Pollutants follow various subsurface and surface water pathways from sources within a catchment to its outlet and may cause detrimental effects on downstream water quality and ecosystems. Along their different transport pathways through a catchment, pollutants may be attenuated subject to different physical and biogeochemical processes. In this thesis, physical process effects on such catchment-scale pollutant transport and attenuation, resulting coastal pollutant loading and its efficient abatement are investigated. For this purpose, pollutant transport-attenuation is modeled both generically using a Lagrangian Stochastic Advective-Reactive (LaSAR) approach and site specifically for the Swedish Norrström basin using the GIS-based dynamic nitrogen transport-attenuation model POLFLOW. Furthermore, the role of such modeling for catchment-scale pollutant abatement is also investigated by use of economic optimization modeling. Results indicate that appropriate characterization of catchment-scale solute transport and attenuation processes requires accurate quantification of the specific solute pathways from different sources in a catchment, through the subsurface and surface water systems of the catchment, to the catchment outlet. The various physical processes that act on solute transported along these pathways may be quantified appropriately by use of relevant solute travel time distributions for each water subsystem that the pathways cross through the catchment. Such distributions capture the physical solute travel time variability from source to catchment outlet and its effects on reactive pollutant transport. Results of this thesis show specifically that neglect of such physical solute travel time variability in large-scale models of nitrogen transport and attenuation in catchments may yield misleading model estimates of nitrogen attenuation rates. Results for nitrogen abatement optimization in catchments further indicate that inefficient solutions for coastal nitrogen load reduction may result from simplifying physical transport assumptions made in different catchment-scale nitrogen transport-attenuation models. Modeling of possible future nitrogen management scenarios show also that slow nitrogen transport and reversible mass transfer processes in the subsurface water systems of catchments may greatly delay and temporally redistribute coastal nitrogen load effects of inland nitrogen source abatement over decades or much longer. Achievement of the national Swedish environmental objective to reduce the anthropogenic coastal nitrogen loading by 30% may therefore require up to a 40% reduction of both point sources, for achieving a fast coastal load response, and diffuse sources, for maintaining the coastal load reduction also in the long term. / QC 20100908

The objectives of this research are to measure the aquifer properties (S, T, and K) of selected watersheds delineated to the U.S. Geological Survey gauging stations using streamflow recession and baseflow data and to describe the relations among the properties of shallow aquifers and the physical properties of the basins, such as slope, regolith type and thickness, and land use type. Geographic Information System (GIS) techniques are utilized to investigate critical physiographic controls on transmissivity and storage coefficients on a regional basis. Moreover, the effect of evapotranspiration on recession index is illustrated. Finally, a detailed quantitative comparison of results for the Piedmont and the Blue Ridge Physiographic Provinces in southeast of the U.S. is provided. Recession index, annual groundwater recharge, and annual baseflow data were obtained from 44 USGS-gauging stations with drainage areas larger than 2 (mi2) and less than 400 (mi2). These gauging stations are located in Georgia and North Carolina. Analyses of data focused on GIS techniques to estimate watershed parameters such as total stream length, drainage density, groundwater slope, and aquifer half-width. The hydraulic diffusivity, transmissivity, and storage coefficient of watersheds were computed using hydrograph techniques and the Olmsted and Hely, and Rorabaugh mathematical models. Median recession index values for the Blue Ridge and Piedmont Provinces are 87.8 and 74.5 (d/log cycle), respectively. Median areal diffusivity values for the Blue Ridge and Piedmont are 35,000 and 44,200 (ft2/d), respectively. Median basin-specific estimates of transmissivity for basins in the Blue Ridge and Piedmont are 150 and 410 (ft2/d), respectively. The large values of transmissivity obtained for the Piedmont regolith may be attributed to the thick regolith, low values of basin relief, and voids that develop as a result of fracturing, foliation, weathering, and fractured quartz veins in the saprolite. Median basin-specific estimates of storage coefficient for basins in the Blue Ridge and Piedmont are 0.005 and 0.009, respectively. In general, the results from this study reveal great differences in basin-specific hydraulic parameters of the regolith material within the Piedmont compared to that of the Blue Ridge Physiographic Province.

Pour une meilleure gestion de l’eau, la Directive Cadre sur l’Eau requiert la prise en compte des relations entre les masses d’eau superficielles et souterraines. Dans ce cadre, la dynamique des échanges entre eaux de surface et eaux souterraines est étudiée, pour un aquifère alluvial du Rhône. Deux approches sont utilisées: une analyse des séries temporelles de niveaux de nappes et de rivières, à l’aide de techniques de traitement du signal, et des modèles d’écoulements numériques, déterministes, à base physique. Ces techniques sont mises en œuvre sur un secteur (Péage-de-Roussillon) à forts enjeux socio-économiques pour l’usage de la ressource en eau. Les résultats sont analysés du point de vue de leurs complémentarités.Une analyse en composantes principales, à partir des signaux piézométriques, a montré que les fluctuations de niveaux du Rhône expliquent la majeure partie des variations de niveau de la nappe. Les analyses corrélatoires et spectrales, ont permis de caractériser la relation existant entre les niveaux du Rhône et de la nappe. Des comportements particuliers de l’hydrosystème ont été identifiés : colmatage du fond des cours d’eau, écoulements transverses aux cours d’eau,…. Ces comportements ont ensuite pu être étudiés, plus en détail, à l’aide d’un modèle hydrodynamique de la nappe qui intègre un module de calcul des écoulements surfaciques. Le modèle permet également de quantifier les flux échangés entre la nappe et le cours d’eau. / For better water management, the Water Framework Directive requires to take into account the relationships between surface water and groundwater bodies.In this frame, the exchanges dynamic between surface water and groundwater is studied, for a Rhône alluvial aquifer. Two sets of tools are employed: a time series analysis of groundwater and rivers levels, using signal processing techniques, and numerical flow models, deterministic and physically based. These techniques are implemented on an area (Péage-de-Roussillon) with high socio-economic stakes regarding water resources. The complementarities among the results are analysed.A principal component analysis, based on piezometric head signals, showed that the fluctuations of the Rhône water level explain most of the groundwater variations. Correlative and spectral analysis were used to characterise the relationship between the Rhône and the groundwater level. Specific behaviours of the hydrosystem were identified: clogging of river beds, transversal flows below river beds,… These behaviours were then studied, in details, using a hydrodynamic model of the aquifer, which incorporates a surface runoff calculation module. The model also allows quantifying the exchange rates between rivers and groundwater.

It has long been observed that salts affect proteins in a variety of ways, yet comprehensive explanations for different salt effects are still lacking. In the work presented here, the effect of salts on proteins has been investigated through three different effects: the hydrophobic effect; their conformational stability; the hydrogen bonding network of water in a protein’s hydration shell. UV-vis absorbance and fluorescence spectroscopy were used to monitor changes in two model systems, the phenol-acetate contact pair and the model enzyme ribonuclease t1. It was shown that salts affect the hydrophobicity of the contact pair according to their charge density, induced image charges play an important role in the observed salt-induced increase of ribonuclease t1 stability, and that salts affect ribonuclease t1 activity through modulation of the hydrogen bonds of water in the enzyme’s hydration shell. This work contributes a greater understanding of the effect of salts on proteins.

It has long been observed that salts affect proteins in a variety of ways, yet comprehensive explanations for different salt effects are still lacking. In the work presented here, the effect of salts on proteins has been investigated through three different effects: the hydrophobic effect; their conformational stability; the hydrogen bonding network of water in a protein’s hydration shell. UV-vis absorbance and fluorescence spectroscopy were used to monitor changes in two model systems, the phenol-acetate contact pair and the model enzyme ribonuclease t1. It was shown that salts affect the hydrophobicity of the contact pair according to their charge density, induced image charges play an important role in the observed salt-induced increase of ribonuclease t1 stability, and that salts affect ribonuclease t1 activity through modulation of the hydrogen bonds of water in the enzyme’s hydration shell. This work contributes a greater understanding of the effect of salts on proteins.

Im Zusammenhang mit dem globalen Klimawandel ist die Vegetation besonders wichtig, da sie die anthropogenen CO2-Emissionen aufnehmen und den Wasser- und Energiekreislauf regulieren kann. Während frühere Forschungsarbeiten wertvolle Einblicke in langfristige Veränderungen des Grüns der Vegetation und in Bezug auf die Reaktion der Vegetation auf steigende Temperaturen und atmosphärisches CO2 lieferten, sind die Wechselwirkungen zwischen Vegetation und Wasser noch immer nicht vollständig verstanden. Tatsächlich hat die Dynamik der Bodenfeuchte in der Wurzelzone einen grundlegenden Einfluss auf die Veränderung des Grüns und die Produktivität der Vegetation. Dennoch sind weder die die Empfindlichkeit der Vegetationsproduktivität gegenüber der Bodenwasserversorgung noch die funktionelle Reaktion der Vegetation (d. h. Photosynthese und Transpiration) auf Bodentrockenheitsepisoden auf globaler Ebene vollständig geklärt worden. Forschungsengpässe sind fehlende globale Beobachtungen von Vegetationsfunktion und Bodenwasservariabilität. Außerdem werden die statistischen Instrumente für die Analyse umfangreicher und vielschichtiger Daten nur unzureichend genutzt, was ein besseres Verständnis der globalen Reaktion der Vegetation auf Wasser verhindert. Gleichzeitig trägt eine bessere Kenntnis der Reaktion der Vegetation auf die Wasserversorgung zu einem besseren Verständnis des terrestrischen Wasserkreislaufs bei. Hydrologische Extremereignisse schädigen die Infrastruktur, können das menschliche Wohlergehen beeinträchtigen und treten Berichten zufolge in vielen Regionen der Welt immer häufiger und intensiver auf. Während ein Konsens über die Bedeutung meteorologischer Faktoren für die Regulierung des Wasserkreislaufs und der damit verbundenen Extremereignisse besteht, ist die Rolle der Vegetationsdynamik und -eigenschaften noch nicht ausreichend erforscht. Ihre stärkere Berücksichtigung in hydrologischen Studien bietet das Potenzial, die Prozesse, die hydrologische Extreme antreiben, genauer zu verstehen. Dadurch kann ein besseres Verständnis der Wechselwirkungen zwischen Vegetation und Wasser im Hinblick auf die Wasserempfindlichkeit der Vegetation und die Rückkopplung der Vegetation auf Klimaextreme die Genauigkeit der Landoberflächenmodellierung verbessern, was für die Verbesserung der Klimaprojektionen unerlässlich ist. Dank der jüngsten Entwicklungen im Bereich der Erdbeobachtung und der Anwendbarkeit leistungsfähiger statistischer Analysewerkzeuge ist es nun möglich, globale Wechselwirkungen zwischen Vegetation und Wasser mit noch nie dagewesener Genauigkeit zu untersuchen. In diesem Zusammenhang stützt sich diese Arbeit insbesondere auf (i) neuartige Datenprodukte wie sonneninduzierte Chlorophyllfluoreszenz oder globale Bodenfeuchte und Evapotranspiration, die aus der Hochskalierung von Stationsmessungen mit Algorithmen des maschinellen Lernens gewonnen wurden, (ii) längere Aufzeichnungen und aktualisierte Aufbereitungen etablierter Datenprodukte wie Blattflächenindex und terrestrische Wasserspeicherung und (iii) die Entwicklung erklärbarer Methoden des maschinellen Lernens, mit denen Informationen effizient aus multivariaten Datenströmen abgeleitet werden können und die darüber hinaus leicht implementier- und in ökohydrologischen Studien anwendbar sind. Basierend auf diesen Datensätzen und Werkzeugen, wird in dieser Arbeit die Empfindlichkeit der globalen Vegetation gegenüber der Bodenwasserversorgung über Raum und Zeit hinweg neu untersucht.:Summary 7 Zusammenfassung 11 1 Introduction 15 1.1 Motivation 16 1.2 Terrestrial vegetation and its relationship with water supply 18 1.2.1 Vegetation functioning 18 1.2.2 Hydro-meteorological drivers of evaporation and vegetation productivity 19 1.2.3 Vegetation structure and physiology 21 1.3 Terrestrial water cycle and its relationship with vegetation 24 1.3.1 Water balance 24 1.3.2 Vegetation regulating the water cycle 26 1.3.3 The relevance of vegetation on hydrological extremes 27 1.4 Advances in observations and models 30 1.4.1 Spaceborne remote sensing 30 1.4.2 Data-driven and physical-based models 34 1.5 Research questions and thesis outline 37 1.5.1 What is the relationship between vegetation productivity and water supply? 37 1.5.2 Can vegetation regulate hydrological extremes? 38 1.5.3 Can land surface models capture vegetation-water interplay? 40 1.5.4 Thesis outline 40 2 Global vegetation controls using multi-layer soil moisture 41 2.1 Introduction 42 2.2 Data and methods 43 2.3 Results and discussion 45 2.4 Conclusions 53 2.A Appendix 54 3 Widespread increasing vegetation sensitivity to soil moisture 70 3.1 Introduction 71 3.2 Data and methods 72 3.3 Results and discussion 78 3.4 Conclusions 85 3.A Appendix 86 4 The drought effect on vegetation physiology inferred from space 101 4.1 Introduction 102 4.2 Data and methods 104 4.3 Results and discussion 111 4.4 Conclusions 122 4.A Appendix 123 5 Drought propagation into the terrestrial water cycle 136 5.1 Introduction 137 5.2 Data and methods 139 5.3 Results and discussion 145 5.4 Conclusions 155 5.A Appendix 157 6 Drivers of high river flows in European near-natural catchments 171 6.1 Introduction 172 6.2 Data and methods 173 6.3 Results and discussion 179 6.4 Conclusion 184 6.A Appendix 186 7 Synthesis 193 7.1 What is the relationship between vegetation productivity and water supply? 194 7.2 Can vegetation regulate hydrological extremes? 197 7.3 Can land surface models capture the observed vegetation-water interplay? 199 7.4 Limitations 200 7.4.1 Difficulties in predicting SIF in tropical regions 200 7.4.2 Observing terrestrial photosynthesis and evaporation 201 7.4.3 Methods related to variable importance quantification 202 7.5 Outlook 202 7.5.1 Vegetation sensitivity to soil moisture and its implications 203 7.5.2 Vegetation functioning and related structure and physiology 203 7.5.3 Extreme events: floods and drought 204 References 206 Statement of authorship contributions 238 Acknowledgements 239 Curriculum Vitae 241 Scientific publications 242 IMPRS certificate 244 / In the context of global climate change, vegetation is particularly relevant as it can take up anthropogenic CO2 emissions and regulate water and energy cycling. While previous research provided valuable insights into long-term changes in vegetation greenness and in terms of the vegetation response to increasing temperature and atmospheric CO2, vegetation-water interactions are still not fully understood. In fact, root-zone soil moisture dynamics have a fundamental influence on modulating vegetation greenness and productivity. Nevertheless, neither the sensitivity of vegetation productivity to soil water supply nor the vegetation functional response (i.e., photosynthesis and transpiration) to soil drought episodes have been fully resolved at the global scale. Missing global observations of vegetation functioning and terrestrial water variability are bottlenecks, and statistical tools for analyzing large and multi-stream data are poorly exploited, preventing a better understanding of global vegetation water response. At the same time, a better knowledge of the vegetation response to the water supply in turn advances the understanding of the terrestrial water cycle. Hydrological extremes are damaging infrastructure and can affect human well-being, and have been reported to become more frequent and intense in many regions around the world. While a consensus exists regarding the importance of meteorological drivers for regulating the water cycle and related extreme events, the role of vegetation dynamics and characteristics is understudied. Its greater consideration in hydrological studies offers the potential to more accurately understand the processes driving hydrological extremes. Thereby, a better understanding on vegetation-water interactions in terms of vegetation water sensitivity and vegetation feedbacks on climate extremes can advance the accuracy of land surface modelling which is essential to improve climate projections. Thanks to recent developments in Earth observations and in the applicability of powerful statistical analyses tools, investigating global vegetation-water interactions is now possible with unprecedented accuracy. In this context, this thesis builds particularly on (i) novel data products such as Sun-induced chlorophyll fluorescence or global gridded soil moisture and evapotranspiration products obtained from upscaling station measurements with machine learning algorithms, (ii) longer records and updated processing of established data products such as leaf area index and terrestrial water storage, and (iii) the development of explainable machine learning methods which can efficiently derived information from multivariate data streams, and are furthermore implemented and readily applicable in ecohydrological studies. With these datasets and tools, this thesis revisits the sensitivity of global vegetation to soil water supply across space and time.:Summary 7 Zusammenfassung 11 1 Introduction 15 1.1 Motivation 16 1.2 Terrestrial vegetation and its relationship with water supply 18 1.2.1 Vegetation functioning 18 1.2.2 Hydro-meteorological drivers of evaporation and vegetation productivity 19 1.2.3 Vegetation structure and physiology 21 1.3 Terrestrial water cycle and its relationship with vegetation 24 1.3.1 Water balance 24 1.3.2 Vegetation regulating the water cycle 26 1.3.3 The relevance of vegetation on hydrological extremes 27 1.4 Advances in observations and models 30 1.4.1 Spaceborne remote sensing 30 1.4.2 Data-driven and physical-based models 34 1.5 Research questions and thesis outline 37 1.5.1 What is the relationship between vegetation productivity and water supply? 37 1.5.2 Can vegetation regulate hydrological extremes? 38 1.5.3 Can land surface models capture vegetation-water interplay? 40 1.5.4 Thesis outline 40 2 Global vegetation controls using multi-layer soil moisture 41 2.1 Introduction 42 2.2 Data and methods 43 2.3 Results and discussion 45 2.4 Conclusions 53 2.A Appendix 54 3 Widespread increasing vegetation sensitivity to soil moisture 70 3.1 Introduction 71 3.2 Data and methods 72 3.3 Results and discussion 78 3.4 Conclusions 85 3.A Appendix 86 4 The drought effect on vegetation physiology inferred from space 101 4.1 Introduction 102 4.2 Data and methods 104 4.3 Results and discussion 111 4.4 Conclusions 122 4.A Appendix 123 5 Drought propagation into the terrestrial water cycle 136 5.1 Introduction 137 5.2 Data and methods 139 5.3 Results and discussion 145 5.4 Conclusions 155 5.A Appendix 157 6 Drivers of high river flows in European near-natural catchments 171 6.1 Introduction 172 6.2 Data and methods 173 6.3 Results and discussion 179 6.4 Conclusion 184 6.A Appendix 186 7 Synthesis 193 7.1 What is the relationship between vegetation productivity and water supply? 194 7.2 Can vegetation regulate hydrological extremes? 197 7.3 Can land surface models capture the observed vegetation-water interplay? 199 7.4 Limitations 200 7.4.1 Difficulties in predicting SIF in tropical regions 200 7.4.2 Observing terrestrial photosynthesis and evaporation 201 7.4.3 Methods related to variable importance quantification 202 7.5 Outlook 202 7.5.1 Vegetation sensitivity to soil moisture and its implications 203 7.5.2 Vegetation functioning and related structure and physiology 203 7.5.3 Extreme events: floods and drought 204 References 206 Statement of authorship contributions 238 Acknowledgements 239 Curriculum Vitae 241 Scientific publications 242 IMPRS certificate 244

Le nord du Chili est soumis à un contexte climatique aride à semi-aride présentant une variabilité saisonnière et inter-annuelle forte. Dans cette région les zones de haute altitude soutiennent les parties plus basses des bassins versants, mais la ressource en eau reste malgré tout limitée. Afin d'améliorer les méthodes de gestion de l'eau dans ces bassins versants, il est important de préciser le rôle des zones de haute altitude dans le soutien des parties basses, mais aussi de caractériser les modalités de transfert et d'interaction entre les compartiments constitutifs de l'hydrosystème. Ce travail porte sur la caractérisation du fonctionnement hydrologique du bassin versant de l'Elqui depuis la tête de bassin, située au cœur de la cordillère des Andes, jusqu'aux vallées de la zone inférieure situées entre 500 et 2000 mètres d'altitude. En tête de bassin, les processus d'interaction entre les compartiments cryosphériques, hydrologiques et hydrogéologiques, et leurs impacts sur le transfert des masses d'eau vers l'aval de la zone d'étude sont caractérisés. Le comportement hydrologique des sous bassins versant partiellement ou non‑englacés est également étudié. Dans la zone inférieure du bassin, l'étude porte principalement sur les processus d'interactions surface-souterrain en contexte semi‑aride et sur les impacts des forçages climatiques et anthropiques sur ces derniers. Cette étude s'appuie sur plus de 40 ans de données hydro-météorologiques disponibles sur la zone inférieure du bassin, complétés par des mesures hydrologiques sur la zone supérieure (> 2000 mètres d'altitude) et des prélèvements chimiques (majeurs et traces) et isotopiques (²D, 18O) sur la totalité de la zone d'étude, réalisés entre 2011 et 2013.Ces travaux ont montré que le modèle conceptuel de fonctionnement du bassin versant de l'Elqui généralement accepté était incomplet. Dans la zone supérieure, l'étude d'un bassin versant englacé a permis de montrer que le rôle de la cryosphère dépasse la fonction de production d'eau, avec certains compartiments stockant temporairement de l'eau en période humide et la libérant en période sèche. Ce processus permet d'amortir la variabilité temporelle des précipitations et du taux de fonte en altitude. Les analyses physico-chimiques réalisées dans le bassin versant ont également permis d'identifier des compartiments aquifères ignorés jusqu'à maintenant, comme les compartiments volcanique et plutonique. En améliorant les connaissances sur les processus d'interactions entre compartiments cryosphériques, hydrologiques et hydrogéologiques, les résultats de ce travail ont apporté des précisions sur le fonctionnement hydrologique de la zone de haute altitude. Cela a permis l'estimation des impacts potentiels de la variabilité climatique sur ces processus d'interactions et leurs conséquences sur la disponibilité et la qualité de la ressource. Dans la zone inférieure, la caractérisation des interactions surface-souterrain a montré qu'il existe un fort potentiel d'interaction entre le compartiment hydrologique et le compartiment alluvial, mais également entre le compartiment alluvial et le socle plutonique. L'étude des données hydrologiques et physico-chimiques a permis de caractériser le type d'échanges se déroulant entre les compartiments. Dans certains secteurs le processus dominant est la recharge du compartiment alluvial par le compartiment hydrologique, tandis que pour d'autres il existe une alternance entre période de drainage du compartiment alluvial par le compartiment hydrologique et période de recharge du compartiment alluvial. La réponse de ces processus face aux impacts des forçages climatiques et anthropiques contraindra la disponibilité et la qualité de la ressource dans les années à venir. Ainsi, les résultats apportés par ce travail permettront certainement de mieux anticiper les modifications futures du fonctionnement hydrologique des bassins versant montagneux en contexte semi-arides. / The north Chile is affected by an arid to semi-arid climate, associated with a strong seasonal to inter-annual variability. In this region, while mountainous areas are supporting low areas, the availability of water resources remains limited. In order to improve the water management in these basins, it is necessary to precise how the high areas support the low areas, and to characterize water transfers and interaction processes between the constitutive compartments of the hydrosystem. This work concern the characterization of the hydrodynamic behavior of the Elqui watershed from the headwaters, in the Andes, to the valleys, ranging between 500 and 2000 m.a.s.l.In the headwaters, the interactions processes between cryospheric and hydrologic compartments and their impact on water transfers to the low areas are characterized. The behavior of unglacierized or partially glacierized watershed is also studied. In the low area of the watershed, the study mainly considers groundwater-surface water interactions under semi-arid context and the impact of the climatic variability on these processes. This study is based on more than 40 years of hydro-meteorological data available in the lower zone of the basin, completed by hydrological measurements in the upper zone (> 2000 m.a.s.l.) and chemical (majors and traces elements) and isotopic samples (²D, 18O) over the whole study area realized between 2011 and 2013.This work demonstrated that the conceptual model of the Elqui basin hydrological behavior, generally accepted, was incomplete. In the high area (> 2000 m.a.s.l.), the study of a glacierized watershed show that the function of the cryosphere overpass the water production with some compartments storing water during humid periods and draining their water content during dry periods. This process buffers the temporal variability of precipitations and melting rates in the high area. Physico-chemical analysis, allows to identify some ignored aquifer compartments, as the volcanic and plutonic compartments. The results of this study improve the knowledge about interactions processes between cryospheric, hydrologic and hydrogeologic compartments, which precise the hydrological functioning of the high area. The interpretation of the hydrological behavior of the high altitude area allows to better understand the way that it support the low area, and the way that climate variability may affects it.In the low area, results show that the groundwater-surface water interaction potential is good between alluvial and hydrological compartments, but also between the plutonic and the alluvial compartments. The study of hydro-meteorological and physico-chemical data allowed to characterize the type of exchanges that take place between groundwater and surface water. In some sectors the main process is the recharge of the alluvial compartment by the hydrological compartment, while in other sectors the processes show a seasonal variability with periods of alluvial compartment recharge and periods of hydrological compartment support. The answer of these processes face to climatic and anthropic forcing will constrain the evolution of the availability and quality of the water resources in the Elqui basin. Finally, the results of this study will certainly allow to better anticipate the future modifications of the semi-arid mountainous watershed hydrological functioning.

Die Arbeit besteht aus mehreren Studien zur Quantifizierung des Grundwasserstroms in Seen (Exfiltration; engl.: lacustrine groundwater discharge, LGD) und damit verbundener Nährstoffeinträge. In zwei einleitenden Kapiteln dieser Arbeit werden eine Gründe für die Vernachlässigung der Grundwasserexfiltration (LGD) in Seen und der daran gekoppelten Nährstoffeinträge identifiziert. Diese Literaturstudien fassen den aktuellen Kenntnisstand zum Einfluss des Grundwassers auf die Hydrologie von Seen und ihre Nährstoffhaushalte zusammen. Den Kern der vorliegenden Arbeit bilden zwei empirische Studien, die sich mit der Quantifizierung der grundwasserbürtigen Phosphor (P)-Fracht in den Arendsee in Deutschland befassen. Das Gesamtvolumen des Grundwasserzustroms wird basierend auf der Grundwasserneubildung im Einzugsgebiet des Sees ermittelt. Lokale Muster der Grundwasserexfiltration werden anhand von Temperaturtiefenprofilen des Seesediments bestimmt. Eine Kombination der Ergebnisse ermöglicht es, die quantitativen Daten mit lokalen Informationen zu unterstützen. Die Untersuchung der Grundwasserqualität zeigt, dass die P-Konzentrationen im Grundwasser im besiedelten Bereich teilweise stark erhöht sind. Als Konsequenz daraus haben die grundwasserbürtigen P-Frachten einen Anteil von mehr als 50% an der gesamten externen P-Last des Arendsees. Das Grundwasser ist damit eine maßgebliche Ursache für die Eutrophierung des Gewässers. Drei weitere Studien widmen sich der Entwicklung und Optimierung von Ansätzen zur qualitativen und quantitativen Bestimmung der Grundwasserexfiltration in Seen. Die kritische Auseinandersetzung mit den Ergebnissen der Studien zeigt die Notwendigkeit weiterer Forschung zur Verbesserung und Standardisierung der Methoden zur Bestimmung von LGD und damit verbundenen Stofftransporten auf. Der Fall des Arendsees sollte alle, Wissenschaftler und Praktiker, dazu motivieren, das Grundwasser als relevante Eutrophierungsquelle in Betracht zu ziehen. / The present work is a collection of studies on lacustrine groundwater discharge (LGD) and groundwater-borne phosphorus (P) loads. For a number of reasons, groundwater exfiltration (i.e., LGD) is often not considered in water and nutrient budgets of lakes. This is also and especially true for P which was often regarded to be immobile in groundwater until recently. Two chapters review the scientific literature regarding the impacts of groundwater on hydrology and nutrient budgets of lakes, respectively. They present mechanisms and processes of LGD as well as techniques and methods to measure LGD and related nutrient transports. Moreover, numbers of LGD volumes and loads reported in literature are presented. The core of the present work is represented by two case studies dealing with the quantification of P loads from LGD to a lake in Germany. A combination of different methods is applied to overcome the problem of quantitative large scale LGD determination without losing local spatial information. P concentrations in groundwater and LGD are investigated by detailed spatial water sampling. The results reveal that P is actually present in concentrations far above natural background concentrations in the urban groundwater. LGD-derived P loads account for more than 50% of the overall external P loads to the lake and by that contribute significantly to lake eutrophication. Three further studies are devoted to the development and improvement of approaches to determine LGD. Critical reviews of the above mentioned studies reveal the need for further research in order to standardize and improve methods for LGD and mass load determination. It is found that the appropriate method for LGD determination depends on the spatial scale of interest. The identification of P introduced by LGD as a main driver of lake eutrophication is an important finding which should encourage scientists, policy makers, and lake managers to consider groundwater as a relevant P source for lakes.