Freshwater flood plumes packed with herbicide run-off have wiped out large areas of coral on the Great Barrier Reef, writes Rebecca Isaacs.

A blue Linckia starfish on the Great Barrier Reef

When it rains in Queensland, it pours. Floods are nothing new in the tropics, nor are the repercussions. Damaged property, dead cattle and ruined crops are a sad reminder of the savage force of the wet season. While millions of dollars are dolled out to farmers, fishermen and tourist operators for rebuilding and repairs, the Great Barrier Reef suffers in silence, a fragile eco-system bearing the brunt of bad weather and polluting pesticides.

Multiple teams of Reef researchers have observed widespread coral death in recent months, which they say spreads from Townsville to Cairns, affecting popular tourist destinations around Magnetic Island, the Palm Island Group, Dunk Island, the Family Island and the Franklin Island Reefs.

Jon Brodie, who headed the Water Quality Research and Management Program of the Great Barrier Reef Marine Park Authority for 11 years says that the widespread coral mortality has gone largely unreported. But she continues to find devastating evidence of their decline now as a Principal Research Officer at Australian Centre for Tropical Freshwater Research (ACTFR). From 2005 to 2008 Brodie and his colleagues analysed 600 water samples for pesticide concentrations from 76 rivers and creeks in Northern Queensland. They found high concentrations of controversial pesticides, including the herbicides Diruon and Atrazine, particularly at sites draining sugarcane. Sightings were made by various people before the Marine Park Authority then sent out teams who verified the initial sightings.

The findings have confirmed fears that herbicide pollution considerably heightens the existing natural threat of flood plumes to the Reef.

“Freshwater itself will kill coral but now we’ve got another three stressors,” says Brodie, “Freshwater has always been going out and causing damage that the Reef recovers from, but nowadays sediment, nutrients and pesticides are no doubt having a worse effect.”

“If it was just freshwater without those other elements the effects of the flood plumes would have been no where near as bad.

The coral damage correlates with satellite images taken by NASA and released by the CSIRO earlier this year, which show flood plumes up to 100km off shore. Such plumes were previously thought to travel no further than 10-15km offshore.

Dr Arnold Dekker, Senior Research Scientist at the CSIRO Land and Water Division, says he predicted that these far-reaching flood plumes would have serious health implications for the Reef.

“The inner reefs have always been exposed to more turbid waters because they are closer to the shore, so they’re more resilient. The outer reefs are clear, oceanic waters and if a flood plume goes over those reefs it will have a higher impact because they’re not accustomed to it.”

Dr Andrew Negri, from the Australian Institute of Marine Science, says that the effects of herbicides such as Diuron and Atrazine on the Reef have already been documented.

“The concentrations of many of these herbicides on the Reef are generally lower than the guideline levels,” he says, “but they can definitely exceed guideline levels in the rivers and for several kilometres out to sea during flood plumes.”

Studies conducted by the Institute have revealed that even low concentrations of herbicides can reduce photosynthesis in coral and seagrass, and affect algae growth.

Dr Negri says that herbicides can also make the Reef more vulnerable to other stressors.

“The exposure to pollution has the potential to make corals and other important organisms more susceptible to climate change”.

“Our current studies include testing how herbicides and nutrients may interact with rising sea surface temperatures to affect corals in the long term,” he says.

Negri’s findings are supported by the ACTFR study, which concluded that the mix of herbicide residues from river discharge events can cause cumulative and chronic effects and a general change in the structure of mangrove, seagrass and coral reef ecosystems due to the sensitive natures of these species.

These effects are compounded when flooding dumps huge volumes of pesticide-filled freshwater into the Reef. Floods earlier this year dumped a reported half-tonne of pesticides into the Reef.

Atrazine is a herbicide used to stop the emergence of weeds in major crops. In 2003, Professor Tyrone Hayes of the University of California, Berkeley, publishing findings that revealed Atrazine is an endocrine disruptor in fish, amphibians, reptiles and mammals. In 2004, Atrazine was banned in the EU due to persistent groundwater contamination.

Diuron is used to kill weeds in all of North Queensland’s most prolific crops- sugarcane, cotton, oats, citrus fruits, banana and pineapple. In 2005, the herbicide was found in North Queensland waters at concentrations known to be harmful to seagrass, an essential component of the Reef eco-system and the primary food source of the protected dugong. Severe mangrove dieback in the Whitsunday region over the past ten years has been linked to chronic exposure to Diuron.

A review of Atrazine by the Australian Pesticides and Veterinary Medicines Authority (APVMA), which ran from 1995 to 2008, resulted in a ban on atrazine use in homes and gardens. The Review also amended label instructions on products containing the herbicide.

An APVMA review of Diuron, released in 2005, proposed ways to reduce the amount of the herbicide being used on farms, especially those close to waterways,

Brodie says these recommendations do not adequately address the serious threat of herbicides to the Reef,

“Labelling doesn’t work properly because it can’t predict when it is going to rain,” he says.

“It’s especially difficult in areas like Tully where it almost always rains.

“The APVMA regulations suggest that if you comply with the label instructions you won’t have a problem with run-off, but even in areas with perfect compliance we still find run-off of these herbicides.”

On June 4 the Great Barrier Reef Amendment Bill 2009 was introduced in the state parliament of Queensland. The Queensland Minister for Climate Change and Sustainability said the legislation lives up to Premier Anna Bligh’s election promise to reduce the amount of pesticides entering the Reef by 50% in four years.

The legislation places new regulations on the use of pesticides including Atrazine and Diuron. Nearly 4500 North Queensland farmers, of which sugarcane farmers are the majority will be forced to comply.

The new regime, to take effect from January 2010, bans sugarcane farmers and graziers in Mackay-Whitsunday, the Burdekin Dry Tropics and the Far North’s wet tropics from using the pesticides Atrazine, Diuron, Ametryn, Hexazinone and Tebuthiuron along drainage lines. The farmers must also have the right certifications and undergo training before use as well as ensure secure storage for the pesticides.

Those farms considered particularly of high risk will have to keep Environmental Risk Management Plans detailing improved practice. The plans will include pesticide and fertiliser monitoring and soil testing.

While the legislation appears to be a simple and effective mechanism for reducing pesticide run-off from farms, Brodie says that in practice, implementation will be difficult.

“You need people to enforce this type of monitoring and collection and the Environmental Protection Agency has few staff out in regional Queensland.

“In the past they (the Government) haven’t resourced this type of thing properly, so once again this could just end up another piece of paper legislation.”

The new legislation has also alienated farming groups such as Canegrowers, who have expressed concern that the Bill uses them as political scapegoats. These farmers are frustrated with the strict regulatory conditions of the Bill, which are in direct conflict with the Rudd Government’s $200 million voluntary Reef Rescue Program.

Brodie, who works closely with sugarcane growers to improve farming practices, says that the Bill has been met with strong resistance.

“The farmers are afraid that the numbers they produce will be used against them because the results will be made publicly available,” he says.

A spokesperson for Minister Jones said the Minister would not be available for comment until after the second reading of the Bill in Queensland state parliament later this year.

A spokesperson for Federal Environment Minister, Peter Garrett, said he was not sure if the Minister had read the Bill.

While conservationists, and both the Queensland and Federal Government are certainly taking action in regards to pesticide run-off into the Reef, it is unknown as to what damage has already been done. Scientists are unsure of the long-term implications of pesticide-filled flood plumes to the Reef, and how long it will take coral and seagrass to recover, if they recover at all.