Since the Industrial Revolution, human society has rapidly developed and flourished. Meanwhile, some interconnected side effects, particularly in realms of water, energy, food and environment, are tackling the sustainability of society. These grand challenges are intricately interconnected, underscoring the importance of addressing these problems through the lens of the water-energy-environment (WEE) nexus, which emphasizes the interlinkages between these sectors. For instance, the unprecedented scale of CO₂ has accumulated in the atmosphere, and it has accelerated global warming and the chained environmental problems, such as droughts and floods. This insecurity for water resources has encouraged water recycling. At the same time, a new class of anthropogenic contaminants, including pharmaceutical and personal care products (PPCP), heavy metals, herbicides or pesticides, and per-fluoroalkyl substances (PFAS), have been accumulated in natural water bodies. These contaminants are called emerging contaminants, and these can potentially cause severe problems in ecology and human health. Thus, this thesis aimed to tackle these multifaceted issues by investigating the interfacial chemistries between the natural or engineered solids and aqueous phases, particularly in the context of in-situ carbon mineralization and water remediation.To mitigate climate change, we should not only reduce CO₂ emissions but also remove the previously emitted CO₂ from the air. In-situ carbon mineralization is a critical technology to meet the agenda of carbon dioxide removal from the air (CDR) as the potential capacity and offer a thermodynamically downhill reaction to store CO₂ permanently in solid form. During the in-situ carbon mineralization, water plays a pivotal role in the interactions at Rock-H₂O-CO₂ interfaces. However, the kinetics and mechanisms of interfacial reactions in the mineral-aqueous phases with various compositions still need to be fully understood. Additionally, in-situ carbon mineralization demands substantial water usage; therefore, addressing water security become imperative. However, during the water usage and recycling process, the accumulation of ions, including heavy metals, and the spreading of organic pollutants can intensify the concerns about water security. Thus, this thesis’s objectives are to focus on a fundamental understanding of reaction kinetics and mechanisms occurring at the interested interfaces to address these challenges. At the mineral-aqueous phase for in-situ carbon mineralization, the effect of parameters, such as temperature, pH, and mineralogy has been assessed for mineral dissolution in the aqueous phase, and both basalt and peridotite were investigated. Related to the dissolution kinetics, this thesis discussed the frameworks for determining the dissolution rate, which can affect our understanding of experimental results. The dissolution studies exploring the effect of various parameters related to the in-situ carbon mineralization provided valuable insights into the reactivity of feedstock and morphological alterations that can be utilized for reactive-transportation modeling. Also, the experiment results may suggest the system boundary to engineer the geological CO₂ storage process. Also, carbonation behaviors were studied in terms of direct carbonation and nucleation. For the direct carbonation, olivine mineral and peridotite rock retrieved from a potential CO₂ storage site were tested, and the effects of parameters including pH, additives, and temperature were discussed. During the in-situ carbon mineralization, dissolved cations and dissolved CO₂ can be nucleated and precipitated on the different types of mineral surfaces. Therefore, this study investigated the interfacial interactions with different types of mineral surfaces and containing ions in the aqueous phase. These studies provide the fundamental understanding of the thermodynamics and kinetics of carbonation during in-situ carbon mineralization. Lastly, this study explored the kinetics and mechanisms of adsorption at adsorbent–emerging contaminant containing fluid interfaces in regard to water remediation and recycling. In this study, biochar from waste streams and MOFs with different modifications were used for the strategical development of adsorbents, while spectroscopic analysis methods were adopted to elucidate the mechanisms. Also, the effect of coexisting ions or reusability was discussed. Further, the results and insights from this investigation can be utilized for developing future generations of adsorbents and designing the remediation process. Consequently, through understanding the various regimes of interfaces, this study may contribute to the advancement of strategic approaches for addressing the complex challenges within the WEE nexus, particularly related to sustainable in-situ carbon mineralization.

Due to concern over the increasing concentration of carbon dioxide in the atmosphere, forest researchers and managers are currently studying the effects of varying silvicultural and harvesting practices on the carbon dynamics of intensely managed forest ecosystems. Soil carbon dioxide efflux resulting from soil microbial activity and root respiration is one of the major components of the total carbon flux in forested ecosystems. In an effort to examine the response of soil carbon dioxide efflux to changes in soil factors, nutrient availability, temperature, and moisture, soil respiration rates were measured monthly over an entire year in a two-year-old loblolly pine (Pinus taeda L.) plantation subjected to fertilization and mulching treatments. A dynamic, closed-chamber infrared gas analysis system was used to measure efflux rates from plots treated with one of four treatment combinations including: nitrogen (115 kg/ha) and phosphorus (11.5 kg/ha) fertilization with black landscape cloth (mulch), fertilization without mulch, mulch without fertilization, and no treatment (control). For each treatment combination, plots were established at the seedling base and 1.22 m away from the seedling base to examine the effect of seedling roots on soil carbon dioxide efflux rates. Soil temperature and moisture were measured at each chamber position monthly and soil coarse fragments, soil nutrient levels, percent carbon, root biomass and coarse woody debris were measured beneath 64 chambers at the end of the study. Fertilization had no significant effect on efflux rates during any of our monthly sampling sessions despite the fact that fertilized seedlings experienced significant increases in both above and belowground biomass. Conversely, regression analysis of growing season soil carbon dioxide efflux rates revealed a slightly negative correlation with both total seedling nutrient uptake and biomass. Rates in plots with mulching were significantly higher than rates from non-mulched plots during five monthly measurement sessions, and higher rates in mulched plots during winter months was attributable to warmer soil temperatures. Rates at the seedling base were always significantly higher than rates in plots away from the seedling. Although rates were always higher at the seedling base, the variability observed was only weakly correlated with the amount of pine roots present beneath respiration chambers. Utilizing soil temperature and moisture, soil carbon, and cuvette fine root biomass in a regression model explained 54% of the variance observed in efflux rates across the yearlong study period. Soil temperature alone explained 42.2% of the variance, followed by soil carbon and soil moisture at 5.2% and 2.7% respectively. The amount of pine fine roots under measurement chambers accounted for only 2.4% of the variance. An additional 1.5% was explained by other factors such as soil phosphorus, coarse woody debris, non-pine root biomass, and soil calcium. An examination of the factors affecting the spatial patterns of soil carbon dioxide efflux revealed that total soil carbon and the amount of fine pine root biomass beneath cuvette base rings explain 38% and 11% respectively, of the observed variability in mean annual soil carbon dioxide efflux from differing plots. The most influential factor affecting soil carbon dioxide efflux during the yearlong study period was soil temperature and modeling of seasonal soil carbon dioxide efflux rates from managed forests using both soil temperature and moisture should be achievable with the establishment of data sets and statistical models covering a range of sites differing in productivity, stand age, and management intensity. The establishment of data sets and statistical models across a variety of forest sites should account for the changing influence of soil carbon levels, aboveground biomass, microbial activity, organic matter inputs, and root biomass on soil carbon dioxide efflux. / Master of Science

About 12% of earth’s peatlands have been drained for peat extraction or agriculture and turned peatlands into carbon sources with reduced biodiversity, water retention and downstream water quality. Rewetting is a strategy used to restore peatlands water table and peat forming vegetation, including Sphagnum spp. which are key species in facilitating water retention, peat- and carbon accumulation in bogs. Halmstad University and Sydvatten have been conducting a scientific study, including a one-year-baseline study on a drained bog in Halmstad, scheduled to be rewetted by ditch blocking. The collected data on bog vegetation in this thesis shall be used as baselines for the scientific study. The aim was to understand if rewetting increases the coverage of peat forming vegetation in drained bogs with the hypotheses that Sphagnum moss have higher degree of coverage in wet compared to drained bogs, and that the plant community in wet bogs are dominated by Sphagnum moss while the drained bog is dominated by brown moss. The estimated mean percent coverage of Sphagnum moss, brown moss (other Bryophytes), heather shrubs, sedges, and reeds was compared between the drained bog, scheduled to be rewetted to a wet bog where ditch clearing has not happened for the last 80 years. My result showed that brown mosses of woody species had a greater and dominant mean coverage at the drained bog, indicating a shift to forest vegetation following drainage. Reeds, sedges, and heathers showed no significant difference between sites. Sphagnum moss demonstrated a significantly higher mean coverage in the wet bog, dominating the vegetation. This reflects a typical bog succession, influenced by Sphagnum mosses capacity of outcompeting other plants. These findings support the hypothesis and indicate that within 80 years, there can be a shift to a peat forming-Sphagnum- dominated bog community in previously drained bogs, through ditch blocking.

A storage and enhanced coalbed methane (CO2-ECBM) test will store up to 20,000 tons of carbon dioxide in a stacked coal reservoir in southwest Virginia. The test involves two phases of CO2 injection operations. Phase I was conducted from July 2, 2015 to April 15, 2016, and injected a total of 10, 601 tons of CO2. After a reservoir soaking period of seven months, Phase II is scheduled to begin Fall 2016. The design of the monitoring program for the test considered several site-specific factors, including a unique reservoir geometry, challenging surface terrain, simultaneous CBM production activities which complicate the ability to attribute signals to sources. A multi-scale approach to the monitoring design incorporated technologies deployed over different, overlapping spatial and temporal scales selected for the monitoring program include dedicated observation wells, CO2 injection operations monitoring, reservoir pressure and temperature monitoring, gas and formation water composition from offset wells tracer studies, borehole liquid level measurement, microseismic monitoring, surface deformation measurement, and various well logs and tests. Integrated interpretations of monitoring results from Phase I of the test have characterized enhanced permeability, geomechanical variation with depth, and dynamic reservoir injectivity. Results have also led to the development of recommended injection strategy for CO2-ECBM operations. The work presented here describes the development of the monitoring program, including design considerations and rationales for selected technologies, and presents monitoring results and interpretations from Phase I of the test. / Ph. D. / Recent efforts to manage and reduce atmospheric carbon dioxide (CO₂) emissions include the development of technologies for carbon capture, utilization, and storage (CCUS) operations. CCUS technologies are used to capture CO₂ emissions from a power plant or other point source, transport the captured CO₂ to a field site, and inject the CO₂ underground into a geologic reservoir. There it is securely stored within a deep, sealed geologic formation and/or is utilized to enhance oil or gas recovery from the formation. CCUS operations conducted on a commercial scale could play an important role in combating anthropogenic climate change. Field tests for carbon storage and utilization operations support the objective of scaling up by demonstrating the storage potential of target reservoirs, the profit potential from enhanced recovery, and the safety of all field operations. Field tests are monitored intensively in order to understand reservoir behavior in response to CO₂ injection and to evaluate progress toward project objectives. An ongoing small-scale carbon storage and utilization test in southwest Virginia is testing the potential for CO₂ storage and enhanced gas recovery from a depleted coalbed methane reservoir. The carbon storage and enhanced coalbed methane (CO₂-ECBM) test will store up to 20,000 tons of carbon dioxide in a coal reservoir composed of approximately 20 individual seams. The test involves two phases of CO₂ injection operations. Phase I was conducted from July 2, 2015, to April 15, 2016, and injected a total of 10,601 tons of CO₂. After a reservoir soaking period of seven months, Phase II is scheduled to begin in Fall 2016. The design of the monitoring program for the test considered several site-specific factors, including a unique reservoir geometry, challenging surface terrain, and simultaneous coalbed methane production activities which complicate the ability to attribute signals to sources. A multi-scale approach to the monitoring design incorporated technologies deployed over different, overlapping spatial and temporal scales. The work presented here describes the development of the monitoring program, including design considerations and rationales for selected technologies, and presents monitoring results and interpretations from Phase I of the test.

This thesis investigates innovative and sustainable methods for the extraction and recovery of critical metals from various waste streams, with the goal of reducing reliance on primary ores and minimizing the associated environmental impact. As global demand for these essential materials grows, finding effective alternatives becomes increasingly urgent. This research is structured around four main chapters, each addressing different aspects of metal recovery in the hydrometallurgical process and focusing on integrating environmentally friendly processes. By exploring advanced extraction techniques and the use of novel materials, this work aims to contribute to the development of greener technologies in the field of materials recovery. Chapter 1 introduces a new framework that combines critical element recovery from waste-to-energy fly ash (WTE FA) with carbon sequestration, addressing environmental concerns related to the growing demand for materials in green technologies. This study integrates electrochemical Zn recovery with carbon capture, utilization, and storage (CCUS), demonstrating the potential for carbon-neutral Zn recovery. Using renewable acids (HNO₃), Ca and Zn were leached undermild conditions (pH 3), followed by electrochemical separation for high-purity Zn recovery. The unique morphology of the feedstock facilitated rapid metal extraction, while water wash pretreatment removed Ca-rich salts for subsequent carbonation, converting the remaining Ca into high-purity calcite. Chapter 2 develops new ligand systems that selectively extract and release critical elements, such as lanthanides, from solutions containing competing metal ions. A tunable molecular scaffold based on tris(2-aminoethyl)amine was functionalized with salicylaldehydes to create imine ligands that effectively extracted Ce, even in the presence of Mg and Ca. The study employed CO₂ as a stimulus for re-extraction, producing cerium carbonate and high-purity ceria. This pHswing mechanism, driven by controlled CO₂ partial pressure, enables efficient recovery of energy-relevant elements from unconventional resources, demonstrating the potential of green chemistry in metal recovery. Chapter 3 develops silica gel functionalized with polyethyleneimine (PEI), known as μOHMs, for the efficient and selective capture of heavy metal ions on both batch and continuous scales. Maximum adsorption capacities for Cu, Zn and Ni ions are 63.5, 43.1, and 36.2 mg/g, respectively, at pH 5.5. The adsorption process follows pseudo-second-order kinetics and the Langmuir isotherm model. Thermodynamic experiments indicate spontaneous, exothermic removal governed by monolayer chemisorption. Performance tests demonstrate a consistent removal rate of 33.5 mg/g for Cu after fifty cycles, highlighting the effectiveness of amine group complexation in heavy metal capture. Chapter 4 examines 2-hydroxyaryloximes as effective candidates for metal separation, forming stable, size-selective pseudo-macrocyclic dimers through hydrogen-bonding networks. These ligands exhibit pH-dependent coordination properties influenced by the phenolic oxygen's protonation state. The chapter explores the structure-property relationships of seven 2-hydroxyaryloximes in liquid-liquid extraction schemes for Ni and Co. It presents a generalizedmultigram synthesis and concentration- and solvent-dependent characterization. Steric and electronic effects from peripheral substituent modifications on the dimerization constant and pKa values were systematically investigated using NMR and potentiometric titrations. These findings demonstrate the potential of these ligands for "pH-swing" separations of energy-relevant metals. Overall, this thesis addresses critical challenges in sustainable metal recovery by employing interdisciplinary approaches that encompass chemistry, materials science, and chemical engineering. By integrating innovative techniques and materials, the research identifies effective strategies for extracting valuable metals from unconventional waste sources while minimizing environmental impact. The findings contribute significantly to the development of greener processes and materials, presenting viable alternatives to traditional extraction methods. Furthermore, this work supports sustainability in metal recovery by promoting the efficient use of resources, reducing waste, and enhancing the overall viability of circular economy principles in the field of materials recovery.

With rising concentrations of CO₂ in the Earth's atmosphere causing concern about climate change, many solutions are being presented to decrease emissions. One of the proposed solutions is to sequester excess CO₂ in geological formations such as basalt. The deep subsurface is known to harbor much of the microbial biomass on earth and questions abound as to how this deep life is going to respond to the injection of CO₂. Many studies have used model microorganisms to demonstrate the ability of microbes to aid in the safe, permanent sequestration of CO₂ in the subsurface. The objective of this research is to characterize the microbial community present in the basalts at the Wallula pilot carbon sequestration well prior to the injection of CO₂ and then perform laboratory studies to determine how the native microbial community will respond to carbon sequestration conditions. Six samples were collected from the Wallula pilot well prior to the injection of CO₂ into the system. The microorganisms in these samples were characterized by pyrosequencing of 16S rRNA genes, revealing a community dominated by the Proteobacteria, Firmicutes, and Actinobacteria. The organisms detected were related to microbes known to metabolize hydrogen, sulfur, and single carbon compounds. These microorganisms may be stimulated in formations located at the fringe of the pool of injected CO₂. Laboratory studies revealed that the native microbial community suffered a two order of magnitude loss of population upon exposure to CO₂ under carbon sequestration conditions. The community also shifted from being dominated by Proteobacteria prior to CO₂ exposure to being dominated by Firmicutes after exposure. Specifically, the genus Alkaliphilus, which was previously undetected, appeared after CO₂ exposure and became dominant. The dominance of Alkaliphilus, along with other rare organisms which did not compose a majority of the population prior to the introduction of CO₂ to the system, indicates that members of the rare biosphere may be better adapted to changing environmental conditions specific to CO₂ sequestration than other indigenous cells. Thus, the rare biosphere should be examined closely as part of any environmental study, as these minority microorganisms may be the first indication of perturbation or impact. / Graduation date: 2013

This paper models the supply curve of carbon sequestration on Pacific Northwest rangelands. Rangeland managers have the ability to sequester carbon in agricultural soils by implementing alternative management practices on their farms. Their low adoption rate in practice suggests a high opportunity cost associated with their implementation. To increase their adoption, a payment for ecosystem services plan is proposed, where the public compensates farms for lost profits. The TOA-MD model is used to estimate the resulting sequestration incentivized by payments for soil carbon sequestration. Methodological questions of geographical stratification and estimating variation from available data are tested. Sensitivity analysis is also run on key assumptions in the study. Results show that while the economic potential of both systems is much lower than the technical potential, at reasonable CO��� payment levels rangeland sequestration could be a significant mitigation strategy for Pacific Northwest states. / Graduation date: 2012

This thesis investigates the abiotic control of carbon (C) and water vapour fluxes (FCO₂ and E, respectively) in a New Zealand Pinus radiata D. Don plantation and a nearby clearcut. It concentrates on the limitation of these fluxes imposed by growing season soil water deficit. This results from low precipitation (658 mm a⁻¹) in combination with a limited root zone water storage capacity of the very stony soil (> 30% by volume). The thesis analyses results from seven eddy covariance flux measurement campaigns between November 1994 and March 1996. The study site was located in Balmoral Forest, 100 km north-west of Christchurch (42° 52' S, 172° 45' E), in a (in November 1994) 8-year-old stand. One set of measurements was conducted in an adjacent clearcut. Ecosystem flux measurements were accompanied by separate measurements of ground fluxes and of the associated environmental variables. Flux analysis focussed on the underlying processes of assimilation (Ac), canopy stomatal conductance (Gc) and respiration (Reco), using biophysical models coupled to soil water balance and temperature subroutines. Aiming to link time inegrated net ecosystem C (NEP) to tree growth, sequestration in tree biomass (NPP) was quantified by regular measurements of stem diameter using allometric relationships. Average rates of FCO₂ and E were highest in spring (324 mmol m⁻² d⁻¹ and 207 mol m⁻² d⁻¹, respectively) when the abiotic environment was most favourable for Gc and Ac. During summer, fluxes were impeded by the depletion of available soil water (θ) and the co-occurrence of high air saturation deficit (D) and temperature (T) and were equal or smaller than during winter (FCO₂ = 46 mmol m⁻² d⁻¹ in summer and 115 mmol m⁻² d⁻¹ in winter; E = 57 and 47 mol m⁻² d⁻¹, respectively). With increasingly dry soil, fluxes and their associated ratios became predominantly regulated by D rather than quantum irradiance, and on particularly hot days the ecosystem was a net C source. Interannually, forest C and water fluxes increased strongly with rainfall, and the simultaneously reduced D and T. For two succeeding years, the second having 3 % more rain, modelled NEP was 515 and 716 g C m⁻² a⁻¹, Ac 1690 and 1841 g C m⁻² a⁻¹ and Reco 1175 and 1125 g C m⁻² a⁻¹. NEP / E increased in wetter (and cooler) years (1.3 and 1.5 g kg⁻¹), reflecting a relatively larger gain in NEP. Responding mainly to increased rainfall during commonly dry parts of the year (ie summer), and reflecting the otherwise benign maritime climate of New Zealand, NEP during the winter months could exceed NEP during the middle of the notional tree growing season. Annual Ac, NEP, and NPP were strongly linearly related. This relation did not hold during bi-weekly periods when the processes of intermediate C storage were influential. Separate knowledge of tree growth and C fluxes allowed quantification of autotrophic, and heterotrophic respiration (Rhet≈ 0.4 NEP), as well as fine-root turnover (≈0.2 NEP). The ratio of NEP and stem volume growth was conservative (0.24 t C m⁻³) and allows a direct connection to be made between ecosystem carbon fluxes and forest yield tables. In the absence of living roots, the clearcut flux measurements demonstrated the expected limitation of Rhet by soil temperature (Ts) and θ. However, an additional 'pumping effect' was discovered at the open site whereby turbulence increased CO₂ efflux considerably when the soil surface was wet. Accounting for the combined effects of Ts, θ and turbulence, annual Rhet at the clear-cut site (loss to the atmosphere) was »50 % of NEP (C sequestered from the atmosphere) in the nearby forest. Clearly, there is an important contribution of C fluxes during early stages of ecosystem development to the total C sequestered over the lifetime of a plantation.

Bibliography: leaves 135-145 / Climate Change poses a great risk to our future as species on Earth. The impacts thereof will have far reaching consequences on every aspect of our daily lives and ultimately on our ability to survive and thrive as humans. It is therefore important, particularly in urban areas where most of the human population live, for the investment of resources and expertise into mitigating these impacts and ensuring the resilience of urban areas. The urban forest provides climate change mitigation benefits for urban areas through carbon sequestration. In order to encourage investment and protection of the urban forest, this benefit must be quantified and afforded a monetary value. This study calculated the amount of carbon dioxide sequestrated by the Jacaranda mimosifolia street tree in the City of Tshwane and afforded this amount a monetary value in both South African Rands and American Dollars through the South African Carbon Tax Bill. This study followed the baseline study by Stoffberg (2006) looking at how much carbon dioxide had been sequestrated by the Jacaranda trees over the past 15 years post the baseline study and what monetary value do the trees now have through legislation that was not available during the baseline study. The study also observed the variables that may have affected the amount of carbon dioxide sequestrated by the trees. Although some areas saw a drop in the Total Carbon Dioxide Equivalent sequestrated since 2004, the total amount for the whole city remained stable. Through the Carbon Tax Bill, the value of these trees has increased significantly encouraging the municipality to invest in the maintenance and protection of the Jacaranda street trees in the City of Tshwane in order to preserve their carbon sequestration benefits / Environmental Sciences / M. Sc. (Environmental management)

In the dominantly small-scale subsistence agricultural system of Ethiopia, where most of the organic inputs are not returned to soil and land is not used based on its best suitability, the contribution of agriculture to climate change mitigation/adaptation through reduction of greenhouse gases emission is undermined. When this low-input agricultural practice is coupled with rugged topography, high population pressure, generally low soil fertility, and looming climate change, ensuring food and nutrition security of society as well as sustainable use of land resources is practically impossible. Under such circumstances, finding alternative land uses, through scientific investigation, that meet the triple mandates of climate-smart agriculture under current and future climate is imperative. In view of this, a study was conducted in Hades Sub-watershed, eastern Ethiopia, to evaluate the carbon stock of major land uses, evaluate suitability of land for rainfed production of sorghum (Sorghum bicolor L.), Maize (Zea mays L.), coffee (Coffea arabica), upland rice (Oryza sativa L.) and finger millet (Eleusine coracana L.), and project biomass production of late-maturing sorghum and maize varieties under changing climate and its contribution to carbon sequestration and reduction of greenhouse gases (GHGs) emission. Soil and vegetation samples were collected following recommended procedures. Secondary data on required crop parameters were collected for model calibration and validation in the biomass projection study made using the AquaCrop v6.0 model. Climate data of the study area was obtained from the National Meteorology Agency of Ethiopia and analyzed following standard procedures. Near-century (NC) (2017-2039) and Mid-century (MC) (2040-2069) climate was projected under two emission scenarios (RCP4.5 and RCP8.5) using four models (CNRM-CERFACS-CNRM-CM5, ICHEC-EC-Earth, MOHC-HadGEM2-ES, and MPI-M-MPI-ESM-LR) and a Multi-model Ensemble. Biomass production projection, for the climate projected under the two emission scenarios using the four models and the ensemble, was made for late-maturing sorghum (Muyira-1) and maize (BH661) varieties. From the projected biomass, organic carbon and its equivalent CO2 were estimated. Furthermore, adaptation measures, involving adjusting planting dates and irrigation, under the changing climate were evaluated for their influence on biomass production under the time slices, RCPs, and models mentioned above. The carbon stock assessment study was conducted on four major land uses (cultivated, grazing, coffee agroforestry, and forest lands) identified in the study area. The land suitability assessment, using the maximum limitation method, study was conducted on four soil mapping units identified in the sub-watershed. Results indicate that total organic carbon stock (soil, litter plus live vegetation) in the sub-watershed ranged from 138.95 ton ha-1 in the crop land to 496.26 ton ha-1 in the natural forest. The soil organic carbon stock was found to be relatively higher than that of the vegetation carbon stock in the natural forest and coffee agroforestry land uses. The results of suitability evaluation revealed that the maximum current and potential (after corrective xix measures are taken) land suitability class for production of late-maturing sorghum (180-240 days cycle), maize (180-210 days crop cycle), finger millet (120 – 150 days cycle) and coffee in the sub-watershed is marginally suitable (S3c). The maximum current and potential land suitability for upland rice (120 days) is not suitable (N2c). The major permanent limiting factor is low mean temperature (14.6 C) of the growing period in the study area as compared to the optimum temperature required for optimum growth of the selected crops. The major soil and landscape limitations include steep slope, poor drainage of low-lying areas, shallow effective root zone in the upper slopes, low organic matter and available P for sorghum and maize, high pH for maize and wetness for coffee. In all the climate models and emission scenarios, minimum and maximum temperature increment is high during June-July-August-September (JJAS) compared with the other seasons. The modest rise in minimum temperature and the slight increment of maximum temperature during the crop growing seasons (February-March-April-May (FMAM) and JJAS will benefit late-maturing sorghum and maize production in the study area. For the same model, the projected biomass yield and organic carbon sequestration of the two crop varieties varied with time slice and the type of emission scenario used. Generally, increasing biomass production and carbon sequestration were projected for Mid-century (MC) than Near-century (NC) for most of the models used. Late planting would increase sorghum biomass yield and the corresponding organic carbon as compared to early planting as projected by most of the models under both RCPs. Most models predicted an increase in maize biomass yield and organic carbon sequestration if supplementary irrigation is used. The results of this study indicate that the current land uses are not enhancing carbon sequestration because of their exploitative nature and the soil/landscape and climate are not optimum for production of the crops studied. The rise in temperature in the coming 50 years is expected to create a more favorable condition for production of late-maturing sorghum and maize varieties. In order to enhance carbon sequestration, soil productivity and crop yield, and reduce greenhouse gas emissions, the current land uses and their management require re-visiting. / College of Agriculture and Environmental Sciences / Ph. D. (Environmental Sciences)