Indicator: IW-34 Examples of deterioration of condition of wetland vegetation

Data

River Red Gum decline along the River Murray

Surveys in 2003 indicated that approximately 80% of trees on the River Murray floodplain in South Australia were stressed to some degree, with between 20 - 30% of them severely stressed. Many severely stressed trees are likely to die unless the stress is removed.

Severely stressed trees were observed on the floodplain where saline groundwater is entering creeks, well away from the influence of the main stem of the river. River Red Gums were not the only species demonstrating signs of stress; Black Box and River Cooba communities, as well as understorey and shrub layers, were also impacted, although to a lesser extent.

Drought, reduced flooding regimes and rising saline groundwater appear to be the main contributors to the decline in tree health, which varies with geographical position along the river, biogeophysical characteristics of each site, river regulation and surrounding land use.

Flooding under current conditions is not insufficient to provide the additional water supply necessary for survival, nor is it sufficient to leach salt from the soils that accumulate between floods. Flooding that normally would have been sufficient has been reduced from a frequency of one year in three, to an average frequency of one every eight years.

In ecological terms, the floodplain corridor of the lower River Murray is of critical importance as a refuge in times of drought. A serious decline in the health of the River Red Gum population on the floodplain has severe consequences for many native fauna species. The River Murray is an important destination for national and international migratory species.

There is evidence that unless an adequate flooding regime is reintroduced in the near future, it is likely that a significant loss of vegetation communities on the lower River Murray floodplain will occur.

Source: Murray-Darling Basin Commission 2003, Preliminary investigations into observed River Red Gum decline along the River Murray below Euston, Technical Report 03/03, Murray-Darling Basin Commission, Canberra, viewed 15 Nov 2005, http://thelivingmurray.mdbc.gov.au/reports.

What the data mean

River Red Gums and many other wetland communities are under stress in areas where natural river flow regimes have been reduced.

Data Limitations

The effects of the drought, relative to the altered flow regime, may require further elaboration.

Issues for which this is an indicator and why

Inland Waters — Response of biota - Wetland and floodplain communities

Assessment of the condition of wetland vegetation is an important tool for monitoring wetland health. The dominance of particular species of vegetation may provide an indication of hydrological or water quality changes that have taken place (e.g. without semi-regular flooding, river red gums may decline; or, the dominance by Typha, an emergent wetland bulrush, tends to indicate disturbance in the surrounding landscape). In the absence of data on the condition of all Australian wetlands, particular wetlands where condition has been assessed may provide insights into wetland condition more broadly.