1,721,047 research outputs found
C, N, pH of different aggregate fractions of a tropical savanna soil amended with organic and mineral amendments
No full textSoil samples (0 – 5 cm) were taken from a tropical topsoil at the premises of the University of Ngaoundéré, Ngaoundéré, Cameroon. A field experiment was installed in May 2018, with t0 sampling in December 2017 and in May 2018. Four treatments were implemented: A control receiving no amendment, a mineral control receiving NPK fertiliser (20-10-10), a compost treatment receiving a compost that was prepared from Tithonia diversifolia whole plants at an annual rate of 75 t/ha, and a combined biochar and compost treatment, where compost and biochar prepared from Tithonia diversifolia were co-composted (10 % v/v biochar) and applied at an annual biochar rate of 25 t/ha. Amendments were applied in June 2018 and 2019 to a depth of approximately 10 cm and Sorghum bicolor var. S35 was sown at 0.5 m distance within the rows and 0.5 m distance between the rows approximately two weeks after the amendment. The experimental design was a Latin Square with five field repetitions of each treatment, rendering a total of 20 plots of 2 x 2 m each. Soil samples were taken from the centre of each plot with a small shovel in December of 2017, 2018, and 2019 for dry season sampling, and in May of 2018 and 2019 right before amendment and in June of 2018 and 2019 right before sowing for rainy season sampling. In 2019, a total of four sampling campaigns was carried out in May and June due to additional mesofauna sampling. Samples taken in December 2018 and in December 2019 were dry sieved on site into four different aggregate sizes: 400 – 2000 µm; 200 – 400 µm; 50 – 200 µm; < 50 µm. C and N contents were obtained by grinding air-dried soil samples using a kitchen blender for homogenisation, and then measuring C and N by dry combustion. pH was measured by suspending 5 g of air-dried soil sample in 12.5 mL of either 0.01 M CaCl2 (pHCaCl2), demineralised water (pHH2O), or 1 M KCl (pHKCl). Samples were gently shaken for 2 h, allowed for sedimentation and pH was measured using a digital pH-meter. All measurements were conducted in duplicates. Due to limited sample availability, no pH values could be obtained for aggregate fractions < 400 µm. \nThe field experiment was part of the PhD dissertation project of Laura Sophie Schnee which was carried out in partnership between the Unviersities of Bremen, Germany, and Ngaoundéré, Cameroon
Does the exposure mode to ENPs influence their toxicity to aquatic species? A case study with TiO2 nanoparticles and Daphnia magna
No full textRecent studies suggest that the ecotoxicity of engineered nanoparticles (ENPs) is dependent upon the treatment of ENPs in suspensions (e.g. sonication or use of solvents) and on the mode of exposure to test organisms. We conducted several bioassays with Daphnia magna in order to determine how adverse effects of TiO2 nanoparticles (n-TiO2) are influenced by experimental set-up. Several treatments were applied, including three test media, several treatments of n-TiO2 suspensions (stirring, sonication) and different exposure modes (exposure duration and volume of test suspension). No adverse effects were observed when D. magna were exposed to 50 mL of suspension, regardless of TiO2 concentration (up to 250 mg/L) and exposure duration. Conversely, adverse effects were observed when D. magna were exposed to 2 mL of suspension for 96 h with a 50 % effect concentration EC50 values ranging from 32 mg/L to 82 mg/L. Test media had no significant influence on the outcome of all treatments. For a better mechanistic understanding of the experimental set-up at which adverse effects were observed, the particle size of n-TiO2 in the test media was characterized throughout the test duration. These measurements revealed a fast and strong agglomeration with a secondary particle size in the order of magnitude of micrometers. Our study describes how the effects of n-TiO2 on D.magna are influenced by the duration of exposure and volume of media, highlighting the need for standardization of experimental methods
Bodenökologie : Langfristige sekundäre Sukzession von Collmbolengemeinschaften auf einer ehemaligen Bauschuttdeponie
No full textEighteen sampling campaigns were evaluated for investigating the long-term secondary succession of Collembola communities in relation to climate change and vegetation and in comparison with Gamasina communities at two different managed experimental plots. One plot (SUC) was left undisturbed for natural secondary succession, the other plot (REC) was recultivated with rotary-tilling and sowing of grass. This experiment was done on a former rubble deposit over 20 years and samplings took place from 1980 to 2000. Selected sampling campaigns, the first three years (1980, 1981, 1982), the last three years (1998, 1999, 2000) and in -between with an interval of four years (1986, 1990, 1994), were evaluated and studied between 2014 and 2017. In total, 14,742 Collembola individuals were counted and identified by the author. Those consisted of 33 species of which 25 species were identified by the author herself. The most dominant species were: Mesaphorura krausbaueri, Parisotoma notabilis and Isotomodes productus. The analysis of Collembola from this collection posed great challenges in clearing the specimens stored in 70% ethanol for 15-32 years for microscopical inspection. None of the five media with different clearing properties tested for permanent slide mounts cleared the old specimens sufficiently, therefore, pretreatment procedures had to be applied. As such, to achieve good clearing of old ethanol collection material, it is recommended to incubate it in DNA extraction buffer solution such as SNET plus proteinase K and to mount it in Marc Andre 2 for best optical results. Long-term successional development of Collembola was investigated at the species level with calculation of abundance (ind/m2), dominance, diversity indices, presence-absence and dominance similarity and species turnover rate. Successional stages of Collembola species in both experimental plots were identified. Ecological groups were also distinguished for Collembola species. Long-term succession of Collembola was related to the changes of climatic variables and vegetation in the studied area over 20 years. This relationship was analysed and modeled applying canonical correspondence analysis, linear regression analysis and average linkage clustering for the Collembola abundance data. The model reveals four distinct climatic groups of evaluated data and shows a significant influence of soil temperature on the long-term successional development of Collembola species. No evidence was found for the correlation of Collembola species abundance with vegetation covers. Thus, they are both either independent from each other or at least not related directly. A comparative study was performed to study the synchronicity of the successional development of Collembola, Gamasina and plant species. This was also compared between two experimental plots. To compare the abundance data from Collembola with Gamasina, the same calculations were performed for successional development of Gamasina species, and the model of successional stages and the structure of ecological groups were also provided for Gamasina species. The successional synchrony among the three organism Groups was evaluated and modeled with detrended correspondence analysis. Redundancy analysis and linear regression revealed models for the evaluation of the influence of environmental variables on the successional development of investigated microarthropod groups. Again, soil temperature was proved as a significant factor for both groups, and pH was significantly influential in the longterm development of Gamasina species. Different management in SUC and REC played an important role in successional changes of the three organism groups; the difference between two plots was observable especially in Gamasina. Overall, Collembola community was more similar between both plots and Gamasina community was generally more diverse. Replacement of species during a successional study is mainly related to time i.e. their temporal shifts. Moreover, some environmental variables may influence this process effectively and significantly; in particular soil temperature and pH are determined as such important factors in this study
Abiotische und biotische Einflüsse auf den Verbleib und die Effekte von Silbernanopartikeln in aquatischen Model-Ökosystemen
No full textSilver nanoparticles (AgNP) are used dominantly for disinfection purposes due to their high toxicity against bacteria. Even though this property is desired during use, it may become unwanted, if AgNP are released into the environment. As the toxicity of AgNP is not limited to bacteria, also other taxonomic groups may suffer from release of AgNP into the environment. Release of silver ions from the AgNP represents an important source for toxicity, however, also AgNP themselves can act toxic. In aquatic systems, toxicity of AgNP is highly affected by their colloidal stability (dissolution and agglomeration) in the medium, which is in turn closely related to the coating of the used AgNP. As also the test conditions, such as pH, medium composition, light intensity, or test duration interact with the coating, generalizations on the mode of action or toxicity of AgNP to aquatic organisms can only be made for a single coating or a certain test design. Still, the high number of studies using AgNP provide a good reference for investigating the relation between colloidal stability in the test medium and toxicity in more detail. For this dissertation, two rarely considered aspects of this relation were chosen 1) the influence of surface area and surface properties on colloidal stability and actual concentrations of AgNP in the test medium, and 2) the effect of resource reduction on AgNP toxicity. By using these two topics, biological as well as chemical influences on AgNP toxicity could be investigated. For this purpose, an aquatic model system was used including two differently coated AgNP, two green algae, Raphidocelis subcapitata and Desmodesmus subspicatus, and the big water flea, Daphnia magna, in varying compositions. The investigation of surface-related effects revealed that differences in surface area were of minor importance for AgNP colloidal stability and fate compared to surface properties. Higher hydrophobicity increased the attachment of detergent stabilized AgNP to the test vessela s surface, thus reducing the actual exposure concentrations and causing lower levels of toxicity in this test vessel. In case of variation of the AgNP surface itself, the coating, higher degrees of attachment of the AgNP to each other, so a higher degree of agglomeration, increased uptake of the corresponding AgNP and caused higher levels of toxicity. These results support the importance of surface properties for the fate of AgNP in a given test system and identified hydrophobicity as well as surface charge as most important properties for the attachment of AgNP to surfaces. In addition, the interactions between biological surfaces and citrate coated AgNP were identified as most probable link between colloidal stability and observed toxicity, suggesting further investigations on this topic. The reduction of resources had a close connection to the other topic of research, as changes in media composition, as required for changes in nutrient supply for algae, highly affected colloidal stability of the AgNP. By the use of intensive analytics, however, effects resulting from changes in colloidal stability could be separated from changes caused by differences nutrient reduction. Resource reduction caused an increase in AgNP toxicity in both trophic levels with the response also differing between the two algae species. Consequently, AgNP toxicity can be expected to be higher for various taxa when resource provision is low, but the intensity of this change is likely to vary between species
Gefährdungsbeurteilung von flüssigen organischen Wasserstoffträgern (LOHCs) in terrestrischen Umgebungen
No full textLiquid Organic Hydrogen Carriers (LOHCs) are part of a novel energy system that can efficiently and relatively safely store and transport hydrogen, which is a clean, high energy density fuel. LOHCs have high hydrogen holding capacities and are superior to most current energy sources, such as fossil fuels, because they have the potential to reduce CO2 emission and have advantages in operational and handling safety; they are also adaptable to renewable energy. Therefore, massive integration and circulation of hundreds of thousands of tons of LOHCs in the market are anticipated in the near future. However, LOHC chemicals will likely be released into the environment during the process of producing and circulating the large forecasted volumes of these compounds. In addition to the interest in developing LOHC systems to improve the technological performance, increasing attention has been focused on the behavior, fate and toxicity of LOHCs in the environment. When LOHCs enter the environment, the behavior and subsequent toxic effects of LOHCs on organisms are critical metrics used to evaluate and predict the environmental hazards of LOHCs. However, limited data are available to perform such comprehensive predictions. To help fill this gap, this thesis was conducted to characterize the potential adsorption and mobility behavior of different LOHC candidates in soils. Specifically, the organic carbon-water partition coefficient (Koc), soil-water partition coefficient (Kd) and leaching capacity of LOHCs were investigated via instrumental analyses and software predictions. These outcomes were correlated to the physicochemical properties of the compounds to determine their potential adsorption mechanisms. In general, the Koc values were correlated to hydrophobicity in the following order: indoles quinaldines carbazole derivatives benzyltoluenes dibenzyltoluene. When ionizable LOHC structures were investigated, the Kd and leaching capacity (with quinaldines as examples) revealed adsorption governed by ionic interactions. In such a case, ionization corrected octanol-water partition coefficient (log D) was found a propriate indicator for the prediction of adsorption. Ecotoxicity tests for acute and chronic toxicity were conducted in soil (quinaldines) and aquatic (quinaldines and carbazole derivatives) test scenarios. Data were compiled and integrated with the adsorption and mobility of LOHCs in soils to interpret the extent of the exposure, bioavailability and mode of toxic action. The toxicity of LOHCs appeared to be dominated by hydrophobicity. With the deduction of toxicity classification and predicted no-effect concentrations (PNECs) as well as the evaluations for the behavior and fate, a proactive assessment of the potential environmental hazards of these chemicals was ultimately conducted in the context of realistic environmental conditions and potential application quantities. A comparative analysis showed that LOHCs presented fewer potential environmental hazards than traditional energy systems (e.g., gasoline, diesel, and oil) and analogous compound structures, such as typical N-PAHs (nitrogen-substituted polycyclic aromatic hydrocarbon, which share a similar structure with certain LOHCs). Although LOHCs seem not appear to present the same hazards as these equivalent energy sources, further studies regarding several key considerations are recommended for a better understanding of the potential environmental hazards of LOHCs. The careful application of LOHCs under appropriate monitors is suggested because of the likelihood that these compounds will be used in large application volumes in the future
Interactions between Collembola and different food resources in particular algae
No full textCollembola feed on a wide range of soil fungi, but possible interactions with other resources like algae, Cyanobacteria or seeds are poorly understood. The results of this thesis show that algae differ in their attractiveness and quality for Collembola and even euedaphic species benefit from them. Sympatric species of Collembola show differences in their food choice behaviour as well as in the utilisation of ingested food. The lipid analysis of consumers and their recourses assigned two new trophic biomarkers for Collembola reared on algal diets. Furthermore, this study provided proof that living algal cells can be detected in the faeces of Collembola. This confirms the assumption that Collembola contribute to the dispersal of algae. Simultaneously, fatty acid pattern of faecal pellets suggested that faeces are enriched with gut-associated microorganisms which were also deposited. This mechanism could have important influence on soil microbial communities
Artbestimmung von Collembolen mittels PCR-basierter Markersysteme
No full textThe MOLART project on which this PhD thesis bases deals with the development and standardisation of molecular methods for safe and efficient identification of species which can not - or only with great effort and expertise - be distinguished by morphological analysis. These aims were exemplified by two problematic species groups within the Collembola as examples of taxa that combine ecological importance and controversial species status, the Protaphorura armata group (Onychiuridae, Poduromorpha) and the Isotoma viridis group (Isotomidae, Entomobryomorpha). For this purpose, DNA sequencing, PCR-RFLP, RAPD, AP-PCR and AFLP were applied and evaluated according to their diagnostic power, their efficiency for different taxa, the effort of time and the experience required. It was aimed to extract information from individual specimens to avoid mixing of genetic information. We could show that DNA can be extracted successfully from single specimens. Based on identification by morphological keys, molecular markers were tested for their accordance with morphological taxonomy and molecular identification tools were designed based on the results. For the I. viridis group, the mitochondrial COII sequence was used to infer a molecular phylogeny that is in accordance with morphological findings. Molecular traits were found suitable to provide a fast and more robust discrimination compared to morphological characters. A fourth member of this group recently proposed by morphological hints, I. caerulea, could be confirmed to represent a distinct species. Genetic differences were used to establish a set of restriction enzymes that will provide a fast and efficient identification system for I. viridis group from different European countries. For the P. armata group, sequences were obtained from three gene loci, mitochondrial COI, COII and nuclear ITS1, in order to resolve the systematics of this group. Concordant patterns for nuclear and mitochondrial markers suggest that the P. armata group consists of more than one species. Especially P. fimata and P. armata seem to represent distinct species. Differences were found between phylogenies derived from the three gene loci, most of them due to the small number of individuals tested in some species. In the phylogenetic trees, morphologically intermediate forms were not found to represent distinct species. The ITS1 sequence confirmed the findings of both mitochondrial gene regions but did not provide a more detailed taxonomic resolution. Obviously a detailed resolution of a species group consisting of about 40 species will require a larger molecular marker set, about 10 to 20 specimens per 'species' from different sampling sites and several independent marker sets to check for possible inconsistencies. Both RAPD and AP-PCR methods did not reveal reproducible results and yielded fragment patterns rather on the level of populations than of species. Whereas TE-AFLP failed to produce visible bands, AFLP yielded reproducible fragment patterns in both species groups as the only method that includes two amplification steps, indicating a low template concentration to be the reason for failure of amplification or reproducibility. Contamination by alien DNA, especially from gut content, was found to be a severe problem when investigating small-sized taxa by molecular methods, and a long-time storage in ethanol further decreases the extraction yield due to DNA degradation. Based on these investigations, standardised methods are proposed to be used in future molecular taxonomy, especially in cooperation with traditional morphological taxonomy, for optimising DNA yield and purity for better characterisation of small-sized specimens and for establishing reference collections and future identification keys. As implications for future molecular taxonomy, it is recommended to use live specimens that can be cleaned from alien DNA prior to extraction and to use species-specific primers that bear a lower risk than universal primers to amplify unwanted contaminations. When sequencing single gene loci, mitochondrial protein-coding genes seem to be most appropriate since they are present in high copy numbers and fixed differences suitable for discriminating closely related taxa are more likely to be found in faster evolving mitochondrial genes than in nuclear sequences. Methods known to be influenced easily by reaction conditions, like RAPD and AP-PCR, should be tested for their reproducibility prior to use. Among fingerprinting methods, AFLP seems to be the best choice, since it produces a reproducible and complex information pattern that, if desired, can be reduced to a level suitable for faster taxon identification
Ecotoxicological evaluation of soil remediation using a battery of bioassays: The case of TNT-contaminated soils
No full textThe objective of the presented research was to address the suitability of a battery of bioassays for a site-specific ecotoxicological evaluation of contaminated soils. Experimental fields are located at an abandoned armament site where the topsoil was contaminated by the explosive 2,4,6-Trinitrotoluene (TNT) and several co-contaminants. At this site, different soil treatments were established at technical scale to investigate the efficiency of a newly developed phytoremediation technology. Being part of an extensive monitoring programme, the test battery was intended to evaluate changes of soil toxicity in the course of remediation. The battery was compiled of five rather standardised test methods used in ecotoxicology: a phytotoxicity test with garden cress (Lepidium sativum), a springtail reproduction test with Folsomia candida (Collembola) and soil respiration measurements (basal and substrate induced respiration). In addition to these soil assays two aquatic tests based on the luminescent bacterium Vibrio fischeri (acute toxicity and mutagenicity) were included to assess the toxicity of aqueous soil extracts. Biological data generated by the test battery reveal a differentiated toxicity of complex contaminated soil samples. Observed differences in toxicity are in relative agreement with a gradient of TNT-contamination between experimental fields as described by chemical analyses. The five bioassays revealed clear differences in sensitivity. The acute luminescent bacteria toxicity test conducted with soil leachates proved to be a sensitive screening indicator of water-extractable toxicity. Bioassay data from all treatment variants largely indicate a reduction of soil toxicity during a 17 months remediation period, supposedly reflecting decreased soil concentrations of nitroaromatic compounds as shown by chemical analyses. These observations indicate a positive impact of the remediation procedures applied, but further monitoring is essential
Risikoabschätzung von genetisch veränderten Organismen: Potentielle Effekte von Bt Mais auf Spinnen
No full textConcerns have been raised that genetically modified Bt maize expressing the Cry1Ab protein of the soil bacterium Bacillus thuringiensis (Bt toxin) may harm non-target organisms. Spiders can be exposed to the Bt toxin by active Bt maize pollen feeding, by ingesting their pollen-dusted webs, and by preying on herbivorous or pollen-collecting prey. In this thesis, the risk potentially arising from Bt maize for foliage-dwelling spiders was assessed by the investigation of exposure pathways of Bt maize to spiders and by assessing the actual Bt effects on foliage-dwelling spiders on laboratory and field scale. The investigations showed that spiders are potentially exposed to Bt maize pollen and Bt-contaminated prey. No lethal effect of Bt maize on spiders on laboratory as well as on field scale was found. Thus a high risk of Bt maize event 176 to spiders can not be confirmed. However, high variation as well as small effect sizes may have masked existing effects and further studies on different temporal and spatial scales as well as studies on potential sublethal or longterm effects are required to allow general statements
Verwilderungspotential von Raps (Brassica napus L.) unter Ruderalbedingungen im Hinblick auf die Risikoabschätzung gentechnisch veränderter Pflanzen
No full textA comprehensive risk assessment is needed to evaluate whether genetically modified (GM) herbicide-resistant (HR) lines of oilseed rape (OSR) pose a threat to the environment. The probability for an unintended spread of transgenes is high: OSR can grow outside cultivation in feral (wild) populations, typically seen on disturbed ruderal sites. The aim of my thesis is to provide baseline data on the establishment success of ruderal OSR populations and to determine environmental factors of relevant impact focusing on the effects of soil quality. Several field experiments were carried out on ruderal sites in Northern Germany. Establishment success was compared with the success of weedy relatives. Dwarfing, intended as a method of transgenic mitigation, might lead to higher fitness under stressors relevant on ruderal sites, i.e. mowing and low soil quality. I therefore compared the fitness of a dwarfed OSR cultivar with that of a tall cultivar on a ruderal site. The potential for seed dormancy is important for long-term establishment success of OSR. The influence of soil quality and soil organisms on buried OSR seeds was therefore investigated
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