The aim of this study is to assess the current situation of energy and carbon flows through the waste sector in Jämtland. An energy flow analysis is performed by balancing the inflows and outflows of the lower heating value and embodied energy. A carbon flow analysis was made on the same principles although with the carbon content and embodied CO2eq.  The results are showing that over a period of one year, 75 000 tons of waste flows through the waste sector in Jämtland. Approximately 60 % of all the waste is incinerated. The energy analysis shows that 970TJ flows through the waste sector every year. Household waste is the category with most energy consumption and emissions in total. However, other materials like metal and electronics have higher energy and carbon content per ton than the household category. The results of the analyses can further be implemented in the Sustainable Jämtland model and it can then be used as a base when making strategies for a sustainable waste treatment.

Dissolved oxygen concentrations are declining in the bottom waters of many lakes around the world, posing critical water quality concerns. Throughout my dissertation, I assessed how bottom-water dissolved oxygen may mediate the effects of climate and land use change on water quality in lakes. First, I characterized causes of variation in summer bottom-water temperature and dissolved oxygen. I demonstrated that spring air temperatures may play a greater role than summer air temperatures in shaping summer bottom-water dynamics. I then characterized the effects of declining bottom-water oxygen concentrations across diverse scales of analysis (i.e., using microcosm incubations, whole-ecosystem oxygenation experiments, and data analysis of >600 widespread lakes). I found that low dissolved oxygen concentrations contributed to release of nutrients and organic carbon from lake sediments, potentially altering the role of lakes in global biogeochemical cycles. Importantly, I also found support for a previously-hypothesized Anoxia Begets Anoxia feedback, whereby bottom-water anoxia (i.e., no dissolved oxygen) in a given year promotes increasingly severe occurrences of anoxia in following summers. This finding demonstrates the need for forecasts of future oxygen dynamics in lakes, as management actions to preempt the first occurrence of anoxia will be more effective than actions to restore ecological function after oxygen concentrations have already declined. To build the capacity for such forecasts, I led a systematic review of ecological forecasting literature that characterized the state of the field, emerging best practices, and relative predictability of four ecological variables. Combined, my dissertation provides a mechanistic examination of the effects of climate change on water quality in lakes worldwide, ultimately helping to anticipate, mitigate, and preempt future water quality declines. / Doctor of Philosophy / Changes in climate and land use have caused dissolved oxygen concentrations to decline in many lakes around the world. These declines are concerning because low oxygen concentrations can cause substantial water quality problems. If we could better predict future water quality, we may be able to develop more effective lake management programs. To help meet this need, I analyzed how dissolved oxygen has mediated historical changes in water quality, and how dissolved oxygen may affect water quality in the future. I focused on bottom-water (rather than surface-water) dissolved oxygen, because bottom waters are more likely to experience very low oxygen concentrations that can lead to water quality problems. I started by assessing the drivers of summer bottom-water dissolved oxygen in 615 lakes. Across these lakes, spring air temperatures played a greater role than summer air temperatures in shaping summer bottom-water temperature and dissolved oxygen. I then characterized the effects of declining bottom-water oxygen concentrations using small-scale incubations in the lab, manipulations of oxygen concentrations in a whole reservoir, and data analysis across 656 lakes. I found that low dissolved oxygen conditions led to the release of nutrients and organic carbon from lake sediments, which may worsen water quality. Importantly, I also found support for a feedback effect, whereby low bottom-water dissolved oxygen in one summer perpetuates oxygen declines in following summers. This finding motivates the need for forecasts of future dissolved oxygen concentrations, as management actions to stop the first occurrence of low oxygen concentrations will be more effective than actions to restore water quality after oxygen concentrations have already started to decline. To build capacity for lake oxygen forecasts, I synthesized many published papers that have predicted future ecological states, and I documented proposed best practices in this emerging field. Ultimately, by advancing our understanding of how climate and land use change affect water quality in lakes worldwide, my dissertation research will help to anticipate, mitigate, and preempt future water quality declines.

A ciclagem de matéria orgânica (MO) no ambiente marinho é um processo-chave para o ciclo global de carbono. Os sedimentos costeiros são de suma importância para a ciclagem de carbono pois atuam como receptores de grandes quantidades de MO alóctone (i.e. terrestre) e autóctone (i.e. marinho). A miríade dos componentes orgânicos e suas diferentes características dificultam o entendimento das fontes de MO em ambientes costeiros. Este trabalho visou entender a origem e a composição da MO (através de biomarcadores lipídicos) e a dinâmica da comunidade microbiana (método ATP) em sedimentos superficiais de diferentes ecossistemas marinhos da costa sudeste do Brasil: (i) margem continental de Cabo Frio; (ii) sistema lagunar de Saquarema; (iii) áreas costeiras e a plataforma continental de Ubatuba; (iv) e a plataforma adjacente ao estuário de Santos. Os resultados apontaram uma origem predominantemente autóctone para a MO nestes sistemas, com contribuição terrestre reduzida e limitada à áreas próximas à costa. Processos oceanográficos e forçantes ambientais são cruciais para a composição da MO sedimentar e são discutidas para cada um dos ecossistemas estudados. / The cycling of the organic matter (OM) in the marine environment is a key process in the global carbon cycle. Coastal sediments are important to the global carbon cycle, since they receive large inputs from both marine and terrestrial OM. The myriad of organic compounds and their spectrum of reactivity complicate the understanding of OM sources in coastal environments. In this work, we aimed to access the origin and composition of the OM (through lipid biomarkers) and the microbial dynamics (ATP method) in surface sediments of diverse marine ecosystems from the SE Brazilian coast: (i) the continental margin off Cabo Frio; (ii) the lagoonal system of Saquarema; (iii) coastal and shelf areas from Ubatuba; and (iv) the continental shelf adjacent to Santos estuary. The results showed a dominance of autochthonous OM, with a minor fraction of the OM derived from terrestrial sources and restricted to areas close to the coast. Oceanographic processes and environmental forces are crucial to the composition of sedimentary OM and are discussed for each of those ecosystems.

Les réchauffements climatiques associés aux activités anthropiques ont soumis les écosystèmes arctiques à des changements rapides qui menacent leur stabilité à court terme. La diminution dramatique de la banquise arctique est une des conséquences les plus concrètes de ce réchauffement. Dans ce contexte, comprendre et prédire comment les systèmes arctiques évolueront est crucial, surtout en considérant comment les flux de carbone (C) de ces écosystèmes - soit des puits nets, soit des sources nettes de CO2 pour l'atmosphère - pourraient avoir des répercussions importantes sur le climat. Le but de cette thèse est de dresser un portrait saisonnier de l’activité bactérienne afin de déterminer l’importance de sa contribution aux flux de carbone en Arctique. Plus spécifiquement, nous caractérisons pour la première fois la respiration et le recours à la photohétérotrophie chez les microorganismes du golfe d’Amundsen. Ces deux composantes du cycle du carbone demeurent peu décrites et souvent omises des modèles actuels, malgré leur rôle déterminant dans les flux de C non seulement de l’Arctique, mais des milieux marins en général. Dans un premier temps, nous caractérisons la respiration des communautés microbiennes (RC) des glaces de mer. La connaissance des taux de respiration est essentielle à l’estimation des flux de C, mais encore limitée pour les milieux polaires. En effet, les études précédentes dans le golfe d’Amundsen n’ont pas mesuré la RC. Par la mesure de la respiration dans les glaces, nos résultats montrent des taux élevés de respiration dans la glace, de 2 à 3 fois supérieurs à la colonne d'eau, et une production bactérienne jusqu’à 25 fois plus importante. Ces résultats démontrent que la respiration microbienne peut consommer une proportion significative de la production primaire (PP) des glaces et pourrait jouer un rôle important dans les flux biogéniques de CO2 entre les glaces de mer et l’atmosphère (Nguyen et Maranger, 2011). Dans un second temps, nous mesurons la respiration des communautés microbiennes pélagiques du golfe d’Amundsen pendant une période de 8 mois consécutif, incluant le couvert de glace hivernal. En mesurant directement la consommation d'O2, nous montrons une RC importante, mesurable tout au long de l’année et dépassant largement les apports en C de la production primaire. Globalement, la forte consommation de C par les communautés microbiennes suggère une forte dépendance sur recyclage interne de la PP locale. Ces observations ont des conséquences importantes sur notre compréhension du potentiel de séquestration de CO2 par les eaux de l’Océan Arctique (Nguyen et al. 2012). Dans un dernier temps, nous déterminons la dynamique saisonnière de présence (ADN) et d’expression (ARN) du gène de la protéorhodopsine (PR), impliqué dans la photohétérotrophie chez les communautés bactérienne. Le gène de la PR, en conjonction avec le chromophore rétinal, permet à certaines bactéries de capturer l’énergie lumineuse à des fins énergétiques ou sensorielles. Cet apport supplémentaire d’énergie pourrait contribuer à la survie et prolifération des communautés qui possèdent la protéorhodopsine. Bien que détectée dans plusieurs océans, notre étude est une des rares à dresser un portrait saisonnier de la distribution et de l’expression du gène en milieu marin. Nous montrons que le gène de la PR est présent toute l’année et distribué dans des communautés diversifiées. Étonnamment, l’expression du gène se poursuit en hiver, en absence de lumière, suggérant soit qu’elle ne dépend pas de la lumière, ou que des sources de photons très localisées justifie l’expression du gène à des fins sensorielles et de détection (Nguyen et al., soumis au journal ISME). Cette thèse contribue à la compréhension du cycle du C en Arctique et innove par la caractérisation de la respiration et de l’efficacité de croissance des communautés microbiennes pélagiques et des glaces de mer. De plus, nous montrons pour la première fois une expression soutenue de la protéorhodopsine en Arctique, qui pourrait moduler la consommation de C par la respiration et justifier son inclusion éventuelle dans les modélisations du cycle du C. Dans le contexte des changements climatiques, il est clair que l'importance de l’activité bactérienne a été sous-estimée et aura un impact important dans le bilan de C de l'Arctique. / Arctic ecosystems are undergoing rapid changes, primarily due to unprecedented climatic warming as a function of anthropogenic activities, which threaten their short-term stability. One of the most dramatic impacts has been the loss and change in annual sea ice. Understanding and predicting how these systems will evolve is crucial, especially if considering how carbon (C) fluxes from these ecosystems – either net sinks or net CO2 sources for the atmosphere – could have important repercussions on global climate. The objective of this thesis is to establish a seasonal portrait of bacterial activity to characterize its contribution to Arctic carbon fluxes. Specifically, we quantify for the first time microbial respiration in sea-ice and the water column and explore the use of photoheterotrophy by microorganism over an annual cycle in the Amundsen Gulf of the Arctic Ocean. These components of carbon cycling remain poorly understood and infrequently directly measured. As a consequence they are either extrapolated or omitted from models, despite their significant role in C dynamics not only in the Arctic, but also in marine systems in general. First, we characterise respiration in sea-ice microbial communities (CR). An understanding of respiration rates is essential for accurate estimation of C fluxes, but the role of respiration in sea ice is poorly understood. This work represents the first comprehensive evaluation of respiration in polar sea ice to date. Using novel O2 consumption measurements in sea-ice, we found high respiration rates in sea-ice, 2 to 3 times higher than in the water column and bacterial production rates up to 25 times higher. These results show that microbial respiration can consume a significant portion of sea ice primary production (PP) and play a key role in biogenic CO2 fluxes between sea-ice and the atmosphere (Nguyen and Maranger, 2011). Second, we measure respiration of pelagic microbial communities of Amundsen Gulf over an eight-month period, including under the winter ice-cover. By measuring directly O2 consumption, we show high CR, measurable over the whole year and greatly surpassing C inputs from PP. Globally, high C consumption by microbial communities supports a high reliance on internal recycling of local PP. These observations have important consequences on our understanding of the CO2 sequestering potential of the Arctic Ocean (Nguyen et al., 2012) Finally, we describe the seasonal patterns in presence (DNA) and expression (RNA) of the proteorhodospin (PR) gene, involved in bacterial photoheterotrophy. The PR gene, combined with the retinal chromophore, allows bacteria to capture energy from light towards energetic or sensory purposes. This additional energy source could contribute to the survival and proliferation of bacterial communities expressing the gene in the highly variable polar environment. Although PR has been found in many oceans, this study represents a unique time-series that follows the seasonal distribution and expression of the gene in a natural marine system. We show that the PR gene was present over the whole study period and widely distributed in diverse bacterial communities. Surprisingly, we observed continued PR expression over winter, in the absence of sunlight. This suggests either that the PR’s expression does not depend on light or, that other very localized photon sources could justify PR expression for detection and sensory functions (Nguyen et al., submitted to the ISME journal). This thesis contributes to the understanding of Arctic carbon cycling and includes several novel elements such as the characterization of respiration and bacteria growth efficiency in both pelagic and sea-ice habitats. The use of an alternative C pathway by bacteria in the Polar ocean was also explored for the first-time in a time-series. The observed sustained expression of the PR gene in the Arctic could modulate C consumption by respiration and justify its inclusion in future models of C cycling. In a context of climate change, it is clear that bacterial activity has been underestimated and how this will change in a warmer Arctic will have a significant impact in the ecosystem’s overall C budget.

The replacement of the native vegetation by pastures and silviculture can result in clear changes on the carbon and nitrogen pools, stocks and dynamics. We aimed to assess the impact of the woodland cerrado (cerradão) conversion into pastures and Eucalyptus plantations on the soil organic carbon (SOC) labile pools and dynamics, on the concentrations of N variables and on the potential for nitrogen mineralization (PMN) in the first 200 cm of the soil profile. We also assessed the seasonal variation on the overall variability in soil C and N pools and dynamics. Finally, we investigated the C and N stocks belowground (up to 50 cm depth) and C stocks aboveground. We had three sampling sites in a region originally covered by cerradão physiognomy. Each sampling included a control area (Cerrado) and two land uses (Pasture, Eucalyptus). Soil samples were taken at 0-10, 10-30, 30-50, 50-100 and 100-200 cm depths during the dry and wet climate seasons, from which we used the first three depths for stocks calculation. We also collected litter and herbs+shrubs biomass, and measured the tree biomass for C stocks calculation. Our results showed ~50% reduction of the microbial biomass (MBC) and MBC:SOC for pastures and Eucalyptus plantations, indicating lower SOC stability. Reduction in the dissolved organic carbon (DOC) and DOC:SOC, and increment on the metabolic quotient were also registered for both land uses along the soil profile up to 30 or 50 cm depth. Higher SBR and qCO2 rates are associated to a microbial community under stress. Land use effect on SOC labile pools and dynamics was more marked in the dry season. The inorganic forms of nitrogen (NH4-N and NO3-N) and PMN were significantly affected by land use conversion, with decreases in both land uses compared to native Cerrado, with lower values found in Eucalyptus. Urease activity also decreased with land conversion. The N variables all decreased with depth from 10 to 50 cm depth. Land conversion also resulted in C and N stock losses, and in redistribution among the system compartments. Pastures showed 53% less overall C stock, and Eucalyptus plantations had 20% more. Carbon was mostly stored belowground in pastures, and aboveground in Eucalyptus, as the native Cerrado showed a balanced distribution. Aboveground, C was 94% reduced in pastures compared to Cerrado, and 80% increased in Eucalyptus plantations; belowground, pastures had 19% and 25% reductions in the overall C and N stocks respectively, with significant decreases for the stocks of arboreal C, MBC, coarse root C and N, NO3-N and PMN. Eucalyptus plantations had 23% decrease in C and 19% in N stocks, with significant reductions in the stocks of herbs+shrubs C, MBC, fine and coarse root C, fine root N, NH4-N and PMN. Both land uses had similar overall losses of C and N belowground, which were evident until 50 cm depth, but higher at the 10-30 cm layer. Our results show negative impacts on carbon and nitrogen pools, cycling processes and stocks due to Cerrado conversion to pastures and Eucalyptus plantations / A substituição da vegetação nativa por pastagem e silvicultura pode resultar em mudanças nas concentrações, estoques e dinâmica do carbono e nitrogênio. O objetivo do trabalho foi analisar o impacto da conversão de cerradão em pastagens de braquiária e plantações de eucalipto na dinâmica e na concentração de variáveis da fração lábil do carbono orgânico do solo (SOC), nas concentrações das variáveis de nitrogênio e no seu potencial de mineralização (PMN), para os primeiros 200 cm de profundidade do solo. Foi ainda avaliada a variação sazonal na variabilidade das concentrações e dinâmicas de C e N no solo. Além disso, investigamos os estoques de C e N abaixo do solo (até 50 cm de profundidade) e os estoques de C acima do solo. Nossas amostragens foram realizadas em três áreas de pesquisa, numa região originalmente coberta por cerradão. Cada área de pesquisa era constituída por um sítio controle (Cerrado) e dois usos das terras (pastagem, eucalipto). Amostras de solo foram coletadas nas profundidades de 0-10, 10-30, 30-50, 50-100 e 100-200 cm durante as estações seca e chuvosa, para as análises das frações de C e N; para o cálculo dos estoques de C e N, foram utilizadas somente as três primeiras profundidades. Também coletamos serapilheira e biomassa de herbáceas + arbustos, assim como tiramos medidas das árvores para o cálculo do estoque de C acima do solo. Nossos resultados mostraram uma redução de aproximadamente 50% da biomassa microbiana (MBC) e da taxa MBC:SOC para pastagens e plantios de eucalipto, indicando menor estabilidade do carbono orgânico do solo. Também foram registrados decréscimos para o carbono orgânico dissolvido (DOC) e para as taxas DOC:SOC, além de aumentos para o quociente metabólico em ambos os usos, ao longo do perfil do solo até 30 ou 50 cm de profundidade. Taxas mais altas de respiração edáfica e do quociente metabólico estão associadas a uma comunidade microbiana sob estresse. O efeito do uso das terras nas concentrações e na dinâmica das variáveis lábeis do C orgânico do solo foi mais acentuado na estação seca. As formas inorgânicas de nitrogênio (NH4-N e NO3-N) e PMN foram significativamente afetados pela conversão do uso da terra, com decréscimos em ambos os usos em comparação ao Cerrado nativo, sendo menores os valores encontrados no Eucalipto. A atividade da urese também decresceu com a mudança de uso. Todas as variáveis de N diminuíram com a profundidade de 10 a 50 cm. A conversão de uso também resultou em perdas nos estoques de C e N e em sua redistribuição entre os compartimentos acima e abaixo do solo. O estoque total de C em pastagens reduziu em 53% e nas plantações de eucalipto ocorreu aumento de 20%. O carbono foi armazenado principalmente abaixo do solo em pastagens e acima do solo nos plantios de eucaliptos, enquanto que o Cerrado nativo apresentou uma distribuição equilibrada entre esses dois grandes compartimentos. Na pastagem, foi registrada uma redução de 94% no estoque da biomassa aérea, em comparação com o Cerrado, enquanto que as plantações de eucalipto apresentaram um aumento de 80%; abaixo do solo, as pastagens tiveram reduções de 19% e 25% nos estoques totais de C e N, respectivamente, com decréscimos significativos para o estoque C de árvores, de MBC, de C e N de raizes grossas, de NO3-N e de PMN. As plantações de eucalipto tiveram redução de 23% para o estoque total de C abaixo do solo e de 19% para o estoque de N (abaixo do solo), com reduções significativas para estoque C da biomassa de ervas + arbustos, de MBC, de C de raízes finas e grossas, bem como para os estoque de N de raízes finas, de NH4-N e de PMN. Ambos os usos da terra tiveram perdas totais semelhantes para os estoques de C e N abaixo do solo, que ficaram evidentes até 50 cm de profundidade, porém, mais significativos na camada de 10-30 cm. Nossos resultados demonstraram impactos negativos da conversão do cerrado em pastagens e plantações de eucalipto para as concentrações de carbono e nitrogênio, assim como em seus processos de ciclagem e estoques

A ciclagem de matéria orgânica (MO) no ambiente marinho é um processo-chave para o ciclo global de carbono. Os sedimentos costeiros são de suma importância para a ciclagem de carbono pois atuam como receptores de grandes quantidades de MO alóctone (i.e. terrestre) e autóctone (i.e. marinho). A miríade dos componentes orgânicos e suas diferentes características dificultam o entendimento das fontes de MO em ambientes costeiros. Este trabalho visou entender a origem e a composição da MO (através de biomarcadores lipídicos) e a dinâmica da comunidade microbiana (método ATP) em sedimentos superficiais de diferentes ecossistemas marinhos da costa sudeste do Brasil: (i) margem continental de Cabo Frio; (ii) sistema lagunar de Saquarema; (iii) áreas costeiras e a plataforma continental de Ubatuba; (iv) e a plataforma adjacente ao estuário de Santos. Os resultados apontaram uma origem predominantemente autóctone para a MO nestes sistemas, com contribuição terrestre reduzida e limitada à áreas próximas à costa. Processos oceanográficos e forçantes ambientais são cruciais para a composição da MO sedimentar e são discutidas para cada um dos ecossistemas estudados. / The cycling of the organic matter (OM) in the marine environment is a key process in the global carbon cycle. Coastal sediments are important to the global carbon cycle, since they receive large inputs from both marine and terrestrial OM. The myriad of organic compounds and their spectrum of reactivity complicate the understanding of OM sources in coastal environments. In this work, we aimed to access the origin and composition of the OM (through lipid biomarkers) and the microbial dynamics (ATP method) in surface sediments of diverse marine ecosystems from the SE Brazilian coast: (i) the continental margin off Cabo Frio; (ii) the lagoonal system of Saquarema; (iii) coastal and shelf areas from Ubatuba; and (iv) the continental shelf adjacent to Santos estuary. The results showed a dominance of autochthonous OM, with a minor fraction of the OM derived from terrestrial sources and restricted to areas close to the coast. Oceanographic processes and environmental forces are crucial to the composition of sedimentary OM and are discussed for each of those ecosystems.

In Australia, significant effort goes into reducing the amount of nitrogen and phosphorus entering inland waters from point sources. However, little is known of the extent to which riparian organic matter may act as a source of these nutrients. Also, whilst the relationships between the nitrogen, phosphorus and carbon cycles are broadly known, there is little quantitative data regarding the release of these elements from Australian riparian organic matter and their subsequent microbial mineralisation within aquatic environments. In particular, comparatively little is known of their comparative role in nutrient and organic matter cycling within anoxic zones, and the influence that different riparian organic matter may have on stream water quality. This lack of such data presently hampers the ability of water managers to make educated decisions regarding the management of riparian zones in Australia. In order to improve understanding in this area, a combination of laboratory and in situ experiments were carried out in order to compare the abiotic release and aerobic/ anaerobic mineralisation of leaf derived dissolved organic carbon (DOC), dissolved nitrate/nitrite (NOx) and soluble reactive phosphorus (SRP) under different environmental conditions. Four plants common to Australian riparian zones were investigated: two native species, Eucalyptus camaldulensis (gum) and Phragmites australis (common reed), and two exotic species, Salix babylonica (willow) and Lolium multiflorum (rye grass). After 30 days, formaldehyde inhibited 1g willow and rye grass extracts contained the most SRP (0.7 mg/L), whilst gum extracts contained 0.3 mg/L and common reed 0.1 mg/L of SRP.Willow and rye grass abiotically released twice as much NOx than gum and common reed, although concentrations were only between 0.05-0.1 mg/L. Gum and common reed released the most DOC per gram of leaf matter (14 and 12 mmol/g of leaf matter respectively), but based on the initial carbon content of each leaf type, the largest percentage contributor of DOC under abiotic conditions was common reed and rye grass (both 38% mass/mass), with gum (33% mass/mass) and willow (30% mass/mass) being smaller contributors. The most bioavailable DOC was released by rye grass and common reed, with between 83 and 94% of this DOC microbially mineralised after 30 days in oxic conditions. When conditions were not inhibited, microbial growth was evident almost immediately in willow, rye grass and common reed leaf extracts. However, microbial growth was suppressed for the first 48 hours in gum leaf extracts. After this suppression period, the rate of DOC mineralisation was equal in willow and gum leaf extracts (0.1 day-1). Under anoxic conditions, the rate and extent of DOC mineralisation of willow and gum leaves depended on the type of electron acceptor provided. Added nitrate and iron III enhanced the mineralisation of both willow and gum leaves relative to no terminal electron acceptors (from zero to 0.01-0.04 and 0.002- 0.004 moles/day respectively), but added sulphate only enhanced the mineralisation of gum leaves (0.04 moles/day). When no additional electron acceptors were provided, particulate leaf mineralisation was more extensive under oxic than anoxic conditions. However, the mineralisation of leaf derived DOC were the same regardless of oxygen availability, and after 35 days in either condition the percentage of leaf DOC mineralised for each leaf type was of the order common reed > rye grass > willow > gum. All the leaf types tested were able to sustain the caddis fly larvae Triplectides australis under controlled laboratory conditions, and survival rates were high using all four leaf types as a food source. Triplectides australis did not significantly increase the amount of DOC released from each type of leaf matter, but they did consistently increase the proportion of simple carbohydrates present within the DOC fraction. The results of these experiments suggest that changes to riparian vegetation, particularly from the native to exotic species used in this study, will inherently alter in-stream concentrations of dissolved carbon and nutrients (particularly SRP). This potentially will affect in-stream, hyporheic and subsurface processes, particularly in areas where surface water flow is low and riparian leaf inputs are high.

Anticipated increases in the frequency, duration or intensity of high temperature events ('heat waves') have the potential to significantly impact forest form and functioning, but these events remain virtually unstudied in forest ecosystems. This thesis presents the results of an event-driven research effort into the impacts of three days of record-setting high temperatures in late May 2010 on key ecophysiological parameters in Sugar Maple (Acer saccharum. Marsh). High temperatures reduced photosynthetic capacity by ~66% versus previous years and total end-of-season leaf litter production by ~33% versus prior measurements. It is predicted that these reductions substantially reduced productivity for Sugar Maple in 2010. These results constitute the first description of the impacts of a short-duration heat wave on productivity-related parameters in a temperate forest tree. The predicted increase in high temperature events could make such impacts a significant, though so far overlooked, pathway of climate change impacts on temperate forests.

Anticipated increases in the frequency, duration or intensity of high temperature events ('heat waves') have the potential to significantly impact forest form and functioning, but these events remain virtually unstudied in forest ecosystems. This thesis presents the results of an event-driven research effort into the impacts of three days of record-setting high temperatures in late May 2010 on key ecophysiological parameters in Sugar Maple (Acer saccharum. Marsh). High temperatures reduced photosynthetic capacity by ~66% versus previous years and total end-of-season leaf litter production by ~33% versus prior measurements. It is predicted that these reductions substantially reduced productivity for Sugar Maple in 2010. These results constitute the first description of the impacts of a short-duration heat wave on productivity-related parameters in a temperate forest tree. The predicted increase in high temperature events could make such impacts a significant, though so far overlooked, pathway of climate change impacts on temperate forests.

The presented thesis investigates the role of bryophytes in the deadwood and carbon (C) cycle of boreal black spruce forests in Labrador, Canada. All major forest C pools (live-tree, standing and downed deadwood, organic layer, mineral soil) were quantified for three old-growth, nine clearcut harvested, and three burned forest stands in order to characterize forest C dynamics of a high-latitude humid boreal forest ecosystem. Tree and aboveground deadwood C dynamics of Labrador black spruce forests were similar to those of drier or warmer boreal forests. However, due to bryophyte-driven processes such as woody debris (WD) burial and paludification, the studied forests contained high organic layer, mineral soil, and buried wood C stocks. The comprehensive field-measured data on C stocks was used to evaluate the CBM-CFS3, a Canadian national-scale C budget model, with respect to its applicability to Labrador black spruce and humid boreal forests elsewhere. After selected biomass estimation and deadwood decay parameters had been adjusted, the CBM-CFS3 represented measured live-tree and aboveground deadwood C dynamics well. The CBM-CFS3 was initially designed for well-drained upland forests and does not reflect processes associated with bryophytes and high forest floor moisture content, thus not capturing the large amounts of buried wood and mineral soil C observed in the studied forests. Suggestions are made for structural changes to the CBM-CFS3 and other forest ecosystem C models to more adequately represent the bryophyte-regulated accumulation of buried wood, organic layer, and mineral soil C. Accuracy of forest C models could be further improved by differentiating WD decomposition rates by disturbance history, because WD respiration reflects disturbance-induced changes in temperature and moisture regimes. In Labrador, WD respiration was limited by low WD moisture levels and high temperatures in burned stands, and by high WD moisture contents and low temperatures in old-growth stands. Following harvesting, residual vegetation prevents the desiccation of WD, resulting in significantly higher WD respiration compared to old-growth and burned stands. Moreover, the bryophyte layer recovers faster following harvest than following fire, which reduces WD desiccation due to moisture retention, water transfer, and moisture-induced cooling and results in higher WD decomposition rates. Bryophytes are thus a key driver of the deadwood and C cycle of humid boreal Labrador black spruce forests. The author recommends to classify these and similar boreal forests as a functional ecosystem group called “humid boreal forests”, preliminarily defined as “boreal forest ecosystems featuring a bryophyte-dominated ground vegetation layer associated with low soil temperatures, high moisture levels, low dead organic matter decomposition rates, and subsequently (in the absence of stand-replacing disturbances) an accumulation of buried wood embedded in a thick organic layer”. Bryophytes are also an integral component of many coniferous forests outside the boreal biome. Bryophyte-regulated processes such as WD burial or paludification are thus likely significant to the global C cycle. The potential climate change-induced release of large amounts of CO2 from buried wood and soil C pools necessitates an increased understanding of how bryophyte productivity and decomposition constraints will change with increasing temperature and varying moisture regimes. Ecosystems such as humid boreal forests with potentially high C losses to the atmosphere may thus be identified and counteractive forest management strategies can be developed and implemented. / Cette thèse de doctorat s’intéresse à l’influence qu’exercent les mousses sur les cycles du bois mort et du carbone (C) dans des pessières noires boréales humides du Labrador, Canada. Toutes les réservoirs majeurs de C (arbres vivants, bois mort sur pied et effondré, l’horizon de matière organique, sol minéral) de trois pessières vierges, neuf coupes à blanc et de trois pessières brûlées ont été quantifiés pour caractériser le cycle du C des forêts humides boréales du nord. Les dynamismes de C des arbres vivants et du bois mort supraterrestre ressemblaient à ceux des forêts boréales plus sèches ou aux températures plus chaudes. À cause des processus régulés par les mousses (l’enterrement du bois mort ou la paludification), les forêts étudiées contenaient des stocks élevés de C au sein de l’horizon de matière organique, le sol minéral et le bois enterré. Les données ont aussi été utilisées pour évaluer le MBC-SFC3, un modèle national canadien du bilan du C, concernant son applicabilité aux pessières boréales humides de Labrador et d’ailleurs. Suite à l’ajustement de quelques paramètres, p.ex. des taux de décomposition, le MBC-SFC3 reproduisait bien le dynamisme mesuré des arbres vivants et du bois mort supraterrestre. Le MBC-SFC3 a initialement été développé pour les sites bien drainés et ne considère pas les processus associés avec les mousses ou l’humidité élevée du sol. Conséquemment, le MBC-SFC3 ne représentait pas les stocks élevés de C mesurés pour le bois enterré et pour le sol. Les modifications structurelles du MBC-SFC3 et d’autres modèles du C forestier sont nécessaires pour représenter adéquatement l’accumulation du C au sein de ces réservoirs. La précision des modèles du C forestier pourrait encore être améliorée par une différenciation des taux de décomposition selon le régime de perturbations, parce que la respiration du bois mort reflète les changements de la température et d’humidité associés avec une perturbation spécifique. Dans les pessières brûlés du Labrador, la respiration du bois mort était limitée par a faible humidité du bois et des températures élevées; dans les pessières vierges, par l’humidité élevée du bois et des températures basses. Dans les coupes à blanc, la végétation résiduelle empêchait le dessèchement du bois mort. Il s’y ensuivit que la respiration du bois mort y est nettement plus élevée en comparaison avec des pessières brûlés ou vierges. La décomposition du bois mort après coupe à blanc est aussi favorisée par la récupération plus rapide de la couche de mousses, diminuant conséquemment le dessèchement du bois mort par la conservation d’humidité, les transports vertical et horizontale d’eau et le refroidissement induit par l’humidité. Ainsi, les mousses sont les facteurs clés dans les cycles du bois mort et du C des pessières noires boréales au Labrador. L’auteur préconise la classification de ces pessières et des forêts semblables comme un groupe fonctionnel d’écosystèmes nommé : « pessières boréales humides » ; provisoirement définies comme « des écosystèmes forestiers avec une végétation terrestre dominée par les mousses et par conséquent associée avec des températures basses du sol, une humidité élevée, des taux de décomposition faibles et (en l’absence de perturbations) l’accumulation du bois enterré dans des couches organiques epaisses ». En outre, les mousses sont des éléments principaux des nombreuses forêts résineuses n’appartenant pas au biome boréal. Les processus régulés par les mousses tels l’enterrement du bois mort ou la paludification sont probablement importants pour le cycle global de C. La libération potentielle de grandes quantités de CO2 des réservoirs « bois enterré » et « sol » à la suite des changements climatiques exige une meilleure compréhension des transformations de la productivité des mousses et des limitations de la décomposition dues aux températures plus élevées et au taux d’humidités variables. Ainsi, les écosystèmes aux pertes potentielles de C élevées (p.ex. les pessières boréales humides) peuvent être identifiés et des mesures d’aménagement antagonistes peuvent être développées et implémentées. Traduction assistée par : Karl-Heinrich von Bothmer, Géry van der Kelen / Die vorliegende Arbeit untersucht die Einflüsse von Moosen auf den Totholz- und Kohlenstoff-(C)-Kreislauf in borealen Schwarzfichtenwäldern in Labrador, Kanada. Um den C-Kreislauf dieses humiden borealen Waldökosystems zu charakterisieren, wurden alle bedeutenden C-Speicher (lebende Bäume, stehendes und liegendes Totholz, organische Auflage, Mineralboden) von drei Primärwald-, neun Kahlschlags- und drei Brandflächen quantifiziert. Die C-Dynamiken der Bäume und des oberiridischen Totholzes der Untersuchungsflächen ähnelten denen von trockeneren und/oder wärmeren borealen Wäldern, während die organische Auflage, der Mineralboden und das begrabene Totholz bedingt durch von Moosen regulierte Prozesse wie Totholzeinlagerung und Paludifizierung besonders hohe C-Vorräte aufwiesen. Mit dem umfangreichen C-Datensatz wurde das CBM-CFS3, das nationale kanadische C-Modell, am Beispiel Labradors im Hinblick auf seine Anwendbarkeit in humiden borealen Wäldern evaluiert. Nach Anpassung ausgewählter Parameter, z.B. der Totholzabbauraten, wurden die gemessenen C-Dynamiken der Bäume und des oberiridischen Totholzes vom Modell abgebildet. Das CBM-CFS3 wurde ursprünglich für staunässefreie, terrestrische Waldstandorte entwickelt und berücksichtigt keine mit Moosen oder hoher Bodenfeuchte assoziierten Prozesse, so dass es die hohen C-Vorräte des begrabenen Totholzes und des Bodens nicht widerspiegelte. Eine adäquate Abbildung der Akkumulation von C in diesen Speichern erfordert strukturelle Änderungen des CBM-CFS3 und anderer Wald-C-Modelle. Die Genauigkeit von Wald-C-Modellen könnte darüber hinaus durch eine Differenzierung der Totholzabbauraten in Abhängigkeit vom Störungsregime verbessert werden, da störungsspezifische Veränderungen von Temperatur und Feuchte von der Totholzatmung widergespiegelt werden. Im Untersuchungsgebiet limitierten geringe Holzfeuchten und hohe Holztemperaturen die Totholzatmung auf Brandflächen. In Primärwäldern wirkten dagegen hohe Holzfeuchten und geringe Holztemperaturen hemmend. Auf Kahlschlägen verhinderte die verbleibende Vegetation die Austrockung des Totholzes, was zu signifikant erhöhten Atmungsraten im Vergleich zu Brand- und Primärwaldflächen führte. Zudem wird der Totholzabbau auf Kahlschlen durch eine schnellere Erholung der Moosdecke als auf Brandflächen gefördert, da Moose durch ihr hohes Wasserspeichervermögen, vertikalen und horizontalen Wassertransport und feuchte-induzierte Kühlung der Austrockung des Totholzes entgegenwirken. Moose sind somit ein Schlüsselfaktor im Totholz- und C-Kreislauf der humiden borealen Schwarzfichtenwälder Labradors. Die Autorin empfiehlt die Klassifikation dieser und ähnlicher borealer Wälder als eine funktionelle Ökosystemgruppe namens “humid boreal forests”; vorläufig definiert als “boreale Waldökosysteme mit durch Moose dominierter Bodenvegetation und damit assoziierten niedrigen Bodentemperaturen, hohen Bodenfeuchten, geringen Abbauraten und (in Abwesenheit großflächiger Störungen) der Akkumulation von begrabenem Totholz in mächtigen organischen Auflagen”. Auch außerhalb des borealen Bioms sind Moose ein wesentlicher Bestandteil vieler Nadelwälder. Durch Moose regulierte Prozesse wie Totholzeinlagerung und Paludifizierung sind daher wahrscheinlich relevant für den globalen C-Kreislauf. Die durch den Klimawandel bedingte potentielle Freisetzung von großen Mengen CO2 aus begrabenem Totholz und dem Boden macht ein besseres Verständnis der zu erwartenden Veränderungen von Mooswachstum und Abbauhemmnissen als Folge erhöhter Temperaturen und variabler Feuchteverhältnisse erforderlich. Somit können Ökosysteme mit potentiell hohen C-Verlusten, wie z.B. humide boreale Wälder, identifiziert und diesen entgegenwirkende Bewirtschaftungsmaßnahmen entwickelt und umgesetzt werden.