A agricultura pode ser uma aliada importante para a mitigação da concentração de gás carbônico (CO2) na atmosfera. Pela fotossíntese pode-se converter o CO2 da atmosfera em massa vegetal, e, além disso, por meio de um manejo adequado desta massa pode-se reter parte do carbono (C) no solo, caracterizando um \"seqüestro de C\" da atmosfera pelo solo. Pesquisas têm se voltado para entender o papel da produção agrícola, como os sistemas conservacionistas de manejo, ou seja, o plantio direto (PD), e das pastagens de Brachiaria sobre a dinâmica do C no solo. Estudos sobre a dinâmica e a estabilidade da matéria orgânica do solo (MOS) são necessários, já que variáveis como estoques de carbono (EC) e graus de humificação podem ser avaliados, e sendo assim, obter parâmetros fundamentais para a mitigação de CO2 na atmosfera, tema que se insere num dos enfoques das Mudanças Climáticas Globais. Nesse contexto, espectroscopias, como por exemplo, a Ressonância Paramagnética Eletrônica (RPE), a Fluorescência de luz no ultravioleta-visível (UV-vis) e a Fluorescência Induzida por Laser (FIL) podem ser fundamentais na avaliação da estabilidade da MOS. Este trabalho teve como objetivo verificar o comportamento da MOS em áreas com potencial para seqüestro de C, por meio da avaliação dos estoques deste no solo, em diferentes sistemas de manejo e posterior caracterização por Espectroscopia. Além disso, e em função das dificuldades encontradas na seleção da melhor metodologia para a quantificação de C, foi também possível avaliar métodos de determinação de C, comparando-os entre si pelos coeficientes de variação e análise multivariada, e assim propondo uma melhor metodologia. Em área tropical de pastagens de Brachiaria decumbens, no Brasil, os resultados mostraram que a determinação dos EC foram maiores nesses sistemas, comparado com a vegetação nativa de cerradão, após 27 anos de experimento. Os maiores EC obtidos pelas pastagens foram favorecidos pela constante entrada de material vegetal na superfície do solo, também influenciado pela entrada do nitrogênio (N), além do sistema radicular da gramínea, considerando o tratamento de pastagem com adição anual de N e aplicação de 2 t ha-1 de calcário (com reforço de 1 t ha-1 anual), o melhor tratamento em função do acúmulo da MOS. Os resultados mostraram que essas pastagens bem manejadas podem possibilitar um seqüestro de 6,1 a 12,8 Mg CO2 ha-1 ano-1 da atmosfera. Com a avaliação qualitativa da MOS, também foi possível obter resultados promissores na determinação da estabilidade da MOS. A detecção do aumento do conteúdo de C no solo foi acompanhada pela redução do grau de humificação, por meio da FIL. Esta redução na humificação foi devido à entrada de material orgânico mais lábil, ou seja, menos transformado. Na Fluorescência convencional e RPE, com amostras de AH em solução, os maiores graus de humificação foram obtidos para os AH dos tratamentos de pastagem, principalmente os que tiveram adição de calagem. O Ca2+, além de aumentar a atividade microbiana, pode complexar com os AH, associado ao aumento da estabilidade da MO. No sistema de PD de soja com renovação de cana-de-açúcar, os maiores teores de C foram obtidos nas amostras referentes aos sistemas sob PD após 7 anos sob esse manejo, em comparação com áreas sob manejo convencional. O acúmulo de MOS foi devido principalmente à preservação da cobertura vegetal associada com o não revolvimento do solo, rotação de culturas e a não queimada da cana-de-açúcar. Nessa área experimental, foi possível constatar um seqüestro de 0,15 a 5,29 Mg CO2 ha-1 ano-1 da atmosfera. Com relação à estabilidade da MO avaliada por Espectroscopia de FIL, verificou-se que o sistema de PD apresentou menor grau de humificação, devido à maior entrada de material orgânico lábil. Os resultados obtidos em área experimental de PD com grãos, com até 22 anos de duração, estão provavelmente associados com o tipo de solo analisado. Nos Latossolos com alto conteúdo de argila pode haver proteção física da MO, provavelmente impedindo alterações estruturais desse material, mesmo após longo período sem o revolvimento do solo. Outro fato importante é que o estudo de seqüestro de C depende muito da área avaliada, ou seja, delineamento do experimento, histórico do local, duração, condições climáticas, taxas de decomposição do C, produção de massa vegetal e aporte de resíduos. / Agriculture can play an important role in mitigating carbon dioxide (CO2) concentration in the atmosphere. Through photosynthesis, it is possible to convert CO2 from atmosphere to plant biomass, and moreover, through an adequate agricultural system CO3 can be stored in soil, characterizing \"carbon sequestration\". Nowadays, many researches want to understand the role of agriculture production, as no-tillage, and Brachiaria pastures, in carbon dynamics in soil. Studies about organic matter dynamics and stability are necessary, since variables such as carbon stocks and degree of humification can be evaluated, and as a result, to obtain essential parameters to CO2 mitigation to the atmosphere. This topic is inserted in some Global Climate Change interests. In this context, spectroscopic methods, for example, Electron Paramagnetic Resonance (EPR), UV-Vis light fluorescence and Laser Induced Fluorescence (LIF) can be fundamental in the stability of soil organic matter (SOM) evaluation. The present study aims to examine the SOM behavior in areas with carbon sequestration potential, through evaluation of carbon stocks in soils, in different tillage systems followed by characterization by spectroscopy. Therefore, the knowledge of the organic matter (OM) quantity is important in soil management regarding to a sustainable agriculture. However, little consistent information is found to compare and recommend the most adequate method to obtain satisfactory results for each study. Consequently, it was possible to evaluate the OM quantity in Oxisols by different methods and compare them, using coefficient of variation and principal component analysis, to propose the best methodology. In the tropical regions of Brazil, in Brachiaria decumbens pastureland, the results showed that the greatest SOM content occurred under pastureland, against the native dense Cerrado vegetation, after 27 years of experiment. The highest carbon stocks obtained by pasture samples were favored by accumulations of plant biomass on the soil surface, nitrogen input, besides Brachiaria root systems. According to the results obtained, the annual input of adequate amounts of limestone (2 t ha-1 addition and 1 t ha-1 year-1 reinforcement) and N seemed to be the best treatment regarding different pastureland treatments, mainly due to its higher C accumulation. The results also showed that non-degraded pastures can enable an annual sequestration rate ranging from 6.1 to 12.8 Mg CO2 ha-1 year-1. Qualitative evaluation of SOM also obtained satisfactory results on the soil surface. Results showed that higher C amount was followed by lower degree of humification, obtained by LIF. This lower humification was due to labile organic material, or greater fresh input of crop residues. In conventional fluorescence and EPR, with humic acids, the greatest degree of humification was obtained in pastures treatments, especially in treatments with lime input. Ca2+, in addition to increasing the biological activity, can combine with humic acids, increasing OM stability. In the no-tillage system of soya and sugar cane renovation, higher C amounts were obtained in no-tillage samples, after 7 years of experiment. The maintenance of a permanent vegetal cover, without soil disturbing and without sugar cane burning was essential to SOM accumulation against conventional management. In the no-tillage system, in a period of 7 years, it was possible to verify a sequestration rate ranging from 0.15 to 5.29 Mg CO2 ha-1 year-1. In relation to SOM stability by LIF, no-tillage presented lower degree of humification, due to input labile OM. The results obtained under no-tillage cropping system after 22 years are probably associated with the kind of soil analyzed. In Latossols, with high amount of clay, there may be a physical protection of OM, probably preventing structural changes in this material, even after a long period without soil disturbing. Another important factor is that C sequestration studies depend on the evaluated area, such as experiment outline, historical area, time, climate conditions, C decomposition rates, vegetal biomass production and residue input.

Le rôle joué par les forêts tropicales dans le cycle du carbone à l'échelle planétaire est majeur. Tant par les énormes quantités stockées sous forme de bois, que par les flux de CO2 séquestrées annuellement dans les troncs et le sol. Plusieurs études mettent en évidence des changements structuraux au sein des forêts pantropicales durant les 20 dernières années, notamment une augmentation de la dynamique (recrutement et mortalité) (Lewis et al. 2004b; Phillips et al. 2004b) et de la biomasse aérienne ligneuse en forêt Amazonienne (Baker et al. 2004a). Ces changements de dynamique ont été mis en relation avec une disponibilité accrue en ressources auparavant limitantes (azote et CO2) et donc liés aux changements climatiques globaux. Cependant, les processus de régénération après perturbation dans un peuplement forestier génèrent, eux aussi, une réelle accumulation de biomasse. Des perturbations endogènes (chablis, glissements de terrains) ou exogènes (sécheresses, tempêtes ou actions anthropiques) pourraient être à l'origine de ces fluctuations de dynamique forestière. Sans une connaissance approfondie de l'état initial des forêts étudiées, il semble difficile de distinguer, localement, une accumulation de biomasse liée à un effet de régénération de celle liée à un forge climatique. La présente thèse cherche à investiguer s'il existe des stades de régénération au sein d'un même massif forestier, qui illustreraient différentes perturbations asynchrones. Ces stades sont déterminés sur la base de la structure forestière (densité, diamètre quadratique moyen) et au travers de l'architecture des arbres. Après avoir estimé les flux, stocks et bilans de biomasse sur le site d'étude, ceux-ci sont mis en relation avec des stades de régénération, pour montrer que les parcelles sont formées d'une majorité de stades en croissance et que cela engendre une accumulation nette de carbone durant la période de suivi (1991-2009). / As living trees constitute one of the major stocks of carbon in tropical forests, assessing the role of these ecosystems in the carbon cycle received an increasing scientific and political interest. A better understanding of variations in the dynamics and structure of tropical forests is necessary to predict the potential of these ecosystems to lose or store carbon, and to understand how they recover from disturbances. Recent findings showed an increase of the turn-over in pantropical forests (Phillips et al. 2004a) and an increase of above-ground biomass in neotropical forests (Baker et al. 2004a). These results were attributed to an increasing availability of abiotic ressources (CO2, nitrogen) enhancing forest dynamics. Nevertheless, these findings were controversial and some scientists pointed out statistical and methodological errors (Lewis et al. 2006a; Wright 2006).The present project is based on a very different point-of-view and makes a nother interpretation of these results. The main hypothesis of this study is that the observed changes in forest dynamics around the Amazonian basin and in French Guyana are the consequence of natural endogenous processes. Tropical forests are facing recurring disturbances of various intensities and scales, ranging from tree fall (several square meters) to major drought linked to El Niño events (thousands of hectares). Thus forests would never reach equilibrium, but would rather fluctuate between short periods of disturbance and long periods of regeneration. The main findings of this study are that forests at our site can be seen as a mosaic of areas at different structural and dynamical stages, most of them increasing in mean stem diameter and accumulating biomass. The overall biomass balance is a net biomass increase that might mainly be related to endogenous forest dynamic.

This study focuses on certain urban forestry aspects of the City of Tshwane (previously Pretoria) and in particular that of growth rate and carbon sequestration estimates of street trees with the aim of quantification of the value of these trees. The relationships between tree height and crown dimensions to stem diameter and tree age, as well as the relationship between stem diameter to tree age enable the development of growth rate equations that predict tree dimensions and carbon storage. This permits the calculation of monetary values of urban trees and thus the modelling of costs and benefits of urban forests. The main objectives were (1) to develop tree height, crown diameter, crown height, and crown base height to stem diameter relationships for the indigenous street tree species Combretum erythrophyllum, Rhus lancea andRhus pendulina, (2) to develop tree height, crown diameter, crown height, crown base height and stem diameter to tree age relationships for the above street tree species, (3) to determine the 30 year carbon sequestration estimate and monetary value of 115 000 street trees to be planted mainly in poorer previously disadvantaged communities during the period 2002 to 2008 and (4) to determine the monetary value of the 33 630 Jacaranda mimosifolia street trees in the City based on the quantity of carbon stored in the trees. Combretum erythrophyllum had the most rapid growth rate in many instances, thereafter came Rhus pendulina and then Rhus lancea, which consistently had the slowest growth rate for the investigated parameters. It is estimated that the 115 000 street trees to be planted will sequestrate more than 200 000 tonne CO2 equivalent and have an estimated monetary value of more than US$2 million if a market related CO2 price of US$10.00 per tonne is assumed. The Jacaranda street trees have an estimated carbon stock of 41 978 tonne CO2 equivalent and this would value the Jacaranda urban forest at US$419 786. Copyright / Thesis (PhD)--University of Pretoria, 2010. / Plant Science / unrestricted

Seagrasses are considered highly important CO2 sinks, with the capacity to store substantial quantities of organic carbon in the living biomass and sediments, and thereby acting as a buffer against climate change. In this thesis, I have studied carbon storage variability in temperate and tropical seagrass habitats and identified factors influencing this variation. In addition, as seagrass areas are decreasing worldwide, I have assessed effects of different anthropogenic disturbances on carbon sequestration processes. The result from this thesis showed that there was a large variation in carbon storage within and among temperate, tropical and subtropical regions. The highest organic carbon stocks were found in temperate Zostera marina meadows, which also showed a larger carbon storage variability than the subtropical and tropical seagrass habitats. The tropical and subtropical seagrass meadows had inorganic carbon pools exceeding the organic carbon accumulation, which could potentially weakens the carbon sink function. The variability in organic carbon stocks was generally strongly related to the sediment characteristics of the seagrass habitats. In Z. marina meadows, the strength of the carbon sink function was mainly driven by the settings of the local environment, which in turn indicates that depositional areas will likely have higher organic carbon stocks than more exposed meadows, while in the tropics seagrass biomass was also influencing sedimentary carbon levels. Furthermore, locations with large areas of seagrass were associated with higher carbon storage in tropical and subtropical regions, which could be related to increased accumulation of both autochthonous and allochthonous carbon. In an in situ experiment, impacts on carbon sequestration processes from two types of disturbances (with two levels of intensity) were tested by simulating reduced water quality (by shading) and high grazing pressure (through removal of shoot biomass). At high disturbance intensity, reductions in the net community production and seagrass biomass carbon were observed, which negatively affected carbon sequestration and could impact the sedimentary organic carbon stocks over time. In the treatments with simulated grazing, erosion was also seen, likely due to an increase in near-bed hydrodynamics. When experimentally testing effects of increased current flow on organic carbon suspension in Z. marina sediment, a ten-fold release of organic carbon with higher current flow velocities was measured, which resulted in an increase in the proportion of suspended organic carbon by three times in relation to other sediment particles. Therefore, periods with enhanced hydrodynamic activity could result in a removal of organic carbon and thereby likely reduce the seagrass meadows’ capacity to store carbon. The findings of this thesis add to the emerging picture that there is a large natural variability in seagrasses’ capacity to store carbon, and highlight how human-induced disturbances could negatively affect the carbon sink function in seagrass meadows. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

Made available in DSpace on 2016-05-02T13:54:09Z (GMT). No. of bitstreams: 1 LazaroQuintinoAlves-Dissertacao.pdf: 282398 bytes, checksum: 6c06233155f4edef4588242b671b2afa (MD5) Previous issue date: 2009-02-17 / One of the greatest challenges of humankind is sustainable production with clean development mechanisms (CDM) in order to reduce the emission of greenhouse gases and provide a better world to future generations. In this context, sugarcane brandy production should be considered an agroindustrial complex which is capable of contributing to carbon sequestration. As a traditional activity in Brazil, it also generates jobs and wealth. The purpose of this research was to economically evaluate the potentialities of carbon emission and sequestration balance of sugarcane in brandy production, and verify whether the sale of carbon credits could provide additional income and increase the gross revenue in each harvest. An attempt was made to understand the history of sugarcane, a primary source of brandy, and it was found that its history is mixed with Brazil s own history, even today. We studied aspects of carbon balance, economical aspects, and the amount of trading of carbon and brandy, from April to October 2008, to assess the economic viability of sugarcane carbon sequestration and brandy. To determine the carbon sequestration balance in the sugarcane brandy agribusiness a survey was made of all the carbon sequestered by the sugarcane plantation, and also of the carbon emission during all the stages of the productive process. All this survey was based on data obtained from scientific papers. Carbon trading can be done at BM&F (Futures and Commodities Exchange) or directly by the companies that to lower their pollution levels. It is understood that the best way for small producers to engage in carbon trading is through a cooperative of CO2 trading. Alongside with the search for production of clean energy, the correctly managed sugarcane cultivation can contribute to agriculture sustainability as both a great carbon sequesterer and an additional source of income for brandy producers. / Atualmente, um dos maiores desafios da humanidade é produzir, de maneira sustentável, a partir de mecanismos de desenvolvimento limpo (MDL), reduzindo as emissões dos gases do efeito estufa (GEE) e proporcionando um mundo melhor às gerações futuras. Neste contexto, a produção de aguardente é um segmento produtivo que deve ser considerado como complexo agroindustrial com possibilidades de contribuir para o sequestro de carbono, sendo, ainda, atividade tradicional no Brasil, geradora de emprego e renda. Este trabalho teve como objetivo avaliar economicamente as potencialidades do balanço de emissão e sequestro de carbono da cana-de-açúcar utilizada no fabrico de aguardente, para verificar se a venda dos créditos de carbono pode proporcionar rendimentos extras e aumentar a receita bruta da propriedade a cada safra. Como fonte primaria da aguardente, procurou-se compreender a história da cana-de-açúcar, que se confunde com a própria história do Brasil até os dias atuais. Procurou-se estudar os aspectos do balanço de carbono e os aspectos econômicos a montante do macrossegmento da comercialização do carbono e da aguardente, no período de abril a outubro de 2008, para verificar a viabilidade econômica do sequestro de carbono e da aguardente procedentes da cana-de-açúcar. Para apurar o saldo do sequestro de carbono no agronegócio da aguardente foi realizado um levantamento de todo o carbono sequestrado pela lavoura canavieira, bem como as emissões de carbono durante todas as etapas do processo produtivo. Todo este levantamento foi estimado a partir de dados retirados de artigos publicados em revistas científicas especializadas. A comercialização de carbono pode ser através da BM&F ou diretamente com as empresas que desejam baixar o seu nível de poluição. Percebe-se que a melhor maneira de realizar a transação do carbono pelos pequenos produtores é através de uma cooperativa que tenha como objetivo a comercialização do CO2. Paralelamente à corrida pela produção de energia limpa, o cultivo da cana-de-açúcar, manejado corretamente pode contribuir para a sustentabilidade da agricultura como grande sequestradora de carbono e como fonte extra de rendimentos dos produtores de aguardente.

M. Tech (Department of Chemistry, Faculty of Applied and Computer Sciences) Vaal University of Technology. / Macadamia activated carbon (MAC) was impregnated with different concentrations of nitric acid and heated under reflux to improve the structural characteristics of the adsorbent for both considerable reduction and enhanced removal of Cr(VI). The chemical oxidation of ACs increased the surface oxygenated functional groups. Adsorption of Cr(VI) was carried out by varying parameters such as contact time, pH, concentration, and adsorbent dosage. The optimum operating conditions for the adsorption of Cr(VI) were pH 1, contact time 240 min, adsorbent dosage 10.67 g/L and Cr(VI) concentration 100 mg/L. The results showed that the Macadamia–based AC could be used efficiently for the treatment of chromium-containing solutions as a low-cost alternative compared to commercial AC and other adsorbent reported. The results showed that treated MAC performed better than untreated MAC, signifying the effect of secondary treatment on the enhanced removal of pollutants. Comparable to the application of ACs is the development of imprinting technologies for selective metal ion remediation in environmental samples. The combination of ion imprinting effects and functionalized carbon adsorbents produce materials which effectively remove and selectively recognize the target analyte. Macadamia activated carbon (MAC) was chemically pre-treated with nitric acid to generate carboxyl groups on the surface. The carboxylated MAC was then reacted with triethylenetetramine, N,N’-diisopropylcarbodiimide and CrCl3.6H2O to produce MACN20-imprinted sorbents (MACN20-IIP). MACN20-non imprinted (MACN20-NIP) counterparts were prepared, but Cr3+ was excluded in the synthesis. Alteration of surface structural characteristics and characterization of prepared adsorbents as confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, Brunauer–Emmett–Teller and scanning electron microscopy. MACN20-IIP and MACN20-NIP adsorbents were evaluated for their Cr3+ uptake from aqueous solution in batch format. Maximum conditions were achieved at pH 5, 50 mg/L Cr(III) initial concentration and 33.33 g/L of adsorbent dosage. Presence of co-ions slightly diminished the removal of Cr(III) by MAC-IIP adsorbents. Application of the MACN20-IIP and MACN20-NIP on spiked acid mine drainage artificial sample led to collapse in the removal efficiency of MACN20-NIP while MACN20-IIP still showed good removal efficiencies. These results demonstrated that surface imprinting led to better adsorption rates and capacity. The data was better described by the Freundlich multilayer adsorption and pseudo-second order kinetic rate model. The combination of both the carbon sorbent and the surface-mediated IIPs effectively improved total chromium remediation in aqueous systems.

M. Tech (Department of Chemistry, Faculty of Applied and Computer Sciences) Vaal University of Technology. / Persisting challenges associated with remediation of heavy metals from aqueous media have stirred the need for enhancement of current technologies. Cellulosic agro waste materials (AWM) as well as ion-imprinted polymers (IIP) have received ardent attention from researchers. These materials are often employed in the following industries: water and wastewater treatment, medical, pharmaceutical and packaging. Applications in water and wastewater treatment have gained significant interest due to desirable features they possess. In the case of AWM, these features include a tuneable surface area and poor porosity, basic surface functional groups and chemical stability. Some desired features in IIP include adsorption sites compatible for the ion imprint obtained after leaching with suitable reagents, rigidity and reusability. The efficacy of employing AWM and IIP for the remediation of toxic chromium from aqueous solution was explored. The current study is made up of part A and B. In part A, Macadamia nutshell powder was treated using HNO3, NaOH, as well as Fenton’s reagent. The three materials underwent a new modification which involved reacting treated adsorbents with cetyltrimethylammonium chloride (CTAC), followed by immobilization of 1,5' diphenylcarbazide (DPC) ligand. The adsorbents were ultimately washed, dried and stored for Cr(VI) batch adsorption experiments. Part B involved a synthesis of IIP and their non-imprinted polymer counterpart (NIP) for Cr(VI) sequestration in aqueous solution. This was done by precipitation polymerization of functional monomers, crosslinker and DPC-Cr(VI) complex as a template. Non-imprinted polymers were fashioned in a manner like that of IIP but with the exclusion of Cr(VI) ion template. Characterizations of the adsorbents were done using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray fluorescence (XRF), and carbon, hydrogen, nitrogen and sulphur (CHNS) analyzer. Batch adsorption experiments were done and parameters such as solution pH, adsorbent dosage, initial Cr(VI) concentration and contact time were optimized. Working solutions were analyzed using ultraviolet-visible (UV-Vis) and atomic absorption (AA) spectroscopy. Adsorption parameters found to be optimum for DPC immobilized cellulosic adsorbents were pH 1.4, adsorbent mass of 0.1 g, 100 mg/L initial concentration and 125 minutes of contact time. The adsorption parameters determined to be optimum for IIP and NIP were pH 2.6, 0.2 g adsorbent mass, 80 mg/L initial concentration and 240 minutes of contact time. Reusability studies demonstrated the potential of adsorbents to remove Cr(VI) ions from aqueous media after successive adsorption-desorption cycles. Selectivity studies indicated that DPC immobilized adsorbents as well as IIP were able to selectively adsorb Cr(VI) ions from aqueous media in the presence of Zn(II), Cu(II), Co(II) and NI(II) ions. Kinetic models revealed that DPC immobilized cellulosic adsorbents and synthetic IIP were most fitting for pseudo-second order and pseudo first order, respectively. On the other hand, adsorption isotherm studies demonstrated that DPC immobilized cellulosic adsorbents and synthetic polymers were best fit for Freundlich and Langmuir adsorption isotherm, respectively.

京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第13262号 / 論農博第2875号 / 新制||農||1071(附属図書館) / 学位論文||R1||N5217(農学部図書室) / (主査)教授 山下 洋, 教授 澤山 茂樹, 教授 吉岡 崇仁 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Afforestation projects in China have substantially contributed to national CO2 sequestration and play an important role in international climate change mitigation. However, these nation-wide afforestation projects are usually funded by the national government, with very large and unsustainable investments. It is important to find alternative sources of funding to finance afforestation, and convince poor farmers to become involved in afforestation projects. Carbon-subsidized afforestation could be the solution. The current study aims to find i) whether farmers need additional subsidies to reforest their marginal farmland; if so, ii) whether the value of carbon sequestration of afforestation can offset farmers' net costs. To do this, first I determine the amount of carbon sequestration though afforestation. Second, I assess the value of carbon sequestration, the costs and benefits of afforestation projects, and the costs and benefits of crop production. Third, I investigate the optimal rotation period of the plantations considering a joint production of timber and carbon, for different species. Results show that total carbon sequestration through tree biomass and soil carbon following afforestation differs among tree species and stand age as well as across regions. Economic trees sequester less carbon than ecological trees and bamboo. Among economic trees, nut trees with an inedible hard shell sequester more carbon than fruit trees. The regional context significantly influences the carbon sequestration potential, with more carbon sequestered in southern and eastern regions than in northern regions. Bamboo also shows a remarkable carbon sequestration potential, which is even greater than Chinese fir and Poplar in northern regions. Although afforestation programs have huge potential to store carbon, the voluntary acceptance by landowners crucially depends on their economic outcome. I found that usually carbon credits can compensate for the opportunity costs of alternative land uses, except i) when highly profitable croplands are afforested, in which case carbon credits are not sufficient, and ii) when croplands that generates low incomes are afforested, in which case carbon credits are not needed. Fruit trees are the most cost-effective option for afforestation. Bamboo afforestation is economically attractive if carbon revenues is included. The minimum price of carbon credit decreases with increasing project duration because more carbon is stored when time increases. This does not hold for fast-growing trees like Eucalyptus, for which the minimum price increases with extended project duration. Given the temporal variations of joint production of timber and carbon sequestration, the carbon accounting regimes (tCER, temporary Certified Emission Reductions and lCER, long-term Certified Emission Reductions) have a significant impact on the optimal rotation as well as on the revenue. Forest managers have an incentive to use tCER accounting to finance slow-growing plantations, and lCER for fast-growing ones. I perform a sensitivity analysis detects the changes of rotation period with different carbon prices and discount rates. While the optimal decision for slow-growing species (e.g. Chinese fir) is highly sensitive to changes in both variables under tCER accounting, the results concerning fast-growing species (e.g. Eucalyptus) are most sensitive under the lCER accounting regime. In contrast, carbon revenues have a minimal impact on the optimal rotation of Poplar plantations, no matter which regime is applied. I conclude that carbon-subsidized afforestation is a feasible way to offset the opportunity costs of retired farmland and support the livelihood of farmers. The findings can contribute to the efficient and sustainable management of forestry projects using carbon sequestration, while the methodology can also be applied to other regions in the world.

Since the industrial revolution, the atmospheric CO2 concentration has steadily increased due to the combustion of fossil fuels, reaching 410 ppm. According to the 2018 IPCC report, it was recognized that the anthropogenic greenhouse gas emissions caused by human activities are major drivers for global warming of 1.0 oC above the pre-industrial level. Due to the unprecedented scale of human driven CO2 emission and its environmental impact, the mitigation of climate change requires a wide range of multifaceted solutions. Thus, enormous global efforts have been placed on the development of Carbon Capture, Utilization, and Storage (CCUS) to mitigate CO2 emissions in the immediate future. Most recent reports by the U.S. National Academies and the Mission Innovation presented that ex-situ carbon mineralization is a CO2 utilization technology with a great carbon storage potential and a large market size. Also, fixing CO2 into a solid matrix of carbonate minerals is one of the most permanent methods for carbon storage. Although the ex-situ carbon mineralization presents many advantages and great potential as CCUS technology, its commercialization has been limited due to the mammoth scale of the process, slow reaction kinetic between CO2 and silicate minerals, and high energy and operating cost. In order to minimize energy and chemical (acid and base) consumption of this technology, recent researches have been focused on a two-step carbon mineralization via Pco2 swing using highly reactive heat-treated serpentine mineral. However, the elemental (Mg and Si) extractions from the complex silicate structures of heat-treated serpentine are still poorly understood and a more fundamental understanding of the Pco2 swing process is required to develop a commercial-scale plant. Thus, the objectives of this study are directed toward addressing these technical challenges. The effect of operating conditions, such as temperature, slurry density, and CO2 partial pressure, on the dissolution of heat-treated serpentine and subsequent Mg-carbonate precipitation behaviors, were studied to provide a fundamental understanding of the Pco2 swing carbon mineralization process of highly reactive silicate materials. The dissolution experiments with a wide range of temperature and slurry densities provided valuable insights into the formation of the Si-rich passivation layer and its role in the mass transfer limitation during mineral dissolution. The heat-treated serpentine dissolution behaviors with chemical additives (ligand) were also investigated to overcome the effect of the Si-rich passivation layer on Mg extraction kinetics. What is more, a unique internal grinding system was proposed and integrated with the Pco2 swing process to physically remove the Si-rich passivation layer. The diffusion-limited slow elemental (Mg and Si) extraction from the heat-treated serpentine silicate structures was significantly enhanced in the internal grinding system. A stress intensity, which is proportional to the energy transferred from grinding media to the heat-treated serpentine particles during a stress event, was used to describe the effect of the reaction parameters on the extent of the physical activation and the enhancements in mineral dissolution. For the fundamental understanding of the complex dissolution behaviors of heat-treated serpentine, the changes in the silicate structures (Q0 – Q4) of heat-treated Mg-bearing mineral (serpentine) exposed to a CO2-water system (carbonic acid) was investigated using 29Si MAS NMR and XRPD. The identified silicate structures were employed to provide insight into how Mg and Si are liberated from the different silicate structures during the dissolution process. Thermodynamic and kinetic modeling was performed to understand the Mg-carbonate precipitation behaviors in the Pco2 swing process. The effects of carbonic anhydrase, seed particles, and ligand (citrate) on precipitation behaviors were studied to improve the precipitation kinetics. This approach will bring a great paradigm shift in the energy and environmental field since the less energy-intensive and low-cost ex-situ carbon mineralization process via Pco2 swing will be able to allow long-term and sustainable carbon utilization.