A ripple of whoopers

When 12 whooper swans fly up out of a marsh it is an event, a disturbance, a hullabaloo: all those white wings conjured suddenly out of the golden haze of reeds. There is a sharing of space; an alignment; a determination of arc; an excited, confirmatory chorus, like kids let out of school.

I paused on the strand to let them away to the lake, enjoying that ripple of effort that runs through a flying swan, rocking it gently, lengthwise, beak to tail, and thus from one swan to another, right down the line.

What marsh is this, mentioned out of nowhere? In two decades, not a word here about Thallabawn's wildest - certainly most impenetrable - habitat. There it sits in the hem of green fields between hillside and strand: a hectare or two of land lost in a tawny fog, with a low cliff on one side, a curve of the mountain river on another. Sometimes, in winter, enough water floods in from the river to set up glittering spaces for swans to land on.

Once, right at the start, I did actually wade into the marsh a little bit, until it began to feel uncertain underfoot. I had grown a lot of potatoes and was planning to pit them outdoors for the winter in what I hoped was the traditional way. This needed rushes, a lot of them, and rushes, to me, were what, suitably woven into a carry-cot, floated baby Moses down the Nile. Such innocent associations led me through the abundant green rushes of the fields to start hacking away at the tall stems of phragmites at the marsh's feathery fringe. What a joke. Since then, the marsh has just been there, a brown splodge in the landscape, marched around on St Stephen's Day by shooters hoping for duck. Perhaps it's that association that has put me off exploring; perhaps marshes are meant to be anonymous, no-go areas, hugging their secrets to themselves.

There are mallard, of course, and moorhen, probably, and even, conceivably, a water rail, Rallus aquaticus: "Scarce resident", says one of my books. "Elusive and rarely seen, though easily identified by its call, which is reminiscent of a squealing pig." Can I die without seeing a bird that squeals like a pig? I think so. Do I mind not knowing, for sure, how many reed-buntings nest there, or wagtails roost there, or whether the reeds hide caterpillars of the rarer sorts of wainscot moth? Let them be: we need our mysteries.

The common reed, Phragmites australis, seems to include itself in its cloak of anonymity: a stack of bundled stems at a roadside near the Shannon, harvested for thatching, reminds one what a robust, substantial - and useful - plant it is.

The ancient reed swamps of the midlands laid the peaty foundations of the raised bogs, before the mosses took over, and there have been proposals for creating new reed beds in the cutaway bog for a continuing harvest of dead reed stems squeezed into domestic briquettes. Reeds grow even more vigorously when fertilised with sewage or farm slurry, and their deep and intricate roots and associated microbes do an excellent job of breaking sewage down and taking out nitrates and heavy metals. It's this filtering and purifying aspect of marshy wetlands, known since ancient times, that is promoting new experiments in land use.

Constructed wetlands planted with reeds are central to the Anne Valley Project on the Co Waterford coast west of Tramore. This community-based project, supported by Duchas and other agencies, aims at restoring the ecological diversity of the valley, including the return of sea trout to its stream and tributaries.

A priority has been the cleansing of dirty waters from farmyards, and the valley's landowners have helped in creating a wetland system that extends the full length of the seven-kilometre valley. It leads their streams through a series of ponds, some planted with vegetation - mainly reeds and sedges and semi-aquatic plants - which absorb the nutrients released by the microbes and bind at least some of them in their own decay on the bottom of the wetland. By the final pool, the water is pure enough for trout to live in.

Constructed wetlands have tremendous promise in restoring polluted fisheries, and in the many rural areas with sewage problems. In the UK, water authorities have begun to use stands of reed as a practical alternative to sewage treatment beds. In Ireland, too, artificial reed-bed systems have been developed commercially as an alternative to domestic septic tanks, and several local authorities in our western counties are happy to consider their use.

Meanwhile, our mysterious marshes are slowly winning a place in the landscape as more than wastelands for "reclamation" or prime sites for urban landfill. Coastal marshes like Kilcoole, in Co Wicklow, constantly threatened with agricultural drainage, are vital refuges for wildfowl. The saltmarsh waders of the eastern estuaries are well defended by BirdWatch Ireland. Even little Booterstown Marsh, in Dublin, earns its keep both as a sanctuary and as an object of meditation by travellers on the Dart: a wasteland literally beyond the developers' purse.

It's the odd wet little corners of the countryside, forgotten behind their screen of reeds, that need watching out for now. Too small and insignificant to be anyone's official concern, they will survive in the long run only if we actually learn to see them, in the same way that we now see hedgerows and copses. Perhaps the appearance of "instant" reed-bed systems will make people think differently about the nature and value of wetlands. How many septic tanks, after all, have reed-buntings nesting in them?