Thermal pollution & Lake Macquarie’s shrinking seagrasses
Seagrasses are flowering plants occupying coastal waters in temperate and tropical climates providing food & breeding habitat for marine animals, shoreline stabilization as well as a highly-effective carbon store. The east coastline of Australia boasts one of the largest collective areas of four common species of seagrasses: Halophila ovalis, Zostera muelleri, Ruppia and the Endangered Posidonia australis. In Southern Lake Macquarie, all four of these species have been identified with Zostera muelleri (“Eelgrass”) and Halophila ovalis (“Paddleweed”) dominating the Southern bays including Wyee and Myuna where the impacts of thermal pollution from the Vales Point and Eraring coal fired power stations has resulted in both incremental and abrupt losses in seagrass extent and the gradual replacement of Zostera with the more thermally-tolerant Halophila.
Seasonal thermal plume imaging, Southern Lake Macquarie
When cooling water is released back into lake via power station outlets, it has been treated with chlorine and other chemicals and heated by an average of 10⁰C, causing adverse impacts to seagrass within two kilometers from the outlet. Vales Point power stations thermal pollution has been discharged up to 11.3⁰C above average ambient Lake temperatures in Winter and 15.7⁰C above ambient temperatures in Summer. No power station built anywhere in the world today would be approved to discharge thermal pollution at such temperature differentials. Since 1956, coal power stations have been using tens of gigalitres of Lake water every day to operate – Origin Energy is permitted to discharge up to 11.8 billion litres (GL) a day into Myuna Bay from Eraring and Delta Electricity’s Vales Point is allowed to discharge up to 6.5 billion litres (GL) a day into Wyee Bay. HCEC estimates that these volumes combined circulate six times the entire volume of the Lake annually. The maximum temperature at which Lake Macquarie’s coal power stations can discharge their cooling water is 38.5 degrees Celsius, but Zostera seagrass has been documented to be adversely affected by temperatures of just 30°C.
Thermal pollution impacts on Lake Macquarie seagrasses include;
• Loss of seagrass in the vicinity of cooling water outlets;
• Replacement of zostera with halophila in Wyee Bay;
• Increased temperature changes fish distribution
• Less snapper, squid, tailor, mullet, leather jackets, cardinal fish, glassy perchlets, goatfish, and toadfish,
• More tarwhine, silver biddy, bream and southern butterfish;
• Since Munmorah power station decommissioned in 2012, Zostera re-established close to the cooling water outlet.
Resources & Research
◦ Please see Research & Reports in the menu for more
◦ SUMMARY: Ecological impacts of thermal pollution in Lake Macquarie
◦ PRESENTATION: Thermal pollution impacts in Lake Macquarie
◦ Scientific articles + papers on seagrass and thermal impacts
◦ Reading + factsheets
◦ LAKE TEMPERATURE READINGS_DEC 23 – MARCH 2024
◦ EPL SEAGRASS MONITORING REPORTS: VALES POINT
◦ (COMING SOON) EPL SEAGRASS MONITORING REPORTS: ERARING
HCEC seagrass mapping
Desktop analysis to estimate seagrass cover and loss in Myuna Bay. HCEC. 2021.
So, what’s the solution to Lake Mac’s seagrass loss?
Reduce thermal pollution & restore seagrass beds
The publication of our most recent report, Delta’s dirty deeds: done dirt cheap in 2023 saw HCEC issue two key recommendations pertaining to seagrass health and restoration for the NSW EPA and power station operators. We believe the following actions will bring Lake Macquarie closer to full seagrass recovery and see the decades-long impacts of Vales Point and Eraring power stations on the all-important “ecosystems engineer” of Australia’s largest saltwater estuary justly compensated for:
◦ To encourage the rejuvenation of Zostera seagrass within Wyee Bay, a study be undertaken that determines ambient water quality, appropriate seasonal temperature differentials, seagrass sensitivity, and the assimilative capacity of Wyee Bay, and EPL 761 be varied accordingly to incorporate a scientifically established thermal mixing zone south of Wyee Marina.
◦ To offset seagrass loss in Myuna and Wyee Bays, a Lake Macquarie Seagrass Trust be established with funding of $12M a year from Delta Electricity and $8M a year from Origin Energy to enhance seagrass meadows within Lake Macquarie and replace seagrass damaged and killed by the operations of Vales Point and Eraring power stations.