Browsing by Author "Fluin, J"

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    Anthropogenic acceleration of sediment accretion in lowland floodplain wetlands, Murray–Darling Basin, Australia
    (Elsevier, 2009-07-01) Gell, PA; Fluin, J; Tibby, J; Hancock, G; Harrison, JJ; Zawadzki, A; Haynes, D; Khanum, SI; Little, F; Walsh, B
    Over the last decade there has been a deliberate focus on the application of paleolimnological research to address issues of sediment flux and water quality change in the wetlands of the Murray–Darling Basin of Australia. This paper reports on the research outcomes on cores collected from sixteen wetlands along the Murrumbidgee–Murray River continuum. In all sixteen wetlands radiometric techniques and exotic pollen biomarkers were used to establish sedimentation rates from the collected cores. Fossil diatom assemblages were used to identify water source and quality changes to the wetlands. The sedimentation rates of all wetlands accelerated after European settlement, as little as two-fold, and as much as eighty times the mean rate through the Late Holocene. Some wetlands completely infilled through the Holocene, while others have rapidly progressed towards a terrestrial state due to accelerated accretion rates. Increasing wetland salinity and turbidity commenced within decades of settlement, contributing to sediment inputs. The sedimentation rate was observed to slow after river regulation in one wetland, but has accelerated recently in others. The complex history of flooding and drying, and wetland salinisation and eutrophication, influence the reliability of models used to establish recent, fine-resolution chronologies with confidence and the capacity to attribute causes to documented effects. © 2009 Elsevier B.V
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    Changing fluxes of sediments and salts as recorded in lower River Murray wetlands, Australia
    (International Association of Hydrological Sciences (IAHS), 2006-07-06) Gell, PA; Fluin, J; Tibby, J; Haynes, D; Khanum, SI; Walsh, B; Hancock, G; Harrison, JJ; Zawadzki, A; Little, F
    The River Murray basin, Australia’s largest, has been significantly impacted by changed flow regimes and increased fluxes of salts and sediments since settlement in the 1840s. The river’s flood plain hosts an array of cut-off meanders, levee lakes and basin depression lakes that archive historical changes. Pre-European sedimentation rates are typically approx. 0.1–1 mm year-1, while those in the period after European arrival are typically 10 to 30 fold greater. This increased sedimentation corresponds to a shift in wetland trophic state from submerged macrophytes in clear waters to phytoplankton dominated, turbid systems. There is evidence for a decline in sedimentation in some natural wetlands after river regulation from the 1920s, but with the maintenance of the phytoplankton state. Fossil diatom assemblages reveal that, while some wetlands had saline episodes before settlement, others became saline after, and as early as the 1880s. The oxidation of sulphurous salts deposited after regulation has induced hyperacidity in a number of wetlands in recent years. While these wetlands are rightly perceived as being heavily impacted, other, once open water systems, that have infilled and now support rich macrophyte beds, are used as interpretive sites. The rate of filling, however, suggests that the lifespan of these wetlands is short. The rate of wetland loss through such increased infilling is unlikely to be matched by future scouring as regulation has eliminated middle order floods from the lower catchment. © 2006 IAHS Press
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    Multiproxy palaeoeology reconstruction of the mid-Holocene to present salinity, marine incursions and flow regime of Lake Alexandrina and the Goolwa channel, South Australia.
    (Elsevier Ltd and the International Union for Quaternary Research (INQUA), 2007-07) Skinner, R; Fluin, J; Cann, J; Harrison, JJ
    Multiproxy palaeoecology techniques are used to reconstruct the mid-Holocene to present salinity, marine incursions and flow regime of Lake Alexandrina and the Goolwa channel, South Australia. Microfossils (foraminiferal, ostracoda and diatoms) are analysed in three sediment cores. Foraminiferal remains are used to reconstruct the frequency, duration, and spatial extent of marine incursions upstream through the Goolwa channel to Lake Alexandrina. Diatom analysis provides a quantitative reconstruction of salinity, while the ostracoda analysis is currently exploratory. Three C-14 AMS radiocarbon dates and eight Pb-210 dates for each of the three cores have been submitted for analysis. To support the flow-regime-reconstruction with quantitative data, grain size analysis is included. Preliminary data from the foraminiferal assemblage of core RS1 (taken from just above the Goolwa barrage) illustrates a substantial change in both grain size and presence of foraminifera at a core depth of 130 cm. This may represent a sedimentation rate of 2 cm/yr, since the placement of the Goolwa barrage in 1939. At depths between 130 cm and 0 cm the sediment is barren of foraminifera. Below 130 cm foraminifera are abundant; inner-shelf marine species, especially Elphidium crispum, are dominant from 130 cm to the bottom of the core (216 cm). Only three increments (140-144 cm; 164-168 cm; 174-182 cm) have very low foraminiferal counts (<100). The sediment at these depths is of a much finer grain size. For a majority of the time, it is likely that pre-river-regulation-flow rates of the Murray River were high enough to maintain an open mouth, allowing the mixing of marine and estuarine waters.