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. / Quantification of the heterotrophic component of total soil respiration is important for estimating forest carbon (C) pools and fluxes, and for understanding how silvicultural management and climate change may influence forest C dynamics. The separate evaluation of root-derived, autotrophic (R_A) and microbially-derived heterotrophic (R_H) soil respiration is necessary, as environmental and ecological factors often differentially affect these components, and R_H can be weighed against net primary productivity (NPP) to estimate the C sink or source status of forest ecosystems. This research examined the dynamics of R_H in loblolly pine plantations of the southeastern U.S., and the drivers of RH and organic matter decomposition in response to forest management (fertilization) and reduced precipitation (throughfall reduction) to improve the quantitative and mechanistic understanding of this important C flux. This work provided estimates of R_H 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 R_H, such as substrate quality and microbial community activity and biomass, are dynamic and influenced in the short-term by fertilization and altered moisture availability, with the greatest impact on properties affecting forest floor R_H compared to mineral soil R_H. Future research should work to improve the mechanistic understanding of the seasonal and spatial variability of R_H and related controlling biotic and abiotic parameters to remedy the variability in existing R_S and ecosystem C models. Understanding how management and climate change may impact factors that control R_H will ultimately improve our understanding of what drives changes in forest C fluxes.

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 / Forests are considered among the best carbon stocks on the planet, and estimates of total tree aboveground biomass are needed to maintain the National Carbon Inventory. Tree stump volumes contribute to total tree aboveground biomass estimates. Agencies and organizations that are concerned with carbon accounting would benefit from an improved method for predicting tree stump volume. In this work, existing mathematical equations used to estimate tree stump volume are evaluated. A larger and more inclusive data set was utilized to improve the current equations, and to gather more insight in to which equations are best for different tree species and different areas of the eastern United States.

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 / Geologic carbon sequestration (GCS) is a means of reducing greenhouse gas emissions using currently available technology. It consists of trapping carbon dioxide (CO<i>2</i>) released by the burning of fossil fuels at a large emitter, such as a coal fired power plant, and injecting it deep beneath the earth’s surface for permanent storage. This research builds on an increasing body of evidence that suggests that the Columbia River Basalt Group (GRBG), a large lava formation located in the northwestern United States, may be a suitable target for GCS. This is largely because CO<i>2</i> reacts with basalt rocks within a few years of injection to form stable minerals, after which it is permanently immobilized. This basalt province also contains alternating layers of rock, some of which have high permeability, meaning that they can accept CO<i>2</i> injections, and some of which have low permeability, meaning that they would block CO<i>2</i> rising from the injection layers. Layers with low permeability are called confining layers, and in the CRBG, they contain fractures that formed when the lava initially cooled. While some information about these fractures is known, it is impossible to know how easily fluid might flow through them at any given point (permeability) at the depths of interest for GCS. This study seeks to quantify the effects of that uncertainty, by building a model of CO<i>2</i> flow through a CRBG fracture set, and running that same model 50 times with all variables held constant, except the exact location of permeability values within the fracture network. Chemical reactions are not considered, so this model represents behavior in the network very soon after CO<i>2</i> is injected, before minerals start to form. The results of this model suggest that uncertainty in permeability values within fractures influences predictions of fluid pressure within the confining layer. This is important, because fluid pressure has a large influence on whether or not CO<i>2</i> will leak through the confining layer. This research will be useful in informing the model design of future researchers attempting to simulate GCS efforts in the CRBG and similar geologic formations.

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

Black carbon (BC), a stable form of organic carbon (OC), is a byproduct of the incomplete combustion of biomass, biofuels, and fossil fuel. The main objectives of this research are to examine the spatial distribution of OC and BC in urban soil and determine the influence of tree canopy cover and landscape maintenance on soil carbon accumulation. Soil sampling was conducted at 29 sites throughout the City of Denton, Texas, in May 2019. Samples were collected from underneath post oak canopies and in adjacent open areas and were analyzed for total carbon (TC), total organic carbon (TOC), total N (TN), C:N ratio, and BC. Although maintenance levels had no significant effect, TOC was greater underneath trees (5.47%, 5.30 kg/m2) than lawns (3.58%, 4.84 kg/m2) at the surface 0-10 cm. Total nitrogen concentration was also greater underneath trees (0.43%) than lawns (0.31%) at the surface 0-10 cm. Preliminary results for BC were closely correlated to TOC. The lack of difference in C:N ratio between cover types indicates that leaf litter quality may not be the primary driving factor in soil C and N accumulation. Instead, differences in soil properties may be best explained by manual C inputs and greater atmospheric deposition of C and N to soils with tree canopy cover. Identifying patterns and potential drivers of soil OC and BC accumulation is important because soil carbon sequestration not only reduces atmospheric CO2, but also may provide additional pollution mitigation benefits, thereby contributing to a more sustainable urban environment.

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.

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.

This research simulates the response of the Quebec cropping sector to the introduction of carbon credit revenue which could be made available through the implementation of a greenhouse gas emissions trading and offset system in Canada. Eligible carbon sequestering practices investigated in the simulations include adoption of moderate tillage and no-till as well as the conversion to a permanent cover crop. Monetary demand for greenhouse gas emissions offsets from the cropping sector is endogenized in the objective function of the Canadian Regional Agriculture Model (CRAM) which has been modified to account for the simulations and for the disaggregation of the single crop region of Quebec into eleven sub-regions. Changes in the cropping sector induced by the introduction of seven different carbon price levels, ranging from $1/t CO2 to $100/t CO2, are compared to a baseline. Variables covered in the simulation results include: relative profitability of carbon sequestering crops/technology; adoption rates of moderate tillage and no-till; carbon sequestration levels; carbon credit revenue; cropping pattern, crop production and livestock. / Results indicate that carbon sequestration in agricultural soils could only contribute a minor share of the total emission reduction in Quebec, even with very high carbon price levels. At a carbon price of $15/t CO2, it is estimated that changes in tillage practices and permanent cover would result in an additional 12,328 t CO2 per year sequestered by the cropping sector in Quebec. However, some regions display higher adoption rates of carbon sequestering practices than other regions and appear to be more responsive to the price incentive. The introduction of a monetary demand for GHGE offsets from the cropping sector induces some changes in terms of cropping pattern and crop production level, while it has almost no impact on the livestock sector.

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