Blue carbon in South Australian coastal ecosystems
Date
2024
Authors
Russell, Sophie Kate
Editors
Advisors
Jones, Alice
Gillanders, Bronwyn
Gillanders, Bronwyn
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Thesis
Citation
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Abstract
Blue carbon ecosystems (including seagrass, mangroves, saltmarshes and supratidal forests) provide an important opportunity to contribute to climate change mitigation and ensure the future provision of many ecosystem services. They are effective carbon sinks due to the plant's structure capturing organic detritus, constant accretion of sediment allowing for continual sequestration of carbon, and waterlogged soils which slow the decomposition of organic material. Ecosystem services include water filtration, shoreline protection and provision of nursery habitat for ecologically and commercially important fish species. Protection and restoration of these ecosystems for climate change mitigation will require a comprehensive understanding of the existing carbon stocks, what drives the variation in carbon storage and where the organic material is coming from. The overarching aim of this thesis is to provide the information and methods necessary to make informed management decisions for enhancing the soil carbon sequestration and storage potential of blue carbon ecosystems in South Australia. The second chapter aimed to determine key drivers of variability in soil organic carbon stocks – to achieve this, a model was created using a range of factors to assess which were having the strongest influence on soil organic carbon stocks. Distance to the nearest tidal creek, vegetation type and soil type were key factors driving the variability of soil organic carbon stocks on a regional scale. The next study aimed to develop a method for spatial predictions of soil organic carbon stocks informed by key environmental variables determined in the previous chapter. Soil cores were collected across the case study region of Adelaide, South Australia and used in conjunction with environmental spatial data to create spatial predictions using a boosted regression tree approach. Vegetation type, elevation and percentage of clay had the most influence on the model-predicted soil organic blue carbon stocks. This study also identified substantial ‘fossil’ blue carbon stocks in areas not currently vegetated with blue carbon ecosystems. The fourth chapter investigated the contributions of organic matter sources to soil organic carbon stocks and examined the geographic variation in contributions from different source materials. Mixing models with stable isotope signatures and elemental ratios were used to determine the contributions of organic matter from different vegetation types and locations. Between 48 to 73 percent of the organic carbon source material originated from a location different from where it was deposited. The final study summarises all available information on soil organic carbon stocks and accumulation rates in South Australia. All data collected for this thesis were combined with pre-existing data for South Australia to form a comprehensive summary of state average soil organic carbon stocks and accumulation rates for each ecosystem, and environmental drivers of variability of soil organic carbon stocks. An important finding of this thesis is that soil organic carbon stocks in South Australia are lower and influenced by different drivers of variability compared to the rest of Australia, highlighting the importance of incorporating regional data into national estimates. This thesis provides insights to strategically prioritise conservation and restoration efforts. It identifies environmental conditions, vegetation types, and spatial connectivity conducive to optimising the management of temperate to arid blue carbon ecosystems for climate change mitigation.
School/Discipline
School of Biological Sciences
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 2024
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