Wasserverfügbarkeit ist in Wäldern Mitteleuropas wie auch in anderen Regionen der Welt oftmals ein limitierender Faktor für die Produktivität eines Bestandes. Ebenso wurde bereits in zahlreichen Studien untersucht, inwiefern Biodiversität einen Einfluss auf die Produktivität von Pflanzengemeinschaften hat. Es gibt jedoch nur wenig Informationen darüber, wie sich Baumartenvielfalt auf die Wassernutzung eines Waldbestandes auswirkt. Die Wassermenge, die für Transpiration und Zuwachs unter gegebenen Umweltbedingungen zur Verfügung steht ist davon abhängig, wie gut Pflanzen den vorliegenden Wasservorrat nutzen können. Es wird angenommen, dass Wasserverfügbarkeit für den Bestand durch komplementäre Wasseraufnahme zwischen gemeinsam auftretenden Pflanzenarten steigt. Daher zählt eine komplementäre Nutzung von Resourcen in ökologischen Studien allgemein zu den wichtigen funktionellen Effekten von Artenvielfalt. Jedoch setzt Komplementarität vorraus, dass funktionale Eigenschaften bestimmter Arten es diesen ermöglichen, entweder für andere Arten nicht verfügbare Resourcen zu nutzen, oder aber die selbe Resource räumlich und/ oder zeitlich getrennt voneinander zu nutzen. In gemischten Pflanzengemeinschaften ist oftmals eine erhöhte Produktivität im Vergleich zu Monokulturen zu beobachten, welche häufig durch Aufteilung von Resourcen und eine damit verbundene effektivere Nutzung erklärt wird. Im mitteleuropäischen Raum hat die Einrichtung von gemischten Laubwäldern in den letzten Jahrzehnten deutlich zugenommen. Gleiches gilt für die Umwandlung von Monokulturen (z. B. Fichte) in Bestände mit höherer Artenvielfalt, insbesondere von Arten die an die jeweiligen Standortbedingungen angepasst sind. Dieses Konzept der „naturnahen“ Forstwirtschaft zielt auf eine nachhaltige Produktion, erhöhte Stabilität angesichts möglicher extremer klimatischer Verhältnisse und eine Verbesserung der Erholungsfunktion von Wäldern ab. Infolgedessen ist es jedoch möglich, das Bestände mit erhöhter Baumartenzahl ebenso einen vergleichsweise höheren Verbrauch an Wasser aufweisen, was wiederum in erhöhtem Stress bei Trockenperioden resultieren könnte. Ein derartiger Effekt wäre demnach gegensätzlich zu den Zielen einer naturnahen Forstwirtschaft. Das Ziel dieser Studie war, die Auswirkung von Baumartenvielfalt (-mischung) auf die Wassernutzung eines temperaten Laubmischbestandes zu untersuchen und einen Beitrag zum besseren Verständnis dieser Zusammenhänge zu leisten. Hierfür wurden Untersuchungen innerhalb kleiner Baumgruppen durchgeführt, so genannter „Cluster“, die aus drei Bäumen der Kronenschicht bestanden, welche der potenziellen natürlichen Vegetation im Waldgebiet Hainich angehören (Fagus sylvatica, Tilia sp., Fraxinus excelsior, Acer pseudoplatanus, and Carpinus betulus). Die Cluster (n = 100) beinhalteten alle theoretisch denkbaren Kombinationen der 5 Untersuchungsarten in Ein- Zwei- und Dreiart Baumgruppen (25 Artkombinationen auf drei Diversitätsstufen), wobei jede Kombination in vier Wiederholungen vorlag (20 Einart-, 40 Zweiart- und 40 Dreiart-Cluster). In der ersten Studie wurde getestet, ob stabile Isotope von Wasser (2H und 18O) unter den gegebenen Bodenbeschaffenheiten im Hainich genutzt werden können, um die Wasseraufnahmetiefe von Bäumen zu identifizieren. Stabile Isotope von Wasser werden mittlerweile immer häufiger eingesetzt, um die Tiefe der Wasseraufnahme von Pflanzen festzustellen. Dabei wird ein Isotopengradient, der sich im Boden als Folge von Evaporation bildet, genutzt. Damit sich ein solcher Gradient bilden kann, benötigt es daher eine ausgedehnte Periode der Bodenaustrockung. Durch einen Vergleich der Isotopensignatur zwischen Wasserproben aus dem Stammxylem und verschiedenen Bodentiefen lässt sich die Tiefe der Wasseraufnahme der Bäume ermitteln. Allerdings lässt sich aus bisherigen Studien entnehmen das Bodeneigenschaften (z. B. Textur) die Signatur von 2H und 18O im Bodenwasser beeinträchtigen können. In Laborversuchen wurde daher getestet, ob eine Variation der Bodenfeuchte, des Tongehalts oder des Vorkommens von Calciumcarbonat im Boden eine Auswirkung auf die Isotopensignatur von extrahiertem Bodenwasser hat. Im ersten Versuch wurden getrocknete Bodenproben unterschiedlichen Tongehalts mit unterschiedlichen Mengen Wasser bekannter Isotopensignatur wiederbefeuchtet. Im zweiten Versuch wurde außerdem vor der Wiederbefeuchtung das Carbonat aus Teilproben des Bodens chemisch entfernt (Kontrollproben blieben unbehandelt), um den Effekt von Carbonat zu ermitteln. Für die Extraktion des Wassers aus den Proben wurde die kryogene Vakuum-Extraktion angewandt. Die Versuchsergebnisse deuteten darauf hin, dass mit abnehmendem Wassergehalt und zunehmendem Tongehalt in der Bodenprobe eine deutliche Veränderung von δ2H and δ18O im extrahierten Wasser auftrat. Weiterhin bewirkte die Anwesenheit von Carbonat im Boden eine Abreicherung von δ18O im Bodenwasser, wohingegen δ2H nicht verändert wurde. Den Ergebnissen Zufolge könnte der Einfluss eines hohen Carbonatgehalts im Boden so stark sein, dass eine unabhängige Anwendung von δ2H and δ18O zu widersprüchlichen Ergebnissen bei der Schätzung der Wasseraufnahmetiefe in hydrologischen Studien führen kann. Daher ist es zu empfehlen, deratige Analysen nicht nur auf einem, sondern auf beiden Isotopen zu stützen und auch die physikalischen sowie chemischen Bodeneigenschaften zu untersuchen. Da die erste Studie gezeigt hat, dass insbesondere 18O durch den Carbonatgehalt im Boden beeinflusst werden kann, wurde in der zweiten Studie ausschließlich die natürliche Abundanz von 2H genutzt, um die Wasseraufnahmetiefe einzelner Baumarten (Fagus sylvatica, Tilia sp. and Fraxinus excelsior) und deren Mischung während einer Periode der Bodenaustrocknung zu untersuchen. Hierbei sollte die Hypothese getestet werden, dass die Tiefe der Wasseraufnahme sich zwischen den Baumarten unterscheidet, was zu einer komplementären Wassernutzung in den Mehrart-Clustern führt. Weiterhin wurde angenommen, dass die Wasseraufnahmetiefe mit zunehmendem Baumdurchmesser ebenfalls ansteigt. Um die Tiefenverteilung der Wasserentnahme sowie mögliche Auswirkung der Baumgröße auf diese zu identifizieren, wurde die isotopische Zusammensetzung von Xylem- und Bodenwasserproben aus Einart- und Mehrart-Clustern analysiert und miteinander verglichen. Dafür wurden Bodenproben aus fünf Tiefenintervallen (0-0.1, 0.1-0.2, 0.2-0.3, 0.3-0.5, 0.5-0.7 m) in Stammnähe jedes untersuchten Baumes zusammen mit jeweiligen Stammproben entnommen. Mittels eines Isotopen Mischungsmodels konnte ermittelt werden, dass die relative Wasseraufnahmetiefe zwischen den Baumarten in Einart- sowie in Mehrart-Clustern variierte. Zusätzlich beeinflusste der Baumdurchmesser die Hauptaufnahmetiefe von Wasser in Mehrart-Clustern. Mit zunehmendem Durchmesser entnahmen die Bäume unabhängig von der Baumart Wasser vorwiegend aus vergleichsweise höheren Bodenschichten. Diese Resultate deuten auf eine Komplementarität in Bezug auf die relative Wasseraufnahme während einer Trockenperiode hin. Aufgrund des vorangegangenen Methodentests zu stabilen Isotopen wurde in dieser Studie lediglich 2H genutzt, um die Tiefe der Wasseraufnahme zu ermitteln. Zur Vollständigkeit wurde die Analyse jedoch auch mittels δ18O durchgeführt. Ebenso wie bei δ2H zeigte sich ein deutlicher Zusammenhang zwischen der Signatur der Hauptaufnahmetiefe und den Durchmessern der Bäume. Obwohl bei direktem Vergleich (grafische Analyse) und in der Modelberechnung δ2H and δ18O gegensätzliche Resultate zur relativen Wasseraufnahmetiefen der Bäume ergaben, ist der Zusammenhang zwischen Baumdurchmesser und Hauptiefe der Wasserentnahme gleich. Der letzte Teil der Studie befasste sich mit dem Einfluss unterschiedlicher Baumartenkombinationen, Artenvielfalt, Bestandesstruktur und klimatischen Bedingungen auf die Menge der täglichen Bodenwassernutzung während der Austrockungsperiode. Die Hypothese für diese Studie war, dass sich die Menge der täglichen Wasseraufnahme zwischen den Baumarten unterscheidet und mit ansteigender Baumartenvielfalt zunimmt (gemessen auf Einart- Zweiart-und Dreiart-Clustern). Die tägliche Wassaufnahme (mm Tag-1) wurde mittels eines einfachen Modelansatzes für die Bodentiefe von 0-0.3 m auf allen 100 Clustern und für die Tiefe 0-0.7 m auf 16 Clustern berechnet. Bis auf eine geringfügig höhere Wasseraufnahme in Einart-Clustern von Fraxinus excelsior im Zeitraum von Juni bis Mitte September 2009, konnte weder ein Einfluss der Artidentität der Bäume noch der Artenvielfalt auf die Menge der Wasseraufnahme in den Clustern festgestellt wurden. Die An- oder Abwesenheit der fünf untersuchten Baumarten in den Clustern zeigte ebenfalls kein Einfluss auf die Menge der Wasseraufnahme. Es lässt darauf schließen, dass unter den gegebenen Umständen Arteingenschaften und Artenvielfalt einen untergeordneten Einfluß auf die Nutzung von Bodenwasser haben, welcher möglicherweise auch von anderen Faktoren überdeckt wurde. Denkbar wäre hierbei ein Einfluss der Krautschicht oder die räumliche Anordnung der Bäume im Bestand, wobei die wichtigste Einflussgröße die vorherrschende Globalstrahlung war. Obwohl innerhalb der Cluster keine deutlichen Unterschiede gefunden wurden, die durch Arteigenschaften oder Artenvielfalt bedingt wurden, ist es dennoch möglich, dass diese auf einer größeren räumlichen Skala auftreten können. In Bezug auf die Wassernutzung eines Bestandes lässt sich demnach schliessen, dass Artenvielfalt alleine keine geeignete Vereinfachung für ein sehr komplexes Netzwerk aus verschiedenen Interaktionen zwischen Arteigenschaften innerhalb und zwischen Arten, sowie Bestandeseigenschaften und Umweltbedingungen ist. Jeder dieser Bestandteile könnte sich auf zeitlicher und räumlicher Ebene unterschiedlich auf die Wassernutzung eines Waldbestandes, unabhängig von der Biodiversität des Bestandes auswirken. Weiterhin ist es für Altbestände, mit geringem menschlichen Eingriff denkbar, dass sich Bäume im Laufe der Zeit gemäß der ihnen zur Verfügung stehenden Resourcen räumlich verteilen, wodurch ausgeglichene Nachbarschaftsbeziehungen entstehen könnten. Diese Arbeit zeigte, dass sich die physikalische und chemische Beschaffenheit des Bodens auf die Isotopensignatur von Wasser auswirkt. Dennoch können Isotopenversuche zur Ermittlung der Tiefenverteilung der Wasseraufnahme in temperaten Wäldern angewandt werden. Die Wasseraufnahmetiefe der Baumarten unterschied sich zwischen Ein- und Mehrart-Clustern, und deutete in Mehrart-Clustern auf eine Komplementarität hin, die durch Durchmesserunterschiede bedingt war. Baumartenvielfalt per se erhöhte jedoch nicht die Menge der absoluten Wasseraufnahme in den Clustern. Demnach gab es auch keinen Hinweis darauf, dass eine erhöhte Wassernutzungseffizienz zu einer deutlich verstärkten Ausnutzung der Bodenwasserresourcen während einer Austrocknungsperiode führt.

The metasupracrustal-hosted, often polymetallic REE-Fe-deposits of Bastnäs-type are found along the “REE-line” in the Palaeoproterozoic Bergslagen ore province, south central Sweden. They essentially comprise REE silicate-bearing magnetite skarn mineralisations with variable contents of other metals. Even though these deposits have been important for mining and research for centuries, their origin still remains unclear. In this study, samples from 10 different deposits along the REE-line have been charactarised as to mineralogy, petrography and bulk geochemistry, in addition to their isotope systematics. Mineral separates of magnetite and, when present, co-existing quartz or carbonates have been analysed for their oxygen and (for carbonates) carbon isotope compositions, in order to put constraints on the sources for metals and fluids in these deposits. Magnetites have δ18O-values of -1.79 to 1.12 ‰, while quartzes lie between 7.19 and 8.28 ‰. Carbonates have δ18O-values between 5.77 and 7.15 ‰ and δ13C-values between -5.35 and -3.32 ‰. Thermometric calculations based on mineral pairs (magnetite-quartz, magnetite-calcite/dolomite), combined with available fluid inclusion data, indicate formation of primary magnetite assemblages between c. 650 to 400 °C. At these temperatures, magnetites from some of the deposits would have been in equilibrium with a magmatic fluid (δ18O = 6-8 ‰), while magnetites from other deposits would have been in equilibrium with fluids of lower δ18O (4-6 ‰). Oxygen and carbon isotope trends in carbonates can be explained by interaction between original host carbonates and a fluid of magmatic composition. The combined results indicate that the Bastnäs-type magnetite-REE mineralisations were deposited from an originally magmatic fluid at relatively high temperatures. At local scale, variable modification of the fluid isotopic composition can be explained by mixing with seawater-dominated fluids.

Food webs are good ecological macro-descriptors and their study is important in ecology in understanding nutrient cycles, tracing and quantifying energy and in describing trophic interactions within an ecosystem. The knowledge of food web finds applications in various natural sciences disciplines but also in many productive sectors. This study investigated the structure of the food web of a shallow lake in the Pantanal flood plain. The food web included two macrophytes, six aquatic insects, four crustaceans and 24 fish species. Sources of carbon for the various organisms living in the lake were identified through the values of δ13C exhibited by the organisms. The δ15N signature was used to estimate the trophic position of each organism. A cluster analysis based on the two isotopic signatures revealed six different feeding guilds and emphasized on the broad occurrence of omnivory among animals living in the lake. This study revealed that the use of food carbon was the most important factor that structured the lake community. Very low values of δ13C in zooplankton, benthic dwellers and bottom-feeder organisms as well as similarities between the gradient of δ13C and that of use of methane oxidizing bacteria informed on the possible use of biogenic methane as a source carbon and energy for the lake biota.

The Pierina high-sulphidation epithermal Au-Ag deposit is located in the Cordillera Negra of north-central Perú, ~ 5km north of the coeval intermediate-sulphidation Ag–base metal Santo Toribio deposit, and in rocks of the Calipuy Supergroup. The deposit contains ~ 8 M oz Au, hosted in non-refractory iron oxides and, with heap-leach extraction, is one of the lowest-cost Au producers in the world. Stage Ia (15 Ma) and Ib (14.4 Ma) advanced-argillic alteration formed from mixed magmatic and meteoric waters. The main, 14.4 Ma event produced vuggy quartz alteration, focussed in a 16.9 Ma dacitic pumice-lithic tuff, and surrounded by quartz-alunite, quartz-dickite, and illite-montmorillonite alteration zones, the product of increased meteoric water contributions towards the periphery of the deposit. Stage II sulphide-barite mineralization introduced gold and silver, hosted submicroscopically in the disseminated high-sulphidation pyrite-enargite assemblage. Precipitation occurred from a low-to-medium - salinity magmatic fluid that mixed with meteoric waters at the site of ore deposition. A 14.1 Ma 40Ar/39Ar age for supergene alunite records the rapid incursion of meteoric waters into the deposit. The resulting oxidation of sulphides to schwertmannite, goethite, and hematite was facilitated by microbes, recorded by the stable-isotopic compositions of supergene barite+acanthite. Schwertmannite is enriched in Au and Ag and is the main precious-metal host. Regional pedimentation is inferred to have initiated retrograde boiling of the source magma chamber at 15 Ma, with renewed magma incursion triggering major alteration at 14.4 Ma. Both events involved the exsolution of an SO2-rich vapour and a more saline aqueous fluid. The latter migrated to Santo Toribio generating phyllic alteration and intermediate-sulphidation mineralization, whereas the SO2-rich vapours caused pyrite-bearing feldspar-destructive alteration along fluid pathways during ascent to Pierina. The subsequent single-phase, H2S-rich mineralizing fluid exsolved from the retracting magma at higher pressures. Vapour contraction during ascent along altered, unreactive pathways minimized the loss of S- and H+, optimizing the transport of Au as AuHS0. Watertable displacement resulting from pediment incision promoted the flow of groundwater into the epithermal environment where mixing with magmatic fluids precipitated gold. Supergene oxidation optimized conditions for microbial activity, a critical factor in the generation of economic mineralization. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2009-04-01 16:02:47.525

No description available.

Nitrous oxide (N???O) is a potent greenhouse gas, an important driver of climate change, and its concentration in the atmosphere is rising at an unprecedented rate. Agriculture is the leading contributor of all the anthropogenic N???O sources, and the vast majority of agricultural N???O emissions originate from soil. Of all the natural N???O emissions, two-thirds originate from soil and temperate forests contribute approximately one-sixth of the natural soil emissions. Consequently, there is great interest in understanding the soil nitrogen processes responsible for N???O production so that effective policies and management practises can be implemented to successfully mitigate climate change. The stable isotopes of nitrogen (N) and oxygen (O) in soil N???O emissions are hypothesized to be useful indicators of the biogeochemical processes that produce and consume N???O, and they may be used to apportion different environmental sources. The primary objective of this thesis was to assess the utility of ???????N and ???????O values to differentiate N???O produced by nitrification and denitrification. Most of the previous research on N???O isotopes has utilized microbial cultures of single organisms; yet natural systems contain a consortium of N-metabolizing microorganisms so the relevance of this early work to natural environments is uncertain. This thesis presents the results of experimental incubations of soil from an agricultural site and a temperate forest located within Ontario, Canada. Two well-drained soils (upland), two poorly-drained soils (wetland), and one stream sediment were incubated under varying conditions (temperature, moisture, and N-availability) to achieve a wide range in the rate of N???O production. The ???????N and ???????O values of N???O produced from the different experiments were characterized and the isotope effects (??) of N???O production were calculated. Experiments were conducted in aerobic or anoxic atmospheres to stimulate N???O formation by nitrification and denitrification, respectively. The ???????N-N???O produced by denitrification in all soils was 7???35??? lower than the ???????N-nitrate (NO??????). The ???????N-N???O produced by nitrification in the upland forest soil and the agricultural soils was 28???54??? lower than the ???????N-ammonium. Nitrification in the forested wetland soil yielded higher ???????N-N???O values (?? = ???16???), which was likely caused by an increase in the ???????N-substrate. With the exception of the latter soil, there was clear ?????N-separation between the nitrification- and denitrification-derived N???O in all soils. Consequently, ???????N values can be used to apportion different environmental sources of N???O on a site-by-site basis, provided that the rates of N metabolism are known and the isotopic endmembers are well-characterized. A novel approach was employed in this thesis to help unravel the key controls of ???????O-N???O and ???????O-NO?????? formation. Different ?????O-labelled soil waters were used to demonstrate that the abiotic exchange of oxygen atoms between water and nitrite (in equilibrium) is an important control of the ???????O-N???O formed by nitrifier-denitrification and the ???????O-NO?????? formed by nitrification. O-exchange in these incubations was highly variable between soils (37???88%) and it appeared to be rate-related. Furthermore, the ???????O value of microbial NO?????? is partially controlled by ?????O/?????O fractionation that occurs during O-exchange (equilibrium fractionation) and the uptake of molecular oxygen (O???) and water (H???O) (kinetic fractionation). This research showed that the ???????O value of microbially-produced NO?????? cannot be successfully predicted in soils based upon the commonly used ???one third, two-thirds rule???, which only takes into account the ???????O values of O??? and H???O. Successful predictions of ???????O-NO?????? using this rule appear to be fortuitous and are because of the range of ???????O-H???O at natural abundance and the magnitude of the isotope effects involved. Enzyme-catalyzed (biotic) O-exchange between water and nitrite/nitric oxide in denitrification was also quantified for the first time in soils. O-exchange during denitrification was significant and variable (39???95%), but uniquely confined to narrow ranges for each soil type. Almost complete O-exchange occurred in the well-drained agricultural and forested soils (86???95%); less O-exchange occurred in the agricultural and forested wetland soils (63???70%); and even less O-exchange occurred in the agricultural stream sediment (39???51%). The magnitude of O-exchange during denitrification was independent of soil temperature and moisture for a given soil, and it was not related to the rate of N???O production. This implies that the amount of O-exchange that occurs during soil denitrification is controlled by the dominant microbial community. For the first time, estimates of the net O isotope effect were determined for N???O production by soil denitrifiers that accounted for the complicating effects of O-exchange. The net ?????O-discrimination (N???O???NO??????) ranged between +32??? and +60???, with the exception of one treatment that was cooled (?? = +17???). The O isotope separation (??) that is actually observed in natural systems is often much lower, and in some cases negative. This is because the atomic O-exchange between water and nitrite/nitric oxide effectively diminishes the net ?????O separation between NO?????? and N???O because ???????O values of environmental water are usually lower than the ???????O values of N???O-precursors. The determinants of ???????O-N???O produced by nitrification pathways are complex and there is no holistic explanation of the O isotope dynamics in the literature. This thesis provides the first systematic model to describe ???????O-N???O formation by aerobic pathways. In addition to O-exchange between water and nitrite (at equilibrium), ???????O-N???O is controlled by ?????O/?????O fractionation that results from this O-exchange mechanism, and from fractionation that occurs during ammonia-oxidation and nitrite-reduction. Although explaining ???????O-N???O values produced by nitrification is complex, reports of nitrifier-derived ???????O-N???O in the literature and this thesis are narrowly confined between +13??? and +31??? (rel. VSMOW). This is distinct from much of the denitrifier-produced ???????O-N???O, which is often ?????O-enriched and higher than +33???. In three out of the five different soils investigated in this thesis, ???????O-N???O could be used to separate N???O formed by nitrification and denitrification. There was poor ???????O separation between nitrifier- and denitrifier-derived N???O in the well-drained soils because high amounts of biotic O-exchange and reduced O isotope separations yielded lower (predicted) estimates of denitrifier-produced ???????O-N???O. On the other hand, ???????N values could be used to apportion nitrifier- and denitrifier-derived N???O sources in these soils. Thus, stable isotope ratios of N???O are a valuable and promising tool that may help differentiate nitrifier-N???O from denitrifier-N???O in natural soil environments.

Developing critical loads for nitrogen (N) in the Athabasca Oil Sands Region (AOSR) requires an understanding of the hydrological connectivity and potential for N transport among uplands, fens and bogs typical in the wetland-rich Boreal region of northern Alberta. The Cumulative Environmental Management Association’s (CEMA) overarching mandate is to determine a nitrogen critical load specific to the Boreal region of northern Alberta. To this end, nitrogen amendment experiments were initiated at two Boreal wetland sites: an upland – rich fen gradient at Jack Pine High (JPH) and an upland – fen – bog mosaic at Mariana Lakes (ML), 45 km north and 100 km south of Fort McMurray respectively. The objectives of this study are to use geochemical and isotopic tracers to describe baseline hydrogeochemical variability and connectivity between bog, fens and upland areas in the AOSR. Sites were instrumented with piezometer nests and water table wells along transects that cover the targeted landscape units (n = 108 sampling locations). Fieldwork related to this thesis was conducted during the open-water season: in June and August 2011, and in May, July, and September 2012. Field campaigns also included a snow survey (March 2012), and spring melt/freshet sampling (April 2012). The analysis of spatiotemporal variability of water isotopes and geochemistry in the years 2011-2012 yielded: i) a characterization of baseline conditions from which perturbations can be assessed, and ii) evidence of connectivity among landscape units. No evidence for elevated concentrations of nitrogen related to the amendment experiments was found in 2011 or 2012. The baseline characterization and annual monitoring did show increasing concentrations of inorganic ammonium with increasing depth associated with increasing solute concentrations: average concentrations of inorganic ammonium were 23 mg/L at deepest sampling locations (7 m) at ML bog and ML fen landscape units. These ammonium concentrations in porewaters, given a porosity of 0.90 for peatlands, constitute a store of ammonium that may be a significant source of nitrogen if the hydrology is altered due to co-occurring changes in vegetation (due to, for example, elevated nitrogen inputs), climate and/or landuse. Hydrologic connectivity at JPH is likely driven by topography. Hydraulic head in 2011 and 2012 field seasons showed that flow persisted from the upland to the fen. The consistent and distinct geochemical signatures and isotopic labelling of mid-depth and deep groundwater samples of fen and upland landscape units is consistent with such a stable groundwater continuum. Near-surface water samples at JPH fen however varied hydrogeochemically in response to seasonal changes in precipitation inputs, water levels, and biogeochemical productivity. At ML, hydrological connectivity is a function of antecedent moisture conditions (which determines run-off) and low and variable (10-6 to 10-9 m/s) hydrological conductivity of the peatland substrate (which may result in lateral flow where hydraulic head shows potential for vertical re- or discharge). Near-surface samples showed greater temporal than spatial variability as snowmelt inputs, variations in antecedent moisture conditions and seasonal changes in biogeochemical process rates affected nutrient and solute concentrations. In contrast, shallow, mid-depth and deep samples showed greater spatial than temporal variability. The spatial distributions of parameters could be associated to some degree with vegetation, distance along a surficial flowpath, or depth to mineral substrate or distance from the upland/edge transition. / Graduate / 0996 / 0388 / 0425 / cbkusel@yahoo.ca

Developing critical loads for nitrogen (N) in the Athabasca Oil Sands Region (AOSR) requires an understanding of the hydrological connectivity and potential for N transport among uplands, fens and bogs typical in the wetland-rich Boreal region of northern Alberta. The Cumulative Environmental Management Association’s (CEMA) overarching mandate is to determine a nitrogen critical load specific to the Boreal region of northern Alberta. To this end, nitrogen amendment experiments were initiated at two Boreal wetland sites: an upland – rich fen gradient at Jack Pine High (JPH) and an upland – fen – bog mosaic at Mariana Lakes (ML), 45 km north and 100 km south of Fort McMurray respectively. The objectives of this study are to use geochemical and isotopic tracers to describe baseline hydrogeochemical variability and connectivity between bog, fens and upland areas in the AOSR. Sites were instrumented with piezometer nests and water table wells along transects that cover the targeted landscape units (n = 108 sampling locations). Fieldwork related to this thesis was conducted during the open-water season: in June and August 2011, and in May, July, and September 2012. Field campaigns also included a snow survey (March 2012), and spring melt/freshet sampling (April 2012). The analysis of spatiotemporal variability of water isotopes and geochemistry in the years 2011-2012 yielded: i) a characterization of baseline conditions from which perturbations can be assessed, and ii) evidence of connectivity among landscape units. No evidence for elevated concentrations of nitrogen related to the amendment experiments was found in 2011 or 2012. The baseline characterization and annual monitoring did show increasing concentrations of inorganic ammonium with increasing depth associated with increasing solute concentrations: average concentrations of inorganic ammonium were 23 mg/L at deepest sampling locations (7 m) at ML bog and ML fen landscape units. These ammonium concentrations in porewaters, given a porosity of 0.90 for peatlands, constitute a store of ammonium that may be a significant source of nitrogen if the hydrology is altered due to co-occurring changes in vegetation (due to, for example, elevated nitrogen inputs), climate and/or landuse. Hydrologic connectivity at JPH is likely driven by topography. Hydraulic head in 2011 and 2012 field seasons showed that flow persisted from the upland to the fen. The consistent and distinct geochemical signatures and isotopic labelling of mid-depth and deep groundwater samples of fen and upland landscape units is consistent with such a stable groundwater continuum. Near-surface water samples at JPH fen however varied hydrogeochemically in response to seasonal changes in precipitation inputs, water levels, and biogeochemical productivity. At ML, hydrological connectivity is a function of antecedent moisture conditions (which determines run-off) and low and variable (10-6 to 10-9 m/s) hydrological conductivity of the peatland substrate (which may result in lateral flow where hydraulic head shows potential for vertical re- or discharge). Near-surface samples showed greater temporal than spatial variability as snowmelt inputs, variations in antecedent moisture conditions and seasonal changes in biogeochemical process rates affected nutrient and solute concentrations. In contrast, shallow, mid-depth and deep samples showed greater spatial than temporal variability. The spatial distributions of parameters could be associated to some degree with vegetation, distance along a surficial flowpath, or depth to mineral substrate or distance from the upland/edge transition. / Graduate / 0996 / 0388 / 0425 / cbkusel@yahoo.ca

The stable isotopes of oxygen and hydrogen have been employed worldwide as natural hydrological tracers, and most successfully in areas where extremes of climatic seasonality or relief exist. This project aims to assess the viability of the stable isotope technique for studies in the U.K. Systematic sampling was undertaken over two years in the Malham (Carboniferous limestone) and Lambourn (Chalk) areas. The monthly isotopic input signal in precipitation was found to be clearly definable, but less strongly seasonal than found elsewhere. Larger isotopic variations were revealed in weekly and within-storm samples. Snowmelt appeared to provide the most reliable 'spike' for tracing purposes. An attempt to relate weekly precipitation δ¹⁸0 values to air mass characteristics was encouraging for further investigations. Variations of isotope signal with altitude were erratic and not in accordance with normally accepted relationships. Isotopic variations in groundwaters of both areas, and in surface waters of the Lambourn area, rarely exceeded measurement error, and were close to mean annual values in precipitation. This indicated complete mixing of the input waters over one year or more. The isotopic range in precipitation was reduced by ~60% in surface waters of the Malham area. Early mixing and storage of water in the soil and/or upper karstic zone were indicated by comparison of the isotope data with conventional hydrological measurements at resurgences, and supported by strong signal attenuation measured in soil moisture. At certain sites, isotopic evidence revealed a persistence of winter recharge into summer baseflow. A smooth and strongly seasonal isotope signal, discovered in the waters of Malham Tarn, was attributed to evaporation processes and suggests important practical uses. It is concluded that the general application of the stable isotope technique may be more restricted in the U.K. than elsewhere, but that its provision of a new dimension to conventional data should contribute significantly in the future to selected hydrological studies.

Diverse fish species consume fruits and seeds in the Neotropics, in particular in the lowland reaches of large rivers, such as the Amazon, Orinoco, and Parana in South America. Floodplains of the Amazon River and its lowland tributaries are characterized by marked hydrological seasonality and diverse assemblages of frugivorous fishes, including closely related and morphologically similar species of several characiform families. Here, I investigated whether or not these fishes are capable of detecting fluctuations in food availability and if they are, how they adjust their feeding strategies. I tested predictions of optimal foraging, limiting similarity and resource partitioning theories with regard to expansion or compression of niche breadth and reduction in trophic niche overlap among species in relation with fluctuations in the availability of alternative food resources. I monitored fruiting phenology patterns to assess food availability and conducted intensive fishing during the high-, falling-, and low-water seasons in an oligotrophic river and an adjacent oxbow lake in the Colombian Amazon. I combined analysis of stomach contents and stable isotope ratios to evaluate dietary patterns, niche breadth, and niche overlap. Diets of six characiform fish species (Brycon falcatus, B. melanopterus, Myloplus asterias, M. rubripinnis, and M. torquatus) changed in a manner that indicated responses to fluctuations in food availability. Feeding strategies during the peak of the flood pulse were consistent with predictions of optimal foraging theory. During times of high fruit abundance, fish preferentially consumed items to which their phenotype is best adapted, maximizing net energy gain and enhancing fitness. As the flood pulse subsided and the availability of forest food resources was reduced in aquatic habitats, there was not a consistent pattern of diet breadth expansion or compression, even though diet shifts occurred, suggesting interspecific differences in foraging efficiencies. Analyses of diets and isotopic ratios revealed a general pattern of increased dietary segregation as the water level receded. Although there never was complete niche segregation among these fishes, these dietary changes effectively reduced interspecific niche overlap. Implications of these results and contribution of allochthonous food resources to diversity maintenance of floodplain fishes are discussed.