Another Life: Small is beautiful – Ireland’s lakes, ponds and pools

My favourite lake lies at the end of the machair, the grassy plain behind the dunes. I’m not sure I can even call it a lake, at least officially, as the EU’s water framework directive says a lake has to span at least 50 hectares, and I doubt if this one makes even an old-fashioned acre. But it has long been Dooaghtry Lough on the maps, and that’s good enough.

On a crisp January morning the sun glows in the reeds and gleams, perhaps, on a pair of mute swans, taking refuge from the whoopers bugling on the big lagoon next door. Or the peace may yield to a squealing swoop of choughs, bouncing between heights, each beak a bright flash of vermilion.

In this remote corner sea-feeding otters come to rinse the salt and fish scales from their fur. Their pawprints begin at the edge of the tide, print a line on the sand before disappearing into a watery ravine in the dunes, then furrow up through mosses and liverworts to the lake. At its moist margins, too, a hand lens finds tiny snails, Vertigo-somethings, rare survivors from a chilly antiquity.

Pristine and protected, Dooaghtry is a rarity among some 12,200 small lakes across Ireland – placid lakes on peatland and pools in raised bogs, park ponds, constructed wetlands, reservoirs and turloughs, rich lakes over limestone and hungry ones on mountains. Only 4 per cent of them are more than 50 hectares, and some 8,000 don’t span even a hectare.

Like the streams that help make up Ireland’s 74,000km of rivers, relatively few have attracted much attention to their chemistry or aquatic life, yet they contribute powerfully to the island’s biodiversity and fish life – and to its drinkable water.

The figures come from Martin McGarrigle in a special issue of the Royal Irish Academy's journal Biology and Environment, edited by Mary Kelly-Quinn and Jan-Robert Baars. "There is a growing realisation across Europe," writes McGarrigle, "that 'small is beautiful' insofar as small water bodies are concerned."

His special concern is with "diffuse pollution", the sort that seeps out from farmland, forestry and septic tanks into ditches and winding streams, thence to small lakes and their outflows into tributaries and rivers. It is only here that monitoring picks up the pollution that gets reported, under the water framework directive, to the European Commission. Tracking it back, McGarrigle says, needs boots on the ground.

His is one of a dozen studies in the issue, called Small Water Bodies: Importance, Threats and Knowledge Gaps. Looking at streams as narrow, tumbling cascades from mountain lakes, threads of water woven from the bogs, pools welling up from deep limestone springs, it is hard to credit how much life they can support, even in their first couple of kilometres.

One study found 24 species of freshwater insects special to these headwaters and many more that are shared downstream. Apart from their own distinctive biodiversity, these high beginnings can help bring life back to damaged and distant rivers.

Even narrow drainage ditches in farmland can be richer in life than we suppose. Often heavily fed with the run-off of fertilisers, pesticides, herbicides, silt, silage liquor and slurry, do they promote biodiversity or kill it off? Jane Kavanagh and Simon Harrison, of University College Cork, studied slow-flowing permanent ditches in intensive farmland in southwest Ireland and found them supporting "high numbers of unique and rare taxa, including nationally rare and threatened species".

So that is one surprise. There are more in the findings of an 11-strong interuniversity team, led by Harrison, who compared populations of brown trout and salmon in the headwaters of 64 streams across the Republic. Some streams drained uplands forested with conifers, others ran through open moorland.

Conifer plantations have long been blamed for acidifying streams, especially on the western hills, thus extinguishing insect life that supports trout and juvenile salmon. It was first thought that the trees intercepted airborne pollutants from power stations and industry and trickled their acids down to the ground. Acidification has persisted even after such pollution was controlled from the 1980s, however.

Research has now found other toxic flows, not least the natural organic acids released from the thick layer of conifer needles and concentrated by plantation drains that pour rain into streams and surge onwards. Such chemical changes, the team reports, hit the many life stages of salmon, particularly as eggs and young smolts but even as ocean-going adults.

Brown trout, on the other hand, are not nearly as sensitive to low pH as is commonly believed. This first European study to compare the effects on both trout and salmon, living in similar streams, is unequivocal: there is “a clear negative impact from conifer plantations on the chemical and biological quality of small upland streams”. Replanting conifers in our moorland salmon catchments will have to be looked at again.