Impacts of anthropogenic modification on the taxonomic and functional structure of estuarine sediment communities

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Embargoed until 2018-05-31
Copyright: Sun, Melanie
Healthy sediment communities are considered highly beneficial for aquatic ecosystem health. Sediments act as sinks for allochthonous materials and may buffer impacts through complexation and adsorption. As such, sediment dwelling organisms are susceptible to stress from compounds stored in the sediments. Factors that influence taxa-compound and inter-taxa interactions can impact important sediment functions. While biogeochemical implications of such impacts have received great attention, understanding the biotic changes that drive most of these functions remains elementary. Using high-throughput sequencing, this thesis investigates the influence of abiotic factors in anthropogenically modified estuarine systems on the relationship between sediment organisms and their potential function. Taxonomic (16S and 18S rDNA sequencing) and functional (amo-based diagnostic microarray) approaches independently found a significant association between anthropogenic activity and changes in sediment community structure across eight southeast Australian estuaries, ranging from relatively pristine to modified states. However, the complex interactions between multiple stressors in natural environments impede our efforts to disentangle the influence of common toxicants (e.g. metals, PAHs) and nutrients (e.g. total organic carbon) on sediment communities. In a replicated field experiment, we therefore focused our attention on sediment community responses to organic enrichment—a common contemporary stressor. Paired metagenome and metatranscriptome sequencing revealed functional shifts between control and organically enriched sediments. Anoxia, toxic sulphide production, lower primary productivity and decreased nitrogen metabolism were favoured under organic enrichment. Ammonification was the primary route of nitrogen removal. These all have negative implications for ecosystem health. Compositional shifts reflected functional attributes, with putative links identified between ammonia oxidation and Crenarcheota, methanogenesis and Methanosarcina taxa, and sulphate reduction and Desulfovibrio taxa. This research highlights the powerful insight gained when both compositional and functional aspects of community structure are viewed in concert.
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Sun, Melanie
Johnston, Emma
Brown, Mark
Chariton, Anthony
Dafforn, Katherine
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PhD Doctorate
UNSW Faculty
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