National Wetlands Update September 2012
Issue No. 21, September 2012
Bibra lake rehabilitation and climate change
Chris Beaton, The City of Cockburn
Bibra Lake revegetation from birdhide in
September 2010. (Linda Metz)
The City of Cockburn is a large outer metropolitan council on the outskirts of Perth Western Australia. Two chains of wetlands, known as the Beeliar wetlands, run through the heart of the City. Bibra Lake is one of the larger lakes within these wetland chains.
Past development and grazing has severely impacted the lake vegetation leaving much of the surrounding area in a degraded condition. The City of Cockburn, in conjunction with the Cockburn Wetlands Education Centre (CWEC), a community volunteer organisation, has been rehabilitating Bibra Lake for a number of years with the intent of restoring the lakes riparian vegetation and re-creating habitat.
The need to rehabilitate our wetlands is becoming increasingly important due to the effects of climate change. South west Western Australia has experienced a 15-20 per cent reduction in rainfall since the 1970s (Petrone et al, 2010). In 2010 Perth experienced its second driest year on record with 503.8 millimetres of rainfall, while the driest year was 466.8 millimetres in 2006. The long term average is 850.0 millimetres. As a result of reduced rainfall, groundwater levels are falling.
Bibra Lake revegetation from the same birdhide in
June 2012. (Linda Metz)
Bibra Lake is one of the wetlands of the Swan Coastal Plain, these wetlands are surface expressions of the groundwater table. If average groundwater levels continue to drop, this could have severe consequences for the wetlands. Although many of the wetlands in the region regularly dry out, the frequency and the length of time they remain dry has been increasing for approximately a decade.
There is little that can be done to supplement water levels in the wetlands. It has been observed over the past 10 years that, as rainfall continues to reduce, dry land species have begun colonising areas that were previously wetland. Correspondingly, wetland species have shifted downslope onto the newly or increasingly exposed mudflats.
In order to allow wetland systems to adapt naturally to the changing climate, the system needs to be as resilient as possible. Both the City and CWEC volunteers are building this resilience by reducing other threats such as weeds, degradation and unauthorised vehicle access.
So far more than 5.25 hectares have been rehabilitated with planting of appropriate endemic species using a combination of volunteer hours, City resources and grants.
Petrone, K. C., Hughes, J. D., Van Niel, T. G. and Silberstein, R. P. 2010, Streamflow decline in southwestern Australia, 1950-2008, Geophysical Research Letters 37.