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- Rämö, Robert A., 1989-
(författare)
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Sediment remediation using activated carbon: amending knowledge gaps
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many coastal sediments have accumulated large quantities of contaminants from past anthropogenic activities and now act as a secondary emission source of legacy pollutants to coastal ecosystems. New sediment remediation strategies are needed to address widespread sediment pollution. This thesis focuses on the harbour of Oskarshamn in the Baltic Sea, contaminated by PAHs, PCBs, TBTs, dioxins, and metals from past emissions, and aims to improve knowledge on in situ sediment remediation using activated carbon, a strong sorbent for hydrophobic organic contaminants. Thin-layer capping using activated carbon aims to sequester contaminants in sediment and reduce their bioavailability to aquatic organisms without having to remove or physically isolate the contaminated sediment from the aquatic environment.Questions remain on the efficacy and persistence of activated carbon thin-layer capping in turbulent waters, and on potential adverse effects of activated carbon on benthic communities. We studied the role of activated carbon particle size on contaminant sequestration, sorbent retention (Paper I), and adverse effects in benthic macroinvertebrates (Paper III). We also assessed effects of activated carbon amendment on nutrient cycling and meiofauna communities (Paper II), and whether granular activated carbon (GAC, >300 µm) reduces toxicity to the benthic sentinel amphipod Monoporeia affinis in Oskarshamn harbour (Paper IV).We found that powdered activated carbon (PAC, <300 µm) is much more effective in sequestering PAHs and PCBs than GAC in the short term (Paper I), but that PAC is readily resuspended in turbulent water, whereas GAC may remain on the sediment surface, leading to a higher persistence of GAC over time (Paper I). Thin-layer capping with PAC raised porewater pH and reduced meiofauna abundance, nitrate reduction, nitrate release fluxes, and phosphate release fluxes by at least 50 % (Paper II). This indicates that thin-layer capping with PAC affected both sediment microbial and meiofaunal communities, potentially through the increased pH and sequestration of dissolved organic matter onto activated carbon, rendering it less available to microbial organisms.We observed strong biological responses in macroinvertebrates, with reduced weight, carbon assimilation, and gut microvilli in the polychaete Marenzelleria spp. exposed to ingestible PAC, contrasted by increased weight and carbon assimilation in polychaetes exposed to noningestible GAC (Paper III). This indicates that amendment with PAC caused starvation, i.e., that the polychaete ceased ingesting sediment or that PAC reduced the bioaccessibility of food co-ingested with the sorbent. These effects were present but less pronounced in the clam Limecola balthica (Paper III), indicating that biological responses are species dependent. A toxicity bioassay (Paper IV) showed that sediment amendment using GAC effectively reduced mortality and reproduction impairments in the amphipod Monoporeia affinis.Overall, the thesis demonstrates that GAC may have positive effects on benthic macroinvertebrates, high persistence in turbulent water, and reduces toxicity of highly contaminated sediments. We show that PAC is a highly effective sorbent, but may cause strong adverse effects on benthic macroinvertebrates, meiofauna, and microbial nutrient cycling. Thus, non-ingestible granular activated carbon appears to be a better choice for remediation of contaminated coastal sediments.
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| 2. |
- Albert, Séréna, 1992-
(författare)
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Benthic-pelagic coupling in a changing world : Structural and functional responses of microbenthic communities to organic matter settling
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Marine soft sediments form the second largest habitat on the planet. Organisms residing in this environment represent a vast reservoir of biodiversity, and play key roles in ecosystem processes. Most benthic organisms depend on organic matter (OM) inputs from phytoplankton in the overlying water column as food supply, but human impacts such as eutrophication and climate change are profoundly altering natural ecosystem dynamics. The consequences of changes in benthic-pelagic coupling for the biodiversity and functioning of soft-sediment communities have yet to be resolved. The aim of this thesis is to assess the role of OM settling on soft-sediments microeukaryotic (small organisms < 1 mm) and bacterial communities. The intents are two-fold, to investigate impacts on (1) community structure and diversity (chapters I, II and IV); and (2) ecosystem functioning, notably in relation to nitrogen (N) cycling (chapters I and III). Our results show that settling OM quantity and quality both had a significant impact on microeukaryotic alpha-diversity. We observed a decrease in alpha-diversity following settling of diatom-derived spring bloom OM, possibly as a result of competitive exclusion, while cyanobacteria-derived summer bloom OM did not affect alpha-diversity (chapters I and IV). We also found that high biomass of diatoms and others fast sinking phytoplankton groups in the water column led to lower microeukaryotic alpha diversity after this material settled on the seafloor (chapter IV). Presumably, following this large sedimentation event, sediment oxygen (O2) demand was strongly stimulated, excluding O2-sensitive taxa. Overall, we propose that the assembly of microeukaryotic communities was primarily mediated by OM settling quantity (chapter IV), while differences in OM quality led to significant but more subtle changes, occurring at fine taxonomic level (chapter I). The response of bacterial communities to OM settling was less pronounced, and probably restricted to the uppermost sediment layer (chapters I and IV). We did, however, observe a significant effect of OM quality on bacterial communities assembly at the sediment-water interface, with taxa favored either by diatom- or by cyanobacteria-derived OM (chapter II). This study also showed that feedback mechanisms from nutrient recycling in the sediment could play a role in this response. Finally, our results indicated a substantial influence of OM quality on N cycling at the sediment-water interface. We found that settling of fresh OM (i.e. low C:N ratio) stimulated denitrification activity (chapters I and III), while simultaneously promoting more N recycling to the water column than settling of degraded OM (i.e. high C:N ratio) did (chapter III). Altogether, our results indicate that current changes in OM settling dynamics in marine systems will likely impact microeukaryotic and, to some extent, bacterial biodiversity in soft sediments. Alterations in settling OM quality, in particular, may also affect crucial microbial processes involved in N cycling. This thesis highlights the importance of considering benthic-pelagic coupling mechanisms to better understand likely future changes in marine ecosystems.
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| 3. |
- Iburg, Sven, 1986-
(författare)
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Microbenthos under Pressure : Impacts of human activities on bacteria and meiofauna communities in Baltic soft sediments
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The marine benthic zone is one of the largest habitats on the planet, harbouring a large diversity of life that underpin many important ecological processes. However, these habitats have been under growing stress from human activities, profoundly altering their living communities. How microbial communities respond to various anthropogenic disturbances has been a central topic in ecology, but the response of meiofauna (benthic microeukaryotes, 40 µm ≥ 1 mm in size) and their use as potential bioindicators in a whole-community approach, has received less attention. The Baltic Sea has been of particular interest in studying how ecological processes are affected due to its history and continuous exposure to various anthropogenic stresses. In this thesis, I explored the effects of chemical contamination (Study I), recreational boating activity (Study II), bottom trawling fishing (Study III), and hypoxia (Study IV) on the Baltic microbenthos in terms of structure and diversity using DNA-inferred community analysis in the context of controlled experiments (Studies I and IV) and field studies (Studies II and III). Study I showed a clear increase in contaminated sediments in PAH degradation, relative abundance of Pseudomonas amongst bacteria, and nematodes amongst meiofauna. Study IV showed that high meiofauna abundance, and its bioturbation, altered sediment oxygen penetration and sulphide oxidation in hypoxic conditions with clear effects on bacterial community structure. Studies II and III showed that select bacteria and meiofauna taxa were favoured in areas with high levels of disturbance. In Study II, the ostracod family Cypridoidea was found in higher abundance in bays with high recreational boating activity (marinas) whilst Cytheruridae was significantly lower. Amongst bacteria, Burkholderiaceae showed to be favoured in active marinas and served as an indicator of chemical contamination. In Study III, highly trawled areas appeared to favour Rhabdocoels flatworms and were accompanied by a decrease in Rhizobiales amongst bacteria, suggesting improved feeding opportunities for motile flatworms, and a negative pressure on substrate dependent bacteria. However, the exposure to the open sea was a major factor in structuring both meiofauna and bacterial communities in shallow bays (Study II) and the impact of trawling (Study III) was more pronounced between areas that were geographically closer. This highlights the importance of abiotic and location specific co-factors that drive microbial and meiofauna assemblages and stress the impact of survey design and sampling locations. Additionally, a common trend throughout my work emphasised the potential of select microbial taxa as bioindicators. For example, the bacteria families Pseudomonadaceae and Burkholderiaceae, and the nematode genera Sabatieria and Leptolaimus could be used as bacterial and meiofauna bioindicators of chemical contamination. In brief, chemical stress had a significant effect on bacterial community structure, whereas physical disturbances had a more pronounced effect on meiofauna, both in terms of structural changes as well as alpha diversity. As such, combining the study of meiofauna and microbial assemblages could be a useful approach in assessing the effects of a wide range of disturbances in benthic habitats.
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