Monitoring of ecosystem responses to a major natural flood in Autumn 2012

Following heavy rainfall in the upper and mid Murrumbidgee catchment in March 2012, a large flood event occurred, filling many of the wetlands where environmental water was provided in 2011. CSU undertook surveys of the wetlands from 23-28 April 2012 to:

• identify any further outcomes from environmental watering undertaken in 2011
• better understand the response to a major natural flooding event
• help inform future environmental watering in the Murrumbidgee catchment.

Executive Summary

In June 2011 the NSW Office of Environment and Heritage managed the delivery of more than 160 gigalitres (GL) of environmental water from the Commonwealth, NSW, The Living Murray Initiative and private donors, to wetlands in the mid-Murrumbidgee region, which included NSW Riverina Red Gum Reserves. A further 98 GL of NSW environmental water was released from the Burrinjuck Dam and Tombullen storage in December 2011 which re-filled a subset of wetlands. These flows were delivered to aid in the long term recovery of the mid-Murrumbidgee wetlands. Charles Sturt University monitored the ecological response the environmental watering. The results can be found in:

• Monitoring of ecosystem responses to the delivery of environmental water in the Murrumbidgee system - Report 2

Following heavy rainfall in the upper and mid catchment in March 2012, a large flood event occurred, filling many of the wetlands where environmental water was provided in 2011. We undertook surveys of the wetlands from 23-28 April 2012 to:

• identify any further outcomes from environmental watering undertaken in 2011
• better understand the response to a major natural flooding event
• help inform future environmental watering in the Murrumbidgee catchment.

The monitoring showed that the large natural flood event in March 2012 led to substantial changes in:

• fish community composition, with the colonisation of wetlands by exotic carp and native golden perch
• frog breeding activity with the flood event triggering a substantial breeding event by L. tasmaniensis
• breeding in waterfowl and small numbers of colonial waterbirds with small number of active nests observed at Yarrada and Gooragool
• vegetation cover with slight declines due to vegetation being knocked down by the flooding in addition to normal winter senescence of summer growing annuals
• dissolved oxygen (DO) levels at Euroley (C1) with DO declining at this site but water quality was generally stable at all the other sites sampled.

A key result that will inform environmental watering decisions into the future is that wetlands which retained water throughout the year (with the help of environmental water) were more resilient to recruitment by exotic fish.