@phdthesis{Leiser2021,
  author    = {Leiser, Rico},
  title     = {Biogeochemical processes governing microplastic transport in freshwater reservoirs},
  doi       = {10.25932/publishup-52024},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-520240},
  school      = {Universit{\"a}t Potsdam},
  pages     = {ix, 143},
  year      = {2021},
  abstract  = {The presented study investigated the influence of microbial and biogeochemical processes on the physical transport related properties and the fate of microplastics in freshwater reservoirs. The overarching goal was to elucidate the mechanisms leading to sedimentation and deposition of microplastics in such environments. This is of importance, as large amounts of initially buoyant microplastics are found in reservoir sediments worldwide. However, the transport processes which lead to microplastics accumulation in sediments, were up to now understudied. The impact of biofilm formation on the density and subsequent sedimentation of microplastics was investigated in the eutrophic Bautzen reservoirs (Chapter 2). Biofilms are complex microbial communities fixed to submerged surfaces through a slimy organic film. The mineral calcite was detected in the biofilms, which led to the sinking of the overgrown microplastic particles. The calcite was of biogenic origin, most likely precipitated by sessile cyanobacteria within the biofilms. Biofilm formation was also studied in the mesotrophic Malter reservoir. Unlike in Bautzen reservoir, biofilm formation did not govern the sedimentation of different microplastics in Malter reservoir (Chapter 3). Instead autumnal lake mixing led to the formation of sinking aggregates of microplastics and iron colloids. Such colloids form when anoxic, iron-rich water from the hypolimnion mixes with the oxygenated epilimnetic waters. The colloids bind organic material from the lake water, which leads to the formation of large and sinking iron-organo flocs. Hence, iron-organo floc formation and their influence on the buoyancy or burial of microplastics into sediments of Bautzen reservoir was studied in laboratory experiments (Chapter 4). Microplastics of different shapes (fiber, fragment, sphere) and sizes were readily incorporated into sinking iron-organo flocs. By this initially buoyant polyethylene microplastics were transported on top of sediments from Bautzen reservoir. Shortly after deposition, the microplastic bearing flocs started to subside and transported the pollutants into deeper sediment layers. The microplastics were not released from the sediments within two months of laboratory incubation. The stability of floc microplastic deposition was further investigated employing experiments with the iron reducing model organism Shewanella oneidensis (Chapter 5). It was shown, that reduction or re-mineralization of the iron minerals did not affect the integrity of the iron-organo flocs. The organic matrix was stable under iron reducing conditions. Hence, no incorporated microplastics were released from the flocs. As similar processes are likely to take place in natural sediments, this might explain the previous described low microplastic release from the sediments. This thesis introduced different mechanisms leading to the sedimentation of initially buoyant microplastics and to their subsequent deposition in freshwater reservoirs. Novel processes such as the aggregation with iron-organo flocs were identified and the understudied issue of biofilm densification through biogenic mineral formation was further investigated. The findings might have implications for the fate of microplastics within the river-reservoir system and outline the role of freshwater reservoirs as important accumulation zone for microplastics. Microplastics deposited in the sediments of reservoirs might not be transported further by through flowing river. Hence the study might contribute to better risk assessment and transport balances of these anthropogenic contaminants.},
  language  = {en}
}
@phdthesis{Kettner2018,
  author    = {Kettner, Marie Therese},
  title     = {Microbial colonization of microplastic particles in aquatic systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-418854},
  school      = {Universit{\"a}t Potsdam},
  pages     = {139},
  year      = {2018},
  abstract  = {The continuously increasing pollution of aquatic environments with microplastics (plastic particles < 5 mm) is a global problem with potential implications for organisms of all trophic levels. For microorganisms, trillions of these floating microplastics particles represent a huge surface area for colonization. Due to the very low biodegradability, microplastics remain years to centuries in the environment and can be transported over thousands of kilometers together with the attached organisms. Since also pathogenic, invasive, or otherwise harmful species could be spread this way, it is essential to study microplastics-associated communities. For this doctoral thesis, eukaryotic communities were analyzed for the first time on microplastics in brackish environments and compared to communities in the surrounding water and on the natural substrate wood. With Illumina MiSeq high-throughput sequencing, more than 500 different eukaryotic taxa were detected on the microplastics samples. Among them were various green algae, dinoflagellates, ciliates, fungi, fungal-like protists and small metazoans such as nematodes and rotifers. The most abundant organisms was a dinoflagellate of the genus Pfiesteria, which could include fish pathogenic and bloom forming toxigenic species. Network analyses revealed that there were numerous interaction possibilities among prokaryotes and eukaryotes in microplastics biofilms. Eukaryotic community compositions on microplastics differed significantly from those on wood and in water, and compositions were additionally distinct among the sampling locations. Furthermore, the biodiversity was clearly lower on microplastics in comparison to the diversity on wood or in the surrounding water. In another experiment, a situation was simulated in which treated wastewater containing microplastics was introduced into a freshwater lake. With increasing microplastics concentrations, the resulting bacterial communities became more similar to those from the treated wastewater. Moreover, the abundance of integrase I increased together with rising concentrations of microplastics. Integrase I is often used as a marker for anthropogenic environmental pollution and is further linked to genes conferring, e.g., antibiotic resistance. This dissertation gives detailed insights into the complexity of prokaryotic and eukaryotic communities on microplastics in brackish and freshwater systems. Even though microplastics provide novel microhabitats for various microbes, they might also transport toxigenic, pathogenic, antibiotic-resistant or parasitic organisms; meaning their colonization can pose potential threats to humans and the environment. Finally, this thesis explains the urgent need for more research as well as for strategies to minimize the global microplastic pollution.},
  language  = {en}
}
@phdthesis{Drago2022,
  author    = {Drago, Claudia},
  title     = {Microplastics in the environment: Assessing the ingestion and effect of microplastics on freshwater rotifers in an environmental scenario},
  doi       = {10.25932/publishup-57335},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-573356},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xv, 116},
  year      = {2022},
  abstract  = {Microplastics in the environments are estimated to increase in the near future due to increasing consumption of plastic product and also due to further fragmentation in small pieces. The fate and effects of MP once released into the freshwater environment are still scarcely studied, compared to the marine environment. In order to understand possible effect and interaction of MPs in freshwater environment, planktonic zooplankton organisms are very useful for their crucial trophic role. In particular freshwater rotifers are one of the most abundant organisms and they are the interface between primary producers and secondary consumers. The aim of my thesis was to investigate the ingestion and the effect of MPs in rotifers from a more natural scenario and to individuate processes such as the aggregation of MPs, the food dilution effect and the increasing concentrations of MPs that could influence the final outcome of MPs in the environment. In fact, in a near natural scenario MPs interaction with bacteria and algae, aggregations together with the size and concentration are considered drivers of ingestion and effect. The aggregation of MPs makes smaller MPs more available for rotifers and larger MPs less ingested. The negative effect caused by the ingestion of MPs was modulated by their size but also by the quantity and the quality of food that cause variable responses. In fact, rotifers in the environment are subjected to food limitation and the presence of MPs could exacerbate this condition and decrease the population and the reproduction input. Finally, in a scenario incorporating an entire zooplanktonic community, MPs were ingested by most individuals taking into account their feeding mode but also the concentration of MPs, which was found to be essential for the availability of MPs. This study highlights the importance to investigate MPs from a more environmental perspective, this in fact could provide an alternative and realistic view of effect of MPs in the ecosystem.},
  language  = {en}
}