to the production of these gases around the world, due to the enteric fermentation process. In the search for strategies to reduce methane emissions and to improve animal productivity, food additives have been used in animal diets lately. Thus, the aim of this trial was to assess the inclusion of food additives on methane emissions in cattle, using the sulfur hexafluoride (SF6) tracer technique, as well as on dry matter intake, rumen dynamics and total and differential counts of ruminal protozoa. Six non-pregnant and non-lactating rumen-cannulated cows (784 &plusmn; 87 kg) were assigned to a replicated 3x3 Latin square (18 experimental units). Treatments were: 1) Control (CON) basal diet with no additive inclusion; 2) Monensin (MON) addition of 300 mg of sodium monensin per animal per day, 3) Tannin (TAN) addition of 68 g of concentrated extract of condensed tannin (Acacia mearnsii) per animal per day. The animals were fed total mixed ration twice daily. Each experimental period consisted of 21 days the first 10 days were used for diet adaptation. From day 16 up to 21, data about dry matter intake and methane production were collected, the latter done every 24 hours using the sulfur hexafluoride (SF6) tracer technique. On the day 21, ruminal content was sampled for protozoa determination. Regarding the rumen dynamics, the rumen was emptied on days 10 (3 hours post-morning feeding) and 11 (right before morning feeding) of each experimental period. The results were analyzed by MIXED procedure; the model included the effect of treatment as fixed factor and the effects of period, square and animal within square as random factors. There were no significant differences (P&gt;0.05) among treatments for dry mater intake variables, nor for ruminal dynamics parameters (ruminal content dry matter, liquid mass, solid mass, total mass or disappearance rate). Methane emission (expressed in g/day, g/kg LW, g/kg LW0.75 or Mcal/Ani/day) was lower for the group receiving monensin compared to the control group. For total and differential counts of protozoa, the additives affected the Diplodiniinae subfamily, i.e. monensin decreased the count of this subfamily by 27.5%, compared to tannin. Regarding the Isotricha genus, treatments with monensin or tannin decreased it by 31 and 30% respectively, compared to the control treatment. The addition of monensin (17 mg/kg DMI) revealed to be an alternative to reduce the energy lost by methane production, as well as to decrease the protozoa, which host methanogen microorganisms. Regarding tannin (0.4% in the diet), it is believed that higher doses in the diet can lead to a reduction in methane emission

O Metano (CH4) é o segundo gás de efeito estufa mais importante, com aproximadamente 40% de sua emissão proveniente de fontes naturais, enquanto as fontes antrópicas representam cerca de 60%. Sua média global em 2009 foi de 1803ppb, que representa um aumento de 5ppb em relação ao ano anterior. Neste estudo foram calculados os fluxos de CH4, utilizando medidas de perfis verticais com aviões de pequeno porte, desde a superfície até 4,4km na Bacia Amazônica, sobre Santarém (SAN), Alta Floresta (ALF), Rio Branco (RBA) e Tabatinga (TAB), por meio do Método de Integração de Coluna. Estas medidas de CH4 em escala regional até o presente momento são únicas e representam uma nova abordagem nas emissões nesta escala. As medidas em SAN foram realizadas entre 2000 e 2010 e o fluxo de CH4 encontrado para este período foi de 53,0 ± 27,9mgCH4.m-2.dia-1. Para o ano de 2010, o maior fluxo de emissão de CH4 foi observado no lado leste da Bacia Amazônica, entre a costa e SAN, 56,4 ± 22,4mgCH4.m-2.dia-1. Entre a costa e ALF, ao sul da Bacia Amazônica, o fluxo médio anual foi de 17,1 ± 2,3mgCH4.m-2.dia-1, e entre a costa e os locais TAB e RBA, no lado oeste da Bacia, foi observado um fluxo médio anual de 18,7 ± 4,2 e 19,3 ± 10,2mgCH4.m-2.dia-1, respectivamente. Extrapolando os resultados obtidos em TAB e RBA para toda a área da Bacia Amazônica (5 milhões Km2) obtêm-se uma emissão de 34,7 ± 13,5TgCH4.ano-1. Com o objetivo de determinar a influência da queima de biomassa no fluxo regional de emissão de CH4, foi utilizada a correlação 6,4ppbCO/ppbCH4 calculada neste estudo, ALF foi o local de estudo que apresentou a maior influência no fluxo de CH4 oriundo da queima de biomassa, 23% do fluxo total anual. / Methane (CH4) is the second most important greenhouse gas with approximately 40% of emission from natural sources, while anthropogenic sources account for about 60%. The global average was 1803ppb in 2009, representing an increase of 5ppb in relation to the previous year. This study calculated the fluxes of CH4, using measurements of vertical profiles with small aircraft, from the surface to 4.4km in the Amazon Basin, over Santarém (SAN), Alta Floresta (ALF), Rio Branco (RBA) and Tabatinga (TAB), using the Column Integration Technique. These measurements of CH4 at a regional scale until now are unique and represent a new approach to emissions on this scale. SAN measurements were realized between 2000 and 2010 and CH4 flux found for this period was 53.0 ± 27.9mgCH4.m-2.day-1. For the year 2010, the largest flux of CH4 emission was observed in the eastern Amazon Basin, between the coast and SAN, 56.4 ± 22.4mgCH4.m-2.day-1. Between the coast and ALF, located in the south of the Amazon Basin, the annual mean flux was 17.1 ± 2.3mgCH4.m -2.day-1, and between the coast and the local TAB and RBA on the west side of the Basin was observed an mean annual flux of 18.7 ± 4.2 and 19.3 ± 10.2mgCH4.m-2.day-1, respectively. Extrapolating the results obtained in TAB and RBA for the whole area of the Amazon Basin (5 million km2) to obtain an emission of 34,7 ± 13,5TgCH4.year-1. In order to determine the influence of biomass burning on regional emission flux of CH4, was used a correlation 6.4ppbCO/ppbCH4 calculated in this study, ALF was the site that had the most influence on the CH4 flux from the burning biomass, 23% of the total annual flux.

Soil organic carbon (SOC) is important not only for improving soil quality but also for contributing to climate change mitigation in agriculture. However, net greenhouse gas (GHG) balances, including methane (CH4) and nitrous oxide (N2O), need to be considered, as practices that increase SOC might increase GHG emissions. Sustainable use of soil resources needs to be assessed over long time periods and across spatial scales; biogeochemical models are useful tools to estimate GHG emissions and corresponding mitigation potentials. A process-based, ecosystem model DayCent that simulates soil carbon and nitrogen dynamics from diverse agroecosystems, has been applied to observe SOC sequestration, GHG emissions and yield in a contrasting climatic region UK and Bangladesh agriculture. The study mainly focus on determination of GHG mitigation potentials under improved management practices in rice based cropland Bangladesh. We hypothesized that alternative management would increase SOC and reduce net GHG emissions. As crop yield is the most important variable for Bangladesh, it was includes in the simulations. Since site test simulations under different management using the DayCent model were satisfactory, the model was used to simulate GHG covering 64 districts of Bangladesh, considering climate, soil and SOC content for the period 1996-2015. An integrated management scenario consisting of irrigation, tillage with residue management, reduced mineral nitrogen fertilizer and manure application increased annual SOC stocks, and offset net GHG emissions while maintaining yield. The model outcome suggests that the “4 per mille” target is feasible for Bangladesh. It is also possible to contribute to the GHG reduction target by 2030 set by policy makers.

No description available.

Peat soils store a large fraction of the global soil carbon (C) pool and comprise 95% of wetland C stocks. They also have the capability to produce and release significant amounts of greenhouse gasses (CO2, CH4) into the atmosphere. Most studies of wetland soil C and gas flux dynamics have been done in expansive peatlands in northern boreal and subarctic biomes. However, wetlands in temperate and tropical climates are vastly understudied despite accounting for more than 20% of the global peatland C stock and storing large amounts of biogenic gasses Although studies investigating greenhouse gas dynamics from peatlands have increased during the last decade, the spatial and temporal distribution of these gases still remains highly uncertain, mainly due to the limitations in terms of spatial and temporal resolution and invasive nature of most methods traditionally used. This thesis combines a series of field and laboratory studies at several sites in the Greater Everglades as examples to show the potential of hydrogeophysical methods to better understand: 1) the belowground C distribution and overall contribution to the global C stocks of certain wetlands (Chapter 2); and 2) the spatial and temporal variability in both C accumulation and releases from peat soil monoliths from several wetland sites in the Greater Everglades (Chapter 3 and 4). To estimate belowground C in the field, I used a combination of indirect non-invasive geophysical methods (GPR), aerial imagery, and direct measurements (coring) to estimate the contribution of subtropical depressional wetlands to the total C stock of pine flatwoods landscape at the Disney Wilderness Preserve (DWP, Orlando, FL). Three-dimensional (3D) GPR surveys were used to define the thickness of stratigraphic layers from the wetland surface to the mineral soil interface within depressional wetlands. Depth-profile cores in conjunction with C core analysis were utilized to visually confirm depths of each interface and estimate changes in soil C content with depth and were ultimately used to estimate total peat volume and C stock for each depressional wetland. Aerial photographs were used to develop a relationship between surface area and total wetland C stock, that were applied to estimate total landscape C stock of all depressional wetlands throughout the entire preserve. Additionally, low-frequency GPR surveys were conducted to image the stratigraphy underneath the peat basin of depressional wetlands to depict lithological controls on the formational processes of depressional wetlands at the DWP. Spatial and temporal variability in biogenic greenhouse gas (i.e. methane and carbon dioxide) production and release were investigated at the laboratory scale. Two 38 liter (0.5 m x 0.23 m x 0.3 m) peat monoliths from two different wetland ecosystems in central Florida (sawgrass peatland and a wet prairie) were compared in order to understand whether changes in matrix properties influence gas dynamics in a controlled environment (i.e. constant temperature). Gas content variability (i.e. build-up and release) within the peat matrix was estimated using a series of high frequency (1.2 GHz) GPR transects along each sample about three times a week. An array of gas traps (eight per sample) fitted with time-lapse cameras were also used in order to constrain GPR measurements and capture gas releases at 15-minute intervals. Gas chromatography was performed on gas samples extracted from the traps to determine CH4 and CO2 content. Also, at the lab scale, temporal variability in biogenic gas accumulation and release was investigated in a large 0.073 m3 peat monolith from the Blue Cypress Preserve in central Florida. An autonomous rail system was constructed in order to estimate gas content variability (i.e. build-up and release) within the peat matrix using a series of continuous GPR transects along the sample. This system ran virtually nonstop using high frequency (1.2 GHz) antennas. GPR measurements were again constrained with an array of gas traps (6) fitted with time-lapse cameras and gas chromatography. The aim of this study is to better constrain temporal scale, and better understand the heterogeneous nature (both in time and space) of gas releases from peat soils. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

Trace gases can have a significant impact on the Earth's climate, and the analysis of changes in these gases and an understanding of how much of these changes are a result of human activity is important for understanding global climate change. Methane (CH4) is the second only to CO2 in radiative forcing over the last 200 years, and its concentration in the atmosphere has more than doubled since 1750. Sources and sinks of CH4 have characteristic isotopic effects, which shift the relative concentration of the methane isotopologues. Spectroscopic techniques for of analysis the isotopic composition of methane have been evolving since the early 1990's, and promise real-time, in-situ measurements that would provide unprecedented information on the methane atmospheric cycle. Here we present our development and results of a new optical spectroscopic isotope ratio instrument using cavity ringdown spectroscopy in the near IR region using the ν2+2ν3 overtone band. This region has limited interference from other molecules, and an advantageous juxtaposition of a 13CH4 triplet, and a single 12CH4 peak, allowing near-simultaneous measurement of both isotopologues. We present the results of two datasets showing high linearity over a wide range of isotope ratios, which achieved a precision of ±4 /. We present analysis of the data and consider the effects of temperature and molecular interference.

The rise in atmospheric CO2 partial pressures that is predicted for the 21st Century is likely to increase productivity and alter nutrient of C3 crop plants. Consequently, physiological data on plant growth and nutrition at elevated CO2 are required, because these data underpin simulation models, which are needed for management of crops under the CO2 scenario for the mid to late 21st Century.In particular, information is required about management of nitrogen(N) fertilisation because this mineral nutrient plays a central role in the growh of many crops. Rice was chosen as a model plant because of its widespread consumption throughout the world and its responsiveness to CO2 and N fertilisation. There were three major hypotheses: first, that early exposure of rice plants to high CO2 is required to achieve the maximum growth and tillering response; secondly, that early increases in growth and tillering at high CO2 are associated with the phytohormone, ethylene; and thirdly, that growth at elevated CO2 decreases leaf N concentrations required to support maximum dry mass production and photosynthetic rates (critical concentrations).Several tests and experiments were conducted and results noted. It is likely that grain yield will be greater as the atmospheric CO2 partial pressure rises even when N supplies are low, providing that high CO2 does not cause accelerated tiller abortion at low N. / Doctor of Philosophy (PhD)

Establecer una cota global a las emisiones de gases de efecto invernadero ha sido imposibilitado por la complejidad que conlleva demostrar los efectos de la contribución humana al efecto invernadero. Para alcanzar un desarrollo sostenible es necesario, primero limitar y en lo posible eliminar las emisiones de dichos gases a la atmosfera. En este contexto, la adsorción de gases se ha establecido como una de las alternativas más efectivas a mediano plazo para la reducción de emisiones de gases de efecto invernadero. Por lo tanto, en esta tesis, el objetivo principal es estudiar a nivel molecular la adsorción de gases de efecto invernadero y comprender mejor la interacción entre las distintas variables que afectan el proceso de captura. En la primera parte de esta tesis se estudió, la separación de una mezcla de hexafluoruro de azufre (SF6) y nitrógeno (N2). El SF6 se emite en pequeñas cantidades, sin embargo por ser un potente gas de efecto invernadero con un tiempo de vida extremadamente alto se requiere un control estricto de sus emisiones. En este trabajo se estudió, empleando modelos simples, el efecto del tamaño de poro, la presión y la composición de la mezcla en la separación selectiva del SF6. Posteriormente, se realizaron simulaciones con modelos realistas de dos carbonos réplicas de zeolitas y se encontró que la selectividad predicha para el SF6 en dichos materiales es superior a la de los materiales previamente reportados en la literatura. En la segunda parte del trabajo se estudió el uso de estos materiales de carbono para la captura de dióxido de carbono (CO2) a temperatura ambiente, y se encontró que su capacidad de captura de CO2 a altas presiones es comparable a la de los mejores adsorbentes de CO2 reportados. Para comprender mejor la captura en los carbonos réplicas de zeolitas, se emplearon simulaciones moleculares para obtener información acerca de su compleja estructura interna y predecir las interacciones del CO2 con el interior de estos materiales. En la parte final de esta tesis se estudiaron materiales híbridos organo-inorgánicos, en particular, adsorbentes de sílica funcionalizados con grupos amino. Se desarrolló una nueva metodología de simulación para la generación de materiales de sílica funcionalizados con cadenas orgánicas y el cálculo de sus propiedades de adsorción. La metodología se evaluó empleando modelos de sílica gel y MCM-41 funcionalizados con diferentes cadenas orgánicas, comparando los resultados de las simulaciones de las isotermas de adsorción y la densidad de funcionalización con datos experimentales. Simultáneamente, se desarrolló un nuevo método que permite calcular adicionalmente a la fisisorción la quimisorción del CO2 en las aminas empleando simulaciones moleculares. En resumen, esta tesis de doctorado resalta diferentes posibilidades para la captura y separación de gases de efecto invernadero y proporciona nuevas herramientas de simulación para evaluar y optimizar sistemas de captura de gases. Esta tesis se enmarca dentro de la ciencia de materiales y muestra como la investigación básica en este campo puede ser usada como una herramienta para evaluar y optimizar procesos industriales. / The establishment of a global limit on the emissions of greenhouse gases has been hindered by the complexity to prove the effects of manmade greenhouse gases on a global scale. In order to achieve a sustainable development it is important to limit, and when possible eliminate, emissions of industrial greenhouse gases to the atmosphere. In this context, adsorption has been established as one of the best cost-effective means of reducing emissions of greenhouse gases in the short-term. Thus, in this thesis, the main objective is to study at a molecular level the adsorption of greenhouse gases and to obtain a better insight into the capture processes for their future optimization. Molecular simulations are used in order to find the optimal diameter for the separation of sulfur hexafluoride (SF6) from nitrogen (N2); this mixture is commonly used in electrical applications. SF6 is typically emitted in small quantities, but because it is a potent greenhouse gas and possesses extremely long lifetimes, there is a pressing need for a strict control of its emissions. The effect of pore size, pressure, and mixture compositions on the selective adsorption of SF6 was investigated using simple models. Subsequently, simulations using two atomistic models of zeolite templated carbons were performed. The separation selectivities compared favorably to the materials previously reported for the separation of this mixture. Moreover, the potential use of these two templated carbon materials to capture carbon dioxide (CO2) at room temperature is reported. Their high-pressure CO2 adsorption isotherms are among the highest carbon capture capacity for carbonaceous materials and are comparable to the best CO2 adsorbing materials. In addition, the simulated adsorption isotherms were used to obtain new insights into the adsorption process of the templated carbons. In the final part of the thesis hybrid organic-inorganic adsorbents were studied. For CO2 capture, solid adsorbents are functionalized with amino groups that largely increase their adsorption capabilities. However, the underlying mechanism of the adsorption process in the functionalized materials is not fully understood, limiting the possibility of designing optimal adsorbent materials for different applications. The adsorption of CO2 in aminefunctionalized silica materials was studied using Monte Carlo molecular simulations. A simulation methodology for the design of functionalized silica materials was proposed. The methodology was evaluated using models of silica gel and MCM-41 functionalized with different organic groups, comparing the resulting adsorption isotherms and grafting density to available experimental data. Furthermore, a new scheme that allows accounting for the chemisorbed CO2 on the adsorption isotherms is presented In summary, this PhD thesis highlights different possibilities for the capture and separation of greenhouse gases and provides new tools for evaluating and optimizing capture systems. Finally, this dissertation shows the use of basic research in Materials Science as an established tool for evaluating and optimizing thermodynamics of engineering processes.

Reservoirs impound and store large volumes of water and flood land. The water is used for electricity generation, irrigation, industrial and municipal consumption, flood control and to improve navigation. The decomposition of flooded soil and vegetation creates greenhouse gases and thus reservoirs are a source of greenhouse gases. Reservoirs are not well studied for greenhouse gas flux from the water to the atmosphere. The FLooded Upland Dynamics EXperiment (FLUDEX) involves the creation of three experimental reservoirs in the upland boreal forest to study greenhouse gas and mercury dynamics. The balance of biological processes, decomposition, primary production, CH₄ oxidation and the nitrogen cycle in the reservoirs controls the greenhouse gas flux from the reservoir to the atmosphere. Understanding the importance and controlling factors of these processes is vital to understanding the sources and sinks of greenhouse gases within reservoirs. The carbon and oxygen dynamics near the sediment-water interface are very important to the entire reservoir because many processes occur in this area. Light and dark benthic chambers were deployed, side-by-side, to determine the benthic flux of DIC and CH₄ across the sediment-water interface and to determine the role of benthic photoautotrophs in benthic DIC, CH₄ and O₂ cycling. Benthic chambers have shown photoautotrophs use the decomposing soil, rocks and exposed bedrock as a physical substrate to colonize and the CO₂ produced by the decomposing soil as a carbon source since the delta¹³C-DIC value of the DIC added to light chambers is enriched relative to dark chambers and net photosynthesis rates are linked to community respiration. Benthic photoautotrophs consume 15-33% of the potential DIC flux into the water column. CH₄ produced by the decomposition of soils is partially oxidized by methanotrophs that use the photosynthetically produced oxygen. The delta¹³C-CH₄ values of the CH₄ added to light chambers is enriched relative to dark chambers and 15-88% of the potential CH₄ flux into the water column is oxidized. An isotope-mass budget for DIC and CH₄ is presented for each reservoir to identify the importance of processes on areservoir scale. Input of DIC to the reservoirs from overland flow can be important because concentration is greater and delta¹³C-DIC values are depleted relative to inflow from Roddy Lake. Estimates of total reservoir primary production indicate that 3-19% of the total DIC production from decomposition is removed by photoautotrophs. The carbon cycling in biofilm and the importance of periphytic primary production needs to be better understood. Dissolved delta¹³C-CH₄ values of CH₄ in reservoir outflow enriched 45-60permil, indicating that CH₄ oxidation was an important CH₄ sink within the reservoirs. Stable carbon isotope data indicates that the CH₄ in the bubbles is partially oxidized so the site of bubble formation is the upper portion of the flooded soil. The fraction of CH₄ converted to CO₂ in the FLUDEX reservoirs is similar to that of the wetland flooded for the Experimental Lakes Area Reservoir Project (ELARP). Approximately half of the dissolved CH₄ in the FLUDEX reservoirs was removedby CH₄ oxidation. The ebullitive flux of CH₄ from FLUDEX reservoirs is reduced 25-75% by CH₄ oxidation. The CH₄ flux to the atmosphere from peat surface of the ELARP reservoir became less oxidized after flooding: 91% to 85% oxidized. The floating peat islands of the ELARP reservoir were less oxidized than the peat surface. Similar to the CH₄ in the FLUDEX reservoirs, CH₄ in the ELARP peat islands was oxidized 56%. CH₄ oxidation is an important process because it reduces the global warming potential of the greenhouse gas flux since CO₂ is less radiatively active than CH₄.