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Institute
Leaf litter breakdown is a fundamental process in aquatic ecosystems, being mainly mediated by decomposer-detritivore systems that are composed of microbial decomposers and leaf-shredding, detritivorous invertebrates. The ecological integrity of these systems can, however, be disturbed, amongst others, by chemical stressors. Fungicides might pose a particular risk as they can have negative effects on the involved microbial decomposers but may also affect shredders via both waterborne toxicity and their diet; the latter by toxic effects due to dietary exposure as a result of fungicides’ accumulation on leaf material and by negatively affecting fungal leaf decomposers, on which shredders’ nutrition heavily relies. The primary aim of this thesis was therefore to provide an in-depth assessment of the ecotoxicological implications of fungicides in a model decomposer-detritivore system using a tiered experimental approach to investigate (1) waterborne toxicity in a model shredder, i.e., Gammarus fossarum, (2) structural and functional implications in leaf-associated microbial communities, and (3) the relative importance of waterborne and diet-related effects for the model shredder.
Additionally, knowledge gaps were tackled that were related to potential differences in the ecotoxicological impact of inorganic (also authorized for organic farming in large parts of the world) and organic fungicides, the mixture toxicity of these substances, the field-relevance of their effects, and the appropriateness of current environmental risk assessment (ERA).
In the course of this thesis, major differences in the effects of inorganic and organic fungicides on the model decomposer-detritivore system were uncovered; e.g., the palatability of leaves for G. fossarum was increased by inorganic fungicides but deteriorated by organic substances. Furthermore, non-additive action of fungicides was observed, rendering mixture effects of these substances hardly predictable. While the relative importance of the waterborne and diet-related effect pathway for the model shredder seems to depend on the fungicide group and the exposure concentration, it was demonstrated that neither path must be ignored due to additive action. Finally, it was shown that effects can be expected at field-relevant fungicide levels and that current ERA may provide insufficient protection for decomposer-detritivore systems. To safeguard aquatic ecosystem functioning, this thesis thus recommends including leaf-associated microbial communities and long-term feeding studies using detritus feeders in ERA testing schemes, and identifies several knowledge gaps whose filling seems mandatory to develop further reasonable refinements for fungicide ERA.
Population genetic structure in European Hyalodaphnia species: Monopolization versus gene flow
(2012)
Cyclic parthenogens displays an alternation of asexual and sexual reproduction which has consequences for the genetic structure of these organisms. The clonal diversity of cyclic parthenogenetic zooplankton populations is influenced by the size of the dormant egg bank, i.e., the amount of sexually produced dormant eggs that assembled in the sediment, as these dormant eggs contribute new genetic variants to the populations. Further, the clonal diversity is impacted by clonal erosion over time, which reduces the number of different clones through stochastic and selective processes. Although freshwater invertebrates are good dispersers through their dormant stages, the influence of gene flow is assumed to be negligible, as the local population successfully monopolizes the available resources. As these populations reach carrying capacity fast due to the asexual reproduction, the first colonizing individuals are able to successfully establish in the habitat, resulting in a priority effect which hinders the invasion of new genotypes. Due to clonal selection and sexual reproduction a population will locally adapt over time and will establish a dormant egg bank which facilitates the fast re-colonization after a hostile period. This thesis evaluates the processes altering the population genetic structure of cyclic parthenogenetic zooplankton with a special focus on the concepts of monopolization as well as the counteracting effects of gene flow, using large-lake Daphnia species. Thirty-two variable microsatellite DNA markers were developed and a subset of twelve markers was evaluated regarding their suitability for species assignment and hybrid class detection. With this marker set and an additional mitochondrial DNA marker forty-four natural European populations of the species D. cucullata, D. galeata and D. longispina were studied. In D. galeata, most populations were characterized by low clonal diversities which suggest high influence from clonal erosion over the growing season and a low contribution from the dormant egg bank. Further, recent expansions as well as gene flow were detected, probably caused by the anthropogenic alteration of freshwater habitats, in particular eutrophication of many European lakes. D. longispina and D. cucullata revealed a different genetic structure compared to D. galeata, with high genetic differentiation among populations. This indicates low levels of effective gene flow which is in line with the predictions of monopolization. Further, high clonal diversities were found in populations of the two taxa, suggesting a high contribution from the dormant egg bank while clonal erosion was often not detectable. In D. longispina, mitochondrial data revealed an ancient expansion which was probably initiated by the formation of glacial lakes after the last ice age.
In addition, in D. longispina not only clonal diversity but also genetic diversity was high, indicating that during the build-up of the studied populations the influence from gene flow was probably high. To better understand the processes that act on early populations the population build-up in regard to the temporal advantage of clones during invasion succession was experimentally studied and revealed that priority effects shape population structure of Daphnia species. However, in certain cases the highly superior clones resulted in the extinction of inferior clones independent of the temporal advantage the single clones had.
This clearly shows that not only the time of succession is important but also the competitive strength. rnIn conclusion, the results obtained show that the population genetic structure in cyclic parthenogenetic zooplankton species is impacted by various processes. In addition to earlier studies, which mainly focus on local adaptation, clonal erosion and the size of the dormant egg bank to understand population genetic structure, this thesis could show that gene flow may be effective as well. During population build-up the advantage of early arriving individuals does not necessarily predict the outcome of population assembly, as additional genotypes may contribute to the population. Finally, the genetic structure of established populations may be severely impacted by effective gene flow, if severe environmental changes alter the habitat of the locally adapted population.
Agricultural pesticides, especially insecticides, are an integral part of modern farming. However, these may often leave their target ecosystems and cause adverse effects in non- target, especially freshwater ecosystems, leading to their deterioration. In this thesis, the focus will be on Insect Growth Regulators (IGRs) that can in many ways cause disruption of the endocrine system of invertebrates. Freshwater invertebrates play important ecological, economic and medical roles, and disruption of their endocrine systems may be crucial, considering the important role hormones play in the developmental and reproductive processes in organisms. Although Endocrine Disruption Chemicals (EDCs) can affect moulting, behaviour, morphology, sexual maturity, time to first brood, egg development time, brood size (fecundity), and sex determination in invertebrates, there is currently no agreement upon how to characterize and assess endocrine disruption (ED). Current traditional ecotoxicity tests for Ecological Risk Assessment (ERA) show limitations on generating data at the population level that may be relevant for the assessment of EDCs, which effects may be sublethal, latent and persist for several generations of species (transgenerational).
It is therefore the primary objective of this thesis to use a test method to investigate adverse effects of EDCs on endpoints concerning development and reproduction in freshwater invertebrates. The full life-cycle test over two generations that includes all sensitive life stages of C. riparius (a sexual reproductive organism) allows an assessment of its reproduction and should be suitable for the investigation of long-term toxicity of EDCs in freshwater invertebrates. C. riparius is appropriate for this purpose because of its short life cycle that enables the assessment of functional endpoints of the organism over several generations. Moreover, the chironomid life cycle consists of a complete metamorphosis controlled by a well-known endocrine mechanism and the endocrine system of insects has been most investigated in great detail among invertebrates. Hence, the full life-cycle test with C. riparius provides an approach to assess functional endpoints (e.g. reproduction, sex ratio) that are population-relevant as a useful amendment to the ERA of EDCs. In the laboratory, C. riparius was exposed to environmentally-relevant concentrations of the selected IGRs in either spiked water or spiked sediment scenario over two subsequent generations.
The results reported in this thesis revealed significant effects of the IGRs on the development and the reproduction of C. riparius with the second (F1) generation showing greater sensitivity. These findings indicated for the first time the suitability of multigenerational testing for various groups of EDCs and strongly suggested considering the full life-cycle of C. riparius as an appropriate test method for a better assessment of EDCs in the freshwater environment. In conclusion, this thesis helps to detect additional information that can be extrapolated at population level and, thus, might contribute to better protection of freshwater ecosystems against the risks of Endocrine Disrupting Chemicals (EDCs.) It may furthermore contribute to changes in the ERA process that are necessary for a real implementation of the new European chemical legislation, REACH (Registration, Evaluation Authorization and Restriction of Chemicals). Finally, significant interactions between temperature, chemical exposure and generation were reported for the first time and, may help predict impacts that may occur in the future, in the field, under predicted climate change scenarios.
Assessment of bat activity in agricultural environments and the evaluation of the risk of pesticides
(2013)
Although agriculture dominates with around 50% area much of Europe- landscape, there is virtually no information on how bats use this farmed environment for foraging. Consequently, little is known about effective conservation measures to compensate potential negative effects of agrarian management practice on the food availability for bats in this habitat. Moreover, there are currently no specific regulatory requirements to include bats in European Union risk assessments for the registration of pesticides since no information about pesticide exposure on this mammal group is available. To evaluate the potential pesticide exposure of bats via ingestion of contaminated insects, information about bat presence and activity in agricultural habitats is required. In order to examine bat activity on a landscape scale it was necessary to establish a suitable survey method. Contrary to capture methods, telemetry, and direct observations, acoustic surveys of bat activity are a logistically feasible and cost-effective way of obtaining bat activity data. However, concerns regarding the methodological designs of many acoustic surveys are expressed in the scientific literature. The reasons are the failing of addressing temporal and spatial variation in bat activity patterns and the limitations of the suitability of the used acoustic detector systems. By comparing different methods and detector systems it was found that the set up of several stationary calibrated detector systems which automatically trigger the ultrasonic recording has the highest potential to produce reliable, unbiased and comparable data sets on the relative activity of bats.
By using the proposed survey method, bat diversity and activity was recorded in different crops and semi-natural habitats in southern Rhineland-Palatinate. Simultaneously, the availability of aerial prey insects was studied by using light and sticky traps. In more than 500 sampling nights about 110,000 call sequences were acoustically recorded and almost 120,000 nocturnal insects were sampled. A total of 14 bat species were recorded, among them the locally rare and critically endangered northern bat (Eptesicus nilssonii) and the barbastelle (Barbastella barbastellum), all of them also occurring over agricultural fields. The agricultural landscape of southern Palatinate is dominated by vineyards, a habitat that was shown to be of low quality for most bat species because of the demonstrated low availability of small aerial insects. By surveying bat activity and food availably in a pair-wise design on several rain water retention ponds and neighbouring vineyards it was demonstrated that aquatic insect emergence in artificial wetlands can provide an important resource subsidy for bats. The creation of artificial wetlands would be a possibility to create important foraging habitats for bats and mitigate negative effects of management practice in the agricultural landscape.
In several other agricultural crops, however, high abundances of suitable prey insects and high bat activity levels, comparable or even higher than in the nearby forests and meadows known to be used as foraging habitats were demonstrated. Especially high bat activity levels were recorded over several fruit orchards and vegetable fields where insects were also present. Both crops are known for high pesticide inputs, and, therefore, a pesticide exposure through ingestion of contaminated insects can not be excluded. To follow the current risk assessment approach for birds and mammals pesticide residues were measured on bat-specific food items in an apple orchard following insecticide applications and bat activity was recorded in parallel. The highest residue values were measured on foliage-dwelling arthropods which may results in a reproductive risk for all bat species that, even to a small extent, include this prey group in their diet. The presence of bats in agricultural landscapes that form a majority of the land area in Europe but also on a global scale leads to exposure of bats by contaminated food and depletion of their food resources by pesticide use. So far conservation efforts for bats focussed on securing hibernation sites and the creation of artificial roost sites since especially the latter were thought to be limiting population growth. However the potential pesticide effects might be also crucial for the population persistence in agricultural landscapes of bats and need to be addressed adequately, especially in risk assessment procedures for the regulation of pesticides.
This habilitation thesis deals with the effects of toxicants on freshwater ecosystems and considers different toxicant classes (pesticides, organic toxicants, salinity) and biotic endpoints (taxonomic community structure, trait community structure, ecosystem functions).
The thesis comprises 12 peer-reviewed international publications on these topics. All of the related studies rely on mesocosm or field investigations, or the analysis of field biomonitoring or chemical monitoring data. Publications I and II are devoted to passive sampling of a neonicotinoid insecticide and polycyclic aromatic hydrocarbons (PAHs), respectively. They show that biofouling and a diffusion-limiting membrane can reduce the sampling rate of the pulsed insecticide exposure and that receiving phases of different thicknesses can be used to assess the kinetic regime during field deployment of passive samplers. Publications III to VI mainly focus on trait-based approaches to reveal toxicant effects on invertebrates in streams. An overview on the framework and several applications of a trait-based approach to detect effects of pesticides (SPEARpesticides index) are given in publication III. Publication IV describes the development of a trait database for South-East Australian stream invertebrates and its successful application in the adaptation of SPEARpesticides as well as the development of a salinity index. Moreover, a conceptual model for the future development of trait-based biomonitoring indices is proposed. Publication V reports a mesocom study on the effects of a neonicotinoid insecticide on field-realistic invertebrate communities. The insecticide had long-term effects on the invertebrate communities, which were only detected when grouping the taxa according to their life-history traits. A comprehensive field study employing different pesticide sampling methods including passive sampling and biomonitoring of the invertebrate and microbial communities is presented in publication VI. The study did not find pesticide-induced changes in the microbial communities, but detected adverse effects of current-use pesticides on the invertebrate communities using the trait-based SPEARpesticides index. This index is also applied in a meta-analysis on thresholds for the effects of pesticides on invertebrate communities in publication VII. It is shown that there is a similar dose-response relationship between SPEARpesticides and pesticide toxicity over different biogeographical regions and continents. In addition, the thresholds for effects of pesticides are lower than derived from most mesocosm studies and than considered in regulatory pesticide risk assessment. The publications VIII to X use statistical data analysis approaches to examine effects of toxicants in freshwater ecosystems. Using governmental monitoring data on 331 organic toxicants monitored monthly in 4 rivers over 11 years, publication VIII finds that organic toxicants frequently occurred in concentrations envisaging acute toxic effects on invertebrates and algae even in large rivers. Insecticides and herbicides were the chemical groups mainly contributing to the ecotoxicological risk. Publication IX introduces a novel statistical method based on a similarity index to estimate thresholds for the effects of toxicants or other stressors on ecological communities. The application of the method for deriving thresholds for salinity, heavy metals and pesticides in streams is presented in three case studies. Publication X tackles the question of interactive effects between different toxicants using data from a field study on stream invertebrates in 24 sites of South-East Australia. Both salinity and pesticides exhibited statistically significant effects on the invertebrate communities, but no interaction between the stressors was found. Moreover, salinity acted on a higher taxonomical level than pesticides suggesting evolutionary adaptation of stream invertebrates compared to pesticide stress. Publications XI and XII concentrate on the effects of toxicants on biodiversity, ecosystem functions and ecosystem services, with publication XI summarising different studies related to the ecological risk assessment for these endpoints. A field study on the effects of pesticides and salinity on the ecosystem functions of allochthonous organic matter decomposition, gross primary production and ecosystem respiration is presented in publication XII. Both pesticides and salinity reduced the breakdown of allochthonous organic matter, whereas no effects on the other ecosystem functions were detected. A chapter following these publications synoptically discusses all studies of this habilitation thesis and draws general conclusions. It is stressed that in order to advance the understanding of effects of toxicants on freshwater ecosystems more ecological realism is needed in ecotoxicological approaches and that the spatiotemporal extent of toxicant effects needs more scrutiny.
Worldwide one third to one half of the freshwater crayfish species are threatened with population decline or extinction. Besides habitat deterioration, pollution, and other man-made environmental changes, invasive species and pathogens are major threats to the survival of European crayfish species. Freshwater crayfish are the largest freshwater invertebrates and strongly influence the structure of food webs. The disappearance of crayfish from a water body may change the food web and could have dramatic consequences for an ecosystem.rnOne goal in modern species conservation strategies is the conservation of genetic diversity, since genetic diversity is an advantage for the long-term survival of a species. The main aim of my thesis was to reveal the genetic structure and to identify genetic hotspots of the endangered noble crayfish (Astacus astacus) throughout Europe (part 1 of my thesis). Since the most significant threat to biodiversity of European crayfish species is the crayfish plague pathogen Aphanomyces astaci I studied new aspects in the distribution of A. astaci (part two of my thesis). The results serve as a basis for future conservation programs for freshwater crayfish. In the first part of my thesis I conducted a phylogeographic analysis of noble crayfish using mitochondrial DNA and nuclear microsatellite data. With these methods I aimed to identify its genetic hotspots and to reconstruct the recolonization history of central Europe by this species. I detected high genetic diversities in southestern Europe indicating that noble crayfish outlasted the cold climate phases during the Pleistocene in this region (Appendix 1). Because of the high genetic diversity found there, southeastern Europe is of particular importance for the conservation of noble crayfish. The mitochondrial DNA analysis points to a bifurcated colonization process from the eastern Black Sea basin to a) the North Sea and to b) the Baltic Sea basin (Appendix 2). A second independent refugium that was localized on the Western Balkans did not contribute to the colonization of central Europe. Furthermore, I found that the natural genetic structure is dissolved, probably due to the high human impact on the distribution of noble crayfish (e.g. artificial translocation). In the second part of this thesis using real-time PCR I identified calico crayfish (Orconectes immunis) as the fourth North American crayfish species to be carrier of the agent of the crayfish plague (Appendix 3). Furthermore I detected the crayfish plague pathogen in American spiny-cheek crayfish (Orconectes limosus) and native narrow-clawed crayfish (Astacus leptodactylus) in the lower Danube in Romania (Appendix 4). The distribution of infected spiny-cheek crayfish poses a threat to the native biodiversity in southeastern Europe and shows the high invasion potential of this crayfish species. Moreover, I found that even the native narrow-clawed crayfish in the Danube Delta, about 970 km downstream of the current invasion front of American crayfish, is a carrier of A. astaci (Appendix 5). This finding is of high importance, as the native species do not seem to suffer from the infection. In Appendix 6 I elucidate demonstrate that the absence of the crayfish plague agent is the most likely explanation for the coexistence of populations of European and American crayfish in central Europe. In my thesis I show that the common assumption that all North American crayfish are carrier of A. astaci and that all native crayfish species die when infected with A. astaci does not hold true. The studies presented in my thesis reveal new aspects that are crucial for native crayfish conservation: 1) The genetic diversity of noble crayfish is highest in southeastern Europe where noble crayfish outlasted the last glacial maximum in at least two different refugia. 2) Not all American crayfish populations are carrier of A. astaci and 3) not all Europen crayish populations die shortly after being infected with the crayfish plague pathogen.rnTo conserve native crayfish species and their (genetic) diversity in the long term, further introductions of American crayfish into European waters must be avoided. However, the introduction will only decrease if the commercial trade with non-indigenous crayfish species is prohibited.
To assess the effect of organic compounds on the aquatic environment, organisms are typically exposed to toxicant solutions and the adverse effects observed are linked to the concentration in the surrounding media. As compounds generally need to be taken up into the organism and distributed to the respective target sites for the induction of effects, the internal exposure is postulated to best represent the observed effects.
The aim of this work is to contribute to an improved effect assessment of organic compounds by describing experimental and modelling methods to obtain information on the internal exposure of contaminants in organisms.
Chapter 2 details a protocol for the determination of bioconcentration parameter for uptake (k1) and elimination (k2) of organic compounds in zebrafish (Danio rerio) eggs. This enables the simulation of the internal exposure in zebrafish eggs from an ambient exposure concentration over time. The accumulated contaminant amount in zebrafish eggs was also determined, using a biomimetic extraction method. Different bioconc-entration estimation models for the determination of internal steady-state concentrat-ion of pharmaceutical compounds in fish to an environmental exposure are presented in Chapter 3. Bioconcentration factors were estimated from the compounds octanol: water partition coefficient (KOW) to determine the internal exposure to an ambient concentration.
To assess the integral bioavailable fraction from the water and sediment phase of environmental contaminants for rooted aquatic plants, the internal exposure in river-living Myriophyllum aquaticum plants were determined over time, presented in Chapter 4. The plants were collected at different time points, with the accumulated organic contaminants determined using a liquid extraction method.
In Chapter 5 a protocol was established to enable the non-invasive observation of effects in M. aquaticum plants exposed to contaminated sediments over time. Since the toxicant effects are a result of all uptake and distribution processes to the target site and the toxico-dynamic process leading to an observed effect during static exposure, information on the internal exposure could thus be gained from the temporal effect expression.rn
Field margins are often the only remaining habitats of various wild plant species in agricultural landscapes. However, due to their proximity to agricultural fields, the vegetation of field margins can be affected by agrochemicals applied to the crop fields. The aim of this thesis was to investigate the individual and combined effects of herbicide, insecticide and fertilizer inputs on the plant community of a field margin. Therefore, a 3-year field experiment with a randomized block design including seven treatments (H: herbicide, I: insecticide, F: fertilizer, H+I, F+I, F+H and F+H+I) and one control was conducted on a low-production meadow. Each treatment was replicated 8 times in 8 m x 8 m plots with a distance of 2 m between each plot. The fertilizer rates (25 % of the field rate) and pesticide rates (30 % of the field rate) used for the plot applications were consistent with realistic average input rates (overspray + drift) in the first meter of a field margin directly adjacent to a wheat field.
The study revealed that fertilizer and herbicide misplacements in field margins are major factors that affect the natural plant communities of these habitats. In total, 20 of the 26 abundant species on the study site were significantly affected by the fertilizer and herbicide treatment. The fertilizer promoted plants with high nutrient uptake and decreased the frequencies of small species. The herbicide caused a nearly complete disappearance of three species directly after the first application, whereas sublethal effects (e.g., phytotoxic effects and reduced seed productions of up to 100 %) were observed for the other affected species. However, if field margins are exposed to repeated agrochemical applications over several years, then such sublethal effects (particularly reproduction effects) also reduce the population size of plant species significantly, as observed in this study.
Significant herbicide-fertilizer interaction effects were also detected and could not be extrapolated from individual effects. The fertilizer and herbicide effects became stronger over time, leading to shifts in plant community compositions after three years and to a 15 % lower species diversity than in the control. The insecticide significantly affected the frequencies of two plant species (1 positively and 1 negatively). The results of the experiment suggest that a continuous annual agrochemical application on the study site would cause further plant community shifts and would likely lead to the disappearance of certain affected plants. A clear trend of increasing grass dominance at the expense of flowering herbs was detected. This finding corresponds well with monitoring data from field margins near the study site.
Although herbicide risk assessment aims to protect non-target plants in off-field habitats from adverse effects, reproduction effects and combined effects are currently not considered. Furthermore, no regulations for fertilizer applications next to field margins exist and thus, fertilizer misplacements in field margins are likely to occur and to interact with herbicide effects.
Adaptations of the current risk assessment, a development of risk mitigation measures (e.g., in-field buffers) for the application of herbicides and fertilizers, and general management measures for field margins are needed to restore and conserve plant diversity in field margins in agricultural landscapes.
Chemical plant protection is an essential element in integrated pest management and hence, in current crop production. The use of Plant Protection Products (PPPs) potentially involves ecological risk. This risk has to be characterised, assessed and managed.
For the coming years, an increasing need for agricultural products is expected. At the same time, preserving our natural resources and biodiversity per se is of equally fundamental importance. The relationship of our economic success and cultural progress to protecting the environment has been made plain in the Ecosystem Service concept. These distinct 'services' provide the foundation for defining ecological protection goals (Specific Protection Goals, SPGs) which can serve in the development of methods for ecological risk characterisation, assessment and management.
Ecological risk management (RM) of PPPs is a comprehensive process that includes different aspects and levels. RM is an implicit part of tiered risk assessment (RA) schemes and scenarios, yet RM also explicitly occurs as risk mitigation measures. At higher decision levels, RM takes further risks, besides ecological risk, into account (e.g., economic). Therefore, ecological risk characterisation can include RM (mitigation measures) and can be part of higher level RM decision-making in a broader Ecosystem Service context.
The aim of this thesis is to contribute to improved quantification of ecological risk as a basis for RA and RM. The initial general objective had been entitled as "… to estimate the spatial and temporal extent of exposure and effects…" and was found to be closely related to forthcoming SPGs with their defined 'Risk Dimension'.
An initial exploration of the regulatory framework of ecological RA and RM of PPPs and their use, carried out in the present thesis, emphasised the value of risk characterisation at landscape-scale. The landscape-scale provides the necessary and sufficient context, including abiotic and biotic processes, their interaction at different scales, as well as human activities. In particular, spatially (and temporally) explicit landscape-scale risk characterisation and RA can provide a direct basis for PPP-specific or generic RM. From the general need for tiered landscape-scale context in risk characterisation, specific requirements relevant to a landscape-scale model were developed in the present thesis, guided by the key objective of improved ecological risk quantification. In principle, for an adverse effect (Impact) to happen requires a sensitive species and life stage to co-occur with a significant exposure extent in space and time. Therefore, the quantification of the Probability of an Impact occurring is the basic requirement of the model. In a landscape-scale context, this means assessing the spatiotemporal distribution of species sensitivity and their potential exposure to the chemical.
The core functionality of the model should reflect the main problem structures in ecological risk characterisation, RA and RM, with particular relationship to SPGs, while being adaptable to specific RA problems. This resulted in the development of a modelling framework (Xplicit-Framework), realised in the present thesis. The Xplicit-Framework provides the core functionality for spatiotemporally explicit and probabilistic risk characterisation, together with interfaces to external models and services which are linked to the framework using specific adaptors (Associated-Models, e.g., exposure, eFate and effect models, or geodata services). From the Xplicit-Framework, and using Associated-Models, specific models are derived, adapted to RA problems (Xplicit-Models).
Xplicit-Models are capable of propagating variability (and uncertainty) of real-world agricultural and environmental conditions to exposure and effects using Monte Carlo methods and, hence, to introduce landscape-scale context to risk characterisation. Scale-dependencies play a key role in landscape-scale processes and were taken into account, e.g., in defining and sampling Probability Density Functions (PDFs). Likewise, evaluation of model outcome for risk characterisation is done at ecologically meaningful scales.
Xplicit-Models can be designed to explicitly address risk dimensions of SPGs. Their definition depends on the RA problem and tier. Thus, the Xplicit approach allows for stepwise introduction of landscape-scale context (factors and processes), e.g., starting at the definitions of current standard RA (lower-tier) levels by centring on a specific PPP use, while introducing real-world landscape factors driving risk. With its generic and modular design, the Xplicit-Framework can also be employed by taking an ecological entity-centric perspective. As the predictive power of landscape-scale risk characterisation increases, it is possible that Xplicit-Models become part of an explicit Ecosystem Services-oriented RM (e.g., cost/benefit level).
The increasing application of titanium dioxide nanoparticles (nTiO2) entails an increased risk regarding their release to surface water bodies, where they likely co-occur with other anthropogenic stressors, such as heavy metals. Their co-occurrence may lead to an adsorption of the metal ions onto the particles. These nanoparticles often sediment, due to their agglomeration, and thus pose a risk for pelagic or benthic species. The combined toxicity of nTiO2 and heavy metals is likely influenced by the properties of both stressors (since they may alter their interaction) and by environmental parameters (e.g., organic matter, pH, ionic strength) affecting their fate.
These issues were not yet systematically examined by the recent literature. Therefore, this thesis investigated the influence of nTiO2-products with differing crystalline phase composition on the toxicity of copper (as representative for heavy metals) in presence of different organic matters using the pelagic test organism Daphnia magna.
Moreover, the duration of the stressors` interaction (=aging) likely modulates the combined toxicity. Hence, the influence of nTiO2 on copper toxicity after aging as a function of environmental parameters (i.e., organic matter, pH, ionic strength) was additionally investigated.
Finally, the transferability of the major findings to benthic species was examined using Gammarus fossarum. The present thesis discovered a reduction of the copper toxicity facilitated by nTiO2 for all assessed scenarios, while its magnitude was determined by the surface area and structure of nTiO2, the quantity and quality of organic matter as well as the aging of both stressors. The general copper toxicity reduction by nTiO2 was also transferable to benthic species, despite their potentially increased exposure due to the sedimentation of nTiO2 with adsorbed copper. These observations suggest the application of nTiO2 as remediation agent, but potential side effects (e.g., chronic toxicity, reactive oxygen species formation) require further investigations. Moreover, questions regarding the transferability to other stressors (e.g., different heavy metals, organic chemicals) and the fate of stressors adsorbed to nTiO2 in aquatic ecosystems remain open.