Browsing by Author "Gillanders, BM"

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    Environmental change in the coastal wetlands near Adelaide, Australia.
    (Elsevier, 2007-07) Nicholson, ED; Krull, ES; Smernik, RJ; Zawadzki, A; Gell, PA; Gillanders, BM
    The coastal wetlands located near metropolitan Adelaide are comprised almost exclusively of the Grey Mangrove (Avicennia marina). This native vegetation is a natural resource that has numerous suggested functions, including coastal buffering, mitigation of terrestrially derived nutrient runoff, fish nursery habitat and also ecotourism. The coastal wetlands that are the focus of this study exist primarily within two aquatic reserves. As such, it is important to understand how this coastal environment once existed so as to provide a reference for assessing its current condition. In the relatively calm marine environment provided by the Grey Mangrove, sediments are trapped amongst the roots and pneumatophores. Within these sediments, a number of proxies exist, by which past environmental conditions may be reconstructed. These proxies include microfossils, such as diatoms and forams, macrofossils, such as pollen and seeds, but also relatively indistinguishable fractions of the soil matrix generally referred to as OM (organic matter). The ultimate question being asked within the larger context of this palaeoecological study is, “What impact has European settlement had on the coastal environment near Adelaide?” The research presented here will focus on the palaeoecological utility of OM, found in mangrove sediments, toward answering this question. Sediment samples were collected and analysed from among twenty-three modern sites and three sediment cores. In addition, plant samples representing the types of organic matter typically found in the study region (e.g. samphire OM, mangrove OM, seagrass OM, macroalgal OM), were collected from the same modern sites. An analysis of 13C and 15N isotopes was performed, as organic matter sources may be differentiated based upon recognisable isotopic signatures (e.g. marine vs. terrestrial plant origins). 13C-NMR spectroscopy was then used to supplement the stable isotope analysis, providing an additional means of differentiating carbon types and their sources. In order to make inferences about post-European impacts upon the study region, a modern chronology was obtained. 210Pb profiling of the sediment cores was performed in combination with an analysis of exotic Pinus pollen occurrences. This study describes the environmental changes that have occurred in Adelaide’s coastal wetlands since European settlement and the level of impact that may be attributable to anthropogenic influence.
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    Palaeohydrology of the southern Coorong Lagoon, inferred from oxygen isotope ratios of the bivalve Arthritica helmsi
    (Australasian Quaternary Association, 2021-07-08) Chamberlayne, BK; Tyler, JJ; Gillanders, BM; Jacobsen, GE; Tibby, J; Haynes, D
    Understanding the resilience of aquatic ecosystems to climate and human impacts requires a long term perspective that is rarely attainable via standard monitoring programs. This is evident in the South Lagoon of the Coorong in South Australia where a history of ecosystem management has been based on limited knowledge of the range of natural variability. Here, we present a ~1750 year record of hydrological variability inferred from the oxygen isotope ratios of the bivalve Arthritica helmsi. Analysis of the controls of oxygen isotope fractionation in modern waters, and modern populations of A. helmsi inform the interpretation that the oxygen isotope ratios of shells preserved in the Coorong sediments reflect the precipitation/evaporation balance of lagoonal waters. Centennial scale variability in the oxygen isotope based hydroclimate record from the Coorong is consistent with other records in the region, contributing to a deeper understanding of the scale of natural hydrological variability in southeastern Australia during the last 2000 years. While the sedimentary bivalve data suggest that the lagoon was slightly less saline in pre-European times, the range of oxygen isotope variability within sedimentary bivalve shells is not statistically distinguishable from the range predicted by the hydrological conditions of the modern day Coorong South Lagoon, suggesting that present day hydrological conditions are not markedly unusual in the context of the past 1750 years. As a consequence, our bivalve oxygen isotope data suggest that major hydrological alterations to the Coorong South Lagoon – for example flushing the lagoon with sea water – could result in a departure from the natural hydrological state of the system over the last 2000 years.