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Pelagic oxyclines, the transition zone between oxygen rich surface waters and oxygen depleted deep waters, are a common characteristic of eutrophic lakes during summer stratification. They can have tremendous effects on the biodiversity and the ecosystem functioning of lakes and, to add insult to injury, are expected to become more frequent and more pronounced as climate warming progresses. On these grounds, this thesis endeavors to advance the understanding of formation, persistence, and consequences of pelagic oxyclines: We test, whether the formation of metalimnetic oxygen minima is intrinsically tied to a locally enhanced oxygen consuming process, investigate the relative importance of vertical physical oxygen transport and biochemical oxygen consumption for the persistence of pelagic oxyclines, and finally assess their potential consequences for whole lake cycling. To pursue these objectives, the present thesis nearly exclusively resorts to in situ measurements. Field campaigns were conducted at three lakes in Germany featuring different types of oxyclines and resolved either a short (hours to days) or a long (weeks to months) time scale. Measurements comprised temperature, current velocity, and concentrations of oxygen and reduced substances in high temporal and vertical resolution. Additionally, vertical transport was estimated by applying the eddy correlation technique within the pelagic region for the first time. The thesis revealed, that the formation of metalimnetic oxygen minima does not necessarily depend on locally enhanced oxygen depletion, but can solely result from gradients and curvatures of oxygen concentration and depletion and their relative position to each other. Physical oxygen transport was found to be relevant for oxycline persistence when it considerably postponed anoxia on a long time scale. However, its influence on oxygen dynamics was minor on short time scales, although mixing and transport were highly variable. Biochemical consumption always dominated the fate of oxygen in pelagic oxyclines. It was primarily determined by the oxidative breakdown of organic matter originating from the epilimnion, whereas in meromictic lakes, the oxidation of reduced substances dominated. Beyond that, the results of the thesis emphasize that pelagic oxyclines can be a hotspot of mineralization and, hence, short-circuit carbon and nutrient cycling in the upper part of the water column. Overall, the present thesis highlights the importance of considering physical transport as well as biochemical cycling in future studies.
Today’s agriculture heavily relies on pesticides to manage diverse pests and maximise crop yields. Despite elaborate regulation of pesticide use based on a complex environmental risk assessment (ERA) scheme, the widespread use of these biologically active compounds has been shown to be a threat to the environment. For surface waters, pesticide exposure has been observed to exceed safe concentration levels and negatively impact stream ecology leading to the question whether current ERA schemes ensure a sustainable use of pesticides. To answer this, the large-scale “Kleingewässer-Monitoring” (KgM) assessed the occurrence of pesticides and related effects in 124 streams throughout Germany, Central Europe, in 2018 and 2019.
Based on five scientific publications originating from the KgM, this thesis evaluated pesticide exposure in streams, ecological effects and the regulatory implications. More than 1,000 water samples were analysed for over 100 pesticide analytes to characterise occurrence patterns (publication 1). Measured concentrations and effects were used to validate the exposure and effect concentrations predicted in the ERA (publication 2). By jointly analysing real-world pesticide application data and measured pesticide mixtures in streams, the disregard of environmental pesticide mixtures in the ERA was evaluated (publication 3). The toxic potential of mixtures in stream water was additionally investigated using suspect screening for 395 chemicals and a battery of in-vitro bioassays (publication 4). Finally, the results from the KgM stream monitoring were used to assess the capability to identify pesticide risks in governmental monitoring programmes (publication 5).
The results of this thesis reveal the widespread occurrence of pesticides in non-target stream ecosystems. The water samples contained a variety of pesticides occurring in complex mixtures predominantly in short-term peaks after rainfall events (publications 1 & 4). Respective pesticide concentration maxima were linked to declines in vulnerable invertebrate species and exceeded regulatory acceptable concentrations in about 80% of agricultural streams, while these thresholds were still estimated partly insufficient to protect the invertebrate community (publication 2). The co-occurrence of pesticides in streams led to a risk underestimated in the single substance-oriented ERA by a factor of about 3.2 in realistic worst-case scenarios, which is further exacerbated by a high frequency at which non-target organism are exposed to pesticides (publication 3). Stream water samples taken after rainfall caused distinct effects in bioassays which were only explainable to a minor extent by the many analytes, indicating the relevance of unknown chemical or biological mixture components (publication 4). Finally, the regulatory monitoring of surface waters under the Water Framework Directive (WFD) was found to significantly underestimate pesticide risks, as about three quarters of critical pesticides and more than half of streams at risk were overlooked (publication 5).
Essentially, this thesis involves a new level of validation of the ERA of pesticides in aquatic ecosystems by assessing pesticide occurrence and environmental impacts at a scale so far unique. The overall results demonstrate that the current agricultural use of pesticides leads to significant impacts on stream ecology that go beyond the level tolerated under the ERA. This thesis identified the underestimation of pesticide exposure, the potential insufficiency of regulatory thresholds and the general inertia of the authorisation process as the main causes why the ERA fails to meet its objectives. To achieve a sustainable use of pesticides, the thesis proposes substantial refinements of the ERA. Adequate monitoring programmes such as the KgM, which go beyond current government monitoring efforts, will continue to be needed to keep pesticide regulators constantly informed of the validity of their prospective ERA, which will always be subject to uncertainty.
Statistical eco(-toxico)logy
(2017)
Freshwaters are of immense importance for human well-being.
Nevertheless, they are currently facing unprecedented levels of threat from habitat loss and degradation, overexploitation, invasive species and
pollution.
To prevent risks to aquatic ecosystems, chemical substances, like agricultural pesticides, have to pass environmental risk assessment (ERA) before entering the market.
Concurrently, large-scale environmental monitoring is used for surveillance of biological and chemical conditions in freshwaters.
This thesis examines statistical methods currently used in ERA.
Moreover, it presents a national-scale compilation of chemical monitoring data, an analysis of drivers and dynamics of chemical pollution in streams and, provides a large-scale risk assessment by combination with results from ERA.
Additionally, software tools have been developed to integrate different datasets used in ERA.
The thesis starts with a brief introduction to ERA and environmental monitoring and gives an overview of the objectives of the thesis.
Chapter 2 addresses experimental setups and their statistical analyses using simulations.
The results show that current designs exhibit unacceptably low statistical power, that statistical methods chosen to fit the type of data provide higher power and that statistical practices in ERA need to be revised.
In chapter 3 we compiled all available pesticide monitoring data from Germany.
Hereby, we focused on small streams, similar to those considered in ERA and used threshold concentrations derived during ERA for a large-scale assessment of threats to freshwaters from pesticides.
This compilation resulted in the most comprehensive dataset on pesticide exposure currently available for Germany.
Using state-of-the-art statistical techniques, that explicitly take the limits of quantification into account, we demonstrate that 25% of small streams are at threat from pesticides.
In particular neonicotinoid pesticides are responsible for these threats.
These are associated with agricultural intensity and can be detected even at low levels of agricultural use.
Moreover, our results indicated that current monitoring underestimates pesticide risks, because of a sampling decoupled from precipitation events.
Additionally, we provide a first large-scale study of annual pesticide exposure dynamics.
Chapters 4 and 5 describe software solutions to simplify and accelerate the integration of data from ERA, environmental monitoring and ecotoxicology that is indispensable for the development of landscape-level risk assessment.
Overall, this thesis contributes to the emerging discipline of statistical ecotoxicology and shows that pesticides pose a large-scale threat to small streams.
Environmental monitoring can provide a post-authorisation feedback to ERA.
However, to protect freshwater ecosystems ERA and environmental monitoring need to be further refined and we provide software solutions to utilise existing data for this purpose.
Wild bees are essential for the pollination of wild and cultivated plants. However, within the
last decades, the increasing intensification of modern agriculture has led to both a reduction and fragmentation as well as a degradation of the habitats wild bees need. The resulting loss of pollinators and their pollination poses an immense challenge to global food production. To support wild bees, the availability of flowering resources is essential. However, the flowering period of each resource is temporally limited and has different effects on pollinators and their pollination, depending on the time of their flowering.
Therefore, to efficiently promote and manage wild bee pollinators in agricultural landscapes, we identified species-specific key floral resources of three selected wild bee species and their spatial and temporal availability (CHAPTERS 2, 3 & 4). We examined, which habitat types predominantly provide these resources (CHAPTERS 3 & 4). We also investigated whether floral resource maps based on the use of these key resources and their spatial and temporal availability explain the abundance and development of the selected wild bees (CHAPTERS 3 & 4) and pollination (CHAPTER 5) better than habitat maps, that only indirectly account for the availability of floral resources.
For each of the species studied, we were able to identify different key pollen sources, predominantly woody plants in the early season (April/May) and increasingly herbaceous plants in the later season (June/July; CHAPTERS 2, 3 & 4). The open woody semi-natural habitats of our agricultural landscapes provided about 75% of the floral resources for the buff-tailed bumblebees, 60% for the red mason bees, and 55% for the horned mason bees studied, although they accounted for only 3% of the area (CHAPTERS 3 & 4). In addition, fruit orchards provided about 35% of the floral resources for the horned mason bees on 4% of the landscape area (CHAPTER 3). We showed that both mason bee species benefited from the resource availability in the surrounding landscapes (CHAPTER 3). Yet this was not the case for the bumblebees (CHAPTER 4). Instead, the weight gain of their colonies, the number of developed queen cells and their colony survival were higher with increasing proximity to forests. The proximity to forests also had a positive effect on the mason bees studied (CHAPTER 3). In addition, the red mason bees benefited from herbaceous semi-natural habitats. The proportion of built-up areas had a negative effect on the horned mason bees, and the proportion of arable land on the red mason bees. The habitat maps explained horned mason bee abundances equally well as the floral resource maps, but red mason bee abundances were distinctly better explained by key floral resources. The pollination of field bean increased with higher proportions of early floral resources, whereas synchronous floral resources showed no measurable reduction in their pollination (CHAPTER 5). Habitat maps also explained field bean pollination better than floral resource maps. Here, pollination increased with increasing proportions of built-up areas in the landscapes and decreased with increasing proportions of arable land.
Our results highlight the importance of the spatio-temporal availability of certain key species as resource plants of wild bees in agricultural landscapes. They show that habitat maps are ahead of, or at least equal to, spatio-temporally resolved floral resource maps in predicting wild bee development and pollination. Nevertheless, floral resource maps allow us to draw more accurate conclusions between key floral resources and the organisms studied. The proximity to forest edges had a positive effect on each of the three wild bee species studied. However, besides pure food availability, other factors seem to co-determine the occurrence of wild bees in agricultural landscapes.
Soil organic matter (SOM) is a key component responsible for sequestration of organic molecules in soil and regulation of their mobility in the environment. The basic structure of SOM is a supramolecular assembly responding dynamically to the environmental factors and the presence of interacting molecules. Despite of the advances in the understanding of sorption processes, the relation between sorbate molecules, SOM supramolecular structure and its dynamics is limited. An example of a dynamic nature of SOM is a physicochemical matrix aging that is responsible for SOM structural arrangement. The underlying process of the physicochemical aging is the formation of water molecule bridges (WaMB) between functional groups of molecular segments. Since WaMB influence the stiffness of SOM structure, it was hypothesized that formation of WaMB contributes to the sequestration of organic molecules. However, this hypothesis has not been tested experimentally until now. Furthermore, the knowledge about the influence of organic molecules on WAMB is based solely on computer modeling studies. In addition, the influence of organic molecules on some physical phases forming SOM is not well understood. Especially, the interactions between organic molecules and crystalline phases represented by aliphatic crystallites, are only presumed. Thus, the investigation of those interactions in unfractioned SOM is of high importance.
In order to evaluate the involvement of WaMB in the sequestration of organic molecules and to increase our understanding about interactions of organic chemicals with WaMB or aliphatic crystallites, the following hypotheses were tested experimentally. 1) Similarly to crystalline phases in synthetic polymers, aliphatic crystallites, as a part of SOM, cannot be penetrated by organic molecules. 2) The stability of WaMB is determined by the ability of surrounding molecules to interact with water forming WaMB. 3) WaMB prevent organic molecules to leave the SOM matrix and contribute thus to their immobilization. In order to test the hypotheses 1 and 2, a set of experiments including treatment of soils with chosen chemicals was prepared. Interaction abilities of these chemicals were characterized using interaction parameters from the Linear Solvation Energy Relationship theory. WaMB characteristics were monitored using Differential Scanning Calorimetry (DSC) allowing to measure the WaMB thermal stability and the rigidity of SOM matrix; which in turn was determined by the heat capacity change. In addition, DSC and 13C NMR spectroscopy assessed thermal properties and the structure of aliphatic crystallites. The spiking of samples with a model compound, phenol, and measurements of its desorption allowed to link parameters of the desorption kinetics with WaMB characteristics.
The investigation showed that the WaMB stability is significantly reduced by the presence of molecules with H-donor/acceptor interaction abilities. The matrix rigidity associated with WaMB was mainly influenced by the McGowan’s volume of surrounding molecules, suggesting the importance of dispersion forces. The desorption kinetics of phenol followed a first order model with two time constants. Both of them showed a relation with WaMB stability, which supports the hypothesis that WaMB contribute to the physical immobilization of organic molecules. The experiments targeted to the crystallites revealed their structural change from the ordered to the disordered state, when in contact with organic chemicals. This manifested in their melting point depression and the decrease of overall crystallinity. Described structural changes were caused by molecules interacting with specific as well as non-specific forces, which suggests that aliphatic crystallites can be penetrated and modified by molecules with a broad range of interaction abilities.
This work shows that chosen organic molecules interact with constituents of SOM as exemplified on WaMB and aliphatic crystallites, and cause measurable changes of their structure and properties. These findings show that the relevance of aliphatic crystallites for sorption in soil may have been underestimated. The results support the hypothesis that physicochemical matrix aging significantly contributes to the immobilization of organic chemicals in SOM.
The estimation of the potential risk of pesticide entries into streams - and therefore the potential risk for the ecosystems - is an important requirement for the planning of risk mitigation strategies. Especially on the landscape level the required event triggered sampling methods are conjuncted with considerable efforts with regard to input data, time and personnel. To circumvent these problems simulation models form a reasonable alternative. The aims of this work were (A) the development of a simulation tool for the estimation of pesticide entries into surface waters on the landscape level, and (B) the application of the simulator for an exposure- and risk-assessment as well as the assessment of negative effects of pesticides on aquatic communities. Section 1 - Exposure-, Risk- and Effects In sections 1.1 and 1.2 the simulation model was applied to a multitude of small and medium sized streams in an agricultural impacted study area around the city of Braunschweig, Germany. Section 1.3 gives an overview of the simulators field of application and the general system structure. Section 1.1 - Scenario based simulation of runoff-related pesticide entries into small streams on a landscape level (English publication, p. 27): In this paper we present a simulation tool for the simulation of pesticide entry from arable land into adjacent streams. We used the ratio of exposure to toxicity (REXTOX) model proposed by the OECD which was extended to calculate pesticide concentrations in adjacent streams. We simulated the pesticide entry on the landscape level at 737 sites in small streams situated in the central lowland of Germany. The most significant model parameters were the width of the no-application-zone and the degree of plant-interception. The simulation was carried out using eight different environmental scenarios, covering variation of the width of the no-application-zone, climate and seasonal scenarios. The highest in-stream concentrations were predicted at a scenario using no (0 m) buffer zone in conjunction with increased precipitation. According to the predicted concentrations, the risk for the aquatic communities was estimated based on standard toxicity tests and the application of a safety factor. Section 1.2 - Linking land use variables and invertebrate taxon richness in small and medium-sized agricultural streams on a landscape level (English publication, p. 50): In this study the average numbers of invertebrate species across an arable landscape in central Germany (surveys from 15 years in 90 streams at 202 sites) were assessed for their correlation with environmental factors such as stream width, land use (arable land, forest, pasture, settlement), soil type and agricultural derived stressors. The stress originating from arable land was estimated by the factor "risk of runoff", which was derived from a runoff-model (rainfall induced surface runoff). Multivariate analysis explained 39.9% of the variance in species number, revealing stream width as the most important factor (25.3%) followed by risk of runoff (9.7%). Section 1.3 - Informationssystem zur ökotoxikologischen Bewertung der Gewässergüte in Bezug auf Pflanzenschutzmitteleinträge aus der Landwirtschaft - Systemaufbau und Anwendungsmöglichkeiten (German publication, p. 61): Section 1.3 contains a short overview of the simulation tool, the field of application and some examples of use, covering the effects of the width of the buffer zone as well as the creation of risk maps on the landscape level. Section 2 - The simulation tool An important aspect for the employment of a simulation model in the context of risk assessment is the applicability in practice: the accessibility of the needed input data, the conversion of the mathematical model into a software application that can be run on any current personnel computer and also an appropriate end-user documentation of the system. Section 1.4 - Informationssystem zur ökotoxikologischen Bewertung der Gewässergüte in Bezug auf Pflanzenschutzmitteleinträge aus der Landwirtschaft - Simulationsmodell und Systemaufbau (German report, p. 67): In this section a general overview of the simulation model as well as the schematic system structure given. Section 1.5 - Benutzerhandbuch (German report, p. 71): The user manual contains details concerning the installation of the system, generation of the required input data and the general use of the system. Moreover it presents some application examples (what-if analyses). Section 1.6 - Technical documentation (German report, p. 104): The technical documentation describes internal structures and processes of the simulation system. Section 1.6 provides information regarding the required structure of input/output tables.
Inland waters play an active role in the global carbon cycle. They collect carbon from upstream landmasses and transport it downstream until it finally reaches the ocean. Along this path, manifold processing steps are evident, resulting in (permanent) retention of carbon by sediment burial as well as loss by evasion to the atmosphere. Constraining these carbon fluxes and their anthropogenic perturbation is an urgent need. In this context, attention needs to be set on a widespread feature of inland waters: their partial desiccation. This results in the emergence of formerly inundated sediments to the atmosphere, referred to as dry inland waters. One observed feature of dry inland waters are disproportional high carbon dioxide (CO2) emissions. However, this observation was so far based on local case studies and knowledge on the global prevalence and fundamental mechanisms of these emissions is lacking. Against this background, this thesis aims to provide a better understanding of the magnitude and mechanisms of carbon emissions from dry inland waters on the global and local scale and to assess the impact of dry inland waters on the global carbon cycle. The specific research questions of this thesis were: (1) How do gaseous carbon emissions from dry inland waters integrate into the global carbon cycle and into global greenhouse gas (GHG) budgets? (2) What effect do seasonal and long term drying have on the carbon cycling of inland waters? The thesis revealed that dry inland waters emit disproportional large amounts of CO 2 on a global scale and that these emissions share common drivers across ecosystems. Quantifying global reservoir drawdown and upscaling carbon fluxes to the global scale suggests that reservoirs emit more carbon than they bury, challenging the current understanding of reservoirs as net carbon sinks. On the local scale, this thesis revealed that both, heterogeneous emission pattern between different habitats and seasonal variability of carbon emissions from the drawdown area, needs to be considered. Further, this thesis showed that re-mobilization of buried carbon upon permanent desiccation of water bodies can explain the observed emission rates, supporting the hypothesis of a positive feedback-loop between climate change and desiccation of inland waters. Overall, the present thesis highlights the importance of adding emissions from dry inland waters as a pathway to the global carbon cycle of inland waters.
The increasing, anthropogenic demand for chemicals has created large environmental problems with repercussions for the health of the environment, especially aquatic ecosystems. As a result, the awareness of the public and decision makers on the risks from chemical pollution has increased over the past half-century, prompting a large number of studies in the field of ecological toxicology (ecotoxicology). However, the majority of ecotoxicological studies are laboratory based, and the few studies extrapolating toxicological effects in the field are limited to local and regional levels. Chemical risk assessment on large spatial scales remains largely unexplored, and therefore, the potential large-scale effects of chemicals may be overlooked.
To answer ecotoxicological questions, multidisciplinary approaches that transcend classical chemical and toxicological concepts are required. For instance, the current models for toxicity predictions - which are mainly based on the prediction of toxicity for a single compound and species - can be expanded to simultaneously predict the toxicity for different species and compounds. This can be done by integrating chemical concepts such as the physicochemical properties of the compounds with evolutionary concepts such as the similarity of species. This thesis introduces new, multidisciplinary tools for chemical risk assessments, and presents for the first time a chemical risk assessment on the continental scale.
After a brief introduction of the main concepts and objectives of the studies, this thesis starts by presenting a new method for assessing the physiological sensitivity of macroinvertebrate species to heavy metals (Chapter 2). To compare the sensitivity of species to different heavy metals, toxicity data were standardized to account for the different laboratory conditions. These rankings were not significantly different for different heavy metals, allowing the aggregation of physiological sensitivity into a single ranking.
Furthermore, the toxicological data for macroinvertebrates were used as input data to develop and validate prediction models for heavy metal toxicity, which are currently lacking for a wide array of species (Chapter 3). Apart from the toxicity data, the phylogenetic information of species (evolutionary relationships among species) and the physicochemical parameters for heavy metals were used. The constructed models had a good explanatory power for the acute sensitivity of species to heavy metals with the majority of the explained variance attributed to phylogeny. Therefore, the integration of evolutionary concepts (relatedness and similarity of species) with the chemical parameters used in ecotoxicology improved prediction models for species lacking experimental toxicity data. The ultimate goal of the prediction models developed in this thesis is to provide accurate predictions of toxicity for a wide range of species and chemicals, which is a crucial prerequisite for conducting chemical risk assessment.
The latter was conducted for the first time on the continental scale (Chapter 4), by making use of a dataset of 4,000 sites distributed throughout 27 European countries and 91 respective river basins. Organic chemicals were likely to exert acute risks for one in seven sites analyzed, while chronic risk was prominent for almost half of the sites. The calculated risks are potentially underestimated by the limited number of chemicals that are routinely analyzed in monitoring programmes, and a series of other uncertainties related with the limit of quantification, the presence of mixtures, or the potential for sublethal effects not covered by direct toxicity.
Furthermore, chemical risk was related to agricultural and urban areas in the upstream catchments. The analysis of ecological data indicated chemical impacts on the ecological status of the river systems; however, it is difficult to discriminate the effects of chemical pollution from other stressors that river systems are exposed to. To test the hypothesis of multiple stressors, and investigate the relative importance of organic toxicants, a dataset for German streams is used in chapter 5. In that study, the risk from abiotic (habitat degradation, organic chemicals, and nutrients enrichment) and biotic stressors (invasive species) was investigated. The results indicated that more than one stressor influenced almost all sites. Stream size and ecoregions influenced the distribution of risks, e.g., the risks for habitat degradation, organic chemicals and invasive species increased with the stream size; whereas organic chemicals and nutrients were more likely to influence lowland streams. In order to successfully mitigate the effects of pollutants in river systems, co-occurrence of stressors has to be considered. Overall, to successfully apply integrated water management strategies, a framework involving multiple environmental stressors on large spatial scales is necessary. Furthermore, to properly address the current research needs in ecotoxicology, a multidisciplinary approach is necessary which integrates fields such as, toxicology, ecology, chemistry and evolutionary biology.
Studies on the toxicity of chemical mixtures find that components at levels below no-observed-effect concentrations (NOECs) may cause toxicity resulting from the combined effects of mixed chemicals. However, chemical risk assessment frequently focuses on individual chemical substances, although most living organisms are substantially exposed to chemical mixtures rather than single substances. The concepts of additive toxicity, concentration addition (CA), and independent action (IA) models are often applied to predict the mixture toxicity of similarly and dissimilarly acting chemicals, respectively. However, living organisms and the environment may be exposed to both types of chemicals at the same time and location. In addition, experimental acquisition of toxicity data for every conceivable mixture is unfeasible since the number of chemical combinations is extremely large. Therefore, an integrated model to predict mixture toxicity on the basis of single mixture components having various modes of toxic action (MoAs) needs to be developed. The objectives of the present study were to analyze the challenges in predicting mixture toxicity in the environment, and to develop integrated models that overcome the limitations of the existing prediction models for estimating the toxicity of non-interactive mixtures through computational models. For these goals, four sub-topics were generated in this study. Firstly, applicable domains and limitations of existing integrated models were analyzed and grouped into three kinds of categories in this study. There are current approaches used to assess mixture toxicity; however, there is a need for a new research concept to overcome challenges associated with such approaches, which recent studies have addressed. These approaches are discussed with particular emphasis on those studies involved in computational approaches to predict the toxicity of chemical mixtures based on the toxicological data of individual chemicals. Secondly, through a case study and a computational simulation, it was found that the Key Critical Component (KCC) and Composite Reciprocal (CR) methods (as described in the European Union (EU) draft technical guidance notes for calculating the Predicted No Effect Concentration (PNEC) and Derived No Effect Level (DNEL) of mixtures) could derive significantly different results. As the third and fourth sub-topics of this study, the following two integrated addition models were developed and successfully applied to overcome the inherent limitations of the CA and IA models, which could be theoretically used for either similarly or dissimilarly acting chemicals: i) a Partial Least Squares-Based Integrated Addition Model (PLS-IAM), and, ii) a Quantitative Structure-Activity Relationship-Based Two-Stage Prediction (QSAR-TSP) model. In this study, it was shown that the PLS-IAM might be useful to estimate mixture toxicity when the toxicity data of similar mixtures having the same compositions were available. In the case of the QSAR-TSP model, it showed the potential to overcome the critical limitation of the conventional TSP model, which requires knowledge of the MoAs for all chemicals. Therefore, this study presented good potential for the advanced integrated models (e.g., PLS-IAM and QSAR-TSP), while considering various non-interactive constituents that have different MoAs in order to increase the reliance of conventional models and simplify the procedure for risk assessment of mixtures.
Natural pest control and pollination are important ecosystem services for agriculture. They can be supported by organic farming and by seminatural habitats at the local and landscape scale.
The potential of seminatural habitats to support predatory flies (chapters 2 and 3) and bees(chapter 7) at the local and landscape scale was investigated in seminatural habitats. Predatory flies were more abundant in woody habitats and positively related to landscape complexity. The diversity and the abundance of honey and wild bees were positively related to the supply of flowers offered in the seminatural habitats.
The influence of organic farming, adjacent seminatural habitats and landscape complexity on pest control (chapter 4) and pollination (chapter 6) was investigated in 18 pumpkin fields. Organic farming lacked strong effects both on the pest control and on the pollination of pumpkin.
Pest control is best supported at the local scale by the flower abundance in the adjacent habitat. The flower supply positively affected the density of natural enemies and tended to reduce aphid densities in pumpkin fields.
Pumpkin provides a striking example for a dominant role of wild pollinators for pollination success, because bumble bees are the key pollinators of pumpkin in Germany, despite a higher visitation frequency of honey bees. Pollination is best supported by landscape complexity. Bumble bee visits and as a result pollen delivery in pumpkin were negatively related to the dominance of agricultural land in the surrounding landscape.
The influence of aphid density (chapter 8) and pollination (chapter 5) on pumpkin yield was evaluated. Pumpkin yields were not affected by aphid densities observed in the pumpkin fields and not limited by pollination at the current levels of bee visitation.
In conclusion, especially seminatural habitats, that provide diverse, continuous floral resources, are important for natural enemies and pollinators. A sufficient proportion of different seminatural habitat types in agricultural landscapes should be maintained and restored. Thereby natural enemies such as predatory flies, wild pollinators such as bumble bees, and the pest control and pollination provided by them can be supported.