Paul & Irene Osborn wrote:
A couple of years ago one of our farm dams dried out because of
> drought. The bottom of the dam developed that lovely hexagonal
> cracked mud look. When we finally got enough rain to put some
> water in the dam it exploded into life. More tadpoles than I've
> ever seen in one place before (or since) and heaps of dragonflies,
> damselflies and other dam loving species. Common water plants
> sprung up where none had been before the drying. The water was
> crystal clear, rather than the opaque clay colour it had always
> been, you could still see the mud cracks in the bottom. I don't
> have any theory about why this happened, but can imagine that the
> effect, magnified to the scale of Barmah-Millewa, would attract a
> lot of birdlife.
A few semi-random thoughts that come to mind:
* Cracked mud has a higher surface area than solid mud.
* Cracks in dry mud acts as a trap for wind-blown material (seeds,
sand, minerals etc.) This provides an ideal nursery for plants,
and a food source for animals.
* The cracks provide habitat/refuge for animals - both while dry
and after being inundated.
* Dried mud solidifies and captures the particles that make water
turbid; any loose particles can be blown away by wind. Salt can
also help clear water by acting as a flocculant, helping the
particles settle out of suspension.
* Clear water lets sunlight penetrate deeper into the water column,
which should provide greater opportunities for algae and other
aquatic plants to thrive, providing more food for herbivores.
A dramatic example of the difference between freshwater and saline
habitats are Lakes Numalla (freshwater) and Wyara (saline) at
Currawinya NP. Both are of similar size and less than 3km apart;
Numalla has only dried out three times last century, while Wyara
dries out to a saltpan more frequently. Both were "full" in 1985
for the RAOU campout. From memory, Wyara was favoured by waterfowl
(especially Black Swans), while Numalla was best for land birds
Paul Taylor Veni, vidi, tici -
I came, I saw, I ticked.
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