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Institute
- Institut für Umweltwissenschaften (19) (remove)
In the last decades, it became evident that the world is facing an unprecedented, human-induced global biodiversity crisis with amphibians being one of the most threatened species groups. About 41% of the amphibian species are classified as endangered by the IUCN, but even in amphibian species that are listed as "least concern", population declines can be observed on a local level. With land-use change and agrochemicals (i.e. pesticides), two of the main drivers for this amphibian decline are directly linked to intensive agriculture, which is the dominant landscape type in large parts of Europe. Thus, understanding the situation of amphibians in the agricultural landscape is crucial for conservation measures. In the present thesis, I investigated the effects of viticulture on amphibian populations around Landau in der Pfalz (Germany) in terms of habitat use, pesticide exposure, biometric traits as well as genetic and age structure. From the perspective of amphibians, land-use change means usually the destruction of habitats in agricultural landscapes, which often leads to landscape fragmentation. Thus, I followed the question if also vineyards lead to the fragmentation of the landscape and if pesticides that are frequently used in viticulture have to be considered as a factor too, so if there is a chemical landscape fragmentation. Using telemetry, I could show that common toads (Bufo bufo) can be found directly in vineyards, but that they tend to avoid them as habitat. Analysing the genetic structure of common frogs (Rana temporaria) revealed that vineyards have to be considered as a barrier for amphibians. To identify if pesticides contribute to the resulting landscape fragmentation, I conducted an arena choice experiment in the laboratory in which I found evidence for an avoidance of pesticide-contaminated soil. Such an avoidance could be one of the underlying reasons for a potential chemical landscape fragmentation. By combining telemetry data with information about pesticide applications from local wine growers, I could show that a large part of the common toads is likely to come in contact with pesticides. Further, I demonstrated that the agricultural landscape, probably due to the application of pesticides, can have negative effects on the reproduction capacity of common toads. By studying palmate newts (Lissotriton helveticus) I found that adult newts from agricultural ponds are smaller than those from forest ponds. As I did not find differences in the age structure and growth, these differences might be carry-over effects from earlier life stages. While agricultural ponds might be suitable habitats for adult palmate newts, the potential carry-over effect indicates suboptimal conditions for larvae and/or juveniles. I conclude that the best management measure for sustaining amphibians in the agricultural landscape would be a heterogeneous cultural landscape with a mosaic of different habitat patches that work without or at least a reduced amount of pesticides. Green corridors between populations and different habitats would allow migrating individuals to avoid agricultural and thus pesticide-contaminated areas. This would reduce the pesticide exposure risk of amphibians, while preventing the fragmentation of the landscape and thus the isolation of populations.
This thesis was motivated by the need to advance the knowledge on the variability and dynamics of energy fluxes in lakes and reservoirs, as well as about the physical processes that regulate the fluxes at both the air and water side of the air-water interface.
In the first part, I re-examine how mechanical energy, resulting from its major source – the vertical wind energy flux - distributes into the various types of water motions, including turbulent flows and surface and internal waves. Although only a small fraction of the wind energy flux from the atmosphere is transferred to the water, it is crucial for physical, biogeochemical and ecological processes in lentic ecosystems. Based on extensive air- and water-side measurements collected at two small water bodies (< 10 km2), we estimated the energy fluxes and energy content in surface and in internal waves. Overall, the estimated energy fluxes and energy content agree well with results reported for larger water bodies, suggesting that the energetics driving the water motions in enclosed basins is similar, independently of the basin size. Our findings highlight the importance of the surface waves that receive the largest fraction of the wind energy flux, which strongly nonlinearly increases for wind speeds exceeding 3 m s-1. We found that the existing parameterization of the wave height as a function of wind speed and fetch length did not reproduce the measured wave amplitude in lakes. On average, the highest energy content was observed in basin-scale internal waves, together with high-frequency internal waves exhibiting seasonal variability and varies among the aquatic systems. During our analysis, we discovered the diurnal variability of the energy dissipation rates in the studied lake, suggesting biogenic turbulence generation, which appears to be a widespread phenomenon in lakes and reservoirs.
In the second part of the thesis, I addressed current knowledge gaps related to the bulk transfer coefficients (also known as the drag coefficient, the Stanton number and the Dalton number), which are of a particular importance for the bulk estimation of the surface turbulent fluxes of momentum, sensible and latent heat in the atmospheric boundary layer. Their inaccurate representation may lead to significant errors in flux estimates, affecting, for example, the weather and climate predictions or estimations of the near-surface current velocities in lake hydrodynamic models. Although the bulk transfer coefficients have been extensively studied over the past several decades (mainly in marine and large-lake environments), there has been no systematic analysis of measurements obtained at lakes of different size. A significant increase of the transfer coefficients at low wind speeds (< 3 m s-1) has been observed in several studies, but, to date, it has remained unexplained. We evaluated
the bulk transfer coefficients using flux measurements from 31 lakes and reservoirs. The estimates were generally within the range reported in previous studies for large lakes and oceans. All transfer coefficients increased substantially at low wind speeds, which was found to be associated with the presence of gusts and capillary waves (except the Dalton number). We found that the Stanton number is systematically higher than the Dalton number. This challenges the assumption made in the Bowen-ratio method, which is widely used for estimating evaporation rates from micrometeorological measurements. We found that the variability of the transfer coefficients among the lakes could be associated with lake surface area. In flux parameterizations at lake surfaces, it is recommended to consider variations in the drag coefficient and the Stanton number due to wind gustiness and capillary wave roughness while the Dalton number could be considered as constant at all wind speeds.
In the third part of the thesis, I address the key drivers of the near-surface turbulence that control the gas exchange in a large regulated river. As all inland waters, rivers are an important natural source of greenhouse gases. The effects of the widespread alteration and regulation of river flow for human demands on gas exchange is largely unknown. In particular, the near-surface turbulence in regulated rivers has been rarely measured and its drivers have not been identified. While in lakes and reservoirs, near-surface turbulence is mainly related to atmospheric forcing, in shallow rivers and streams it is generated by bottom friction of the gravity-forced flow. The studied large regulated river represents a transition between these two cases. Atmospheric forcing and gravity were the dominant drivers of the near-surface turbulence for a similar fraction of the measurement period. Based on validated scalings, we derived a simple model for estimating the relative contributions of wind and bottom friction to near-surface turbulence in lotic ecosystems with different flow depths. Large diel variability in the near-surface energy dissipation rates due to flow regulation leads to the same variability in gas exchange. This suggests that estimates of gas fluxes from rivers are biased by measurements performed predominantly during daytime.
In addition, the novelty in all the analyses described above is the use of the turbulent surface fluxes measured directly by the eddy-covariance technique – at the moment of writing, the most advanced method. Overall, this thesis is of a potential interest for a broad range of scientific disciplines, including limnology, micrometeorology and open channel hydraulics.
The decline of biodiversity can be observed worldwide and its consequences are alarming. It is therefore crucial that nature must be protected and, where possible, restored. A wide variety of different project options are possible. Yet in the context of limited availability of resources, the selection of the most efficient measures is increasingly important. For this purpose, there is still a lack of information. This pertains, as outlined in the next paragraph, in particular, to information at different scales of projects.
Firstly, there is a lack of information on the concrete added value of biodiversity protection projects. Secondly, there is a lack of information on the actual impacts of such projects and on the costs and benefits associated with a project. Finally, there is a lack of information on the links between the design of a project, the associated framework conditions and the perception of specific impacts. This paper addresses this knowledge gap by providing more information on the three scales by means of three empirical studies on three different biodiversity protection projects in order to help optimize future projects.
The first study “Assessing the trade-offs in more nature-friendly mosquito control in the Upper Rhine region” examines the added value of a more nature-friendly mosquito control in the Upper Rhine Valley of Germany using a contingent valuation method. Recent studies show that the widely used biocide Bti, which is used as the main mosquito control agent in many parts of the world, has more negative effects on nature than previously expected. However, it is not yet clear whether the population supports a more nature-friendly mosquito control, as such an adaptation could potentially lead to higher nuisance. This study attempts to answer this question by assessing the willingness to pay for an adapted mosquito control strategy that reduces the use of Bti, while maintaining nuisance protection within settlements. The results show that the majority of the surveyed population attaches a high value to a more nature-friendly mosquito control and is willing to accept a higher nuisance outside of the villages.
The second study “Inner city river restoration projects: the role of project components for acceptance” examines the acceptance of a river restoration project in Rhineland-Palatinate, Germany. Despite much effort, many rivers worldwide are still in poor condition. Therefore, a rapid implementation of river restoration projects is of great importance. In this context, acceptance by society plays a fundamental role, however, the factors determining such acceptance are still poorly understood. In particular, the complex interplay between the acceptance or rejection of specific project components and the acceptance of the overall project require further exploration. This study addresses this knowledge gap by assessing the acceptance of the project, its various ecological and social components, and the perception of real and fictitious costs as well as the benefits of the components. Our findings demonstrate that while acceptance of the overall project is generally rather high, many respondents reject one or more of the project's components. Complementary social project components, like a playground, find less support than purely ecological components. Overall, our research shows that complementary components may increase or decrease acceptance of the overall project. We, furthermore, found that differences in the acceptance of the individual components depend on individual concerns, such as perceived flood risk, construction costs, expected noise and littering as well as the quality of communication, attachment to the site, and the age of the respondents.
The third study “What determines preferences for semi-natural habitats in agrarian landscapes? A choice-modelling approach across two countries using attributes characterizing vegetation” investigates people's aesthetic preferences for semi-natural habitats in agricultural landscapes. The EU-Common Agricultural Policy promotes the introduction of woody and grassy semi-natural habitats (SNH) in agricultural landscapes. While the benefits of these structures in terms of regulating ecosystem services are already well understood, the effects of SNH on visual landscape quality is still not clear. This study investigates the factors determining people’s visual preferences in the context of grassy and woody SNH elements in Swiss and Hungarian landscapes using picture-based choice experiments. The results suggest that respondents’ choices strongly depend on specific vegetation characteristics that appear and disappear over the year. In particular, flowers as a source of colours and green vegetation as well as ordered structure and the proportion of uncovered soil in the picture play an important role regarding respondents’ aesthetic perceptions of the pictures.
The three empirical studies can help to make future projects in the study areas of biodiversity protection more efficient. While this thesis highlights the importance of exploring biodiversity protection projects at different scales, further analyses of the different scales of biodiversity protection projects are needed to provide a sound basis to develop guidance on identifying the most efficient biodiversity protection projects.
Vertebrate biodiversity is rapidly decreasing worldwide with amphibians being the most endangered vertebrate group. In the EU, 21 of 89 amphibian species are recognized as being endangered. The intensively used European agricultural landscape is one of the major causes for these declines. As agriculture represents an essential habitat for amphibians, exposure to pesticides can have adverse effects on amphibian populations. Currently, the European risk assessment of pesticides for vertebrates requires specific approaches for fish regarding aquatic vertebrate toxicity and birds as well as mammals for terrestrial vertebrate toxicity but does not address the unique characteristics of amphibians. Therefore, the overall goal of this thesis was to investigate the ecotoxicological effects of pesticides on Central European anuran amphibians. For this, effects on aquatic and terrestrial amphibian life stages as well as on reproduction were investigated. Then, in anticipation of a risk assessment of pesticides for amphibians, this thesis discussed potential regulatory risk assessment approaches.
For the investigated pesticides and amphibian species, it was observed that the acute aquatic toxicity of pesticides can be addressed using the existing aquatic risk assessment approach based on fish toxicity data. However, lethal as well as sublethal effects were observed in terrestrial juveniles after dermal exposure to environmentally realistic pesticide concentrations, which cannot be covered using an existing risk assessment approach. Therefore, pesticides should also be evaluated for potential terrestrial toxicity using risk assessment tools before approval. Additionally, effects of co-formulants and adjuvants of pesticides need specific consideration in a future risk assessment as they can increase toxicity of pesticides to aquatic and terrestrial amphibian stages. The chronic duration of combined aquatic and terrestrial exposure was shown to affect amphibian reproduction. Currently, such effects cannot be captured by the existing risk assessment as data involving field scenarios analysing effects of multiple pesticides on amphibian reproduction are too rare to allow comparison to data of other terrestrial vertebrates such as birds and mammals. In the light of these findings, future research should not only address acute and lethal effects, but also chronic and sublethal effects on a population level. As pesticide exposure can adversely affect amphibian populations, their application should be considered even more carefully to avoid further amphibian declines. Overall, this thesis emphasizes the urgent need for a protective pesticide risk assessment for amphibians to preserve and promote stable amphibian populations in agricultural landscapes.
Stream ecosystems are one of the most threatened ecosystems worldwide due to their exposure to diverse anthropogenic stressors. Pesticides appear to be the most relevant stressor for agricultural streams. Due to the current mismatch of modelled and measured pesticide concentrations, monitoring is necessary to inform risk assessment or improve future pesticide approvals. Knowing if biotic stress responses are similar across large scales and long time frames could ultimately help in estimating protective stressor thresholds.
This thesis starts with an overview of entry pathways of pesticides to streams as well as the framework of current pesticide monitoring and gives an outline of the objectives of the thesis. In chapter 2, routine monitoring data based on grab sampling from several countries is analysed to identify the most frequently occurring pesticide mixtures. These mixtures are comprised of relatively low numbers of pesticides, of which herbicides are dominating. The detected pesticide mixtures differ between regions and countries, due to differences in the spectrum of analysed compounds and limits of quantification. Current routine monitoring does not include sampling during pesticide peaks associated with heavy rainfall events which likely influences the detected pesticide mixtures. In chapter 3, sampling rates of 42 organic pesticides for passive sampling are provided together with recommendations for the monitoring of field-relevant peaks. Using this information, in chapter 4 a pesticide gradient is established in an Eastern European region where agricultural intensity adjacent to sampled streams ranges from low to high. In contrast to current routine monitoring, rainfall events were sampled and a magnitude of pesticides were analysed. This led to the simultaneous detection of numerous pesticides of which one to three drive the pesticide toxicity. The toxicity, however, showed no relationship to the agricultural intensity. Using microcosms, the stress responses of fungal communities, the hyphomycetes, and the related ecosystem function of leaf decomposition, is investigated in chapter 5. Effects of a field-relevant fungicide mixture are examined across three biogeographical regions for three consecutive cycles of microbial leaf colonisation and decomposition. Despite different initial communities, stress responses as well as recoveries were similar across biogeographical regions, indicating a general pattern.
Overall, this thesis contributes to an improved understanding of occurrence and concentrations of pesticides mixtures in streams, their monitoring and impact on an ecosystem function. We showed that estimated pesticide toxicities reach levels that affect non-target organisms and thereby potentially whole ecosystems. Routine monitoring, however, likely underestimates the threat by pesticides. Effects leading to a loss in biodiversity or functions in streams ecosystems can be reduced by reassessing approved pesticides with ongoing targeted monitoring and increased knowledge of effects caused by these pesticides.
Environmental processes transforming inorganic nanoparticles: implications on aquatic invertebrates
(2020)
Engineered inorganic nanoparticles (EINPs) are produced and utilized on a large scale and will end up in surface waters. Once in surface waters, EINPs are subjected to transformations induced by environmental processes altering the particles’ fate and inherent toxicity. UV irradiation of photoactive EINPs is defined as one effect-inducing pathway, leading to the formation of reactive oxygen species (ROS), increasing EINP toxicity by exerting oxidative stress in aquatic life. Simultaneously, UV irradiation of photoactive EINP alters the toxicity of co-occurring micropollutants (e.g. pesticides) by affecting their degradation. The presence of natural organic matter (NOM) reduces the agglomeration and sedimentation of EINPs, extending the exposure of pelagic species, while delaying the exposure of benthic species living in and on the sediment, which is suggested as final sink for EINPs. However, the joint impact of NOM and UV irradiation on EINP-induced toxicity, but also EINP-induced degradation of micropollutants, and the resulting risk for aquatic biota, is poorly understood. Although potential effects of EINPs on benthic species are increasingly investigated, the importance of exposure pathways (waterborne or dietary) is unclear, along with the reciprocal pathway of EINPs, i.e. the transport back from aquatic to terrestrial ecosystems. Therefore, this thesis investigates: (i) how the presence of NOM affects the UV-induced toxicity of the model EINP titanium dioxide (nTiO2) on the pelagic organism Daphnia magna, (ii) to which extent UV irradiation of nTiO2 in the presence and absence of NOM modifies the toxicity of six selected pesticides in D. magna, (iii) potential exposure pathway dependent effects of nTiO2 and silver (nAg) EINPs on the benthic organism Gammarus fossarum, and (iv) the transport of nTiO2 and gold EINPs (nAu) via the merolimnic aquatic insect Chaetopteryx villosa back to terrestrial ecosystems. nTiO2 toxicity in D. magna increased up to 280-fold in the presence of UV light, and was mitigated by NOM up to 12-fold. Depending on the pesticide, UV irradiation of nTiO2 reduced but also enhanced pesticide toxicity, by (i) more efficient pesticide degradation, and presumably (ii) formation of toxic by-products, respectively. Likewise, NOM reduced and increased pesticide toxicity, induced by (i) protection of D. magna against locally acting ROS, and (ii) mitigation of pesticide degradation, respectively. Gammarus’ energy assimilation was significantly affected by both EINPs, however, with distinct variation in direction and pathway dependence between nTiO2 and nAg. EINP presence delayed C. villosa emergence by up to 30 days, and revealed up to 40% reduced lipid reserves, while the organisms carried substantial amounts of nAu (~1.5 ng/mg), and nTiO2 (up to 2.7 ng/mg). This thesis shows, that moving test conditions of EINPs towards a more field-relevant approach, meaningfully modifies the risk of EINPs for aquatic organisms. Thereby, more efforts need to be made to understand the relative importance of EINP exposure pathways, especially since a transferability between different types of EINPs may not be given. When considering typically applied risk assessment factors, adverse effects on aquatic systems might already be expected at currently predicted environmental EINP concentrations in the low ng-µg/L range.
Lakes and reservoirs are important sources of methane, a potent greenhouse gas. Although freshwaters cover only a small fraction of the global surface, their contribution to global methane emission is significant and this is expected to increase, as a positive feedback to climate warming and exacerbated eutrophication. Yet, global estimates of methane emission from freshwaters are often based on point measurements that are spatio-temporally biased. To better constrain the uncertainties in quantifying methane fluxes from inland waters, a closer examination of the processes transporting methane from sediment to atmosphere is necessary. Among these processes, ebullition (bubbling) is an important transport pathway and is a primary source of uncertainty in quantifying methane emissions from freshwaters. This thesis aims to improve our understanding of ebullition in freshwaters by studying the processes of methane bubble formation, storage and release in aquatic sediments. The laboratory experiments demonstrate that aquatic sediments can store up to ~20% (volumetric content) gas and the storage capacity varies with sediment properties. The methane produced is stored as gas bubbles in sediment with minimal ebullition until the storage capacity is reached. Once the sediment void spaces are created by gas bubble formation, they are stable and available for future bubble storage and transport. Controlled water level drawdown experiments showed that the amounts of gas released from the sediment scaled with the total volume of sediment gas storage and correlated linearly to the drop in hydrostatic pressure. It was hypothesized that not only the timing of ebullition is controlled by sediment gas storage, but also the spatial distribution of ebullition. A newly developed freeze corer, capable of characterizing sediment gas content under in situ environments, enabled the possibility to test the hypothesis in a large subtropical lake (Lake Kinneret, Israel). The results showed that gas content was variable both vertically and horizontally in the lake sediment. Sediment methane production rate and sediment characteristics could explain these variabilities. The spatial distribution of ebullition generally was in a good agreement with the horizontal distribution of depth-averaged (surface 1 m) sediment gas content. While discrepancies were found between sediment depth-integrated methane production and the snapshot ebullition rate, they were consistent in a long term (multiyear average). These findings provide a solid basis for the future development of a process-based ebullition model. By coupling a sediment transport model with a sediment diagenetic model, general patterns of ebullition hotspots can be predicted at a system level and the uncertainties in ebullition flux measurements can be better constrained both on long-term (months to years) and short-term (minutes to hours) scales.
With 47% land coverage in 2016, agricultural land was one of the largest terrestrial biomes in Germany. About 70% of the agricultural land was cropped area with associated pesticide applications. Agricultural land also represents an essential habitat for amphibians. Therefore, exposure of amphibians to agrochemicals, such as fertilizers and pesticides, seems likely. Pesticides can be highly toxic for amphibians, even a fraction of the original application rate may result in high amphibian mortality.
To evaluate the potential risk of pesticide exposure for amphibians, the temporal coincidence of amphibian presence on agricultural land and pesticide applications (N = 331) was analyzed for the fire-bellied toad (Bombina bombina), moor frog (Rana arvalis), spadefoot toad (Pelobates fuscus) and crested newt (Triturus cristatus) during spring migration. In 2007 and 2008, up to 80% of the migrating amphibians temporally coincided with pesticide applications in the study area of Müncheberg, about 50 km east of Berlin. Pesticide interception by plants ranged between 50 to 90% in winter cereals and 80 to 90% in winter rape. The highest coincidence was observed for the spadefoot toad, where 86.6% of the reproducing population was affected by a single pesticide in winter rape during stem elongation with 80% pesticide interception by plants. Late migrating species, such as the fire-bellied toad and the spadefoot toad, overlapped more with pesticide applications than early migrating species, such as the moor frog, did. Under favorable circumstances, the majority of early migrants may not coincide with the pesticide applications of arable fields during spring migration.
To evaluate the potential effect of pesticide applications on populations of the common frog (Rana temporaria), a landscape genetic study was conducted in the vinicultural area of Southern Palatinate. Due to small sample sizes at breeding sites within viniculture, several DNA sampling methods were tested. Furthermore, the novel repeated randomized selection of genotypes approach was developed to utilize genetic data from siblings for more reliable estimates of genetic parameters. Genetic analyses highlighted three of the breeding site populations located in viniculture as isolated from the meta-population. Genetic differentiation among breeding site populations in the viniculture (median pairwise FST=0.0215 at 2.34 km to 0.0987 at 2.39 km distance) was higher compared to genetic differentiation among breeding site populations in the Palatinate Forest (median pairwise FST=0.0041 at 5.39 km to 0.0159 at 9.40 km distance).
The presented studies add valuable information about the risk of pesticide exposure for amphibians in the terrestrial life stage and possible effects of agricultural land on amphibian meta-populations. To conserve endemic amphibian species and their (genetic) diversity in the long run, the risk assessment of pesticides and applied agricultural management measures need to be adjusted to protect amphibians adequately. In addition, other conservation measures such as the creation of new suitable breeding site should be considered to improve connectivity between breeding site populations and ensure the persistence of amphibians in the agricultural land.
Systemic neonicotinoids are one of the most widely used insecticide classes worldwide. In addition to their use in agriculture, they are increasingly applied on forest trees as a protective measure against insect pests. However, senescent leaves containing neonicotinoids might, inter alia during autumn leaf fall, enter nearby streams. There, the hydrophilic neonicotinoids may be remobilized from leaves to water resulting in waterborne exposure of aquatic non-target organisms. Despite the insensitivity of the standard test species Daphnia magna (Crustacea, Cladocera) toward neonicotinoids, a potential risk for aquatic organisms is evident as many other aquatic invertebrates (in particular insects and amphipods) display adverse effects when exposed to neonicotinoids in the ng/L- to low µg/L-range. In addition to waterborne exposure, in particular leaf-shredding invertebrates (= shredders) might be adversely affected by the introduction of neonicotinoid-contaminated leaves into the aquatic environment since they heavily rely on leaf litter as food source. However, dietary neonicotinoid exposure of aquatic shredders has hardly received any attention from researchers and is not considered during aquatic environmental risk assessment. The primary aim of this thesis is, therefore, (1) to characterize foliar neonicotinoid residues and exposure pathways relevant for aquatic shredders, (2) to investigate ecotoxicological effects of waterborne and dietary exposure on two model shredders, namely Gammarus fossarum (Crustacea, Amphipoda) and Chaetopteryx villosa (Insecta, Trichoptera), and (3) to identify biotic and abiotic factors potentially modulating exposure under field conditions.
During the course of this thesis, ecotoxicologically relevant foliar residues of the neonicotinoids imidacloprid, thiacloprid and acetamiprid were quantified in black alder trees treated at field relevant levels. A worst-case model – developed to simulate imidacloprid water concentrations resulting from an input of contaminated leaves into a stream – predicted only low aqueous imidacloprid concentrations (i.e., ng/L-range). However, the model identified dietary uptake as an additional exposure pathway relevant for shredders up to a few days after the leaves’ introduction into the stream. When test organisms were simultaneously exposed (= combined exposure) to neonicotinoids leaching from leaves into the water and via the consumption of contaminated leaves, adverse effects exceeded those observed under waterborne exposure alone. When exposure pathways were separated using a flow-through system, dietary exposure towards thiacloprid-contaminated leaves caused similar sublethal adverse effects in G. fossarum as observed under waterborne exposure. Moreover, the effect sizes observed under combined exposure were largely predictable using the reference model “independent action”, which assumes different molecular target sites to be affected. Dietary toxicity for shredders might, however, be reduced under field conditions since UV-induced photodegradation and leaching decreased imidacloprid residues in leaves and thereby the toxicity for G. fossarum. In contrast, both shredders were found unable to actively avoid dietary exposure. This thesis thus recommends considering dietary exposure towards systemic insecticides, such as neonicotinoids, already during their registration to safeguard aquatic shredders, associated ecosystem functions (e.g., leaf litter breakdown) and ultimately ecosystem integrity.
Organic substances play an essential role for the formation of stable soil structures. In this context, their physico-chemical properties, interactions with mineral soil constituents and soil-water interactions are particu-larly important. However, the underlying mechanisms contributing to soil particle cementation by swollen or-ganic substances (hydrogels) remains unclear. Up to now, no mechanistic model is available which explains the mechanisms of interparticulate hydrogel swelling and its contribution to soil-water interactions and soil structur-al stability. This mainly results from the lack of appropriate testing methods to study hydrogel swelling in soil as well as from the difficulties of adapting available methods to the system soil/hydrogel.
In this thesis, 1H proton nuclear magnetic resonance (NMR) relaxometry was combined with various soil micro- and macrostructural stability testing methods in order to identify the contribution of hydrogel swelling-induced soil-water interactions to the structural stability of water-saturated and unsaturated soils. In the first part, the potentials and limitations of 1H NMR relaxometry to enlighten soil structural stabilization mechanism and vari-ous water populations were investigated. In the second part, 1H-NMR relaxometry was combined with rheologi-cal measurements of soil to assess the contribution of interparticulate hydrogel swelling and various polymer-clay interactions on soil-water interactions and soil structural stability in an isolated manner. Finally, the effects of various organic and mineral soil fractions on soil-water interactions and soil structural stability was assessed in more detail for a natural, agriculturally cultivated soil by soil density fractionation and on the basis of the experiences gained from the previous experiments.
The increased experiment complexity in the course of this thesis enabled to link physico-chemical properties of interparticulate hydrogel structures with soil structural stability on various scales. The established mechanistic model explains the contribution of interparticulate hydrogels to the structural stability of water-saturated and unsaturated soils: While swollen clay particles reduce soil structural stability by acting as lubricant between soil particles, interparticulate hydrogel structures increase soil structural stability by forming a flexible polymeric network which interconnects mineral particles more effectively than soil pore- or capillary water. It was appar-ent that soil structural stability increases with increasing viscosity of the interparticluate hydrogel in dependence on incubation time, soil texture, soil solution composition and external factors in terms of moisture dynamics and agricultural management practices. The stabilizing effect of interparticulate hydrogel structures further in-crease in the presence of clay particles which is attributed to additional polymer-clay interactions and the incor-poration of clay particles into the three-dimensional interparticulate hydrogel network. Furthermore, the simul-taneous swelling of clay particles and hydrogel structures results in the competition for water and thus in a mu-tual restriction of their swelling in the interparticle space. Thus, polymer-clay interactions not only increase the viscosity of the interparticulate hydrogel and thus its ability to stabilize soil structures but further reduce the swelling of clay particles and consequently their negative effects on soil structural stability. The knowledge on these underlying mechanisms enhance the knowledge on the formation of stable soil structures and enable to take appropriate management practices in order to maintain a sustainable soil structure. The additionally out-lined limitations and challenges of the mechanistic model should provide information on areas with optimization and research potential, respectively.
Fresh water resources like rivers and reservoirs are exposed to a drastically changing world. In order to safeguard these lentic ecosystems, they need stronger protection in times of global change and population growth. In the last years, the exploitation pressure on drinking water reservoirs has increased steadily worldwide. Besides securing the demands of safe drinking water supply, international laws especially in Europe (EU Water Framework Directive) stipulate to minimize the impact of dams on downstream rivers. In this study we investigate the potential of a smart withdrawal strategy at Grosse Dhuenn Reservoir to improve the temperature and discharge regime downstream without jeopardizing drinking water production. Our aim is to improve the existing withdrawal strategy for operating the reservoir in a sustainable way in terms of water quality and quantity. First, we set-up and calibrated a 1D numerical model for Grosse Dhuenn Reservoir with the open-source community model “General Lake Model” (GLM) together with its water quality module “Aquatic Ecodynamics” library (AED2). The reservoir model reproduced water temperatures and hypolimnetic dissolved oxygen concentrations accurately over a 5 year period. Second, we extended the model source code with a selective withdrawal functionality (adaptive offtake) and added operational rules for a realistic reservoir management. Now the model is able to autonomously determine the best withdrawal height according to the temperature and flow requirements of the downstream river and the raw water quality objectives. Criteria for the determination of the withdrawal regime are selective withdrawal, development of stratification and oxygen content in the deep hypolimnion. This functionality is not available in current reservoir models, where withdrawal heights are generally provided a priori to the model and kept fixed during the simulation. Third, we ran scenario simulations identifying an improved reservoir withdrawal strategy to balance the demands for downstream river and raw water supply. Therefore we aimed at finding an optimal parallel withdrawal ratio between cold hypolimnetic water and warm epilimnetic or metalimnetic water in order to provide a pre-defined temperature in the downstream river. The reservoir model and the proposed withdrawal strategy provide a simple and efficient tool to optimize reservoir management in a multi-objective view for mastering future reservoir management challenges.
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 physical-biological interactions that affect the temporal variability of benthic oxygen fluxes were investigated to gain improved understanding of the factors that control these processes. This study, for the first time is able to resolve benthic diffusive boundary layer (DBL) dynamics using the newly developed lifetime-based laser induced fluorescence (τLIF) oxygen imaging system, which enables study of the role of small-scale fluid mechanics generated by benthic organism activity, and hence a more detailed analysis of oxygen transport mechanisms across the sediment-water interface (SWI).
The net benthic oxygen flux across the sediment-water interface is controlled by sediment oxygen uptake and oxygen transport. While the oxygen transport is largely influenced by turbulence driven by large-scale flows, sediment oxygen uptake is mainly affected by oxygen production and biological- and chemical-oxygen degradation of organic matter. Both processes can be enhanced by the presence of fauna and are intimately coupled. The benthic oxygen flux can be influenced by fauna in two ways, i.e. by modulating the availability of oxygen, which enhances the sediment oxygen uptake, and by enhancing the transport of oxygen.
In-situ and a series of laboratory measurements were conducted to estimate the short- and seasonal variability of benthic fluxes including the effects of burrow ventilation activity by tube-dwelling animals using eddy correlation (EC) and τLIF oxygen imaging techniques, respectively.
The in-situ benthic oxygen fluxes showed high variability at hourly and seasonal timescales, where statistical analysis indicated that current velocity and water depth were the most significant predictors of benthic oxygen flux at the waterside, which co-varied with the discharge, temperature, and oxygen concentration. The range of variability of seasonal fluxes corresponded to the friction velocities which were driven by large-scale flows. Application of a simplified analytical model that couples the effect of hydrodynamic forcing of the diffusive boundary layer with a temperature-dependent oxygen consumption rate within the sediment showed that friction velocity and temperature cause similar variability of the steady-state benthic oxygen flux.
The application of τLIF oxygen imaging system in bioturbation experiments enabled the investigation and discovery of insights into oxygen transport mechanisms across the sediment-water interface. Distinct oxygen structures above burrow openings were revealed, these were associated with burrow ventilation. The DBL was degraded in the presence of burrow ventilation. Advective transport generated by the energetic plumes released at burrow outlets was the dominant transport driving mechanism. The contribution of diffusive flux to the total estimated decreased with increasing larval density. For a range of larvae densities, commonly observed in ponds and lakes, sediment oxygen uptake rates increased up to 2.5-fold in the presence of tube-dwelling animals, and the oxygen transport rate exceeded chironomid respiration by up to a factor of 4.
The coupled physical-biological factors affecting net benthic oxygen flux can be represented by temperature, which is a prominent factor that accounts for both oxygen transport and sediment oxygen uptake. Low oxygen transport by flow coincided with high summer temperatures, amplified by a reduction of benthic population density and pupation. It can also, however, be offset by increased ventilation activity. In contrast, low temperature coincided with high oxygen concentrations, an abundance of larvae, and higher flow is offset by less burrow ventilation activity. Investigation of the effect of hydrodynamics on oxygen transport alone suggested that the expected increase of benthic oxygen flux under global warming can be offset by a reduction in flow velocity, which could ultimately lead to increasing carbon burial rates, and in a growing importance of anaerobic mineralization pathways with increasing emission rates of methane.
This study suggests a significant contribution of biological induced benthic oxygen flux to physical transport driven by large-scale flow-fields contributing to bottom-boundary layer turbulence.
The European weatherfish (Misgurnus fossilis) is a benthic freshwater fish species belonging to the family Cobitidae, that is subjected to a considerable decline in many regions across its original distribution range. Due to its cryptic behavior and low economic value, the causes of threat to weatherfish remained partly unknown and the species is rarely at the center of conservation efforts. In order to address these concerns, the overall aim of the present thesis was to provide a comprehensive approach for weatherfish conservation, including the development of stocking measures, investigations on the species autecology and the evaluation of potential threats. The first objective was to devise and implement a regional reintroduction and stock enhancement program with hatchery-reared weatherfish in Germany. Within this program (2014-2016), a total number of 168,500 juvenile weatherfish were stocked to seven water systems. Recaptures of 45 individuals at two reintroduction sites supported the conclusion that the developed stocking strategy was appropriate. In order to broaden the knowledge about weatherfish autecology and thereby refining the rearing conditions and the selection of appropriate stocking waters, the second objective was to investigate the thermal requirements of weatherfish larvae. Here, the obtained results revealed that temperatures higher than previously suggested were tolerated by larvae, whereas low temperatures within the range of likely habitat conditions increased mortality rates. As weatherfish can be frequently found in agriculturally impacted waters (e.g. ditch systems), they are assumed to have an increased probability to be exposed to chemical stress. Since the resulting risk has not yet been investigated with a focus on weatherfish, the third objective was to provide a methodical foundation for toxicity testing that additionally complies with the requirements of alternative test methods. For this purpose, the acute fish embryo toxicity test was successfully transferred to weatherfish and first results exhibited that sensitivity of weatherfish towards a tested reference substance (3,4-dichloroaniline) was highest compared to other species. On the basis of these findings, the fourth objective was to apply weatherfish embryos for multiple sediment bioassays in order to investigate teratogenic effects derived from sediment-associated contaminants. In this context, weatherfish revealed particular sensitivity to water extractable substances, indicating that sediment contamination might pose a considerable risk. Moreover, as an endangered benthic fish species with high ecological relevance for European waters that are specifically exposed to hazardous contaminants, the weatherfish might be a prospective species for an ecological risk assessment of sediment toxicity. Overall, the present thesis contributed to the conservation of weatherfish by considering a variety of aspects that interact and reinforce one another in order to achieve improvements for the species situation.
Grassland management has been increasingly intensified throughout centuries since mankind started to control and modify the landscape. Species communities were always shaped alongside management changes leading to huge alterations in species richness and diversity up to the point where land use intensity exceeded the threshold. Since then biodiversity became increasingly lost. Today, global biodiversity and especially grassland biodiversity is pushed beyond its boundaries. Policymakers and conservationists seek for management options which fulfill the requirements of agronomic interests as well as biodiversity conservation alongside with the maintenance of ecosystem processes. However, there is and will always be a trade-off.
Earlier in history, natural circumstances in a landscape mainly determined regionally adapted land use. These regional adaptions shaped islands for many specialist species, and thus diverse species communities, favoring the establishment of a high β-diversity. With the raising food demand, these regional and traditional management regimes became widely unprofitable, and the invention of mineral fertilizers ultimately led to a wide homogenization of grassland management and, as follows, the loss of biotic heterogeneity. In the course of the green revolution, this immediate coherence and the dependency between grassland biodiversity and traditional land use practices becomes increasingly noticed. Indeed, some traditional forms of management such as meadow irrigation have been preserved in a few regions and thus give us the opportunity to directly investigate their long-term relevance for the species communities and ecosystem processes. Traditional meadow irrigation was a common management practice to improve productivity in lowland, but also alpine hay meadows throughout Europe until the 20th century. Nowadays, meadow irrigation is only practiced as a relic in a few remnant areas. In parts of the Queichwiesen meadows flood irrigation goes back to the Middle Ages, which makes them a predestined as a model region to study the long- and short-term effects of lowland meadow irrigation on the biodiversity and ecosystem processes.
Our study pointed out the conservation value of traditional meadow irrigation for the preservation of local species communities as well as the plant diversity at the landscape scale. The structurally more complex irrigated meadows lead to the assumption of a higher arthropod diversity (Orthodoptera, Carabidae, Araneae), which could not be detected. However, irrigated meadows are a significant habitat for moisture dependent arthropod species. In the light of the agronomic potential, flood irrigation could be a way to at least reduce fertilizer costs to a certain degree and possibly prevent overfertilization pulses which are necessarily hazardous to non-target ecosystems. Still, the reestablishment of flood irrigation in formerly irrigated meadows, or even the establishment of new irrigation systems needs ecological and economic evaluation dependent on regional circumstances and specific species communities, at which this study could serve as a reference point.
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.
The largest population of the anadromous Allis shad (A. alosa) of the 19th century was found in River Rhine and has to be considered extinct today. To facilitate the return of A. alosa into River Rhine an EU LIFE-project was initiated in 2007. The overall objective of this thesis was to assist aquaculture and stocking-measures at River Rhine, as well as to support restoration and conservation of populations of Allis shad in Europe.
By culturing the free-swimming nematode T. aceti in a solution of cider vinegar we developed a cost-effective live food organism for the larviculture of fish. As indicated by experiments with C. maraena, T. aceti cannot be regarded as an alternative to Artemia nauplii. However it has to be considered a suitable supplemental feed in the early rearing of C. maraena by providing essential fatty acids, thereby optimizing growth.
Also mass-marking practices with Oxytetracycline, as they are applied in the restocking of Allis shad have been evaluated. In experiments with D. rerio we demonstrated that water hardness can detrimentally affect mortality during marking and has to be considered crucial in the development of marking protocols for freshwater fish.
In order to get independent from wild spawners an ex-situ Broodstock-facility for Allis shad was established in 2011. Upon examination of two complete year classes of this broodstock, we found a high prevalence of various malformations, which could be traced back to distinct cysts developing one month post hatch. Despite applying a variety of clinical tests we could not identify any infectious agents causing these malformations. The observed malformations are probably a consequence of suboptimal feeding practices or the properties of the physio-chemical rearing environment.
The decline of stocks of A. alosa in Europe has been largely explained with the increase of river temperatures as a consequence of global warming. By investigating the temperature physiology of larval Allis shad we demonstrated that A. alosa ranges among the most thermo-tolerant species in Europe and that correlations between rising temperatures and the disappearance of this species have to be understood in a synecological context and by integrating a variety of stressors other than temperature. By capturing and examining juvenile and adult Allis shad from River Rhine, we demonstrated the first natural reproduction of A. alosa in River Rhine since nearly 100 years and the success of stocking measures within the framework of the LIFE project.
Abstract The present work investigates the wetting characteristics of soils with regard to their dependence on environmental parameters such as water content (WC), pH, drying temperature and wetting temperature of wettable and repellent soils from two contrasting anthropogenic sites, the former sewage disposal field Berlin-Buch and the inner-city park Berlin-Tiergarten. The aim of this thesis is to deepen the understanding of processes and mechanisms leading to changes in soil water repellency. This helps to gain further insight into the behaviour of soil organic matter (SOM) and identifying ways to prevent or reduce the negative effects of soil water repellency (SWR). The first focus of this work is to determine whether chemical reactions are required for wetting repellent samples. This hypothesis was tested by time and temperature dependence of sessile drop spreading on wettable and repellent samples. Additionally, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to determine whether various drying regimes cause changes in the relative abundance of hydrophobic and hydrophilic functional groups in the outer layer of soil particles and whether these changes can be correlated with water content and the degree of SWR. Finally, by artificially altering the pH in dried samples applying acidic and alkaline reagents in a gaseous state, the influence of only pH on the degree of SWR was investigated separately from the influence of changes in moisture status. The investigation of the two locations Buch and Tiergarten, each exceptionally different in the nature of their respective wetting properties, leads to new insights in the variety of appearance of SWR. The results of temperature, water content and pH dependency of SWR on the two contrasting sites resulted in one respective hypothetical model of nature of repellency for each site which provides an explanation for most of the observations made in this and earlier studies: At the Tiergarten site, wetting characteristics are most likely determined by micelle-like arrangement of amphiphiles which depends on the concentration of water soluble amphiphilic substances, pH and ionic strength in soil solution. At low pH and at high ionic strength, repulsion forces between hydrophilic charged groups are minimized allowing their aggregation with outward orientated hydrophobic molecule moieties. At high pH and low ionic strength, higher repulsion forces between hydrophilic functional groups lead to an aggregation of hydrophobic groups during drying, which results in a layer with outward oriented hydrophilic moieties on soil organic matter surface leading to enhanced wettability. For samples from the Buch site, chemical reactions are necessary for the wetting process. The strong dependence of SWR on water content indicates that hydrolysis-condensation reactions are the controlling mechanisms. Since acid catalyzed hydrolysis is an equilibrium reaction dependent on water content, an excess of water favours hydrolysis leading to an increasing number of hydrophilic functional groups. In contrast, water deficiency favours condensation reactions leading to a reduction of hydrophilic functional groups and thus a reduction of wettability. The results of the present investigation and its comparison with earlier investigations clearly show that SWR is subject to numerous antagonistically and synergistically interacting environmental factors. The degree of influence, which a single factor exerts on SWR, is site-specific, e.g., it is dependent on special characteristics of mineral constituents and SOM which underlies the influence of climate, soil texture, topography, vegetation and the former and current use of the respective site.
The research described in this thesis was designed to yield information on the impact of particle-bound pesticides on organisms living in the interface between sediment and water column in a temporarily open estuary (TOCEs). It was hypothesized that natural variables such as salinity and temperature and anthropogenic stressors such as particle-bound pesticides contribute to the variability of the system. A multiple line of evidence approach is necessary due to the variability in sediment type, contaminant distribution and spatial and temporal variability within the ecosystem in particular within TOCEs. The first aim of this thesis was to identify which particle-bound pesticides are important to the contamination of the Lourens River estuary (Western Cape, South Africa), taking into account their environmental concentrations, physico-chemical and toxicological properties (Exposure assessment). The second aim was to identify spatial and temporal variations in particle bound pesticide contamination, natural environmental variables and benthic community structure (effect assessment). The third aim was to test the hypothesis: "does adaptation to fluctuating salinities lead to enhanced survival of the harpacticoid copepod Mesochra parva when exposed to a combination of particle associated chlorpyrifos exposure and hypo-osmotic stress during a 96 h sediment toxicity test?" The last aim was to identify the driving environmental variables (including natural and anthropogenic stressors) in a "natural" (Rooiels River) compared to a "disturbed" (Lourens River) estuary and to identify if and how these variables change the benthic community structure in both estuaries. Data produced in this research thus provide important information to understand the impact of pesticides and its interaction with natural variables in a temporarily open estuary. To summarise, this study indicated, by the use of the multi-evidence approach, that the pesticides endosulfan and chlorpyrifos posed a risk towards benthic organisms in a temporarily open estuary in particular during spring season. Furthermore an important link between pesticide exposure/ toxicity and salinity was identified, which has important implications for the management of temporarily open estuaries.