Forests of the southeastern U.S. play an important role in meeting the increasing demand for forest products, and represent an important carbon (C) sink that can be managed as a potential tool for mitigating atmospheric CO2 concentrations and global climate change. However, realizing this potential depends on full accounting of the ecosystem carbon (C) budget. The separate evaluation of root-derived, autotrophic (RA) and microbially-derived heterotrophic (RH) soil respiration in response to management and climate change is important, as environmental and ecological factors often differentially affect these components, and RH can be weighed against net primary productivity (NPP) to estimate the C sink or source status of forest ecosystems. The objective of this research was to improve the quantitative and mechanistic understanding of soil respiratory fluxes in managed loblolly pine (Pinus taeda L.) plantations of the southeastern U.S. To achieve this overall objective, three studies were implemented to: 1) estimate the proportion and seasonality of RH:RS in four stand age classes, and identify relationships between RH:RS and stand characteristics 2) evaluate the effects of forest nutrient management and throughfall reduction on factors that influence RH and decomposition dynamics, including litter quality, microbial biomass, and enzyme activity and 3) evaluate the sensitivity of sources of RH (mineral soil-derived heterotrophic respiration; RHM, and leaf litter-derived heterotrophic respiration; RHL) to varying soil and litter water content over the course of a dry down event, and assess whether fertilization influences RH. Stand age and measurement season each had a significant effect on RH:RS (P < 0.001), but there were no interactive effects (P = 0.202). Mean RH:RS during the 12-month study declined with stand age, and were 0.82, 0.73, 0.59, and 0.50 for 3-year-old, 9-year-old, 18- year-old, and 25-year-old stands, respectively. Across all age classes, the winter season had the highest mean RH:RS of 0.85 while summer had the lowest of 0.55. Additionally, there were highly significant (P < 0.001) and strong (r > 0.5) correlations between RH:RS and peak LAI, stem volume, and understory biomass. Fertilization improved litter quality by significantly decreasing lignin:N and lignin:P ratios, caused a shift in extracellular enzyme activity from mineral soil N- and P-acquiring enzyme activity to litter C-acquiring enzyme activity, and increased microbial biomass pools. Throughfall reduction decreased litter quality by increasing lignin:N and lignin:P, but also increased C-acquiring enzyme activity. RHL was more sensitive to water content than RHM, and increased linearly with increasing litter water content (R2 = 0.89). The contribution of RHL to RH was greatest immediately following the wetting event, and decreased rapidly to near-zero between three – 10 days. RHM also had a strong relationship with soil water content (R2 = 0.62), but took between 200 – 233 days to attain near-zero RHM rates. Fertilization had no effect on RHM (P = 0.657), but significantly suppressed RHL rates after the wetting event (P < 0.009). This research provides estimates of RH:RS in managed loblolly pine systems that can be used to improve regional ecosystem C modeling efforts, and demonstrates the need to consider the impact of stand age and seasonal patterns to identify the point at which plantations switch from functioning as C sources to C sinks. Additionally, it demonstrates that the controls over RH are dynamic and influenced in the short-term by fertilization and changed precipitation regimes, with the greatest impact on properties affecting litter RH compared to mineral soil. Future research should work to improve the mechanistic understanding of the seasonal and spatial variability of RH and related controlling biotic and abiotic parameters to remedy the variability in existing RS and ecosystem C models. Understanding how management and climate change may impact factors that control RH will ultimately improve our understanding of what drives changes in forest C fluxes. / Ph. D.

Forests are considered among the best carbon stocks on the planet. After forest harvest, the residual tree stumps persist on the site for years after harvest continuing to store carbon. A bigger concern is that the component ratio method requires a way to get stump volume to obtain total tree aboveground biomass. Therefore, the stump volumes contribute to the National Carbon Inventory. Agencies and organizations that are concerned with carbon accounting would benefit from an improved method for predicting tree stump volume. In this work, many model forms are evaluated for their accuracy in predicting stump volume. Stump profile and stump volume predictions were among the types of estimates done here for both outside and inside bark measurements. Fitting previously used models to a larger data set allows for improved regression coefficients and potentially more flexible and accurate models. The data set was compiled from a large selection of legacy data as well as some newly collected field measurements. Analysis was conducted for thirty of the most numerous tree species in the eastern United States as well as provide an improved method for inside and outside bark stump volume estimation. / Master of Science

Recent studies suggest that continental flood basalts may be suitable for geologic carbon sequestration due to fluid-rock reactions that mineralize injected CO₂ on relatively short time-scales. Flood basalts also possess a permeability structure favorable for injection, with alternating high-permeability (flow margin) and low-permeability (flow interior) layers. However, little information exists on the behavior of CO₂ as it leaks through fractures characteristic of the flow interior, particularly at conditions near the critical point for CO₂. In this study, a two-dimensional 5 × 5 m model of a fracture network is built based on high-resolution LiDAR scans of a Columbia River Basalt flow interior taken near Starbuck, WA. Three-phase CO₂ flow is simulated using TOUGH3 (beta) with equation of state ECO2M for 10 years simulation time. Initial conditions comprise a hydrostatic pressure profile corresponding to 750-755 m below ground surface and a constant temperature of 32° C. Under these conditions, the critical point for CO₂ occurs 1.5 meters above the bottom of the domain. Matrix permeability is assumed to be constant, based on literature values for the Columbia River Basalt. Fracture permeability is assigned based on a lognormal distribution of random values with mean and standard deviation based on measured fracture aperture values and in situ permeability values from literature. In order to account for fracture permeability uncertainty, CO₂ leakage is simulated in 50 equally probable realizations of the same fracture network with spatially random permeability constrained by the lognormal permeability distribution. Results suggest that fracture permeability uncertainty has some effect on the distribution of CO₂ within the fractures, but network geometry is the primary control in determining flow paths. Fracture permeability uncertainty has a larger influence on fluid pressure, and can affect the location of the critical point within ~1.5 m. Uncertainty in fluid pressure was found to be highest along major flow paths below channel constrictions, indicating permeability at a few key points can have a large influence on fluid pressure distribution. / Master of Science

Managed loblolly pine forests comprise an important pool in the global carbon cycle. Understanding the influences upon inputs and outputs of this pool, including the effects of management activities, will allow landowners to understand how carbon can be sequestered in their stands. Specific to this study, we sought to create multivariate models of the output of carbon from the soil in the form of soil CO2 efflux (Rs) and a component of that total efflux, heterotrophic respiration index (Rh), from data collected across the managed range of loblolly pine in the Southeastern U.S. We also performed tests of significance on controlled subsets of these data for the effects of fertilization and of thinning. Finally, we sought a connection between stand leaf area index (LAI) and total soil CO2 efflux or heterotrophic respiration. Our models indicated variability in both Rs and Rh across latitude and physiographic province, respectively, within this range. The Rs (R2 = 0.56) model included temperature, latitude, a soil moisture by temperature effect, soil nitrogen, and bulk density variables. The Rh (R2 = 0.50) model included soil moisture, a temperature by moisture interaction, and physiographic province. Rs was not significantly affected by either fertilization or thinning, yet Rh was influenced by both (negatively and positively, respectively). This indicates a shift in relative contributions of heterotrophic respiration and root respiration components to Rs in response to these treatments. Heterotrophic respiration was shown to have a weak negative response (R2 = 0.04) to increasing stand LAI. / Master of Science

Conventional farming practices and land-use conversions drive carbon out of soil and into the atmosphere, where it contributes to climate change. Biochar, a soil amendment produced by pyrolyzing organic feedstocks under low-oxygen conditions, is a promising tool to restore soil carbon and draw down atmospheric carbon dioxide. Biochar has received considerable attention from scientists, growers, and environmentalists in the last 20 years, but there is still a gap between academic research and practical recommendations on biochar production and application that are relevant to small-scale growers. Here I present the results from two complementary studies that demonstrate the utility of local-scale biochar systems and provide some recommendations for those looking to work with biochar. The first study sought to determine the impact of biochar amendments on soil carbon and nutrient retention on three working farms across a variety of soil types, cropping systems, and climates in the United States. The effect of biochar amendment depended on initial soil characteristics and the properties of the biochar applied. Biochar amendments increased soil carbon in all three sites and increased soil nitrogen at two of the three. In this study pyrolysis conditions appeared to be as important as local soils and climate influences on the efficacy of biochar treatments. The second study was a life cycle assessment using SimaPro software to quantify the carbon balance and global warming potential of biochar produced from three local feedstocks (softwood, hardwood, and hay) applied to pasture soils in Southwest Virginia. Feedstock type, pyrolysis gas yield, and transportation distance significantly contributed to variation in the carbon balance of each agro-ecosystem. Biochar made from softwood lumber scraps performed best, with the highest net carbon storage and lowest global warming potential, followed by biochar made from hardwood scraps. Hay biochar performed worst, with positive carbon emissions (i.e., more carbon released than stored over its life cycle) in most scenarios tested, mainly because of its low biochar yield and the carbon emissions associated with agronomic production and transportation. Together these studies demonstrate the potential of local biochar systems to improve both soil health and carbon sequestration, and reinforce how important it is to know the characteristics of the soil and the production history and properties of the biochar being applied in order to meet soil health and carbon sequestration goals. / Master of Science / Conventional farming practices break down organic material in the soil, which decreases the capacity of soils to sustain crop growth and contributes to climate change as the soil releases carbon dioxide and other greenhouse gasses into the atmosphere. Biochar, or charcoal that is deliberately incorporated into soil, is gaining popularity among farmers, gardeners, and climate scientists for its ability to improve soil health and draw carbon out of the atmosphere to create stable long-term pools of carbon underground. Unfortunately, much of the research on biochar does not translate easily into recommendations for growers and land-managers to make and use biochar. Here I discuss the results from two studies examining the effect of biochar on soil health and carbon sequestration on local scales. In the first experiment I analyzed soil samples shared by farmers in New Mexico, Minnesota and Virginia who applied locally-sourced biochar to their soils. I found that the initial characteristics of the soil and of the biochar affected how the biochar application changed agriculturally-relevant soil properties. In general, biochar improved soil carbon and nitrogen levels, had mixed effects on soil pH depending on the biochar's pH, and had no effect on electrical conductivity (a measure of soil salinity). The second study was a life cycle assessment that quantified and compared greenhouse gas emissions of three different types of biochar, from feedstock harvest to biochar application to soil. I found that the type of feedstock used to make biochar, the amount of gas emitted during the conversion process, and the distance the feedstocks and biochar were transported all played a role in the overall carbon balance of the life cycle. The biochar made from softwood scraps performed best from a carbon storage perspective, followed by biochar made from hardwood. These two biochars tended to return more carbon to the soil than they emitted over their life cycle. The biochar made from hay performed worst, and emitted more carbon than it stored in most of the scenarios I tested. Together these studies show the potential of local biochar systems to improve both soil health and carbon sequestration and reinforce how important it is to be familiar with the soil and the production history and properties of the biochar being applied in order to meet soil health and carbon sequestration goals.

Agricultural conservation practices can have a vast number of environmental benefits but adoption of these practices may not be widespread. If farm operators are able to reap financial returns for environmental services, adoption of these conservation practices could increase. One source of potential financial returns is in greenhouse gas (GHG) emission reductions or increased GHG sequestration. An example of a conservation management strategy for beef and dairy operations which has the potential to decrease GHG emissions or increase GHG sequestration is an intensively managed rotational grazing system. The objective of this study is to estimate potential financial returns from conversion to rotational grazing and the sale of GHG credits by Virginia beef and dairy farms. The three GHGs examined in the study are carbon dioxide, nitrous oxide, and methane. Primary and secondary data are used to simulate financial performance and GHG emissions for three case study farms under different levels of production and pasture utilization. Each case study farm is simulated under three reference conditions to calculate financial performance and three baseline scenarios and a regional performance standard to calculate GHG emissions on both a per farm and a per metric ton of product sold metric. The change in emissions between the scenarios is found and potential returns from the sale of GHG emissions credits are calculated. Results of the analysis demonstrate that conversion to rotational grazing has the potential to increase overall revenues for the farm operation from $4,197.72 to $50,007.46. GHG emission changes for the farm operation do not show a clear trend towards reduction. The amount of financial return from the sale of GHG reduction credits varies from $37.15 to $76.26 for the three case study farms for the initial calculations, and varies from $24.10 to $755.36 once the study performs sensitivity analysis for methane emissions. Therefore, results indicate that rotational grazing can increase net revenues for farm operations but additional net revenue from the sale of GHG reduction credits is small and dependent on the chosen baseline scenario and metric. Follow up research should address the following areas: changes in the cost of on-farm labor, risk of conversion to rotational grazing, increased accuracy of the measurement of GHG emissions and soil carbon, the effects of rotational grazing on forage TDN, and the water quality impacts of rotational grazing. / Master of Science

Indiana University-Purdue University Indianapolis (IUPUI) / Terrestrial carbon sequestration is one of several proposed strategies to reduce the rate of carbon dioxide (CO2) accumulation in the atmosphere, but the impact of plant invasion on soil organic carbon (SOC) storage is unclear. The results of past studies are often confounded by differences in vegetation and environmental conditions. Reed canary grass (Phalaris arundinacea) is an herbaceous species that invades riparian fringes and wetlands throughout North America, including Beanblossom Bottoms – a wetland complex in south-central Indiana. Because of the prolific growth of P. arundinacea, it was hypothesized that significant alterations in SOC pools and dynamics would occur at invaded sites within the wetland complex. To test this hypothesis, study plots were established in areas colonized either by native herbaceous species or by P. arundinacea. Above and below-ground biomass were collected at the middle and end of the growing season and were analyzed for cellulose, lignin, acid detergent fiber, total phenolics, and organic carbon and nitrogen concentration. Soil samples were analyzed for SOC and nitrogen, bulk density, pH, and texture. The biomass of Scirpus cyperinus – a native wetland species was found to contain significantly (P < 0.05) more lignin (168 g kg-1 versus 98 g kg-1) and phenolics (19 g kg-1 versus 3 g kg-1), and had a higher C to N ratio (28 versus 20) than P. arundinacea biomass, suggesting greater recalcitrance of S. cyperinus tissues compared to P. arundinacea biomass. Results of a laboratory incubation study were consistent with the residue biochemistry data and showed that S. cyperinus biomass degraded at much slower rates than the biomass of P. arundinacea. However, measurements of SOC pools (0-30 cm) showed larger pools under P. arundinacea (25.5 Mg C ha-1) than under stands of S. cyperinus (21.8 Mg C ha-1). Likewise, SOC stocks under stands of mixed native vegetation were significantly (P < 0.05) smaller (18.8 Mg C ha-1) than in areas invaded by P. arundinacea. Biomass of the mixed native vegetation was also considered more recalcitrant than that of P. arundinacea based on residue biochemistry. Therefore, contrary to the study hypothesis, residue quality was not a good predictor of SOC stocks in the wetland soils. Thus, it appears that traditional laboratory assessments of biomass recalcitrance and decomposition do not accurately simulate the various biological interactions occurring in the field.

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.

This dissertation consists of three essays on private landowners' response to incentives for carbon sequestration in forests. The first essay examines private landowner response to incentives for carbon sequestration through various combinations of intermediate management practices. The second essay focuses on agricultural landowners' willingness to participate in an incentive program for carbon sequestration through afforestation, and estimates the potential for carbon sequestration from afforestation, as well as its cost. The third study examines relative performances of incentive targeting strategies for forest carbon sequestration under asymmetric information given spatially heterogeneous land types. The first essay uses an econometric approach to analyze the factors affecting non-industrial private forest landowners' choice of forest management practices, and examines how these choices might change in response to the use of incentives for carbon sequestration. I use estimated parameters to simulate the carbon sequestration potential for different combinations of management practices, and compare the effectiveness and costs of performance-based and practice-based incentive payment schemes in the Western U.S. The results suggest that incentive payments can increase the probability that desirable combinations of management practices are adopted, and particularly that incentives targeting increased fertilization yield the highest carbon sequestration potential. I also find that a performance-based payment scheme produces higher carbon sequestration than a practice-based payments scheme. However, the annual sequestration potential of intermediate forest management in response to incentive payment is not as large as the sequestration potential of afforestation. The second essay uses a survey-based stated preference approach to predict landowners' willingness to participate in a tree planting program for carbon sequestration as a function of various factors affecting landowners' decision making and different levels of incentive payments. The estimation results show that the annual payment for carbon sequestration significantly and positively affects landowners' stated level of enrollment in a tree planting program. I use the estimated parameters to conduct regional level simulations of carbon sequestration in response to incentive payments. These simulations show that the carbon supply function in the Pacific Northwest region is steeper than in the Southeast region because of the lower adoption rate and less available lands. The national level carbon supply functions derived from this study are steeper than those obtained from bottom-up engineering approaches and optimization models, and are in the same range as those from revealed preference approach studies. The third essay uses both a conceptual analysis and a numerical analysis to examine the relative performances of incentive programs for carbon sequestration using alternative targeting criteria in the presence of asymmetric information and heterogeneity in costs and benefits. The results show that in the presence of asymmetric information, the combination of high cost-high benefit variability and negative correlation, which is the combination that achieves the greatest benefit gains under perfect information, can result in the greatest benefit losses. Additionally, a comparison of two targeting schemes shows that if cost variability is greater than benefit variability with negative correlation, the benefit achieved under benefit-cost ratio targeting can be lower than that under acreage targeting, so that an optimal targeting strategy under perfect information may no longer be optimal under asymmetric information. / Graduation date: 2013

The dependency on fossil fuels faces resource limitations and sustainability concerns. This situation requires new strategies for greenhouse gas emission management and the development of new sources of energy. This thesis explores fundamental concepts related to carbon geological storage, including CO2-CH4 replacement in hydrate-bearing sediments. In particular it addresses the following phenomena: - Interfacial tension and contact angle in CO2-water-mineral and CH4-water-mineral systems. These data are needed to upscale pore phenomena through the sediment porous network, to define multiphase flow characteristics in enhanced gas recovery operations, and to optimize the injection and storage CO2 in geological formations. - Coupled processes and potential geomechanical implications associated to CH4-CO2 replacement in hydrate bearing sediments. Results include physical monitoring data gathered for CH4 hydrate-bearing sediments during and after CO2 injection. - Performance of cap rocks as trapping structures for CO2 injection sites. This study focuses on clay-CO2-water systems and CO2 breakthrough through highly compacted fine-grained sediments. Long term experiments help evaluate different sediments according to their vulnerability to CO2, predict the likelihood and time-scale of breakthrough, and estimate consequent CO2 leaks.