Carbon dioxide (CO2) and methane (CH4) fluxes from the soil surface, and concentrations within the soil profile, were measured between June 1998 and Sept. 1999 at four adjacent forest plantations and an old field in Nepean, Ontario. The objectives of this study were to quantify seasonal CO2 and CH4 fluxes from the soil surface and within the soil profile to determine the effect of soil moisture and temperature, and forest age and species on the exchange, and establish a chronosequence of organic carbon accumulation in the forest plantations and the old field soils. / Dynamic and static chamber techniques were used to measure surface fluxes of CO2 and CH4, respectively, and soil gas concentrations were sampled with probes. In the old field and forest plantations, surface soil CO2 flux ranged from 2.9 to 27 g CO2 m-2 d-1 and 2.0 to 39 g CO2 m -2 d-1 respectively. Significant differences due to age and species of plantation were observed. Seasonal variations in CO2 efflux from the soil surface and within the soil profile were related to variation in soil temperature and moisture. Uptake of CH4 was observed at all sites and there was no significant differences in flux due to vegetation type or age. Maximum rate of CH4 consumption was 6.3 mg CH4 m-2 d-1. Methane uptake was positively related to soil moisture conditions. / The carbon content of the soil increased in all sites following the establishment of vegetation on sandy parent material. Carbon content was greatest in the upper soil profile. Rates of carbon accumulation ranged from 109 to 426 g m-2 y-1. Soil carbon increased with increasing age of plantation during the first 30 years following the establishment of vegetation on parent material, but declined as the forest plantation matured.

Recent work has described how gas exchange can occur through sea ice. First, carbon fluxes over sea ice surfaces have been measured. Second, sea ice brine has an elevated capacity over seawater to absorb CO2(g) due to its cold temperature and chemical equilibrium promoting carbon phase changes. Sea ice pCO2 profiles were collected using a new method of remotely sampling gas in situ via diffusive membranes placed within growing sea ice. Gas analysis was complimented by measurements of local meteorology and ice chemistry. The work was part of the CASES 2004 project. The observed elevation in sea ice pCO2 coupled with the mobility of the brine points to the role that brine plays in Arctic carbon transport. The gas transport links the Arctic atmosphere and ocean and indicates that a thinning and receding ice cover may not result in creating a negative feedback to the increasing atmospheric CO2(g) concentration.

A climate controlled, dynamic chamber was used to measure carbon dioxide (CO$ sb2$) and methane (CH$ sb4$) exchange on an ombrotrophic peatland. The study periods were July to early November 1995, and early May to July 1996. Five sample sites, showing ecological and hydrological contrast, were investigated. Measurements of Net Ecosystem Exchange showed peak photosynthetic capacity (GP$ sb{ max})$ ranging from 0.52 $ pm$ 0.04 mg C m$ sp{-2}$ s$ sp{-1}$ (June 1996) to 0.03 $ pm$ 0.02 mg C m$ sp{-2}$ s$ sp{-1}$ (early November 1995). Dark respiration measurements ranged from $-$0.21 $ pm$.02 mg C m$ sp{-2}$ s$ sp{-1}$ (June 1996) to $-$0.02 $ pm$.01 mg C m$ sp{-2}$ s$ sp{-1}$ (late May 1996), and showed significant relationships to soil temperature at all sites. Site average methane measurements ranged from 29-72 mg m$ sp{-2}$ d$ sp{-1}$, and showed a strong relationship to water table on a seasonal basis, but a poor correlation to simultaneous NEE. Modelled Net Ecosystem Productivity (NEP) among sites ranged from 17.1 to 115 gC over the entire study period. The CO$ sb2$ exchanges in late spring and early fall made a large contribution to the figure due to the imbalance in the photosynthetic and dark respiration components of the carbon budget. No discernible relationship was found between seasonal NEP and methane release. The results suggest a large importance of the extreme ends of the growing season in an analysis of the carbon budget of peatlands, periods hitherto little investigated. They also suggest that NEP/methane connections may be restricted in their significance to mainly flooded mires.

Recent work has described how gas exchange can occur through sea ice. First, carbon fluxes over sea ice surfaces have been measured. Second, sea ice brine has an elevated capacity over seawater to absorb CO2(g) due to its cold temperature and chemical equilibrium promoting carbon phase changes. Sea ice pCO2 profiles were collected using a new method of remotely sampling gas in situ via diffusive membranes placed within growing sea ice. Gas analysis was complimented by measurements of local meteorology and ice chemistry. The work was part of the CASES 2004 project. The observed elevation in sea ice pCO2 coupled with the mobility of the brine points to the role that brine plays in Arctic carbon transport. The gas transport links the Arctic atmosphere and ocean and indicates that a thinning and receding ice cover may not result in creating a negative feedback to the increasing atmospheric CO2(g) concentration.

Decomposition and MeHg concentration were measured for Sphagnum fuscum, Sphagnum angustifolium and Chamaedaphne calyculata in a poor fen in the low boreal forest zone of the Canadian Shield. Litter bags were transplanted reciprocally into hummocks, hollows and lawns and retrieved after 1, 2, 3,11 and 15 months. / Mass losses follow the trend: Chamaedaphne calyculata >> S. angustifolium > S. fuscum. Between species differences were far more significant than differences between locations or depths, indicating that litter quality is the major control on decomposition. / McHg concentrations generally increased during decomposition, particularly near the water table: for C. calyculata up to 13000%, for the two Sphagnum mosses up to 500%, suggesting that decomposition stimulates mercury methylation or McHg scavenging. / The discovery of a high McHg substance on C. calyculata leaf surfaces (25 ng g-1) suggests that much plant MeHg data may by skewed by the presence of a biologically active 'film'.

Inland waters process large amounts of organic carbon, contributing to CO2 and CH4 emissions, as well as storing organic carbon (OC) over geological timescales. Recently, it has been shown that the magnitude of these processes is of global significance. It is therefore important to understand what regulates OC cycling in inland waters and how is that affected by climate change. This thesis investigates the constraints on microbial processing of sediment OC, as a key factor of the carbon cycling in boreal lakes. Sediment bacterial metabolism was primarily controlled by temperature but also regulated by OC quality/origin. Temperature sensitivity of sediment OC mineralization was similar in contrasting lakes and over long-term. Allochthonous OC had a strong constraining effect on sediment bacterial metabolism and biomass, with increasingly allochthonous sediments supporting decreasing bacterial metabolism and biomass. The bacterial biomass followed the same pattern as bacterial activity and was largely regulated by similar factors. The rapid turnover of bacterial biomass as well as the positive correlation between sediment mineralization and bacterial biomass suggest a limited effect of bacterial grazing. Regardless of the OC source, the sediment microbial community was more similar within season than within lakes. A comparison of data from numerous soils as well as sediments on the temperature response of OC mineralization showed higher temperature sensitivity of the sediment mineralization. Furthermore, the low rates of areal OC mineralization in sediments compared to soils suggest that lakes sediments are hotspots of OC sequestration. Increased sediment mineralization due to increase in temperature in epilimnetic sediments can significantly reduce OC burial in boreal lakes. An increase of temperature, as predicted for Northern latitudes, under different climate warming scenarios by the end of the twenty-first century, resulted in 4–27% decrease in lake sediment OC burial for the entire boreal zone.

Diss. (sammanfattning) Linköping : Univ., 2004. / Härtill 5 uppsatser.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2007. / Thesis documentation sheet inserted. Includes appendix of four papers and manuscripts, three co-authored with others. Includes bibliographical references. Also issued electronically via World Wide Web in PDF format; online version lacks appendix.

Lic.-avh. Umeå : Sveriges lantbruksUniversity. / Härtill 2 uppsatser.

The modern world faces a number of challenges related to energy and the environment. Atmospheric levels of carbon dioxide have now surpassed the 400 ppm mark due to the burning of fossil fuels, yet despite its abundance and potential use as a C1 feedstock for value-added products, there are both thermodynamic and kinetic barriers associated with the strong carbon-oxygen bonds that preclude its widespread deployment in industry. Nuclear energy is an alternative power source that reduces carbon emissions by billions of tonnes each year, but there are widespread concerns regarding the treatment of the radioactive waste that it accrues (of which the main component is uranyl, [UO2]2+). Most of the work presented in this thesis concerns the synthesis of transition-metal complexes, with the aim of directing catalytic reactivity to convert CO2 to useful products. Part of this thesis also concerns the synthesis of uranyl complexes and the study of uranyl reduction chemistry, which is relevant to uranyl remediation and nuclear waste treatment at a fundamental level. Making use of Earth-abundant metals to carry out hydrocarbon oxidation catalysis is a further focus of this work, as the efficient production of oxygenated compounds under mild conditions is of importance to the fine-chemical industry. Chapter 1 reviews important complexes reported in the literature that successfully convert CO2 to useful products through molecular, homogenous electro-catalysis and ring-opening copolymerisation catalysis. Reactions that exemplify a two-electron reduction of uranyl (i.e. uranium(VI) to uranium(IV)) are reviewed, along with uranyl complexes that undergo ligand-centred redox to give ligand-based radicals. The state of the literature on hydrocarbon oxidation catalysis is reviewed in the introduction. The development of multinuclear, macrocyclic complexes and the reactivity of dinuclear Pacman complexes are also presented. Chapter 2 reports the synthesis and characterisation of a new set of Schiff-base macrocycles and acyclic dipyrrin ligands. A number of attempted synthetic routes towards incorporating a dipyrrin coordination compartment in a macro-cyclic setting are discussed. Differences in electronic structures between dipyrromethanes and dipyrromethenes are also examined by theoretical and experimental methods. Chapter 3 introduces the coordination chemistry of these new macrocycles with zinc(II), where the isolation of dinuclear and tetranuclear complexes is demonstrated using different zinc(II) precursors. Tetranuclear zinc-alkyl complexes presented here are shown to be resistant to insertion chemistry with small molecules, but readily form zinc-oxo, -hydroxyl and -alkoxide clusters upon protonolysis with water and alcohols. These molecular clusters display reactivity towards CO2: a zinc-hydroxyl complex precipitates ZnCO3 at high temperature; and zinc-alkoxide complexes have been used to catalyse the copolymerisation reaction between CO2 and cyclohexene oxide to form polycarbonates. Chapter 4 describes the synthesis of late-transition-metal complexes of macrocyclic ligands and dipyrrins, and explores the relationship between macrocycle geometry and electronic structure. Their reactivities towards CO2 are assessed here, using cyclic voltammetry to assess the electro-catalytic activity of a number of the complexes. Chapter 5 reports the oxidation chemistry of hydrocarbon substrates catalysed by copper(II) complexes. High-temperature catalysis occurs with bimetallic copper(II) complexes, and this chapter describes how added FeCl3 acts as a co-catalyst, leading to greater catalyst stability and allowing the catalytic reaction to occur at room temperature. A range of analytical methods have been used to deduce the catalytically active species, and chemical kinetic measurements have been used to deduce a possible reaction mechanism. Chapter 6 reports the synthesis of a uranyl(VI) dipyrrin complex and details characterisation of its electronic structure by theoretical and experimental methods. Theoretical modelling has indicated that the observed two-electron reduction of uranium(VI) to uranium(IV) is facilitated by the dipyrrin ligand, representing a novel uranyl reduction mechanism.