Hi all,
I thank Gordon for his question about why it is good for waders and
waterbirds if wetlands sometimes dry out and their beds crack.
My observations in the Barmah-Millewa area suggest that birds prefer
wetlands which have wetting and drying phases. Lakes which are kept topped
up all the time ~ e.g. for boating and water-skiing or for town
beautification ~ do not seem to support the same number of birds as those
which have received water after having been dry over a period of time.
To paraphrase the words of a local geomorphologist: when the bed of a
wetland dries and cracks, sediments are likely to consolidate and become
aerated, altering their physical and chemical properties. This may serve to
strengthen macrophyte communities when the wetland next receives water,
thereby increasing the potential food supply available for waders and
waterbirds. (Paraphrased from a note by Keith Ward).
The timing and duration of flooding is of great importance. If water levels
fall too soon or are too low, colonial waterbirds may abort their nesting
cycle. Egrets tend to nest later than some other waterbirds, and this
should be taken into consideration by authorities when deciding whether or
not, and for how long, to release environmental water from water storages
to wetland areas.
Along the mid Murray, most wetlands used to dry out over late summer and
autumn. Regulators have been installed to help prevent them flooding over
summer and autumn when the river level is kept high in order to supply
water to irrigators and urban areas (including Adelaide).
That is why some of us are concerned about the proposal to build a by-pas
around the Barmah-Millewa wetlands. The proposed by-pass could be great
news if used in late summer and autumn, allowing the wetlands to drain and
dry. But it would be bad news if used in late winter, spring and, perhaps,
early summer insofar as it could affect the depth and duration of flooding.
fortunately, at last week's Barmah-Millewa CRG* meeting, my motion
recognising the existence of The Narrows (Barmah Choke) as fundamental to
the existence of the Barmah-Millewa wetlands was passed without dissent.
Several members, including members with an interest in forestry, spoke
strongly in favour of the motion.
Some lakes rarely dry out and are therefore valuable drought refuges for
native fish and water birds.
Water depth, slope and vegetative cover are also important factors. The
requirements of different wader species vary, some having longer legs (and
preferring deeper water) than others. The tendency of authorities to deepen
dams in local reserves (to catch more water for fire fighting) is a concern
as many dams now have steep slopes. Ideally, at least one side of a dam
will have a gentle slope.
Keith S
* CRG stands for Consultative Reference Group, an advisory body to the
forest's Co-ordinating Committee. Each of the six Living Murray icon sites
(Hattah, Chowilla-Lindsay, Gunbower-Perricoota-Koondrook, Murray Mouth,
Barmah-Millewa and the Murray channel) is to have its own CRG and other
management committees. More details on and links to sites about
Barmah-Millewa are on my web site at
http://users.mcmedia.com.au/~stocky/barmah_millewa.html
>Dear all -
>
>Keith wrote:
>
>>Most wetlands in the Barmah-Millewa Forest are presently dry. Moira Lake is
>>being drained and it is hoped that the mud will dry and crack. This means
>>that the lake might be ideal for waterbirds and waders when it next
>>receives water.
>>
>>Keith Stockwell,
>>Moama
>
>
>Could someone please explain to a novice the connection between cracked mud
>and the attraction of waders when it next gets wet?
>
>
>Thanks
>
>Gordon Cain
>
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