Jennifer Marohasy

a forum for the discussion of issues concerning the natural environment

Archives for April 12, 2006

But Reed Beds Need Water!

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I have previously expressed concern that graziers in the Macquarie Marshes are diverting environmental water from the Ramsar-listed nature reserve to private land.

About two weeks ago I asked the NSW government whether the levy bank, as shown in this aerial photograph blocking the flow of water into the southern nature reserve in November 2005, was a legal structure.

Terrigal Nov 05 1 blog.JPG

At the time I was advised by email, following a phone conservation, that:

“We are still trying to identify where this bank/levee/channel is actually constructed. Until we can accurately locate it we cannot say for sure whether it is an approved work or not. Similarly, until we locate it accurately we are unable to ascertain whether it had any impact, adverse or otherwise, on the October/November 05 environmental flow release. The department will contact you again once we have more details.”

Following is a satellite photograph showing the Macquarie Marshes in December 1999 (green areas show flooding) and it is evident that the same levy bank is blocking water from reaching the southern nature reserve and holding it on private land.

marshes mapped blog.bmp

Environmentalists, and graziers, and government, all agree the marshes need more water. Indeed reed beds need water. Yet, I received the following justification for the levy bank from the NSW government today:

“Investigations carried out by DNR have now confirmed that the bank in question is located on a water course known as the Monkeygar Creek Return. This embankment was constructed by the then land-holders approximately 15 years ago with the sanction of the then Department of Water Resources and National Parks & Wildlife Service.

This embankment was constructed to slow down the passage of water in the Monkeygar Creek Return so as to prevent serious headward erosion and channelisation of Monkeygar Creek.

Headward stream channel erosion has been a major cause of wetland degradation and this embankment has been beneficial in the establishment and maintenance of important reed beds in the Marshes.

This work is considered to be an environment improvement work because of the benefit it serves to the preservation of the Macquarie Marshes reed beds and by preventing stream channel erosion.”

It doesn’t make sense.

I would like to see the extent of the change in the area of reed bed since that levy bank went in – bet it has contracted.

Coral Bleaching & The Reef: Walter Starck

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There is a widespread belief, cultivated at least in part by Prof Ove Hoegh-Guldberg that global warming has resulted in more coral bleaching.

Given the interest in the subject, I have copied the following comment from Dr Walter Starck, from yesterday’s rather long and tedious thread:

“Bleaching events result from extended periods of calm weather during which mixing from wave action ceases and surface water becomes exceptionally warm. Such warming is especially marked in very shallow water such as on reef flats. At the same time the absence of waves also eliminates the wave driven currents that normally flush the reef top. Bleaching conditions require at least a week or more of calm weather to develop and this may happen every few years, only once in a century, or never, depending on geographic location. On the outer GBR it is uncommon due to ocean swell and currents even in calm weather. In the mid-shelf and inshore areas it is much more common due to the absence of swell and reduced currents.

Characteristic bleaching scars and isotope temperature records from coral cores commonly show evidence of past bleaching events going back thousands of years. There is no evidence for a recent increase in frequency and/or severity of bleaching events and nothing to link extended periods of calm winds with global warming.

In past geologic periods when global climate was warmer than at present corals enjoyed greater latitudinal distribution. The most likely effect of a warming climate on reefs would seem to be an expansion of their geographic distribution and there is some evidence this is already happening. In Florida recent growth of coral has occurred farther north than it did a few decades ago and in the same areas sub-fossil corals indicate previous such advances in the recent geologic past.

Hoegh-Guldberg has found an attractive GW niche in the well established guild of GBR doomscryers. It has provided notoriety, acclaim and generous research support. Whether his prophesies will stand up to the reality test remains to be seen. Based on the track record of science based doomscrying his odds don’t look too good. In fact sheep’s entrails and tea leaves seem to produce better results, probably because they at least incorporate some element of intuitive judgment.”

Last year Walter wrote a review titled ‘Threats to the Great Barrier Reef’, published by the IPA, it can be downloaded by clicking here.

This picture was taken at the Great Barrier Reef by Roger Steene:
plankton feeders blog.JPG