Künstliches Licht in der Nacht (ALAN) entsteht in Zentren menschlicher Aktivität und erhellt die Nacht, wodurch biologische Rhythmen von Menschen und Wildtieren gestört werden können. Skyglow ist eine diffuse Aufhellung des Nachthimmels aufgrund von Reflexion und Streuung von ALAN, welche indirekt große Bereiche (vor-)städtischer Ökosysteme beleuchtet. Da sich Zentren menschlicher Aktivität häufig in der Nähe von Flüssen und Seen befinden, kann sich Skyglow unverhältnismäßig stark auf wildlebende Tiere in Süßwassergebieten auswirken. In drei Experimenten wurden die Auswirkungen von ALAN auf die Physiologie des Europäischen Flussbarsches untersucht. Die Fische wurden verschiedenen Versuchsbedingungen ausgesetzt: 1) niedrige ALAN-Intensitäten von 0,01, 0,1 und 1 lx unter kontrollierten Bedingungen, 2) höhere ALAN-Intensitäten von 1, 10 und 100 lx unter kontrollierten Bedingungen und 3) eine niedrige ALAN-Intensität von 0,06 lx in einem Feldexperiment. In den vorgestellten Experimenten unterdrückten niedrige ALAN-Intensitäten den nächtlichen Melatoninspiegel sowie teilweise Reproduktionshormone bei Weibchen. Höhere ALAN-Intensitäten verringerten das aktivste Schilddrüsenhormon und das relative Lebergewicht der Fische. Diese Arbeit zeigt physiologische Veränderungen bereits bei schwachen ALAN-Intensitäten, wie sie in großen Bereichen (vor-)städtischer Ökosysteme in Form von Skyglow vorkommen. Die empfindlichste Reaktionsvariable auf die Belastung durch ALAN bei Fischen ist der nächtliche Melatoninspiegel. Mögliche Wirkungen von ALAN auf andere physiologische Parameter können durch direkten Lichteinfall oder indirekt über reduziertes Melatonin ausgelöst werden. Diese Arbeit trägt zum Verständnis der Schwellenwerte für verschiedene physiologische Effekte durch eine mehrwöchige ALAN-Exposition bei. Schwellenwerte für ALAN-Intensitäten könnten zukünftig notwendige Deskriptoren für die Ausarbeitung von regulierenden Maßnahmen zur Reduzierung von Lichtverschmutzung liefern. / Artificial light at night (ALAN) is emitted from centers of human activities and increasingly brightens up nights, which can disturb biological rhythms of humans and wildlife. Skyglow is a diffuse brightening of the night sky due to reflection and scattering of ALAN, which indirectly illuminates large areas of (sub-)urban ecosystems. As centers of human activities are usually located close to rivers and lakes, skyglow may disproportionally affect wildlife of freshwater. Three experiments tested for effects of ALAN on the physiology of Eurasian perch. Fish were exposed 1) to low nocturnal illuminances of 0.01, 0.1 and 1 lx under controlled conditions, 2) to higher nocturnal illuminances of 1, 10 and 100 lx under controlled conditions, and 3) to low nocturnal illuminance of 0.06 lx in a field experiment. In the presented experiments, low nocturnal illuminance suppressed nocturnal melatonin production and reduced reproductive hormones to some extent in females. Higher nocturnal illuminance reduced the most active thyroid hormone and reduced relative liver weight of the fish. This thesis shows physiological changes already at very weak intensities of ALAN, like they occur over large areas of (sub-)urban ecosystems in the form of skyglow. The most sensitive response variable to ALAN exposure is the nocturnal melatonin levels. Possible actions of ALAN on other physiological parameters can be either by direct perception of light or indirectly via reduced melatonin. This thesis contributes to an understanding of thresholds for several physiological effects caused by ALAN exposure of several weeks. Thresholds for ALAN intensities could provide the necessary descriptors for elaborating regulatory measures to reduce light pollution in the future.

Light pollution is a problem that affects both living creatures as well as the perception of the night sky. As artificial lighting becomes more affordable and energy efficient, more and more lights are being used, further increasing the light pollution produced by us humans where cities with larger populations experience the largest amount of light pollution. There is however a knowledge gap in the field of light pollution regarding the possibility of a relationship between sky view factor and the brightness of the night sky. This study attempts to reduce that knowledge gap. By using cameras to take photos in different locations, the brightness of the night sky can be compared and together with the sky view factor of each location in can be determined if there exist such a relationship. Based on the results of this study, trends suggesting that this relationship exists emerges, however not to the extent that any definite conclusions can be drawn without further studies.

Artificial brightness of the night sky caused by the backscatter of artificial light in the atmosphere is a consequence of ongoing urbanization. Skyglow covers 88 % of Europe’s surface and poses significant threats to biodiversity. Extensive research on responses of bats to direct light pollution already revealed significant impacts. However, evidence for the influence of skyglow is scarce. Therefore, this study investigates the effects of skyglow on bat activity patterns, namely Pipistrellus pygmaeus and Myotis species, in a rural area outside of Stockholm, Sweden. Additionally, the analysis includes the role of local habitat structures and landscape composition at multiple scales for both activity rate and timing of emergence.The two focal species showed diverging behaviour in their main habitat on the local scale. While Myotis spp. emergence was delayed by about half an hour above the water surface, P. pygmaeus appeared about 20 minutes earlier in forest edges under brighter night skies. Landscape-level skyglow significantly delays the emergence of Myotis spp. above water surfaces by 18 minutes, but P. pygmaeus did not respond to skyglow at the landscape-level. Both, Myotis species and P. pygmaeus, appeared earlier in forest edges than above water surfaces. Evidence on skyglow affecting bat activity rates was weak. Here, local habitat and landscape structure were more important for both species. The total length of all forest edges decreased bat activity at most scales, while activity was lower with the proportion of water and open land at different scales. In conclusion, bat conservation programmes need to consider the effect of skyglow as well as landscape characteristics.

Freshwater lakes are among the most important ecosystems for both human and other biological communities. They account for about 87% of surface freshwater in the planet, thus constituting a major source of drinking water. They also provide a wide range of ecosystem services that go from the sustenance of a rich biodiversity to the regulation of hydrological extremes; from the provision of a means for recreation to the support of local economies, e.g., through tourism and fisheries, just to cite a few. Lakes are now also widely recognised as natural early warning systems, their responses potentially being effective indicators of local, regional and global scale phenomena such as acidification and climate change, respectively. This is because of their high sensitivity to environmental factors of the most diverse nature that can rapidly alter the course of their evolution. Examples of this are the observed abrupt shifts between alternative stable states in shallow lakes, which led them to become the archetype, go-to example in alternative stable state theory. Therefore, attaining a good scientific understanding of the many processes that take place within these ecosystems is fundamental for their adequate management. Among the tools that serve this purpose, ecological models are particularly powerful ones. Since their introduction in the 1960s, the development of mechanistic ecological models has been driven by their wide spectrum of potential applications. Nevertheless, these models often fall into one of the two following categories: overly simplistic representations of isolated processes, with limited potential to explain real-world observations as they fail to see the bigger picture; or overly complex and over-parameterised models that can hardly improve scientific understanding, their results being too difficult to analyse in terms of fundamental processes and controls. Moreover, it is now well known that an increased complexity in the mechanistic description of ecological processes, does not necessarily improve model accuracy, predictive capability or overall simulation results. To the contrary, a simpler representation allows for the inclusion of more links between model components, feedbacks which are usually overlooked in highly-complex models that partially couple a hydro-thermodynamic module to a biogeochemical one. However, ecological processes are now known to have the potential to significantly alter the physical response of aquatic ecosystems to environmental forcing. For example, steadily increasing concentrations of coloured dissolved organic carbon, a process known as brownification (also browning), as well as the intense phytoplankton blooms that characterise lakes undergoing severe nutrient enrichment, a process known as eutrophication, have been shown to have the potential to alter the duration of the stratified period, thermal structure and mixing regime of some lakes. In this thesis, with the aim of addressing the limitation of partially-coupled models to account for such feedbacks, we further develop a process-based model previously reported in scientific literature. Subsequent studies have already built upon this model in the last few years. In Chapter 2, we do so too by integrating hydro-thermodynamics and biogeochemistry in a reduced complexity framework, i.e., customising the model so that each version only includes the fundamental processes that, brought together, sufficiently describe the studied phenomena. Two case studies served the purpose of testing the adaptability and applicability of the developed model under different configurations and requirements. Limnological data for these two studies were measured at high spatial and temporal resolutions by means of an automated profiling system and recorded as part of two large-scale mesocosm experiments conducted in 2015 and 2016 at the IGB LakeLab in Lake Stechlin, Brandenburg, Germany. Meteorological datasets were also made available to us for both periods by the German Federal Environment Agency. The scope of the first experiment, which we describe in Chapter 3, was that of detecting any changes attributable to eutrophication and browning, in the competition for nutrients and light between four different groups of lake primary producers. These four groups are phytoplankton, periphyton, epiphyton and macrophytes. The model version for this study, therefore, includes equations for all four groups. By tailoring the model to these very specific needs with relative ease, we demonstrate its versatility and hint at its potential. The second experiment, described in Chapter 4, sought to shed light on the largely unknown effects of an increase in the diffuse luminance of the night sky that is due to artificial light at night (artificial skyglow) on lake metabolic rates, i.e., gross primary productivity, ecosystem respiration and net ecosystem productivity (the difference between the first two). For this purpose, an empirical equation for dissolved oxygen concentration was included, the parameters of which were estimated by means of a Markov Chain Monte Carlo sampling method within a Bayesian statistical framework, showing the compatibility, with these statistical methods, of our otherwise fully deterministic model. In Chapter 5, we present a theoretical study on the ecological controls of light and thermal patterns in lake ecosystems. A series of simulations were performed to determine in which cases ecological processes such as eutrophication and brownification may have an observable effect on the physical response of lakes to environmental forcing, which we assessed along a latitudinal gradient. Results show that, in general, across all examined latitudes, and consistent with previous studies, accounting for phytoplankton biomass results in higher surface temperatures during the warm-up phase, slightly lower water temperatures during the cool-down phase, and a shallower thermocline throughout the entire stratified period. This effect is relatively more important in eutrophic lakes where intense blooms are likely. This importance, however, decreases as lakes get browner. Finally, in line with the overall scope of the SMART EMJD, in Chapter 6 we illustrate the case of Ypacaraí Lake, the most important lake in landlocked Paraguay, hoping to provide an example of how interdisciplinary research and international intersectoral collaboration can help bridge the gap between science and management of freshwater ecosystems. This lake presents very special hydro-ecological conditions, such as very high turbidity that can impair phytoplankton growth despite its nutrient-based trophic state indices having consistently fallen within the hyper-eutrophic range in recent years. A strong interest in its complex functioning, through modelling, was taken early on. This led to a collaborative research line being established among several public and private institutions in Italy, Germany and Paraguay. Results so far include: • three concluded UniTN Master theses in Environmental Engineering, partly developed in Paraguay, the first two in collaboration with the “Nuestra Señora de la Asunción” Catholic University (UCNSA) and the third one with the National University of Asunción (UNA); • a collaborative UCNSA-UniTN research proposal submitted for consideration to receive funding through the PROCIENCIA Programme of the National Council of Science and Technology of Paraguay (CONACYT); and • the first multidisciplinary review that has ever been published about the case of Ypacaraí Lake, which highlights the importance of such a collaborative and integrative approach to further advance scientific knowledge and effectively manage this ecosystem.

Ljusförorening är ett miljöproblem vilket inbegripes som ett nytt och globalt framväxande fenomen i samband med himlaglim. Miljöproblemet i Sverige erkänns i viss mån med det nuvarande kunskapsläge. Dock saknas det en del kunskap för att komplettera ontologin för att bidra till ökad legitimitet för miljöproblemet bland allmänheten och Sveriges instanser. Studiens teoretiska analysramverket bestod av allmänningens tragedi, biogeoastronomiska natten och legitimitet, som användes till att analysera empirin härlett från studiens intervjumetod. Metoden hade en kvalitativ fenomenografisk ansats som innefattade ett strategiskt urval som var Sveriges instanser. Där uppdagades bristen på opinionsbildning i Riksdagen och Regeringen, trots att det finns motioner som har framlagts som vill att ljusförorening ska uppmärksammas, men att problemet hanteras snarare som en trafikfråga istället för miljöfråga. En del av förklaringen till varför det påverkar samverkan mellan Sveriges instanser för att motverka miljöproblemet. Ljusföroreningar påverkar ekologin och alla dess arter, varav krävs det tydligare riktlinjer för kommuner i deras belysningsplaner gällande att minska deras miljöpåverkan (särskilt för de nattaktiva arter som drabbas) för att nå målet till en mer hållbar belysning; varav ekologiska, ekonomiska och sociala aspekter vävs samman. Varav satsningar att bevara och etablera mörkerreservat är en pusselbit, vilket kan genomföras i samklang med Miljöbalkens författningar. / Light pollution is an environmental problem which is part of a new and globally emerging phenomenon in connection with skyglow. The environmental problem in Sweden is recognized to some extent with the current state of knowledge. However, there is also a lack of knowledge to complete the ontology in order to contribute to increased legitimacy for the environmental problem among the public and within its instances. The study's theoretical analytical framework consisted of the tragedy of the commons, biogeoastronomical night and legitimacy, which were used to analyze the empirical data derived from the study's interview method. The method had a qualitative phenomenographic approach that included a strategic selection of Sweden's instances. Where the lack of opinion formation was discovered in the Parliament and the Government, despite the fact that there is a proposition that has been presented that wants to light pollution to be noticed, but the problem is handled rather as a traffic issue instead of an environmental issue. Part of the explanation for why it affects the collaboration between Sweden's instances to counteract the environmental problem. Light pollution affects the ecology and all its species, which requires clearer guidelines for municipalities in their lighting plans regarding reducing their environmental impact (especially for the nocturnal species affected) in order to achieve the goal of more sustainable lighting; whereof which ecological, economic, and social aspects are woven together. In which investments to preserve and establish the dark sanctuary is a piece of the puzzle, which can be carried out in accordance with the Swedish Environmental Code constitutions.