Dissertations / Theses on the topic 'Stable isotopes of water'

The use of stable water isotopes as 18O and 2H are widely used in the last 50 years as tracer in climatic and hydrological studies. Stable water isotopes have slightly different physical properties and require different latent energy for phase changes, so the concentration of water isotopes varies during water phase changes, which is known as fractionation. Specifically in the tropics, the stable water isotopes have a very particular behavior unlike other regions, by the influence of large rainfalls amount, temperature and relative humidity. Cuba is an inland in the middle of the Caribe Sea, where studies about isotopic characterization of precipitations have never been made. In order to understand and explain some issues related to the isotopic behavior of precipitation in this inland, the research work was developed making use of data from that area. The general objective of this research proposal is to characterize the isotopic composition of rainfall in west of Cuba, including the demonstration of the vegetation influence in rainfall isotopic composition, and to determine mathematical models that describe the relationship between rainfall amount, intensity and isotopic composition for future paleoclimatic studies there. Data from the Global Network of Isotopes in Precipitation (GNIP) of the International Atomic Energy Agency (IAEA) were used. Thus, the thesis was developed in three chapters of contents. The first topic addressed was in relation to demonstrate the isotopic fractionation resulting from transpiration by a green canopy. As results, it was shown that transpiration is a fractional process with respect to water isotopes. The magnitude of this fractionation is determined by environmental factors, such as soil water content, rainfall amount, temperature, and the relative humidity. The environmental factors influence the behavior of such important variables as stomatal aperture, the different diffusion resistances, and the kinetic fractionation. Then were proposed eight mathematical models that describes the relationship between rainfall isotopic composition, amount and erosivity for paleoclimatic studies. The trend founded in this research is that months with highest rainfall erosivity were less heavy isotopically. ?2H and ?18O were negatively correlated with erosivity and with the rainfall amount. The rainfall amounts were the higher negative correlation with the isotopic composition for this tropical region. In the third chapter, finally, it was evaluated if even Cuba being an island could be seen the classic effects of the isotopic hydrology as, continentality, rainfall amount and seasonality. As results, rainfalls in western Cuba are in general isotopically enriched in ?18O and ?2H in comparison with other regions at higher latitudes. The annual mean values for ?18O vary between (1 to -8) ? and for ?2H between (15 to -40) ?. Nevertheless, there is marked seasonal behavior, being the rainfalls heavier in winter and more depleted in summer, showing the established patterns for tropical region. The influence of the air masses movement on the rainfall isotopic behavior could be affirming the presence of the continental effect
Isótopos estáveis da água como 18O e 2H foram amplamente utilizados nos últimos 50 anos como traçadores em estudos climáticos e hidrológicos. Os isótopos estáveis da água têm propriedades físicas ligeiramente diferentes, incluindo uma energia latente diferente para as mudanças de fase, de modo que a concentração de isótopos da água se altera em mudanças da fase aquosa, fenômeno conhecido como fracionamento isotópico. Especificamente nos trópicos, os isótopos estáveis da água têm um comportamento muito particular, contrário ao nas regiões temperadas, pela influência dos grandes acumulados da chuva, altas temperaturas e umidade relativa. Cuba é uma ilha no meio do mar Caribe, onde estudos sobre a caracterização isotópica das precipitações nunca foram feitos. Para entender e explicar algumas questões relacionadas ao comportamento isotópico da precipitação nesta ilha, o trabalho de pesquisa foi desenvolvido fazendo uso de dados da área. O objetivo geral desta proposta de pesquisa é caracterizar a composição isotópica das chuvas no oeste de Cuba, incluindo a demonstração da influência da vegetação na composição isotópica da precipitação e determinar modelos matemáticos que descrevem a relação entre a quantidade e intensidade da chuva com a composição isotópica para futuros estudos paleoclimáticos. Para isto foram utilizados dados da Rede Global de Isótopos em Precipitação (GNIP) da Agência Internacional de Energia Atômica (AIEA). Assim, essa tese se apresenta em três capítulos. O primeiro capítulo trata da demonstração do fracionamento isotópico resultante da transpiração através da folha de árvores. A magnitude desse fracionamento é determinada por fatores ambientais, como o teor da água no solo, a quantidade da precipitação, a temperatura e a umidade relativa do ar. Os fatores ambientais influenciam o comportamento de variáveis tão importantes como a abertura estomática, as diferentes resistências de difusão e o fracionamento cinético. No segundo capítulo propõem-se oito modelos matemáticos que descrevem a relação entre a composição isotópica da precipitação, sua quantidade e erosividade, úteis para estudos paleoclimáticos. A tendência encontrada nesta pesquisa é que meses com chuvas mais erosivas foram menos pesadas isotopicamente. Os valores de ?2H e ?18O foram negativamente correlacionados com a erosividade e com os acumulados de precipitação, sendo que os acumulados de precipitação foram os de maior correlação negativa com a composição isotópica nesta região tropical. No terceiro capítulo foi avaliado se em Cuba, uma ilha, podiam ser detectados os efeitos clássicos da hidrologia isotópica. Os valores médios anuais para ?18O variam entre 1 e -8? e para ?2H entre 15 e -40?. No entanto, há um comportamento sazonal marcado, sendo as chuvas isotopicamente mais pesadas no inverno e mais leves no verão, mostrando os padrões estabelecidos para a região tropical. A influência do movimento das massas do ar sobre o comportamento isotópico da chuva pode afirmar a presença do efeito de continentalidade

Stable water isotopes (H2O, H18O, and HDO) are incorporated into the microphysics schemes of two different atmospheric models. This thesis describes the use of these molecules as tracers in precipitation budgets to assess the processes controlling the isotopic signatures of precipitation in the tropics and orographic snow in the mid-latitudes. The idealized simulations of seasonal precipitation budgets in the tropics determine that increased vapor convergence during intense precipitation is most important for setting the isotopic composition of the convective precipitation. The isotopic signal of the converged vapor is more important than the local evaporation and smaller scale post-condensational processes. Flow over a 2D-mountain and realistic simulations of orographic clouds show that the isotopic signature of precipitation is more sensitive to changes in mountain height and initial temperature profiles than to the cloud droplet number concentration. Riming of cloud liquid and vapor deposition onto ice are the largest source terms for orographic precipitation, and have distinct isotopic signatures that are altitude-dependent. When riming is the larger source term, precipitation tends to be more enriched than when vapor deposition dominates.
Earth and Planetary Sciences

Thesis (M.S.)--University of Nevada, Reno, 2007.
"May, 2007." Includes bibliographical references (leaves 54-57). Online version available on the World Wide Web. Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2007]. 1 microfilm reel ; 35 mm.

The aim of this thesis was to collect available stable isotopic data of precipitation from Finland and analyze it. Stable isotopes of precipitated water can be used as traces in hydrology. They can be used to study the origin of waters, the mechanisms of groundwater recharge, to study meteoric waters and to study the prehistorical climate and geology. The most often used stable water isotopes are oxygen-18 isotope and hydrogen-2 (also called deuterium) isotope. For this thesis, the stable isotopic data was collected from 13 stations. The precipitation samples had been collected by Geological Survey of Finland, Finnish Meteorological Institute and University of Oulu researchers. The isotopic composition of the precipitation samples was analyzed by University of Oulu, Geological Survey of Finland, University of Helsinki and Finnish Meteorological Institute laboratories. Also, as part of this thesis, some of the precipitation samples from Oulu station was collected and analyzed with Picarro L2120-i-analyzator. To analyze precipitated water, the local meteoric water lines, LMWL, were derived for 13 collection stations and for Finland (δ²H = 7.78 δ¹⁸O + 6.83). Also, the weather data was summoned for collection stations to time periods corresponding to precipitation collection time periods from Finnish Meteorological Institute weather data. The isotopic data was also studied for seasonal, temperature, altitude, latitude, amount, oceanic and continental effects. The weather parameters linear regressions with δ18O values were also studied. According the analysis, the temperature of surface during precipitation had the strongest effect on isotopic composition of the precipitation. In Finland, also latitude and oceanic and continental locations and especially seasons affected the isotopic composition of the precipitation. Weather parameters that had some relation to δ¹⁸O values were evaporation and humidity. Wind speed and the amount of rain had very little relation to δ¹⁸O values. As LMWLs of collection stations were studied, it was found that LMWL vary from one year and a season to another. Thus, it is recommended to have at least two years of isotopic data of precipitation when forming the lines. The isotopic data of precipitation collected in this thesis is available for future studies in Finland and internationally
Työn tavoitteena oli kerätä Suomen saatavilla olevat sateen stabiilit isotooppitiedot ja analysoida niitä. Sadannan stabiileja isotooppeja voidaan käyttää merkkiaineena hydrologiassa. Sadannan isotoopeja voidaan käyttää esimerkiksi tutkittaessa pohjaveden uusiutumista, veden viipymisaikaa hydrologisessa systeemissä, tutkittaessa esihistoriallista ilmastoa sekä geologiassa. Yleisimmin merkkiaineena käytetyt stabiilit veden isotoopit ovat happi-18 ja vety-2. Tässä työssä kerättiin sadannan isotooppitietoja 13 keräysasemalta. Sadenäytteet olivat kerätty Geologian tutkimuskeskuksen, Ilmatieteen laitoksen ja Oulun yliopiston toimesta. Sadenäytteiden isotooppikoostumus oli analysoitu Geologian tutkimuskeskuksen, Ilmatieteen laitoksen, Oulun yliopiston ja Helsingin yliopiston laboratorioissa. Osa Oulun keräysaseman sadenäytteistä kerättiin ja analysoitiin Picarro L2120-i-analysaattorilla osana tätä työtä. Sadannan isotooppiarvoista määritettiin meteorisille vesille Local Meteoric Water Line- suorat, (LMWL), kolmelletoista keräysasemalle sekä koko Suomelle (δ²H = 7.78 δ¹⁸O + 6.83). Työssä kerättiin myös Ilmatieteenlaitoksen tiedostoista sääparametrit keräysasemille näytteiden keräysajalle. Työssä tukittiin myös vuoden aikojen, lämpötilan, korkeusaseman, leveysasteen, sadannan määrän, merellisyyden ja mantereellisuuden vaikutusta sadannan isotooppeihin. Myös sääparametrien lineaarista regressiota isotooppiarvoihin tutkittiin. Analyysien tuloksena havaittiin sadannan aikaisella ilman lämpötilalla olevan suurin vaikutus sadannan isotooppikoostumukseen. Suomessa myös leveysaste, manterellisuus, merellisyys ja erityisesti vuodenajat vaikuttavat sadannan isotooppikoostumukseen. Sääparametreistä haihdunnalla ja ilmankosteudella löydettiin jonkin verran riippuvuutta sadannan isotooppikoostumuksen kanssa, mutta tuulella ja sateen määrällä ei juurikaan. Määritettyjä LMWL-suoria analysoitaessa todettiin, että LMWL-suorat poikkeavat toisistaan vuosittain. Samoin eri vuodenajoille määritetyt suorat poikkesivat toisistaan. Analyysin perusteella LMWL-suoria määriteltäessä on suositeltavaa olla käytettävissä vähintään kahden vuoden sadannan isotooppitiedot. Tässä työssä kootut sadannan isotooppitiedot ovat käytössä jatkotutkimuksiin niin Suomessa kuin kansainvälisestikin

Total evapotranspiration (ET) is the key process that links the land and the atmosphere via water, energy and carbon exchange. ET is a combination of evaporation and transpiration, which behave dynamically in very different ways. In this work we investigate the relative contribution of transpiration and soil evaporation to total ET in a semi-wooded, semi-arid forest in the Manitou Research Park northwest of Colorado Springs, CO. We use stable water isotopes measured at different levels within and outside the canopy, over a 30-day period (June 26 - July 26, 2010), using a field-deployable cavity ring-down spectrometer. The traditional "Keeling plot" analysis is used to partition the ET flux from moisture that comes from outside of the ecosystem, and then a simple model is used to partition the transpiration flux. In addition, we introduce a new alternative "multi-level" method to calculate the fraction of transpiration to total ET. Both the "Keeling plot" method and the "multi-level" method yield very similar fractions of transpiration to total ET, ranging from about 15% to about 85%. We compare both methodologies and discuss some of the corrections that must be made when measuring with high-frequency field-deployable instruments.

This thesis compares paleoclimate records with isotope-enabled paleoclimate model simulations. δ¹⁸0 against salinity and temperature relationships are investigated during periods of altered ice sheets, sea ice and meltwater input. We concentrate on 0, 21, 125 and 128 thousand years ago. Chapter 2 examines the use of δ¹⁸0 measurements in reconstructing salinity from ocean cores. Chapter 3 examines how Antarctic ice core δ¹⁸0 responds to changes in West Antarctic Ice Sheet (WAIS) morphology and sea ice extent. We find that ice sheet changes can decouple the δ¹⁸0-temperature relationship. The most significant contribution of this thesis focusses on explaining the last interglacial (LIG) δ¹⁸0 maximum, approximately 128 thousand years ago. Here, by replacing the WAIS with ocean and including the effects of WAIS meltwater, we provide a relatively realistic simulation of WAIS collapse. We find that a full WAIS collapse during the early LIG was unlikely. Instead a major reduction in sea ice, driven by bipolar seesaw warming of the Southern Hemisphere in response to circum-North Atlantic ice sheet melting, is a more likely explanation for the LIG isotope maximum. However, model simulations of 600 years duration, presented in Chapter 4, indicate that the bipolar seesaw mechanism only partially explains the observed isotope maximum. This leaves a significant portion of the observed Southern Ocean warming, estimated sea ice retreat and observed 6180 enrichment unaccounted for. It is currently unclear whether this result is repeatable using other General Circulation Models. The connectivity between the Southern Ocean, sea ice and the Antarctic ice sheet are suggested as a high-priority areas for future study to reconcile the remaining model-data disagreement.

The expansion of Eucalyptus plantations to supply timber for an increasing population in South Africa will result in a great reduction in the country's run-off water. If Eucalyptus continues to be the source of timber in South Africa, the selection of more water use efficient species for planting in existing and new areas has to be implemented. An understanding of the physiological factors ruling growth and water use efficiency in Eucalyptus is needed to develop selection criteria for improved water use efficiency and harvestable stem production under a limited water supply. This study investigated the effects of soil moisture availability on the growth and water use efficiency of 6 commercial clones of Eucalyptus commonly grown in South Africa with the aim of determining the following: (i) The extent of clonal variation in growth, dry mass allocation patterns, water use efficiency and the water cost of wood production at 16 months after planting. (ii) The influence of plant physiological traits such as patterns of dry mass allocation, canopy leaf area, leaf canopy density, specific leaf area, foliar nitrogen concentration and instantaneous rates of photosynthesis and transpiration, on growth, water use efficiency and the water cost of wood production. (iii) The complications associated with sampling for stable carbon isotope ratios (δ¹³C) within a eucalypt canopy and the potential use of δ¹³C in plant tissues as a tool for ranking clonal water use efficiencies.

The marked decline in tree island cover across the Everglades over the last century, has been attributed to landscape-scale hydrologic degradation. To preserve and restore Everglades tree islands, a clear understanding of tree island groundwater-surface water interactions is needed, as these interactions strongly influence the chemistry of shallow groundwater and the location and patterns of vegetation in many wetlands. The goal of this work was to define the relationship between groundwater-surface water interactions, plant-water uptake, and the groundwater geochemical condition of tree islands. Groundwater and surface water levels, temperature, and chemistry were monitored on eight constructed and one natural tree island in the Everglades from 2007-2010. Sap flow, diurnal water table fluctuations and stable oxygen isotopes of stem, ground and soil water were used to determine the effect of plant-water uptake on groundwater-surface water interactions. Hydrologic and geochemical modeling was used to further explore the effect of plant-groundwater-surface water interactions on ion concentrations and potential mineral formation. A comparison of groundwater and surface water levels, along with calculated groundwater evapotranspiration rates, revealed that the presence of a water table depression under the islands was concurrent with elevated groundwater uptake by the overlying trees. Groundwater chemistry indicated that the water table depression resulted in the advective movement of regional groundwater into the islands. A chloride budget and oxygen isotopes indicated that the elevated ionic strength of tree island groundwater was a result of transpiration. Geochemical modeling indicated that the elevated ionic strength of the groundwater created conditions conducive to the precipitation of aragonite and calcite, and suggests that trees may alter underlying geologic and hydrologic properties. The interaction of tree island and regional groundwater was mediated by the underlying soil type and aboveground biomass, with greater inputs of regional groundwater found on islands underlain by limestone with high amounts of aboveground biomass. Variations in climate, geologic material and aboveground biomass created complex groundwater-surface water interactions that affected the hydrogeochemical condition of tree islands.

Delineating spatial patterns of precipitation isotopes (“isoscapes”) is important for studies including the hydrology of terrestrial systems, present and past interpretations of climate, and tracer-aided hydrological modelling, among others. However, the extent to which precipitation isoscapes can be predicted across Canada has not been fully articulated. This thesis combines isotopes in precipitation (δ18Oppt) observations from two regional and one global network to create long term and time series precipitation isoscapes for Canada and the northern United States. Multi-linear regressions of a small suite of geographic and climate variables generate the best performing long-term and seasonal models of δ18Oppt. These models are used to develop long term isoscapes for Canada, which capture the general spatial and seasonal trends in δ18Oppt, showing an improvement upon results from previous studies using global models. Building upon long-term δ18Oppt prediction, δ18Oppt observations alongside climatological and geographic predictors are used to create empirical time series prediction models. Five regionalization approaches are used to separate the study domain into isotope zones to explore the effect of spatial grouping on simulations. Generally, the models capture the timing and magnitude of intra-annual (seasonal) δ18Oppt cycles across the study domain while simulating moderate inter-annual variation; however often fail to capture the anomalies in observed δ18Oppt. Uncertainty in predictions is quantified spatially and temporally, and the Köppen-Geiger (Kpn) regionalization is selected as the preferred regionalization scheme for future applications due to adequate model performance and lack of border issues at regional boundaries. Finally, estimates of monthly δ18Oppt from Kpn models, long term annual averages, and daily REMOiso output are used to force an isotope-enabled hydrological model, isoWATFLOOD, in the Fort Simpson Basin, NWT, Canada. Results show streamflow simulations are not significantly impacted by choice of δ18Oppt input; however, oxygen-18 in streamflow and the internal apportionment of water (and model parameterizations) are impacted, particularly during large precipitation and snowmelt events. This work shows how isoWATFLOOD can be used in regions with limited δ18Oppt observations, and that the model can be of value in such regions. This study reinforces that a tracer-aided modelling approach works towards diagnosing issues surrounding model equifinality.
February 2017

The stable isotopic composition of groundwater within a watershed in eastern Iowa was studied in order to understand how water moves through the system. Samples were gathered using multiple observation wells and pore water samplers and then analyzed to determine the δ18O and δ2H of each sample. Shallow pore water is much more variable in its isotopic composition than deeper water and seems to be more greatly affected by evapotranspiration, whereas groundwater below the water table appears to show a stable isotopic signature suggesting the integration of multiple rain events. Other samples of similar depths across the slope of a hill were also used to observe differences across the area. By observing changes over time in the signatures of these samples, it can be seen that the crest of the hill is most greatly influenced by infiltration from precipitation while the side of the hill is influenced more by throughflow. By combining stable isotope analyses, knowledge of the medium through which the water is moving and the general mechanics of a watershed, a more advanced understanding of how water interacts with and moves through the ground can be gained.

Regions of surface water and groundwater exchange are major sites for the transfer and transformation of solutes and nutrients between stream and subsurface environments. Conventional stream and groundwater exchange investigations are limited by methodologies that require intensive field investigations and/or the set-up of expensive infrastructure. These difficulties are exacerbated where hydraulic gradients are very low and stream discharge highly variable. This thesis uses a suite of environmental tracers (Cl-, Rn-222, H-2 & O-18, Sr-87/Sr-86) to characterise the extent of stream and groundwater exchange between a sand bed stream and adjacent alluvial aquifer in a subtropical catchment (the Wollombi Brook) of eastern Australia. The aims were to identify sources and relative contributions of different sources of groundwater to stream discharge and specifically to improve the methodology of using Rn-222 to obtain quantitative estimate of groundwater fluxes. The sensitivity of the Rn-222 technique for identifying groundwater discharge based on the Rn-222 concentration in stream water was improved via an iterative numerical approach to account for Rn-222 loss from stream water via turbulent gas exchange and radioactive decay. Optimal distances between stream sampling points for defining the magnitude of groundwater discharge to stream flow based on Rn-222 concentrations in stream water is a function of average stream velocity and water depth. The maximum allowable distance between sampling points for determining the magnitude of groundwater discharge to the Wollombi Brook was 2 km. This work showed that groundwater discharged to all reaches of the Wollombi Brook during baseflow and flood recession conditions. Alluvial groundwater contributed less than 30% of water to stream flow in the mid Wollombi Brook catchment. Dilution of steady-state Rn-222 concentrations measured in transects from the stream to the alluvial sediments showed that significant surface water and groundwater exchange occurs even when gradients between surface water and groundwater are low. Lateral stream water influx to the adjacent alluvial aquifer was more extensive in the lowland areas of the Wollombi Catchment during low flow than flood recession conditions. Extensive stream water influx to the adjacent alluvial aquifer occurs contrary to the net direction of surface water and groundwater flux (as indicated by hydraulic gradients toward the stream channel). The rate of stream and groundwater exchange within the adjacent alluvial aquifer appears to be greatest during baseflow conditions. Fresh alluvial groundwater appeared to provide a buffer against higher salinity regional groundwater discharge to the alluvial aquifer in some reaches of the Wollombi Brook catchment. Pumping of the alluvial aquifer and diversions of surface water may jeopardise the water quality and volume of the alluvial aquifer and induce water flow from the regional aquifer toward the stream, potentially salinising the fresh alluvial aquifer and subsequently the stream. The change in the Cl- concentration and the variation in slope of the deuterium � oxygen-18 line between consecutive stream sampling points could be used to differentiate between regional and alluvial groundwater discharge to stream flow. Incorporating this information with three-component end-member mixing using [Sr2+] and Sr-87/Sr-86 showed that stream and alluvial groundwater exchange within the stream channel was highest in the lowland floodplains during low flow conditions. The least stream and alluvial groundwater exchange occurred in the low streambed gradient mid reaches of the Wollombi Brook regardless of stream stage. The greatest difference in the degree of stream and alluvial groundwater exchange between high and low stream stages occurred in the lowland floodplains of the Wollombi Brook.

Dans un contexte de réchauffement climatique, appréhender l'évolution de la hausse du niveau des mers est un enjeu majeur. Pour cela un des éléments clefs est de comprendre l'évolution du cycle hydrologique atmosphérique dans les régions polaires qui influence directement le bilan de masse de surface des calottes Arctique et Antarctique (les deux plus gros réservoirs d'eau douce de la planète). Des enregistrements existent grâce aux données satellites depuis 50 ans et quelques rares données météo depuis 70 ans en Antarctique mais ces enregistrements sont trop courts pour étudier les modes de variabilité pluri-annuels ainsi que la différence entre signal anthropique et signal naturel. Pour avoir accès à des enregistrements plus longs, une des meilleures solutions est d'utiliser les traceurs climatiques dans les carottes de névé. La composition isotopique de l'eau dans ces carottes est largement utilisée pour reconstruire les variations de température passée. Cela dit, le lien entre température et composition isotopique n'est pas très bien contraint car de nombreux autres paramètres influencent la composition isotopique de la neige au moment de sa formation (i.e. température, altitude, humidité, origine de la masse d'air) ou après le dépôt de neige en surface (i.e. échange atmosphère-neige, diffusion du signal, sublimation de la neige de surface).L'objectif de cette thèse est de mieux comprendre le cycle hydrologique atmosphérique et son influence sur la composition isotopique de la vapeur et de la précipitation dans les régions polaires avec en tête l'idée d'améliorer l'interprétation des carottes de névé dans ces régions. Ce travail se décompose en 3 parties.Dans un premier temps, nous avons développé une solution technique qui répondait au défi de la mesure de la composition isotopique de la vapeur toute l'année en région polaire. En effet, l'hiver étant très sec dans ces régions (jusqu'à 10 ppmv à Dome C, l'hiver), l'utilisation d'un analyseur laser Picarro était limité car il est très sensible aux variations d'humidité en dessous de 2000 ppmv. L'hiver est une saison clé dans les régions polaires car elle est synonyme d'une importante variabilité climatique du fait de nombreux évènements synoptiques. Durant cette thèse, la fabrication de 2 prototypes de générateur de très basse humidité (LHLG) a permis de calibrer les analyseurs Picarro sur une gamme de 200 à 2500 ppmv.Ensuite, j'ai analysé la plus longue série de mesures de la composition de la vapeur et de la précipitation jamais effectuée en région polaire: 4,5 années en continu, à 78°N au Svalbard. J'ai montréque le site de mesure était très peu influencé par des processus locaux agissant sur la composition isotopique de la vapeur d’eau. Grâce à cela, j'ai pu attribuer les variations observées, l'hiver, à des évènements synoptique et ainsi attribuer une signature isotopique différente aux masses d'air en fonction de leur origine (Nord Atlantique ou Arctique).Enfin, j'ai installé le nouvel instrument de calibration fabriqué au début de mon doctorat à Dumont D'Urville (DDU), sur la côte en Terre Adélie. Grâce à cela, la première campagne de mesure continue de la composition isotopique de la vapeur à DDU initiée en janvier 2019 est toujours en cours. Je présente ici les 22 premiers mois de ce nouvel enregistrement. Cette série unique permet de documenter la signature isotopique du cycle hydrologique atmosphérique en Terre Adélie toute l'année. J'ai étudié l'influence des vents catabatiques, de la glace de mer et des rivières atmosphériques sur le signal enregistré dans la vapeur. Ces résultats préliminaires ouvrent des perspectives pour l'interprétation des carottes de névé récemment forées dans le cadre du programme ASUMA
In a global warming context, understanding the evolution of sea level rise is a major challenge. It is key to estimate the evolution of the atmospheric hydrological cycle in the polar regions, which directly influences the surface mass balance of the Arctic and Antarctic ice caps (the two largest freshwater reservoirs on the planet). Records are available from satellite data for the last 50 years and a few rare weather data since the 50's in Antarctica, but these records are too short to study the patterns of interannual variability and the difference between anthropogenic and natural signals. One of the best ways to access longer records is to use climate proxies in snow cores. The water isotopic composition in these cores is widely used to reconstruct past temperature variations. However, the link between temperature and isotopic composition is not very well constrained because many other parameters influence the isotopic composition of snow at the time of its formation (i.e. temperature, altitude, humidity, origin of the air mass) or after snow deposition on the surface (i.e. atmosphere-snow exchange, signal scattering, sublimation of surface snow).The objective of this thesis is to better understand the atmospheric hydrological cycle and its influence on the isotopic composition of vapour and precipitation in polar regions with the idea of improving the interpretation of snow core records in these regions. This work is divided into 3 parts.Firstly, we developed a technical solution to meet the challenge of measuring the vapor isotopic composition all year round in polar regions. Indeed, winter being very dry in these regions (down to 10 ppmv at Dome C in winter), the use of a Picarro laser analyzer is limited because it is very sensitive to humidity variations below 2000 ppmv. Winter is a key season in the polar regions as it is associated with significant climate variability due to numerous synoptic events. During this thesis, the fabrication of 2 prototypes of low humidity level generator (LHLG) allowed the calibration of the Picarro analyzers over a range of 200 to 2500 ppmv.Then, I analyzed the longest series of vapor and precipitation isotopic composition measurements ever performed in a polar region: 4.5 years continuously at 78°N in Svalbard. I showed that the water isotopic composition at this measurement site was unsignificantly influenced by local processes. Thanks to this, I was able to attribute the observed winter variability to synoptic events and thus assign a different isotopic signature to the air masses according to their origin (North Atlantic or Arctic).Finally, I installed the new calibration instrument (LHLG) built at the beginning of my PhD at Dumont D'Urville (DDU), on the coast in Terre Adélie. Thanks to this, the first continuous measurement campaign of the vapor isotopic composition at DDU initiated in January 2019 is still ongoing. I present here the first 22 months of this new record. This unique series makes possible to document the isotopic signature of the atmospheric hydrological cycle in Terre Adélie all year round. I have studied the influence of katabatic winds, sea ice and atmospheric rivers on the signal recorded in the vapor. These preliminary results open perspectives for the interpretation of recently drilled cores from the ASUMA program

Many large terrestrial ecosystems have patterned landscapes as a result of a positive feedback system between vegetation communities and environmental factors. One example is tree island habitats in the Florida Everglades. Although they only occupy a small portion of the Everglades landscape, tree islands are important features as the focus of nutrient accumulation and wildlife biodiversity in the Everglades ecosystem. The hardwood hammock community on the elevated head of tree island habitats can accumulate high phosphorus concentration in the otherwise P-limited Everglades ecosystem. In this dissertation, I examined two hypotheses derived from the chemohydrodynamic nutrient accumulation model, which suggests that high transpiration of tree island hammock plants is the driving force for nutrient accumulation in tree island soil. According to this model, I hypothesized that tree islands with lower dry season transpiration should have less phosphorus accumulated than the tree islands with higher dry season transpiration. By examining the water use and nutrient status from 18 tree islands in both slough (perennially wet) and prairie (seasonally wet) locations, I was able to compare water availability and nutrient accumulation in slough and prairie tree islands with different marsh hydroperiods. Chapter 1 uses elemental and stable isotope analysis to look at water stress and nutrient concentration in tree island plants. I showed that the prairie tree island plants suffer from drought stress during the dry season, when the marshes in the prairies dry out. Prairie tree islands also have lower soil and plant P concentration than the slough tree islands. Moreover, I showed that foliar N isotope ratio serves as a stable proxy for community level P availability for tree island plants, and prairie tree island plants have less P available than slough tree island plants. In Chapter 2, I showed that the satellite imagery derived normalized difference water index (NDWI) provides a robust indicator of community level canopy water content of these tree islands. NDWI, used as a proxy for water status, was positively related to foliar N isotope ratio, which suggests that water availability is linked to nutrient availability in the tree island hardwood hammock plant communities. These findings are consistent to the chemohydrodynamic nutrient accumulation model. In Chapter 3, I used sap flow sensors on individual trees to provide a real-time measurement of plant transpiration. I showed that tree island plant transpiration is affected by multiple factors including weather fluctuations, marsh water depth regulated by local water management, and canopy structure of different tree islands. Overall, my dissertation establishes a link between tree island plant water use and nutrient accumulation. It could be potentially important for future restoration plan of tree islands and Everglades hydrological management.

Stable isotope probing (SIP) is an established technique that can be applied to identify the metabolically active micro-organisms within a microbial population. The SIP method utilises an isotopically-labelled substrate and PCR techniques to discern the members of a microbial community that incorporate the isotope into their DNA or RNA. The current literature gap around using 15N isotopes with RNA-SIP offers real potential and advantages for targeting and identifying active members from mixed communities involved in global biogeochemical nitrogen cycling. This study specifically investigated whether nitrogen based compounds can be used as substrates in RNA-SIP methodologies and whether they can in turn be used to probe mixed community environments known to be actively fixing nitrogen. The nitrogen-limited systems targeted represented an ideal opportunity to assess the suitability of 15N-RNA-SIP approaches due to their known high nitrogen fixation rates. Identifying these nitrogen-fixing bacteria could provide a better representation analysis of the community, leading to an improved prediction on how to manage and optimise the treatment performance of target waste systems and to exploit the unique bioconversion properties of these types of organisms. Initially, the project undertook methodological proof of concept by using a soluble nitrogen source, 15NH4Cl, to label the RNA of Novosphingobium nitrogenifigens and a mixed microbial community. Successful separation of the 14N- (control) and 15N-RNA was achieved for both pure and mixed communities using isopycnic caesium trifluoroacetate (CsTFA) gradients in an ultracentrifuge. The usefulness of this technique to identify active diazotrophs in real environmental samples was tested using a nitrogen-fixing community from a pulp and paper wastewater treatment system. After growing the mixed culture with 15N2 as the sole nitrogen source, the labelled RNA was extracted and fractionated using isopycnic centrifugation in CsTFA gradients. The community composition of the active nitrogen-fixing community in the 15N2 enriched fraction was analysed by establishing a 16S rRNA gene clone library containing over 200 members. These were analysed by comparison with published sequences and by phylogenetic analysis. It was found that the more isotopic label substrate incorporated, the further the buoyant density (BD) separation between 15N- and 14N-RNA. Novosphingobium nitrogenifigens gave an average BD shift of 0.03 + 0.004 g ml-1 (95.0 atom % 15N) with 15NH4Cl. For mixed communities the average BD shift was 0.02 + 0.004 g ml-1 (80.0 atom % 15N) with 15NH4Cl and 0.013 + 0.002 g ml-1 (32.6 atom % 15N) when using 15N2. Clone library analysis of 16S rRNA genes present in the enriched 15N-RNA fraction of the mixed community was shown to consist of a diverse population of bacteria as indicated by a Shannon Weaver index value of gt;2.8. Three dominant genera (Aeromonas, Pseudomonas and Bacillus) were identified by comparison with published sequences and phylogenetic analysis. Many other groups not known as archetypal nitrogen-fixing bacteria were also identified, demonstrating that 15N2-RNA-SIP provides a useful tool for the identification of important and previously unknown contributors to nitrogen fixation in a range of environments. Overall, this project has established that nitrogen based RNA-SIP is a powerful tool that can be used successfully and reproducibly with both pure and complex mixed microbial communities to study active diazotrophs in environmental samples.

Ice formed by water vapour deposition has been identified in different terrestrial environments: 1) in the atmosphere; 2) at the ground’s surface; 3) in caves; 4) in seasonally frozen ground; and 5) in perennially frozen ground (permafrost). Thus far, ground ice formed by diffusion and deposition of vapour in soils (types 4 and 5) has rarely been studied in a natural setting and remains one of the most poorly described ice types on Earth. This thesis focuses on the dynamics of deposition and sublimation of atmospheric water vapour into permafrost and the isotopic signature (D/H and 18O/16O) of the emplaced ground ice under different experimental conditions. Ground ice was produced in sediments with different thermo-physical characteristics (glass beads, JSC Mars-1 simulant). After a two-month growth period, the higher porosity sediments (JSC) had more than 7x the gravimetric water content than the lower porosity soil. Ground ice profiles had a distinct concave downwards shape due to the decrease in saturation vapour pressure with depth. Results also indicate that vapour deposited ground ice has a distinct δD-δ18O composition that plots near regression slope value of 8. Pore water isotopes plot below the global meteoric water line (GMWL) when the source of moisture is directly on top of the sediments. If an air gap is introduced between the source of moisture and the sediments, the pore water isotopes shift above the GMWL due to re-sublimation at the ground surface. Overall, this thesis addressed some fundamental knowledge gaps required to better understand the growth and isotopic evolution of ground ice emplaced by vapour deposition.

Alteration of rock by water is observed in all levels of the Apache Leap Tuff, Superior, Arizona. Possible alteration conditions range from hydrothermal circulation after eruption of the tuff to percolation of low temperature modern water. This study uses stable isotopes of oxygen and hydrogen in matrix phenocrysts and whole rocks to determine temperature and timing of alteration, and the extent of water-rock interaction at progressive distances from fractures. Data indicate low temperatures (20 to 30°C) of water-rock interaction. Water/rock ratios increase stratigraphically upward. Water/rock ratios decrease as distance from fractures decrease, suggesting that fractures may not have been major flow conduits. Calculations indicate a water oxygen isotopic composition similar to modern water, although the water hydrogen isotopic composition is heavier than modern water due to evaporation.

When different water resource components coexist in nature, they usually have an impact on each other. Studies of how they impact each other in terms of water quantities, flow dynamics, quality and contamination are therefore necessary to ensure an appropriate water and environmental management is conducted. A study in Middleburg comprised a literature review and field investigations at and around a cemetery, as part of a Water Research Commission project on impacts on the water resource from large-scale burials. A literature review conducted has enabled familiarisation with similar studies that have been conducted around the subject. Reliable methodologies have therefore been adopted from the published literature and applied on the current research. A seasonal wetland is located downgradient of the cemetery, between the cemetery and a stream that flows past the cemetery. In order to assess possible flow pathways of near-surface and groundwater from the cemetery to the stream, monthly monitoring of surface and groundwater quality and level fluctuations was carried out on the stream, as well as existing and newly installed boreholes at the cemetery. Water samples collected were analysed for inorganic constituents, tritium, and stable water isotopes. The tritium and stable water isotope results – revealed the comparative influence of rainfall and shallow groundwater contributions to streamflow, while groundwater provides base-flows as the stream levels recede. The depth to groundwater reduced with increasing rainfall, indicating direct recharge. The difference in concentrations of some inorganic parameters in the stream compared to the groundwater at the cemetery revealed the effect of natural attenuation in the vadose zone due to reduced conditions and the wetland acting as a filter to improve the water quality of the shallow interflow on reaching the stream. Since isotope data indicated to be a useful tool in studying water resource interactions, the methodology should form part of site investigations for cemetery development or on existing cemeteries to study the current impact and/or predict future impacts that the cemetery may have on the water resources. The methodology best applies in areas with multiple water resources, where there may be an interconnection between them. The isotope studies can also be used to estimate recharge and thus contaminant transport rate of the cemetery leachate.
Dissertation (MSc)--University of Pretoria, 2020.
Geology
MSc
Unrestricted

Carbon tetrachloride (CT) and chloroform (CF) are chlorinated methanes (CMs) which have been released to the environment for decades owing to scarce waste management. Since they are dense non-aqueous phase liquids (DNAPLs), CMs migrate downwards and reach groundwater constituting a contamination source. Thus, this pollution requires a thoughtful monitoring and treatment since CT and CF are toxic and predicted to be carcinogenic substances (IARC, 2017). Although CT and CF are considered quite persistent in aquifers, they undergo abiotic and biotic natural attenuation. This degradation occurs mainly through reductive pathways under anoxic conditions, but CF oxidative microbial cometabolism could be also plausible (Cappelletti et al., 2012; Penny et al., 2010). Hence, CMs transformation processes are expected under field conditions. Òdena field site (Barcelona, Spain) is polluted by CMs among other volatile organic compounds (VOCs) due to industrial activity during the 70s and 80s. Chlorinated ethenes (CEs) degradation was detected in the fractured aquifer by carbon isotope (δ13C) enrichment over time (Palau et al., 2014b). CF alkaline hydrolysis (AH) was also revealed by δ13C monitoring in the interception trenches filled with construction wastes (pH ~12) built in the unsaturated zone after 2005 source removal, whereas the cause of CT δ13C enrichment over time in these trenches remains unknown (Torrentó et al., 2014). Induced reactions bear potential to overcome the challenges derived from the slow degradation rates of CMs natural attenuation. Biostimulation, zero valent iron permeable reactive barriers (Fe(0)-PRB) or those made of other reducing agents are receiving increasing attention as alternative remediation strategies. However, in situ chemical oxidation (ISCO) and alkaline hydrolysis are techniques of interest only for CF as a result of the high oxidation state of carbon in CT. Compound specific isotopic analysis (CSIA) is a useful tool to evaluate the efficiency of both CMs natural attenuation and induced strategies in the field. CSIA not only verifies that the concentration decrease is due to reactive processes (instead of dispersion or dilution) but also permits quantification. Moreover, dual isotope plots in which shifts in isotope values of one element are plotted against those of a second element, allow distinction between different CMs reaction mechanisms by means of specific slopes (Λ). Thus, laboratory CMs degradation experiments under controlled conditions are required to gain understanding of the expected isotopic changes in the field and to evaluate whether it is feasible to quantitatively detect degradation. Although relatively new, Cl-CSIA for CEs and chlorinated ethanes has been gradually incorporated in the last 6 years in combination with consolidated C-CSIA. However, Cl-CSIA was only used in few laboratory experiments for CF and the method was not validated for any CMs prior to this thesis. The main aims of this thesis have been to better understand CMs natural attenuation together with potential CMs remediation strategies to improve the assessment of CMs fate in Òdena site and, by extension, in other polluted sites all over the world. These goals were addressed primarily by C-CSIA and Cl-CSIA, among other techniques. Prior to their use in laboratory or field samples, Cl-CSIA method has been developed and evaluated for CT and CF by both, gas chromatography-isotope ratio mass spectrometry (GC-IRMS) and by gas chromatography-quadrupole mass spectrometry (GC-qMS validated in an interlaboratory comparison) through an international collaboration (Helmholtz Zentrum München and Université de Neuchâtel) during different thesis stays. Three relevant abiotic CF transformation mechanisms were studied in batch experiments: oxidation by heat-activated persulfate (abbreviated as PS); AH and reductive dechlorination by Fe(0), obtaining similar Λ values for PS and AH (17±2, 13.0±0.8) which are distinguishable from reductive dechlorination (8±2). CT and CF degradation by Fe(0) and Fe-bearing minerals (pyrite (Py, FeS2) and magnetite (Mag, Fe3O4) in the presence of FeCl2 were carried out in laboratory experiments at pH 7 and 12 simulating groundwater in the saturated zone and in alkaline interception trenches in the unsaturated zone of Òdena site, respectively. CF hydrogenolysis to dichloromethane (DCM) by milli-sized Fe(0) was characterized at both pHs, whereas CF degradation by Fe- bearing minerals was only identified at pH 12. In this case, AH was hypothesized since no VOCs by-products were detected except for DCM only with Py, evidencing CF hydrogenolysis. CT degradation by both Fe(0) and Fe-bearing minerals was confirmed at pH 12, whereas at pH 7, CT degradation was only obtained by nano-sized Fe(0) and Py. pH did not affect Λ values of CT and CF degradation by Fe(0) nor CT degradation by Py. CT thiolytic reduction to carbon disulphide (CS2) occurred in parallel to CT hydrogenolysis in experiments with Py at both pH values, showing different Λ values to net CT hydrogenolysis by Fe(0), but similar Λ values to CT reduction by Mag at pH 12. These differences provide good chances to detect these pathways in the field. Additionally, CT and CF microcosm experiments were performed separately for each compound by using slurry from one of the most polluted wells in Òdena site (S3). Biotically- mediated CT hydrogenolysis was confirmed in the microscoms. Biostimulation with vitamin B12 catalyzed CT biodegradation and stimulates CF biodegradation, the latter not observed without B12. For both target compounds, no relevant accumulation of other chlorinated compounds neither CS2 was detected with B12. CT experiments with B12 might be linked to a major activity of Pseudomonas stutzeri able to reduce CT to CO2. Acidovorax, Ancylobacter and Pseudomonas were the most metabolically active genera observed in the experiments, whereas commonly found organo-halide respiring bacteria, Dehalobacter and Desulfitobacterium, were below 0.1% of relative abundance. The Λ of CF biodegradation by B12 (7±1) was similar to that reported for CF reductive dechlorination by Fe(0) (hydrogenolysis plus reductive elimination) (8±2). Λ of CT biodegradation without B12 showed no difference to CT hydrogenolysis by Fe(0) which indicates the same pathway. Furthermore, Λ of CT degradation was statistically different despite their 95% of confidence interval (CI) with and without B12 (5±1 vs. 6.1±0.5, respectively), indicating possible influence of other reduction processes different from CT hydrogenolysis. δ13C enrichment of CEs, once CMs were completely degraded by B12-catalyzed biotic reactions, confirmed CMs inhibition of CEs degradation. The obtained laboratory data improved the knowledge on CMs degradation processes and established the basis applicable in multi-contaminant polluted sites like Òdena. A long-term monitoring to study 2005 source’s removal effects on groundwater CMs has been performed from 2002 to 2014. Through by-products and C-CSIA monitoring, CMs transformation processes over time have been confirmed. The source’s removal was inefficient since active CMs leaching was proved in the outskirts of the dismantled wastewater pipe and in the wastewater tank. Nevertheless, by-products and Λ studies disclosed CT and CF reduction processes precisely in those areas. In contrast, in former disposal pit source, where removal was more efficient, isotopic values unveiled a migration of the focus downstream as well as an influence of hydrolysed CF coming from the alkaline trench and/or CF oxidation processes in the saturated zone of this area. To sum up, this thesis has provided progress in Cl-CSIA methodology for CMs and new compelling C and Cl-isotope laboratory data related with CT and CF degradation processes. These data combined with other microbial and geochemical tools have allowed the discrimination of CMs degradation processes at field scale and are promising for monitoring the efficiency of remediation strategies in other polluted sites. The routine use of Cl-CSIA analyses are worthwhile for further research together with well-stablished C-CSIA. Moreover, the up-scale application and evaluation of studied CMs remediation techniques such as biostimulation by economical B12 sources in combination or not with Fe(0) or Fe-bearing minerals (which implies mining wastes revalorization) are challenges ahead.
El tetracloruro de carbono (CT) y el cloroformo (CF) son compuestos orgánicos que pertenecen al grupo de los metanos clorados (CMs) los cuales han sido vertidos descontroladamente al medio ambiente durante décadas debido a la escasa gestión y tratamiento de residuos. Puesto que son disolventes más densos que el agua, una vez vertidos, estos contaminantes migran en profundidad hasta las aguas subterráneas creando frecuentes fuentes de contaminación ambiental que, por su persistencia, constituyen un riesgo para la salud pública. Por lo tanto, este tipo de contaminación requiere de un seguimiento exhaustivo, así como de hallar tratamientos específicos debido a que el CT y el CF son consideradas substancias tóxicas y carcinogénicas (IARC, 2017). Aunque el CT y el CF son persistentes en acuíferos, estos compuestos experimentan atenuación natural tanto biótica como abiótica. Los CMs se degradan principalmente a través de mecanismos de reducción bajo condiciones anóxicas, aunque la oxidación microbiana del CF por cometabolismo también es un proceso de degradación potencial (Cappelletti et al., 2012; Penny et al., 2010). Por consiguiente, se esperan procesos de transformación de los CMs en emplazamientos contaminados. El enclave contaminado de Òdena (Barcelona) se encuentra afectado tanto por CMs como por otros compuestos orgánicos volátiles (VOCs, por sus siglas en inglés) debido a actividad industrial en los años 70 y 80. La degradación de etenos clorados (CEs por sus siglas en inglés) en este acuífero fracturado fue detectada ya que se observó un enriquecimiento isotópico del carbono (δ13C) a lo largo del tiempo (Palau et al., 2014b). La presencia de hidrólisis alcalina (AH, por sus siglas en inglés) del CF fue también revelada mediante el seguimiento de la δ13C del CF en las rasas de intercepción de agua de lluvia creadas con residuos de la construcción (pH~12) en la zona no saturada, una vez que se extrajeron las fuentes de contaminación en 2005. Sin embargo, aún se desconoce el motivo del enriquecimiento de la δ13C del CT a lo largo del tiempo en estas rasas (Torrentó et al., 2014). Para mejorar las limitaciones de los potenciales procesos de atenuación natural de los CMs y hacerlos más eficientes, se pueden usar diferentes técnicas de remediación inducida. La bioestimulación y el uso barreras reactivas permeables de Fe(0) o construidas con otros agentes reductores son de creciente interés. La oxidación química in situ (ISCO) y la AH son técnicas de remediación abiótica pertinentes únicamente para el CF, debido al alto estado de oxidación del carbono en el CT. El análisis isotópico de compuesto específico (CSIA por sus siglas en inglés) es una herramienta muy útil para evaluar la eficiencia tanto de la atenuación natural de los CMs como la de las estrategias de remediación aplicadas en emplazamientos contaminados. El método de CSIA no solo verifica, mediante el seguimiento de la composición isotópica a lo largo del tiempo, que la disminución de la concentración de los CMs sea debida a procesos reactivos (vs. otros no destructivos, como por ejemplo la dispersión o la dilución), sino que también permite la cuantificación del alcance de la degradación del contaminante. Asimismo, los gráficos binarios de isótopos, en los que los cambios isotópicos de un elemento se grafican respecto al de un segundo elemento de la molécula estudiada, permiten la discriminación entre diferentes vías de degradación de los CMs, a través de la obtención de pendientes específicas de cada mecanismo (Λ). Para aplicar el CSIA con tales fines, deben realizarse previamente experimentos de laboratorio bajo condiciones controladas para estudiar las reacciones de degradación de los CMs. De este modo es posible evaluar de forma fiable los cambios isotópicos esperados en el campo y, por lo tanto, conocer si se puede detectar de forma cuantitativa la degradación, así como también, estudiar la viabilidad de los potenciales tratamientos. El CSIA del carbono (C-CSIA) está ampliamente consolidado para el análisis de VOCs. El CSIA del Cl (Cl-CSIA) ha sido extensamente usado en los últimos años para los CEs y los etanos clorados. Sin embargo, el Cl-CSIA solamente ha sido aplicado en algún experimento para el CF y no ha sido utilizado previamente para el CT. Por consiguiente, el método de Cl-CSIA no había sido evaluado ni validado pormenorizadamente para ningún CMs antes de la presente tesis. Los principales objetivos de esta tesis son la adquisición de un mejor conocimiento de los procesos de atenuación natural de los CMs a través de experimentos de laboratorio, así como también de las potenciales estrategias de remediación de éstos, con el fin de aplicar dichos avances en emplazamientos tales como el de Òdena. El C-CSIA y el Cl-CSIA han sido las herramientas de seguimiento principales de los estudios realizados, aunque se han utilizado otras técnicas geoquímicas y microbiólogas dando un carácter pluridisciplinar a la tesis. Previamente al uso del método de Cl-CSIA en los CMs de las muestras de laboratorio y campo, se ha desarrollado y validado el método para el CT y CF con un cromatógrafo de gases acoplado a un espectrómetro de relación isotópica (GC-IRMS) y con un cromatógrafo de gases acoplado a un espectrómetro de masas cuadrupolo (GC-qMS, siendo la metodología para este último comparada en un interlaboratorio). Este desarrollo se ha llevado a cabo en colaboración con grupos de investigación internacionales (Helmholtz Zentrum Müenchen y Université de Neuchâtel) durante las tres estancias del doctorado. Han sido estudiados tres mecanismos diferentes de transformación abiótica del CF en experimentos batch: oxidación por persulfato activado térmicamente (abreviado como PS); AH y decloración reductiva del CF con Fe(0). Se han obtenido valores similares de Λ del CF para PS y AH (17±2 y 13.0±0.8, respectivamente) que se pueden distinguir de la decloración reductiva (8±2). Se han realizado experimentos de degradación de CT y CF con Fe(0) y minerales de hierro (pirita (Py, FeS2) y magnetita (Mag, Fe3O4)), estos últimos con la presencia de FeCl2 a pH 7 y pH 12, simulando el agua subterránea de la zona saturada y la de las rasas de intercepción alcalinas de la zona no saturada de Òdena, respectivamente. Se detectó hidrogenólisis del CF a diclorometano (DCM) mediante Fe(0) de tamaño milimétrico para ambos valores de pH, mientras que la degradación del CF por minerales de hierro solo fue identificada a pH 12. En este último caso, se hipotetiza la existencia de AH ya que no se detectan VOCs como productos, salvo cierta acumulación de DCM con Py, lo que evidenciaría hidrogenólisis solo en el experimento con Py. La degradación del CT, mediante Fe(0) o minerales de hierro, ha sido confirmada a pH 12. Sin embargo, a pH 7 la degradación del CT solo ha sido confirmada con Fe(0) nanométrico y Py. Se ha observado la existenia paralela de reducción tiolítica del CT a CS2 e hidrogenólisis del CT a CF en ambos valores de pH, dando lugar ambos procesos a un valor de Λ diferente al obtenido para la hidrogenólisis neta del CT con Fe(0) y similar al de la reducción del CT con Mag a pH 12. De esta manera, se evidencia el potencial para detectar y diferenciar estos procesos en el campo mediante gráficos binarios de isótopos C-Cl. Así mismo, se deduce que el pH no afecta al valor de Λ de la degradación del CT ni del CF mediada por el Fe(0), ni a la degradación del CT por acción de la Py o del Fe(0). Adicionalmente, se han realizado experimentos de microcosmos con CT y CF, separadamente, con lodo del fondo de uno de los pozos más contaminados de Òdena (S3). Se ha confirmado una biodegradación natural de CT siguiendo la vía de hidrogenólisis a CF. La bioestimulación con vitamina B12 ha catalizado la degradación de CT y estimulado la biodegradación del CF, siendo la última inexistente sin la presencia de B12. Para ambos compuestos, no se detecta una acumulación de compuestos clorados ni de CS2 en los tratamientos con B12. La ausencia de acumulación de CF con la adicción de B12 durante la degradación de CT puede estar relacionada con una mayor actividad de la especie Pseudomonas stutzeri detectada más activa en esos tratamientos y capaz de reducir el CT a CO2. Los géneros más metabólicamente activos en los tratamientos del microcosmos son Acidovorax, Ancylobacter and Pseudomonas son, mientras que bacterias ampliamente conocidas como decloradoras (como Dehalobacter y Desulfitobacterium), se encuentran por debajo de un 0.1% de abundancia relativa. El valor de Λ para la biodegradación del CF (solo detectada con la adicción de B12, 7±1) es similar al registrado para la decloración reductiva del CF con Fe(0) (8±2), el cual incluye hidrogenólisis y eliminación reductiva. El valor de Λ de la biodegradación del CT sin la vitamina B12 y el de la hidrogenólisis neta del CT por Fe(0) no muestran diferencia estadística, lo cual confirma la misma vía para ambos experimentos. También cabe destacar que los valores de Λ de la degradación del CT con y sin B12 son estadísticamente diferentes (5±1 vs. 6.1±0.5), respectivamente, a pesar de su similitud a juzgar por su intervalo de confianza del 95%. Este hecho indicaría una posible influencia de otros procesos de reducción del CT diferentes a la hidrogenólisis cuando la vitamina B12 está presente. Por último, añadir que este estudio de microcosmos revela un enriquecimiento en 13C de los CEs, una vez los CMs son totalmente degradados mediante reacciones bióticas catalizadas por la B12, lo cual confirma la inhibición que ejercen los CMs en la degradación de los CEs. Considerando todo lo anteriormente mencionado, el conjunto de datos obtenido en los experimentos sienta las bases para un mejor conocimiento de la atenuación natural e inducida de los CMs aplicable a nivel práctico en acuíferos contaminados por múltiples contaminantes como el citado de Òdena. De esta forma, ha sido llevado a cabo un estudio a largo plazo (del 2002 al 2014) del efecto de la remoción de las fuentes de contaminación de CMs en 2005 en las aguas subterráneas del emplazamiento monitorizado de Òdena. A través del seguimiento de la concentración de los CMs y sus productos de degradación, así como del C-CSIA de los CMs, se han sido confirmado procesos de transformación de estos contaminantes a lo largo del tiempo. La remoción de las fuentes de contaminación se considera ineficiente dado que se han detectado procesos de lixiviado de CMs tanto en la zona no saturada alrededor del conducto de transporte de aguas residuales que fue desmantelado, como también entorno al tanque de almacenamiento subterráneo. No obstante, los productos de degradación y el estudio de los valores de Λ han evidenciado procesos de reducción del CT y del CF en ambas áreas. Por otro lado, en la zona donde se realizaron vertidos al aire libre sí se ha detectado una remoción eficiente de la fuente de contaminación y los valores isotópicos han revelado una migración del foco aguas abajo, así como también, cierta influencia de CF afectado por AH en las zanjas de intercepción y/o por procesos de oxidación del CF en la zona saturada de esta área. Para concluir, subrayar que esta tesis proporciona avances en la metodología de Cl- CSIA de los CMs, así como nuevos datos isotópicos de carbono y cloro para caracterizar procesos de degradación del CT y del CF. Estos datos combinados con otras técnicas geoquímicas y microbiológicas permiten discriminar y evaluar de forma pluridisciplinar procesos de atenuación natural en emplazamientos contaminados, así como realizar un asesoramiento y seguimiento de la eficiencia de las potenciales técnicas de remediación de CMs aquí descritas por parte de consultorías ambientales y administraciones. El uso rutinario del método de Cl- CSIA en los CMs es prometedor para futuras investigaciones y proyectos de remediación, paralelamente al ya consolidado C-CSIA. La implementación y evaluación de las técnicas de remediación de CMs a escala de campo, como la bioestimulación a través de fuentes económicas de B12, en combinación o no con el uso de Fe(0) o minerales de hierro a través de la puesta en valor de residuos mineros, son desafíos a corto plazo.

Afforestation and reforestation programs utilizing available fields for biofuel production, carbon sequestration, and other uses linked to climate change are looking to tree physiologists to identify species and genotypes best-suited to their purposes. The ideal poplar genotype for use in Canadian programs would be drought-resistant, cold-climate adapted, and fast-growing, thus requiring an understanding of links between a variety of physiological traits linked to growth and productivity. This study examined the basis for variations in water-use efficiency within four selected populations of Populus trichocarpa and Populus balsamifera (2 provenances each). Each species included both a northern and a southern provenance. Correlations between water-use efficiency, nitrogen-use efficiency, ¹³C/¹²C isotope ratio, stomatal conductance, and overall productivity were evaluated. Gas exchange variables measured included net photosynthesis, transpiration rate, stomatal conductance, and intercellular CO₂ content. Water-use efficiency and ¹³C content across all genotypes were highly correlated. Results suggested that variation in water-use efficiency was primarily related to variation in stomatal conductance across all genotypes. Whereas differences in net photosynthesis in this study were not significant between species, P. balsamifera did reveal a higher average stem volume overall. Although variation in stomatal conductance was the major determinant of differences in water-use efficiency, positive correlations were found between ¹³C isotope abundance and net photosynthesis in both P. balsamifera provenances. In this regard, results for the northern P. balsamifera provenance are the most consistent across all gas-exchange and growth trait correlations, in terms of meeting expectations for sink-driven water-use efficiency. The findings in this study suggest the possibility of identifying poplar genotypes with an absence of trade-off between water-use efficiency and nitrogen-use efficiency, notably among genotypes from the northern P. balsamifera provenance, near Gillam.

Im Fokus dieser Arbeit steht die physiologische Reaktion von Einzelbäumen gegenüber Trockenheit. Das angewandte hydrodynamische Xylemwasserfluss (XWF) Model liefert eine hydrologische Abbildung der Einzelbäume. Aufgrund des funktionalen Zusammenhanges zwischen dem Blattwasserpotential und der stomatären Leitfähigkeit erlaubt das XWF Modell eine öko-physiologische Simulation der stomatären Reaktion auf Blattebene. Hieraus ergeben sich auch Rückschlüsse auf die Assimilationsleistung. Als integratives Maß des Verhältnisses zwischen der Kohlenstoffaufnahme und dem Wasserverbrauch werden die stabilen (Jahrring-) Isotope des Kohlen- und des Sauerstoffs analysiert. Des Weiteren werden Messungen des jährlichen Dickenwachstums sowie des Tagesganges der Xylem-Saftflussdichte untersucht. Die XWF Simulationen zeigen eine gute Übereinstimmung mit den Saftflussdichtemessungen an Buchen (Fagus sylvatica L.). Eine effektive stomatäre Regulation der Transpiration während der extreme Trockenheit des Jahres 2003 schütze die untersuchten Buchen vor einer Fehlfunktion des Wassertransportes. Gleichfalls konnte das Wachstum aufrechterhalten werden, was eine Remobilisierung von gespeichertem Kohlenstoff während Zeiten eingeschränkten Gasaustausches nahe legt. Des Weiteren zeigte sich Unterschiede in den (Wasser-) Nutzungsstrategien von Fichten (Picea abies L. Karst.), was auf eine physiologische Prädisposition der Gefährdung einzelner Bäume gegenüber Trockenstress hinweist. Die gemeinsame Betrachtung von hydrodynamischen Simulationen und öko-physiologischen Messungen kann dazu beitragen die komplexen physiologischen Prozesse auf Blattebene abzubilden und diese auf Baumebene zu projizieren. Weiterführend können somit die Vorhersagen des Wasserhaushaltes auf Bestandesebene angepasst und Auswirkungen des Klimawandels besser abgeschätzt werden.
This study focuses on the physiological response of individual trees towards drought. The hydrodynamic model of xylem water flow (XWF) applied provides a hydraulic map of the individual trees. Due to the functional linkage between the leaf water status and the stomatal conductance, the XWF model enables an eco-physiological representation of the stomatal response at the leaf level. As an integrative record of the ratio between water loss and carbon gain, the tree ring carbon and oxygen stable isotopes have been analyzed. Furthermore, measurements of seasonal growth and diurnal sap flow densities include in my study. The hydrodynamic XWF simulation shows good agreement with sap flow density measurements of beech trees (Fagus sylvatica L.). It demonstrates that the study trees were able to cope with the extreme drought events of the years 2003 due to a strong limitation of water loss by stomatal closure. The assessment of growth data and stable isotope measurements suggest an increased remobilization of stored carbohydrates during periods of limited gas exchange. Furthermore, differences in the resource use strategies of Norway spruce trees (Picea abies L. Karst.) suggest a physiological predisposition of individual trees toward drought stress. The combined investigation of hydrodynamic modeling and eco-physiological approaches helps to bridge the gap between the detailed examinations of physiological processes at the leaf level to the forecast of water use at the tree level. Thus, predictions of the water balance at the stand level may be adjusted for a better representation of the impact of climate change.

Triple oxygen and hydrogen isotope analysis of the structurally-bound water in gypsum can provide a direct measure of past hydrologic variability. This thesis presents the development of the water extraction and isotopic measurement procedures, the calculation of the gypsum-water isotope fractionation factors, and the application of the method to constrain the palaeohydrologic conditions in two temporally and geographically disparate sites. Measurement of the isotopic composition of gypsum hydration water is used to examine the hydrological changes that occurred during the Terminal Classic Drought of the Maya lowlands (~800-1000 CE), coincident with the period when the Classic Maya Civilization of Mesoamerica collapsed. The data provide a complete and direct archive of hydrological conditions that have previously been limited to ice core records. Mean annual rainfall is shown to have decreased by between 41% and 54%, with intervals of up to 70%, compared to present-day conditions. This study has also shown for the first time that relative humidity was 2%-7% lower during the Terminal Classic Drought compared to today. The methodology is also applied to the massive gypsum deposits in the marginal and deep basins of the Mediterranean to interpret the chemical evolution of parent water bodies during the Messinian Salinity Crisis (5.97-5.3 Ma). By combining the measurement of gypsum hydration water with other traditional (e.g. strontium) and novel (e.g. calcium and barium) isotope tracers, the hydrological changes during the deposition of Primary Lower Gypsum units of the Sorbas Basin in southeastern Spain, the Upper Gypsum units of Sicily, and deep basin deposits have been constrained. The results indicate that all deposits experienced a significant freshwater contribution to the mother fluids from which they formed. It is proposed that obliquity-controlled sea level and eccentricity-modulated precession, superimposed on longer-term tectonic restriction of the Mediterranean-Atlantic exchange, together controlled the varying depositional environments during the formation of the Messinian Salt Giant. This thesis demonstrates that the analysis of gypsum hydration water is a powerful tool for palaeoclimate reconstruction. The methodology can be applied to gypsum (and other hydrated minerals) in a wide range of settings across geological space and time, providing a rich source of information about the environmental conditions under which they formed.

Les carottes de glace permettent de reconstruire le climat du passé, à partir entre autre de la composition isotopique de l’eau (δ18O, δ17O et δD). Sur le plateau Est Antarctique, les températures très froides et les faibles accumulations permettent de remonter le plus loin dans le passé (jusqu’à 800 000 ans) mais compliquent l’interprétation du signal isotopique. Premièrement, les reconstructions des variations de température dans les carottes de glace à partir des isotopes de l’eau se basent sur des modèles pour décrire l'évolution de la composition isotopique de la vapeur et de la phase condensée le long du cycle de l’eau. Ces modèles, qui ont été développés au cours des dernières décennies, reposent sur la connaissance de coefficients du fractionnement isotopique associé à chaque transition de phase et sur des hypothèses pour représenter la micro-physique des nuages.Lors de la formation de flocons de neige à basse température, 2 types de fractionnements isotopiques doivent être pris en compte : le fractionnement isotopique à l'équilibre, associé à la transition de phase vapeur-glace et le fractionnement isotopique cinétique lié aux différentes diffusivités des différents isotopes. A basse température, les déterminations des coefficients du fractionnement du fractionnement à l’équilibre présentent d’importantes différences et n’ont jamais pu être mesurées à des températures inférieures à -40°C. Or la température moyenne annuelle à Dome C est de -54°C atteignant jusqu’à -85°C l’hiver. Les diffusivités des différents isotopes quant à elles n’ont jamais été mesurées à des températures inférieures à 10°C. Toutes ces lacunes résultent dans des incertitudes importantes sur le lien entre la composition isotopique et la température dans des conditions comme celles du Plateau Est Antarctique.De plus, dans ces conditions froides et arides, les processus physiques qui affectent la composition isotopique de la neige après la déposition des flocons deviennent importants compte tenu du faible apport annuel de précipitation. Pour estimer l’impact de ces processus de post-déposition sur la composition isotopique, il est nécessaire de bien caractériser le fractionnement isotopique à l’interface neige/atmosphère pour des températures allant jusqu’à -90°C.Afin d’améliorer les reconstructions quantitatives de température l’étude des processus affectant la composition isotopique de la glace à très basse température est donc primordiale. Dans cette optique, ma thèse a été à l’interface entre les études de processus au laboratoire et en Antarctique et le développement instrumental afin de pouvoir réaliser des mesures isotopiques encore inédites, en particulier à très basse humidité. D’un côté, j'ai développé d’un nouveau spectromètre infrarouge aux performances bien au-delà des instruments commerciaux. En effet, la fréquence du laser est stabilisée par rétroaction optique par une cavité ultra-stable jusqu’à un niveau de stabilité de l’ordre du hertz. La lumière est ensuite injectée dans une cavité CRDS hautes performances avec une sensibilité de 10-13 cm-1.Hz-1/2. Ceci permet de mesurer la composition isotopique avec une précision inférieure au ppm.En parallèle, des expériences au laboratoire ont permis de renforcer les connaissances sur les processus affectant les isotopes de l’eau, en particulier le fractionnement lié à la transition de phase vapeur - glace et le fractionnement cinétique lié aux différentes diffusivités des différents isotopes en modélisant le fractionnement lié à la diffusion près d’un point froid. Enfin, durant une campagne en Antarctique, j’ai pu réaliser parmi les premières mesures de la composition isotopique de la vapeur et de la glace en Antarctique et appliquer les modèles physiques des processus à des données de terrain. Ces mesures montrent que le cycle de sublimation/condensation contribue de manière importante à la composition isotopique de la neige sur le plateau Est Antarctique
Ice cores enable reconstruction of past climates, from among others water stable isotopic composition (δ18O, δ17O et δD). On the East Antarctic Plateau, very cold temperature and low accumulation provide the longest ice core records (up to 800 000 years) but embrangle the interpretation of isotopic composition. First, reconstructions of temperature variations from ice core water isotopic composition are based on models used to describe the evolution of the isotopic composition of the vapour and of the condensed phase over the entire water cycle. These models have been developed during the last decades and depend upon precise determinations of isotopic fractionation coefficients associated to each phase transition and upon hypotheses to describe cloud microphysics.During the formation of snowflakes at low temperature, two types of isotopic fractionations need to be taken into account: equilibrium fractionation, associated to the vapour to ice phase transition and kinetic fractionation associated to the difference of diffusivity of the different isotopes. At low temperature, determinations of equilibrium fractionation coefficients present important discrepancies and have never been realised for temperature below -40°C. However, mean annual temperature at Dome C is around -54°C reaching -85°C in winter. For the diffusivities of the different isotopes, they have never been measured at temperature below 10°C. All these gaps result in important uncertainties on the link between isotopic composition and temperature, especially for cold and dry conditions such as encountered on the East Antarctic Plateau.Furthermore, because of the very low amount of precipitation, physical processes affecting the isotopic composition of the snow after the deposition of snowflakes can results in an important contribution to the isotopic budget. In order to estimate the impact of the post-deposition processes on the water vapour isotopic composition, it is necessary to characterise the isotopic fractionation at the snow/atmosphere interface for temperature down to -90°C.In order to improve isotopic paleothermometer performances, it is primordial to study processes affecting snow isotopic composition. Toward this goal, my Ph-D has been at the interface between monitoring of processes affecting isotopes, both in laboratory experiments and field studies, and instrumental development to push the limits of water vapour isotopic composition trace detection. On one hand, new developments in optical feedback frequency stabilisation applied for the first time to water isotopic composition monitoring provide performances beyond any commercial instrument and can be used for thorough processes studies. The laser frequency is stabilised by optical feedback from an ultra-stable cavity to the hertz level. Then, the light is injected in high performances cavity with a sensibility of 10-13 cm-1.Hz-1/2. This enables measuring isotopic composition with a precision below the ppm level.On the other hand, laboratory experiments have supported theories about isotopic fractionation associated to the vapour to ice phase transition and to kinetic fractionation linked to the difference of diffusivities of the different isotopes. Finally, these physical models have been collated to field measurements realised at Dome C in Antarctica, which are among the first water vapour and snow isotopic composition measurements realised inland Antarctica. These measurements show how important is the contribution of the sublimation condensation cycles to the snow isotopic composition budget on the East Antarctic Plateau

Nutrient inputs from productive marine environments have been shown to directly and indirectly subsidise primary producers and consumers in terrestrial ecosystems (e.g. Polis and Hurd 1995; 1996; Anderson and Polis 1998; 1999). But does this theory hold true on islands surrounded by oligotrophic waters, which account for a significant proportion of the marine environment? The aim of the present study was to examine the applicability of the spatial subsidisation hypotheses proposed by Polis and his co-authors to an oligotrophic system in south-western region of Western Australia. These aims were achieved by comparing soil and plant nutrients, and the nitrogen stable isotope signatures of soil, plants, detritus and invertebrates in areas with (islands) and without (mainland sites) inputs from seabirds. In addition, the responses of plant nutrients and vegetation assemblages to guano additions were examined in a controlled field experiment.

Earth's near-surface environment sustains nearly all terrestrial life, yet this critical zone is threatened by the environmental migration of new and potentially harmful compounds produced to support a growing human population. Traditional transport equations often fail to capture the environmental behavior of these emerging contaminants due to issues such as flow heterogeneity. Thus, there is a need to better evaluate controls on pollutant partitioning in Earth's critical zone. Our first study investigated the transport and distribution of the neonicotinoid insecticide thiamethoxam (TMX) by growing TMX-coated corn seeds in coarse vs fine-textured soil columns maintained with versus without growing corn plants. Fine-textured soil transported TMX at concentrations that were two orders of magnitude higher than coarse-textured soil, due to preferential flow in the fine-textured soil columns and higher evapotranspiration (ET) concentrating more TMX in the coarse-textured soil. Living plants increased the concentration of TMX at depth, indicating that growing plants may drive preferential transport of neonicotinoids. For the second study we planted TMX-coated corn seeds and maintained field plots with and without viable crops (n = 3 plots per treatment), measuring TMX concentrations in three hydrological compartments (surface runoff, shallow lateral flow, and deep drainage) and soil. TMX was transported in the highest concentrations via surface runoff, while also showing continual migration within the subsurface throughout the growing season. Plants facilitated downward migration of TMX in soil yet restricted losses in drainage. For our final study, we used a simple isotope mixing method to evaluate how preferential flow alters the influence of compound chemical properties on solute transport. We applied deuterium-labeled rainfall to plots containing manure spiked with eight veterinary antibiotics with a range of mobility, and quantified transport to suction lysimeters (30 and 90 cm). We showed that low preferential flow (<20%) eliminates the influence of compound chemical properties and, contrary to conventional understanding, more preferential flow (~ >20%) amplifies these chemical controls, with more mobile compounds appearing in significantly higher concentrations than less mobiles ones. Altogether, we provide a refined understanding of solute partitioning in the critical zone necessary to improve process-based transport modeling.
Doctor of Philosophy
Earth’s near-surface environment sustains nearly all terrestrial life, yet this critical zone is threatened by the environmental migration of new and potentially harmful pollutants produced to support a growing human population. Additionally, traditional mathematical methods fail to accurately describe the behavior of these emerging pollutants in soils due to complex flow patterns. Thus, scientists need to better understand how these pollutants contaminate water bodies in the critical zone. We first conducted a greenhouse experiment to understand and measure the amount of the neonicotinoid insecticide thiamethoxam (TMX) that could move from coated corn seeds through the soil environment. Water draining from fine-textured soil had >100 times more TMX than water draining from course-textured soil, due to commonly occurring fractures/cracks in the finer-particle soil and more evaporation from soil and plant leaves sequestering TMX in the sandy soil. Growing plants amplified TMX movement through soil voids to lower depths. We then conducted a field study to determine how much TMX could move to the surrounding environment throughout the corn growing season. We found that plants aided in downward movement of TMX yet restricted total losses from the plot overall by removing soil water. Our third study investigated the degree to which chemical pollutant properties control movement of solutes when water flows preferentially through soil void space. Common dairy manure was spiked with eight pollutants ranging in chemical attraction to soil and was added to an agricultural field. After irrigation, we found that when total drainage water was less than 20% derived from preferential flow, chemical properties had a negligible effect on the amount of pollutant in draining soil water. Contrary to conventional understanding, when draining water contained more than 20% preferential flow, chemical properties had a strong influence on the amount of pollutant detected. Altogether, we provide new understanding of how solutes move though the critical zone. These findings are necessary to create mathematical tools that more accurately depict pollutant behavior below-ground.

L’Antarctique joue un rôle majeur dans le climat de la Terre, car le gradient de température entre l’équateur et les pôles contrôlent la circulation atmosphérique. L’Antarctique est également utile pour comprendre la variabilité du climat, puisque les informations préservées dans la glace peuvent complémenter les observations récentes. Cependant, l’emplacement des forages de carotte de glace sont irrégulièrement répartis sur le continent, et les reconstructions de température sur le plateau Est-Antarctique sont entravées par la faible résolution temporelle résultant d’une trop faible accumulation de neige à haute altitude. Nous présentons ici de nouvelles reconstructions de température à partir de la carotte de glace d’Aurora Basion North (ABN, 77°S, 111°E, 2700 m d’altitude). D’abord, nous utilisons le Modèle Atmosphérique Régional (MAR) pour caractériser le climat récent à ABN, et montrons que les événements de précipitation sont intermittents, et sont marqués par une température 2°C supérieure à la moyenne. Les événements de fortes précipitations sont enregistrés dans les isotopes de l’eau, avec des valeurs de δ18O avoisinant les valeurs estivales, même en hiver, comme l’attestent des mesures dans la neige et le modèle atmosphérique ECHAM5-wiso, qui est équipé avec les isotopes de l’eau. Les précipitations sont systématiquement associées avec un blocage atmosphérique sur la côte de Wilkes Land, au nord-est d’ABN, et ces blocages sont favorisés par les phases négatives du Southern Annular Mode (SAM), le principal mode de variabilité dans le climat de l’hémisphère Sud. Par conséquent, les phases positives du SAM sont marquées par des température froides à ABN, mais pas nécessairement par un δ18O faible, car les précipitations peuvent être réduites. La température reconstruite à partir de la carotte forée à ABN, qui fait 300 m et couvre 2000 ans, reste relativement stable, à ± 1°C de la température moyenne. Nous détaillons une deuxième reconstruction de température faite sur la même carotte, basée sur l’inversion de la température de trou de forage et des anciens gradients de température dans le névé, estimés avec les isotopes stables des gaz Ar et N2 piégés dans les bulles. Cette seconde reconstruction de température révèle deux périodes environ 3°C plus froides à ABN au cours des 2000 dernières années : de 300 à 550 EC, et de 1000 à 1400 EC. Cette anomalie froide médiévale est synchrone avec une phase positive du SAM, et n’a pas pu être identifiée à partir du δ18O seul. Cette étude souligne l’importance d’utiliser plusieurs indicateurs pour déterminer les variations passées de température, car le δ18O pourrait surreprésenter les événements chauds à forte précipitation
Antarctica is a major component in Earth’s climate system, as the equator to pole temperature gradient controls the characteristics of the general circulation of the atmosphere. Antarctica is also very useful to understand climate variability, as past climate information preserved in the ice may help extend the short observational records. However, the ice core drilling locations are unevenly spread across the glaciated continent, and the temperature reconstructions from the high elevation East Antarctic plateau suffer from poor temporal resolution, because low snow accumulation hampers our interpretation of water isotopes. Here, we present new temperature reconstructions from the Aurora Basin North (ABN, 77°S, 111°E, 2700 masl) ice core. First, we use the regional atmospheric model MAR to characterize the recent climate at ABN, and show that precipitation events are intermittent, and occur under temperature 2°C warmer than average. The large precipitation events are marked in the snow isotopes with δ18O values on par with summer levels, even during the winter, as attested by snow measurements and the isotope-enabled atmospheric model ECHAM5-wiso. Precipitations are consistently associated with a blocking on the Wilkes Land coast, North-East of ABN, and the blockings are more likely to occur during negative phases of the Southern Annular Mode (SAM), the main mode of variability in the southern hemisphere climate. Consequently, SAM positive phases are marked by cold temperatures at ABN, but not necessarily low δ18O, as precipitations may be weakened. The temperature reconstructed from the δ18O in the 300-m-deep, 2000-year ice core drilled at ABN supports stable conditions, with a temperature remaining within a ± 1°C range. We present a second temperature reconstruction from the same core, based on the inversion of borehole temperature and past firn temperature gradients, estimated with the stable isotope composition of Ar and N2 gases trapped in bubbles. This second temperature reconstruction, representative of changes in the snow, suggests that temperature at ABN was about 3°C colder during two periods of the last 2000 years: from 300 to 550 CE, and from 1000 to 1400 CE. This medieval cold anomaly is concurrent with a positive SAM phase, and could not be identified from the δ18O alone. This work highlights the importance of using multiple proxies to determine past temperature variability in Antarctica, as δ18O may be biased towards warm precipitation events

This study aims to investigate the stable isotopic characteristics of meteoric and ground waters, and to obtain spring flow rates in the Coronet Peak Skifield, Queenstown. Spring flows were gathered during the winters of 2008 and 2009, whilst water samples were collected from precipitation, springs, reservoirs and groundwater during July, August and September 2009. The spring flows were examined and the water samples were analysed for δD and δ¹⁸O values using the CF-IRMS at the University of Canterbury. A database has been gathered from all natural water sources to give a local meteoric water line (LMWL) for the area that fits clearly with the global meteoric water line. The LMWL has an R2 value of 0.97 and the equation is δD = 8 δ¹⁸O +10. An understanding of evaporation as it occurs in the water storage reservoirs of the mountain has also been obtained, giving rise to a local evaporation line. The stable isotope ratios of hydrogen and oxygen within precipitation have been used extensively to characterise the hydrogeology with emphasis on altitude effects, storm duration and variations in storm track trajectories. Of these three phenomena, it is the trajectory of the storm track that is best shown to affect the composition of precipitation in this area. The air masses advancing on the study area from the north being more depleted in their isotopic signatures, with approximate δD and δ¹⁸O values of –130‰ and -16‰. The air masses approaching from a southerly direction are more positive in comparison, having approximate δD and δ¹⁸O values of –65‰ and -9‰. The altitude effect in precipitation on the Skifield has led to an altitude gradient being found: for every 100-metre increase in elevation, δ¹⁸O decreases by 0.71‰. However there were some inconsistencies. The influence on precipitation from storm duration is also inconsistent in this area. The R2 values range from 0.14 to 0.99, but this method does not take into account the position of the individual samples. Some samples did not plot in the expected order that is governed by a decrease in stable isotopic ratios with storm duration. The stable isotopic compositions within meteoric waters can be used as tracers of water sources. The isotope date of the springs also infers an altitude effect. The springs gave an altitude gradient of a decrease –0.43‰ with each 100-metre increase in elevation. This indicates that precipitation is the main influence on the stable isotopic composition of the springs in this area. However, data shows differences between the current precipitation and the groundwater compositions, indicating that present precipitation is not flowing from the springs, past precipitation is. The stable isotopic compositions of the springs have also been correlated with groundwater isotope data and suggest the sources of the springs are groundwater dominated. Although some springs compositions indicate an influence by current precipitation. This is shown by a negative stable isotopic trend in the precipitation sampled in August, corresponding with a relatively negative stable isotopic composition in some springs during this time period. Monitoring of spring flows on Coronet Peak have led to an average winter flow rate being established of 26.5 litres per second. Spring flow rates range from 0.25 – 6 litres per second. This monitoring has indicated the springs of the greatest yield that are not already being utilised on the Skifield. It is these springs that should be further investigated as to whether they would provide a sustainable source of water on the mountain. This locally derived water would then be utilised for the purposes of artificial snowmaking and other activities and amenities that are currently operated by NZ Ski on Coronet Peak.

Spatial and temporal heterogeneity of water and nutrient pools is closely associated with the existence of different plant communities in hydrologically-controlled ecosystems such as the Everglades. These various communities differ in their flooding and fire tolerances as well as nutrient requirements. Upland plant communities are of particular ecological significance since they have high biodiversity and provide habitat to terrestrial fauna, yet comprise less than 10 % of the total area. Restoration and maintenance of such communities requires an understanding of their water and nutrient requirements. Chapter 2 compares water source utilization in hammocks and pine rocklands on the Miami Rock Ridge using stable isotopes of water. Hammocks do not flood, while adjacent pinelands may flood between 2-3 months. In the wet season, hammocks were found to use phosphorus (P) rich soilwater, a local pool of water and nutrients while pineland plants primarily relied upon groundwater, the regional pool. Access to a rich pool of P in the oligotrophic Everglades was associated with higher community-level foliar P concentration in hammocks. However in the dry season, hammocks utilized groundwater, which suggests sensitivity to extended droughts. Chapter 3 compares the hammock (upland or head) and swamp forests (lowland or tail) on tree islands in the Shark River Slough. Uplands were associated with P-rich soilwater uptake in the wet season, with regional water uptake in the dry season. Accordingly, tree island heads are rich in foliar P and thereby P-hotspots in the Everglades. Foliar nutrient concentrations can thus indicate limiting nutrient availability in the Everglades. Chapter 4 looks at how leaf phenology patterns are tied to water and nutrient pools. Leaf fall in ridge hammocks is associated with high foliar carbon isotope values over the dry season, which is not the case for tree island hammocks. However, in some species, high levels of foliar nitrogen are also associated with high foliar C13 values indicating stomatal limitation of photosynthesis. Growing season for most hammock species is the wet season coinciding with high availability of P, as reflected in high foliar P in this season. Linking water sources to foliar nutrients elucidates roles of water and nutrient pools in leading to different plant communities within an ecosystem.

>Magister Scientiae - MSc
In the Kruger National Park (KNP) which is the flagship conservation area in South Africa, the impact on groundwater should be kept to a minimum as groundwater plays a vital role in sustaining ecosystem functioning and sustaining baseflow to streams and rivers. For this reason groundwater has been recognized as one of the environmental indicators that need to be monitored. The KNP has adopted a Strategic Adaptive Management (SAM) approach with clear ecosystem management goals. The achievement of these goals is evaluated by using environmental indicators. These indicators are evaluated against thresholds of potential concern (TPC). TPCs are a set of boundaries that together define the spatiotemporal conditions for which the KNP ecosystem is managed. TPCs are essentially upper and lower limits along a continuum of change in selected environmental indicators. Historically, groundwater recharge and surface water interaction with rivers has tended to be overlooked in the KNP. This study proposes a conceptual model of groundwater recharge processes in the KNP, defining when and how groundwater recharge occurs. Two methods were used, the Cumulative Rainfall Departure (CRD) and stable isotopes of ²H and ¹⁸O. An adapted version of the CRD which incorporates a long and short term memory of the system was used to identify possible recharge processes. Further, using the CRD method a reliable reconstruction of the long term groundwater level trends are simulated using monthly rainfall totals with reference to the average rainfall over the entire time series 1936-2009. The stable isotope of ²H and ¹⁸O samples from cumulative rainfall samplers, surfacewater (streams and rivers) and groundwater from boreholes were collected monthly for approximately one year (May 2010 to July 2011). The isotope composition of the groundwater was used to establish whether recharge was immediate or delayed. Additionally, the isotopic composition of surface-water from rivers and streams were compared to that of groundwater to identify surface-water interactions. Groundwater recharge in KNP occurs during the rainy summer months (December to March) and very little to none during the dry winter season (April to September). Recharge takes place during rainfall sequences 100mm or more. The stable isotope records collected from cumulative rainfall, groundwater and surface water (streams and rivers) indicate that groundwater experiences evaporation prior to infiltration. As the KNP experiences high evaporation rates, insignificant rainfall sequences contribute little or zero to recharge. The CRD analysis of groundwater level fluctuations shows that recharge to the aquifers respond to dry and wet cycles that last for 6 to 14 years. The KNP experienced several periods of below-average rainfall and hence no significant recharge took place to the basement aquifers. During a normal rainy season the water levels rise somewhat then starts receding again. It is only during major rainfall events that may occur every 100yrs to 200yrs causing the aquifers to fully recharge. This was perfectly illustrated by the high groundwater levels after the 2000 major rainfall event that recharged the aquifers fully. During below average rainfall years the overall water level trend is drastically declining. The system experiences higher natural losses than gains due to outflow of groundwater to streams and rivers. The KNP is divided down the center by two geological formations, granites along the west and basalts along the east. The combination of the CRD model and the stable isotopic analysis suggest that the dominant recharge processes that occur in the southern region of the KNP are direct recharge via piston flow and indirect recharge via preferred pathways particularly streams and rivers. Along the eastern half of the KNP on the Basalts and Rhyolite direct recharge via piston flow are dominant. Groundwater is not recharged via small streams and rivers (Sweni and Mnondozi Rivers) as it was found that at these particular sites these rivers are detached and do not interact with groundwater. Along the western granitic areas the dominant recharge process are indirect recharge. Recharge takes place via preferred pathways particularly streams and rivers. It was found that ephemeral rivers (Nwatsisonto River) act as sinks for groundwater recharge and influent-effluent conditions are experienced along seasonal rivers (Mbyamiti River). The large perennial Sabie and its tributary the Sand River are consistently fed by groundwater, above all maintaining base flow during the dry season. These rivers act as basin sinks receiving groundwater discharge all year round. Using the stable isotope composition of rainfall, surface-water and groundwater to act as a natural tracer, in combination with the CRD method proved invaluable to confirm the plausible recharge processes. The study provided a conceptual understanding of the groundwater system in the KNP forming the foundation to developing acceptable limits (TPCs) of the groundwater levels in the KNP. The model will serve as a guide for the recharge processes and for deciding on the location and time frames for data collection to ultimately set TPCs for groundwater in the KNP to sustainably manage the resource.

New methods, based on tracer gas measurements and isotopicanalysis can be used to evaluate the moisture properties ofbuilding materials and provide the means for forensic analysisof the origins and history of excessive water in buildings, theimmediate practical consequences of which will be the abilityto improve the moisture performance of constructions. It is shown, in theory and through measurements how thewater vapour permeability of porous building materials can witha good degree of accuracy be estimated with tracer gasmeasurements that provide an efficient alternative to the cupmethod. Complementary measurements may be carried out in orderto evaluate the contribution of surface diffusion and theeventual enhancing effects of moisture content on the diffusioncoefficient. The Random Hopping Model is used to illustrate howthe surface diffusion coefficient depends on the amountadsorbed and the activation energy of migration that can beevaluated from the sorption isotherms. It is explained how the abundance ratios of two of the mostordinary isotopes of hydrogen and oxygen in water can be usedto determine its history. These isotopes are stable and givethe water a distinct signature that can be used to reveal itssource as shown in a case study. In a contrary manner themeasured isotopic separation can be used to determine therelevance of different transport processes and reactions. It isof central importance that not only does the magnitude ofisotopic separation for the reactions vary for deuterium andoxygen-18 but even the ratio thereof. One of the challenges hasbeen to construct an experimental method for retrieving samplesof water for comparison. Furthermore this thesis includes an evaluation of a new typeof a light weight construction with loose-fill cellulose fibre,in which the conventional polyethylene vapour barrier has beenreplaced with polypropylene fabric. With a verified model ithas been investigated how the construction would perform fordifferent internal moisture loads and reference climate fromthe literature. The results suggest that this type ofconstruction is not to be recommended. KEYWORDS:tracer gas, water vapour permeability,diffusion, surface diffusion, isotopic analysis, deuterium,oxygen-18, fractionation, vapour barrier, transient numericalmodelling of diffusion.
QC 20100611

We hypothesized that rainwater had a different and distinct isotopic signal to groundwater, and thus plants growing on groundwater-fed areas would have a unique and distinct isotopic composition compared to plants growing on freely-drained soils. We studied two groundwater-fed areas and adjacent freely-drained areas in the Cape Point Nature Reserve, Cape Peninsula. We sampled groundwater and analyzed the isotopic composition and compared this to the isotope composition of rainfall. We found that δ¹⁸O and oD values of rainwater (δ¹⁸O = O%o to -5.6%o and oD = +11 %o to -22%o) overlapped the isotopic composition of groundwater (δ¹⁸O = -4.2%o to -4.5%o and oD = -11.9%o to -13.2%o). Thus isotopic analysis could not determine which areas were groundwater-fed and which were rain-fed. We also sampled xylem water from five species, namely Leucadendron laureolum and Metalasia muricata (both of which grew on both dry and wetland areas), Mimetes hirtus (wetland only), Erica labialis (dry area only), and Erica multumbellifera (wet area orily). Our results suggest that both of L. laureolum and Metalasia muricata had access to groundwater on both groundwater-fed sites and the free-drained site. E. multumbellifera at a groundwater-fed marsh was likely also using groundwater, however on the adjacent freely drained site E. labialis was likely using rainwater. M. hirtus had a much more positive isotopic composition (δ¹⁸O = -1.5 ±1.2%o and δD = 5.1 ± 18.0%o) than either groundwater or rainwater, indicating that it was using evaporated water, which suggests the species were very shallow rooted. Thus M. hirtus would be very sensitive to drying out of the soil. This study has demonstrated that stable water isotopes cannot clearly distinguish rainwater and groundwater and we may have use other methods such as thermal imagery, chemical analysis, and xylem pressure potentials to determine the degree of dependency of vegetation on groundwater.

Stable isotopes of hydrogen and oxygen, major ions, and trace elements were used as geochemical tracers to identify ground-water flow paths and potential source waters that eventually discharge into the Verde River, one of Arizona's last remaining perennial rivers. Identifying and quantifying the various source waters to the Verde River provides an improved understanding of how ground water moves and sustains perennial base flow in the river on a regional scale. More specifically, these chemical constituents allow for the identification and quantification of source-water contributions to the river. In addition, two- and three-component mass-balance equations incorporating stable-isotope data were used to construct a conceptual model of ground-water flow for the upper and middle Verde River watersheds study area. A stable-isotope end member value was calculated for four ground water regions, which were delineated based on geologic structure, hydrology, and chemical characteristics of the ground water. Mixing calculations indicate that ground water discharging as springs in the headwaters of the Verde River is predominantly from regional aquifers in Big and Little Chino Valleys but includes water from higher-elevation sources in the northwestern part of the study area. An abrupt change in the chemical signature of the Verde River base flow about 48 km downstream from the headwaters indicates where ground water from the highest elevation sources in the study area discharges to the river. Ground water from low elevation sources in the southeastern part of the study area enters the river about 135 km downstream from the headwaters. The spatial and temporal variability of recharge was determined using stable-isotope measurements from precipitation and ground water samples within the watershed (fig.l.l ). Stable-isotope values from winter precipitation samples are within the range of stable-isotope values measured in ground-water samples throughout the study area. Summer precipitation samples from North American monsoons are enriched with respect to ground-water values and therefore are only a small contributor to ground-water recharge. Recharge to ground water that discharges to the river is predominantly from winter precipitation on the basis of temporal trends of stable-isotope data.

Ce travail de thèse s’intéresse à deux zones de l’Atlantique Nord : la région subpolaire et la région subtropicale. Cette large couverture permet d’étudier le cycle de l’eau dans des régions hydrologiquement différentes, où des processus variés rentrent en jeu comme l’évaporation, la convection atmosphérique, la formation des précipitations, le cycle saisonnier de la glace de mer, les apports des rivières et des glaciers, et l’advection des masses d’eau et des masses d’air. Dans la région subtropicale, les variations des compositions isotopiques de la vapeur d’eau sont étudiées afin de comprendre le rôle de l’évaporation et du mélange avec la troposphère libre dans le contrôle de l’humidité et des compositions isotopiques à la surface des océans. Ces données innovantes recueillies in situ principalement au cours de l’été 2012 dans le gyre subtropical de l’Atlantique nord (campagne STRASSE) ont offert l’opportunité d’étudier les processus de fractionnement isotopique lors de l’évaporation océanique et le renouvellement de l’air de la couche limite atmosphérique. Aux plus hautes latitudes de l’océan Atlantique nord, la circulation de surface du gyre subpolaire permet le transfert d’eaux froides et dessalées en provenance de la région (sub)arctique vers l’intérieur du gyre. Dans le cadre de cette thèse, un jeu de données a été recueilli sur la période 2010-2014 et porte plus particulièrement sur la région du courant du Labrador et permet de se poser les questions suivantes : Comment le cycle de la glace de mer affecte la salinité de ces courants dessalés ? Comment évolue l’apport en eau météorique dans un contexte de fonte accélérée des glaciers continentaux ?
This thesis focuses on two regions of the North Atlantic: the subtropical gyre and the subpolar gyre. This large coverage allows an investigation of the water cycle in different hydrological regimes, where various processes take place such as sea ice seasonal cycle, rivers runoff, continental ice melt and advection of air and water masses. In the subtropical region, the variability of the isotopic composition of the water vapor is studied to understand the role of evaporation and mixing with free troposphere in humidity and isotopic compositions at the ocean surface. In particular, new data collected during summer 2012 (STRASSE cruise) gave the opportunity to explore kinetic fractionation processes during oceanic evaporation and air renewal in the atmospheric boundary layer. In the subpolar region, the surface circulation is cyclonic and transfers cold and fresh water from the arctic region to the interior of the subpolar gyre. For this thesis, data were collected between 2010 and 2014 from oceanographic cruises and commercial vessels to study the gyre interior and the main coastal currents carrying water from the arctic to lower latitudes. The study is mainly focused on the Labrador Current. There, isotopic measurements are used to identify the freshwater sources and to consider the following questions: How is the salinity of fresh currents affected by the sea ice formation and melting? How is the contribution of meteoric waters changing in a context of an acceleration of the melting of continental glaciers?

The arrival of the North American Monsoon System (NAMS) terminates a presummer hyperarid period in the southwestern United States (U.S.), providing summer moisture that is favorable for forest growth. Montane forests in this region rely on winter snowpack to drive much of their growth; the extent to which they use NAMS moisture is uncertain. We addressed this by studying stable carbon and oxygen isotopes in earlywood and latewood from 11 sites along a latitudinal gradient extending from Arizona and New Mexico to Utah. This study provides the first regional perspective on the relative roles of winter versus summer precipitation as an ecophysiological resource. Here we present evidence that Ponderosa pine uses NAMS moisture differentially across this gradient. C-13/C-12 ratios suggest that photosynthetic water use efficiency during latewood formation is more sensitive to summer precipitation at the northern than at the southern sites. This is likely due to the fact that NAMS moisture provides sufficiently favorable conditions for tree photosynthesis and growth during most years in the southern sites, whereas the northern sites experience larger summer moisture variability, which in some years is limiting growth. Cellulose O-18 and C-13 values revealed that photoassimilates in the southern sites were produced under higher vapor pressure deficit conditions during spring compared to summer, demonstrating a previously underappreciated effect of seasonal differences in atmospheric humidity on tree ring isotope ratios. Our findings suggest that future changes in NAMS will potentially alter productivity and photosynthetic water use dynamics differentially along latitudinal gradients in southwestern U.S. montane forests.

This thesis addresses the utility of deep-water coral geochemistry and its potential to reconstruct oceanographic conditions in the Straits of Florida. Through stable isotope and elemental analyses of the carbonate skeletons and use of available geochemical proxy calibration equations, present and past environmental parameters were determined. Over the last several years, scientific expeditions to the bottom of the Straits of Florida have revealed hundreds of deep-water coral mounds and led to the collection of extensive oceanographic data, sediment samples, and deep-water coral specimens. In 2005-2006, an Autonomous Underwater Vehicle (AUV) was used to map the coral mound fields at five sites with the use of geophysical imaging technology, and the manned Johnson-Sea-Link II submersible was deployed for further exploration and sample collection. The AUV and the submersible CTD also measured numerous environmental parameters, including temperature and salinity. With the goal of reconstructing environmental parameters across the Straits of Florida, Scleractinian and gorgonian deep-water coral specimens were selected from three sites spanning the Straits. Each coral was sampled at the highest resolution possible and analyzed for stable isotopes and elemental concentrations. Resulting geochemical data, specifically d18O, d13C, Sr/Ca, and Mg/Ca, was then used with previously published and newly developed calibration equations to calculate temperature, salinity, and seawater density. Kinetic and vital effects were also examined and taken into account while reconstructing environmental parameters using the coral geochemistry. Additional reconstructions using stable isotopic values from benthic foraminifera corroborated the geochemical reconstructions, and analyses of pteropods and surface sediment samples provided further insight into the oceanographic conditions at the bottom of the Straits of Florida. Results from geochemical reconstructions agreed with in situ data, indicating that slightly warmer bottom temperatures exist on the eastern side of the Straits and salinity variability among the three sites is minimal. This suggests that the deep-water coral skeletons are sensitive recorders of the environmental conditions in which they lived. Ultimately, in situ measurements and reconstructed parameters showed that there is little variability across the bottom of the Straits and that Antarctic Intermediate Water (AAIW) is the only apparent water mass in the area at that depth. Moreover, comparison of the coral habitat from this study with others from around the world demonstrated that certain conditions are required for deep-water coral growth, and that these same parameters are common to deep-water reef systems throughout the globe. Further sampling and geochemical analyses of deep-water corals in the region may be used to gain additional insight into the oceanographic conditions surrounding the coral mounds both presently and in the past. As with other previously studied deep-water coral systems, this highlights the potential for the reconstruction of paleo environmental records from deep-water corals in the Straits of Florida.

Freshwater ostracods (crustacea, ostracoda) are sensitive to environmental conditions, and are widely used as biological indicators for past and present environmental changes. The abundance and diversity of ostracods from permafrost areas is currently documented in scattered records with incomplete ecological characterizations. The objectives of the thesis were to determine the taxonomic and ecological range of ostracod assemblages and their habitat conditions in polygon ponds in different landscape units of the Indigirka Lowland (north-east Siberia, Russia). A monitoring approach focused seasonal meteorological and limnological variability of a selected pond site, its ostracod population dynamics, and the geochemical properties of ostracod valve calcite. Shallow, well-oxygenated, and dilute ponds with slightly acidic to circumneutral pH hosted an abundant and diverse ostracod fauna. A total of 4849 identified ostracods from eight species and three taxa represent the first record of the ostracod fauna in the Indigirka Lowland. Fabaeformiscandona krochini and Fabaeformiscandona groenlandica were documented for the first time in continental Siberia. Fabaeformiscandona sp. I and Fabaeformiscandona sp. II were newly found taxa holding a strong indicative potential for hydrochemical parameters. Repeated sampling of a typical low-center polygon pond revealed detailed insights in the population dynamics of Fabaeformiscandona pedata and its reproduction strategy. Substrate properties, physical and hydrochemical conditions in the studied ponds offered largely homogeneous habitats across different landscape units and pond types to ostracods. River flooding and differences in morphology between pond types resulted in variations in sediment, vegetation, hydrochemical and stable water isotope composition of the ponds. Ponds in the river floodplain and intrapolygon ponds hosted the most diverse ostracod fauna while species diversity was lowest in thaw lakes. Air temperature and precipitation were identified as the main external drivers of water temperatures, water levels, ion concentrations, and stable water isotope composition in small periglacial waters on diurnal and seasonal scales. Ostracod valve calcite recorded seasonal variations in stable oxygen isotopes of the ambient waters, but needs to be interpreted carefully with regard to species-specific background knowledge.
POLYGON - Polygons in tundra wetlands: state and dynamics under climate variability in polar regions

Ce travail de thèse est centré sur l'analyse des compositions isotopiques de la glace (d18O et dD) de deux nouvelles carottes de glace longues provenant des régions subtropicale et tempérée des Andes. La première carotte, longue de 42m, a été extraite en 2003 au col du glacier Coropuna au Pérou (72°39'W, 15°32'S, 6425m) et la deuxième de 122m au sommet du glacier San Valentin au Chili (46°35'S, 73°19'W, 4032m) en 2007. L'étude a porté sur la représentativité du signal isotopique comme archive du climat sur le dernier siècle, correspondant à la totalité de la carotte du Coropuna et les 70 premiers mètres au San Valentin, dans deux régions climatiques différentes. Nous avons observé que les enregistrements des signaux isotopiques sont affectés par des processus de post-dépôt. Au col du Coropuna, le signal est lissé par homogénéisation en dessous de 3m de profondeur à cause de la percolation d'eau de fonte et de la diffusion isotopique via un flux de vapeur, et aucune interprétation climatique n'est possible à partir du signal isotopique. Au so mmet du San Valentin, les vents forts, présents toute l'année, érodent et/ou redistribuent la majorité des précipitations annuelles en créant certainement des hiatus sur une voire plusieurs années ou, au contraire, des dépôts exceptionnels de plusieurs mètres. Ces conditions rendent l'identification des cycles isotopiques annuels difficile et aucune relation entre les isotopes et les paramètres climatiques n'a pu être établie due à une datation très incertaine
This work is focused on the analyses of two new isotopic records (d18O and dD) from Andean ice cores in the subtropics and temperate latitudes. The first 42 m-long ice core was extracted in 2003 from the saddle of Coropuna glacier in Peru (72°39'W, 15°32'S, 6425 m), and the second 122 m-long core in 2007 from the San Valentin summit in Chile (46°35'S, 73°19'W, 4032 m). The isotopic signals were investigated for their suitability as climate archives over the last century, covering the 42 m-long ice core from Coropuna and the first 70 meters of the core from San Valentin, in two different climatic regions. We observed that the isotopic records are affected by post-depositional processes. At the saddle of Coropuna, isotopic homogenization occurs below 3 m as a result of meltwater percolation and isotopic diffusion, and thus the climatic interpretation is not possible. At the San Valentin summit, removal and/or re-deposition of snow by strong winds occurring throughout the year may create a lack of one or more annual snow layers or, on the other hand, may cause unexpected deposits of several meters. Due to these potential conditions, we cannot always identify the annual isotopic cycles and the isotopes histories show no significant correlation with the climatic parameters because of an uncertain dating

129I is a radioactive isotope (T1/2= 15.7 million years) produced through natural and anthropogenic pathways, but the anthropogenic production is presently dominating the Earth’s surface environments. Sparse data from previous investigations in the Baltic Sea clearly indicated the occurrence of 129I at levels 3-4 orders higher than natural pre-atomic era (before 1940) without comprehensive evaluation of distribution and inventory. In this thesis extensive data on the distribution and inventory of iodine isotopes, 129I and 127I, and their species in waters of the Baltic Sea, Kattegat and Skagerrak are presented and used for estimation of water masses exchange and impact on the environment.  To fulfill these objectives seawater samples were collected in August 2006 and April 2007 in the Baltic Proper, Kattegat and Skagerrak as well as in December 2009 in the Bothnian Sea. After elaborative chemical separation of total iodine and iodine species, the analysis was performed using ICP-MS for 127I and AMS for 129I. The results reveal considerable differences in 129I concentration in terms of spatial and temporal variability and expose relatively high concentrations in the deep waters. Inventory estimates show higher amounts of 129I in August 2006 (24.2 ±15.4 kg) than in April 2007 (14.4± 8.3 kg) within the southern and central Baltic Proper, whereas almost a constant inventory is found in the Kattegat Basin. Relatively high 127I-/127IO3- and 129I-/129IO3- values in water of the Baltic Proper suggest effective reduction of iodate at a maximum rate of  8×10-7 (127IO3-) and 6×10-14 (129IO3-) (g/m3.day). The combination of 129I and 127I as tracers of water circulation in the Baltic Sea suggest that upwelling deep basinal water occurs into the surface along the Gotland deep and intrusion of North Atlantic water into southern Baltic. Furthermore, 129I-based model inventory reveals inflow of 330 km3/y (230-450 km3/y) water from the Kattegat into the Baltic Proper. Water exchange between the Baltic Proper and the Bothnian Sea and vice versa is estimated at 980 km3/y (600-1400 km3/y) and 1180 km3/y (780-1600 km3/y) respectively. Finally, an environmental assessment of radioactivity associated with 129I burden in the Baltic Sea region is discussed.

Biological and physical sampling of a 10km long, east-west transect was performed during 2007, off the coast of southeast Florida. Temperature and salinity measurements were recorded using a conductivity-temperature-depth (CTD) sensor, and current direction and magnitude measurements were recorded using an acoustic Doppler current profiler (ADCP). Zooplankton samples were collected, during the daytime, using a Tucker multiple net mid-water trawl, with 760μm mesh, at intended depths of ~25m and ~200m, at three stations along the transect. Laboratory analysis indicated that several currents and water masses influenced the density distribution of calanoid copepods and chaetognaths. During April and September 2007, a Subsurface Counter Current existed in conjunction with an offshore meander of the Florida Current. Physical data confirmed the presence of Continental Edge Water and Yucatan Water occupying different spatial and temporal scales, and the boundary between these two water masses existed as the western boundary of the Florida Current. Temperature and salinity profiles confirmed that the Subsurface Counter Current was composed of Continental Edge Water and not Yucatan Water. Therefore, the Subsurface Counter Current observed during the transect was not a cross section of a passing eddy caused by the meandering front of the Florida Current. Densities of both taxa were highest in the Subsurface Counter Current and the Intermediate water, while the lowest densities are found in the Florida Current. Calanoid copepod and chaetognath densities exhibited typical zooplankton trends for tropical and subtropical coastal waters. Densities were highly influenced by the physical parameters of each month. Highest densities were observed in April and the lowest in July/September, typically the nutrient limited season. Analysis by location showed that the calanoid copepod and chaetognath densities were highest inshore and decreased offshore. The Florida Current exhibited the lowest densities for both taxa, while the Subsurface Counter Current and Intermediate water had higher densities. Previously documented southward flow had been associated with an offshore meander of the Florida Current, but during May and July there was a Subsurface Counter Current and an onshore meander of the Florida Current. Densities of both taxa were still lowest in the Florida Current. The stable isotope values of the zooplankton were skewed because of the preservation media and it was not possible to determine if the currents and water masses were isotopically different, and thus creation of a correction factor for the preservation effect was not possible. The δ13C values were variable in magnitude and direction from the control for each taxon. The δ15N values were less variable, but increased from the control, rather than decrease, as was expected for each taxon.