Russ Grayson

More habitat than swamp

Randwick's ephemeral urban wetland

Native ducks come in large numbers when the lake fills.
All photos: Russ Grayson, 2012, 2013, 2014.
YOU TAKE the sandy track that starts where locals cut away the chain link fence. This you follow for only a short distance. Then, there it is — Randwick's own ephemeral urban wetland.

An ephemeral wetland? Yes, a wetland that comes and goes with the wet and the dry. Through 2012 it was brim full. Then, come the summer of 2013-14, it became a progressively diminishing pond.

The wetland, with its bird life, is a touch of nature in the city and demonstrates that cities and nature can coexist quite well. The wetland is not far from where I live so I often visit the place to check out the birdlife and the extent of the water coverage. That's how I came to make these photos over a year and a half or so.
Here's the wetland as lake, filled after period of wet weather.

What happened here? The wetland — when it's full it's better to call it a lake — is at the lowest point of the surrounding area whose edges you can see as the line of a low ridge. When water falls in this area — we call it a catchment — it eventually drains into the wetland. Here it builds up through periods of wet weather until the lake fills. But when the wet ends all of that water slowly drains into the aquifer below and evaporates from the surface. Then, when the rains return, it starts to fill again... and the fill/drain cycle repeats. This is how the wetland comes and goes... it's why it is an ephemeral wetland... one time it's a lake, next time you visit it's just a pond.
It's August, and it's wattle flowering time and soon the trees are covered in the bright yellow glow of acacia flowers.

As the wetlands dry out the acacia move in to colonise the newly-exposed land. As a short-lived pioneer species, a legume, the acacia grows rapidly and soon seedlings are seen sprouting among the new grasses that are also busy making a home on the newly exposed land.

It's a different story when wet times return. As the wetland fills to become a lake the roots of the acacia become waterlogged and the trees die off. They become skeletal patterns of branches silhouetted against the sky, resting places for the bird population that starts to build up.

But, sooner or later, the rains ease off and the weather becomes drier. With less water flowing into it, the lake starts to diminish in size.
As the wetland becomes a moist, grassy lowland, a hollow depression in the landscape, the birds, too, depart. Gone are black swans, ducks and other avifauna that make this place home during the wet. Only the ibis, the odd swamp hen and a few native ducks hold out in the drying wetland.
Although the fill/empty cycle of the ephemeral wetland is a natural cycle, the wetland itself is a modified structure. Sand miners excavated their minerals here during the 1950s and 1960s, making significant changes to the landscape and to the wetland itself.

In that sense, the wetland and the surrounding Eastern Suburbs Banksia Scrub — there's only something like three percent of that ecosystem left — are a reconstructed landscape. Whatever seeds remained in the soil grew into the scrubland we see today. That includes the indigenous Sydney Golden Wattle (Acacia longifolia), the casuarinas and the tea trees (Malaluca) — all lower-growing species — there are few tall trees in this ecosystem. It also includes the glossy-leaved bitou bush with its showy, bright yellow flowers you find growing wild in the surrounding Eastern Suburbs Banksia Scrub. It's an artefact of the sand miners who planted it to stabilise the mined sands.

The lesson here is that nature reclaims abandoned lands even when they have been degraded and denuded of vegetation, however nature uses whatever plant species are at hand and the new ecosystem might not be the same as what was there — it will have species from the old ecosystem but it will also have new species, such as the exotics that are brought in by birds and other means. It's the same with the bird and other life that makes the ecosystem home. Along with returning native species come the exotics.

The good news is that this new, recombinant landscape continues to provide the same environmental services that the earlier ecosystem provided — the filtering of water into the aquifer, habitat for wildlife, soil stabilisation, a diversity of plant and animal life, photosynthesis and carbon absorption and all the rest.
Now reduced in size thanks to less rainfall in the catchment, the lake shrinks to a big pond and grasses start to grow where once there was water.

As you can see by comparing the photo above with those at the top of this story, when the lake is full the water level comes over the rocks in the foreground.
When it's full, wetland becomes birdland...
The water retreats to reveal the skeletons of dead acacia as ibis and native ducks populate the shrinking water body.
Above, left, the mudlark or peewee. Right, the spoonbill is an inhabitant of the wetland while there is enough water for it to wade and filter-feed in.
REGROWTH... land exposed by the retreating waters is rapidly colonised by grasses
Drier weather comes and there's not much water left now. Native ducks make best use of what remains.

Below, the waters recede.
By the last week of Autumn the wetland has shrunk to a couple larger pools. New grasses encroach the banks; much of the bird life has departed.
Something happens as the wetland starts to fill. Birds come. Birds of many types, many sizes.

As the lake reached its flooded height in 2012, a couple big black swans made it home as did those inhabitants of the water margin, the scurrying waterhens. There was also a large population of native ducks, several varieties, and a flock of big, elegant, white ibis.
A week later, the native ducks that were there a week ago have gone. What was once a larger though much-diminished body of water has become separate ponds. Wetland becomes grassy hollow.

Below... all that remains is a pond filled by overnight rains.
By the second month of winter, like the birdlife the lake has largely gone.
Above, left, the crow and the magpie are visitors irrespective of how much water is in the lake.
Above, ibis preen themselves at the water margin.
For local people, Randwick's ephemeral wetland is a place to watch nature at work in the city. Its wet/dry cycle, its visiting birdlife, the trees, shrubs and grasses of the Randwick Environment Park — as the wetland and Eastern Suburbs Banksia Scrub is known — remind us that cities and nature are compatible combinations and that plants and animals return to colonise even degraded land.

You can find the ephemeral wetland at the southern edge of the Randwick Environment Park adjacent to Randwick Community Centre at 27 Munda Street, Randwick, NSW, Australia.
The wetland — a place for people, birds and nature in the city.
More a habitat than a swamp...