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Effects of Eutrophication on the viability of seed and egg banks in seasonal wetlands

Curd, Shannyn (2019) Effects of Eutrophication on the viability of seed and egg banks in seasonal wetlands. Honours thesis, Murdoch University.

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Wetland sediments provide a refuge for invertebrate and aquatic plant propagules in the form of seed and egg banks that can lay dormant for a period after a wetland dries out. They allow species to complete their lifecycle despite periods of desiccation, thereby enabling wetlands to be resilient and establish the ecosystem quickly after the wetland is inundated. The aim of this study was to determine whether eutrophication alters the physical properties of wetland sediments, and whether this changed the plant and invertebrate assemblages that emerge from sediments when they are reflooded. This was achieved by sampling the sediments of thirteen seasonal urban wetlands on the Swan Coastal Plain in south-western Australia during the period where wetland water levels were at their lowest. For invertebrate and plant samples, eight cm diameter cores were taken from the top 3 cm of sediment. From there, plant samples were inundated in a greenhouse and left for eight-weeks before being identified. Invertebrate samples were inundated in the laboratory for 30 days and decanted and immediately re-inundated every 10 days. Sediment properties (pH, CaCl2 pH, electrical conductivity and particle size classification) did not differ between oligotrophic and eutrophic wetlands because ooze sediments found in all eutrophic wetlands, and peat/sand sediments found in all oligotrophic wetlands had similar organic matter content. Organic matter content is important as it allows sediments to retain water for longer periods after drying and reduces sediment temperatures, allowing many species to survive longer after drying. The richness of macrophyte species that germinated in the sediments did not differ between oligotrophic and eutrophic wetlands, but submerged macrophytes were more common in oligotrophic wetlands, whereas grasses were more common in eutrophic wetlands. Invertebrate assemblages did not differ between the ooze and peat/sand sediments because the high organic matter content provided the same refuge potential, with no indication that the small particle size of ooze sediments impeded this. Sand however was found in both eutrophic and oligotrophic wetlands and demonstrated reduced macrophyte and invertebrate diversity due to low organic matter content and large grain size, which affects nutrient flow and water retention in sediments. This study provided no evidence that eutrophication affected seed and egg bank viability in seasonal wetlands, so, the ooze sediment found in eutrophic wetlands can be considered ecologically comparable to the peat/sand sediment found in oligotrophic wetlands on the SCP. Eutrophication has many negative effects on wetland ecosystems, but it appears that seed and egg bank function in temporary wetlands remains unaffected.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): Environmental and Conservation Sciences
United Nations SDGs: Goal 15: Life on Land
Supervisor(s): Robson, Belinda, Chambers, Jane and Strachan, Scott
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