National Wetlands Update September 2012
Issue No. 21, September 2012
Creating refuge habitat during drought at Narrung Wetland in the Lower River Murray, South Australia
Adrienne Frears and Kate Mason, Department of Environment, Water and Natural Resources, South Australia
Narrung Wetland during drought. (Adrienne Frears)
Monitoring the effects of environmental water delivery in the Narrung wetland is providing important information about the value of these flows to the long term health of the system.
Narrung wetland, situated between Lakes Alexandrina and Albert in the Lower Lakes, Coorong and Murray Mouth Icon Site, received 250 megalitres of environmental water from The Living Murray program in 2009.
The Living Murray program was established in 2002 and is a joint initiative funded by the New South Wales, Victorian, South Australian, Australian Capital Territory and Australian governments and coordinated by the Murray-Darling Basin Authority to address the declining health of the River Murray system.
After being disconnected from the system for several years during the drought, monitoring conducted by the South Australian Murray-Darling Basin Natural Resources Management (SA MDB NRM) Board and The Living Murray program, determined that the aquatic seedbank of the wetland was at risk. This was due to a series of 'false starts' triggered by rainfall pooling and then drying in the wetland bed before aquatic plants could complete their life cycle and replenish the seedbank.
Environmental water was pumped into Narrung wetland in October and December 2009. The wetland responded well, with a thick layer of submerged aquatic plants forming after about a month, and invertebrates hatching from the previously dry sediments, providing much-needed food and refuge habitat for water fowl and waders. A net increase in aquatic seed density was determined as a result of the watering. Delivering environmental water to the wetland provided an important four-month window of inundation during drought. Narrung was one of only a handful of 'wet' wetlands across a 250 kilometre section of the River Murray between Lock 1 and the Barrages.
Recovery of Narrung Wetland post drought.
The following year, flows returned to the River Murray, and the weir pool below Lock 1 refilled. Water levels increased allowing the Narrung Wetland flow control structure to be opened and refilling of the wetland to occur naturally (see video ). South Australian Government staff and the Narrung Wetland community group joined forces to open the wetland structure and celebrate the end of the drought. Since this time, the wetland has continued to be managed jointly by government staff and the local community to fluctuate water levels and maintain sufficient aquatic plants and invertebrates for waterbirds.
Local ornithologist David Dadd conducts monthly bird monitoring at Narrung Wetland. The highest abundance and diversity of waterbirds on record was observed following reconnection of the wetland in late spring 2010. Amongst the 47 bird species recorded since environmental watering in 2009, banded stilts, glossy ibis and Australasian shovellers (South Australian listed) are regular visitors. Many of these birds are observed feeding on or amongst the dense submerged plants including widgeon grass and charophytes. Carp screens at the flow control structure ensure these soft-rooted water plants are not damaged by adult common carp.
River Murray water levels were managed through the summer of 2010 at approximately 20 centimetres lower than the normal pool level to expose large areas of mudflats, providing ideal habitat for wading birds. Common greenshanks and marsh sandpipers were two of 11 migratory bird species recorded at the wetland during this period.
Monitoring has determined that applying environmental water during drought can increase resilience, and lead to a more immediate and magnified ecological response when flows are returned.