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Water resources in the semi-arid to arid areas of Central Asia are often limited by low precipitation, and hence vulnerable to impacts of global change, i.e. socio-economic development and climate change. Both, socio-economic development and climate change are very likely causing significant changes as water resources are affected by two main effects: Firstly, growing population and industrial activities in the region raise the pressure on water resources due to increasing water abstractions. Secondly, air temperature in the region has been rising in the past far above global average and it is expected to increase further, which will lead to changes in runoff generation and therefore water availability. Increasing temperature as well as increasing water abstractions will affect water quantity and consequently water quality as a result of higher pollution intake or reduction in dilution capacity. Thus, it is of crucial importance to analyse and assess the state of current and future water resources to implement sustainable water management as the above mentioned effects very likely causing significant changes of water resources. Within the last years, the number of scientific research studies using large-scale models to simulate water availability and water use has increased substantially. Several new datasets from earth observations and new or improved models have been published (Werth et al. 2009; Werth and Güntner 2010; van Beek et al. 2011). Nevertheless, those studies focussed on water quantity and did not take into account impacts on water quality induced by global change although changes in water quality affecting aquatic ecosystems and species. Furthermore, spatially explicit large-scale modelling studies have not been carried out for Mongolia and Central Asia to get a comprehensive overview and assessment. To address this research gap, the large-scale water resource modelling framework WaterGAP 3 was applied to Central Asia with a focus on Mongolia to simulate impacts on current and future water resources. WaterGAP 3 consists of hydrology, water use and water quality sub-models in order to simulate current and future water quantity and quality.

L'émergence de maladies telles que le SRAS et le SIDA au cours des dernières décennies a fait prendre conscience des liens étroits existant entre santé animale, santé humaine et santé des écosystèmes. En effet, les pathogènes émergents ont pour la plupart une origine zoonotique (i.e. ils circulaient à l'origine au sein des populations animales). Les risques sanitaires associés à ces émergences sont en constante évolution sous l'influence des changements globaux qui modifient les écosystèmes et les contacts entre les hôtes. La prévention et le contrôle des maladies infectieuses émergentes nécessitent la compréhension de leur dynamique dans l'ensemble des compartiments dans lesquels elles circulent. Le travail présenté ici avait pour objectif d'améliorer cette compréhension au sein des zones humides méditerranéennes en ce concentrant sur deux pathogènes émergents : les virus Influenza A (VIA) et le virus West Nile. Il a été structuré selon trois axes de recherche : i) Utiliser la surveillance épidémiologique de l'avifaune sauvage pour comprendre la circulation du virus West Nile dans le bassin méditerranéen ii) Comprendre la dynamique des VIA au sein des différents compartiments où ils circulent et à leur interface iii) Comprendre le rôle des conditions environnementales dans la dynamique des VIA notamment au sein des populations humaines. Nos résultats mettent en évidence l'intérêt de mener des études multidisciplinaires sur le long terme pour comprendre l'épidémiologie des maladies émergentes. Ils soulignent également le rôle des activités anthropiques et des conditions environnementales dans la dynamique de ces maladies. Nos études apportent des éléments de réflexion pour allier gestion des risques d'émergence et gestion des écosystèmes et des populations. Elles encouragent à développer ce type d'approche afin de relever le défi de la prévention et du contrôle des pathogènes émergents. / During the last decades, the emergence of numerous infectious diseases such as SARS and AIDS has raised awareness of the close links that exist between animal health, human health and ecosystem health. Many of the emerging pathogens have a zoonotic origin (i.e. they originally circulated among animal populations). The health risks associated with the emergence of these diseases are progressing under the influence of global changes that affect ecosystems and contacts between hosts. The prevention and control of emerging infectious diseases require an in-depth understanding of their dynamics in all the compartments in which they occur. The aim of the present work is to improve our understanding of these phenomena within the context of Mediterranean wetlands by focusing on two emerging pathogens: Influenza A viruses (IAV) and West Nile virus. The thesis is structured around three research axes i) Using epidemiological surveillance of wild birds to investigate the circulation of West Nile virus in the Mediterranean Basin ii) Exploring IAV dynamics in the different compartments in which they circulate and at their interface iii) Determining the role of environmental conditions in IAV dynamics, especially within human populations. Our results highlight the value of long-term interdisciplinary studies for the understanding of the epidemiology of emerging diseases. They also emphasize the role of human activities and environmental conditions in the dynamics of these diseases. Our studies open up perspectives for combining emerging disease risk management and the management of ecosystems and populations. They also argue in favour of further developing this type of approach in order to meet the challenge of emerging pathogen prevention and control.

O presente estudo foi desenvolvido em uma área de Cerrado stricto sensu, localizado no Parque Estadual de Vassununga, próximo ao município de Santa Rita do Passa Quatro, interior de São Paulo. O objetivo deste trabalho foi mensurar os fluxos de CO2, liberado pelos processos respiratórios da vegetação e do solo (heterotrófica + autotrófica) para aferir a importância relativa destes compartimentos na respiração total do ecossistema, utilizando-se da técnica isotópica. Foi utilizada a técnica da reta de keeling plot, para determinar os valores isotópicos respirados pelo ecossistema, e pelos componentes vegetais (serapilheira, madeira morta, raízes, folha e ramo). De acordo com os resultados, os valores isotópicos do CO2 respirado pelos componentes autotróficos e heterotróficos, foram significativamente influenciados pela sazonalidade, ficando mais enriquecidos em 13C durante o período seco. As correlações encontradas entre os valores do \'delta\'13C- CO2 respirado pelos componentes e os fatores ambientais, como temperatura e umidade indicaram uma relação significativa. Os valores do \'delta\'13C-CO2 respirado pelo ecossistema foram menos enriquecidos em 13C quando houve maior disponibilidade de água no sistema. O valor isotópico do \'delta\'13C-CO2 respirado pelo ecossistema Cerrado foi de - 25,26%o . Particionando a respiração do ecossistema em acima e abaixo do solo, verificou-se que 75% foi realizada pela respiração abaixo do solo (microrganismo+raízes). Particionando a respiração em autotrófica e heterotrófica, observou-se que 54% foi realizado pela respiração da vegetação. Portanto, para tais resultados, a disponibilidade hídrica no solo, seguida da precipitação representaram um dos mais importantes fatores que contribuiram para a variabilidade nos valores isotópicos do \'delta\'13C orgânico e \'delta\'13C-CO2 respirado e no CO2 fixado pelo ecossistema. Os resultados obtidos neste estudo são de fundamental importância para uma melhor compreensão do ciclo do carbono no bioma Cerrado, bem como, abre a oportunidade de utilizar a técnica isotópica para definir padrões do \'delta\'13C-CO2 respirado em nível de ecossistema, utilizando estes resultados como indicadores de mudanças nas trocas gasosas frente ao cenário das mudanças climáticas / The presente study was carreid out in area o Cerrado strictu senso located at the State Park of Vassununga, closed to the Santa Rita do Passa Quatro city, São Paulo State, Brazil. The aim was of the present work was to measure de CO2 fluxes released through respiration processes of the vegetation and soil (heterotrophic and autotrophic) to check the relative importance of each of these ecosystems components on the respiration of overall ecosystem using the isotopic approach. The Keeling plot line was used to determine the isotopic values of carbon dioxide respired by the ecosystem and its components (litter, dead wood, roots, leaves and branches). The results show that isotopic values of the carbon dioxide were significantly affected by seasonality, being more enriched in 13C during the wet period. The correlations among \'delta\'13C-CO2 values respired by the ecosystem components and the environmental factors such as humidity and temperature indicated a significant relation with the gas exchanges. The \'delta\'13C-CO2 values respired by the entire ecosystem were less enriched in 13C when there was high level of water in the soil. This \'delta\'13C-CO2 value was 25,26%o . Partitioning the ecosystem respiration below and above ground, the data show that 75% of the total respiration has its origin of belowground (roots + microorganisms). Partioning the autotrophic and heterotrophic respiration, 54% of the total respiration has its origin on the vegetation. Therefore, for these results, the plant water availability followed by precipitation were the most important factors that contributed to the variability of \'delta\'13C of organic carbon, \'delta\'13C-CO2 respired carbon and fixed by the ecosystem. The results found in the study are relevant to a better comprehension of the carbon cycle within the Cerrado biome, as well as, open an opportunity to utilize the isotopic approach to define \'delta\'13C-CO2 patterns respired by the entire ecological system, utilizing these results as indicators of gas exchange alterations in the global change scenario

Idéalement située à la confluence entre climat tropical et climat tempéré, l'Afrique australe est une zone très sensible aux variations des conditions climatiques. Cette région fait cependant preuve d'un manque de données paléoclimatiques important, et les méthodes de reconstruction traditionnelles trouvent rapidement leurs limites face aux conditions particulières qui y sévissent. Les méthodes de reconstruction quantitatives communément employées se révèlent inutilisables face aux conditions d'aridité extrêmes qui ne permettent que très rarement l'accumulation et la préservation de pollen moderne et fossile et se confrontent également aux particularités de la végétation abritée par cette région. L'objectif de ces travaux de thèse vise à développer une méthode de reconstruction quantitative basée sur des données polliniques fossiles, à partir de la relation entre la distribution actuelle des taxons polliniques et le climat en Afrique australe. Nous avons développé une fonction de transfert utilisant les propriétés des fonctions de densité de probabilité (pdfs), permettant de transformer l'information contenue dans un assemblage pollinique en estimation quantitative du climat. En parallèle, cette étude a permis de développer une méthode permettant de sélectionner les espèces les plus probables à inclure dans chaque type pollinique qui compose un assemblage. Cette méthode de sélection des espèces (SSM) a permis de pallier la faible résolution taxonomique des données polliniques de cette région caractérisée par une biodiversité élevée et d'affiner la méthode des espèces indicatrices, afin de la rendre utilisable en Afrique australe. Cette méthodologie a été appliquée aux données polliniques du site de Wonderkrater (Afrique du Sud). Les résultats observés et leur comparaison avec ceux provenant de sites régionaux ont permis de déterminer que les températures estivales et hivernales étaient 6±2°C inférieure au cours du LGM et du Younger Dryas et que les précipitations au cours de la saison humide étaient 50% moins importantes qu'actuellement. Ces résultats montrent que les SST enregistrées dans le canal du Mozambique régissent les conditions hydrologiques du continent adjacent, en opposition avec la possible implication de l'ITCZ sous ces latitudes. Les résultats indiquent également que les deux tropiques montrent des tendances climatiques similaires au cours des derniers 20 000 ans. La méthode a ensuite été appliquée à un enregistrement pollinique provenant de la région du fynbos (Afrique du Sud). Les résultats ont montré les limites de la méthode au vu de la faible amplitude de reconstruction obtenue pour les températures entre le LGM et l'Holocène (~2°C). Les résultats ont néanmoins permis de mettre en évidence que les températures montraient un pattern similaire à celui observé en Antarctique. Nous avons également pu montrer que les périodes glaciaires coïncidaient avec les périodes les plus humides, en accord avec le modèle de Cockroft (1987). Ce modèle dérive du mécanisme de migration des « westerlies » vers l'équateur au cours des périodes glaciaires, en réponse au déplacement du vortex circcum polaire. Les travaux issus de cette thèse ont montré qu'il était possible d'utiliser la distribution actuelle des plantes pour estimer les variations quantitatives des changements climatiques passés, dans la plupart des configurations botaniques et climatiques rencontrées en Afrique australe. La méthode de sélection des espèces se révèle être un outil indispensable dans cette région de haute biodiversité. Ces travaux offrent des perspectives intéressantes dans cette zone actuellement dépourvue de reconstructions climatiques quantitatives. Cependant, les résultats émanant des deux cas d'études ont mis en évidence des faiblesses et des limites méthodologiques qui devront faire l'objet d'études supplémentaires afin d'en améliorer les performances. / Located at the interface between tropical and temperate climate systems, southern Africa is a particularly sensitive region in terms of long-term climate change. However, few reliable paleoclimatic records exist from the region – largely as a result of the arid climate with precludes the preservation of wetland sequences - , and virtually no quantitative reconstructions are available.The aim of this thesis is to develop quantitative palaeoclimate reconstruction method based the relation between modern plant distributions and climate in southern Africa. We develop botanical-climatological transfer functions derived from probability density functions (pdfs), allowing for quantitative estimates of the palaeoclimatic variables to be calculated from fossil pollen assemblages. In addition, a species-selection method (SSM) based on Bayesian statistics is outlined, which provides a parsimonious choice of most likely plant species from what are otherwise taxonomically broad pollen-types. This method addresses limitations imposed by the low taxonomic resolution of pollen identification, which is particularly problematic in areas of high biodiversity such as many regions of southern Africa.This methodology has been applied to pollen record from Wonderkrater (South Africa). Results indicate that temperatures during both the warm and cold season were 6±2°C colder during the Last Glacial Maximum and Younger Dryas, and that rainy season precipitation during the Last Glacial Maximum was ~50% of that during the mid-Holocene. Our results also imply that changes in precipitation at Wonderkrater generally track changes in Mozambique Channel sea-surface temperatures, with a steady increase following the Younger Dryas to a period of maximum water availability at Wonderkrater ~3-7 ka. These findings indicate that the northern and southern tropics experienced similar climatic trends during the last 20 kyr, and highlight the role of variations in sea-surface temperatures over the more popularly perceived role of a shifting Intertropical Convergence Zone in determining long-term environmental trends.This method has also been applied to a pollen record from Pakhuis Pass, in the Fynbos Biome (South Africa). Results show the limitations of quantitative methods, with only unrealistically low amplitude being reconstructed between the Last Glacial Maximum and Holocene (~2°C). However, results indicate that the reconstructed temperature trends, if not amplitudes, are similar to trends observed in Antarctic ice core records. Further, in reconstructing past humidity, we show that over the last 18 kyr, cooler conditions appear to be generally wetter at the site. These results are consistent with Cockcroft model (1987), derived from equatorward shift of the westerlies resulting from expansions of the circum-polar vortex.This study shows the potential of using modern plant distributions to estimates past climate parameters in southern Africa, and the species selection method proves to be a useful tool in region with high biodiversity. This work provides a novel perspective in the region, where no quantitative paleoclimatic reconstructions have been available. However, results from Pakhuis Pass highlight some of the limitations of this methodology, which will be subject of future work in this promising field of inquiry.

O presente estudo foi desenvolvido em uma área de Cerrado stricto sensu, localizado no Parque Estadual de Vassununga, próximo ao município de Santa Rita do Passa Quatro, interior de São Paulo. O objetivo deste trabalho foi mensurar os fluxos de CO2, liberado pelos processos respiratórios da vegetação e do solo (heterotrófica + autotrófica) para aferir a importância relativa destes compartimentos na respiração total do ecossistema, utilizando-se da técnica isotópica. Foi utilizada a técnica da reta de keeling plot, para determinar os valores isotópicos respirados pelo ecossistema, e pelos componentes vegetais (serapilheira, madeira morta, raízes, folha e ramo). De acordo com os resultados, os valores isotópicos do CO2 respirado pelos componentes autotróficos e heterotróficos, foram significativamente influenciados pela sazonalidade, ficando mais enriquecidos em 13C durante o período seco. As correlações encontradas entre os valores do \'delta\'13C- CO2 respirado pelos componentes e os fatores ambientais, como temperatura e umidade indicaram uma relação significativa. Os valores do \'delta\'13C-CO2 respirado pelo ecossistema foram menos enriquecidos em 13C quando houve maior disponibilidade de água no sistema. O valor isotópico do \'delta\'13C-CO2 respirado pelo ecossistema Cerrado foi de - 25,26%o . Particionando a respiração do ecossistema em acima e abaixo do solo, verificou-se que 75% foi realizada pela respiração abaixo do solo (microrganismo+raízes). Particionando a respiração em autotrófica e heterotrófica, observou-se que 54% foi realizado pela respiração da vegetação. Portanto, para tais resultados, a disponibilidade hídrica no solo, seguida da precipitação representaram um dos mais importantes fatores que contribuiram para a variabilidade nos valores isotópicos do \'delta\'13C orgânico e \'delta\'13C-CO2 respirado e no CO2 fixado pelo ecossistema. Os resultados obtidos neste estudo são de fundamental importância para uma melhor compreensão do ciclo do carbono no bioma Cerrado, bem como, abre a oportunidade de utilizar a técnica isotópica para definir padrões do \'delta\'13C-CO2 respirado em nível de ecossistema, utilizando estes resultados como indicadores de mudanças nas trocas gasosas frente ao cenário das mudanças climáticas / The presente study was carreid out in area o Cerrado strictu senso located at the State Park of Vassununga, closed to the Santa Rita do Passa Quatro city, São Paulo State, Brazil. The aim was of the present work was to measure de CO2 fluxes released through respiration processes of the vegetation and soil (heterotrophic and autotrophic) to check the relative importance of each of these ecosystems components on the respiration of overall ecosystem using the isotopic approach. The Keeling plot line was used to determine the isotopic values of carbon dioxide respired by the ecosystem and its components (litter, dead wood, roots, leaves and branches). The results show that isotopic values of the carbon dioxide were significantly affected by seasonality, being more enriched in 13C during the wet period. The correlations among \'delta\'13C-CO2 values respired by the ecosystem components and the environmental factors such as humidity and temperature indicated a significant relation with the gas exchanges. The \'delta\'13C-CO2 values respired by the entire ecosystem were less enriched in 13C when there was high level of water in the soil. This \'delta\'13C-CO2 value was 25,26%o . Partitioning the ecosystem respiration below and above ground, the data show that 75% of the total respiration has its origin of belowground (roots + microorganisms). Partioning the autotrophic and heterotrophic respiration, 54% of the total respiration has its origin on the vegetation. Therefore, for these results, the plant water availability followed by precipitation were the most important factors that contributed to the variability of \'delta\'13C of organic carbon, \'delta\'13C-CO2 respired carbon and fixed by the ecosystem. The results found in the study are relevant to a better comprehension of the carbon cycle within the Cerrado biome, as well as, open an opportunity to utilize the isotopic approach to define \'delta\'13C-CO2 patterns respired by the entire ecological system, utilizing these results as indicators of gas exchange alterations in the global change scenario

Pelagic Sargassum is one type of marine macroalgae that is known to be abundant in the Gulf of Mexico and Sargasso Sea. It is also known to serve as a critical habitat for many marine animals. In the past few years, large amounts of Sargassum have been reported in the Tropical Atlantic and Caribbean Sea (CS), causing significant environmental and economic problems. The goal of this study is to improve the understanding of Sargassum distributions, quantity, transport pathways, and bloom mechanisms in the CS and Tropic Atlantic through combining a variety of techniques including satellite remote sensing, field and laboratory measurements, and numerical modeling. The first question is where and how much Sargassum is in the CS and Tropic Atlantic. Previous field observations revealed strong seasonal and spatial variations of Sargassum, yet these observations are all limited in their spatial and temporal coverage. Satellite observations offer an effective means to measure their distributions with synoptic coverage and high sampling frequency, yet it is technically challenging to extract and quantify the small Sargassum features in coarse-resolution satellite imagery. Chapter 2 focuses on Sargassum detection and quantification algorithm development using Moderate Resolution Imaging Spectroradiometer (MODIS) data (Appendix A). The algorithm is based on MODIS alternative floating algae index (AFAI), which examines the red-edge reflectance of floating vegetation. The algorithm includes three basic steps: 1) classification of Sargassum-containing pixels through correction of large-scale gradient, masking clouds and cloud shadows, and removal of ambiguous pixels; 2) linear unmixing of Sargassum-containing pixels; and, 3) statistical analysis of Sargassum area coverage in pre-defined grids at monthly, seasonal, and annual intervals. The algorithm is applied to MODIS observations between 2000 and 2015 over the Central West Atlantic (CWA) region (0 – 22oN, 38 – 63oW) to derive the spatial and temporal distribution patterns as well as the total areal coverage of Sargassum. Results indicate that the first widespread Sargassum distribution event occurred in 2011, consistent with previous findings from the Medium Resolution Imaging Spectrometer (MERIS). Since 2011, only 2013 showed minimal Sargassum coverage similar to the period of 2000 to 2010; all other years showed significantly more coverage. More alarmingly, the summer months of 2015 showed mean coverage of > 2000 km2, or about 4 times of the summer 2011 coverage and 20 times of the summer 2000 to 2010 coverage. Analysis of several environmental variables provided some hints on the reasons causing the inter-annual changes after 2010, yet further multi-disciplinary research (including in situ measurements) is required to understand such changes and long-term trends in Sargassum coverage. To better understand the potential ecological and environmental impacts of Sargassum, field and laboratory experiments are conducted to link the Sargassum areal coverage observations to biomass per area (density) and measure the nutrient contents and pigment concentrations (Chapter 3, Appendix B). An AFAI-biomass density model is established to derive Sargassum biomass density from the spectral reflectance, with a relative uncertainty of ~ 12%. Monthly mean integrated Sargassum biomass in the CS and CWA reached > 4.4 million tons in July 2015. The average % C, % N, and % P per dry-weight, measured from samples collected in Gulf of Mexico and Florida Straits in summer 2017, are 27.16, 1.06, and 0.10, respectively. The mean chlorophyll-a concentration is ~ 0.05% of the dry-weight. With these parameters, the amounts of nutrients and pigments can be estimated directly from remotely-sensed Sargassum biomass. During bloom seasons, Sargassum carbon can account for ~ 18% of the total particulate organic carbon in the upper water column. This chapter provides the first quantitative assessment of the overall Sargassum biomass, nutrients, and pigment abundance from remote-sensing observations, thus helping to quantify their ecological roles and facilitate management decisions. To investigate the Sargassum transport patterns and potential bloom sources, a Lagrangian particle tracking model is established to track the Sargassum transport driven by surface currents and winds (Chapter 4, Appendix C). The mean Sargassum distributions derived from MODIS observations are used to initiate and evaluate a Lagrangian particle tracking model that tracks Sargassum advection under surface currents and winds. Among the thirty-nine experiments, adding surface currents alone improves model performance (i.e., by reducing difference between modeled and observed Sargassum distributions) in 82% of the cases after tracking Sargassum for one month. Adding 1% wind forcing to the advection model also shows improved performance in 67% of the cases. Adding a time- and location-dependent Sargassum growth/mortality rate (i.e., change rate), derived from time-series of the MODIS-based Sargassum abundance and the corresponding environmental data via a Random Forest regression, leads to further improvement in model performance (i.e., by increasing the matchup percentage between modeled and observed Sargassum distributions) in 64% of the cases, although the modeled change rates only explain ~ 27% of the variance of the validation dataset, possibly due to uncertainties in such-derived change rates. The Sargassum transport model, with the mean currents, winds, and change rates acting as the forcing, is applied to track the mean Sargassum distributions forward and backward. The results demonstrate the model’s capacity of simulating the Sargassum distribution patterns, with emphasis on the role of biological terms in determining the large-scale distributions. These tracking experiments also suggest that Sargassum blooms in the CS are strongly connected to the Central Atlantic regions, and blooms in the Tropical Atlantic show relatively weak connections to the Atlantic regions further north. Although it is straightforward to apply the transport model to predict Sargassum blooms, such long-term prediction could suffer from large error accumulations and unable to achieve satisfactory performance. Therefore historical Sargassum distributions derived from MODIS are used to provide an alternative way to realize the bloom prediction. Chapter 5 proposes such a prediction based on a hindcast of 2000–2016 observations from MODIS, which shows Sargassum abundance in the CS and the CWA, as well as connectivity between the two regions with time lags (Appendix D). This information is used to derive bloom and nonbloom probability matrices for each 1° square in the CS for the months of May–August, predicted from bloom conditions in a hotspot region in the CWA in February. A suite of standard statistical measures is used to gauge the prediction accuracy, among which the user’s accuracy and kappa statistics show high fidelity of the probability maps in predicting both blooms and nonblooms in the eastern CS with several months of lead time, with an overall accuracy often exceeding 80%. The bloom probability maps from this hindcast analysis will provide early warnings to better study Sargassum blooms and prepare for beaching events near the study region. This approach may also be extendable to many other regions around the world that face similar challenges and opportunities of macroalgal blooms and beaching events. Using this forecasting scheme, the summer blooms in the CS in 2017 were successfully predicted. Since February 2018, we have also generated monthly-updated 1-page Sargassum outlook bulletins to help these regions to better prepare for potential beaching events. Currently, the mean Sargassum distribution statistics used in this study are derived from MODIS, which has been operating well beyond the designed mission life, arousing concerns as to whether the Sargassum observation statistics can be continued in the future. As a follow-on sensor, the Visible Infrared Imaging Radiometer Suite (VIIRS) has the appropriate spectral bands to detect and quantify floating macroalgae. Based on previous works on MODIS, Chapter 6 presents an improved procedure to extract floating algae pixels from VIIRS AFAI imagery, with image filtering used to suppress noise and adjusted thresholds used to mask sun glint, clouds, and cloud shadows. The overall extraction accuracy is about 85%. Simultaneous daily observations from MODIS and VIIRS over the CWA show consistent spatial patterns, but VIIRS estimations of the algae coverage (in km2) are consistently lower than MODIS (around – 19% mean relative difference or MRD), possibly due to lower sensitivity of the VIIRS near-infrared (NIR) bands than the corresponding MODIS bands. Similarly, at monthly scale VIIRS also shows lower coverage than MODIS, and their difference (around – 29% MRD) is larger than the difference between MODIS-Aqua and MODIS-Terra estimates (around – 14% MRD). Despite these differences, the spatial and temporal patterns between VIIRS and MODIS observed algae distributions match very well at all spatial and temporal scales. These results suggest that VIIRS can provide continuous and consistent observations of floating algae distributions and abundance from MODIS as long as their differences are accounted for, thus assuring continuity in the future. In summary, this study has worked on four connected topics regarding Sargassum distributions, biomass and nutrients, transport pathways, and bloom predictions through combined efforts in satellite remote sensing, field and laboratory measurements, physical modelling, and statistical analyses. To my best knowledge, this is the first comprehensive and multi-disciplinary study to investigate pelagic Sargassum at synoptic scale in the Intra-Americas Sea (IAS) and Atlantic Ocean. Although several questions remain to be answered (e.g., “What cause the inter-annual variations of Sargassum blooms?” and “Where are the bloom origins?”), the outcomes of this study (remote sensing algorithms, Sargassum distribution and abundance maps, established bio-physical model, and a bloom forecast model) are expected to make significant contributions in both scientific research (including new critical baseline data) and management decision support.

This thesis aims to quantify the human impact on the natural resource water at the landscape scale. The drivers in the federal state of Brandenburg (Germany), the area under investigation, are land-use changes induced by policy decisions at European and federal state level. The water resources of the federal state are particularly sensitive to changes in land-use due to low precipitation rates in the summer combined with sandy soils and high evapotranspiration rates. Key elements in landscape hydrology are forests because of their unique capacity to transport water from the soil to the atmosphere. Given these circumstances, decisions made at any level of administration that may have effects on the forest sector in the state are critical in relation to the water cycle. It is therefore essential to evaluate any decision that may change forest area and structure in such a sensitive region. Thus, as a first step, it was necessary to develop and implement a model able to simulate possible interactions and feedbacks between forested surfaces and the hydrological cycle at the landscape scale. The result is a model for simulating the hydrological properties of forest stands based on a robust computation of the temporal and spatial LAI (leaf area index) dynamics. The approach allows the simulation of all relevant hydrological processes with a low parameter demand. It includes the interception of precipitation and transpiration of forest stands with and without groundwater in the rooting zone. The model also considers phenology, biomass allocation, as well as mortality and simple management practices. It has been implemented as a module in the eco-hydrological model SWIM (Soil and Water Integrated Model). This model has been tested in two pre-studies to verify the applicability of its hydrological process description for the hydrological conditions typical for the state. The newly implemented forest module has been tested for Scots Pine (Pinus sylvestris) and in parts for Common Oak (Quercus robur and Q. petraea) in Brandenburg. For Scots Pine the results demonstrate a good simulation of annual biomass increase and LAI in addition to the satisfactory simulation of litter production. A comparison of the simulated and measured data of the May sprout for Scots pine and leaf unfolding for Oak, as well as the evaluation against daily transpiration measurements for Scots Pine, does support the applicability of the approach. The interception of precipitation has also been simulated and compared with weekly observed data for a Scots Pine stand which displays satisfactory results in both the vegetation periods and annual sums. After the development and testing phase, the model is used to analyse the effects of two scenarios. The first scenario is an increase in forest area on abandoned agricultural land that is triggered by a decrease in European agricultural production support. The second one is a shift in species composition from predominant Scots Pine to Common Oak that is based on decisions of the regional forestry authority to support a more natural species composition. The scenario effects are modelled for the federal state of Brandenburg on a 50m grid utilising spatially explicit land-use patterns. The results, for the first scenario, suggest a negative impact of an increase in forest area (9.4% total state area) on the regional water balance, causing an increase in mean long-term annual evapotranspiration of 3.7% at 100% afforestation when compared to no afforestation. The relatively small annual change conceals a much more pronounced seasonal effect of a mean long-term evapotranspiration increase by 25.1% in the spring causing a pronounced reduction in groundwater recharge and runoff. The reduction causes a lag effect that aggravates the scarcity of water resources in the summer. In contrast, in the second scenario, a change in species composition in existing forests (29.2% total state area) from predominantly Scots Pine to Common Oak decreases the long-term annual mean evapotranspiration by 3.4%, accompanied by a much weaker, but apparent, seasonal pattern. Both scenarios exhibit a high spatial heterogeneity because of the distinct natural conditions in the different regions of the state. Areas with groundwater levels near the surface are particularly sensitive to changes in forest area and regions with relatively high proportion of forest respond strongly to the change in species composition. In both cases this regional response is masked by a smaller linear mean effect for the total state area. Two critical sources of uncertainty in the model results have been investigated. The first one originates from the model calibration parameters estimated in the pre-study for lowland regions, such as the federal state. The combined effect of the parameters, when changed within their physical meaningful limits, unveils an overestimation of the mean water balance by 1.6%. However, the distribution has a wide spread with 14.7% for the 90th percentile and -9.9% for the 10th percentile. The second source of uncertainty emerges from the parameterisation of the forest module. The analysis exhibits a standard deviation of 0.6 % over a ten year period in the mean of the simulated evapotranspiration as a result of variance in the key forest parameters. The analysis suggests that the combined uncertainty in the model results is dominated by the uncertainties of calibration parameters. Therefore, the effect of the first scenario might be underestimated because the calculated increase in evapotranspiration is too small. This may lead to an overestimation of the water balance towards runoff and groundwater recharge. The opposite can be assumed for the second scenario in which the decrease in evapotranspiration might be overestimated. / Das übergreifende Ziel der vorliegenden Arbeit ist es, die Interaktion zwischen Landnutzungsänderung und dem Landschaftswasserhaushalt zu quantifizieren. Das Untersuchungsgebiet für die Analyse ist das Land Brandenburg. Bedingt durch seine Kombination geringer Sommerniederschläge mit der Dominanz sandiger Böden und hoher Verdunstungsraten, insbesondere von den großflächigen Wäldern und Forsten, ist es besonders empfindlich gegenüber Landnutzungsänderung. Waldflächen sind Schlüsselelemente im Landschaftswasserhaushalt, da sie den Bodenwasserspeicher effizienter mit der Atmosphäre koppeln als die meisten anderen Vegetationsformen. Im ersten Teil der Arbeit war es daher notwendig, ein geeignetes Modellkonzept zu finden. Der Ansatz sollte in der Lage sein, die hydrologischen Effekte auf Landschaftsebene zu modellieren, ohne dabei die Datenverfügbarkeit in diesem Anwendungsbereich zu überschreiten. Das entwickelte Modellkonzept wurde in das ökohydrologische Einzugsgebietsmodell SWIM (Soil Water Integrated Model) integriert. Nach einer Test- und Entwicklungsphase konnte das Modell für die integrierte Analyse der Wirkung von zwei Szenarien auf den Landeswasserhaushalt verwendet werden. Das erste Szenario beschäftigt sich mit der möglichen Zunahme der Waldfläche als Folge der Neuausrichtung der Agrarsubventionspolitik der Europäischen Union. Die Waldflächenzunahme führt zu einer Steigerung der Evapotranspiration im langjährigen Mittel. Das zweite Szenario behandelt die Auswirkung des Brandenburger Waldumbauprogramms und hat eine vergleichsweise geringe Abnahme der langjährigen mittleren Verdunstung zur Folge. Der lineare mittlere Verlauf überdeckt ein ausgeprägtes räumliches und saisonales Muster der Veränderung. Die Zonen starker Effekte der beider Szenarien überlappen sich nur in einigen Fällen, so ist es möglich, dass die positiven Wirkungen des Waldumbauprogramms in einigen Regionen durch eine mögliche Ausweitung der Waldfläche aufgehoben werden. Die vorgestellten Ergebnisse zeigen deutlich, dass Landnutzungsänderungen, die durch politische oder administrative Entscheidungen ausgelöst werden, Auswirkungen auf elementare Landschaftsfunktionen wie den Wasserhaushalt haben. Es wird deutlich, dass ein integrativer Modellierungsansatz, der die wahrscheinlichen Wirkungen administrativer Entscheidungen in Betracht zieht, Grundlagen für eine nachhaltige Entwicklung liefern kann. Diese Ergebnisse werden umso relevanter, je stärker die betroffene Ressource bereits eingeschränkt ist. In Bezug auf die Wasserressourcen im Land Brandenburg ist das der Fall und aktuelle Studien zum Globalen Wandel in der Region prognostizieren eine Verschärfung dieser Situation.

Human-induced alterations of the environment are causing biotic changes worldwide, including the extinction of species and a mixing of once disparate floras and faunas. One type of biological communities that is expected to be particularly affected by environmental alterations are herb layer plant communities of fragmented forests such as those in the west European lowlands. However, our knowledge about current changes in species diversity and composition in these communities is limited due to a lack of adequate long-term studies. In this thesis, I resurveyed the herb layer communities of ancient forest patches in the Weser-Elbe region (NW Germany) after two decades using 175 semi-permanent plots. The general objectives were (i) to quantify changes in plant species diversity considering also between-community (β) and functional diversity, (ii) to determine shifts in species composition in terms of species’ niche breadth and functional traits and (iii) to find indications on the most likely environmental drivers for the observed changes. These objectives were pursued with four independent research papers (Chapters 1-4) whose results were brought together in a General Discussion. Alpha diversity (species richness) increased by almost four species on average, whereas β diversity tended to decrease (Chapter 1). The latter is interpreted as a beginning floristic homogenization. The observed changes were primarily the result of a spread of native habitat generalists that are able to tolerate broad pH and moisture ranges. The changes in α and β diversity were only significant when species abundances were neglected (Chapters 1 and 2), demonstrating that the diversity changes resulted mainly from gains and losses of low-abundance species. This study is one of the first studies in temperate Europe that demonstrates floristic homogenization of forest plant communities at a larger than local scale. The diversity changes found at the taxonomic level did not result in similar changes at the functional level (Chapter 2). The likely reason is that these communities are functionally “buffered”. Single communities involve most of the functional diversity of the regional pool, i.e., they are already functionally rich, while they are functionally redundant among each other, i.e., they are already homogeneous. Independent of taxonomic homogenization, the abundance of 30 species decreased significantly (Chapter 4). These species included 12 ancient forest species (i.e., species closely tied to forest patches with a habitat continuity > 200 years) and seven species listed on the Red List of endangered plant species in NW Germany. If these decreases continue over the next decades, local extinctions may result. This biotic impoverishment would seriously conflict with regional conservation goals. Community assembly mechanisms changed at the local level particularly at sites that experienced disturbance by forest management activities between the sampling periods (Chapter 3). Disturbance altered community assembly mechanisms in two ways: (i) it relaxed environmental filters and allowed the coexistence of different reproduction strategies, as reflected by a higher diversity of reproductive traits at the time of the resurvey, and (ii) it enhanced light availability and tightened competitive filters. These limited the functional diversity with respect to canopy height and selected for taller species. Thirty-one winner and 30 loser species, which had significantly increased or decreased in abundance, respectively, were characterized by various functional traits and ecological performances to find indications on the most likely environmental drivers for the observed floristic changes (Chapter 4). Winner species had higher seed longevity, flowered later in the season and had more often an oceanic distribution compared to loser species. Loser species tended to have a higher specific leaf area, to be more susceptible to deer browsing and to have a performance optimum at higher soil pH values compared to winner species. Multiple logistic regression analyses indicated that disturbances due to forest management interventions were the primary cause of the species shifts. As one of the first European resurvey studies, this study provides indications that an enhanced browsing pressure due to increased deer densities and increasingly warmer winters are important drivers. The study failed to demonstrate that eutrophication and acidification due to atmospheric deposition substantially drive herb layer changes. The restriction of the sample to the most base-rich sites in the region is discussed as a likely reason. Furthermore, the decline of several ancient forest species is discussed as an indication that the forest patches are still paying off their “extinction debt”, i.e., exhibit a delayed response to forest fragmentation. / Umweltveränderungen beeinträchtigen weltweit die Artenvielfalt. Die Lebensgemeinschaften fragmentierter Lebensräume gelten als besonders anfällig für Veränderungen. In dieser Arbeit wurden Untersuchungen an Krautschichtgemeinschaften historisch alter Waldfragmente im Elbe-Weser-Dreieck nach zwei Jahrzehnten wiederholt. Ziel war es anhand von 175 semi-permanenten Aufnahmeflächen (i) die Veränderungen der Pflanzenartendiversität zu quantifizieren, (ii) Artenverschiebungen in Bezug auf Nischenbreite und funktionale Merkmale festzustellen und (iii) Hinweise auf die verantwortlichen Umweltveränderungen zu finden. Die α-Diversität (Artenzahl) stieg durchschnittlich um vier Arten an. Die β-Diversität (Artenturnover zwischen den Flächen) nahm tendenziell ab. Letzteres wird als Beginn einer floristischen Homogenisierung interpretiert. Diese Studie ist eine der ersten im gemäßigten Europa, die eine floristische Homogenisierung von Waldpflanzengemeinschaften auf einer größeren als der lokalen Ebene aufzeigt. Die Diversitätsveränderungen auf taxonomischer Ebene führten nicht zu ähnlichen Veränderungen auf funktionaler Ebene. Bereits einzelne Gemeinschaften wiesen den Großteil der funktionalen Vielfalt des regionalen Artenpools, also ein Maximum an funktionaler Diversität auf. Gleichzeitig waren sie untereinander funktional redundant, also bereits homogen. Die mit der beginnenden taxonomischen Homogenisierung verbundene floristische Verarmung wird als gering eingestuft, da die Homogenisierung primär das Ergebnis der Zuwanderung häufig vorkommender Standortgeneralisten war. Unabhängig von der Homogenisierung gingen 30 Arten signifikant in ihrer Abundanz zurück, darunter 12 an historisch alte Wälder gebundene Arten sowie sieben Rote-Liste-Arten. Ein weiterer Rückgang oder ein lokales Aussterben dieser Arten stünde im Widerspruch zu regionalen Naturschutzzielen. Nullmodelltests und der Vergleich funktionaler und taxonomischer Diversitätskomponenten lassen auf regionaler Ebene auf eine zeitliche Konstanz der grundlegenden Mechanismen der Artenvergesellschaftung schließen. Auf der lokalen Ebene veränderten sich die Vergesellschaftungsmechanismen erheblich, insbesondere auf forstwirtschaftlich gestörten Standorten. Einerseits ermöglichte dort eine Abschwächung der Umweltfilter die Koexistenz von Arten mit unterschiedlichen Reproduktionsstrategien. Andererseits führte die erhöhte Lichtverfügbarkeit zu einer Verstärkung der Konkurrenzfilter und einer Selektion hochwüchsiger Arten. Gewinner- und Verliererarten wurden anhand funktionaler Merkmale und ihres ökologischen Verhaltens charakterisiert, um Hinweise auf die verantwortlichen Umweltveränderungen zu finden. Gewinnerarten wiesen eine höhere Langlebigkeit der Samen auf, blühten später in der Vegetationsperiode und hatten öfter eine ozeanische Verbreitung. Verliererarten hatten eine höhere spezifische Blattfläche, einen höheren Attraktivitätswert als Wildäsung und ein ökologisches Optimum bei höheren pH-Werten. Logistische Regressionsanalysen zeigen, dass Störung durch forstwirtschaftliche Eingriffe hauptverantwortlich für die Artenverschiebungen war. Zusätzlich liefert diese Wiederholungsstudie als eine der ersten in Europa Hinweise darauf, dass ein erhöhter Äsungsdruck sowie zunehmend mildere Winter entscheidende Einflussfaktoren darstellen. Der Rückgang mehrerer an historisch alte Wälder gebundener Arten wird als Anzeichen für eine verspätete Reaktion auf die Waldfragmentierung diskutiert.

Background: Food nourishes us, sustains us, and has the potential to both heal us and make us sick. Among many Indigenous cultures, traditional activities, ceremonies, events and practices often involve or use food, grounding Indigenous peoples within the context of their local, natural surroundings. This suggests that food is important not only for physical health, but also emotional, mental and spiritual health. The relationships that Indigenous peoples have with food can help us to understand the health of individuals, and the communities in which they live. Purpose: The following qualitative study explores how three generations of adults who live in one Labrador Inuit-Metis community experience and understand their relationships to food in a context of global change. Theoretical Orientation: The research is guided by Two-Eyed Seeing. Two-Eyed Seeing acknowledges that there are many different ways of seeing and understanding the world, some of which can be encompassed through a Western eye and some through an Indigenous eye. If we learn to see through both eyes, we can gain a perspective that looks very different than if we only view the world through a single lens. Methods: For the study, twenty-four people from the south-eastern Labrador community of St. Lewis participated in individual and joint story-telling sessions. A group story-telling session also took place where community members could share their stories with one another. During many of the story-telling sessions, participants shared photographs, which helped to illustrate their relationships to food. Findings/Discussion: Historically, the people of St. Lewis relied almost entirely upon their own wherewithal for food, with few, if any, government services available and very little assistance from the market economy. This fostered and upheld an Inuit-Metis culture that promoted sharing, reciprocity and respect for the natural world. Currently, greater access to government services and the market economy has led to the creation of certain policies and programs that undermine or ignore established social and cultural norms in the community. Conclusions: Existing Inuit-Metis knowledge should work alongside non-Indigenous approaches to policy and program development. This would serve to protect and promote the health of both individuals and communities.