Browsing by Author "Haynes, D"

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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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    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.