THE MACQUARIE MARSHES IN ARID AUSTRALIA AND THEIR WATERBIRDS - A 50-YEAR HISTORY OF DECLINE

We investigated the relationship between total annual flow of water in the Macquarie River and the extent of flooding in the northern part o f the Macquarie Marshes and trends in waterbird populations from 1983 to 1993. The amount of water in the Macquarie River measured each year within the Macquarie Marshes explained about 86% of the variation in area flooded in the northern part of this wetland. This allowed use of long-term data on flow at Oxley, a gauge within the Macquarie Marshes , as an index to flooding. Annual flows at Oxley have decreased signif icantly for high and medium rainfall events in the catchment, despite no trend in rainfall between 1944 and 1993. The area flooded by large floods has contracted by at least 40-50% during the last 50 years (194 4-1993). Water use has progressively increased upstream in the period, depriving the Macquarie Marshes of water: 51% of ail water passing Du bbo each year, a gauge 100 km upstream, reached the Macquarie Marshes in the period 1944-1953, but by 1984-1993 this had declined to 21%. Nu mbers of species and density of waterbirds on the northern part of the Macquarie Marshes declined between 1983 and 1993. Three other wetland s, not affected by water abstractions, showed no declines. We believe the decline was due to wetland degradation as a result of decreased fl ooding. We estimated more than 88,000 waterbirds in the Macquarie Mars hes in October 1984, establishing the site as an important wetland sit e in Australia. The extent and viability of this wetland will depend o n maintaining or increasing the water supply.