Changing fluxes of sediments and salts as recorded in lower River Murray wetlands, Australia

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

Keywords

Rivers, Wetlands, Salinity, Sedimentation, Diatoms, Phytoplankton, Australia

Citation

Gell, P., Fluin, J., Tibby, J., Haynes, D., Khanum, S. I., Walsh, B., Hancock, G., Harrison, J. J., Zawadzki, A. & Little, F. (2006). Changing fluxes of sediments and salts as recorded in lower River Murray wetlands, Australia. Paper presented to the IAHS ICEE Dundee 2006, Sediment Dynamics and the Hydromorphology of Fluvial Systems, Dundee, Scotland, 2nd-7th July 2006. In Rowan, J. S., Duck, R.W. & Werrity, A. (eds), Sediment dynamics and the hydromorphology of fluvial systems: Proceedings of a symposium held in Dundee, UK, July 2006. Wallingford, Oxfordshire, UK: IAHS Publications. 306, (pp. 416-424).