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Aquatic habitats are closely linked to the adjacent riparian area. Fluxes of nutrients, energy and matter through emerging aquatic insects are a key component of the aquatic subsidy to terrestrial systems. In fact, adult insects serve as high-quality prey for riparian predators. Stressors impacting the aquatic subsidy can thus translate to consequences for the receiving terrestrial food web, while mechanistic knowledge is extremely limited. Against this background, this thesis aimed at (i) assessing the impact of a model stressor specifically targeting insect emergence, that is the mosquito control agent Bacillus thuringiensis var. israelensis, on quantity, temporal dynamics and (ii) quality of emerging aquatic insects. For this purpose, outdoor floodplain pond mesocosms (n = 6) were employed. Since emergence is, in most cases, no point event but occurs over a longer period emergence was monitored over 3.5 months. The model stressor, i.e., Bti applied three times during spring at 2.88 × 10^9 ITU/ha, shifted the emergence time of aquatic insects, especially of non-biting midges (Diptera: Chironomidae), by ten days with a 26% reduced peak, while the nutrient content was not altered. On this basis, (ii) the propagation of the effects in aquatic subsidy emergence to riparian predators was investigated. Stable isotope analyses were used to assess the diet of a model predator, that is the web-building riparian spider Tetragnatha extensa. Results suggested changes in the composition of the spider’s diet to replace missing Chironomidae by other aquatic and terrestrial prey organisms pointing to further negative consequences. Finally, the thesis aimed at (iii) the understanding of processes underlying an altered emergence of aquatic subsidy mainly consisting of chironomids. Using a laboratory-based test design, populations of Chironomus riparius (n = 6) were assessed for their sensitivity towards Bti under different food qualities (high and low nutritious) before and after a long-term (six months) Bti exposure. Signs of phenotypic adaptation were observed in emergence time and nutrient content over multiple generations, resulting in changes in chironomids’ quantity and quality as food source. Overall, it can be concluded that direct and indirect effects of an aquatic stressor, as well as the adaptive response to it, can alter ecosystems at different levels, including individual, population and community level. Furthermore, this thesis highlights the importance of a temporal perspective when investigating the impact of aquatic stressors beyond ecosystem boundaries. It illustrates potential bottom-up effects on riparian predators through altered emergence of aquatic insects, feeding our understanding of meta-ecosystems and how stressors and their effects are transferred across systems. These insights will support efforts to protect and conserve natural ecosystems.
Aflatoxins, a group of mycotoxins produced by various mold species within the genus Aspergillus, have been extensively investigated for their potential to contaminate food and feed, rendering them unfit for consumption. Nevertheless, the role of aflatoxins as environmental contaminants in soil, which represents their natural habitat, remains a relatively unexplored area in aflatoxin research. This knowledge gap can be attributed, in part, to the methodological challenges associated with detecting aflatoxins in soil. The main objective of this PhD project was to develop and validate an analytical method that allows monitoring of aflatoxins in soil, and scrutinize the mechanisms and extent of occurrence of aflatoxins in soil, the processes governing their dissipation, and their impact on the soil microbiome and associated soil functions. By utilizing an efficient extraction solvent mixture comprising acetonitrile and water, coupled with an ultrasonication step, recoveries of 78% to 92% were achieved, enabling reliable determination of trace levels in soil ranging from 0.5 to 20 µg kg-1. However, in a field trial conducted in a high-risk model region for aflatoxin contamination in Sub-Saharan Africa, no aflatoxins were detected using this procedure, underscoring the complexities of field monitoring. These challenges encompassed rapid degradation, spatial heterogeneity, and seasonal fluctuations in aflatoxin occurrence. Degradation experiments revealed the importance of microbial and photochemical processes in the dissipation of aflatoxins in soil with half-lives of 20 - 65 days. The rate of dissipation was found to be influenced by soil properties, most notably soil texture and the initial concentration of aflatoxins in the soil. An exposure study provided evidence that aflatoxins do not pose a substantial threat to the soil microbiome, encompassing microbial biomass, activity, and catabolic functionality. This was particularly evident in clayey soils, where the toxicity of aflatoxins diminished significantly due to their strong binding to clay minerals. However, several critical questions remain unanswered, emphasizing the necessity for further research to attain a more comprehensive understanding of the ecological importance of aflatoxins. Future research should prioritize the challenges associated with field monitoring of aflatoxins, elucidate the mechanisms responsible for the dissipation of aflatoxins in soil during microbial and photochemical degradation, and investigate the ecological consequences of aflatoxins in regions heavily affected by aflatoxins, taking into account the interactions between aflatoxins and environmental and anthropogenic stressors. Addressing these questions contributes to a comprehensive understanding of the environmental impact of aflatoxins in soil, ultimately contributing to more effective strategies for aflatoxin management in agriculture.
Aquatic emergent insect communities form an important link between aquatic and terrestrial
ecosystems, yet studying them is costly and time-consuming as they are usually
diverse and superabundant. Metabarcoding is a valuable tool to investigate arthropod
community compositions, however high-throughput applications, such as for biomonitoring,
require cost-effective and user-friendly procedures. To investigate if the time-consuming
and labour-intensive DNA extraction step can be omitted in metabarcoding, we
studied the difference in detection rates and individual read abundance using standard
DNA extraction versus direct PCR protocols. Metabarcoding with and without DNA extraction
was performed with artificially created communities of known composition as
well as on natural communities both of the dipteran family Chironomidae to compare
detection rates, individual read abundances and presence-absence community composition.
We found that the novel approach of direct PCR metabarcoding presented here
did not alter detection rates and had a minor effect on individual read abundances in
artificially created communities. Furthermore, presence-absence community compositions
of natural chironomid communities were highly comparable using both approaches.
In conclusion, we showed that direct PCR protocols can be applied in chironomid
metabarcoding approaches, with possible application for a wider range of arthropod
taxa, enabling us to study communities more efficiently in the future.
River ecosystems are being threatened by rising temperatures, aridity, and salinity due to climate change and increased water abstractions. These threats also put human well-being at risk, as people and rivers are closely connected, particularly in water-scarce regions. We aimed to investigate the relationship between human well-being and biological and physico-chemical river water quality using the arid Draa River basin as a case study. Physico-chemical water measurements, biological monitoring of aquatic macroinvertebrates, and household surveys were used to assess the state of the river water, ecosystem, and human well-being, as well as the associations between them. Salinity levels exceeded maximum permissible values for drinking water in 35 % and irrigation water in 12 % of the sites. Salinity and low flow were associated with low biological quality. Human satisfaction with water quantity and quality, agriculture, the natural environment, and overall life satisfaction were low particularly in the Middle Draa, where 89% of respondents reported emotional distress due to water salinity and scarcity. Drinking and irrigation water quality was generally rated lower in areas characterized by higher levels of water salinity and scarcity. The study found positive associations between the river water quality and biological quality indices, but no significant association between these factors and human satisfaction. These findings suggest that the relationship between human satisfaction and the biological and physicochemical river water quality is complex and that a more comprehensive approach to human well-being is likely needed to establish relationships.
Mit der vorliegenden Dissertation wurde ein Werkzeug für die Erstellung volldigitaler binnendifferenzierter Arbeitsblätter im Regelunterricht Chemie evaluiert und weiterentwickelt, das ein motivations- und interessensförderndes Potential aufweist. Es konnten Zusammenhänge zur Benutzbarkeit der Anwendung und zum Cognitive Load hergestellt werden. Die Ergebnisse stützen damit die Erkenntnisse im Bereich des Lernens mit digitalen Medien. Die Integration von digitalen Werkzeugen in den Lernprozess ist berechtigt. Sie zeigen einerseits für Schüler:innen ein motivationsförderndes Potential und andererseits für Lehrende praktische Vorteile, indem auf vielfältige Weise Informationen dargeboten werden können – zum Beispiel im Bereich der Differenzierung. Mit HyperDocSystems können binnendifferenzierte digitale Arbeitsblätter erstellt und bearbeitet werden. Diese so genannten HyperDocs können von Lehrenden mit Lernhilfen in verschiedenen Darstellungsformen angereichert und von Lernenden volldigital im Browser mit einem Stylus oder der Tastatur bearbeitet werden.
Im Rahmen einer quasi-experimentellen Feldstudie wurde der Einsatz dieser neuartigen HyperDocs erstmals unter Betrachtung der intrinsischen Motivation und des Interesses, der Usability sowie der Nutzung des multimedialen Differenzierungsangebots analysiert. Die Studie fand über vier Schulstunden im Regelunterricht Chemie der Mittelstufe (Gymnasium / Gesamtschule) und Oberstufe (Gymnasium) statt. Dabei wurden auch der Cognitive Load und die tabletbezogenen Kompetenzen der Lernenden berücksichtigt. Die Ergebnisse lassen auf ein motivationsförderndes Potential der HyperDocs gegenüber analogen Arbeitsblättern schließen. Dabei zeigen sich Unterschiede zwischen den Geschlechtern, die zum Teil auf den Cognitive Load zurückzuführen sind und abhängig vom Alter der Lernenden (Mittel- und Oberstufe) auftreten. Die Lernhilfen werden in diesem Zusammenhang häufig aus Interesse und Neugier verwendet. Schüler:innen nutzen insbesondere Lernhilfen in Form von Text und Bild. Die Nutzungshäufigkeit des Differenzierungsangebots gibt jedoch nicht unmittelbar Aufschlüsse über die Motivation oder den Cognitive Load der Lernenden. Bei der Usability handelt es sich um ein wichtiges Kriterium beim Einsatz von digitalen Lernprogrammen, da sich unter anderem ein Zusammenhang zu den Variablen der intrinsischen Motivation und zum Cognitive Load beim Lernen mit HyperDocs herstellen lässt. Die Usability ist dabei jedoch abhängig vom Messzeitpunkt. HyperDocs weisen eine hohe Usability auf und können daher uneingeschränkt in der Mittel- und Oberstufe eingesetzt werden.
Production, purification and analysis of novel peptide antibiotics from terrestrial cyanobacteria
(2024)
Cyanobacteria are a known source for bioactive compounds, of which several also show antibiotic activity. In regard to the growing number of multi-resistant pathogens, the search for novel antibiotic substances is of great importance and unexploited sources should be explored. So, this thesis initially dealt with the identification of productive strains, especially within the group of the terrestrial cyanobacteria, which are less well studied than marine and freshwater strains. Amongst these, Chroococcidiopsis cubana, an extremely desiccation and radiation tolerant, unicellular cyanobacterium was found to produce an extracellular antimicrobial metabolite effective against the Gram-positive indicator bacterium Micrococcus luteus as well as the pathogenic yeast Candida auris. However, as the sole identification of a productive cyanobacterium is not sufficient for further analysis and a future production scale-up, the second part of this thesis targeted the identification of compound synthesis prerequisites. As a result, a limitation of nitrogen was shown to be the production trigger, a finding that was used for the establishment of a continuous production system. The increased compound formation was then used for purification and analysis steps. As a second approach, in silico identified bacteriocin gene clusters from C. cubana were cloned and heterologously expressed in Escherichia coli. By this, the bacteriocin B135CC was identified as a strong bacteriolytic agent, active predominantly against the Gram-positive strains Staphylococcus aureus and Mycobacterium phlei. The peptide showed no cytotoxic effects against mouse neuroblastoma (N2a-) cells and a high temperature tolerance up to 60 °C. In order to facilitate the whole project, two standard protocols, specifically adapted for the work with cyanobacteria, were established. First, a method for a quick and easy in vivo vitality estimation of phototrophic cells and second, an approach for a high throughput determination of nitrate concentrations in microalgal cultures. Both methods greatly helped to proceed the main objectives of this work, the first one by simplifying the development of suitable cryopreservation protocols for individual cyanobacteria strains and the second one by accelerating the determination of the optimal nitrate concentration for the production of the antimicrobial compound from C. cubana. In the course of this cultivation optimization, the ability of cyanobacteria to utilize organic carbon sources for an accelerated cell growth was examined in greater detail. It could be shown that C. cubana reaches significantly higher growth rates when mixotrophically cultivated with fructose or glucose. Interestingly, this effect was even further enhanced when light intensity was decreased. Under these low-light conditions, phototrophically cultivated C. cubana cells showed a clearly decreased cell growth. This effect might be extremely useful for a quick and economic preparation of precultures.
Plant-specific factors affecting short-range attraction and oviposition of European grapevine moths
(2024)
The spread of pests and pathogens is increasingly intensified by climate change and globalization. Two of the most serious insect pests threating European viticulture are the European grape berry moth, Eupoecilia ambiguella (Hübner) and the European grapevine moth Lobesia botrana (Denis & Schiffermüller). Larvae feed on fructiferous organs of grapevine Vitis vinifera, resulting in high yield and quality losses. Under the aspects of integrated pest management, insecticide measures are only reasonable when other control strategies become ineffective. In order to support the development of novel decision support system for the application of insecticides, the aim of this thesis was to decipher plant-specific factors, which affect the short-range attraction and oviposition of L. botrana and E. ambiguella.
The focus was set on the visual, volatile, tactile and gustatory stimuli provided by their host plant after settlement. The use of artificial surfaces as model plant showed that oviposition of both species is affected by the color, the shape and the texture of the oviposition site. To explain a susceptibility of certain grapevine cultivars and phenological stages of the berries to egg infestations, we analysed and compared the chemical composition of the epicuticular waxes of the berry surface as well as the volatile organic compounds emitted by the berries. Thereby it turned out that the attractiveness to wax extracts decreased during ripening of the berries, highlighting a preference of earlier phenological stages of the berries for oviposition. In addition, grapevine cultivars exhibited variations in their volatile composition. The principle components perceived by female’s antennae could not explain the differentiation between cultivars, suggesting volatiles do not trigger orientation to certain cultivars. Furthermore, a method was developed to measure real-time behavioural response of female moths to volatiles. The setup allowed to quantify the orientation to a volatile source as well as movements of the antennae and ovipositor. They could be linked to the olfactory and gustatory perception of volatiles during the evaluation of suitable host plants for oviposition. In addition, the risk of potential alternative host plants in the vicinity of the vineyard was investigated. This confirmed that L. botrana in particular prefers the stimuli provided by some plants to those of grapevine. Overall, the results suggest that during oviposition, volatiles emitted by the plants and the composition of the plant surface are the most important factors for host plant differentiation.
Biodiversity has declined by approximately 70% in the last 50 years for vertebrate and invertebrate species. This loss in biodiversity is strongly connected with anthropogenic activities, such as agricultural intensification and pollution. Currently, pesticides are needed to secure the growing global food demand, although they are recognized as one of the main drivers of biodiversity loss, mainly in agricultural areas.
In the European Union, pesticides are regulated within the risk assessment framework, which aims to protect both the environment and human health from undesirable effects. The effects on non-target organisms are mostly assessed following a “one-size-fits-all” approach, focused on sensitive species tests. However, it has been recognized that the current methodology can be improved in order to minimize undesirable effects. Aiming to provide valuable data to inform future risk assessment, this thesis focused on two terrestrial organism groups that play beneficial roles, especially in agroecosystems: earthworms and spiders.
Although the earthworm Eisenia fetida is included in pesticide regulation, its use as the only earthworm representative may lead to uncertainties for the risk assessment. Therefore, we collected ecotoxicological data on field-captured earthworm species via acute exposure to imidacloprid and copper. In addition, we investigated the relationships between earthworm chemical sensitivity, biological traits and habitat preferences, and potential links with their ecosystem services (Chapter 2). We found that earthworms sampled from extremely acidic soils were less sensitive to copper than earthworms from neutral soils. Moreover, anecic and endogeic earthworms were more sensitive to imidacloprid than epigeic earthworms.
Spiders have, thus far, been understudied in regulatory risk assessment in comparison to other non-target arthropods. Thus, we aimed to collect ecotoxicological data of spider species sampled in different European climates via acute exposure to lambda-cyhalothrin. Moreover, we explored relationships between spider chemical sensitivity, phylogeny, biological traits and habitat preferences, as well as potential links with their ecosystem services (Chapter 3). Spiders showed a high sensitivity to lambda-cyhalothrin. Furthermore, our results showed that spider sensitivity varies depending on climate. We confirmed this relationship by incorporating different rearing and test temperatures into the toxicity testing protocol (Chapter 4).
The outcomes of this thesis contribute to informing pesticide regulatory practices, allowing for an improved protection and conservation of terrestrial organism groups and the ecosystem services they provide. The consideration of ecological traits, habitat variability and related plasticity, key species, and ecological network structure could improve the risk assessment framework and minimize the effects of pesticides and other stressors on an ecosystem-level.
With the transition of fluid-capillary-based “Lab on a chip 1.0″ concepts in analytical chemistry to “Lab on a chip
2.0″ approaches relying on distinct fluid droplets (“digital microfluidics”, DMF), the need for reliable methods for
droplet actuation has increasingly come into focus. One possible approach is based on “electrowetting on
dielectric” (EWOD). This technique has the disadvantage that any possible desired later positions of the droplets
on the chip have to be defined prior to chip realization because one of the EWOD electrode layers has to be
structured accordingly. “Optoelectrowetting” (OEW) goes a step further in the sense that the later droplet positions
do not have to be known before, and none of the electrode layers has to be structured. Instead, the
electrical parameters of the layer sequence can be altered locally by an impinging (and movable) light spot.
Although some research groups have succeeded in demonstrating OEW actuation of droplets, the optimization of
the relevant parameters of the layer sequence and the droplet – at least half a dozen parameters altogether – is
tedious and not straight-forward. In this contribution, for optimization purposes, the equations governing OEW
are revisited and altered again, e.g., by numerical implementation of the experimentally well-known saturation
of the contact angle change. Additionally, a Nelder-Mead algorithm is applied to find the parameters, on which
the optimization has to focus to maximize contact angle changes and, thus, mechanical forces on the droplets.
The numerical investigation yields diverse results, e.g., the finding that the droplet’s contact area on the
dielectric layer has a strong influence on the contact angle change and the question whether the droplet is pulled
or pushed. Moreover, the interplay between frequency and amplitude of the applied rectangular alternate voltage
is important for optimization.
The booming global market of nanomaterials in the last few decades has led to the inevitable emission of these materials into aquatic environments; hence, understanding their physical, chemical, and biological transformations has become a big concern for environmental scientists. Despite a great deal of effort made to understand the mobility, fate, and risk assessment of e.g, TiO2 nanoparticles, it is still unclear if the obtained results, under lab-controlled conditions, can be generalized to realistic released nanoparticles in aquatic environments since the complex dynamics of environmental conditions are not completely reproducible under controlled conditions.
In the present study, we proposed a new approach to expose TiO2 nanoparticles to environmental conditions of natural surface waters by making use of dialysis membranes as passive reactors. The function of these reactors is based on the permeability of the membrane to the dissolved matter of surface waters while TiO2 nanoparticles do not pass through the membrane. These systems benefit from the fact that although the complexity and temporal variability of most of the environmental parameters of surface waters are reproducible inside the reactors, colloidal and particulate interferences remain separated. Furthermore, no significant reduction in pore size i.e., membrane fouling is observed in dialysis bags after exposure to surface waters which validates the efficiency of the system.
Taking advantage of these reactors to expose nanoparticles to surface waters, we investigated the influential physicochemical parameters of the surface waters on the formation of natural coating onto nanoparticles. Hence, dialysis bags were used to expose TiO2 nanoparticles, in situ, to ten different surface waters in the spring and summer of 2019. Due to the complexity of the natural dissolved matter of the surface waters as long as their low natural concentrations, we needed to use a combination of analytical techniques and multivariate data analysis to investigate the coatings. The initial findings were similar to the lab-controlled exposure studies in the literature showing pH, electrical conductivity, and Ca2+- Mg2+ concentration as the three most important parameters of surface waters controlling the formation of coatings. Nonetheless, we came across a phenomenon being overlooked under lab-controlled conditions; natural coatings are composed of not only organics (DOM: dissolved organic matter) but also inorganics (carbonate) which implies that their realistic coatings are more complex than what the previous studies described.
The second part of this thesis focused on investigating the interactions of more realistic nanoparticles (extracted TiO2 nanoparticles from 11 sunscreens) with DOM. Using ToF-SIMS combined with high-dimensional data analysis, we tried to find a general DOM-sorption pattern among TiO2 nanoparticles since finding this pattern could have ultimately opened a way to assess the fate of (more) realistic nanoparticles in aquatic environments. Contrary to our expectations, the results showed a unique sorption pattern for each sunscreen controlled by the composition of the sunscreens implying that the sorption pattern of each sunscreen should be investigated individually. In the next step of this study, we used random forest to extract the most important fragments of DOM sorbed onto each sunscreen followed by an effort to assign these important masses to chemical fragments.
Trying to provide a comprehensive understanding of interactions of the released n-TiO2 in aquatic environments, in future studies, we are going to expand our coating research to different types of TiO2 nanoparticles, such as extracted particles from paint, where the reaction media (surface waters) are covering a wide range of water parameters representative of various ecosystems. Making use of state-of-the-art techniques as long as multivariate data analysis, we will try to achieve a model describing the sorption mechanisms of dissolved matter of surface waters onto nanoparticles. Such studies can eventually lead us to a better understanding of the fate of the released nanoparticles under natural conditions.