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.

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.

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.

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.

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….?

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.

What are the application levels to ensure toxicity for mangroves by Diuron?

http://www.mwnrm.org.au/publications/downloads/Mangrove-health-in-the-Pioneer-River-estuary-04-05.pdf

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.