ASFB Home > 2003 > Biological Invasions: Consequences for Parasites, Pathogens, Emerging Diseases, and Fisheries in the Marine Environment.

Management of lowland Murray River wetland habitats: Salinisation and acidification impacts on fish communities.

Anthony Conallin and Bernard McCarthy

Murray Darling Freshwater Research Centre: Lower Basin Laboratory, 13^th Street Mildura, Victoria, Australia.
Email: anthony.conallin@csiro.au

Murray River floodplain wetlands are a valuable resource for a variety of native fish species providing food, shelter and habitat. River regulation in the Murray River has substantially altered the hydrology of floodplain wetlands in the lower Murray River by reducing variability and altering wetting and drying cycles. In recent times there has been a push towards restoring more natural hydrological regimes to floodplain wetlands by manipulating wetting and drying cycles.

In May 2002, a fish survey was conducted in an oxbow billabong in southwest New South Wales undergoing a partial drying cycle. A total of 3,572 fish including 5 native and 2 exotic species were collected despite poor water quality in terms of salinity (27,000 μS/cm) and pH (5.44). In October 2002 another survey was conducted during the wetting cycle and only 48 individuals from one native species were collected, despite a comparative effort between the two surveys. The water quality of the wetland had deteriorated with a reduction in the pH to 3.14. Further investigation revealed that groundwater levels adjacent to the wetland were high due to the influence of the Mildura Weir and had infiltrated the wetland during the partial drying phase causing a salinisation and acidification event.

The findings from this study have major implications for the restoration of floodplain wetland habitats in the lower Murray River where the majority of these wetlands are influenced by regulating weirs. Due to the groundwater impacts that can be associated with these weirs, it is crucial that extensive groundwater monitoring of floodplain wetlands be undertaken prior to the manipulation of wetting and drying cycles.

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