Geological carbon dioxide (CO2) sequestration (GCS) in deep saline aquifers is viewed as a viable solution to dealing with the impact of anthropogenic CO2 emissions on global warming. The trapping mechanisms that control GCS include capillary trapping, structural trapping, dissolution trapping, and mineral trapping. Wettability and density-driven convection play an important role in GCS, because wettability significantly affects the efficiency of capillary trapping, and density-driven convection greatly decreases the time scale of dissolution trapping. This work focuses on the role of wettability on multiphase flow in porous media, density-driven convection in porous media, and their implications for GCS in deep saline aquifers. Wettability is a critical control over multiphase fluid flow in porous media. However, our understanding on the wettability heterogeneity of a natural rock and its effect on multiphase fluid flow in a natural rock is limited. This work innovatively models the heterogeneous wettability of a rock as a correlated random field. The realistic wetting condition of a natural rock can be reconstructed with in-situ measurements of wettability on the internal surfaces of the rock. A Bentheimer sandstone was used to demonstrate the workflow to model and reconstruct a wettability field. Relative permeability, capillary pressure-water saturation relation are important continuum-scale properties controlling multiphase flow in porous media. This work employed lattice Boltzmann method to simulate the displacement process. We found that pore-scale surface wettability heterogeneity caused noticeable local scCO2 and water redistributions under less water-wet conditions at the pore scale. At the continuum scale, the capillary pressure-water saturation curve under the heterogeneous wetting condition was overall similar to that under the homogeneous wetting condition. This suggested that the impact of local wettability heterogeneity on the capillary pressure-water saturation curve was averaged out at the entire-sample scale. The only difference was that heterogeneous wettability led to a negative entry pressure at the primary drainage stage under the intermediate-wet condition. The impact of pore-scale wettability heterogeneity was more noticeable on the relative permeability curves. Particularly, the variation of the scCO2 relative permeability curve in the heterogeneous wettability scenario was more significant than that in the homogenous wettability scenario. Results showed that higher wettability heterogeneity (i.e., higher standard deviation and higher correlation length) increased the variations in the CO2/brine relative permeability curves. Dissolution of CO2 into brine is a primary mechanism to ensure the long-term security of GCS. CO2 dissolved in brine increases the CO2-brine solution density and thus can cause downward convection. Onset of density-driven instability and onset of convective dissolution are two critical events in the transition process from a diffusion-dominated regime to a convection-dominated regime. In the laboratory, we developed an empirical correlation between light intensity and in-situ solute concentration. Based on the novel and well-controlled experimental methods, we measured the critical Rayleigh-Darcy number and critical times for the onset of density-driven instability and convective dissolution. To further investigate the impact of permeability heterogeneity on density-driven convection, a three-dimensional (3D) fluidics method was proposed to advance the investigation on density-driven convection in porous media. Heterogeneous porous media with desired spatial correlations were efficiently built with 3D-printed elementary porous blocks. In the experiments, methanol-ethylene-glycol (MEG), was used as surrogate fluid to CO2. The heterogeneous porous media were placed in a transparent tank allowing visual observations. Results showed that permeability structure controlled the migration of MEG-rich water. Permeability heterogeneity caused noticeable uncertainty in dissolution rates and uncertainty in dissolution rates increases with correlation length. To sum up, this work comprehensively employed novel experimental methods and large-scale direct simulations to investigate the sequestration of CO2 in saline aquifers at a pore scale and a continuum scale. The findings advanced our understanding on the role of wettability heterogeneity and permeability heterogeneity on GCS in deep saline aquifers. / Doctor of Philosophy / Global warming caused by anthropogenic CO2 emissions is a pressing issue to address of our time. The storage of CO2 in deep saline aquifers is a promising solution because of saline aquifers' vast storage capacity. Property heterogeneity exists extensively in saline aquifers from a continuum scale to a pore scale. The implications of pore-scale wettability heterogeneity and continuum-scale permeability heterogeneity for the storage of CO2 in saline aquifers are not clear. This work is to employ novel experimental methods and powerful simulation tools to investigate the role of wettability heterogeneity and permeability heterogeneity on the storage of CO2 in saline aquifers. This work measured contact angles on the scanned micro-CT images of a Bentheimer sandstone after a CO2 flooding. A correlated lognormal wettability model was put forward with the statistical information of the contact angle measurements. Simulations on the CO2/brine flow in the Bentheimer sandstone were performed. Results showed that the wettability heterogeneity caused noticeable redistributions of CO2/brine compared to scenarios under homogeneous wettability. Impact of wettability on capillary pressure-water saturation curve was not noticeable because the effects were averaged out through the entire rock sample. The standard deviation and correlation length caused variations on the relative permeabilities. This means that we need to take them into consideration in simulating the migration of CO2 in saline aquifers at a reservoir scale. After CO2 pools beneath the impermeable cap rock, dissolution of CO2 into brine dominates the trapping process. Convection caused by CO2 dissolution can greatly accelerate the dissolution rate. The onset of convection is a critical issue and lack of experimental evidence. This work firstly determined the onset time of instability. To further investigate the heterogeneity on the convection, this work proposed a 3D-print-based method to efficiently build heterogeneous porous media with a designed permeability distribution. The experiments were conducted, and results showed that heterogeneity structure of porous media can cause great variations on the dissolution rate of CO2. The findings of this work advanced our understanding on the migration of CO2 in saline aquifers, provided solid basis for assessment and decision on the storage of CO2 into saline aquifers.

Deep row incorporation (DRI) is a biosolids recycling method that is especially appropriate for reclaiming disturbed land because of the extremely high application rates used. Nutrient additions in excess of the vegetation requirements, especially in coarse-textured soils, can potentially impair water quality. Increasing C and N additions with biosolids DRI can also generate emissions of greenhouse gases N₂O and CH₄ and decrease the value of C sequestration. Objectives of this research were: (i) compare the effects of DRI biosolids type and rate and annual conventional fertilizer application on N and P leaching losses; (ii) determine the effects of aging on the N, C and P dynamics in the DRI biosolids seams; (iii) compare the effects of biosolids type and conventional N fertilization on N₂O, CH₄ and CO₂ emissions; and (iv) compare the effects of DRI biosolids and conventional N fertilization on hybrid poplar biomass dynamics, C, N and P sequestration. The following eight treatments were established to achieve objectives (i) and (iv): 0 (control), 167, 337, 504 kg N ha⁻¹ yr⁻¹ as conventional fertilizer; 213 and 426 Mg ha⁻¹ anaerobically digested (AD) and 328 and 656 Mg ha⁻¹ lime stabilized (LS) biosolids applied in trenches. The amount of N lost from the DRI biosolids was 261–803 kg N ha⁻¹, while the fertilizer treatments were not different from 0 kg N ha⁻¹ yr⁻¹ control. Orthophosphate and TKP leached in negligible amounts. Deep row biosolids incorporation did not pose P leaching risks but did result in high N leaching below the biosolids seams. Aboveground biomass production in the biosolids treatments was not different from the control treatment and ranged from 2.1±0.3 to 4.0±0.5 kg tree⁻¹. The fertilizer treatments produced significantly less biomass than the control and the biosolids treatments. Hybrid poplars sequestered up to 3.20±0.54 Mg C ha⁻¹, 71±12 kg N ha⁻¹, and 11.0±1.8 kg P ha⁻¹. The planting density capable of the N uptake in order to avoid N leaching was estimated at 3912 to 11363 trees ha⁻¹. Our results suggest increased hybrid poplar planting density and decreased application rates of DRI biosolids may decrease the risk of groundwater contamination with N. Three treatments were compared to address objective (ii): 426 Mg ha⁻¹ AD and 656 Mg ha⁻¹ LS biosolids. Organic C losses were 81 Mg ha⁻¹ and 33 Mg ha⁻¹ for LS and AD biosolids, respectively. Total N lost over the course of two years was 15.2 Mg ha⁻¹ and 10.9 Mg ha⁻¹ for LS and AD biosolids, respectively, which was roughly 50% of the N applied. No significant losses of P were detected. Most of the P was Al- and Fe-bound in the AD biosolids and Ca-bound in the LS biosolids. Our results indicated that recommended rates of DRI biosolids in coarse textured soils should be based on crop N requirements and N mineralization considerations, and P mobility from biosolids of the type used should not pose a water quality risk. Four treatments were compared to address objective (iii): 426 Mg ha⁻¹ AD and 656 Mg ha⁻¹ LS biosolids; 0 (control) and 504 kg N ha⁻¹ y⁻¹ as conventional fertilizer. Contributions from CH₄ and CO₂ emissions to the radiative forcing were very small compared to N₂O. More N₂O was produced in the DRI biosolids treatments than in the conventional fertilizer treatments, and N₂O production was higher in AD than in LS. Expressed as global warming potentials, N₂O emissions from AD (101.5 Mg C ha⁻¹) were 4.6 times higher than from LS and 14.5-16.1 times higher than from the fertilizer treatments. High N₂O emissions from deep row incorporated biosolids reduce the C sequestration benefits of the DRI method. / Ph. D.

Land application of biosolids has been demonstrated to improve nutrient availability (mainly N and P) and improve organic matter in soils, but the effects of biosolids on C sequestration and N cycling in the Mid-Atlantic region is not well understood. The objectives were: 1) to investigate soil C sequestration at sites with a long-term history of biosolids either in repeated application or single large application; 2) to characterize and compare soil C chemistry using advanced 13C nuclear magnetic resonance (NMR) and C (1s) near edge x-ray absorption fine structure (NEXAFS) spectroscopic techniques; and 3) to compare biosolids types and tillage practices on short-term N availability in the Coastal Plain soils. Biosolids led to C accumulation in the soil surface (< 15 cm) after long-time application in both Piedmont and Coastal Plain soils. The C saturation phenomenon occurred in Coastal Plain soils, thus additional soil C accumulation was not achieved by increasing C inputs from biosolids to the Coastal Plain. Soil organic C from profiles in the field sites was not different at depths below the plow layer (15-60 cm). The quantitative NMR analyses concluded that O-alkyl C was the dominant form in the particulate organic matter (POM), followed by aromatic C, alkyl C, COO/N-C=O, aromatic C-O, OCH3 / NCH and ketones and aldehydes. The aliphatic C and aromatic C were enriched but the O-alkyl C was decreased in the biosolids-amended soils. The changes indicated that the biosolids-derived soil C was more decomposed and, thus, more stable than the control. The NEXAFS spectra showed that O-alkyl C was the dominant form in the POM extracted from biosolids-amended soils, followed by aromatic C, alkyl C, carboxylic C and phenolic C groups. These results were similar to those from NMR analysis. The regression and correlation analyses of C functional groups in the POM between NEXAFS and NMR indicated that both techniques had good sensitivity for the characterization of C from biosolids-amended soils. To evaluate short-term biosolids N availability, a three-year field study to investigate the effects of lime-stabilized (LS) and anaerobically digested (AD) biosolids on N availability in a corn-soybean rotation under conventional tillage and no-tillage practices was set up in 2009-2011. Results showed that both LS and AD biosolids increased spring soil nitrate N, plant tissue N at silking, post-season corn stalk nitrate N, grain yield, and soil total N by the end of the growing season. The same factors used to calculate plant available N for incorporated biosolids can be used on biosolids applied to no-till systems in coarse-textured soils. All these results indicated that the application of biosolids affects the long-term quantification and qualification of soil organic C and also improve short-term N availability in the Mid-Atlantic region. / Ph. D.

Site preparation is fundamental for establishing loblolly pine (Pinus taeda L.) plantations, but long-term sustainability of plantations established using mechanical treatments is in question because of concerns regarding soil tillage and the removal of harvest residue and soil organic matter. A study was installed in 1981 on 12 locations in northeastern Georgia and west-central South Carolina to evaluate pine plantation response to mechanical site preparation. Site preparation treatments induced gradients of organic matter manipulation and soil tillage. The treatments included: Control, Chop/Burn, Shear/Disc, Shear/V-Blade, Shear/Rake, and Shear/Rake/Pile. Research was conducted to address the following objectives: (i) compare rotation-age forest response to several intensive site preparation treatments used to establish pine plantations in the Piedmont of the southeastern United States; (ii) correlate growth response with the gradients of soil organic matter removal, soil tillage, and hardwood control; (iii) determine the influence of intensive management on the amount of carbon contained in pine plantations. All site preparation treatments increased year-18 volume accumulation compared to the control treatment. Chop/Burn and Shear/Disc treatments, with pine volumes of 214 m3 ha-1 and 232 m3 ha-1, respectively, conserved harvest residue and out-performed the Shear/Rake treatment (191 m3 ha-1), which completely removed harvest residue. Treatments that included tillage provided growth benefits that lasted throughout the rotation even when tillage was accompanied by complete organic matter removal. Hardwood competition had the greatest influence on pine volume accumulation, explaining over 54% of the variation in pine growth at age 18. Treatments that included tillage most effectively controlled hardwood competition. At year 18, site preparation treatments significantly affected soil organic matter (SOM) content; however, soil nitrogen, foliar nitrogen, bulk density, and macroporosity were not affected by site preparation. All treatments were equally deficient in foliar nitrogen. The Shear/Disc and Shear/Rake/Disc treatments had a significantly positive relationship between foliar nitrogen and pine volume. These treatments had lower hardwood basal areas (below 15%), indicating that once hardwoods were controlled, nitrogen became limiting to pine growth. Using pre-harvest characterization data, carbon accumulation during old-field succession increased fourfold compared to agricultural sites on the nearby Calhoun Experimental Forest. Carbon accumulation on these old-field loblolly pine sites reached quasi-equilibrium after 40 years as shown by uncut reference stands. Site preparation significantly affected the amount of soil C in the upper 20 cm of the soil. Those site preparation treatments that removed harvest residue and accelerated SOM decomposition through tillage had the lowest soil carbon levels. The Shear/Rake/Disc treatment had 10% lower soil carbon content than the Control and Shear/V-Blade treatments. / Master of Science

An understanding of ecosystem-level carbon (C) sequestration, or net ecosystem production (NEP), requires the separation of heterotrophic, microbial respiration (RH) from autotrophic, root-derived respiration (RA) as the components of RS (i.e., NEP = NPP - RH). However, separating these two sources in situ has been problematic since they are closely coupled. This study utilizes two similarly aged Pinus taeda L. stands, 8 and 9 years-old, aimed at quantifying these two respiration components through in-situ root severing. In order to use root-severing treatments to separate RS into RH and RA components, confirmation of carbohydrate depletion coupled to RA decline is crucial. This study evaluated the changes in CO2 flux rates and carbohydrate supply upon root severing in Pinus taeda L. using a controlled laboratory validating a two-part field study. The first field study used root-severing cores to test in-situ if respiration components can be attained based on the depletion of carbohydrate supply. The second field study was aimed at how future changes in climate might affect the ability of forests to store C and how modern forestry practices might affect changes and was conducted over the course of two installations, spring and summer 2012. In this study we examined the effects of fertilization (0 and 100.9 kg N ha-1 ) and throughfall reduction (0 and -30%) on total soil respiration (RS) as well as the heterotrophic contribution to RS, in a fully replicated (n=4), 2x2 factorial design. In the controlled lab experiment RS and RA declined by 86% and 95% respectively by the end of an 86 day trial and NSC carbohydrates declined by 60% for soluble, 29% for insoluble, and 43% for total (soluble + insoluble). The decline of RA was highly correlated to with the decline of NSC’s at 0.90, 0.69 and 0.93 for soluble, insoluble and total, respectively. The companion field study revealed a mean decrease 21±0.5% of over the final three dates when severed root respiration stabilized. In the second study, testing throughfall reduction and fertilization levels there were no fertilization by throughfall reduction interactions on the contribution of RH to RS in either the spring or summer; however, the main effect of throughfall reduction was significant in the spring. During the spring, the mean contribution of RH to RS for ambient throughfall plots was 96±6.4%, while the mean contribution under throughfall reduction was 68±1.9%. During the summer, there were no differences among treatments and the overall contribution of RH to RS was 78±1.6%. Collectively, both of these studies revealed that the severing of roots from their primary energy source and the subsequent depletion of stored NSC that the use of in-situ methods allows for the quantification of soil respiration components RA and RH. Using these estimates to model NEP in the short-term can be variable by season, however, long-term monitoring may simplify future NEP modeling scenarios / Master of Science

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.

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 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)