The Reef, the Reef and nothing but the Reef

It is very difficult to obtain accurate data because of the stupendous complexity of even the simplest river, a problem compounded by annual and seasonal variability. A few partial quotations from the document show just how difficult:

“… the Euramo gauge only records 73 per cent to 86 per cent of the flood discharge … the Murray Upper gauge only records 5 per cent to 12 per cent of the discharge.

And again: “… these additional amounts range from 2 per cent to 99 per cent of annual river loads…” and “… it is believed that …” and “it is generally assumed that …” and “the annual TSS load … may be 60 per cent greater …” and “... nutrients may be double that estimated from river data alone …” and “these data suggest …”.

Another illustration of the problem of accuracy is to be found in The Reef Water Quality Report (EPA 2008) which considered “GBR catchments and inshore ecosytems”. For the Tully, this report, (page 51), gives chlorophyll concentrations of “0.44 g/L in the Wet season and 0.31g/L in the Dry”. These figures, which were sourced from GBRMPA (page 29), are less than half the figures in the draft WQIP!

Problems with uncertainty compound on each other. For example, the estimate for present day DIN is compared to the 1850 estimate with the statement that it “appears to have increased by a factor of 3”. This estimate is fed into yet another model that attempts to relate Chl-a with nitrogen. The Chl-a concentration from the model was 0.6 microgram/litre. However the footnote on page 29 shows that GBRMPA has dropped that figure to “0.5 for open coastal waters and 0.3 for marine offshore waters”. So suddenly the target is halved.

The position therefore is that on the strength of (a) a modelled and unverifiable 1850 figure, (b) (inevitably) very rubbery figures for the present, (c) ignoring the EPA/GBRMPA chlorophyll data, (d) a modelled figure for required chlorophyll concentration, (e) cutting that figure in half and (f) another model to estimate what reduction in nitrogen is required, the document asserts that DIN must be reduced by 80 per cent with, as usual, no estimate of uncertainty.

With all the uncertainties it is possible that this figure is correct; however the WQIP did yet more modelling to determine what affect all the best land management practices, both known and putative, might have. That model predicts that the catchment would still not meet GBRMPA’s demands for an 80 per cent decrease in nitrogen discharge.

Undaunted, the document proposes that 285.5km (!) of streams should be revegetated with 10 metre strips on both banks to denitrify ground water. They state that such action would cost $10 million only. The WQIP also proposes to restore 124km of “riparian buffer zones” on some of the worst degraded streams at a total cost of $3.72 million. The sublime optimism of that proposal is shown by the fact that a recent repair on one bank of the nearby Johnstone river cost well over half a million dollars for a couple of hundred meters. Another repair a short distance away will cost over $1.25 million for far less than a kilometre. Welcome to the real world.

Premier Bligh is concerned that there are “… chemical residues in biologically harmful concentrations … in waters up to 60km offshore”. To the contrary, statements in the WQIP such as “inshore coral reefs of the GBR … exposed to sediments nutrients and pesticides … inshore marine water quality, inshore reef and intertidal seagrass health …” all imply that only reefs close to the coast may be at risk.

However, the WQIP also includes a well known satellite image of river plumes covering the whole reef. While it does not actually state that the images prove that all the GBR is being damaged, it sows that idea in the reader’s minds - including Premier Bligh’s.

Other research by Ametisova and Jones observed similar plumes from the Herbert River just to the south of the Tully. They also actually measured concentrations in the water and stated: “… under favourable conditions for across reef dispersal, none of the plumes managed to carry harmfully significant amounts of inorganic and nutrient rich sediments to the mid-shelf reefs.”

It is probable that the presentation of these images is at best irrelevant and at worst deceptive.