Many lakes whose existence depends wholly on rainwater runoffs are seasonal.
They are known as turloughs.
Lough Bunny in The Burren, County Clare, Ireland, is a turlough.
Every summer it drains into fissures around the lake’s northern end.
The central requirement for a turlough to form is a porous bed of limestone.
Limestone is a sedimentary rock composed of the skeletal fragments of marine organisms such as coral and molluscs.
Their main component is calcium carbonate, which is soluble in water.
When this happens the limestone is said to have karstified.
About 65 percent of Ireland is made up of limestone.
The karst landscape formed some 250 millions years ago.
By this time, tectonic movement had pushed Ireland well out of water.
Subsequent glacialization deposited a thick layer clay and sand, over which bogs and lakes formed.
Lough Aroolagh, County Galway, Connaught, Ireland.
Turloughs are very predictable.
A dry turlough near Gort, County Clare.
But some turloughs fill and empty through the same hole.
Some turloughs can also be connected to the ocean and are affected by oceanic tides.
Most turloughs flood to a depth of about 2 meters but some are much deeper.
Some of the turloughs near Gort reach about 5 meters deep in midwinter.
Although turloughs are seasonal, they support a variety of animal and plant life.
Frogs and newts commonly use turloughs to spawn.
Some troughs have water fleas and fairy shrimps found nowhere else in Ireland.
Ballinacourty turlough, January 2005.
Ballinacourty turlough, May 2005.
Many farmers have sought to drain turloughs so that the land can be used throughout the year.
But the benefits are not always that great.
The poorly developed soil is also not able to withstand the presence of animals through the winter.
Others complain that the conservation status of turloughs in Ireland is unfavourable.
