Browsing by Author "Hancock, G"

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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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    Late holocene evolution of the coastal and estuarine lakes of the Snowy River floodplain (SE Australia): salinity regimes, nutrient dynamics and anthropogenic impacts
    (Elsevier, 2007-07) MacGregor, A; Gell, PA; Tibby, J; Harrison, JJ; Jacobsen, GE; Hancock, G
    Coastal lake and estuarine systems across south eastern Australia act as both sedimentary and biological amplifiers, and are more sensitive to cumulative catchment-driven hydrological change than previously recognised (see Tibby et al., this volume). Deciphering natural responses to climate change and geomorphology, and ensuing historical responses to catchment clearance and regulation reveals whether these systems now lie within pre-disturbance variability, and the extent to which anthropogenic change is unidirectional. A multi-proxy palaeoecological assessment of the terminal coastal and estuarine lakes of the Snowy River floodplain will be presented. The Snowy River is one of Australia’s hallmark river systems. Its catchment has been substantially modified since the mid 1800s. The ecological and water quality impacts of a major inter-basin transfer of up to 99% of its flow since the mid 1960s are poorly understood. Incorporating a diatom-water quality inference model, stable isotope and fossil pigment reconstruction, this study has examined (a) notions of variability in the progressive evolution of the system (b) how the records compare to that of a relatively un-impacted (control) system nearby (c) the influence of natural perturbations on the ecology of these lakes (with respect to salinity and nutrient status), as well as (d) the nature and timing of anthropogenic disturbance. Explained as a combination of land clearance, drainage practices, and more recently, substantial flow diversion in the Snowy River, recent water quality changes are as pronounced as any experienced through the Holocene. However, they have occurred at a rate faster than those brought on by past climatic or geomorphic change.