About 10 years ago the Pioneer River which runs through the North Queensland town of Mackay flooded and some mangroves died. A few years later the World Wildlife Fund (WWF) launched its ‘Save the Reef’ campaign focusing on claimed impacts of farming on the Great Barrier Reef and an academic at the University of Queensland, Norm Duke, released a report implicating cane farming in the mangrove dieback at Mackay in particular farm runoff containing the herbicide Diuron.
The WWF campaign generated political momentum for some sort of action and a Reef Taskforce was formed to advise government. At the time I was working for the Queensland Sugar Industry and made a member of the Taskforce. It was clear that there was no substantial evidence for an impact from farming on the reef, but the government had committed itself to there being a problem and the Taskforce was to conclude as much.
Dr Duke’s unpublished report to the Queensland Fisheries Service became a key document for the Taskforce, purportedly providing evidence for “localized deterioration on individual nearshore reefs” from farm runoff.
At the time I explained that the Duke report, and the hypothesis that the dieback was a consequence of the herbicide Diuron, had some major flaws, including: “Only four of 21 potential sites were tested for Diuron. Traces of Diuron were found in the sediment at all four sites. This included the control site at which there was no mangrove dieback. In other words, Diuron was found at one site where there was no mangrove dieback as well as at three sites where there was mangrove dieback. No evidence was presented to indicate that the levels of Diuron at any of the sites were herbicidal.”
But the campaign against the farmers supported by a compliant media rolled on, politicians were elected on the basis they cared about the reef including mangroves, plans were developed to save the reef from farming, hundreds of millions of dollars provided for research programs to save the reef from farming. Indeed there is now a large bureaucracy including academics and sugar industry personnel associated with saving the reef.
There is ongoing monitoring of the stands of mangrove in the vicinity of Mackay but there is still no evidence implicating the herbicide Diuron in the mangrove dieback.
Indeed today I was assured by those who have spent years monitoring the mangroves that diuron can still be found in sediment, but it doesn’t seem to be affecting the mangroves that “there is no indication that the herbicides at the levels detected in the Pioneer River estuary have impacted on the health of the mangroves.”
I had a wander around the mangroves, including in the Bassett Basin near Barnes Creek, today with Carl Mitchell from Reef Catchments and John Abbot from the University of Queensland.
************************************
Additional reading:
Jennifer Marohasy & Gary Johns, 2002, WWF Says ‘Jump!’, Governments Ask ‘How High?’ Institute of Public Affairs, Occasional Paper
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
Am I correct in assuming that this herbicide is normally applied to the leaves of the target weeds? It is not applied to the soil and is not taken up through the soil? If so, how would it get from the sediments to the mangrove leaves?
That little issue of causality again.
Hi Ian,
Wrong.
Diuron, unlike say roundup, is applied as a prememergent herbicide to bare soil and watered in for control of broad leaved weeds in ‘grass crops’.
It can move off-farm bound to sediment in runoff. While it can be detected in the mangrove areas downstream of the caneland around Mackay, it is at very low concentrations i.e. non-herbicide levels.
Well here in Rockhampton the mangroves and surrounding bush life has been dying off ever since the river flooded this February.
So I’ve no reason to believe that we aren’t responsible for these sort of events.
Just another article from Jennifer which puts the interests of the enviroment last and paints humankind as being blameless for the deterioration of the environment.
Thanks, Jen. My understanding is that most pre-emergents are short lived, breaking down in months rather than years.
If it is applied to bare soil that means it is applied in the dry season, usually six months before the floods begin.
Justin, “mangroves and surrounding bush life”? Are you suggesting that the herbicide is now killing wildlife as well? Give us all a break, fella, and spare us the unsubstantiated anecdotal crap.
It would appear that you do not understand the concept and purpose of an experimental control, let alone the need for double blinding to remove experimenter bias.
But then, Duke seems to have failed in that respect as well.
“Just another article from Jennifer which puts the interests of the enviroment last and paints humankind as being blameless for the deterioration of the environment.”
Limited observation, limited facts, limited knowledge and limited imagination make for dangerous conclusions.
What you do now is feed these limited assumptions into a computer model and see how exciting you can make it.
Hi Justin
It would be great to learn more about the situation in Rockhampton. Have herbicides been implicated? What do you think has caused the dieback?
Might not be enough to convict but you’d have Diuron under surveillance …
http://www.marine.uq.edu.au/marbot/publications/pdffiles/Mackay.pdf
The damage last event was substantial. tp://www.springerlink.com/content/h688j7652ug71551/
But you have all sorts of issues in the Fitzroy – the flood itself, herbicides, Ensham mine pump out – clearly the locals are not happy and answers being demanded.
Another perspective
http://www.mwnrm.org.au/publications/downloads/Mangrove-health-in-the-Pioneer-River-estuary-04-05.pdf
….. Just guessing… But wouldn’t a waxy leaved plant like mangroves be more impervious to a herbicide like Diuron than say grasses or lantana, etc….?
What are the application levels to ensure toxicity for mangroves by Diuron?
JH – the delivery pathway is from terrestrial runoff not from aerial overspray. It’s not a foliage application issue. Any absorption would be through mangrove roots or pneumatophores.
Seems to me, the only concrete connection in both cases is the flooding. If that?
Has anyone looked for other contaminants, than Diuron?
I know it was only natural to assume both man made, and herbicide as the cause, but it may not have been?
Problem of course is, that if it wasn’t the herbicide, than we are practically looking for the needle in a haystack.
Luke…. I was thinking it was absorbed through the leaves similar to glyphosate. But your are right, Diuron is absorbed through the roots.
Strikes me though that it would be inordinately dilute to be effective as a toxic constituent in flood water.
It would seem some tests to find the level of Mangrove sensitivity to Diuron would be in order…. Surely this kind of data exists and can be compared to the levels in Mackay’s mangroves?
But aside from that it seems only one specific type of mangrove is affected by this unknown dieback…. I’d be more inclined to think that a specific type of mangrove is sensitive to a change in the environment…. Too much fresh water may have stressed them… It’s been a while since Mackay flooded maybe….?
JH – read http://www.marine.uq.edu.au/marbot/publications/pdffiles/Mackay.pdf – some tests have been done on live plants in glasshouses. Other herbicides are also present. Evidence of more impact near drains.
It may be a cumulative impact issue of many factors in combination so hard to track down to a specific cause. But there is a sensitivity implication as one species seems more susceptible.
Duke has now published his work BTW.
However there isn’t much research on live systems – of course it’s not easy or responsible to go around squirting Diuron in natural estuarine environments. You’d need to go to VietNam to see serious purposeful defoliation from the war.
However cane industry has also done a fair bit – green trash blanketing at harvest to minimise erosion, creation of artificial wetlands etc.
Diuron breaks down onto DMA which is a precursor to many other chemicals including the carcinogen NDMA and the chemical weapon Tabun.
http://pubs.acs.org/subscribe/journals/esthag-w/2008/jan/science/nl_ndma.html
Clearly there is a lot more work to be done before Diuron’s innocence can be established.
Interesting photo at http://www.publish.csiro.au/?act=view_file&file_id=EC119p32.pdf
Note how the dieback is not uniform, as should be the case in a broad sediment borne problem. So we need to ask, if the healthy tree beside the dead ones are different species or the same species but different age class.
I note that the reported half life of diuron is 1 to 12 months. The longest being when it is in stable water, as when sprayed in a ditch. I understand that this practice is no longer common.
Jen has indicated that one of the four tested sites with “high” (unspecified) levels had no dieback so we can conclude that the photo includes live and dead grey mangroves. And we are bound to ask, why?
It should also be noted that the chemical is applied to bare soil in the dry season with at least 4 months of cane growth before the first flood. This cane growth is sufficient to turn the cane field into a net accumulator of sediment, not a source.
Note also that the chemical has the shortest half life (as low as 1 month) when applied to bare soil that is subsequently protected by non-broadleaf growth.
And this combination of shorter half life, reduced sediment loss from slowed water flow, and the volume of flood flows, means that accumulations of the chemical in downstream mangrove soils can only be in extremely small fractions of the level deemed to be effective when it is applied to the cane field.
It should also be noted that Duke has given only generalised statements of the extent of the problem. We can assume that the photo is of the worst case but we still don’t have indications of total area of grey mangrove, the total area affected by dieback, the percentage of canopy affected by dieback, and the relevance of this to the rest of the grey mangrove ecosystem in the state.
Until we do it is pure shonkademia.
Another interesting aspect of the second photo on the above link is the apparent lack of impact on young regrowth adjoining the dead tree. The most likely impact of sediment deposited herbicide would be to kill off the youngest plants first, but this is not the case here.
The first to go would be the current years seedlings, followed by the young “advanced growth”. But the photo shows a total absence of any seedlings under the dead tree and very thick and healthy advanced growth just outside the drip line of the dead stem.
The site is essentially level so there is no reason why a flood that would have obviously covered the whole area would not also have evenly distributed any chemical residues it carried.
Indeed, the thick, low foliage of the young trees beside the dead stem would have acted as a silt trap and produced higher chemical deposition rates than under the dead stem.
Curioser and curioser, said Alice.