Hi all
Generally speaking, many wetlands along the River Murray have been altered
as a result of regulation of the river system. Some have become permanently
inundated, while others have been starved of water. Here in SA, and I'm sure
further up the river, for those wetlands, that have been permanently
inundated, rehabilitation projects typically focus on installing a flow
regulator and re-introducing some sort of wetting and drying regime,
mimicking what would have happened historically. But there are many, many
wetlands (over 1,000 along the SA river Murray alone, of which 27 have been
fitted with flow regulators) and therefore draining some of the wetlands
that have not been fitted with such regulators may not necessarily be a bad
thing. One thing to keep in mind is that generally we're not talking about
physically draining these wetlands, rather disconnecting them from the
mainstream, thereby stopping the continuous flow of water into the wetland
to make up for evaporation.
However, care should be taken in that blocking off wetlands should only
occur if there are no ecological values that have established as a result of
the man-made water regime (eg, threatened fish populations) that will be
placed at risk by a possible drying out of these wetlands. It is imperative
to know what lives in these wetlands, and whether there are other
non-biological processes that could jeopardize their long-term health if the
water regime was to be changed (for example, many wetlands have a freshwater
lens underneath them that keep saline groundwater inflows at bay; by drying
out for too long a period, salinisation may start to affect the wetland and
its vegetation. Another example is the risk of development of acid-sulfate
soils (the rotten-egg smell)).
Over the last five years, through my work for the SA Murray Darling NRM
Board I have commissioned and project managed numerous biological surveys of
wetlands (covering 90 wetlands thus far) along our stretch of the river. The
data collected by these surveys is currently informing further proposals for
drying out wetlands to save water.
A little known fact is, that seems to have stayed out of the recent
publicity on this topic, that between August and December last year we have
closed off no less than 27 wetlands along the SA River Murray saving in
total about 40 GL (40 billion litres). A further nine wetlands will be
closed progressively over the next few months saving a further 20 GL. I have
written up an ecological risk assessment report based on the known data for
these 9 wetlands.
Some of the effects we're starting to see in the wetlands that were closed
last year are as described above. In two wetlands, salinisation is starting
to occur. Waterbirds seem to concentrate in those wetlands which still have
water in them or have moved away out of the catchment all together. Lots of
new mudflat habitat is starting to appear. We are keeping a close eye on
each individual wetland but it will be near impossible to convince the
decision makers to allocate water to wetlands that are coming under severe
stress if there is no water to allocate to consumptive users...
Cheers
Peter Waanders
Waikerie, South Australia
mob.: 0407 800264
sat.: 0424 212889
SA Birding: http://www.sabirding.com
E-mail1:
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