Effect of rising sea levels on the geochemistry of coastal soils in Southern Australia
Date
2022
Authors
Leyden, Emily Ruth
Editors
Advisors
Mosley, Luke
Farkas, Juraj
Hutson, John
Farkas, Juraj
Hutson, John
Journal Title
Journal ISSN
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Thesis
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Abstract
In coming decades, sea level rise will increasingly cause ecosystem change in coastal nearshore environments. Seawater will inundate intertidal and supratidal zones more frequently and for longer durations, some for the first time in nearly 3000 years. Sea level rise will both increase flooding and inundation over the short term, but also cause more long-term progressive inundation through the current unsaturated zone. Little is currently known about how the soil and shallow groundwater will change geochemically from seawater inundation over both these timescales. This thesis aimed to investigate the effect of both short term and long-term inundation of seawater on coastal soils in temperate Southern Australia using a suite of novel approaches.
Chapter 2 details a novel ‘collision cell’ based ICP-MS/MS approach which was developed to determine the sulfur isotope abundances (i.e., 34S/32S ratios, expressed as δ34S) in natural waters rapidly, accurately and with minimal sample preparation. The ICP-MS/MS approach was then used to investigate the δ34S signature of porewaters from a variety of coastal systems in South Australia (including acid sulfate soils), and importantly observe how the δ34S isotope ratio ‘shifts’ to that of seawater when inundated. This novel approach increases the applicability of sulfur isotope analysis to trace seawater inundation. This research titled “A simple and rapid ICP-MS/MS determination of sulfur isotope ratios (34S/32S) in complex natural waters: A new tool for tracing seawater intrusion in coastal systems” was published in Talanta https://doi.org/10.1016/j.talanta.2021.122708
Chapter 3 details an experiment where 12 soils from three distinct environments in South Australia (fresh water streams and lakes; hypersaline saltmarsh and mangroves; acid sulfate soils) were inundated with seawater over a two week period under laboratory conditions, to replicate a short-term storm surge. All soils in the experiment are predicted to be affected by sea level rise in the next 20 years. Dissimilatory reductive dissolution of Mn-oxides and Fe oxyhydroxides and competitive ion exchange processes were two important phenomena which instigated a rapid increases in metal and metalloid concentrations in soil porewaters following seawater inundation, particularly in freshwater environments and in acid sulfate soils. This research titled “Short-term seawater inundation induces metal mobilisation in freshwater and acid sulfate soil environments” was published in Chemosphere https://doi.org/10.1016/j.chemosphere.2022.134383
Chapter 4 details a long term (540 day) laboratory experiment where the progressive sea level rise through coastal soils was investigated by slowly inundating intact soil columns with seawater from the ‘bottom up’. This experiment gave new insights into the biogeochemical cycling of sulfur and iron in soils experiencing seawater inundation from sea level rise over longer timescales, and the geochemical conditions to which sulfidization (due to in-situ sulfate reduction) will affect coastal soils over time following progressive seawater inundation. This research titled “Controls on sulfide accumulation in coastal soils during simulated sea level rise” is under review in Geochimica et Cosmochimica Acta.
In Chapter 5, the data collected from the above experiments was used to formulate hydro-geochemical models using PHREEQC to help predict changes in coastal soils and shallow groundwater following sea water inundation at longer time scales and with different soil properties (reactive iron oxide and organic carbon content).
Chapter 6 summaries the overall findings and provides suggestions for future research.
School/Discipline
School of Biological Sciences
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 2022
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