Dryland ecosystems provide a unique opportunity to study the effects of water limitation on ecosystem activity. The sensitivity of these systems to small inputs of moisture is well-documented, but the expression of water limitation in terms of carbon dioxide flux between the ecosystem and atmosphere remains unclear. Applying a simple conceptual approach to soil moisture dynamics, patterns in carbon flux become clear. Release of carbon dioxide via respiration is primarily driven by moisture in the shallow soil, and differences in respiration rates among plant functional types are only evident after controlling for soil moisture. Alternatively, carbon uptake by a semiarid shrubs ecosystem is largely driven by the availability of deep soil moisture. This link to deep soil moisture improves spatial scaling of gross and net carbon uptake using remote sensing data. Lateral redistribution of moisture on the landscape connects readily observed physical features, namely topography, to ecosystem function, but redistribution is generally not considered in carbon models. A simple runoff scheme coupled to a conceptual model for carbon flux demonstrates the high degree of spatial heterogeneity in carbon dioxide flux resulting from moisture redistribution. The importance of redistribution in carbon modeling is highlighted by interannual variability in modeled carbon fluxes under different rainfall characteristics (event size, event duration, interstorm duration). The links between hydrology and ecology across spatial scales become clearer when topographically-based moisture distribution is used as an organizing variable. In all, this research identifies new avenues for research where moisture dynamics are of central interest in dryland ecohydrology.

Studying the effects of extreme conditions, such as high temperatures and low humidity, on soil properties is important to various disciplines, including geotechnical engineering, soil science, waste management, crop management, and ceramics. The goal of this research is to investigate the effect of environmental and geometrical factors on microstructure, desiccation cracking, and CO2 flux in clays. The objectives of this research are threefold. (1) Understand the effects of temperature on the microstructure of clay soils; (2) develop a standardized procedure for studying desiccation cracking in a laboratory setting with reliable and repeatable results; and (3) develop an environmental chamber capable of monitoring CO2 flux through a soil sample large enough to accommodate a fully developed crack network. To accomplish these objectives, an array of laboratory testing was conducted. First, this study examines the effects of extreme temperatures on the microstructural properties of clay using FESEM, cation-exchange capacity (CEC) tests, thermal gravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) surface area analyzer. Second, a standardized procedure for producing accurate and repeatable laboratory tests on the desiccation cracking of soils is presented. The procedure includes specifications for sample collection, material preparation and characterization (including microstructural properties), and the determination of a representative elemental area (REA) for a fully developed crack network. Finally, a new climatic chamber capable of controlling temperature and relative humidity is designed and tested. The chamber can monitor CO2 flux through a fully developed crack network, enabling fundamental research on the relationship between desiccation cracking and the oxidation of soil organic carbon. The key findings indicate a dependency of soil microstructure on temperature changes. CEC and BET surface area significantly decrease with temperatures beyond 100ºC, indicating a relationship that needs further study. Additionally, compacted and slurry cracking behavior was found to be sensitive to boundary geometry and sample thickness. A REA was identified for each slurry sample thickness. The procedures of this research can be repeated for other soil types and used to connect existing and future research to improve understanding of desiccation cracking behavior, and to study the effects of desiccation cracking on other important geo-environmental phenomena.

This thesis deals with the estimation of plant-atmosphere trace gas exchange and isotopic discrimination from atmospheric concentration measurements. Two space scales were investigated: canopy and regional. The canopy-scale study combined a Lagrangian model of turbulent dispersal with ecophysiological principles to infer vertical profiles of fluxes of CO2, H2O and heat as well as carbon and oxygen isotope discrimination during CO2 assimilation, from concentration measurements within a forest. The regional-scale model used a convective boundary layer budget approach to infer average regional isotopic discrimination and fluxes of CO2 and sensible and latent heat from the evolution during the day of boundary layer height and mean concentrations of CO2 and H2O, temperature and carbon and oxygen isotope composition of CO2. For the canopy study, concentrations of five scalar quantities, CO2, 13CO2, C18O16O, H2O and temperature, were measured at up to nine heights within and above a mixed fir and spruce forest in central Siberia over several days just after snow melt in May 2000. Eddy covariance measurements of CO2, H2O and heat fluxes were made above the canopy over the same period, providing independent verification of the model flux estimates. Photosynthesis, transpiration, heat exchange and isotope discrimination during CO2 assimilation were modelled for sun and shade leaves throughout the canopy through a combination of inversion of the concentration data and principles of biochemistry, plant physiology and energy balance. In contrast to the more usual inverse modelling concept where fluxes are inferred directly from concentrations, in this study the inversion was used to predict unknown parameters within a process-based model of leaf gas and energy exchange. Parameters relating to photosynthetic capacity, stomatal conductance, radiation penetration and turbulence structure were optimised by the inversion to provide the best fit of modelled to measured concentration profiles of the five scalars. Model results showed that carbon isotope discrimination, stomatal conductance and intercellular CO2 concentration were depressed due to the low temperatures experienced during snow melt, oxygen isotope discrimination was positive and consistent with other estimates, radiation penetrated further than simple theoretical predictions because of leaf clumping and penumbra, the turbulence coherence was lower than expected and stability effects were important in the morning and evening. For the regional study, five flights were undertaken over two days in and above the convective boundary layer above a heterogeneous pine forest and bog region in central Siberia. Vertical profiles of CO2 and H2O concentrations, temperature and pressure were obtained during each flight. Air flask samples were taken at various heights for carbon and oxygen isotopic analysis of CO2. Two budget methods were used to estimate regional surface fluxes of CO2 and plant isotopic discrimination against 13CO2 and C18O16O, with the first method also used to infer regional sensible and latent heat fluxes. Flux estimates were compared to ground-based eddy covariance measurements. Model results showed that afternoon estimates for carbon and oxygen isotope discrimination were close to those expected from source water isotopic measurements and theory of isotope discrimination. Estimates for oxygen isotope discrimination for the morning period were considerably different and could be explained by contrasting influences of the two different ecosystem types and non-steady state evaporative enrichment of leaf water.

<p><strong><p>Studie av koldioxidgradienter i havets ytskikt</p><p>Sofia Söderholm</p></strong></p><p>Denna studie bygger på ett nyligen utvecklat instrument som har mätt koldioxidkoncentrationer på tre olika djup i vattnet samt en nivå i luften. Då detta instrument var oprövat i vatten har en utvärdering av mätmetodens lämplighet för vattenmätningar utförts. Syftet med mätningarna var att undersöka ytvattnets vertikala koldioxidgradient för att med hjälp av denna kunna beskriva flödet av koldioxid mellan hav och atmosfär bättre. Detta flöde är en viktig del av den globala kolcykeln och en djupare förståelse för koldioxidflödets beteende kan i framtiden bidra till mer noggranna klimatprognoser. Hur de beräknade flödena från profilinstrumentet påverkas av temperaturgradienterna i vattnets ytskikt har även det studerats. Mätningarna utfördes i vattnet utanför mätstationen på Östergarnsholm, öster om Gotland. En del av studien fokuserar på de horisontella koldioxidgradienterna i ytvattnet som erhållits genom fartygsdata.</p><p>Instrumentet som har använts vid mätningarna bygger på hydrofoba, luftgenomträngliga membran och förefaller fungera mycket väl i vatten. Vid vindhastigheter som inte är högre än 3 - 4 m/s kan tydliga koldioxidgradienter i vattnets ytskikt ses, men detta samband behöver verifieras med en större mängd mätdata. Temperaturgradienten i vattnets ytskikt har ingen större påverkan på vare sig koldioxidgradienten eller flödet av koldioxid och dess effekt kan försummas i detta fall. De horisontella koldioxidgradienterna påverkas huvudsakligen av temperaturen, den biologiska aktiviteten samt transport av vattenmassor. På en större skala kan tydliga effekter av temperaturen på koldioxidhalterna ses och på en mindre skala samt nära kuster och under våren är den biologiska aktiviteten dominerande.</p><p><em><p>Nyckelord: Koldioxidgradient, koldioxidflöde, temperaturgradient, hydrofoba luftgenomträngliga membran, transferhastighet, vindhastighet, biologisk aktivitet.</p></em></p> / <p><strong><p>A study regarding the carbon dioxide gradients in the surface water.</p><p>Sofia Söderholm</p></strong></p><p>This study is based on a recently developed instrument that measures the concentration of carbon dioxide at three different depths in the water and one level in the air. Since this instrument has not previously been used for measurements in water, an evaluation regarding the usefulness of the instruments for measurements in water was made. The purpose of the measurements was to study the vertical gradient of carbon dioxide in the surface water and to describe the vertical flux of carbon dioxide between the ocean and the atmosphere in an improved way. This flux is an important part of the global carbon cycle and a deeper understanding of the behavior of the air-sea exchange of carbon dioxide could contribute to more accurate forecasts of the future climate. The impact on the calculated carbon dioxide flux by the temperature gradients in the surface waters was also analyzed. The measurements were performed in the waters outside of the island of Östergarnsholm, east of Gotland. Part of the study focuses on the horizontal carbon dioxide in the surface water, which was obtained by ship data.</p><p>The instrument used when performing the measurements is based on hydrophobic, air-permeable membranes and appears to function very well in water. During wind speeds below 3 - 4 m/s distinct carbon dioxide gradients can be seen for the investigated data, but more data is needed to quantify this gradient for different situations. The temperature gradient in the surface water doesn't have a significant effect on the carbon dioxide gradient or the flow of carbon dioxide, and the effect of the temperature gradient can in this particular case be neglected. The horizontal gradients of carbon dioxide are mainly affected by temperature, biological activity and transportation of water mass. On a larger scale the effects of temperature on the concentrations of carbon dioxide are visible and on a smaller scale along with the coastal areas and during springtime, the biological activity is the dominating influence.</p><p><em><p>Keywords: Carbon dioxide gradient, carbon dioxide flux, temperature gradient, hydrophobic airpermeable membranes , transfer velocity, wind speeds, biological activity.</p></em></p>

Studie av koldioxidgradienter i havets ytskikt Sofia Söderholm Denna studie bygger på ett nyligen utvecklat instrument som har mätt koldioxidkoncentrationer på tre olika djup i vattnet samt en nivå i luften. Då detta instrument var oprövat i vatten har en utvärdering av mätmetodens lämplighet för vattenmätningar utförts. Syftet med mätningarna var att undersöka ytvattnets vertikala koldioxidgradient för att med hjälp av denna kunna beskriva flödet av koldioxid mellan hav och atmosfär bättre. Detta flöde är en viktig del av den globala kolcykeln och en djupare förståelse för koldioxidflödets beteende kan i framtiden bidra till mer noggranna klimatprognoser. Hur de beräknade flödena från profilinstrumentet påverkas av temperaturgradienterna i vattnets ytskikt har även det studerats. Mätningarna utfördes i vattnet utanför mätstationen på Östergarnsholm, öster om Gotland. En del av studien fokuserar på de horisontella koldioxidgradienterna i ytvattnet som erhållits genom fartygsdata. Instrumentet som har använts vid mätningarna bygger på hydrofoba, luftgenomträngliga membran och förefaller fungera mycket väl i vatten. Vid vindhastigheter som inte är högre än 3 - 4 m/s kan tydliga koldioxidgradienter i vattnets ytskikt ses, men detta samband behöver verifieras med en större mängd mätdata. Temperaturgradienten i vattnets ytskikt har ingen större påverkan på vare sig koldioxidgradienten eller flödet av koldioxid och dess effekt kan försummas i detta fall. De horisontella koldioxidgradienterna påverkas huvudsakligen av temperaturen, den biologiska aktiviteten samt transport av vattenmassor. På en större skala kan tydliga effekter av temperaturen på koldioxidhalterna ses och på en mindre skala samt nära kuster och under våren är den biologiska aktiviteten dominerande. Nyckelord: Koldioxidgradient, koldioxidflöde, temperaturgradient, hydrofoba luftgenomträngliga membran, transferhastighet, vindhastighet, biologisk aktivitet. / A study regarding the carbon dioxide gradients in the surface water. Sofia Söderholm This study is based on a recently developed instrument that measures the concentration of carbon dioxide at three different depths in the water and one level in the air. Since this instrument has not previously been used for measurements in water, an evaluation regarding the usefulness of the instruments for measurements in water was made. The purpose of the measurements was to study the vertical gradient of carbon dioxide in the surface water and to describe the vertical flux of carbon dioxide between the ocean and the atmosphere in an improved way. This flux is an important part of the global carbon cycle and a deeper understanding of the behavior of the air-sea exchange of carbon dioxide could contribute to more accurate forecasts of the future climate. The impact on the calculated carbon dioxide flux by the temperature gradients in the surface waters was also analyzed. The measurements were performed in the waters outside of the island of Östergarnsholm, east of Gotland. Part of the study focuses on the horizontal carbon dioxide in the surface water, which was obtained by ship data. The instrument used when performing the measurements is based on hydrophobic, air-permeable membranes and appears to function very well in water. During wind speeds below 3 - 4 m/s distinct carbon dioxide gradients can be seen for the investigated data, but more data is needed to quantify this gradient for different situations. The temperature gradient in the surface water doesn't have a significant effect on the carbon dioxide gradient or the flow of carbon dioxide, and the effect of the temperature gradient can in this particular case be neglected. The horizontal gradients of carbon dioxide are mainly affected by temperature, biological activity and transportation of water mass. On a larger scale the effects of temperature on the concentrations of carbon dioxide are visible and on a smaller scale along with the coastal areas and during springtime, the biological activity is the dominating influence. Keywords: Carbon dioxide gradient, carbon dioxide flux, temperature gradient, hydrophobic airpermeable membranes , transfer velocity, wind speeds, biological activity.

Os aterros de disposição de resíduos sólidos urbanos são equipamentos que, necessariamente, devem ser integrados ao sistema de saneamento e proteção à saúde pública das municipalidades. Independentemente se bem planejados, construídos e operados, os mesmos oferecem impactos ambientais aos locais onde estão implantados e ao seu entorno. Os referidos aterros são fontes de emissão antropogênica de gases indutores do efeito estufa global, como o metano (\'CH IND.4\') e o dióxido de carbono (\'CO IND.2\'). O presente trabalho teve por objetivo medir, estimativamente, in situ, a contribuição destes equipamentos no fluxo destes gases na natureza. Para isso, foram desenvolvidas duas campanhas em oito aterros de municípios do estado de São Paulo (Brasil) nos anos de 2006 e 2007. Foram medidas a concentrações de \'CH IND.4\' e \'CO IND.2\' no ar ambiente dos aterros, a emissão solo-ar e o fluxo a partir dos dissipadores verticais, quando presentes. As amostras coletadas do GAS foram analisadas por cromatografia gasosa. Os resultados evidenciaram que as concentrações de \'CH IND.4\' e \'CO IND.2\' na atmosfera dos aterros foram de 18.000 ppm e 5.500 ppm, respectivamente. Estes valores corresponderam a dez mil vezes e quinze vezes maiores que aquelas medidas em locais distantes dos aterros (background). Os resultados das medidas do fluxo solo-ar apontaram para uma grande variabilidade desta emissão, entre os sítios da coleta, entre os aterros e entre as campanhas. As taxas médias de emissão solo-ar variaram de 5,66 g/\'M POT.2\'.d a 148,20 g/\'M POT.2\'.d para \'CH IND.4\' e de 17,78 g/\'M POT.2\'.d a 223,04 g/\'M POT.2\'.d para \'CO IND.2\'. A emissão estimada solo-ar para os aterros variou de 276,82 a 75.730,20 toneladas por ano de \'CH IND.4\' e de 501,02 a 76.312,74 toneladas por ano para o \'CO IND.2\'. A emissão estimada para os aterros a partir dos dissipadores verticais variou de 73,52 a 307,31 toneladas para \'CH IND.4\' e de 165,83 a 692,32 toneladas por ano para o \'CO IND.2\'. Os resultados também evidenciaram que a concentração dos gases no ar ambiente dos aterros e a emissão solo-ar, especialmente, pareceram independer da operação dispensada: caso aterros sanitários, controlados ou lixões. Todos apresentaram muitas semelhanças no processo de emissão. Mesmo a presença do sistema de sucção do GAS para alimentar a usina termoelétrica (UTEB) no aterro Bandeirantes, São Paulo, Capital, não o diferenciou dos demais. De modo geral, não foi possível correlacionar variáveis que apontassem para tendências gerais na emissão destes sistemas de disposição de RSU. Com base nos resultados supracitados, este trabalho sugere futuras perspectivas de pesquisas. / Urban solid waste disposal landfills are equipments that must be integrated with the drainage and protection of the public health of municipalities system. Regardless of whether they are well planned, built and operated, they offer environmental impacts to the areas where they are deployed and their surroundings. The present work aimed at measuring, as estimates, in situ, the contribution of the aforementioned equipments in the flux of these gases in nature. The research was developed in 2006 and 2007 in two campaigns in eight municipal solid waste landfills in the state of São Paulo, Brazil. Concentrations of \'CH IND.4\' and \'CO IND.2\' were measured in the air from landfills; the ground-air emission and the flux from vertical drains, when present. The samples collected of the GAS were analyzed utilizing gas chromatography. The results showed that the concentrations of \'CH IND.4\' and \'CO IND.2\' in the atmosphere from landfills were 18,000 ppm and 5,500 ppm, respectively. These values correspond to ten thousand and fifteen times greater than those measured on places far away from landfills (background). The results of the ground-air flux indicated a great variability of this emission, not only among the collection sites, but also among the landfills and between the campaigns. The average ground-air emission ranged from 5.66 g/\'M POT.2\'.d to 148.20 g/\'M POT.2\'.d for \'CH IND.4\' and from 17.78 g/\'M POT.2\'.d to 223,04 g/\'M POT.2\'.d for \'CO IND.2\'. The estimated ground-air emission for the landfills ranged from 276.82 to 75,730.20 tons per year of \'CH IND.4\' and from 501.02 to 76,312.74 tons per year for \'CO IND.2\'. The estimated emission for the landfills from the vertical drains ranged from 73.52 to 307.31 tons per year for \'CH IND.4\' and from 165.83 to 692.32 tons per year for \'CO IND.2\'. The results also showed that concentration of gases in the environment air of landfills and the emission, especially ground-air, seems to be independent of the operation given: whether it is sanitary landfill, controlled landfill, or dump. They all presented many similarities in the emission process, and major differences among them were not elucidated. Even the presence of the suction system of the GAS to feed the thermoelectric plant (UTEB) at the Bandeirantes landfill, located at the capital of São Paulo, did not differentiate it from the other landfills from the \'CH IND.4\' and \'CO IND.2\' emission perspective. In a nutshell, it was not possible to correlate variables that pointed to general trends in the emissions of these USW disposal equipments. Based on these results, future prospects for research are suggested.

Os aterros de disposição de resíduos sólidos urbanos são equipamentos que, necessariamente, devem ser integrados ao sistema de saneamento e proteção à saúde pública das municipalidades. Independentemente se bem planejados, construídos e operados, os mesmos oferecem impactos ambientais aos locais onde estão implantados e ao seu entorno. Os referidos aterros são fontes de emissão antropogênica de gases indutores do efeito estufa global, como o metano (\'CH IND.4\') e o dióxido de carbono (\'CO IND.2\'). O presente trabalho teve por objetivo medir, estimativamente, in situ, a contribuição destes equipamentos no fluxo destes gases na natureza. Para isso, foram desenvolvidas duas campanhas em oito aterros de municípios do estado de São Paulo (Brasil) nos anos de 2006 e 2007. Foram medidas a concentrações de \'CH IND.4\' e \'CO IND.2\' no ar ambiente dos aterros, a emissão solo-ar e o fluxo a partir dos dissipadores verticais, quando presentes. As amostras coletadas do GAS foram analisadas por cromatografia gasosa. Os resultados evidenciaram que as concentrações de \'CH IND.4\' e \'CO IND.2\' na atmosfera dos aterros foram de 18.000 ppm e 5.500 ppm, respectivamente. Estes valores corresponderam a dez mil vezes e quinze vezes maiores que aquelas medidas em locais distantes dos aterros (background). Os resultados das medidas do fluxo solo-ar apontaram para uma grande variabilidade desta emissão, entre os sítios da coleta, entre os aterros e entre as campanhas. As taxas médias de emissão solo-ar variaram de 5,66 g/\'M POT.2\'.d a 148,20 g/\'M POT.2\'.d para \'CH IND.4\' e de 17,78 g/\'M POT.2\'.d a 223,04 g/\'M POT.2\'.d para \'CO IND.2\'. A emissão estimada solo-ar para os aterros variou de 276,82 a 75.730,20 toneladas por ano de \'CH IND.4\' e de 501,02 a 76.312,74 toneladas por ano para o \'CO IND.2\'. A emissão estimada para os aterros a partir dos dissipadores verticais variou de 73,52 a 307,31 toneladas para \'CH IND.4\' e de 165,83 a 692,32 toneladas por ano para o \'CO IND.2\'. Os resultados também evidenciaram que a concentração dos gases no ar ambiente dos aterros e a emissão solo-ar, especialmente, pareceram independer da operação dispensada: caso aterros sanitários, controlados ou lixões. Todos apresentaram muitas semelhanças no processo de emissão. Mesmo a presença do sistema de sucção do GAS para alimentar a usina termoelétrica (UTEB) no aterro Bandeirantes, São Paulo, Capital, não o diferenciou dos demais. De modo geral, não foi possível correlacionar variáveis que apontassem para tendências gerais na emissão destes sistemas de disposição de RSU. Com base nos resultados supracitados, este trabalho sugere futuras perspectivas de pesquisas. / Urban solid waste disposal landfills are equipments that must be integrated with the drainage and protection of the public health of municipalities system. Regardless of whether they are well planned, built and operated, they offer environmental impacts to the areas where they are deployed and their surroundings. The present work aimed at measuring, as estimates, in situ, the contribution of the aforementioned equipments in the flux of these gases in nature. The research was developed in 2006 and 2007 in two campaigns in eight municipal solid waste landfills in the state of São Paulo, Brazil. Concentrations of \'CH IND.4\' and \'CO IND.2\' were measured in the air from landfills; the ground-air emission and the flux from vertical drains, when present. The samples collected of the GAS were analyzed utilizing gas chromatography. The results showed that the concentrations of \'CH IND.4\' and \'CO IND.2\' in the atmosphere from landfills were 18,000 ppm and 5,500 ppm, respectively. These values correspond to ten thousand and fifteen times greater than those measured on places far away from landfills (background). The results of the ground-air flux indicated a great variability of this emission, not only among the collection sites, but also among the landfills and between the campaigns. The average ground-air emission ranged from 5.66 g/\'M POT.2\'.d to 148.20 g/\'M POT.2\'.d for \'CH IND.4\' and from 17.78 g/\'M POT.2\'.d to 223,04 g/\'M POT.2\'.d for \'CO IND.2\'. The estimated ground-air emission for the landfills ranged from 276.82 to 75,730.20 tons per year of \'CH IND.4\' and from 501.02 to 76,312.74 tons per year for \'CO IND.2\'. The estimated emission for the landfills from the vertical drains ranged from 73.52 to 307.31 tons per year for \'CH IND.4\' and from 165.83 to 692.32 tons per year for \'CO IND.2\'. The results also showed that concentration of gases in the environment air of landfills and the emission, especially ground-air, seems to be independent of the operation given: whether it is sanitary landfill, controlled landfill, or dump. They all presented many similarities in the emission process, and major differences among them were not elucidated. Even the presence of the suction system of the GAS to feed the thermoelectric plant (UTEB) at the Bandeirantes landfill, located at the capital of São Paulo, did not differentiate it from the other landfills from the \'CH IND.4\' and \'CO IND.2\' emission perspective. In a nutshell, it was not possible to correlate variables that pointed to general trends in the emissions of these USW disposal equipments. Based on these results, future prospects for research are suggested.