Doctoral Research Projects

PhD project: Stress transfer across communities

Working title: Transfer of environmental stress across ecosystems: community and species response to aquatic fungicide or insecticide load.

 

Supervising scientists: Klaus Schwenk, Kathrin Theissinger and Lorenz Fahse.

 

Doctoral researcher: Nina Röder

 

Approach: Genetic variation, whether intraspecific or interspecific, largely determines a communities vulnerability to environmental stress. This project aims to study the impact of agricultural pesticides on aquatic and terrestrial communities in riparian ecosystems.

 

Contact: Klaus SchwenkMolecular Ecology

Genetic variation, whether intraspecific or interspecific, largely determines a communities’s vulnerability to environmental stress. Likewise, environmental stress can lead to a shift in the gene pool, with potential effects on ecological traits and interlinked species.

 

This project aims to study the impact of agricultural pesticides on aquatic and terrestrial communities in riparian ecosystems. We will focus on potential pesticide-induced shifts in the aquatic community, which may have an impact on adjoining terrestrial ecosystems. We will use molecular techniques like DNA-(meta)barcoding and metagenomic high‐throughput sequencing approaches, providing valuable insights into the genetic structure of natural communities.

 

In a pilot study, laboratory batch-scale experiments will give general insights on the effects of pesticides on aquatic community structures, and in particular on the model organism Chironomus riparius. Besides lethal effects and reproductive deficiencies, allele frequency changes will be evaluated. During the second project phase, we plan to test the effect of pesticides on pre-exposed and naive C. riparius populations in common garden experiments. We are planning to analyse the different populations’ viability and reproductive success across a pollution gradient. The results of the scheduled experiments will allow for conclusions regarding the potential adaptation and/or pesticide-induced genetic drift of C. riparius populations. At the final stage, the study will be augmented by performing experiments at the SystemLink riparian stream mesocosm (RSM). In this site-scale experiment, more complex effects of agricultural pesticides will be studied with special regard to species composition shifts in a diverse aquatic community. In addition, we will assess potential top-down directed effects in terrestrial systems via joint analyses of species composition, ecological traits and fitness across both ecosystems.

PhD project: Amphibian ecology​

Working title: Direct and indirect effects of  Bacillus thuringiensis israelensis (Bti) on the European common frog (Rana temporaria) and palmate newt (Lissotriton helveticus)

 

Supervising scientists: Carsten A. Brühl, Martin H. Entling, Kathrin Theissinger.

 

Doctoral researcher: Verena Gerstle

 

Approach: The mosquito control agent Bti has been applied in the floodplain areas on the Upper Rhine. Although it is primarily toxic to larvae of the family Nematocera, negative effects on amphibians on their food web have been observed in laboratory and microcosm studies. The aim of this PhD project is to investigate the effects of anthropogenic stressors like Bti on the food web of amphibians and their role for higher trophic levels in terrestrial ecosystems.

 

Contact: Carsten A. BrühlCommunity Ecology and Ecotoxicology

The mosquito control agent Bti has been applied in the floodplain areas on the Upper Rhine for more than 40 years. Although it is primarily toxic to larvae of the family Nematocera due to its specific mode of action, negative effects on amphibians on their food web have been observed in laboratory and microcosm studies.

 

Since Bti is directly applied into surface waters which also function as breeding habitats for amphibians, the aim of this PhD project is to investigate effects of anthropogenic stressors like Bti on the food web of amphibians and their role for higher trophic levels in terrestrial ecosystems. It is hypothesized that Bti reduces the food quality for amphibians, thus causing temporal emergence shifts. Using the floodplain mesocosms in Eußerthal, we will assess the impact of multiple Bti applications on temporal emergence patterns (phenology) of both amphibians as well as direct effects on different stages of larval R. temporaria and indirect effects on the food web of aquatic R. temporaria and L. helveticus larvae. Therefore, the field experiment is divided into two approaches: (1) Determination of direct sublethal effects using frog larvae in cages for oxidative stress (ROS) and related enzymatic biomarkers, e.g. Glutathione-S-Transferase and Hsp70, and (2) indirect effects on the food web using freely swimming frog and newt larvae for measurements of fatty acids, stable isotopes, proteins and total energy content. Additionally, body mass, length and time-to-metamorphosis of the larvae will be recorded as well as the locomotor activity using video tracking.

 

We expect that Bti will affect the ecotrophology of amphibian larvae since the abundance of the main food source (chironomids) will be reduced. Simultaneously, a lab feeding experiment with newt larvae will be conducted to imitate limited food sources.

PhD project: Rhizosphere biogeochemistry

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Working title: Joint FSstream biogeochemistry (HJ): The impact of anthropogenic stressors on biogeochemical cycling at the root-microorganism-soil interface.

 

Supervising scientists: Hermann Jungkunst, Katherine Muñoz, Melanie Brunn.

 

Doctoral researcherJohanna Girardi

 

Approach: The invasive plant Fallopia japonica is known for its effective niche construction.  Fallopia increases the nitrogen content in the soil-plant system. However, it is still unknown how this interlinked system reacts to external stressors. In the Palatine region copper is a frequently used fungicide, which can also reach riparian systems. This Ph.D. thesis aims to identify the levels on which copper interferes with the nitrogen cycle within soil-plant systems.

 

Contact:  Hermann JungkunstGeoecology

Plants and soil microorganisms are highly interlinked and control important mechanisms of the carbon and nitrogen cycle together. The invasive plant Fallopia japonica is known for its effective niche construction. By adapting the microbial community and inhibiting denitrification, Fallopia increases the nitrogen content in the soil-plant system. However, it is still unknown how this interlinked system reacts to external stressors.

 

In the Palatine region copper is a frequently used fungicide, which can also reach riparian systems. This Ph.D. thesis aims to identify the levels on which copper interferes with the nitrogen cycle within soil-plant systems. Therefore, the joint pot experiment will be used, to observe the microbial community structure, microbial enzyme activity and biogeochemical processes in two plant-soil systems (Fallopia japonica and Urtica dioica) under a gradient of copper concentrations. Furthermore, root exudates will be collected in the pots as well as in field sites belonging to the FS stream experiment.

 

Exudates will be analysed for specific compounds such as flavonoids and the reaction of soil microbial communities to these substances will be tested in laboratory experiments. Thereby we will gain a deeper understanding of the interaction between plants and microorganisms under copper stress and the implications for biogeochemical processes.

PhD project: Biological pollutant transfer

Working title: Implications of physicochemical properties of micropollutants for their emergence-mediated transport to terrestrial ecosystem.

 

Supervising scientists: Ralf Schulz, Gabriele E. Schaumann and Alessandro Manfrin.

 

Doctoral researcher: Alexis Roodt

 

Approach: Adult merolimnic insects emerging from streams in agricultural landscapes contribute to a variety of ecosystem functions. However, these species are increasingly exposed to a broad range of plant protection products with diverse physiochemical properties. In this project we propose to investigate several current use pesticide actives with a range of physiochemical properties and water-borne exposure patterns.

 

Contact:  Ralf SchulzEcotoxicology & Environment

Adult merolimnic insects emerging from streams in agricultural landscapes contribute to a variety of ecosystem functions, furthermore, they serve as an important subsidy in adjacent terrestrial food-webs. However, during their development, the larvae and nymphs of such species are increasingly exposed to a broad range of plant protection products with diverse physiochemical properties. Among these anthropogenic chemicals, organic pesticides have the potential to be accumulated or concentrated in the bodies of developing larvae.  The subsequent emergence of which may potentialy increase the exposure risk of terrestrial food webs when pesticides are retained in the body burden of the imagines.

 

In this project we propose to investigate several current use pesticide actives with a range of physiochemical properties and water-borne exposure patterns. Insects from a range of orders commonly found in European agricultural landscapes will be used in laboratory-batch and mesocosm scale exposure experiments. The resulting body burdens of pesticide active ingredients will be quantified by application of liquid chromatographic (LC) and gas chromatographic (GC) analysis hyphenated with tandem mass spectrometry (MS/MS).

 

The results of these experiments will be used to evaluate the potential spatial transport of pesticides into adjacent terrestrial ecosystems and the related effect on the population dynamics of predatory spider populations.

PhD project: Biogeochemical fluxes

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Working title: Effects of chemical stressors on biogeochemical processes and fluxes in water to land transition zones.

 

Supervising scientistsAndreas Lorke, Clara Mendoza-Lera and Alessandro Manfrin

 

Doctoral researcher: Caroline Ganglo

 

Approach: Land-water transition zones are hotspots of biogeochemical cycling
and make substantial contributions to ecosystem functions at regional to global scales. The project investigates how ecosystem functions in land-water transition
zones, including the emission of greenhouse gases and the retention of nutrients, are affected by chemical and hydrological stressors.

 

Contact: Andreas LorkeEnvironmental Physics

Land-water transition zones are hotspots of biogeochemical cycling and make substantial contributions to ecosystem functions at regional to global scales. The project investigates how ecosystem functions in land-water transition zones, including the emission of greenhouse gases and the retention of nutrients, are affected by chemical and hydrological stressors. Although these functions are predominantly mediated by microbial communities, we hypothesize that they are affected by stressors acting on higher trophic levels.

 

The effect pathways are not only of biotic nature, but include also indirect, physically-mediated pathways, like bio-turbation and bioirrigation. We test this hypothesis using an ecosystem-scale mass balance approach as part of the joint mesocosm experiment (Floodplain Mesocosms FPM) in combination with targeted laboratory experiments. In replicated treatments, the mesocosms will be treated with the Biological mosquito control agent Bti (Bacillus thuringiensis israelensis) and subject to repeated short-term flooding of their terrestrial compartments. Carbon (C) and nutrient (N, P) budgets will be estimated by quantifying all relevant material fluxes and pools. In addition to physically controlled flux paths (water flow, atmospheric evasion and diffusion), we will include mass fluxes of C, N and P associated with motile organisms, including invertebrates and amphibians. Observed differences in the biogeochemical cycling at the landwater interface among the treatments will be related to the application of Bti. Special emphasize will be spent on the identification and mechanistic understanding of the hydrodynamic processes that govern the most relevant physical transport processes in floodplain ponds. This aspect of our research will fill an existing knowledge gap in the field of physical limnology.

 

Similar to former studies that have been conducted in smaller mesocosms, we expect that Bti has adverse effects on the abundance of non-target organisms, such as chironomids, which are important mediators for the transport of oxygen across the sediment-water interface. In laboratory experiments, we analyze the indirect effects of Bti application on the production, oxidation and evasion of the potent greenhouse gas methane (CH4) as a function of abundance and absence of chironomids. 

PhD project: Soil C-N dynamics

Working title: Implications of the interplay between invasive plant colonization and soil structure for the biogeochemical carbon and nitrogen cycle.

 

Supervising scientists: Gabriele E. Schaumann, Eva Kröner, Verena Rösch.

 

Doctoral researcher: Jellian Jamin

 

Approach: Native (U. dioica) and invasive plants (I. glandulifera) have different rootsystems. These will strongly alter soil structure, carbon turnover and the thermodynamics of the soil . We will investigate these interplays on lab-, batch- and landscape scale.

 

Contact: Gabi SchaumannSoil & Environmental Chemistry

Native (U. dioica) and invasive plants (I. glandulifera) have different root systems. These will strongly alter soil structure, carbon turnover and the thermodynamics of the soil. We will investigate these interplays on lab-, batch- and landscape scale. For this, we participate in two joint experiments: the SystemLink joint pot experiment (joint PE) and the SystemLink FSstream (project Bottom-up effects) with selected populations of both root systems.

 

During and after the growing season we will assess root structure and soil hydraulic properties via micro-CT-scans and environmental scanning electron microscopy. Micro-respiration experiments with a long incubation time and thermodynamic measurements (e.g. via heat probes) will help to roughly estimate the effect of water and oxygen distribution on carbon conversion efficiency and carbon turnover thermodynamics. Furthermore, we will select suitable biomolecules e.g. from the root exudates to characterize the carbon conversion efficiency by compound-specific isotope analysis.

 

Water retention and soil pore size distribution in the rhizosphere will be characterized via 1Dand 2D nuclear magnetic resonance (NMR) relaxometry. With this, we will monitor pore size distribution, swelling-shrinking process and water mobility in terms of diffusion and rotation mobility. These results will be linked to the structural stability of the rhizosphere using Rheometry and various soil stability testing methods. The results will ow into the PhD project Soil-plant modelling (link with water transport).

PhD project: Food web ecology

Working title: Pollution and invasive plants reduce the impact of aquatic subsidies on riparian food webs.

 

Supervising scientists: Martin Entling, Nanki Sidhu, Klaus Schwenk.

 

Doctoral researcher: Maike Huszarik

 

Approach: Emerging aquatic insects play an important role in linking streams with surrounding terrestrial food webs, by providing valuable nutrients to riparian predators. The food web ecology project will study indirect effects in the riparian food web in response to anthropogenic stressors of streams.

 

Contact: Martin EntlingEcosystem Analysis

Emerging aquatic insects play an important role in linking streams with surrounding terrestrial food webs, by providing valuable nutrients to riparian predators. However, the presence of chemical pollution and invasive plant species in streams can alter this connection and indirectly affect the terrestrial ecosystem. Previous studies have found changes in riparian food webs near streams containing higher levels of pesticides, but the mechanism behind this has not been fully investigated.

 

The food web ecology project will study indirect effects in the riparian food web in response to anthropogenic stressors of streams. To achieve this, we will perform a field study on two riparian insectivores, namely bats and spiders, at 15 – 20 stream sites. The sites are similar in natural structure, but differ in exposure to pollution as they are located either before or after agricultural and urban landscapes. At each site, bat calls will be recorded to measure the abundance of different species and their feeding attempts. Spiders will also be collected to characterize the contribution of aquatic subsidies to their diets. This will be done using gut content analysis via metabarcoding, and stable isotope analysis. We will also measure pesticides and waste water markers at each study site, and sample emerging insects from the streams.

 

Due to direct effects of chemical pollution on emerging aquatic insects, we expect a negative response in the diets and behaviour of predators at sites with higher pollution. For example, polluted sites may have lower bat abundance with fewer hunting calls, and the contribution of aquatic subsidies to spider diets could also decrease. These effects may also differ for generalist versus specialist predators. By combining the information from this study with other Systemlink projects, we can better understand how the effects of anthropogenic stressors in streams propagate to and change the riparian ecosystem.

 

PhD project: Subsidy quality

Working title: Terrestrial food webs are affected by the selective impacts of aquatic micropollutants on insect emergence.

 

Supervising scientists: Mirco Bundschuh, Ralf B. Schäfer and Alessandro Manfrin

 

Doctoral researcher: Sebastian Pietz

 

Approach: Resource fluxes from freshwaters to adjacent terrestrial ecosystems can be of high relevance for the receiving system. However, micropollutants can adversely affect these ecosystems. It is thus hypothesized in this PhD project that micropollutant-induced adverse effects on the aquatic emergence may propagate to a reduction in predator fitness and potential top-down effects.

 

Contact: Mirco Bundschuh, Functional Aquatic Ecotoxicology

Resource fluxes (subsidies) from freshwaters to adjacent terrestrial ecosystems can be of high relevance for the receiving system, because emerging merolimnic insects can constitute a major part of the diet of riparian predators. However, micropollutants can adversely affect freshwater ecosystems, in turn, altering the connectivity across ecosystems. It is thus hypothesized in this PhD project that micropollutant-induced adverse effects on the aquatic emergence (i.e., diversity, biomass, temporal availability and quality) may propagate to a reduction in predator (i.e., spider) fitness and potential top-down effects.

 

In this year’s experiment, we will examine the effects of a combination of different micropollutants (i.e., organic pesticide mixture and Cu) and food levels (i.e., low and high quality) on the biomass and quality (measured as essential amino acids and PUFAs) of the merolimnic aquatic insect Chironomus riparius over several generations to assess potential alterations over time. Additionally, chironomids will be fed to a terrestrial model predator (i.e., a spider) to investigate if potential treatment-related effects (i.e., altered prey quality) may affect the physiological fitness of spiders.

 

Subsequently, microcosms inside the RSM will be used featuring a simplified food web consisting of a terrestrial predator (i.e., spiders), terrestrial herbivorous prey, a plant, and aquatic prey (i.e., emerging merolimnic insects). Spider survival, growth, fitness (essential amino acids and PUFAs),
and usage of prey items (via stable isotope analysis) as well as terrestrial prey abundance and herbivory will be monitored to infer treatment-related effects.

 

PhD project: Subsidy dynamics

Working title: Anthropogenic changes in the water-to-land transition zones modify the quality and temporal availability of aquatic subsidy for terrestrial predators.

 

Supervising scientists: Mirco Bundschuh, Carsten A. Brühl, Mira Kattwinkel.

 

Doctoral researcher: Sara Kolbenschlag

 

Approach: Insects associated with contaminated water bodies can result in an altered emergence pattern. To investigate effects of pesticides on aquatic insects, a lab experiment with the non-biting midge Chironomus riparius will be conducted.

 

Contact: Mirco BundschuhFunctional Aquatic Ecotoxicology

Pesticides which are regularly applied in agricultural landscapes often enter adjacent water bodies via run off and spray drift. Thus, insects associated with those contaminated water bodies are exposed in their aquatic phase (eggs and larvae) which can result in an altered emergence pattern and may also affect the quality of emerging insects in terms of prey for terrestrial predators. To investigate effects of pesticides on aquatic insects, a lab experiment with the non-biting midge Chironomus riparius will be conducted over five generations. Copper and a pesticide mixture as chemical stressors will be combined with high- and low-quality food and the emergence dynamics as well as the emergence quality will be assessed. Therefore, lipid content, fatty acid composition and amino acid content will be analysed as well as indicators for oxidative stress.


Another anthropogenic stressor for aquatic insects is the biocide Bacillus thuringiensis var. israelensis (Bti), a mosquito control agent which is regularly applied in the floodplains of the German Upper Rhine Valley. To examine the effect of Bti on the aquatic insect community, a field study in flood plain mesocosms will be conducted between spring and autumn. In addition to direct effects on diversity, richness and quality of the insect community, indirect effects on prey (protozoan) and predators (spiders) will be investigated.

 

 

PhD project: Bottom-up effects

Working title: Bottom up effects of aquatic micropollutants and invasive riparian plants on terrestrial food chain and community composition.

 

Supervising scientists: Jens Schirmel, Mirco Bundschuh, Kai Riess.

 

Doctoral researcher: Daniel Schmitz

 

Approach: Aquatic micropollutants and invasive plant species are factors that strongly impact riparian ecosystems. In this project, the bottom up effects these factors exhibit over multiple trophic levels will be investigated, which is one possible pathway by which these factors may affect the ecosystem.

 

Contact: Jens SchirmelEcosystem Analysis

Aquatic micropollutants and invasive plant species are factors that strongly impact riparian ecosystems in many different forms. In this project, the bottom up effects these factors exhibit over multiple trophic levels will be investigated, which is one possible pathway by which these factors may affect the ecosystem. 

 

The project is split into two experiments: a field study investigating the independent contribution of both factors on riparian soil microbial and invertebrate community structure and a laboratory experiment testing the causal effects of micropollutants on the soil microbial community and subsequent effects on the focal plant species and focal herbivores determined in the field study.

 

In the field study stream sections with varying pollution levels where the focal invasive plant species are present (Impatiens glandulifera or Fallopia japonica) will be investigated. At these sites, soil microbial (via DNAmetabarcoding) and invertebrate community structure as well as physiological fitness parameters of the focal plants and representative invertebrates will be determined and  compared with sites that have higher or lower pollution levels. In the laboratory experiment, microcosms filled with a representative riparian soil and its native soil microbial community will be used. The micropollutants will be simulated by introducing copper in different concentration levels into the soil prior to planting one of the focal plant species into the pot. The plants will be grown for two seasons. Root, leaf and soil samples will be taken in regular intervals. At these points, the physiological fitness of each plant will be assessed as well using image-based analysis. In the second season, herbivores will be introduced into the pots.
After the experiment, the soil fungal community will be characterised (via DNA-metabarcoding) and the morphological and physiological fitness of the focal plants and of higher trophic levels will be measured.

PhD project: Ecological stress response modelling

Working title: Modelling the response of a terrestrial food web to a change in aquatic subsidies through environmental stress.

 

Supervising scientists: Ralf B. Schäfer, Mira Kattwinkel, Jens Schirmel.

 

Doctoral researcher: Stephen Osakpolor

 

Approach: Environmental stressors can have effects on the structure and function of meta-environmental systems. In the first part of the project, a description of existing meta-ecosystem ecological models will be done.

 

Contact: Ralf SchäferQuantitative Landscape Ecology

Environmental stressors can have effects on the structure and function of meta-environmental systems. Meta-ecosystem ecological models through abstraction can help us improve understanding and make predictions of such complex systems. In the first part of the project, a description of existing meta-ecosystem ecological models will be done. Inputs from the literature review regarding identified model gaps and needed parameters to further ecological response stress modelling, will be incorporated in developing a meta-ecosystem ecological model that studies the effect of aquatic chemical pollution on the linked riparian food web.

 

The model will consist of a simple tri-trophic riparian food-web consisting of a plant, prey, and predator, which is subsidized by prey from the linked aquatic ecosystem. The model will incorporate a sub-model for environmental stressors of the aquatic ecosystem with endpoints on both the quantity and quality of the aquatic prey. The riparian food web will also have links with the biogeochemical cycles of limiting nutrients, and ecosystem functions such as primary production can be measured. In the first instance, it will be parameterized by literature and estimated parameter ranges to identify highly sensitive parameters. As soon as sufficient experimental data from other SystemLink projects are available, the developed model will be fully parametrized empirically.

PhD project: Soil-plant modelling

Working title: Interplay between plant roots, root exudates and soil structure and their effect on bioavailability of micropollutants and nutrient cycle – a modelling approach.

 

Supervising scientists: Eva Kröner, Lorenz Fahse, Andreas Lorke.

 

Doctoral researcher: Omid E. Jahromi 

 

Approach: This study will use the Lattice Boltzmann method as a powerful tool for fluid dynamics study and the discrete element method for describing elastic networks to present a pore-scale model for more accurate simulation and study of physical processes in the rhizosphere.

 

Contact: Eva KrönerGeophysics

Compared to bulk soil, rhizosphere has different properties because of the existence of root mucilage which affects the physical, chemical and also microbial processes. Hydraulic phenomena like limiting water flow at certain dry soil conditions, modulating extreme water contents by slow response to water potential changes; and also influencing contaminant transport and gas diffusion by varying the connectivity of liquid and gas phases are all classified under the set of the physical processes which are affected by mucilage in the rhizosphere.  

 

Overview of the literature and previous models shows the lack of a  threedimensional pore-scale dynamic model for a better understanding of the connectivity between different phases during imbibition and drainage processes. A major challenge is that mucilage shows a complex behavior which at low concentrations is more like a liquid while at higher concentration, when it is almost dry, it becomes a solid.

In particular, this study will use the Lattice Boltzmann method as a powerful tool for fluid dynamics study and the discrete element method for describing elastic networks to present a pore-scale model for more accurate simulation and study of physical processes in the rhizosphere.


Transport of contaminant through pores, strongly depends on the water distribution and mucilage viscosity. One of the SystemLink researchers, Jellian Jamin, is working on the viscosity of root mucilage of different plant species and her obtained data can be used as input for our simulations to estimate the effect of root exudates of invasive species on contaminant transport.