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Institut
- Fachbereich 7 (93) (entfernen)
Agricultural land-use may lead to brief pulse exposures of pesticides in edge-of-field streams, potentially resulting in adverse effects on aquatic macrophytes, invertebrates and ecosystem functions. The higher tier risk assessment is mainly based on pond mesocosms which are not designed to mimic stream-typical conditions. Relatively little is known on exposure and effect assessment using stream mesocosms.
Thus the present thesis evaluates the appliacability of the stream mesocosms to mimic stream-typical pulse exposures, to assess resulting effects on flora and fauna and to evaluate aquatic-terrestrial food web coupling. The first objective was to mimic stream-typical pulse exposure scenarios with different durations (≤ 1 to ≥ 24 hours). These exposure scenarios established using a fluorescence tracer were the methodological basis for the effect assessment of an herbicide and an insecticide. In order to evaluate the applicability of stream mesocosms for regulatory purposes, the second objective was to assess effects on two aquatic macrophytes following a 24-h pulse exposure with the herbicide iofensulfuron-sodium (1, 3, 10 and 30 µg/L; n = 3). Growth inhibition of up to 66 and 45% was observed for the total shoot length of Myriophyllum spicatum and Elodea canadensis, respectively. Recovery of this endpoint could be demonstrated within 42 days for both macrophytes. The third objective was to assess effects on structural and functional endpoints following a 6-h pulse exposure of the pyrethroid ether etofenprox (0.05, 0.5 and 5 µg/L; n = 4). The most sensitive structural (abundance of Cloeon simile) and functional (feeding rates of Asellus aquaticus) endpoint revealed significant effects at 0.05 µg/L etofenprox. This concentration was below field-measured etofenprox concentrations and thus suggests that pulse exposures adversely affect invertebrate populations and ecosystem functions in streams. Such pollutions of streams may also result in decreased emergence of aquatic insects and potentially lead to an insect-mediated transfer of pollutants to adjacent food webs. Test systems capable to assess aquatic-terrestrial effects are not yet integrated in mesocosm approaches but might be of interest for substances with bioaccumulation potential. Here, the fourth part provides an aquatic-terrestrial model ecosystem capable to assess cross-ecosystem effects. Information on the riparian food web such as the contribution of aquatic (up to 71%) and terrestrial (up to 29%) insect prey to the diet of the riparian spider Tetragnatha extensa was assessed via stable isotope ratios (δ13C and δ15N). Thus, the present thesis provides the methodological basis to assess aquatic-terrestrial pollutant transfer and effects on the riparian food web.
Overall the results of this thesis indicate, that stream mesocosms can be used to mimic stream-typical pulse exposures of pesticides, to assess resulting effects on macrophytes and invertebrates within prospective environmental risk assessment (ERA) and to evaluate changes in riparian food webs.
The intention of this thesis was to characterise the effect of naturally occurring multivalent cations like Calcium and Aluminium on the structure of Soil Organic Matter (SOM) as well as on the sorption behaviour of SOM for heavy metals such as lead.
The first part of this thesis describes the results of experiments in which the Al and Ca cation content was changed for various samples originated from soils and peats of different regions in Germany. The second part focusses on SOM-metal cation precipitates to study rigidity in dependence of the cation content. In the third part the effects of various cation contents in SOM on the binding strength of Pb cations were characterised by using a cation exchange resin as desorption method.
It was found for soil and peat samples as well as precipitates that matrix rigidity was affected by both type and content of cation. The influence of Ca on rigidity was less pronounced than the influence of Al and of Pb used in the precipitation experiments. For each sample one cation content was identified where matrix rigidity was most pronounced. This specific cation content is below the cation saturation as expected by cation exchange capacity. These findings resulted in a model describing the relation between cation type, content and the degree of networking in SOM. For all treated soil and precipitate samples a step transition like glass transition was observed, determined by the step transition temperature T*. It is known from literature that this type of step transition is due to bridges between water molecules and organic functional groups in SOM. In contrast to the glass transition temperature this thermal event is slowly reversing after days or weeks depending on the re-conformation of the water molecules. Therefore, changes of T* with different cation compositions in the samples are explained by the formation of water-molecule-cation bridges between SOM-functional groups. No influence on desorption kinetics of lead for different cation compositions in soil samples was observed. Therefore it can be assumed that the observed changes of matrix rigidity are highly reversible by changing the water status, pH or putting agitation energy by shaking in there.
Agriculture covers one third of the world land area and has become a major source of water pollution due to its heavy reliance on chemical inputs, namely fertilisers and pesticides. Several thousands of tonnes of these chemicals are applied worldwide annually and partly reach freshwaters. Despite their widespread use and relatively unspecific modes of action, fungicides are the least studied group of pesticides. It remains unclear whether the taxonomic groups used in pesticide risk assessment are protective for non-target freshwater fungi. Fungi and bacteria are the main microbial decomposers converting allochthonous organic matter (litter) into a more nutritious food resource for leaf-shredding macroinvertebrates. This process of litter decomposition (LD) is central for aquatic ecosystem because it fuels local and downstream food webs with energy and nutrients. Effects of fungicides on decomposer communities and LD have been mainly analysed under laboratory conditions with limited representation of the multiple factors that may moderate effects in the field.
In this thesis a field study was conducted in a German vineyard area to characterise recurrent episodic exposure to fungicides in agricultural streams (chapter 2) and its effects on decomposer communities and LD (chapter 3). Additionally, potential interaction effects of nutrient enrichment and fungicides on decomposer communities and LD were analysed in a mesocosm experiment (chapter 4).
In the field study event-driven water sampling (EDS) and passive sampling with EmporeTM styrene-divinylbenzene reverse phase sulfonated disks (SDB disks) were used to assess exposure to 15 fungicides and 4 insecticides. A total of 17 streams were monitored during 4 rainfall events within the local application period of fungicides in 2012. EDS exceeded the time-weighted average concentrations provided by the SDB disks by a factor of 3, though high variability among compounds was observed. Most compounds were detected in more than half of the sites and mean and maximum peak (EDS) concentrations were under 1 and 3 µg/l, respectively. Besides, SDB disk-sampling rates and a free-software solution to derive sampling rates under time-variable exposure were provided.
Several biotic endpoints related to decomposers and LD were measured in the same sampling sites as the fungicide monitoring, coinciding with the major litter input period. Our results suggest that polar organic fungicides in streams change the structure of the fungal community. Causality of this finding was supported by a subsequent microcosm experiment. Whether other effects observed in the field study, such as reduced fungal biomass, increased bacterial density or reduced microbial LD can be attributed to fungicides remains speculative and requires further investigation. By contrast, neither the invertebrate LD nor in-situ measured gammarid feeding rates correlated with water-borne fungicide toxicity, but both were negatively associated with sediment copper concentrations. The mesocosm experiment showed that fungicides and nutrients affect microbial decomposers differently and that they can alter community structure, though longer experiments are needed to determine whether these changes may propagate to invertebrate communities and LD. Overall, further studies should include representative field surveys in terms of fungicide pollution and physical, chemical and biological conditions. This should be combined with experiments under controlled conditions to test for the causality of field observations.
Rivers play an important role in the global water cycle, support biodiversity and ecological integrity. However, river flow and thermal regimes are heavily altered in dammed rivers. These impacts are being exacerbated and become more apparent in rivers fragmented by multiple dams. Recent studies mainly focused on evaluating the cumulative impact of cascade reservoirs on flow or thermal regimes, but the role of upstream reservoirs in shaping the hydrology and hydrodynamics of downstream reservoirs remains poorly understood. To improve the understanding of the hydrodynamics in cascade reservoirs, long-term observational data are used in combination with numerical modeling to investigate the changes in flow and thermal regime in three cascade reservoirs at the upper reach of the Yangtze River. The three studied reservoirs are Xiluodu (XLD), Xiangjiaba (XJB) and Three Gorges Reservoir (TGR). In addition, the effects of single reservoir operation (at seasonal/daily time scale) on hydrodynamics are examined in a large tributary of TGR. The results show that the inflow of TGR has been substantially altered by the two upstream reservoirs with a higher discharge in spring and winter and a reduced peak flow in summer. XJB had no obvious contribution to the variations in inflow of TGR. The seasonal water temperature of TGR was also widely affected by the upstream two reservoirs, i.e., an increase in winter and decrease in spring, associated with a delay in water temperature rise and fall. These effects will probably be intensified in the coming years due to the construction of new reservoirs. The study also underlines the importance of reservoir operation in shaping the hydrodynamics of TGR. The seasonal dynamics of density currents in a tributary bay of TGR are closely related to seasonal reservoir operations. In addition, high-frequency water level fluctuations and flow velocity variations were observed in response to periodic tributary bay oscillations, which are driven by the diurnal discharge variations caused by the operation of TGR. As another consequence of operation of cascade reservoirs, the changes in TGR inflow weakened spring thermal stratification and caused warming in spring, autumn and winter. In response to this change, the intrusions from TGR occurred more frequently as overflow and earlier in spring, which caused a sharp reduction in biomass and frequency of phytoplankton blooms in tributary bays of TGR. This study suggests that high-frequency bay oscillations can potentially be used as an efficient management strategy for controlling algal blooms, which can be included in future multi-objective ecological conservation strategies.
World’s ecosystems are under great pressure satisfying anthropogenic demands, with freshwaters being of central importance. The Millennium Ecosystem Assessment has identified anthropogenic land use and associated stressors as main drivers in jeopardizing stream ecosystem functions and the
biodiversity supported by freshwaters. Adverse effects on the biodiversity of freshwater organisms, such as macroinvertebrates, may propagate to fundamental ecosystem functions, such as organic matter breakdown (OMB) with potentially severe consequences for ecosystem services. In order to adequately protect and preserve freshwater ecosystems, investigations regarding potential and observed as well as direct and indirect effects of anthropogenic land use and associated stressors (e.g. nutrients, pesticides or heavy metals) on ecosystem functioning and stream biodiversity are needed. While greater species diversity most likely benefits ecosystem functions, the direction and magnitude of changes in ecosystem functioning depends primarily on species functional traits. In this context, the functional diversity of stream organisms has been suggested to be a more suitable predictor of changes in ecosystem functions than taxonomic diversity.
The thesis aims at investigating effects of anthropogenic land use on (i) three ecosystem functions by anthropogenic toxicants to identify effect thresholds (chapter 2), (ii) the organic matter breakdown by three land use categories to identify effects on the functional level (chapter 3) and (iii)on the stream community along an established land-use gradient to identify effects on the community level.
In chapter 2, I reviewed the literature regarding pesticide and heavy metal effects on OMB, primary production and community respiration. From each reviewed study that met inclusion criteria, the toxicant concentration resulting in a reduction of at least 20% in an ecosystem function was standardized based on laboratory toxicity data. Effect thresholds were based on the relationship between ecosystem functions and standardized concentration-effect relationships. The analysis revealed that more than one third of pesticide observations indicated reductions in ecosystem functions at concentrations that are assumed being protective in regulation. However, high variation within and between studies hampered the derivation of a concentration-effect relationship and thus effect thresholds.
In chapter 3, I conducted a field study to determine the microbial and invertebrate-mediated OMB by deploying fine and coarse mesh leaf bags in streams with forested, agricultural, vinicultural
and urban riparian land use. Additionally, physicochemical, geographical and habitat parameters were monitored to explain potential differences in OMB among land use types and sites. Regarding results, only microbial OMB differed between land use types. The microbial OMB showed a negative relationship with pH while the invertebrate-mediated OMB was positively related to tree cover. OMB responded to stressor gradients rather than directly to land use.
In chapter 4, macroinvertebrates were sampled in concert with leaf bag deployment and after species identification (i) the taxonomic diversity in terms of Simpson diversity and total taxonomic
richness (TTR) and (ii) the functional diversity in terms of bio-ecological traits and Rao’s quadratic entropy was determined for each community. Additionally, a land-use gradient was established and the response of the taxonomic and functional diversity of invertebrate communities along this gradient was investigated to examine whether these two metrics of biodiversity are predictive for the rate of OMB. Neither bio-ecological traits nor the functional diversity showed a significant relationship with
OMB. Although, TTR decreased with increasing anthropogenic stress and also the community structure and 26 % of bio-ecological traits were significantly related to the stress gradient, any of these shifts propagated to OMB.
Our results show that the complexity of real-world situations in freshwater ecosystems impedes the effect assessment of chemicals and land use for functional endpoints, and consequently our potential to predict changes. We conclude that current safety factors used in chemical risk assessment may not be sufficient for pesticides to protect functional endpoints. Furthermore, simplifying real-world stressor gradients into few land use categories was unsuitable to predict and quantify losses in OMB. Thus, the monitoring of specific stressors may be more relevant than crude land use categories to detect effects on ecosystem functions. This may, however, limit the large scale assessment of the status of OMB. Finally, despite several functional changes in the communities the functional diversity over several trait modalities remained similar. Neither taxonomic nor functional diversity were suitable predictors of OMB. Thus, when understanding anthropogenic impacts on the linkage between biodiversity and ecosystem functioning is of main interest, focusing on diversity metrics that are clearly linked to the stressor in question (Jackson et al. 2016) or integrating taxonomic and functional metrics (Mondy et al., 2012) might enhance our predictive capacity.
Während es eine Vielzahl von Arbeiten zu der technologischen Entwicklung im Bereich der erneuerbaren Energien gibt, fehlt es jedoch bislang an einer mikroökonomischen Analyse
der Verhaltensmuster der Akteure im Umfeld von Anlagen nach dem EEG. Als Akteure kommen hier in erster Linie der Anlagenbetreiber selbst und der Staat in Betracht.
Im Hinblick auf Anlagenbetrieb und Vergütung der erzeugten Energie können beide mit unterschiedlichsten Interessen und Nutzenkalkülen aufeinander treffen. Diese Arbeit untersucht
mikroökonomische Aspekte des EEG-Förderungssystems. Im Mittelpunkt der Betrachtung stehen die Förderungsmechanismen für Biogasanlagen, die im Hinblick auf mögliche Prinzipal-Agenten-Konflikte einer Untersuchung unterzogen werden.
Invasive species play increasing roles worldwide. Invasions are considered successful when species establish and spread in their exotic range. Subsequently, dispersal is a major determinant of species’ range dynamics. Mermessus trilobatus, native to North America, has rapidly spread in Europe via aerial dispersal. Here we investigated the interplay of ecological and evolutionary processes behind its colonisation success.
First, we examined two possible ecological mechanisms. Similar to other invasive invertebrates, the colonisation success of Mermessus trilobatus might be related to human-induced habitat disturbance. Opposite to this expectation, our results showed that densities of Mermessus trilobatus decreased with soil disturbance in grasslands suggesting that its invasion success was not connected to a ruderal strategy. Further, invasive species often escape the ecological pressures from novel enemies in their exotic ranges. Unexpectedly, invasive Mermessus trilobatus was more sensitive to a native predator than native Erigone dentipalpis during our predator susceptibility trials. This indicates that the relation between the invasive spider and its native predator is dominated by prey naïveté rather than enemy release.
The remaining three chapters of the thesis investigated the dispersal behaviour of this invasive species. Hitherto, studies of passive aerial dispersal used wind as the primary dispersal-initiating factor despite a recent demonstration of the effects of the atmospheric electric fields on spiders’ pre-dispersal behaviour. During our experiments, only the wind facilitated the flight, although electric fields induced pre-dispersal behaviour in spiders. Consequently, studies around passive aerial dispersal should control electric fields but use wind as a stimulating factor.
Rapidly expanding species might be disproportionately distributed in their exotic range, with an accumulation of dispersive genotypes at the leading edge of their range. Such imbalanced spatial segregation is possible when the dispersal behaviour of expanding species is heritable. Our results showed that the dispersal traits of Mermessus trilobatus were heritable through both parents and for both sexes with recessive inheritance of high dispersal ability in this species.
Following the heritability experiments, we documented an accelerated spread of Mermessus trilobatus in Europe and tested whether dispersal, reproduction or competing ability was at the source of this pattern. Our results showed that the accumulation of more mobile but not reproductive or competitive genotypes at the expansion front of this invasive species gave rise to an accelerated range expansion by more than 1350 km in under 45 years.
Invasive Mermessus trilobatus is inferior to native sympatric species with respect to competing ability (Eichenberger et al., 2009), disturbance tolerance and predation pressure. Nevertheless, the species successfully established in its exotic range and spread by accelerating its expansion rate. Rapid reproduction that balances the high ecological pressures might be the other potential mechanism behind its colonisation success in Europe and deserves further investigation.
Weltweit sind ein Drittel bis die Hälfte der Flusskrebsarten von Populationsrückgang oder Aussterben bedroht. Neben einer Verschlechterung der Habitate, Umweltverschmutzung und anderen vom Menschen verursachten Umweltveränderungen stellen eingeschleppte exotische Arten und Krankheitserreger eine große Bedrohung für das Überleben europäischer Flusskrebsarten dar. Flusskrebse sind die größten Wirbellosen in limnischen Systemen und haben einen entsprechend großen Einfluss auf die Struktur der Nahrungsnetze. Das Verschwinden von Flusskrebsen aus einem Gewässer kann Nahrungsnetze verändern und somit dramatische Konsequenzen für ein Ökosystem zur Folge haben. Ein Ziel im modernen Artenschutz ist die Erhaltung der genetischen Vielfalt. Eine hohe genetische Vielfalt ist für das langfristige Überleben einer Art von Vorteil.
Das Hauptziel meiner Arbeit war es, die genetische Struktur des gefährdeten Edelkrebses (Astacus astacus) in seinem europäischen Verbreitungsgebiet zu untersuchen und die besonders schützenswerten genetische 'Hotspots' zu identifizieren (Teil 1 der Dissertation). Die größte Bedrohung für die Diversität europäischer Flusskrebsarten stellt der Krebspesterreger Aphanomyces astaci dar. Daher muss die Verbreitung des Krankheitserregers bei Schutzprogrammen beachtet werden.
Im zweiten Teil der Dissertation untersuchte ich neue Aspekte der Verbreitung von A. astaci. Die Ergebnisse dienen als Grundlage für zukünftige Artenschutzprogramme für Flusskrebse.
Im ersten Teil dieser Arbeit führte ich eine phylogeographische Analyse der Edelkrebse durch, um genetische 'Hotspots' zu identifizieren und die nacheiszeitliche Wiederbesiedlung Zentraleuropas durch diese Art zu rekonstruieren. Mit mitochondrialer DNA und nuklearen Mikrosatelliten-Markern ermittelte ich eine hohe genetische Vielfalt in Südosteuropa, die darauf hinweist, dass der Edelkrebs die kalten Klimaphasen des Pleistozäns in diesem Gebiet überdauerte (Appendix 1). Wegen der hohen genetischen Vielfalt ist Südosteuropa von besonderer Bedeutung für den Schutz des Edelkrebses. Die mitochondriale DNA-Analyse deutet auf eine gegabelte Kolonisierung vom unteren Donaueinzugsgebiet in a) das Einzugsgebiet der Nordsee und b) das Einzugsgebiet der Ostsee hin (Kapitel 2). Ein zweites, unabhängiges Refugium, welches im westlichen Balkan lokalisiert wurde, hat vermutlich nicht zur Besiedlung Mitteleuropas beigetragen. Außerdem stellte ich fest, dass die natürliche genetische Struktur teilweise überlagert ist, wahrscheinlich aufgrund des hohen menschlichen Einflusses auf die Verbreitung des Edelkrebses (bspw. künstliche Translokation). Im zweite Teil dieser Arbeit konnte ich mittels real-time-PCR ermitteln, dass neben den bekannten drei nordamerikanischen Flusskrebsarten auch Kalikokrebse (Orconectes immunis) Träger des Krebspesterregers sind (Kapitel 3). Des Weiteren habe ich den Krebspesterrreger in der unteren Donau in Rumänien an amerikanischen Kamberkrebsen (Orconectes limosus) und europäischen Galizierkrebsen (Astacus leptodactylus) nachweisen können (Kapitel 4). Die Ausbreitung der infizierten Kamberkrebse bis in die untere Donau stellt eine große Bedrohung für die Artenvielfalt in Südosteuropa dar und zeigt das hohe Invasionspotential der Kamberkrebse. Darüber hinaus stellte ich fest, dass auch einheimische Galizierkrebse im Donaudelta, etwa 970 km hinter der aktuellen Invasionsfront des Kamberkrebses, Träger von A. astaci sind (Kapitel 5). Diese Erkenntnis ist von besonderer Bedeutung, da die einheimischen Arten offenbar nicht an der Infektion leiden. Die Untersuchung koexistierender Populationen europäischer und amerikanischer Flusskrebse ergab, dass die Abwesenheit des Krebspesterregers in diesen Populationen die wahrscheinlichste Erklärung für die erfolgreiche Koexistenz in den untersuchten Gewässern in Mitteleuropa ist (Kapitel 6). Die Ergebnisse meiner Dissertation zeigen neue Aspekte, die von hoher Relevanz für den Schutz und Erhalt einheimischer Flusskrebsarten und deren genetischer Vielfalt sind: 1)Die genetische Diversität des Edelkrebses ist in Südosteuropa am höchsten. Dort überdauerten Edelkrebse die letzte Eiszeit in mindestens zwei unabhängigen Refugien. 2) Nicht alle amerikanischen Flusskrebspopulationen sind Träger der Krebspest und 3) nicht alle europäischen Flusskrebspopulationen sterben innerhalb kurzer Zeit an einer Infizierung mit dem Krebspesterreger. Um einheimische Flusskrebse und deren (genetische) Vielfalt langfristig zu erhalten, dürfen keine weiteren amerikanischen Flusskrebse in der Natur ausgesetzt werden. Das unbefugte Aussetzen wird jedoch erst zurückgehen, wenn der Handel mit exotischen Flusskrebsen verboten wird.
Auf landwirtschaftlichen Flächen ausgebrachte Pflanzenschutzmittel (PSM) können über diffuse Eintragswege (z.B. Oberflächenabfluss) auch in Gewässer gelangen, und eine Bedrohung für die aquatische Lebensgemeinschaft darstellen. Zum Schutz der aquatischen Gemeinschaft werden im derzeitigen Verfahren der deutschen PSM-Zulassung bereits bei Bedarf spezifische Anwendungsbestimmungen festgelegt. Über diese Maßnahmen hinaus, können jedoch weitere Ansätze sinnvoll sein.
Vor diesem Hintergrund wurden in der vorliegenden Dissertation Gewässer innerhalb einer Acker- und einer Weinanbauregion in Deutschland hinsichtlich ihrer PSM-Exposition in Folge von Oberflächenabfluss und (mögliche) Effekte auf aquatische Makroinvertebraten untersucht, um zu überprüfen, ob eine Umsetzung von Risikominderungsmaßnahmen in diesen Gebieten notwendig wäre. Die Ergebnisse zeigten, dass Gewässer in beiden Gebieten PSM-Konzentrationen ausgesetzt sind, in Folge derer Effekte auf die Makroinvertebraten zu erwarten sind. In der Ackeranbauregion war die beobachtete Toxizität dabei überwiegend auf die Insektizide Lambda-Cyhalothrin (in der Wasserphase) und Alpha-Cypermethrin (in der Sedimentphase) zurückzuführen. In der Weinanbauregion waren dagegen Rückstände von Fungiziden von übergeordneter Bedeutung und neben organischen Fungiziden wurden in diesen Gewässern außerdem ökotoxikologisch bedenkliche Kupferkonzentrationen in der Wasser- als auch in der Sedimentphase gefunden. In der Ackeranbauregion wurden neben der PSM-Exposition auch Effekte der PSM auf die Gemeinschaft der aquatischen Gemeinschaften im Freiland untersucht. Die Makroinvertebratengemeinschaft wurde insgesamt überwiegend von, gegenüber PSM toleranten Arten dominiert, was eine hohe PSM-Exposition an allen Probestellen vermuten lässt. Diese Vermutung spiegelt sich auch in den erhöhten PSM-Rückständen wider (logTUMax > -2; TUMax: Maximale Toxic Unit per sample), die in den Proben der Sedimentphase festgestellt wurden. An zwei Probestellen nahm die Abundanz und Anzahl sensitiver Arten (indiziert durch das SPEcies At Risk-Indikatorsystem) in Folge toxischer Lambda-Cyhalothrinkonzentrationen in der Wasserphase (logTUMax > -0,6) ab. An gering mit PSM belasteten Gewässern (logTUMax < -3,5) konnte dagegen eine signifikante Beeinträchtigung sensitiver Makroinvertebraten nicht festgestellt werden. Insgesamt zeigen die Ergebnisse, dass in beiden Untersuchungsgebieten die Umsetzung von Maßnahmen zum Schutz der aquatischen Gemeinschaft notwendig wäre.
Für Oberflächenabfluss werden häufig bewachsene Uferrandstreifen als Minderungsmaßnahme vorgeschlagen. Ein mindernder Einfluss auf die PSM-Konzentration mit zunehmender Breite konnte jedoch für die bereits in den Untersuchungsregionen vorhandenen Uferrandstreifen nicht festgestellt werden. Dieses Ergebnis konnte in der Weinanbauregion auf die hohe Anzahl an befestigten Feldwegen und damit verbundener Wegeinleitungen zurückgeführt werden, die den Oberflächenabfluss in konzentrierter Form zügig in Richtung Gewässer ableiten, und damit die Reduktionseffektivität der Uferrandstreifen erheblich reduzieren. Ein ähnlicher Prozess fand vermutlich auch in der Ackeranbauregion statt, in Folge einer hohen Anzahl an Erosionsrillen, die ein flächenhaftes Eindringen des Oberflächenabflusses in den Randstreifen und damit eine effektive Filterung verhindern. Außerdem dürften Entwässerungsgräben, welche den Oberflächenabfluss von den landwirtschaftlichen Flächen in die Gewässer weiterleiten, zu den beobachteten PSM-Konzentrationen trotz breiter Uferrandstreifen beigetragen haben.
Um PSM-Einträge über Oberflächenabfluss effektiv zu reduzieren, sollten Risikominderungsmaßnahmen umgesetzt werden, die auf die jeweilig identifizierten Haupteintragswege fokussieren. Als geeignete Maßnahmen wurden mit Gras bewachsene Feldwege und bewachsene Gräben oder Rückhaltebecken identifiziert. Darüber hinaus kann auch die Optimierung bereits vorhandener Uferrandstreifen hinsichtlich ihrer Reduktionseffektivität sinnvoll sein. Insgesamt zeigen die Daten der beiden Freilanduntersuchungen die große Bedeutung, Maßnahmen spezifisch für die jeweilige PSM-Belastungssituation von Gewässern zu identifizieren. Um diesen Prozess zu unterstützen wurde im Rahmen der vorliegenden Dissertation ein Leitfaden für die Identifizierung geeigneter Risikominderungsmaßnahmen an belasteten Gewässern entwickelt. Basierend auf einer Kartierung expositionsrelevanter landschaftlicher Parameter wird ein Set an geeigneten Maßnahmen für die jeweilige Belastungssituation vorgeschlagen. Anhand einer Bewertung der Effektivität dieser Maßnahmen PSM-Einträge zu reduzieren, ihrer Umsetzbarkeit und zu erwartenden Akzeptanz kann der Anwender schließlich die jeweiligen Maßnahmen zur Umsetzung auswählen. Der Leitfaden leistet damit einen wichtigen Beitrag zur praktischen Implementierung von Minderungsmaßnahmen.
Diet-related effects of antimicrobials in aquatic decomposer-shredder and periphyton-grazer systems
(2022)
Leaf-associated microbial decomposers as well as periphyton serve as important food sources for detritivorous and herbivorous macroinvertebrates (shredders and grazers) in streams. Shredders and grazers, in turn, provide not only collectors with food but also serve as prey for predators. Therefore, decomposer-shredder and periphyton-grazer systems (here summarized as freshwater biofilm-consumer systems) are highly important for the energy and nutrient supply in heterotrophic and autotrophic stream food webs. However, both systems can be affected by chemical stressors, amongst which antimicrobials (e.g., antibiotics, fungicides and algaecides) are of particular concern. Antimicrobials can impair shredders and grazers not only via waterborne exposure (waterborne effect pathway) but also through dietary exposure and microorganism-mediated alterations in the food quality of their diet (dietary effect pathway). Even though the relevance of the latter pathway received more attention in recent years, little is known about the mechanisms that are responsible for the observed effects in shredders and grazers. Therefore, the first objective of this thesis was to broaden the knowledge of indirect antimicrobial effects in a model shredder and grazer via the dietary pathway. Moreover, although freshwater biofilm-consumer systems are most likely exposed to antimicrobial mixtures comprised of different stressor groups, virtually nothing is known of these mixture effects in both systems. Therefore, the second objective was to assess and predict diet-related antimicrobial mixture effects in a model freshwater biofilm-consumer system. During this thesis, positive diet-related effects of a model antibiotic on the energy processing and physiology of the shredder Gammarus fossarum were observed. They were probably triggered by shifts in the leaf-associated microbial community in favor of aquatic fungi that increased the food quality of leaves for the shredder. Contrary to that, a model fungicide induced negative effects on the energy processing of G. fossarum via the dietary pathway, which can be explained by negative impacts on the microbial decomposition efficiency leading to a reduced food quality of leaf litter for gammarids. For diet-related antimicrobial effects in periphyton-grazer systems, a model algaecide altered the periphyton community composition by increasing nutritious and palatable algae. This resulted in an enhanced consumption and physiological fitness of the grazer Physella acuta. Finally, it was shown that complex horizontal interactions among leaf-associated microorganisms are involved, making diet-related antimicrobial mixture effects in the shredder G. fossarum difficult to predict. Thus, this thesis provides new insights into indirect diet-related effects of antimicrobials on shredders and grazers as well as demonstrates uncertainties of antimicrobial mixture effect predictions for freshwater biofilm-consumer systems. Moreover, the findings in this thesis are not only informative for regulatory authorities, as indirect effects and effects of mixtures across chemical classes are not considered in the environmental risk assessment of chemical substances, but also stimulate future research to close knowledge gaps identified during this work.