Nature on our doorsteps: Special freshwater springs along the Dodder

A particularly special habitat occurs along the River Dodder which is often overlooked as being just another wet marshy spot.

From Glenasmole to Knocklyon, freshwater springs emerge at particular locations along the banks of the river.

While springs are not a very unusual feature in themselves, what makes the Dodder springs so special is the chemical nature of the water.

The water in these springs is rich in carbon dioxide and dissolved calcium carbonate. Carbonate is the chemical compound that forms limestone rock and chalk.

As the lime-rich waters emerge from the riverbank to meet the air, a chemical reaction occurs.

This causes the carbon dioxide gas to be released into the air while also causing the carbonate that is dissolved in the water to become solid.

Spring water cascades down the tufa rock (on the left) to form a special marshy habitat

Tiny flakes of solid carbonate then begin to settle on the mosses, twigs, and stones around the source of the spring. Over time, this carbonate builds up to form a new type of stone called tufa.

Although they may look like just another wet boggy place along the Dodder, tufa springs are very specialised habitats because only certain rare plants and mosses can survive the high carbonate levels around the springs.

The springs can be easily damaged however, by water pollution, by trampling disturbance, or by the dumping of waste.

By Rosaleen Dwyer.