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- Doctoral Thesis (29) (remove)
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Institute
- Institut für Integrierte Naturwissenschaften, Abt. Biologie (29) (remove)
Eine Ursache des Insektenrückgangs ist die Abnahme der für Arthropoden wichtigen Lebensräume. Der kleinstrukturierte Obstanbau als Dauerkultur mit vielfältigen Strukturen (Bäume, Grünland, offener Boden) kann als Refugium wirken. Gerade Dauerkulturen, welche über viele Jahre bestehen bleiben, können einen großen ökologischen Wert für Insekten und Spinnentiere darstellen, wenn die negativen Einflüsse der Bewirtschaftung durch gezielte Maßnahmen minimiert werden. Im Gegensatz zu den gut untersuchten Streuobstwiesen liegen bisher nur wenige oder ungenaue Daten über die Arthropodenfauna in Erwerbsobstanlagen vor. Ziele dieser Arbeit sind eine genauere Erfassung der Arthropodenfauna in Erwerbsobstanlagen, Benennung der Einflussfaktoren und Erarbeitung einer indikatorgestützten Bewertungsmethode mit Entwicklung von Maßnahmen zur Förderung der Biodiversität. Es wurde eine intensive Erfassung der Insekten und Spinnentiere auf Basis von Individuenzahlen, Verteilung der Tiere auf Großgruppen, Artenzahlen der Käfer (inkl. Rote Liste) und Wanzen, deren Diversität und der sie beeinflussenden Faktoren auf vier Erwerbsobstflächen und einer Streuobstwiese als Referenzfläche in der Gemeinde Zornheim (Rheinland-Pfalz) untersucht. Mittels des erarbeiteten Bewertungsbogens wurden die Auswirkungen der fünf Faktorenkomplexe: Sonderstrukturen, Anlagenstruktur, Beschattung, Mahdregime und Einsatz von Pflanzenschutzmitteln auf die Arthropodenfauna erhoben und die auf der Fläche zu erwartende Biodiversität ermittelt. Die visuelle Darstellung der Einflussfaktoren mit Netzdiagrammen zeigt biodiversitätsbeeinträchtigende Faktoren und ermöglicht so Empfehlungen zur Aufwertung der Biodiversität. Die Bewertungsmethode kann nach Verifizierung im Rahmen von erfolgsorientierten Agrarumwelt- und Klimamaßnahmen (AUKM), zur Anerkennung von Kompensationsmaßnahmen (z.B. PIK) und zur Ermittlung des ökologischen Wertes (Ökosystemdienstleistung) von Obstanlagen genutzt werden. In modifizierter Form könnte es ebenfalls im Bereich der Flächenbewertung in Landschafts- und Bauleitplanung eingesetzt werden.
Agricultural intensification is leading to a severe decline in farmland biodiversity worldwide. The resulting landscape simplification through the expansion of monocultures and removal of non-crop habitats has a major impact on arthropod communities in agricultural landscapes. While arable fields are often highly disturbed and ephemeral habitats that are unsuitable for many species, non-crop habitats in agroecosystems can provide important refugia. The creation of non-crop habitats through agri-environmental schemes (AES) in intensive agricultural landscapes, such as the ‘Maifeld’ region in western Germany, is intended to mitigate the negative effects of agricultural intensification, although the effectiveness of these measures for nature conservation is still controversial. Therefore, this work focuses on the taxonomic and functional diversity of beetles (Coleoptera) and spiders (Araneida), being important providers of ecosystem services, between wheat fields and different non-crop habitats, namely grassy field margins adjacent to wheat and oilseed rape fields, small- and large-scale set-aside areas sown with wildflowers, and permanent grassland fallows. Arthropods were collected between 2019 and 2020 using pitfall traps and suction sampling. Land-use type influenced beetle and spider diversity in the study area, with significantly higher values in grassland fallows than wheat fields. Surprisingly, species diversity differed little among all non-crop habitats, but all harboured distinct species assemblages. In particular, large long-term grassland fallows showed the largest within-group variation of beetle and spider assemblages and represented important habitats, especially for habitat specialists and threatened species, likely due to their variable soil moisture and complex habitat structure. In contrast, the homogeneous arthropod assemblages of wheat fields exhibited lower trait richness and were dominated by a few predatory species adapted to such disturbed, man-made habitats. Interestingly, all conservation measures complemented each other in that they contributed in different ways to supporting beetles and spiders in agricultural landscapes. Even small-scale non-crop habitats and existing habitat boundaries in an agricultural matrix appear to be valuable habitats for farmland arthropods by enhancing taxonomic diversity. Field margins and small wildflower-sown patches can link isolated non-crop habitats and contribute to a heterogeneous agricultural landscape. Consequently, a combination of various small- and large-scale greening measures leads to increased compositional and configurational landscape heterogeneity, resulting in improved beetle and spider diversity. Considering the ongoing loss of farmland biodiversity worldwide, agri-environmental schemes should be promoted in the future, as they are particularly important for arthropod conservation in intensive agricultural landscapes such as the Maifeld region.
In this thesis, I present the results of my studies on taxonomy, systematics, and biogeography of Impatiens (Balsaminaceae) in Madagascar and the Comoro islands.
In Chapter 1 I reviewed the literature on taxonomy and classification of Balsaminaceae, on habitat, world distribution, morphology, molecular phylogenetics and infrageneric classification of the genus Impatiens. In Chapters 2-15 (Fischer & Rahelivololona 2002, 2003, 2004, 2007, 2015a, 2015b, 2015c, 2016, Fischer et al. 2004. 2017, 2018a, b submitted, Rahelivololona et al. 2003) I presented the first results of a revision of Balsaminaceae of Madagascar and the Comoro islands including the description of 78 new species. In Chapter 16 (Yuan et al. 2004) we worked on the phylogeny and biogeography of Balsaminaceae inferred from ITS sequences using combined results from molecular phylogenetic and morphological analyses. In Chapter 17 (Rahelivololona et al. 2018) we conducted a phylogeny and assessment of the infrageneric classification of species in the Malagasy Impatiens (Balsaminaceae) with a particular emphasis on taxa collected from Marojejy.
Below I summarise the most important findings of each chapter and provide an outlook for future studies.
How many species of Impatiens occur in Madagascar and the Comoro islands?
To provide additional information on the taxonomic revision of Impatiens in Madagascar and the Comoro islands, the identification of already described species as well as the description of new species was conducted. Based on herbarium specimens from BR, G, K, NEU, P, TAN and on living plants collected during several field trips, 78 new species and 6 nomina nova have been published and another 70 new taxa are already identified. Actually more than 260 species occur in Madagascar and the Comoro islands and all of them are endemic. For each species, a description of the morphology, phenology, ecology and known distribution range was provided. Apart from new taxa, the delimitation of already described species like Impatiens firmula Baker and Impatiens hildebrandtii Baill. could be clarified by studying the types and by observing the variability in the field.
Are the groups of Impatiens in Madagascar monophyletic, and what is the systematic position of Trimorphopetalum?
Yuan & al. (2004) conducted a molecular phylogenetic study to examine the morphological and karyological evolution, and the historical biogeography of the Balsaminaceae family by using nucleotide sequence data of internal transcribed spacer regions of nuclear ribosomal DNA. The results support the monophyly of the Malagasy endemic section Trimorphopetalum and show that the cleistogamous Impatiens inaperta should be included in the sect. Trimorphopetalum which is the most derived within Impatiens. Therefore, the section Preimpatiens proposed by Perrier de la Bâthie (1934) is paraphyletic.
Rahelivololona & al. (2018) provided a phylogenetic study focused on three subdivisions (based on macromorphological characters) proposed by Perrier de la Bâthie (1934). The analysis was done using two nuclear AP3/DEF homologues (ImpDEF1 and ImpDEF2) and the plastid atpB-rbcL spacer to reassess or assess the monophyly of the Malagasy Impatiens, of the sections Preimpatiens (Humblotianae and Vulgare groups) and Trimorphopetalum. A focus was on the species of Impatiens from the Marojejy National Park and of the morphologically variable species I. elatostemmoides, I. “hammarbyoides”, I. inaperta and I. manaharensis, using monophyly as the primary criterion.
As results the Malagasy Impatiens are paraphyletic and the section Preimpatiens sensu Perrier de la Bâthie (1934) (= subgen. Impatiens sensu Fischer & Rahelivololona 2002) was not resolved as a monophyletic group. The section Trimorphopetalum sensu Perrier de la Bâthie (1934) (= subgen. Trimorphopetalum sensu Fischer & Rahelivololona 2002), however, was strongly confirmed as a monophyletic lineage (BS: 92; BPP: 1). Neither the Humblotianae group nor the Vulgare group was supported as monophyletic. None of the morphologically variable species appeared to be monophyletic and the sampled species of Impatiens from the Marojejy National Park do also not form a monophyletic group.
What are the biogeographical position and the distribution patterns of Impatiens in Madagascar and the Comoro islands?
Investigation of the geographical affinities and species distribution of section Impatiens (including Humblotianae group and Vulgare group) and section Trimorphopetalum were conducted and the origin and evolution as well as species richness and endemism were discussed.
The isolation, the climate and the complex topography of Madagascar have generated the microhabitats and ecological niches favourable to the diversification of Impatiens species. Impatiens of Madagascar with 260 endemic species is actually the largest genus in Madagascar. Therefore, Madagascar and the Comoro islands are among the most species-rich regions in the world for Impatiens.
Future studies
In Impatiens on Madagascar, there remain numerous unresolved questions that need to be adressed:
• A further study based on a much larger molecular data set and sampling from the entire geographic ranges of Impatiens in Madagascar is needed to retest the monophyly of the different subgenera and sections, as well as a molecular dating of the Malagasy Impatiens.
• The study of pollinators as a key for understanding the radiation and species richness is required: Within Impatiens the different shapes of spur are related to pollinators (bees, birds, butterflies and moths). Therefore pollinator observation of specific species need to be done to understand the radiation of species by adaptation and coevolution with these pollinators. A pollination study with a large number of species within section Trimorphopetalum will help to understand the mechanism of complete disappearance of the spur, the shift of pollinators and the evolution of species richness.
• The destruction of the natural habitats of Impatiens and the subsequent reduction of humidity in logged area constitute a severe threat for the survival of many species. The conservation and reforestation of vulnerable areas such as Ankaratra, Daraina, Mandraka and Col des Tapia near Antsirabe is required.
• In terms of conservation and to mitigate the threat on the genus, a study on the ex-situ-conservation of Malagasy Impatiens species is very important as long as some species are suitable for horticultural purposes (e.g. Impatiens mayae-valeriae, Impatiens emiliae and species with broad red spur).
• Finally, the publication of the revision of Impatiens of Madagascar and the Comoro islands will help other botanists to identify the species and will thus increase our knowledge on the group.
Cultural eutrophication due to excessive inputs of nutrients seriously threatens aquatic ecosystems worldwide and is one of the major anthropogenic stressors on aquatic biota in European rivers. In streams and shallow rivers, its effects include excessive periphyton growth, which causes biological clogging and thereby oxygen depletion in the hyporheic zone. The result is a serious degradation of habitat quality for benthic invertebrates as well as for the eggs and larvae of gravel-spawning fish. Unlike in standing waters, efficient tools for controlling eutrophication in rivers are lacking. However, top-down control of the food-web by manipulating fish stocks, similar to the biomanipulation successfully applied in lakes, offers a promising approach to mitigating the effects of eutrophication in shallow rivers, especially those in which major reductions in nutrient inputs are not feasible. The overall aim of this thesis was to assess the potential for top-down control by two large cypriniform fish, the common nase (Chondrostoma nasus), the only obligate herbivorous fish species in European rivers, and the omnivorous European chub (Squalius cephalus), to mitigate the effects of eutrophication in medium-sized rivers. I therefore conducted field experiments on different spatial and temporal scales in the hyporhithral zone of a eutrophic gravel-bed river. Generally, the results of those experiments revealed the crucial role of fish-mediated top-down effects in river food webs. In a 4-year reach-scale experiment, the key contribution of my thesis, the enhancement of fish densities significantly increased both oxygen availability and water exchange in the upper layer of the hyporheic zone, even though the top-down effects of the fish on periphyton biomass were relatively small. These findings were supported by those of a 4-week mesocosm experiment, which also provided insights into the mechanisms underlying the mitigation of eutrophication effects by nase and chub. The top-down effects of both fish species reduced hyporheic oxygen depletion, suggesting a reduction of biological clogging. The positive effects of herbivorous nase on hyporheic oxygen availability could be attributed to benthic grazing, whereas the reduction of hyporheic oxygen depletion in the presence of omnivorous chub was best explained by the enhanced bioturbation induced by the fish’s benthic foraging. Overall, the results of my thesis demonstrate that biomanipulation achieved by enhancing herbivorous and omnivorous fish stocks can mitigate the effects of eutrophication in medium-sized European rivers. The results may be the first step towards the establishment of biomanipulation as a supportive management tool for eutrophication control in running waters and therefore as a strategy to preserve aquatic biodiversity.
Aim of this study was the assessment of the conservation status of vascular plants in East African rain forests with the background of establishing an ex-situ culture of local endangered plants at the Botanic Garden of the Maseno University (Kenya).
For a sustainable implementation it was first necessary to learn more about the general species inventory, especially concerning species composition and abundance under human impact, and to assess the conservation priority of each plant species. Representative for East African rain forests, Kakamega Forest (Kenya) and Budongo Forest (Uganda) were selected to serve as model forests.
Beside the general floristic investigations including all vascular plants, a special focus was laid on vascular epiphytes and their vulnerability to forest disturbance. To assess the conservation priority of the plants, a rating system was developed based on seven threat criteria. By carrying out first plant collections, the exsitu culture in Maseno Botanic Garden was already initiated.
Ziel der vorliegenden Arbeit war die Darstellung floristisch-pflanzensoziologischer Abhängigkeiten sommergrüner grundwasserferner Laubwaldgesellschaften vom Naturraumpotenzial im Laacher Kuppenland als Grundlage für die Bewertung der naturräumlichen Zuordnung. An Anfang stand eine Vorstellung des Untersuchungsgebietes, indem die derzeit gültige Gliederung des Naturraumes, die geologischen Verhältnisse, Oberflächenformen und Formungsprozesse sowie Klima dargestellt wurden. Hieran schloss sich die vegetationskundlich-standörtliche Charakterisierung der Waldgesellschaften – Hainsimsen-Buchenwald (Luzulo-Fagetum), Hainsimsen-(Habichtskraut)- Traubeneichenwald (Luzulo luzuloides-Quercetum petraeae), Waldmeister-Buchenwald (Galio-Fagetum), Waldlabkraut-Eichen-Hainbuchenwald (Galio sylvatici-Carpinetum betuli), Eschen-Ahorn-Steinschuttschatthangwald (Fraxino-Aceretum pseudoplatani) und verschiedenartige Trauben-Eichen-Bestände – an. Den Beschreibungen lagen zahlreiche Vegetationsaufnahmen zu Grunde, die eine auf standörtlichen Unterschieden beruhende Differenzierung der Gesellschaften möglich machten. Die Waldtypen zeigten ein abgestuftes Maß an Natürlichkeit. Den naturnächsten Charakter - und daher das standörtliche Potenzial am besten anzeigend – wiesen die Rot-Buchen-dominierten Laubwaldgesellschaften sowie einige Eschen-Ahorn-Steinschuttschatthangwälder auf. Nutzungsbedingt naturferner waren Hainsimsen-(Habichtskraut)- Traubeneichenwald und Waldlabkraut-Eichen-Hainbuchenwald. Forstwirtschaftliche Ersatzgesellschaften von Buchenwaldgesellschaften waren im Untersuchungsgebiet verschiedenartige Trauben-Eichen-Bestände. Auf Grundlage der Untersuchungsergebnisse sowie einer Literaturauswertung erfolgte eine Bewertung des Anschlusses des Laacher Kuppenlandes an eine Gruppe von naturräumlichen Haupteinheiten. Sowohl das floristische als auch das vegetationskundliche Inventar untermauerten die These, dass das Laacher Vulkanbergland als Teilgebiet des Mittelrheinischen Becken zu betrachten ist. Abschließend wurden Betrachtungen zu Biodiversität und Naturschutz vorgenommen. Als deren Fazit wurde vorgeschlagen, einen Nationalpark einzurichten, um zum Erhalt und zur Förderung der Artenvielfalt beizutragen und um der internationalen Verantwortung Deutschlands für Buchenwaldökosysteme nachzukommen.
Diese Dissertation beschreibt Ökologie und Verhalten einer Hirschkäferpopulation im Moseltal im Bereich der Gemeinden Alf und Bullay (Kreis Cochem-Zell). Im Rahmen einer Kartierung werden darüber hinaus Vorkommen im nördlichen Rheinland-Pfalz dokumentiert. Grundlage der Untersuchung ist die Radiotelemetrie der adulten Hirschkäfer im Freiland. Die Anwendung dieser Methode liefert auch über den eigentlichen Untersuchungszweck hinausgehende quantitative und qualitative Erfahrungswerte für diese noch selten bei fliegenden Käfern angewendete Methode. Daneben werden Fundortmeldungen, Brutstättenmonitoring, Morphometrie und Insektarienuntersuchungen als ergänzende und vergleichende Methoden eingesetzt. Es erfolgt so eine quantitative Beschreibung geschlechtsspezifischer Verhaltenweisen adulter Hirschkäfer wie z. B. Aktivitäts-, Dispersions-und Fortpflanzungsverhalten, Habitatpräferenzen sowie eine Beschreibung der Entwicklungsabläufe im Bruthabitat. Die Ergebnisse zeichnen ein Bild vom Leben der Hirschkäfer, das von den bisherigen Vorstellungen weitgehend abweicht. Hirschkäfer brauchen Offenlandstrukturen und sind im Moseltal erfolgreiche Kulturfolger. Sie leben heute dort nahezu unbemerkt in der urbanen Landschaft. Die vielfach beschriebene enge Bindung an die Baumart Eiche ist keine zwingende Voraussetzung für eine erfolgreiche Populationsbildung. Im gesamten Fortpflanzungsverhalten kommt der Brutstätte eine zentrale Bedeutung zu, dabei ist die Vernetzung der Brutstätten eine Grundvoraussetzung. Das Fortpflanzungsverhalten unterliegt einer Regelstrategie, zu der es aber auch Alternativen gibt. Das beobachtete Dispersionsverhalten ermöglicht die Abgrenzung von Populationen. Für den Naturschutz ergeben sich aus den Ergebnissen Konsequenzen und Möglichkeiten für Schutzgebiete und die Anlage künstlicher Bruthabitate. Daneben wirft diese Untersuchung aber auch die Frage der Bewertung von Gefährdung und Seltenheit dieser Art als Ergebnis subjektiver Wahrnehmungen auf.
Diversität und Verbreitung von Schluchtwäldern (Tilio-Acerion) im Rheinischen Schiefergebirge
(2012)
Im Rahmen dieser Studie wurde die Diversität der Gefäßpflanzen von Edellaubmischwäldernrn im Rheinischen Schiefergebirge statistisch erfasst und dabei erstmalig deren Artenzusammensetzung anhand einer angewandten Standortanalyse soziologisch-floristisch beschrieben sowie deren Verbreitung im Einzugsbereich von unterer Mosel, unterer Lahn und dem Mittelrheingebiet zusammenfassend dargestellt.
Zudem war es Ziel dieser Untersuchung die Variabilität und Struktur der Artenzusammensetzung in Abhängigkeit von edaphischen und mikroklimatischen Umweltfaktoren auf Schiefer als anstehendem Gestein zu analysieren und diesbezüglich das Tilio-Acerion des Untersuchungsraums mit den bisher vorwiegend auf kalkhaltigem Untergrund untersuchten Edellaubmischwaldgesellschaften der übrigen deutschen Gebirge zu vergleichen. Mit Blick auf die Einstufung dieser Waldgesellschaft als "prioritären Lebensraum" innerhalb des NATURA 2000-Schutzgebietssystems und der an die FFH-Richtlinie gekoppelten Berichtspflicht von Rheinland-Pfalz, die alle 6 Jahre erfüllt werden muss,wurde die bisherige Einstufung der Ausprägung dieser Waldgesellschaft für die naturräumlichen Haupteinheiten im Untersuchungsraum revidiert. Dabei wurden auch anthropogene Gefährdungen untersucht und Schutzmaßnahmen für den Erhalt dieses in Mitteleuropa streng geschützten Fauna-Flora-Habitats diskutiert sowie Vorschläge zur Eingliederung von bisher unberücksichtigten Regionen in das NATURA 2000-Schutzgebietssystem abgegeben. Insgesamt wurden 191 Taxa in 1209 Aufnahmen erfasst und 29 Arten davon auf Grund ihrer Seltenheit oder Schutzwürdigkeit als bemerkenswert eingestuft. Des Weiteren wurden 3 Assoziationen und eine bisher noch unbekannte Festuca altissima-Tilia cordata-Gesellschaft beschrieben, wobei der überwiegende Teil der Aufnahmen dem Fraxino-Aceretum pseudoplatani zugeordnet wurde, das sich synsystematisch in weitere standörtlich bedingte Untereinheiten differenzieren lässt. Dabei hebt sich das Tilio-Acerion im Rheinischen Schiefergebirge gemeinsam mit Beständen weiterer silikatischer Gebirge von Edellaubmischwäldern auf karbonatischen Gebirgen in Deutschland durch säuretolerante Arten einer Polystichum aculeatum-Variante syntaxonomisch ab. Zudem konnte das in der Literatur bisher umstrittene Adoxo moschatellinae-Aceretum als eigene, dem Tilio-Acerion zugehörige Assoziation anhand von Kennarten wie dem im Untersuchungsraum hochsteten Polystichum aculeatum in der für die syntaxonomische Bewertung prioritären Krautschicht validiert werden. Regionale Unterschiede der Edellaubmischwälder sind im Untersuchungsgebiet anhand der dortigen Verbreitungsgrenzen submediterraner, (sub-)atlantischer und (sub-)kontinentaler Florenelemente erkennbar. Edaphische und mikroklimatische Faktoren haben sich als besonders einflussreich für diverse Ausprägungen der Schluchtwaldflora herausgestellt. Das Tilio-Acerion ist im Einzugsbereich der Mosel besonders artenreich, was lokal auch auf das Lahngebiet zutrifft. Der Straßen- und Wegebau wird als häufigste Gefährdung eingestuft, in den Tieflagen des oberen Mittelrhein- und Moselgebiets kommen Niederwald-Effekte in Form von haselreichen Degradationsstadien hinzu, in den Hochlagen sind Nadelwaldaufforstungen problematisch. Entsprechend wird gefordert derartige Maßnahmen sowie die Abholzung und Totholzentnahme in Edellaubmischwäldern zu vermeiden und diese sich stattdessen ihrer natürlichen Sukzession zu überlassen.
Die Studie hat gezeigt, dass die naturräumlichen Haupteinheiten Hunsrück, Westerwald, Taunus sowie das Mosel-, Lahn- und Mittelrheintal entgegen bisheriger Einstufung ein "Hauptvorkommen" an Schlucht- und Hangmischwäldern mit "guter Ausprägung" aufweisen.
Ecological assessment approaches based on benthic invertebrates in Euphrates tributaries in Turkey
(2019)
Sustainable water management requires methods for assessing ecological stream quality. Many years of limnological research are needed to provide a basis for developing such methods. However, research of this kind is still lacking in Turkey. Therefore, the aim of this doctoral thesis was to provide basic research in the field of aquatic ecology and to present methods for the assessment of ecological stream quality based on benthic invertebrates. For this purpose, I selected 17 tributaries of the Euphrates with a similar typology/water order and varying levels of pollution or not affected by pollution at all. The characterisation of the natural mountain streams was the first important step in the analysis of ecological quality. Based on community indices, I found that the five selected streams had a very good ecological status. I also compared the different biological indications, collected on two occasions ¬– once in spring (May) and once in autumn (September) – to determine the optimal sampling time. The macroinvertebrate composition differed considerably between the two seasons, with the number of taxa and Shannon index being significantly higher in autumn than in spring. In the final step, I examined the basal resources of the macroinvertebrates in the reference streams with an isotope analysis. I found that FPOM and biofilm were the most relevant basal resources of benthic invertebrates. Subsequently, based on the similarity of their community structures, I divided the 17 streams into three quality classes, supported by four community indices (EPT [%], EPTCBO [%], number of individuals, evenness). In this process, 23 taxa were identified as indicators for the three quality classes. In the next step, I presented two new or adapted indices for the assessment of quality class. Firstly, I adapted the Hindu Kush-Himalaya biotic index to the catchment area of the Euphrates and created a new, ecoregion-specific score list (Euph-Scores) for 93 taxa. The weighted ASPT values, which were renamed the Euphrates Biotic Score (EUPHbios) in this study, showed sharper differentiations of quality classes compared to the other considered ASPT values. Thus, this modified index has proved to be very effective and easy to implement in practical applications. As a second biological index, I suggested the proportion of habitat specialists. To calculate this index, the habitat preferences of the 20 most common benthic invertebrates were identified using the new habitat score. The proportion of habitat specialists differed significantly among the three quality classes with higher values in natural streams than in polluted streams. The methods and results presented in this doctoral thesis can be used in a multi-metric index for a Turkish assessment programme.
Because silver nanoparticles (Ag NPs) are broadly applied in consumer products, their leaching will result in the continuous release of Ag NPs into the natural aquatic environment. Therefore, bacterial biofilms, as the prominent life form of microorganisms in the aquatic environment, are most likely confronted with Ag NPs as a pollutant stressor. Notwithstanding the significant ecological relevance of bacterial biofilms in aquatic systems, and though Ag NPs are expected to accumulate within these biofilms in the environment, the knowledge on the environmental and ecological impact of Ag NPs, is still lagging behind the industrial growth of nanotechnology. Consequently, aim of this thesis was to perform effect assessment of Ag NP exposure on bacterial biofilms with ambient Ag NPs concentrations and under environmentally relevant conditions. Therefore, a comprehensive set of methods was applied in this work to study if and how Ag NPs of two different sizes (30 and 70 nm) affect bacterial biofilms i.e. both monospecies biofilms and freshwater biofilms in environmentally relevant concentrations (600 - 2400 µg l-1). Within the first part of this work, a newly developed assay to test the mechanical stability of
monospecies biofilms of the freshwater model bacterium Aquabacterium citratiphilum was validated. In the first study, to investigate the impact of Ag NPs on the mechanical stability of bacterial biofilms, sublethal effects on the mechanical stability of the biofilms were observed with negative implications for biostabilization. Furthermore, as it is still challenging to monitor the ecotoxicity of Ag NPs in natural freshwater environments, a mesocosm study was performed in this work to provide the possibility for the detailed investigation of effects of Ag NPs on freshwater biofilms under realistic environmental conditions. By applying several approaches to analyze biofilms as a whole in response to Ag NP treatment, insights into the resilience of bacterial freshwater biofilms were obtained. However, as revealed by t-RFLP fingerprinting combined with phylogenetic studies based on the 16S gene, a shift in the bacterial community composition, where Ag NP-sensitive bacteria were replaced by more Ag NP-tolerant species with enhanced adaptability towards Ag NP stress was determined. This shift within the bacterial community may be associated with potential detrimental effects on the functioning of these biofilms with respect to nutrient loads, transformation and/or degradation of pollutants, and biostabilization. Overall, bringing together the key findings of this thesis, 4 general effect mechanisms of Ag NP treatment have been identified, which can be extrapolated to natural freshwater biofilms i.e. (i) the identification of Comamonadaceae as Ag NP-tolerant, (ii) a particular resilient behaviour of the biofilms, (iii) the two applied size fractions of Ag NPs exhibited similar effects independent of their sizes and their synthesis method, and (iv) bacterial biofilms show a high uptake capacity for Ag NPs, which indicates cumulative enrichment.