The aboveground and belowground productivity of forest systems are interlinked through complex feedback loops involving tree, soil and environmental factors. With a predicted significant change in environmental conditions through the enhanced greenhouse effect, it is important to understand the response of forest systems to these new conditions. An increase in atmospheric CO2 is predicted to increase photosynthesis, and therefore whole plant productivity at the individual tree level. However this increase in photosynthesis may result in greater requirements for nutrients, particularly nitrogen (N). In order to acquire any additional available N, trees may respond by increasing their proportional allocation of C belowground to the root system. This study aimed to quantify the belowground C allocation in a mature forest system consisting of a single species on a single site, but with different levels of water and nutrient stress. The belowground carbon dynamics of a range of irrigated and fertilized Pinus radiata stands in Australia were investigated during 1992 and 1993. Belowground carbon allocation was estimated using the model proposed by Raich and Nadelhoffer (1989) where belowground C allocation is the difference between soil respiration and carbon input through litterfall, plus coarse root production and an adjustment for any change in soil and litter layer carbon pools. This model is best described by the equation: Belowground C = Csoilresp ?? Clitterfall + Ccoarseroot+ ???Cforest floor+ ???Csoil Soil respiration, measured using a modified soda lime absorption method either every 2 weeks or every 4 weeks for 2 years, showed a range in daily soil C flux from 137 ?? 785 mgCO2.m-2.h-1. Soil respiration showed seasonal trends with summer highs and winter lows. Limited fine root biomass data could not indicate a strong relationship between measured soil respiration and fine root (&gt2mm diameter) biomass. Fifty three percent of the variation in soil respiration measurements in irrigated treatments was explained by a linear relationship between soil respiration, and soil temperature at 0.10 m depth and litter moisture content. In non-irrigated treatments, 61% of the variation in soil xix respiration measurements was explained by a linear relationship between soil temperature at 1 cm depth and soil moisture content. Inter-year variation was considerable with annual soil respiration approximately 20% lower in 1993 compared with 1992. Annual soil C flux was calculated by linear interpolation and ranged from 3.4 ?? 11.2 tC ha-1 across the treatments. Soil C pools remained unchanged over 10 years between 1983 and 1993 for all combinations of irrigated and fertilized stands, despite significant aboveground productivity differences over the decade. Measurements of standing litter showed a change between 1991 and 1993 for only 2 out of the 10 treatments. These two treatments had belowground C allocation estimated both with and without an adjustment for a change in standing litter. Annual litterfall C ranged almost four fold from 0.6 ?? 2.2 tC ha-1 between the treatments in 1992 and 1993, and fell within the ranges of measured litterfall over 10 years at the field site. Again inter-year variation was large, with the 1993 litterfall values being approximately 97% greater across all treatments compared with 1992 values. Belowground carbon allocation was calculated using C fluxes measured at the field site, and ranged 3 fold from 4.4 ?????? 12.9 tC ha-1 between the treatments during 1992 and 1993. In 1993 the belowground C allocation was approximately 30% lower across all treatments compared with 1992 calculations. This was due to an approximate 23% reduction in annual soil C flux, a 97% increase in litterfall C and an 18% reduction in coarse root production between 1992 and 1993. The field site was N limited, and differences in belowground C allocation could be shown across irrigated treatments with different N limitations. As N availability increased belowground C allocation was decreased in the irrigated treatments. It was difficult to determine differences in belowground C allocation caused by water stress as the effects of water and N limitation were confounded. An increase in N availability generally indicated an increase in coarse root and litterfall C production, which were reflected in increased aboveground productivity. In high N treatments the coarse root fraction of belowground C allocation comprised approximately 50% of the total belowground C allocation, whereas in the N stressed treatments coarse roots only comprised 20% of the total belowground allocation The mechanistic model BIOMASS was used to estimate annual gross primary productivity (GPP) for the different treatments at the field site. BIOMASS estimated GPPs of between 30-38 tC ha-1 for the different treatments during 1992 and 1993. The measured belowground carbon allocation ranged from 16 ?? 40 % of simulated GPP, with the lower proportion allocated belowground in the irrigated and high fertility stands. Aboveground competition through the absence of thinning also appeared to reduce allocation belowground in non- irrigated stands. A direct trade off between bole and belowground C could not be demonstrated, unless data were separated by year and by the presence or absence of irrigation. Where data were separated in this manner, only three data points defined the reasonably strong, negative relationship between bole and belowground C. The value of this relationship is highly questionable and should be interpreted with caution. Thus a decrease in belowground C allocation may not necessarily indicate a concomitant increase in bole C allocation. Inter-year variation in a number of C pools and fluxes measured at the field site was at least as great as the variation between stands having different water and N limitation. Extrapolation of belowground productivity estimates from a single years data should be undertaken cautiously. The work undertaken in this study indicated that for a given forest stand in a given soil type, an increase in N availability reduced the absolute and relative C allocated belowground. However this decrease in C belowground may not directly translate as an increase in stem growth or increased timber production. Forest productivity in an enhanced greenhouse environment is likely to result in an increased allocation of C belowground due to increased N limitation, unless adequate N is present to support a more active canopy. Further work is required to more fully understand the dynamics of the belowground system in a changing environment. However further research should focus on mature forest systems in order to isolate the impacts of natural ageing changes from perturbation effects on the forest system. This would be best undertaken in long term monitoring sites where a C history of the stand may be available.

Graduation date: 1994

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 258-283).

Arctic Ocean contributes to the global oceanic uptake of CO2 by about 5% to 14% in taking up from 66 to 199 TgC yr-1. However, the role of the marine cryosphere was ignored because it is considered as an impermeable barrier, impeding the gas exchanges between the ocean and the atmosphere [Bates and Mathis, 2009]. However, a growing body of evidence suggests that gases exchange could occur between sea ice and the atmosphere. In this context, two Arctic surveys were carried out in the framework of the International Polar Year (IPY). From there, we present a snapshot of the partial pressure of CO2 (pCO2) dynamics firstly during the initial sea ice growth and secondly from early spring to the beginning of the summer. We confirmed previous laboratory measurement findings that growing young sea ice acts as a source of CO2 to the atmosphere by measuring CO2 efflux from the ice (4 to 10 mmol m-2 d-1). We also confirmed the precipitation of calcium carbonate as ikaite in the frost flowers and throughout the ice and its negligible role on the effluxes of CO2. In early spring, supersaturations in CO2 (up to 1834 µatm) were observed in sea ice as consequence of concentration of solutes in brines, CaCO3 precipitation and microbial respiration. As the summer draw near, brine shifts to a marked undersaturation (down to almost 0 µatm) because of the brine dilution by ice meltwater, dissolution of CaCO3 and photosynthesis during the sympagic algal bloom. Out of the winter, soon as the ice becomes permeable, CO2 fluxes were observed: (i) from the ice to the atmosphere, as the brine were supersaturated, (ii) from the atmosphere to the ice, as brine shift to an undersaturation. Temperature appears to be the main driver of the pCO2 dynamics within sea ice. It mainly controls the saturation state of the brine (where others processes may be added, e.g., CaCO3 precipitation, primary production) and thus, the concentration gradient of CO2 between sea ice and the atmosphere. It also controls the brine volume and so the brine connectivity, allowing the gas exchanges between sea ice and the atmosphere. We also present a new analytical method to measure the pCO2 of the bulk sea ice. This method, based on equilibration between an ice sample and a standard gas, was successfully applied on both artificial and natural sea ice. However, this method is only applicable for permeable sea ice (i.e., brine volume > 5% [Golden et al., 1998; 2007]) to allow the equilibration between the ice and the standard gas.

Consuming two major greenhouse gases, carbon dioxide (CO2) and methane (CH4), to produce synthesis gas, which is a mixture of carbon monoxide (CO) and hydrogen (H2), CO2 reforming of CH4 shows significant environmental and economic benefits. However, the process has not found wide industrial application due to severe catalyst deactivation, basically caused by carbon formation. Therefore, it is of great interest to develop stable catalysts without severe deactivation. This work is primarily focused on the development of novel nickel-based catalysts to achieve stable operation for CO2 reforming of CH4.<p> Following Dowdens strategy of catalyst design, a series of nickel-based catalysts are designed with a general formula: Ni-Me/AlMgOx (Me = Co, Cu, Fe, or Mn). The designed catalysts are prepared using co-precipitation method and tested for CO2 reforming of CH4. Catalyst screening showed that the Ni-Co/AlMgOx catalyst has superior performance in terms of activity and stability to other Ni-Me/AlMgOx (Me = Cu, Fe, or Mn) catalysts. A 2000 h long-term deactivation test has shown that the Ni-Co/AlMgOx has high activity and excellent stability for CO2 reforming of CH4.<p> Further investigation on the Ni-Co/AlMgOx catalysts shows that adjusting Ni/Co ratio and Ni-Co loading can significantly affect the catalyst performance. Carbon free operation for CO2 reforming of CH4 can be achieved on the catalysts with a Ni/Co close to 1 and Ni-Co overall loading between 4-10 %. In addition, calcination temperature shows important impacts on the performance of Ni-Co/AlMgOx catalysts. A calcination temperature range of 700-900 oC is recommended.<p> The Ni-Co/AlMgOx catalysts are characterized using various techniques such as ICP-MS, BET, CO-chemiosorption, XRD, TPR, TG/DTA, TEM, and XPS. It has been found that the high activity and excellent stability of Ni-Co/AlMgOx catalysts can be ascribed to its high surface area, high metal disperation, small particle size, strong metal-support interaction, and synergy between Ni and Co.<p> Kinetic studies have shown that the CH4 decomposition and CO2 activation could be the rate-determining steps. Both Power-Law and Langmuir-Hinshelwood kinetic models can fit the experiment data with satisfactory results.

This project is mainly focused on the improving and design of the ventilation system of two rooms at different levels of a gym (Friskis and Svettis in Gävle, Sweden) to reduce the  concentration to never be higher than 1000 ppm. For this purpose, several field measurements were performed in different locations and situations. Two main measurements were necessary. On one hand, the  level in different parts of the rooms during different activities. On the other hand, the air flow through the inlet and outlet ducts of the ventilation system. It was also important to take into account the indoor temperature and humidity. These measurements were enough to analyze the failures of the system and to recognize the worst points of each room. Comparing both rooms, the necessity of changing the ventilation system in one of these rooms was much higher, due to there were measured  values up to 3000 ppm during a typical day in the gym. With this information the consequences of high CO2 levels in human people were analyzed. Among various ventilation systems, displacement ventilation system was proposed as the new design. Theoretical calculations were made to reach to the value of 31.8  in the air change rate (ACH), which was the necessary value for the new design to keep the carbon dioxide level under 1000 ppm.

Consuming two major greenhouse gases, carbon dioxide (CO2) and methane (CH4), to produce synthesis gas, which is a mixture of carbon monoxide (CO) and hydrogen (H2), CO2 reforming of CH4 shows significant environmental and economic benefits. However, the process has not found wide industrial application due to severe catalyst deactivation, basically caused by carbon formation. Therefore, it is of great interest to develop stable catalysts without severe deactivation. This work is primarily focused on the development of novel nickel-based catalysts to achieve stable operation for CO2 reforming of CH4.<p> Following Dowdens strategy of catalyst design, a series of nickel-based catalysts are designed with a general formula: Ni-Me/AlMgOx (Me = Co, Cu, Fe, or Mn). The designed catalysts are prepared using co-precipitation method and tested for CO2 reforming of CH4. Catalyst screening showed that the Ni-Co/AlMgOx catalyst has superior performance in terms of activity and stability to other Ni-Me/AlMgOx (Me = Cu, Fe, or Mn) catalysts. A 2000 h long-term deactivation test has shown that the Ni-Co/AlMgOx has high activity and excellent stability for CO2 reforming of CH4.<p> Further investigation on the Ni-Co/AlMgOx catalysts shows that adjusting Ni/Co ratio and Ni-Co loading can significantly affect the catalyst performance. Carbon free operation for CO2 reforming of CH4 can be achieved on the catalysts with a Ni/Co close to 1 and Ni-Co overall loading between 4-10 %. In addition, calcination temperature shows important impacts on the performance of Ni-Co/AlMgOx catalysts. A calcination temperature range of 700-900 oC is recommended.<p> The Ni-Co/AlMgOx catalysts are characterized using various techniques such as ICP-MS, BET, CO-chemiosorption, XRD, TPR, TG/DTA, TEM, and XPS. It has been found that the high activity and excellent stability of Ni-Co/AlMgOx catalysts can be ascribed to its high surface area, high metal disperation, small particle size, strong metal-support interaction, and synergy between Ni and Co.<p> Kinetic studies have shown that the CH4 decomposition and CO2 activation could be the rate-determining steps. Both Power-Law and Langmuir-Hinshelwood kinetic models can fit the experiment data with satisfactory results.

Photonic crystal (PC) technology potentially offers lossless control of light propagation at a size scale near the order of the wavelength of light. The advantages and benefits of using such a technology in commercial devices are staggering. Yet, the commercial development of PC structures has been slow. Challenges associated with the repeatable fabrication and testing of structures has been identified as one cause of the slow development pace. To address these challenges, a development methodology that utilizes PC structures operating in the long-wavelength infrared is presented. One-dimensional PC structures, consisting of alternating regions of silicon and air are fabricated and characterized by measuring the transmittance or reflectance of the structure over the wavelength range from 5 쭠to 15 쭮 For the measurements, a model of the focused infrared beam is developed, tested and employed to characterize the structures. A novel measurement method, enabling the calculation of the single-angle plane-wave transmittances and reflectances from composite, multiple-angle transmittance and reflectance measurements, is formulated, tested and applied to PC structures. A new spectral characterization tool using a discretely tunable carbon-dioxide laser is presented and demonstrated. A measurement apparatus employing an FTIR microspectroscopy system is developed and measurements are recorded for the single-angle plane-wave characterization method. Single-angle plane-wave transmittances and reflectances calculated from composite multiple-angle measurements are shown to be in excellent agreement with theory. The results of this research are analyzed to identify the advantages and limitations of the long-wavelength infrared method.

none

Thesis (Ph. D.)--Cornell University, August, 2006. / Vita. Includes bibliographical references (leaves 201-220).