<p>Soils of Northern Hemisphere forests contain a large part of the global terrestrial carbon (C) pool. Even small changes in this pool can have large impact on atmospheric [CO2] and the global climate. Soil respiration is the largest terrestrial C flux to the atmosphere and can be divided into autotrophic (from roots, mycorrhizal hyphae and associated microbes) and heterotrophic (from decomposers of organic material) respiration. It is therefore crucial to establish how the two components will respond to changing environmental factors. In this thesis I studied the effect of elevated atmospheric [CO2] (+340 ppm, ¹³C-depleted) and elevated air temperature (2.8-3.5 oC) on soil respiration in a whole-tree chamber (WTC) experiment conducted in a boreal Norway spruce forest. In another spruce forest I used multivariate modelling to establish the link between day-to-day variations in soil respiration rates and its δ¹³C, and above and below ground abiotic conditions. In both forests, variation in δ¹³C was used as a marker for autotrophic respiration. A trenching experiment was conducted in the latter forest in order to separate the two components of soil respiration. The potential problems associated with the trenching, increased root decomposition and changed soil moisture conditions were handled by empirical modelling. The WTC experiment showed that elevated [CO2] but not temperature resulted in 48 to 62% increased soil respiration rates. The CO2-induced increase was in absolute numbers relatively insensitive to seasonal changes in soil temperature and data on δ¹³C suggest it mostly resulted from increased autotrophic respiration. From the multivariate modelling we observed a strong link between weather (air temperature and vapour pressure deficit) and the day-to-day variation of soil respiration rate and its δ¹³C. However, the tightness of the link was dependent on good weather for up to a week before the respiration sampling. Changes in soil respiration rates showed a lag to weather conditions of 2-4 days, which was 1-3 days shorter than for the δ¹³C signal. We hypothesised to be due to pressure concentration waves moving in the phloem at higher rates than the solute itself (i.e., the δ¹³C–label). Results from the empirical modelling in the trenching experiment show that autotrophic respiration contributed to about 50% of total soil respiration, had a great day-to-day variation and was correlated to total soil respiration while not to soil temperature or soil moisture. Over the first five months after the trenching, an estimated 45% of respiration from the trenched plots was an artefact of the treatment. Of this, 29% was a water difference effect and 16% resulted from root decomposition. In conclusion, elevated [CO2] caused an increased C flux to the roots but this C was rapidly respired and has probably not caused changes in the C stored in root biomass or in soil organic matter in this N-limited forest. Autotrophic respiration seems to be strongly influenced by the availability of newly produced substrates and rather insensitive to changes in soil temperature. Root trenching artefacts can be compensated for by empirical modelling, an alternative to the sequential root harvesting technique.</p>

Thesis (Ph.D. (Nutrition))--North-West University, Potchefstroom Campus, 2007.

Systeme von Vorlandbecken repräsentieren bedeutende geologische Archive und dienen dem Verständnis von Rückkopplungen zwischen oberflächennahen und tektonischen Prozessen. Außerdem dokumentieren sie die Entwicklung unmittelbar angrenzender Bergketten. Die sedimentären Abfolgen in Vorlandbecken reflektieren das Gleichgewicht zwischen tektonischer Subsidenz, der Bildung langzeitlichen Akkommodationsraumes und des Sedimenteintrages, welcher wiederum die Wirksamkeit von Erosions- und Massenneuverteilungsprozessen wiederspiegelt. Um die Effekte von Klima und Tektonik in einem solchen System zu erforschen, untersuchte ich die Oligo-Miozänen Sedimente in den Vorlandbecken der südlichen Elburs Bergkette, einem intrakontinentalen Gebirge in Nord-Iran, das im Zuge der Arabisch-Eurasischen Kontinent-Kollision herausgehoben wurde. In dieser Studie der Vorlandbeckensedimente wurden Datierungstechniken angewandt (40Ar/39Ar, (U-Th)/He Thermochronologie und Magnetostratigraphie), die Sedimente und deren Herkunft analysiert und die Tonmineralogie, sowie Sauerstoff- und Kohlenstoffisotope untersucht. Die Ergebnisse zeigen, dass auf einer Zeitskala von 105 bis 106 Jahren eine systematische Korrelation zwischen „coarsening upward“ Zyklen und den sedimentären Akkumulationsraten besteht. Während sukzessiver Überschiebungsphasen werden die durch Hebung der Bergkette bereitgestellten groben Kornfraktionen in proximale Bereiche des Beckens geliefert und feinkörnige Fazies in distalen Beckenregionen abgelagert. Variationen in der Sedimentherkunft in Phasen größerer tektonischer Aktivität zeugen von erosionaler Abdeckung und/oder der Umorganisation natürlicher Entwässerungsstrukturen. Außerdem zeigen die Untersuchungen an stabilen Isotopen, dass die verstärkte tektonische Aktivität das Anwachsen der Topographie förderte und damit die Wirksamkeit einer topographischen Barriere erhöhte. Wenn aufgrund nachlassender Beckenabsenkung die grobe Kornfraktion nicht vollständig im Nahbereich des Beckens aufgenommen werden kann breitet sie sich in ferne Beckenregionen aus. Im Elburs wird die verringerte Subsidenz durch eine interne Hebung des Vorlandes hervorgerufen und ist mit einer lateralen Stapelung von Flussbetten assoziiert. Dokumentiert wird dies anhand konsequenten Schichtwachstums, tektonischer Schrägstellung und sedimentärer Umlagerung. Gleichzeitig nehmen die Sedimentationsraten zu. Die Sauerstoff-Isotope der Paläoböden zeigen, dass dieser Anstieg mit einer Phase feuchteren Klimas einhergeht, wodurch Oberflächenprozesse effizienter werden und Heraushebungssraten steigen, was eine positive Rückkopplung erzeugt. Des Weiteren zeigen die isotopischen und sedimentären Daten, dass seit 10-9 Millionen Jahren (Ma) das Klima durch saisonalen Anstieg der Niederschläge zunehmend feuchter wurde. Da bedeutende klimatische Veränderungen zu dieser Zeit auch im Mittelmeerraum und Asien beobachtet wurden, ist anzunehmen, dass die klimatische Veränderung, die im Elburs Gebirge beobachtet wird, höchstwahrscheinlich Änderungen der atmosphärischen Zirkulationen der nördlichen Hemisphäre reflektiert. Aus den Ergebnissen dieser Studie lassen sich zusätzliche Implikationen für die Entwicklung des Elburs Gebirges und die Arabisch-Eurasische kontinentale Kollisionszone ableiten. Die orogen-weite Hauptdeformation propagierte nicht gleichmäßig nach Süden, sondern seit dem Oligozän schrittweise vorwärts und rückwärts. Insbesondere von ~17,5 bis 6,2 Ma wurde das Gebirge durch eine Kombination aus frontaler Akkretion und interner Keildeformation in Schritten von 0,7 bis 2 Millionen Jahren herausgehoben. Darüber hinaus deuten die Sedimentherkunftsdaten darauf hin, dass sich noch vor 10-9 Ma die Haupteinengungsrichtung von NW-SE nach NNE-SSW veränderte. Regional erlaubt die Geschichte der untersuchten Becken und angrenzenden Gebirgszüge Rückschlüsse auf ein neues geodynamisches Model zur Entwicklung der Arabisch-Eurasischen kontinentalen Kollisionszone. Zahlreiche Sedimentbecken des Elburs Gebirges und anderer Lokalitäten der Arabisch-Eurasischen Deformationszone belegen einen Wechsel von einem tensionalen zu einem kompressionalen tektonischen Regime vor ~36 Ma . Dieser Wechsel könnte den Beginn der Subduktion von gedehnter arabischer kontinentaler Lithosphäre unter Zentral-Iran bedeuten, was zu einer moderaten Plattenkopplung und Deformation von Unter- sowie Oberplatte geführt hat. Der Anstieg der Deformationsraten im südlichen Elburs Gebirge seit ~17,5 Ma lässt vermuten, dass die Oberplatte, wahrscheinlich aufgrund steigender Plattenkopplung, seit dem frühen Miozän signifikant deformiert wurde. Diese Veränderung könnte der Subduktion mächtigerer arabischer kontinentaler Lithosphäre zugeschrieben werden und den Anfang echter kontinentaler Kollision bedeuten. Dieses Model erklärt daher die Zeitverzögerung zwischen der Initiation der Arabisch-Eurasischen kontinentalen Kollision (Eozän-Oligozän) and dem Beginn ausgedehnter Deformation in der Kollisionszone (Miozän). / Foreland-basin systems are excellent archives to decipher the feedbacks between surface and tectonic processes in orogens. The sedimentary architecture of a foreland-basin system reflects the balance between tectonic subsidence causing long-term accommodation space and sediment influx corresponding to efficiency of erosion and mass-redistribution processes. In order to explore the effects of climatic and tectonic forcing in such a system, I investigated the Oligo-Miocene foreland-basin sediments of the southern Alborz mountains, an intracontinental orogen in northern Iran, related to the Arabia-Eurasia continental collision. This work includes absolute dating methods such as 40Ar/39Ar and zircon (U-Th)/He thermochronology, magnetostratigraphy, sedimentological analysis, sandstone and conglomerate provenance study, carbon and oxygen isotope analysis, and clay mineralogy study. Results show a systematic correlation between coarsening-upward cycles and sediment accumulation rates in the basin on 105 to 106yr time scales. During thrust loading phases, the coarse-grained fraction supplied by the uplifting range is stored in the proximal part of the basin (sedimentary facies retrogradation), while fine-grained sediments are deposited in distal sectors. Variations in sediment provenance during these phases of enhanced tectonic activity give evidence for erosional unroofing phases and/or drainage-reorganization events. In addition, enhanced tectonic activity promoted the growth of topography and associated orographic barrier effects, as demonstrated by sedimentologic indicators and the analysis of stable C and O isotopes from calcareous paleosols and lacustrine/palustrine samples. Extensive progradation of coarse-grained deposits occurs during phases of decreased subsidence, when the coarse-grained fraction supplied by the uplifting range cannot be completely stored in the proximal part of the basin. In this environment, a reduction in basin subsidence is associated with laterally stacked fluvial channel deposits, and is related to intra-foreland uplift, as documented by growth strata, tectonic tilting, and sediment reworking. Increase in sediment accumulation rate associated with progradation of vertically-stacked coarse-grained fluvial channels also occurs. Paleosol O-isotope data shows that this increase is related to wetter climatic phases, suggesting that surface processes are more efficient and exhumation rates increase, giving rise to a positive feedback. Furthermore, isotopic and sedimentologic data show that starting from 10-9 Ma, climate became less arid with an increase in seasonality of precipitation. Because important changes were also recorded in the Mediterranean Sea and Asia at that time, the evidence for climatic variability observed in the Alborz mountains most likely reflects changes in Northern Hemisphere atmospheric circulation patterns. This study has additional implications for the evolution of the Alborz mountains and the Arabia-Eurasia continental collision zone. At the orogenic scale, the locus of deformation did not move steadily southward, but stepped forward and backward since Oligocene time. In particular, from ~ 17.5 to 6.2 Ma the orogen grew by a combination of frontal accretion and wedge-internal deformation on time scales of ca. 0.7 to 2 m.y. Moreover, the provenance data suggest that prior to 10-9 Ma the shortening direction changed from NW-SE to NNE-SSW, in agreement with structural data. On the scale of the entire collision zone, the evolution of the studied basins and adjacent mountain ranges suggests a new geodynamic model for the evolution of the Arabia-Eurasia continental collision zone. Numerous sedimentary basins in the Alborz mountains and in other locations of the Arabia-Eurasia collision zone record a change from a tensional (transtensional) to a compressional (transpressional) tectonic setting by ~ 36 Ma. I interpret this to reflect the onset of subduction of the stretched Arabian continental lithosphere beneath central Iran, leading to moderate plate coupling and lower- and upper-plate deformation (soft continental collision). The increase in deformation rates in the southern Alborz mountains from ~ 17.5 Ma suggests that significant upper-plate deformation must have started by the early Miocene most likely in response to an increase in degree of plate coupling. I suggest that this was related to the subduction of thicker Arabian continental lithosphere and the consequent onset of hard continental collision. This model reconciles the apparent lag time of 15-20 m.y between the late Eocene to early Oligocene age for the initial Arabia-Eurasia continental collision and the onset of widespread deformation across the collision zone to the north in early to late Miocene time.

<p>The analysis of geologic, hydrologic and hydrogeologic data interpreted to give the characteristics of the Cape Flats aquifer showed the quality of groundwater from the aquifer is suitable for development as a water resource. The conceptual model of the Cape Flats sand shows an unconfined sandy aquifer, grading into semi-confined conditions in some places where thick lenses of clay and peat exists. Recharge rates through the saturated zone of the Cape Flats aquifer have been determined by water table fluctuation (WTF), rainfall-recharge relationship, soil water balance and chloride mass balance methods (CMB). Recharge rates using the WTF vary considerably between wet and dry years and between locations, with a range of 17.3% to 47.5%. Values obtained from empirical rainfall-recharge equation (method 2) agree with those of the WTF. Recharge estimates from the water balance model are comparatively lower but are within the range calculated using empirical method 2 (i.e. 87 &ndash / 194 mm or 4 &ndash / 21% of MAP). These recharge rates also agree with estimates from the series of other methods applied to sites located in the north-western coast of Western Cape and are comparable to recharge rates obtained elsewhere in the world.</p>

First Nations peoples experience many benefits from eating locally-harvested wild foods, but these benefits must be considered along with the potential risks associated with exposure to environmental contaminants. Unlike store-bought foods, wild foods are an important traditional resource and a significant source of dietary protein, essential minerals and polyunsaturated fatty acids, believed to help in the prevention and treatment of obesity and obesity-related diseases such as type-2 diabetes mellitus. Wild foods continue to be an important and healthy food choice for First Nations peoples; however, they are also a primary source of dietary mercury, polychlorinated biphenyls (PCBs) and other persistent organic pollutants (POPs). To assess the effects of wild food consumption on dietary markers and contaminant accumulation, we grouped individuals from two remote Oji-Cree First Nations communities of north-western Ontario (n=71) according to their level of wild food consumption. In this study, I observed significantly higher organic contaminants in blood and higher mercury concentrations in hair for individuals consuming greater amounts of wild food. Age-adjusted contaminant concentrations were on average 3.5-times higher among high-frequency wild food consumers, with many exceeding federal and international health guidelines for mercury and PCB exposures. Contaminants in these populations approach, and in some cases exceed, threshold levels for adverse effects with potential consequences especially for prenatal development. Here, I also investigated the potential for stable isotope ratios of carbon and nitrogen (δ13C and δ15N) to serve as dietary markers and found strong positive correlations between stable isotopes and frequency of wild food and fish consumption. Frequency of fish consumption and δ15N was also shown to be positively correlated with mercury concentrations in hair and PCB concentrations in plasma. The results of this thesis demonstrate that known differences in dietary behaviour are clearly reflected in stable isotope ratios and contaminant concentrations. The data also show that contaminant exposures to those consuming wild foods in remote Boreal ecosystems is comparable to those associated with serious health effects in industrialized areas, and the problem of contaminants in wild foods is more widespread than the available literature would have led us to believe. These results affect our appreciation of contaminant exposures to First Nations peoples and will have implications for dietary choices, particularly if individuals are encouraged to consume greater amounts of wild foods for their proposed health benefits. We recommend further attention be given to the risks of contaminants in locally-harvested wild foods when promoting the benefits of their consumption to First Nations people as the problem of contaminants in remote communities practicing traditional lifestyles is often underreported and underplayed.

Increasing concerns over future anthropogenic effects on climate change as a result of increasing greenhouse gases generate concomitant efforts to better characterize recent climate in order to more accurately predict climate in the future. To this end, a multiproxy study of climate variability in western Ireland from lacustrine sediment was undertaken. The interpretation of paleoclimate records derived from lacustrine carbonate minerals is difficult without a good understanding of the mechanisms that generate variation in isotope values of modern surface waters. Variation in surface waters are ultimately incorporated into lacustrine sediment records conflated by temperature. Therefore, a study of the spatial distribution of ä¹⁸O and äD values of lake and river waters from 144 locations in Ireland has been conducted to provide insight into the behavior of lakes and rivers in Ireland, including source, recycling and loss through evapotranspiration. A 7.6 m sediment core was recovered from Lough Inchiquin that provides evidence for rapid and long-term climate change from the Late Glacial to the Holocene. This was determined using carbon and oxygen isotope analyses of lacustrine calcite as well as carbon from bulk organic sediment fractions. Several significant climate perturbations were identified in the ä¹⁸O_calcite record such as the Oldest Dryas, Younger Dryas, and the 8.2 ka cold event. A previously undescribed climate anomaly between 7,300 to 6,700 cal. yr B.P. characterized by low ä¹⁸O</span>_calcite values with high frequency variability. Variations in carbon isotopes of calcite and bulk organics from the Late Glacial to the Holocene are significant in magnitude (~12) and have similar trends that record temporal shifts in the relative contributions of carbon from the weathering of limestone versus the weathering of terrestrial organic matter. ä¹³C_calcite and ä¹³C_org suggest a rapid recovery of terrestrial vegetation following the Younger Dryas. Change in Ää¹³C_{calcite - org} documents a rapid increase in exogenous fluxes of carbon into the lake at ~9 ka.

Ostracodes, bi-valved crustaceans, are potentially excellent proxies for salinity.They are abundant, react to changes in salinity, and secrete low-magnesium calcite shells that preserve information about their host water chemistry. Changes in valve trace element concentration, stable isotope composition, and sieve pore shape values have been linked to changes in salinity. This study analyzed the response of the euryhaline ostracode, Cyprideis americana, to salinity in six lakes from two Bahamian islands across two seasons. The purpose of this work was to determine which compositional and morphological variables in C. americana are the most useful for paleosalinity reconstructions.Ostracode and water samples were collected from lakes of varying water chemistry on San Salvador Island (winter and summer seasons), and Exuma (winter season). Dissolved oxygen, pH, salinity, and temperature measurements were taken for each lake. The best-preserved valves from each lake were analyzed for sieve pore circularity, Mg and Ca concentrations, and δ18 O isotopic composition. Mg/Ca ratios and Kd[Mg] values were calculated for each lake. Each parameter was plotted against salinity for all of the lakes and for lakes from each season and island. Only the samples collected during the summer followed expected trends: with increases in lake water salinity, Mg/Ca ratio decreased, δ18 O composition increased, and sieve pore circularity decreased. Samples collected from the winter field sessions did not follow expected trends, potentially due to the breeding and moulting habits of C. americana. Temperature was more correlative with valve composition than a previous study of C. americana suggests, but is supportive of similar correlations of Cyprideis species in continental and other island settings. The valve Mg/Ca ratio and mean sieve pore circularity showed the best correlation with salinity and are the variables that will be most useful in paleosalinity studies from sediment cores. Future work should further investigate the relationship between mean sieve pore circularity and lake salinity as well as the breeding and moulting habits of C. americana. Such work may allow for past salinity ranges to be reconstructed from fossil C. americana samples.

This thesis describes a method for calculating lake evaporation as a proportion of water inputs (E/I) for large surface water bodies, using stable isotope ratios of oxygen (18O/16O) and hydrogen (2H/1H) in water. Evaporation as a proportion of inflow (E/I) is calculated for each Laurentian Great Lake using a new dataset of 516 analyses of δ18O and δ2H in waters sampled from 75 offshore stations during spring and summer of 2007. This work builds on previous approaches by accounting for lake effects on the overlying atmosphere and assuming conservation of both mass and isotopes (18O and 2H) to better constrain evaporation outputs. Results show that E/I ratios are greatest for headwater Lakes Superior and Michigan and lowest for Lakes Erie and Ontario, controlled largely by the magnitude of hydrologic inputs from upstream chain lakes. For Lake Superior, stable isotopes incorporate evaporation over the past century, providing long-term insights to the lake’s hydrology that may be compared to potential changes under a future – expectedly warmer – climate. Uncertainties in isotopically derived E/I are comparable to conventional energy and mass balance uncertainties. Isotope-derived E/I values are lower than conventional energy and mass balance estimates for Lakes Superior and Michigan. The difference between conventional and isotope estimates may be explained by moisture recycling effects. The isotope-based estimates include only evaporated moisture that is also advected from the lake surface, thereby discounting moisture that evaporates and subsequently reprecipitates on the lake surface downwind as recycled precipitation. This shows an advantage of applying an isotope approach in conjunction with conventional evaporation estimates to quantify both moisture recycling and net losses by evaporation. Depth profiles of 18O/16O and 2H/1H in the Great Lakes show a lack of isotopic stratification in summer months despite an established thermocline. These results are indicative of very low over-lake evaporation during warm summer months, with the bulk of evaporation occurring during the fall and winter. This seasonality in evaporation losses is supported by energy balance studies. For Lakes Michigan and Huron, the isotope mass balance approach provides a new perspective into water exchange and evaporation from these lakes. This isotope investigation shows that Lake Michigan and Lake Huron waters are distinct, despite sharing a common lake level. This finding advocates for the separate consideration of Lake Michigan and Lake Huron in future hydrologic studies.

Increasing concerns over future anthropogenic effects on climate change as a result of increasing greenhouse gases generate concomitant efforts to better characterize recent climate in order to more accurately predict climate in the future. To this end, a multiproxy study of climate variability in western Ireland from lacustrine sediment was undertaken. The interpretation of paleoclimate records derived from lacustrine carbonate minerals is difficult without a good understanding of the mechanisms that generate variation in isotope values of modern surface waters. Variation in surface waters are ultimately incorporated into lacustrine sediment records conflated by temperature. Therefore, a study of the spatial distribution of ä¹⁸O and äD values of lake and river waters from 144 locations in Ireland has been conducted to provide insight into the behavior of lakes and rivers in Ireland, including source, recycling and loss through evapotranspiration. A 7.6 m sediment core was recovered from Lough Inchiquin that provides evidence for rapid and long-term climate change from the Late Glacial to the Holocene. This was determined using carbon and oxygen isotope analyses of lacustrine calcite as well as carbon from bulk organic sediment fractions. Several significant climate perturbations were identified in the ä¹⁸O_calcite record such as the Oldest Dryas, Younger Dryas, and the 8.2 ka cold event. A previously undescribed climate anomaly between 7,300 to 6,700 cal. yr B.P. characterized by low ä¹⁸O</span>_calcite values with high frequency variability. Variations in carbon isotopes of calcite and bulk organics from the Late Glacial to the Holocene are significant in magnitude (~12) and have similar trends that record temporal shifts in the relative contributions of carbon from the weathering of limestone versus the weathering of terrestrial organic matter. ä¹³C_calcite and ä¹³C_org suggest a rapid recovery of terrestrial vegetation following the Younger Dryas. Change in Ää¹³C_{calcite - org} documents a rapid increase in exogenous fluxes of carbon into the lake at ~9 ka.

Woody plant invasion of grasslands is prevalent worldwide, but the biogeochemical consequences of this vegetation shift remain largely unquantified. In the Rio Grande Plains, TX, grasslands and savannas dominated by C4 grasses have undergone succession over the past century to subtropical thorn woodlands dominated by C3 trees/shrubs. To elucidate mechanisms of soil organic carbon (SOC) and soil total N (STN) storage and dynamics in this ecosystem, I measured the mass and isotopic composition (&#948;13C, &#948;15N) of C and N in whole-soil and soil size/density fractions in chronosequences consisting of remnant grasslands (Time 0) and woody plant stands ranging in age from 10-130 years. Rates of SOC and STN storage averaged 10-30 g C m-2yr-1 and 1-3 g N m-2yr-1, respectively. These accumulation rates increased soil C and N pools 80-200% following woody encroachment. Soil microbial biomass (SMB-C) also increased after woody invasion. Decreasing Cmic/C org and higher qCO2 in woodlands relative to grasslands suggests that woody litter is of poorer quality than grassland litter. Greater SOC and STN following woody invasion may also be due to increased protection of organic matter by stable soil structure. Soil aggregation increased following woody encroachment; however, most of the C and N accumulated in free particulate organic matter (POM) fractions not protected within aggregates. Mean residence times (MRTs) of soil fractions were calculated based on changes in their &#948;13C with time after woody encroachment. Free POM had the shortest average MRTs (30 years) and silt+clay the longest (360 years). Fine POM had MRTs of about 60 years, reflecting protection by location within aggregates. &#948;15N values of soil fractions were positively correlated with their MRTs, suggesting that higher &#948;15N values reflect an increased degree of humification. Increases in SOC and STN are probably being sustained by greater inputs, slower turnover of POM (some biochemical recalcitrance), and protection of organic matter in aggregates and association with silt and clay. Grassland-to-woodland conversion during the past century has been geographically extensive in grassland ecosystems worldwide, suggesting that changes in soil C and N dynamics and storage documented here could have significance for global C and N cycles.