Phosphorus, a mineral nutrient, is an essential element in aquatic systems. It is only available for biological activity in the form of orthophosphate and soluble restrictive phosphate. Eutrophication, caused by nutrient enrichment, is a problem in many freshwater systems, which results in increased algal blooms, anoxic conditions, and consequently, biodiversity loss and ecosystem failure. Low dissolved oxygen levels trigger the release of sediment bound phosphorus, which reinforces eutrophication. Nutrients in aquatic systems are provided by point and non-point sources and these sources can be affected by several factors, including population, land-use, and climate change. There are many long-term historical phosphorus studies on rivers, but there are very few that are conducted on the Grand River watershed and none that look at factors that might be driving the phosphorus loadings. The Grand River watershed, located in Ontario, Canada, is a highly agricultural watershed with a growing population of approximately one million. It has experienced eutrophication, which has led to excessive production of cyanobacteria and regions of hypoxia. In this study, historical phosphorus concentration data (Total Phosphorus, Soluble Reactive Phosphorus, and Particulate Phosphorus) in five sites along the Grand River were analyzed temporally and spatially from 1965 to 2010 in the upper, middle, and lower parts of the watershed. The Particulate Phosphorus was calculated by subtracting SRP from TP. Several other data such as climate, land-use, geology, and population were also explored and considered as possible factors that may have influenced the trends over time. TP, SRP, and PP average flow weighted concentrations and fluxes were calculated in 2-6 year intervals. SRP load was higher prior to the early 1970???s, declined in the 1970???s, was more stable in the 1980???s and 1990???s, and increased in the 2000???s. The initial decrease in SRP in the early 1970???s was likely due to the phosphorus ban in detergents in 1973 that was implemented over several years. The constant SRP loadings in the 1980???s and 1990???s, despite population and urban development growth, may have been due to upgrades in waste water treatment plants during that time period. The recent increase in phosphorus in more recent years coincides with a large increase in the number of livestock in the 2000???s and population growth. SRP and PP loads increase from upstream to downstream regions are likely due to nutrient accumulation by the river. The higher loads and concentrations of SRP in the CGR is expected because the region is highly urbanized and contains most of the tile drainage in the watershed.

The German Ultrafine Aerosol Network (GUAN) has been continuously measuring the particle number size distribution (PNSD) and equivalent black carbon (eBC) mass concentration since 2009 at 17 atmospheric observatories in Germany, covering all environments from roadside to high-Alpine environments. GUAN provides us an opportunity to reduce the knowledge gaps about the spatio-temporal variation of sub-micrometer particles in different size ranges and eBC mass. These data are not only highly valuable for air pollution and health studies but also can help to reduce the uncertainties in the climate model predictions. With these long-term multi-site-category measurements, it was investigated for the first time how pollutant parameters interfere with spatial characteristics and site categories. Based on this first investigation, the long-term changes in size-resolved particle number concentrations (PNC) and eBC mass concentration were investigate to evaluate the effectiveness of the emission mitigation policies in Germany. The emission and pollutants near ground can be frequently transported to the free troposphere (FT) in the mountain areas. To identify if the decreased emissions at lower-altitudes have affected the aerosol loading in the aged, well-mixed FT air over Central Europe, the long-term trends in PNC and eBC mass concentration were analyzed for the FT and planetary boundary layer (PBL) conditions separately, at two high-Alpine observation sites. In summary, this dissertation aims to answer the following related scientific questions: Q1: How do the sub-micrometer PNSD, PNC, and eBC mass concentration interfere with spatial characteristics and site categories? (First publication) In the first publication (Sun et al., 2019), the spatio-temporal variability of aerosol parameters including PNSD, PNCs, and eBC mass concentration from the GUAN network were investigated for the period 2009−2014. Significant differences in the pollutant concentration were observed among various site categories. The six-year median value of sub-micrometer PNC (diameter range 20–800 nm) varies between 900 and 9000 cm−3, while median eBC mass concentration varies between 0.1 and 2.3 μg m-3 in 17 observation sites. PNCs in different size ranges were found in different spatial variabilities. A cross-correlation between PNSD and eBC mass concentration was analyzed to detect the influence of anthropogenic sources for different site categories. The size-dependent spatial variability analysis of PNCs extracted three size intervals: a higher spatial variability size range 10–30 nm, a transition size range 30–100 nm and a lower spatial variability size range 100–800 nm. Based on the evaluated spatial variability, the measured parameters at various sites were clustered by a hierarchical clustering approach, which revealed different spatial clusters for “source-driven” and “long-range transport” parameters. This result suggests that the traditional “site category” (i.e. urban, and regional background, etc.) concerning mainly the influence of local sources cannot always catch the variation of aerosol particle mass or number concentrations. The dominant factors for various parameter are different, leading to different variability and spatial distribution. The result of spatial clustering offers a sound scientific base to compare pollutant parameters measured in different locations and environments. By assessing the relationship between the measured parameters and geographical distance between different sites, the spatial variability of the aerosol parameters follows the “First Law of Geography” that everything is related to everything else, but near things are more related than distant things (Tobler, 1970). However, different parameters show different sensitivities on geographical distance. The analysis provides an important reference for setting up an observation network with a specific research purpose and is also useful for the regional scale dispersion models or land-use regression models. Q2: How do the sub-micrometer PNSD, PNC, and eBC mass concentration change at a decadal scale? Have the implementations of emission mitigation policies affected the observed decadal trend? (Second publication) In the second publication (Sun et al., 2020), long-term trends in atmospheric PNCs and eBC mass concentration for a 10 years period (2009–2018) were determined for 16 sites of the GUAN, ranging from roadside to high-Alpine. To ensure the data consistency for the trend detection, a thorough and detailed data quality check and data cleaning for the large GUAN dataset was performed. Statistically significant decreasing trends were found for 85% of the parameters and observation sites indicating an overall decreasing trend in sub-micrometer PNC (except N[10−30]) and eBC mass concentration all over Germany. Comparing the trends of measured parameters with the long-term change in total emission, we proofed that the observed trends of PNCs and eBC mass concentrations were mainly due to the emission reduction. The detailed diurnal and seasonal trends in eBC mass concentration and PNCs further confirmed that the observed decreasing trends were largely owing to the reduced emissions such as traffic emission, residential emission, and industry emission, etc. Moreover, the inter-annual changes of meteorological conditions and long-range transport pattern were found not to be the main reason for the decreases in pollutant parameters. This study suggests that a combination of emission mitigation policies can effectively improve the air quality over large spatial scales such as Germany. Given the relative novelty of the long-term measurements (PNSD, eBC mass concentration) in a network such as GUAN, the results proved to be quite robust and comprehensive. Q3: Have the decreased PNC and eBC mass concentration due to emission mitigation policies at the lower-altitudes affected the background air in lower FT over Central Europe? (Third publication) In the third publication (Sun et al., 2021), the long-term change of the eBC mass concentration and size-resolved PNCs were determined and analyzed at two high Alpine stations for the period 2009-2018: Schneefernerhaus at mountain Zugspitze in Germany (ZSF, 2671 m a.s.l.) and Jungfraujoch in Switzerland (JFJ, 3580 m a.s.l.). The trend analysis was performed for the FT and PBL-influenced conditions separately, aiming to assess whether the reduced emissions at lower-altitudes over Central Europe can affect the background air in the lower FT on a large spatial scale. The FT and PBL conditions at the two stations were segregated using the adaptive diurnal minimum variation selection (ADVS) method. The result showed that the FT condition in cold months is more prevalent than in warm months. Overall, the FT conditions frequency was ~25% and 6% in the cold and warm seasons at ZSF, respectively. At JFJ, the frequency of FT was ~45% and 10% in these two seasons, respectively. The PNC and eBC mass concentration showed a statistically significant decrease during PBL time. The observed decreasing trends in eBC mass concentration in the PBL-influenced condition are well consistent with the reported trends in total BC emission in Germany and Switzerland. For the FT conditions, decreases in PNC and eBC mass concentration over the years was detected at both sites, suggesting the background PNC and eBC mass in the lower FT over Central Europe has decreased as well. The implementation of emission mitigation policies is the most decisive factor but the weather pattern change over Central Europe also has contributed to the decreasing trends in FT condition.:List of Figures ……………………………………………………………………………………………..I List of Tables ..……………………………………………………………………………………………..I Abbreviations .……………………………………………………………………………………………II 1. Introduction …………………………………………………………………………………………….1 1.1 Role of atmospheric sub-micrometer aerosol particles…...………………………………………...1 1.2 Measurement of sub-micrometer particle number size distribution, particle number concentration, and eBC mass concentration…..……………………………………………….………………………….2 1.3 Previous long-term observations of PNSD, PNC, and eBC mass concentration…………………...4 1.4 Objectives...………………………………………………………………………………………….6 2. Data and Method…..……………………………………………………………………………………9 2.1 The German Ultrafine Aerosol Network (GUAN) …………………………………………………9 2.1.1 Measurement sites in GUAN…………………………………………………………………..10 2.1.2 Instrumental set-up.……….………………………………………………………….…………14 2.1.3 Quality assurance.………………………………………………………………………….……16 2.1.4 Data coverage…..………………………………………………………………………………..17 2.2. High-Alpine observatory Jungfraujoch (JFJ)……………………………………………………..18 2.2.1 Measurement site……….……………………………………………………………………….18 2.2.2 Instrumentation ..………………………………………………………………………………..19 2.3 Data analysis methods……………………………………………………………………………….19 2.3.1 Agglomerative hierarchical clustering….……………………………………………………...19 2.3.2 Customized Sen’s slope estimator…………………..…………………………………………...21 2.3.3 Generalized least-square regression and autoregressive bootstrap confidence intervals (GLS- ARB)…………………………………………………………………………………………………21 2.3.4 Seasonal Mann-Kendal test…..………………….………………………………………………22 2.3.5 Back-trajectory classification method….……………………………………………………...24 3. Results and Discussion…..………………………………………………………………………….27 3.1 First publication….…………………………………………………………………………………..27 3.1.1 Variability of black carbon mass concentrations, sub-micrometer particle number concentrations and size distributions: results of the German Ultrafine Aerosol Network ranging from city street to High Alpine locations……………………………………...………………………………………...27 3.1.2 Supporting information..……………………………………………………………………….41 3.2 Second publication…………………………………………………………………………………..45 3.2.1 Decreasing trends of particle number and black carbon mass concentrations at 16 observational sites in Germany from 2009 to 2018…..…………………………………………………………..45 3.2.2 Supporting information...……………………………………………………………………….66 3.3 Third publication……………………………...……………………………………………………..75 3.3.1 Long-term trends of black carbon and particle number concentration in the lower free troposphere in Central Europe…………………………………………………………………………75 3.3.2 Supporting information..…….……………………………………………………………….92 4. Summary and Conclusions..………………………………………………………………………… 95 5. Outlook….…………………………………………………………………………………………...99 Appendix A….………………………………………………………………………………………...100 Bibliography…………………………………………………………………………………………...101 Acknowledgements….…………………………………………………………………………………115

Ce travail de thèse s'insère dans une démarche globale d'acquisition des connaissances sur la tortue verte (Chelonia mydas) dans l'océan Indien occidental et ce afin de disposer d'éléments scientifiques essentiels à la mise en place d'une gestion cohérente et efficace de cette espèce menacée. Dans un premier temps, appliquant différentes modèles statistiques, ce travail a visé à établir des données de référence sur l'abondance des tortues vertes femelles en reproduction et les tendances sur le long terme des principales populations. Dans un second temps, il a consisté à déterminer la structure génétique et les relations qui existent entre les différentes populations de cette espèce. Enfin, la conservation des tortues marines étant étroitement liée aux pressions extérieures, ce travail a tenté dans un troisième temps de caractériser les pressions anthropiques qu'elles subissent, et notamment celles liées à la pêche. L'ensemble de ces résultats a permis de réaliser des avancées majeures dans la connaissance de la biologie et de l'écologie de la tortue verte et de disposer d'une vision régionale fiable de l'état de conservation de cette espèce dans l'océan Indien occidental. Leur compilation a ainsi permis d'identifier des zones régionales prioritaires de protection mais aussi des sites de vigilance plus spécifiques comme celui d'Europa. Enfin cette synthèse met en lumière les priorités de recherche et les approches scientifiques à favoriser à l'avenir pour améliorer les connaissances et affiner les priorités de conservation non seulement des tortues marines, mais aussi de la mégafaune marine en général. / This thesis is a comprehensive work aiming to improve scientific knowledge on the green turtle (Chelonia mydas) in order to provide key scientific evidences needed for the implementation of coherent and effective management measures to protect at the Western Indian Ocean scale this threatened species. In a first step, this work aimed to established baseline data on the abundance of green turtles nesting females and long term trends of some key nesting populations of the region by applying different modelling methods. In a second step, this work determined the regional genetic structure of this species and the relationships that exists between the different populations. Finally, the conservation of marine turtles being closely dependant to external pressures, this work tried to characterize theanthropogenic pressures they face, more specifically those related to fishing activities. All these results allowed unraveling some key gaps on the biology and ecology of the green turtle in the region and led to a global vision of the conservation status of this species in the Western Indian Ocean. The compilation of the results enabled the identification of regional priority areas for protection, but also some more specific threatened sites such as Europa. Finally, this synthesis shedslight on research priorities and scientific approaches to be promote in the future to unlock other keyscientific issues and refine conservation priorities, not only of marine turtles, but also of marine megafauna as a whole.