Tuesday, December 30, 2014
Greenie misconceptions about the Great Barrier Reef
VISITORS to north Queensland who come to see the reef and rainforest are often perplexed to gaze from their hotel balconies out on to a wind-ruffled, muddy grey to brown-coloured sea.
What happened to the sparkling blue waters, they ponder. Fuelled by dim memories of media misreports, they usually jump to the conclusion that human pollution must be the cause.
Those who live along the Queensland coast, as opposed to those who preach about it from the concrete and glass metropolitan jungle, know that muddy coastal water is an intrinsic part of the natural tropical system, generated by the resuspension of seabed mud by constantly blowing southeast trade winds.
Indeed, special types of coral reef — turbid-water reefs — have evolved to live happily in just these muddy near-shore waters. The Great Barrier Reef itself — growing luxuriantly in pellucid blue, oceanic waters far offshore — is recognised in textbooks as one part of a larger mixed carbonate-terrigenous complex of both muddy (inshore) and bluewater (offshore) reefs with a long, robust geological history.
Along the Queensland coast, the shoreline is made up of sandy beaches and adjacent sandy-mud coastal lagoons and estuaries, punctuated by spaced rocky headlands. The nearby inner shelf seabed is almost flat and covered by a blanket of sandy mud and mud up to several metres thick that has accumulated during the past few thousand years.
This coastal-inner shelf system has been built, and is still nurtured, by sand and mud delivered to the coast from the Queensland hinterland at times of riverine flood — mostly after cyclones.
Dilute muddy water from even the greatest cyclonic floods only reaches from the coast to the offshore bluewater reefs about once every 10 years. It persists there just briefly before being dispersed by waves and currents, and in being dispersed introduces rare nutrients into a nutrient-starved locale.
The coastal wetlands are important ecosystems for mangrove growth and provide a nurturing environment for fish and invertebrate larvae. Also, shallow embayments with sandy low tide and subtidal beach flats provide the conditions for seagrass growth — an essential habitat for dugongs.
Prior to European settlement, this system existed in precarious but dynamic “balance”, with major cyclones causing immediate coastline erosion, followed months to years later by fairweather shoreline accretion and restoration, fed by sediment contributed by the same and earlier cyclones. It is possible that historical tree-clearing and grazing inland has increased the amount of sand and mud delivered to the coast in post-European time, with one computer model estimate of a two to four -fold increase.
If true, such sediment enhancement is no bad thing. First, the pre-European shoreline was, and remains, deficient of enough sediment to maintain its position without continuing sand nourishment, especially at locations away from river mouths. Second, more sediment nurtures not just the shoreline beaches but feeds nutrient into the ecologically vital coastal wetlands.
Ports and their access channels have been dredged along the Queensland coast since the late 19th century, and the spoil dumped at sea. Over a period of months to years, this spoil is redistributed across a wide area and merges insensibly into the sandy mud, inner shelf substrate.
The briefly enhanced turbidity caused by dredging and dumping activity represents but a small, localised disturbance within a dynamic oceanographic background that sees constantly varying rates of mud resuspension caused by wind, and by the regular interchange of shelf waters within a few days to weeks by tidal and other marine currents.
Not surprisingly, therefore, despite expensive nutrient and water quality analysis in the past 30 years, no measured evidence exists for changes in water quality on the near-shore GBR shelf in post-European time.
Furthermore, the historical dredging and spoil dumping on the shelf has had no other known significantly adverse effects either, especially not on the bluewater reefs in the distant offshore.
Spoil has sometimes been dumped at the shoreline to reclaim areas for port development — the Brisbane and Townsville ports are prime examples. Given the value of the land created, this is an entirely sensible procedure when undertaken (as it has been) as an environmentally efficacious and cost-effective commercial venture.
It is simply fallacious for conservationists to trumpet that the GBR is threatened by near-shore dredging, and it is risible and disgraceful that an international agency (UNESCO) is involved in unscientific grandstanding on the matter as well.
Caving in to activists, the federal government has rejected the two best environmental options for the spoil — either seabed dispersal or land reclamation. Instead, Environment Minister Greg Hunt has opted for the worst and possibly the most expensive environmental option — that spoil dredged from near Abbot Point will be dumped on land.
A more perfect combination of scientific ignorance and environmental stupidity would be hard to find.