By John Glue ‒ FoE Far North Queensland
On June 6, Tablelands Regional Council (TRC) in conjunction with SunWater, a Queensland government-owned corporation, commenced aerial herbicide spraying of Lake Tinaroo, with the aim of eradicating the noxious weed Water Hyacinth. While windy weather interrupted the spraying, it's expected to be completed when weather permits.
Water hyacinth is considered one of the world's worst weeds ‒ affecting creeks, rivers and dams, choking wetlands and waterways, killing native wildlife and interfering with recreational use.1 Water hyacinth grows most strongly in warm, nutrient-rich (polluted) waters. Interestingly, it is known for its ability to remove toxins and heavy metals from the water.2 In parts of Asia it is used for biomass in compost, as cattle fodder and in fish food for caged aquaculture.
Under certain conditions, water hyacinth can be argued that it improves water quality, provides habitat for invertebrates and small fish and is a potential agricultural resource. Conversely, when large mats of water hyacinth are poisoned, sink to the bottom and rot, water oxygen levels are depleted, potentially causing an entropic cascade resulting in large scale fish death and algal bloom.
As a restricted invasive plant, TRC has a legal obligation to enact a biosecurity plan to control water hyacinth in Lake Tinaroo. The plan currently being implemented is aerial spraying the herbicide Reglone – with the declared active ingredient diquat dibromide. Diquat is the only herbicide registered for use in water storage areas used for human consumption, though 14 days must elapse after treatment before water can be consumed.3 The Safety Data Sheet declares it as "very toxic to aquatic life with long lasting effects".4
Advice issued by TRC and SunWater was to avoid contact with water in the affected area for 10 days and to avoid using the water for livestock or garden irrigation for 10 days. Despite Lake Tinaroo being the water supply (via the Barron River) for many Tableland towns including Kuranda, Mareeba and Yungaburra5, no direct advice was given about use of town water for human consumption. Should residents have been advised to not drink town water for 14 days after the spraying? Is SunWater in breach of government legislation?
Department of Agriculture and Fisheries guidelines state, "in most cases the best management approach combines herbicide, mechanical, fire and biological control methods with land management changes". Were alternative or complimentary strategies investigated? Mechanical removal by hand or machine offers potential opportunities to stimulate the local economy through employment, as well as the use of harvested material, thereby transforming a problem into a potential resource. Another control measure would be prevention of nutrient flow into the lake. In combining such alternative controls, herbicide use may well become redundant or at least substantially reduced.
Reflecting the current marketing that herbicides are harmless, there is a tendency for natural resource management efforts across Australia to turn to herbicides in the first instance, rather than as the last resort. It's time that all levels of governments take into consideration the long-term impact of polluting the soil, air and water and legislate in favour of environmentally friendly solutions.
Thanks to Les Anwyl for his research.
Published in Chain Reaction #133, September 2018. National magazine of Friends of the Earth Australia. www.foe.org.au/cr133