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The restoration of drained, afforested blanket bogs (forest-to-bog restoration) is an increasing management practice, due to recognition of both the nature conservation and carbon sequestration services provided by peatlands. Forest-to-bog restoration involves conifer felling (and harvesting) along with blocking of forestry drains. Research from conifer felling and drain blocking on open peatlands shows significant effects on pore- and stream- water quality, when practised separately. However, there is very little knowledge of the combination of both these practices in forest-to-bog restoration. This research investigated the effects of forest-to-bog restoration on pore-, surface-, stream- and river water quality in the short-term (0-1) years post-restoration, where the effects of restoration are disturbance-related. We also investigated restoration progress across a chronosequence of restoration sites using pore- and surface-water chemistry. Our results showed significant increases in DOC, phosphate, K and NH4+ (2-99 fold) in pore- and surface- water in the first year post-restoration, which may have implications for the recovery of bog vegetation. In streams significant increases in Fe (1.5 fold) and phosphate (4.4 fold) were found, with no significant impacts on concentrations in rivers or pass rates for drinking water or WFD standards. We also found no significant effects on aquatic carbon exports. However, as more restoration is carried out within the catchments and the proportion felled increases, greater impacts on streams and rivers may be observed. From our results, we recommend felling small percentages (3-23%) of stream and river catchments and the use of drain blocking and silt traps to retain sediment. We observed progress in recovery towards bog conditions across a chronosequence of restoration sites (aged 0-17 years); incomplete recovery of WTD and elevated NH4+ in porewater appeared the main barriers to restoration. Therefore, enhancements such as brash and needle removal and plough furrow blocking may be able to accelerate restoration.

The rapid pace of urbanization heightens our interest to understand the role of urban areas in mediating climate changes at local, regional and global levels. The increasing amount of carbon (C) released by growing cities may influence the surrounding climates and lead to a rise in global ambient temperature. Fortunately, urban greenery may mitigate the risk of rising C by storing it in vegetation and soils. On the other hand, urban greenery may become a net CO₂ or other greenhouse gas emitter due to heavy maintenances. Thus, the exact impact of urban greenery on carbon balance in major metropolitan areas remains controversial. / We first investigated C footprints of urban turf operation and maintenance by conducting a research questionnaire on different Hong Kong turfs, and showed that turf maintenance contributed 0.17 to 0.63 kg Ce m⁻² y⁻¹ to C emissions. We then determined C sequestration capacity by urban turfgrasses and soils through both field study and laboratory-based investigation. Our data from field study showed that the C stored in turfgrass systems at 0.05 to 0.21 kg C m⁻² for aboveground grass biomass and 1.3 to 4.9 kg C m⁻² for soils (to 15 cm depth). We estimated that the C sink capacity of turfs could be offset by C emissions in 5-24 years under current management patterns, shifting from C sink to C source. / We further showed that dissolved organic C (DOC) export also contributed to C release from urban soils, under the influence of the maintenance practices of turfgrasses. Both irrigation and nitrogen (N) fertilizer inputs could enhance DOC export. We also observed that soil enzyme activity was sensitive to turfgrass maintenances practices, and played a key role in soil organic C (SOC) decomposition. In particular, cellulase was found to be a major player in regulating DOC and dissolved organic N (DON) export. On the other hand, urease activity was shown to be dependent on grass species, fertilizer inputs and substrates. / Finally, we then determined the CO₂ fluxes of turfgrass systems by chamber-based measurement. Our data demonstrated that grass species and photosynthetically active radiation (PAR) played a dominant role in CO₂ fluxes in greenhouse study. Maintenance practices also contributed to CO₂ fluxes of turfgrass systems. Both fertilizer and irrigation showed species-specific effect on CO₂ fluxes. We then showed in field studies that CO₂ fluxes and respiration rates of urban turfs varied with grass species, and were higher in wet season than dry season. / Together, our studies suggested that maintenance practices for urban greenery played a key role in SOC decomposition through regulating DOC export and C cycle associated enzymes, therefore may determine the C balance of urban greenery. Our studies further suggest that we can improve maintenance practices to reduce C footprint and enhance the environmental benefits of urban turfgrass systems. We propose that the environmental impact of turfgrass systems should be optimized by the rational design of maintenance schedules based on C sink and emission principles. / 城市化的快速發展提高了我們研究城市的興趣，具體在其對城區和地域性氣候及其對全球气候变化的調節。城區大量碳排放可能影響周圍氣候進而導致全球環境溫度的上升。城市綠化可以緩解這個危機因為植被和土壤能夠通過存儲碳。但是城市綠化系統的大量維護可能是導致二氧化碳或其他溫室氣體的排放。因此城市綠化對碳平衡的影響仍存在爭議。 / 我們以問卷方式調查了香港不同的草坪，計算了維護過程中的碳足跡。研究表明草坪每年的維護造成了相當於每平米0.17至0.63千克碳排放。我們還結合野外和實驗室分析測定了草坪地上生物量和15厘米深土壤的碳儲存量，每平米分別是0.05至0.21，1.3至4.9千克碳。據此我們估計，按照目前的管理模式，草坪的碳儲存量在5至24年可與維護的碳排放相抵，由碳匯轉變為碳源。 / 我們還發現溶解有機碳的流失也加劇了城市土壤碳釋放同時受草坪維護的影响。灌溉和施加氮肥會促進溶解有機碳的釋放。土壤酶對是草坪維護很敏感，而且對土壤有機有機碳分解起關鍵作用。特別是纖維素酶參與并有效調節了溶解有機碳和溶解有機氮的釋放。另外脲酶的活性受草種，施肥和土壤基質的影響。我們用二氧化碳分析儀测定了草坪的碳通量。溫室研究表明，草種和光合有效輻射對碳通量起主導作用。草坪的維護同樣影響草坪的碳通量，其中施肥和灌溉對不同草種的碳通量有不同程度的影響。野外實驗則發現城市草皮的碳通量和呼吸速率隨草種变化，且雨季高於旱季。 / 以上研究表明城市綠化系統的維護可以有效調節溶解有機碳和碳循環相關土壤酶，進而影響土壤有機碳的分解，最終決定城市綠化系統的碳收支。因此我們建議，由以經驗設計轉變為以碳匯和碳排放原則優化維護模式，以減少碳足跡從而提升城市綠化的環境效益。 / Kong, Ling. / Thesis Ph.D. Chinese University of Hong Kong 2014. / Includes bibliographical references (leaves 191-212). / Abstracts and appendixes also in Chinese. / Title from PDF title page (viewed on 24, October, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

Vertical greenery systems (VGSs) on building walls in cities develop rapidly worldwide in recent years, which is a potentially effective way to mitigate urban heat island (UHI) effect mainly through evapotranspiration and shading. Benefits of using vertical greening applications are of social and environmental origins, such as CO₂ emission reduction, energy saving, air quality improvements and enhanced aesthetic. However, little is known about C sequestration and CO₂ flux of vertical greening, and less attention has been paid on the C balance of vertical greening. In addition, many factors have great influence on C sequestration of vertical greening, including plant species, orientations and fertilizer application. However, limited studies report their impacts on C cycling, mitigation of UHI effect and improvement of urban microclimate of vertical greening. / Firstly, C sequestration of seven common plant species and that of Peperomia claviformis under six fertilizer treatments were studied. The results showed that plant species and fertilizer application had significant effects on shoot and root biomass. In contrast, we investigated C sequestration of Schefflera octophylla in four orientations, and showed that orientation had no significant influence. C sequestration of the seven species in VGSs ranged from 61 to 523 g C m⁻² y⁻¹. Meanwhile, the total C footprint of their maintenance ranged from 196 to 434 g Ce m⁻² y⁻¹, including the C footprint of fertilizer, pesticide and electricity consumption for irrigation. Newly established VGSs with these seven species could become C source from C sinks with large amount of C emissions from the maintenance practices between 2.7 and 43.6 years. / Secondly, the CO₂ fluxes of VGSs were determined by chamber-based measurement. Plant species and photosynthetically active radiation (PAR) played a dominant role in CO₂ fluxes. Fertilizer also significantly contributed to CO₂ fluxes of VGSs. Net ecosystem exchange (NEE) of CO₂ and respiration rates of VGSs varied with plant species, and most species in VGSs were higher in summer than other seasons. / Thirdly, VGS in the west-facing wall had the best capacity in terms of daily maximum wall temperature on sunny days. In addition, VGSs decreased the indoor air temperature of the thermal test room with VGSs. Solar radiation, total bright sunshine and relative humidity had the greatest significant correlations and relatively stronger coefficients with thermal indicators. / Finally, we compared the electricity consumption for cooling in flats with and without a VGS (8.22m²) in a pubic housing estate, and quantified the environmental benefits and burdens of a commercially available VGS. The daily electricity saving by the VGS in the flats with and without a VGS (8.22m²) in sunny, cloudy and rainy days in summer was 1.30, 0.84 and 0.71 kWh, respectively. A life cycle assessment (LCA) was conducted to analyze the environmental burdens of the VGS in its material, transportation, use and end-of-life stages. A comparison of the environmental burdens and benefits gained from cooling showed that the environmental burden of the VGS in regard to abiotic depletion of fossil fuels could be paid back in 20 years. / Overall, vertical greeneries installed on building walls did not only play a significant role on alleviation the problems of global warming and climate change through C sequestration and energy saving, but alse contribute to mitigating the UHI effects and improving urban microclimate due to the thermal performance. / 近年來城市中垂直綠化快速發展，主要通過植物蒸騰和遮陰效應而成為一種減緩城市熱島效應的有途徑。垂直綠化的應用由於其多種社會和環境效益，比如降低二氧化碳排放、節能、提高空氣品質和提升審美效果。然而，我们對於垂直绿化的碳匯和二氧化碳通量所知甚少，并且很少有研究關注垂直绿化的碳收支。並且，許多因素影響垂直綠化的碳匯，包括植物品種、朝向和施肥。但是在垂直綠化的碳循環、減緩城市熱島效應和提升城市微氣候方面研究卻很少。 / 首先，我们研究了七種常见的垂直绿化植物的碳汇和黑叶椒草在六种不同施肥处理下的碳匯。结果显示，植物品種和施肥對茎部和根部生物量有顯著促進作用。相比之下，我們還研究了鵝掌柴在四個朝向的碳匯，結果顯示，朝向對其並沒有顯著影響。七種垂直綠化植物的碳匯範圍為每年每平方米61到253克碳。同時，這些植物的維護包括施肥、噴藥和灌溉用電，造成了每年每平方米196到434克碳排放。因此，由於維護所造成的大量碳排放。所以這七種植物垂直綠化系統在2.7年到43.6年之內將從碳源變成碳匯。 / 第二，我們用二氧化碳分析儀測定了垂直綠化的碳通量。植物品種和光合有效輻射在碳通量上起主導作用。施肥也同樣顯著影響垂直綠化的碳通量。淨生態系統碳交換量和呼吸速率隨植物品種而變化，並且在夏天高於其他季節。 / 第三，在晴天最大牆面溫度上，西向的垂直綠化有佳的植物降效應。並且，垂直綠化降低了測試房間的室內空氣溫度。太陽輻射、總日照和相對濕與熱能指標有最多的顯著關係，並且有更高的相關係數。 / 最後，我們比較了在公共住宅的有垂直綠化(8.22平方米)和無垂直綠化的房間用於降溫的電量消耗，並評估了一個商業化垂直綠化系統的環境效益和環境負荷。在對比已安裝和未安裝垂直綠化的兩個房間後，在晴天、陰天和雨天每日省電量分別為1.30, 0.84 and 0.71千瓦時。我們用生命週期評價來對垂直綠化在材料、運輸、使用和最終階段的環境負荷進行了分析。對比了垂直綠化的環境效益和環境負荷後可知，化石燃料的不可再生資源消耗能夠在20年內償還。 / 總之，建築物外牆的垂直綠化不僅通过其碳匯和节能作用能夠對溫室效應和氣候變化有顯著作用，而且由于其熱性能還能緩解城市熱島效應和提升微氣候。 / Pan, Lan. / Thesis Ph.D. Chinese University of Hong Kong 2016. / Includes bibliographical references (leaves 217-246). / Abstracts also in Chinese. / Title from PDF title page (viewed on 24, October, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

This dissertation analyzes the basis for and magnitudes of discount factors based on the characteristics of greenhouse gas emission (GHGE) offsets that are applied to the GHGE reduction projects, concentrating on agricultural projects. Theoretical approaches to discount factors, estimation and incorporation of discount factors procedures are developed. Discount factors would be imposed by credit purchasers due to noncompliance with regulatory program of the credits with GHG program including consideration of shortfall penalties and limited durations. Discount factors are proposed for (i) additionality, (ii) leakage, (iii) permanence, and (iv) uncertainty. Additionality arise when the region where an AO project is being proposed would have substantial adoption of the AO practice in the absence of GHG programs (business as usual GHGE offset). Leakage arises when the effect of a program is offset by an induced increase in economic activity and accompanying emissions elsewhere. The leakage effect depends on demand and supply elasticities. Permanence reflects the saturation and volatility characteristics of carbon sequestration. Carbon is stored in a volatile form and can be released quickly to the atmosphere when an AO practice is discontinued. The permanence discount depends on the project design including practice continuation after the program and the dynamic rate of offset. Also, consideration of multiple offsets is important. Uncertainty arises due to the stochastic nature of project quantity. The uncertainty discount tends to be smaller the larger the size of the offset contract due to aggregation over space and time. The magnitude of these discounts is investigated in Southeast Texas rice discontinuation study. The additionality and the leakage discounts are found to play an important role in case of rice lands conversion to other crops but less so for pasture conversions and yet less for forest conversions. The permanence discount is important when converting to other crops and short rotation forestry. When all discounts are considered, rice lands conversion to forest yields claimable credits amounting to 52.8% ~ 77.5% of the total offset. When converting rice lands to pasture, the claimable credits 45.1% ~ 64.2%, while a conversion of rice lands to other crops yields claimable credits 38.9% ~ 40.4%.

This dissertation analyzes the basis for and magnitudes of discount factors based on the characteristics of greenhouse gas emission (GHGE) offsets that are applied to the GHGE reduction projects, concentrating on agricultural projects. Theoretical approaches to discount factors, estimation and incorporation of discount factors procedures are developed. Discount factors would be imposed by credit purchasers due to noncompliance with regulatory program of the credits with GHG program including consideration of shortfall penalties and limited durations. Discount factors are proposed for (i) additionality, (ii) leakage, (iii) permanence, and (iv) uncertainty. Additionality arise when the region where an AO project is being proposed would have substantial adoption of the AO practice in the absence of GHG programs (business as usual GHGE offset). Leakage arises when the effect of a program is offset by an induced increase in economic activity and accompanying emissions elsewhere. The leakage effect depends on demand and supply elasticities. Permanence reflects the saturation and volatility characteristics of carbon sequestration. Carbon is stored in a volatile form and can be released quickly to the atmosphere when an AO practice is discontinued. The permanence discount depends on the project design including practice continuation after the program and the dynamic rate of offset. Also, consideration of multiple offsets is important. Uncertainty arises due to the stochastic nature of project quantity. The uncertainty discount tends to be smaller the larger the size of the offset contract due to aggregation over space and time. The magnitude of these discounts is investigated in Southeast Texas rice discontinuation study. The additionality and the leakage discounts are found to play an important role in case of rice lands conversion to other crops but less so for pasture conversions and yet less for forest conversions. The permanence discount is important when converting to other crops and short rotation forestry. When all discounts are considered, rice lands conversion to forest yields claimable credits amounting to 52.8% ~ 77.5% of the total offset. When converting rice lands to pasture, the claimable credits 45.1% ~ 64.2%, while a conversion of rice lands to other crops yields claimable credits 38.9% ~ 40.4%.

Thesis--Auburn University, 2009. / Abstract. Includes bibliographic references (p.71-87).

Carbon sequestration is a method of capturing and storing excess anthropogenic CO₂ in the subsurface. When CO₂ is injected, the temperature and pressure at depth turn it into a supercritical (SC) fluid, where density is that of a liquid, but viscosity and compressibility resemble a gas. Ultimately the SC CO₂ is trapped at depth either by low permeability sealing layers, by reactions with minerals, or by dissolving into fluids. The injected CO₂ is buoyant and initially exists as a non-aqueous hydrophobic layer floating on top of the subsurface brine, up against the upper sealing formation, but over time it will dissolve into the brine and potentially react with minerals. The details of that initial dissolution reaction, however, are only poorly understood, and I address three basic questions for this research: What is the fundamental kinetics of SC CO₂ dissolution into water? How fast does dissolved CO₂ diffuse away from the source point? And what geochemical conditions influence the dissolution rate? To answer these questions I employed a high pressure flow-through approach using a column packed with coarse quartz sand. The system was both pressure and temperature controlled to have either liquid or SC CO₂ present, and was typically run at 100 Bar, 0.5 to 2.5 mls/min, and 28-60°C. After establishing the hydraulic parameters for the column using two conservative tracers (Br, As), injections (5 and 20 [mu]l) were made either as aqueous solutions equilibrated to high pressure CO₂, or as pure liquid or SC CO₂ into 0.1 mmol NaOH. For all experiments the pH of the system was monitored, and [CO₂] over time was calculated from those data. For injections of brine with dissolved CO₂, transport was conservative and was nearly identical to the conservative tracers. The CO₂ quickly mixes in the column and does not react with the quartz. The liquid and SC CO₂ injections, however, do not act conservatively, and have a very long tailing breakthrough curve that extends to tens of pore volumes. I hypothesize that the SC CO₂ is becoming trapped as a droplet or many droplets in the pore spaces, and the long breakthrough tail is related either to the rate of dissolution into the aqueous phase, the diffusion of dissolved CO₂ away from the phase boundary, or the reaction with the NaOH, limited to the narrow contact zones in the pore throats. Because of the speed at which acid-base reactions occur (nanosecond kinetics), I infer that the rate limiting step is either surface dissolution or diffusion. From plots of ln[CO₂] v. time I obtained values for k, the specific rate of the dissolution reaction R=-k[CO₂]. No trend for k was seen with respect to changes in temperature, but k did show a trend with respect to changing flow rate. k increased from an average value of 3.05x10⁻³ at 0.5 ml/min to an average value of 3.38x10⁻³ at 1.6 ml/min, and then held constant at the higher flow rates, up to 2.5 ml/min. I interpret these data to show that at low flow rates, the reaction is diffusion limited; the fluid nearest the contact zone becomes saturated with dissolved CO₂. At higher flow rates, the fluid is moving fast enough that saturation cannot occur, and the kinetics of the dissolution reaction dominate. Simple geometric models indicate that the CO₂/water interface is shaped like a spherical cap, indicating that the snapped-off CO₂ is forming a meniscus in the pore throat, limiting the surface area across which dissolution can occur. / text

Implementing geological carbon sequestration at a scale large enough to mitigate emissions will involve the injection of supercritical CO₂ into deep saline aquifers. The principal technical risks associated with such injection are that (i) buoyant CO₂ will migrate out of the storage formation; (ii) pressure elevation during injection will limit storage rates and/or fracture the storage formation; and (iii) groundwater resources will be contaminated, directly or indirectly, by brine displaced from the storage formation. An alternative to injecting CO₂ as a buoyant phase is to dissolve it into brine extracted from the storage formation, then inject the CO₂-saturated brine into the storage formation. This "surface dissolution" strategy completely eliminates the risk of buoyant migration of stored CO₂. It greatly mitigates the extent of pressure elevation during injection. It nearly eliminates the displacement of brine. To gain these benefits, however, it is essential to determine the costs of this method of risk reduction. This work provides a framework for optimization of the process, and hence for cost minimization. Several investigations have tabulated the storage capacity for CO₂ in regions around the world, and it is widely accepted that sufficient pore volume exists in deep subsurface formations to permit large-scale sequestration of anthropogenic CO₂. Given the urgency of implementing geologic sequestration and other emissions-mitigating technologies (storage rates of order 1 Gt C per year are needed within a few decades), the time required to fill a target formation with CO₂ is just as important as the pore volume of that formation. To account for both these practical constraints we describe in this work a time-weighted storage capacity. This modified capacity integrates over time the maximum injection rate into a formation. The injection rate is a nonlinear function of time, formation properties and boundary conditions. The boundary conditions include the maximum allowable injection pressure and the nature of the storage formation (closed, infinite-acting, constant far-field pressure, etc.) The time-weighted storage capacity approaches the volumetric capacity as time increases. For short time intervals, however, the time-weighted storage capacity may be much less than the volumetric capacity. This work describes a method to compute time-weighted storage capacity for a database of more than 1200 North American oil reservoirs. Because all of these reservoirs have been commercially developed, their formation properties can be regarded as representative of aquifers that would be attractive targets for CO₂ storage. We take the product of permeability and thickness as a measure of injectivity for a reservoir, and the product of average areal extent, net thickness and porosity as a measure of pore volume available for storage. We find that injectivity is not distributed uniformly with volume: the set of reservoirs with better than average injectivity comprises only 10% of the total volumetric storage capacity. Consequently, time weighted capacity on time scale of a few decades is 10% to 20% of the nominal volumetric capacity. The non-uniform distribution of injectivity and pore volume in the database coupled with multiphase flow effects yields a wide distribution of “filling times”, i.e. the time required to place CO₂ up to the boundaries of the formation. We define two limiting strategies based on fill times of the storage structures in the database and use them to calculate resource usage for a target storage rate. Since fill times are directly proportional to injectivity, smallest fill time corresponds to best injectivity and largest fill time corresponds to smallest injectivity. If best injectivity structures are used first, then the rate at which new structures would be needed is greater than if worst injectivity structures are used first. A target overall storage rate could be maintained for longer period of time when worst injectivity structures are used first. Because of the kh vs PV correlation, most of the pore volume remains unused when no extraction wells are used. Extraction wells require disposal of produced brine, which is a significant challenge, or beneficial use of the brine. An example of the latter is the surface dissolution process described in this thesis, which would enable use of a much greater fraction of the untouched pore volume. / text

This thesis aimed to examine the possibilities and benefits of implementing agroforestry projects in Sierra Leone by comparing different agroforestry systems used in a Tanzanian project that consider carbon sequestration. Farmers involved in this type of projects get income from sold carbon credits as well as from other products that an agroforestry system could provide. Sierra Leone is one of the most vulnerable countries to climate change, with most of the population living in rural conditions. It was investigated what the potential economic and environmental impact different agroforestry systems considering carbon storage could have in Sierra Leone. The study was based on empirical material from a case community Makari. The conclusions were that Sierra Leone could benefit greatly from agroforestry projects, especially at community level where it could provide additional sources of food and income. From a greater perspective it could give environmental benefits as well as securing wood commodities like fuelwood for the future. Starting up a project would however be a high risk investment with a troublesome implementation process and complications on a daily basis.