General Meeting 15th March
At the March meeting our guest speaker was Peter Wilmot and his topic was “LakeMealup on the road to recovery: an adaptive management approach to acid sulphate soils and typha invasion”. The presentation was co-authored by Heidi Bucktin of the Department of Environment and Conservation (DEC) and was first presented at the WA Wetland conference earlier this year. Peter is a founding member of KRMB but was speaking as one of the driving forces on the committee of the Lake Mealup Preservation Society (LMPS).
LakeMealup is a large (90ha) freshwater wetland 2km east of the Harvey Estuary. It has extensive fringing vegetation and is adjacent to good quality woodland, especially to the west. In 1985 less than 20ha was reserved for conservation. A group of 50 people got together to buy the property. DEC has purchased other parcels of surrounding land over the years such that in 2013 a total of 204ha is reserved for nature conservation.
There is a reasonable corridor south to LakeMcLarty. LMPS is a not for profit organization that owns 123.6ha of wetland and woodland and has provided 26 years of active nature conservation management, fencing, flora and fauna monitoring and control of feral species. It has a cooperative relationship with the DEC.
Problems started to emerge at the wetland in the early 90’s and from 1994 to 2012 the lake dried out each year. The drying was probably due to a combination of reduced winter rainfall and a change to local drainage management, including the closing of a shallow channel that connected LakeMealup to the Mealup Main Drain (MMD). The water in the lake became acidic, with pH dropping from 7 to 4, algal blooms became common, and water birds disappeared. Typha orientalis expanded, covering 80% of the lake. Typha is very difficult to control and comes back quickly after being cut back. LMPS members started to search for solutions.
The pH problem was suspected as resulting from acid sulphate soils (ASS) exposed when the lake dried. Monitoring between 1989 and 1993 showed that acidity was controlled and typha did not spread when the lake did not dry out. It became evident that a source of additional water was required to prevent the lake from drying out in summer. The Mealup Main Drain was known to have flow. In 2007 LMPS proposed to put a culvert in the MMD to divert drainage flows into the lake in winter and spring. The proposal was backed up by 20years of monitoring water quality and typha in the lake. The timing of the proposal was spot on as funds had become available for the management of Ramsar Wetlands.
To consider the proposal a Lake Mealup Technical Advisory Group (TAG) was formed to provide guidance for on-ground activities. The group was comprised of experts and key stakeholders from DEC, Department of Water, Peel Harvey Catchment Council (PHCC) , LMPS, EdithCowanUniversity and private consultants. Step 1 in 2009 saw investigations at LakeMealup during which ASS were confirmed, poor water quality was confirmed and the decline of ecosystem health was confirmed. Also, MMD had sufficient water. Step 2 in 2010 saw the TAG agree to the installation of a variable height weir in the MMD and to carry out typha control prior to diversion. The typha control was conducted in 2011, initially using a D6 bulldozer followed by control of regrowth using roundup. The weir was completed in December 2011, too late to divert flow. Additional typha control was performed in March 2012 and the weir, which cost $200,000 to install, was commissioned in June 2012.As the lake filled the water quality rapidly improved, with pH going from 3.7 to 6.3. It stabilized at a pH of 7. Water level rose to 1.38m AHD. Step 3 saw revegetation coordinated by PHCC. Step 4 was Analyse and Adapt – monitoring each fortnight for pH, Oxygen reduction Potential and Dissolved Oxygen. The recovery of LakeMealup has begun - it did not dry out during the 2012/2013 summer (in fact a top up occurred with some heavy rainfall in December)and there has been a dramatic reduction in typha,. The ducks and other water birds together with frogs have returned.
Peter said that the success of this recovery project has been due to a combination of fortunate timing, the right people in the right organizations and the adaptive management framework. A recent aerial photograph shows the lake is full and a functioning wetland. This was a real good news story and the audience expressed their congratulations to all involved. Colin Prickett