The following are the minutes taken from the TAG meeting of June 19th 2018
The meeting was called to discuss the problems with the Hydrology of Lake McLarty with input with the various experts and decide what can be done to save the lake.
LAKE McLARTY TECHNICAL ADVISORY GROUP
Minutes of meeting held on Tuesday 19th June 2018 at 9.30am.
Meeting opened at Peel Harvey Catchment Council (shed) with Geoff Barrett as chair.
Item 1: Present:
Geoff Barrett DBCA, Karl Brennan DBC, Heidi Bucktin DBCA, Alan Wright DBCA, Bart Huntley DBCA, Jim Lane DBCA, Melita Pennifold DBCA, Steve Appleyard, DWER Brad Degens DWER, Michelle Antao DWER, Peta Kelsey DWER, Teresa Hey FoLM, Bob Paterson FoLM ,Terry Ryan FoLM, Mia D’Alessio EGS, Peter Muirden KareelaWA, Steve Fisher PHCC, Peter Wilmot LMPS, Michael Craig UWA, Vicki Stokes Birdlife Aust, Tom Lerner SoM
Apologies: Andrew Del Marco- PHCC, Paddi Creevey-FoLM, Ian Hey-FoLM, Nancy Fardin-FoLM, Allan Johns-FoLM, Mike Coote-DBCA, Karl Hennig-DWER, Keirin Kilminster-DWER, Jane Chambers-UWA and Adrian Pinder-DBCA.
Item 2: Action items from the minutes of previous meeting have been implemented except for the letter of thanks to the Dept. of Environment and Water as Heidi was transferred to a new job and this has been left to the new replacement. It is not known if Mike Coote has communicated with the Federal Government regarding Acid Sulphate Soils.
Item 3: Lake McLarty Hydrology:
Peter Muirden spoke on the lakes hydrology. Generally, up to 2005 the lake consisted of mudflats which were hydrated 1-2 months/year and used by the waders and shorebirds. From 2005 onwards, there was a change to the hydro period from a dry spell of 1-3 months to a dry period of 5-7 months. Around 2014-2015 possibly driven by climate change, terrestrialisation of the lake floor occurred, going from muddy flats to a covering of couch and samphire. Cracking in the lake floor was first noticed about twelve months ago and the cracks now seem to be extending. In February 2018 when the lake dried, iron and ASS precipitates were noticed in the south end of the lake.
To gain an understanding of the ground water situation, in April-May 2018, a series of piezometer bores were hand-augered on the lake floor and these peizos were monitored as well as some of the Birchmont private bores. Early results indicate that there is local groundwater mounding within Birchmont with the lowest GWLs below southern Lake McLarty. Peter mentioned that he is in the process of developing a conceptual model to explain the groundwater in the area.
The drain diversion into the lake worked well at the gauge station with good discharge measurements and good flow readings over the weir until its forced removal in August 2017. The new gauge station situated downstream at natural water surface level will give us some monitoring and flow data for 2018 season.
The adjacent property (Lot 68, Mills Road) to the drain was heavily fertilized last year. We understand that the drains on this adjacent (Nancarrow) property were also recently excavated to improve drainage, likely explaining the lower than normal pHs feeding into the Lake during 2018. Nutrients entering Lake McLarty in the drain are normally around TN 3.30 and TP 0.35 but with the heavy August 2017 runoff the readings had doubled.
Item 4: ASS risk update and proposed sediment survey scope:
Steve Appleyard informed the group about the likely role of peaty sediments in Lake McLarty in controlling water quality. The sediments will have an effect on water quality which in turn will affect macro-invertebrates which in turn will affect bird population. One of the most important components of the top one metre of peaty material, is that it has a very large influence on water quality. The peat moderates the water quality, buffering against the release of heavy metals, and the loss of peat leads to high instability in the wetland and cracking in the lake as the peat disappears.
The bigger picture is that the peats are storing a colossal amount of carbon and when this dries out it releases carbon dioxide. Peat also has important water storage abilities and helps moderating water levels. More importantly it regulates the amount of nutrients and heavy metals available. When peat dries out it changes in composition and with exposure to oxygen it changes the chemistry.
The ASS problem was triggered around 2014. The prognosis is, that with an unstable system at the start of each year, ASS type problems dominate and as winter progresses, a high sulphate input results in the black ooze (MBO’s or mono-sulphidic black ooze) from the sediments. The source of the phosphorous is natural as well as from agriculture.
The requirements are:
- Information is needed to manage the system.
- ASS investigation to determine the potential acid release at the beginning of the year.
- How MBO forms – incubation tests and phosphorus release from sediments.
- Ongoing measurement rate of peat loss.
Acid Sulphate Soil update and investigation scope:
Brad Degens showed the group a conceptual model of sediment – ASS transition in Lake McLarty.
With the lake drying for a longer period we’re seeing cracks forming with the peat drying and collapsing causing accelerated oxidation. Seasonal MBO formation when inundated and oxidation when dry causing red staining. It’s been noticed there is a variation in the peat substrate across the Lake bed and in some places, the amount of peat is limited.
- Scope ASS survey and sediment investigation.
- Mapping transects across the lake to give a scale of observation.
Item 5: Update on NRM:
Geoff Barrett advised that he and others attended a meeting with Deb Slater-Lee for information and guidance on the State NRM grant. However, the criteria are not publicly available at this stage but we do know it will be a highly competitive process due to changes in the National Landcare Program. Deb has offered help and feedback on the application.
Andrew Del Marco suggested to get the most out of any grant application we must present a proposal of a bigger picture, with key documents being the Lake McLarty Action and Management Plans, Peters Muirden’s hydrology works proposal and the Lake McLarty TAG.
Subsequently a small group (Peter Muirden, Bob Patterson, Andrew DelMarco, Steve Fisher, Karl Brennan, Mark Cugley and Geoff Barrett) met on Friday 15 June 2018 to nut out a structured proposal for the NRM using Peter Muirden‘s proposal, ASS investigation, groundwater/geology, catchment flow and water quality.
Steve Fisher explained that this would have to be a joint application including PHCC, TAG, DBCA, BIRDLIFE and Community based groups.
The application closes on the 8th August.
Item 6: THINK TANK SESSION: Priority actions.
WATER QUALITY OBJECTIVES
- Short term is to maintain status quo.
- Long term is what we need to achieve with water supplementation
Limits of acceptable levels in nutrients and salinity.
These criteria currently being reviewed by PHCC and the TAG.
Target surface water levels.
- Targets for inundation based on objective for maintaining Lakes values as migratory wader habitat.
- Heidi stated, we must be aware that there are water quality targets or objectives and strategies, but if the system keeps going the way it is, our water quality objectives will be very different because we will have a situation that’s “flipped” and the target water level then is going to be to manage ASS and the repercussion of that – so basically maintaining a permanent wet water body.
McLarty drain and other drains.
Target water quality and water flows in the drain from the catchment.
- TAG endorsed/adopted the ANZEC water quality targets proposed in the report by Peter Muirden.
Acceptable change in Lake McLarty
- Steve Fisher spoke about the limits in acceptable change (LAC’s) in aquatic plants, littoral vegetation / paperbarks, macro-invertebrates and waterbirds.
- It was noted by Mike Craig and Bob Paterson that in the past >20,000 migratory waders have been recorded on Lake McLarty on at least 21 dates.
MONITORING AND MANAGEMENT:
Threats to Lake McLarty from declining water levels:
- Oxidation of existing acid sulphate material, acidification: threat, risk and urgency are high.
- Threats to the lake include ASS, changes to vegetation, loss of macro-invertebrates as a food source for wader birds and loss of waders.
- This will require action of a baseline ASS survey and probably also a composition analysis of the ASS material.
Formation of acid sulphate material, acidification – threat, risk and urgency high.
Vegetation changes, terrestrialisation of the lake floor – threat, high risk.
Loss of feeding habitat and access for the birds through terrestrialisation.
- On-going vegetative surveys taking place over transects and quadrants.
- Loss of mud-flats to terrestrialisation will result in a loss of wader bird feeding habitat and also result in increased predation on wader birds by foxes and cats.
- Some Typha control is currently being undertaken by DBCA.
Consequences of decline and/or change in benthic and water-borne macro-invertebrates – threat, risk high if water levels not maintained with maximum 3-4 months dry period only. A longer dry period will expose ASS and result in the loss of some macro-invertebrates.
- There will be an increased risk of midges/mosquitos with declining water quality as they are more tolerant species.
- A survey in water-borne and benthic invertebrates.
- Consequences are a decline or change in water bird population – threat, risk and urgency high due to terrestrialisation and acidification.
- A monthly bird count would greatly assist with knowledge of shorebird and wader numbers. Vicky suggested that Birdlife could perform this task in kind.
Divert more water from local catchment over 1-3 years / short term solution; little additional water is available, but improved drainage will help.
Water efficiencies in Birchmont (GW abstraction) / medium term solution / 5 years. However, Michelle Antao says that DWER do not believe Birchmont GW abstraction has a significant impact on lake water levels. Michelle also suggested there may be GW available in Leederville and Superficial aquifers to supplement water in Lake McLarty
- At this stage we do not know the quantity of water extracted by the local bores. This may require the use of meters. Also installing loggers on existing bores around the lake would supply useful information – Shire of Murray to investigate further.
- Behavioural change in regards to abstraction of water from bores in Birchmont may be possible through community based social marketing.
Divert water from distant catchments / long term solution / 5+ years.
- Sufficient water to meet objectives, water quality / unknown, nutrients / unknown, ASS material disturbance – may be importing acid material.
Acid sulphate materials / highest priority risk threat.
Unable at this stage to divert water to cover cracks.
Addition of lime to neutralise acidity in cracked areas:
- Placing lime on the peat may do more harm than good if it increases the oxidation of the peat. Placing in the south area on the clay substrate will be alright subject to an acid-base balance assessment. This would need to take place annually.
Addition of organic carbon:
- Carbon changes the structure of the peat so we may be able to use the carbon already at the lake – mulch the couch, typha and samphire which could open up the wader habitat areas. Also bring in mulch if needed. The downside in the short term is managing the alkalinity and phosphorus levels and the risk of sediment disturbance.
- The TAG recognised that the Lake bed is not uniform, providing an opportunity to trial the use of mulch as an initial measure to address ASS. While the use of lime could also be trialled, the TAG was less supportive of this option due to the impact on the peat.
- Peter Muirden mentioned that it may be possible to obtain some water from local groundwater and put it in the low lying southern basin in the autumn when it is dry to keep the ground and the cracks wet: hence delaying the onset of ASS.
Peter will estimate the volume of water required for this task.
- The TAG supported the idea of applying bore water to the lake surface during the dry summer/autumn months to stabilise the ASS (as has been done at Lake Jandabup and other lakes in WA).
Tuart trees have been dying on Birch Drive: Possibly due to low water table and salinity held in the wet clay. At this stage, action is not a high priority. Peter mentioned that on the western side of Birchmont with more natural vegetation the water table is higher.
- Heidi suggested that acquiring water meters and loggers for use on local bores would be beneficial in the short term. The Shire of Murray, through their water wise program could support the TAG in kind. Tom Lerner will approach council on this matter.
In summarizing Geoff Barrett suggested that, as decided at previous FoLM/PHCC meetings, Lake McLarty presents a similar scenario to Lake Mealup in that initially, we want to keep the lake hydrated in order to stabilize the problem of ASS and terrestrialisation and get the organics and chemistry stabilized. Then down the track, as a longer-term goal, we can look at the possibility of a two and a half months drying out period.
- It was noted that after 5 years, acid sensitive macro-invertebrates have began to return to Lake Mealup since rehydrating the Lake. The long term goal is to manage Lake Mealup to provide wader habitat, but this cannot be done until the sediment geochemisty stabilises. Between the two Lakes Mealup & McLarty the aim is to manage water levels for maintaining water quality and ultimately provide freshwater wader habitat with diverse benthic communities/ wader food source.
Item 7: Peel-Harvey surface water catchment modelling:
Peta Kelsey showed how Peel-Harvey catchment is modelled to estimate flow and nutrients and identify source of nutrients in receiving water bodies and the land uses that contribute.
Scenario modelling: A what if: how land use change is likely in the future or what improvement could be made through land change management and also look at climate change.
Item 8: Water levels using remote sensing model:
Bart Huntley showed a modelling wetland depth and hydroperiod using Satellite imagery and ‘r’. The software ‘r’, is an open source programming language and software environment for statistical computing and graphics. It’s useful to see the historical water levels of the system and confirm this against data.
Item 9: Macro-invertebrate monitoring:
Melita Pennifold informed the group that in October last year Heidi, Megan and FoLM members did a live pick of aquatic invertebrates. The lake depth was 70cms, PH slightly alkaline and conductivity relatively low at both sites. Twenty-three families were collected with the most abundant being crustaceans. No major changes in composition from 2016-2017. Lake McLarty has a high invertebrate family richness, with a high diversity of water mites, dragonflies, boatman and swimmers.
An isopod –Paramphisopus Palustris – was found at the south site in 2016 and again in 2017. This isopod is endemic to the Swan Coastal Plains wetlands and is found in ground fed water wetlands and is sensitive to acidic soils.
- TAG noted that it would be useful to include some benthic macro-invertebrate surveys.
Item 10: Water birds and Flora survey at Lake McLarty:
Vicky Stokes from Birdlife told of the significance of Lake McLarty. The size of the wetland relative to other wetlands, to be supporting such a high number of birds, is highly significant. It supports 1% of the global population of six species and 1% of the flyaway population of species including the Curlew Sandpiper which is listed as endangered. This is quite significant on a global scale.
Birdlife WA and Birdlife Australia are concerned about the declining availability of habitat for migratory shorebirds which has been reflected in their Shorebird 2020 data, as well as the data collected by Mike Craig. This has given a clear indication that the lake is declining in terms of the time frame in which it offers suitable habitat for migratory shorebirds and waders. Vicky has been informing Birdlife WA of information from some of our meetings and will continue to do so.
Bob Paterson gave the group a slide show of Birds at Lake McLarty also information on the Birdlife WA Peel branch annual count and a Flora survey conducted at the lake.
- The TAG noted that the loss of migratory waterbird habitat through acidification and subsequent loss of macro-invertebrates, as well as the loss of mud-flats due to vegetation growth and terrestrialisation of the lake, is of international significance, and is the major story for getting public attention to the Lake McLarty problem.
Item 11: Fauna monitoring and feral animal control:
Alan Wright informed the group of pig activity at the lake. The cameras are still in place and have shown no pig activity at this stage. The cameras have picked up a lot of activity of emus, kangaroos, bandicoots and foxes.
The fox baiting is ongoing with cameras on baiting stations to see what is taking the bait.
The meeting closed at 1.10pm